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This study investigated torque production resulting from the combined application of wide-pulse neuromuscular electrical stimulation (NMES), delivered over the posterior tibial nerve, and muscle lengthening at two distinct amplitudes. Wide-pulse NMES (pulse duration: 1 ms; stimulation intensity: 5–10% of maximal voluntary contraction) was delivered at both low- (20 Hz) and high- (100 Hz) stimulation frequencies, either alone (NMES condition) or combined with a muscle lengthening at two amplitudes (10 or 20° ankle joint rotation; NMES + LEN10 and NMES + LEN20 conditions, respectively). For each frequency, the torque-time integral (TTI) and the muscle activity following the cessation of stimulation trains (sustained EMG activity) were calculated. At 20 Hz, TTI was higher (P = 0.007) during NMES + LEN10 (233.2 ± 101.5 Nm·s) and NMES + LEN20 (229.2 ± 92.1 Nm·s) than during the NMES condition (187.5 ± 74.5 Nm·s), without any change in sustained EMG activity (P = 0.54). At 100 Hz, TTI was higher (P = 0.038) during NMES + LEN10 (226.6 ± 115.3 Nm·s) than during NMES + LEN20 (180.6 ± 84.0 Nm·s) and NMES (173.9 ± 94.9 Nm·s). This torque enhancement was accompanied by a higher sustained EMG activity (P = 0.045) in the NMES + LEN10 condition. These findings show that, for low-frequency NMES, significant torque increases were observed with both a 10- or a 20-degree lengthening amplitude, probably linked to increased afferents' activation. In contrast, with high-frequency NMES, a significant TTI enhancement was observed only with the 10-degree amplitude, accompanied by increased sustained EMG activity, suggesting neural mechanisms' involvement. When a greater lengthening amplitude was superimposed during high-frequency NMES, these mechanisms were probably inhibited, precluding torque enhancement. NEW & NOTEWORTHY: This study demonstrates that combining wide-pulse low-frequency NMES and muscle lengthening can increase torque production compared with the sole application of NMES. Torque enhancement is most likely linked to the persistent firing of muscle afferents. Although muscle lengthening superimposition also permitted torque increases during wide-pulse high-frequency NMES, increasing the muscle lengthening amplitude did not allow further torque enhancements, probably due to presynaptic inhibitory mechanisms. [ABSTRACT FROM AUTHOR]

The Achilles tendon (AT) is composed of three distinct subtendons, each arising from one of the three heads of the triceps surae muscles: gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (SOL). These subtendons exhibit a twisted structure, classified as low (Type I), medium (Type II), and high (Type III) twist, based on cadaveric studies. Nevertheless, the in vivo investigation of AT twist is notably scarce, resulting in a limited understanding of its functional significance. The aim of this study was to give insights into the complex 3D AT structure in vivo. A total of 30 healthy participants underwent individual stimulation of each of the triceps surae muscles at rest with the foot attached to the pedal of an isokinetic dynamometer. Ultrasound images were captured to concomitantly examine the displacement of the superficial, middle and deep AT layers. SOL stimulation resulted in the highest AT displacement followed by GM and GL stimulation. Independent of the muscle stimulated, non‐uniformity within the AT was observed with the deep layer exhibiting more displacement compared to the middle and superficial layers, hence important inter‐individual differences in AT displacement were noticeable. By comparing these individual displacement patterns during targeted stimulations with insights from cadaveric twist classifications on each subtendon area, our classification identified 19 subjects with a 'low' twist and 11 subjects with a 'high' twist. These findings enable us to move beyond cadaveric studies and relate the twisted microstructure of the AT in vivo to its dynamic behaviour. [ABSTRACT FROM AUTHOR]

Background/Objectives: Acute ruptures of the Achilles Tendon (AT) are common injuries in the active population, in particular among men aged 30 to 50. Full functional recovery after this kind of injury is long and challenging and nowadays there is no universal "gold standard" strategy when dealing with them. Methods: When it comes to surgical treatment, various techniques have been described: in case of a typical lesion at the midportion of the tendon (which is the most common type), the basic principle of surgical repair is the end-to-end suture of the tendon stumps. The AT ("calcaneal tendon" according to the International Anatomical Terminology) is the strongest tendon of the human body, it is the conjunct tendon of the two Gastrocnemii Muscles and the Soleus Muscle and has a well-recognizable twisted structure: the subtendon from the Medial Head of the Gastrocnemius attaches postero-laterally on the calcaneal tendon footprint, the subtendon from the Lateral Head of the Gastrocnemius attaches antero-laterally and the subtendon from the Soleus attaches medially, therefore creating a 90° twist of the tendon structure. Results: the twisted structure of the human AT is of central importance to its biomechanics, since it gives the tendon a higher resistance to deformation and concurs in supination of the subtalar joint during gait. Conclusions: given the abovementioned anatomical and biomechanical premises, we believe that the restoration of the subtendons anatomy can lead to a better functional recovery of the Triceps Surae—Achilles Tendon complex, therefore we recently decided to adopt for open surgical repair the Direct Anatomical Reconstruction of the Achilles Tendon, which we describe in the present article. [ABSTRACT FROM AUTHOR]

The mechanisms responsible for increased metabolic cost of walking in older adults are poorly understood. We recently proposed a theoretical premise by which age-related reductions in Achilles tendon stiffness (kAT) can disrupt the neuromechanics of calf muscle force production and contribute to faster rates of oxygen consumption during walking. The purpose of this study was to objectively evaluate this premise. We quantified kAT at a range of matched relative activations prescribed using electromyographic biofeedback and walking metabolic cost and ankle joint biomechanics in a group of 15 younger (age: 23 ± 4 yr) and 15 older (age: 72 ± 5 yr) adults. Older adults averaged 44% lower kAT than younger adults at matched triceps surae activations during isokinetic dorsiflexion tasks on a dynamometer (P = 0.046). Older adults also walked with a 17% higher net metabolic power (P = 0.017) but indistinguishable peak Achilles tendon forces than younger adults. Thus, data implicate altered tendon length-tension relations with age more than differences in the operating region of those length-tension relations between younger and older adults. In addition, we discovered empirical evidence that lesser kAT—likely due to the shorter muscle lengths and thus higher relative activations it imposes—was positively correlated with higher net metabolic power during walking (r = −0.365, P = 0.048). These results pave the way for interventions focused on restoring ankle muscle-tendon unit structural stiffness to improve walking energetics in aging. NEW & NOTEWORTHY: This study provides the first empirical evidence to our knowledge that age-related decreases in kAT exact a potentially significant metabolic penalty during walking. These results pave the way for interventions focused on restoring ankle muscle-tendon unit structural stiffness to improve walking energetics in aging. [ABSTRACT FROM AUTHOR]

This study investigated the influence of stimulation parameters on torque production when combining a brief muscle lengthening with electrical stimulation. Fifteen volunteers participated in one experimental session where two distinct stimulation modalities were compared: wide-pulse high-frequency (WPHF; pulse duration: 1 ms, frequency: 100 Hz), favoring afferent pathway activation, and narrow-pulse low-frequency (NPLF; pulse duration: 0.05 ms, frequency: 20 Hz), favoring activation of the efferent pathway. Both stimulation modalities were applied to evoke 5–10% of maximal voluntary contraction either in isometric conditions (WPHF and NPLF) or in combination with a muscle lengthening (lengthening condition: WPHF + LEN and NPLF + LEN). The torque-time integral (TTI) during the stimulation trains and the muscle activity after the cessation of the stimulation trains [sustained electromyographic (EMG) activity, normalized to the maximal EMG activity] were assessed and compared between the stimulation modalities and the conditions (2-way ANOVA). An interaction effect was obtained, revealing significant differences in TTI and sustained EMG activity between WPHF + LEN and the other tested conditions (P = 0.048 and P = 0.044, respectively). TTI and sustained EMG activity were higher for WPHF + LEN (228.4 ± 105.3 Nm·s and 0.085 ± 0.070, respectively) compared to WPHF (168.4 ± 72.9 Nm·s; 0.052 ± 0.026), NPLF + LEN (136.4 ± 38.9 Nm·s; 0.031 ± 0.016), and NPLF (125.2 ± 36.1 Nm·s; 0.028 ± 0.015). The increased TTI during the WPHF + LEN condition suggests that the contribution of afferent pathways to the evoked torque can be enhanced with the muscle lengthening superimposition. They highlight the importance of using WPHF stimulation that already solicits Ia afferents, to benefit from the cumulative afferent activation induced by the muscle lengthening to further increase torque production. NEW & NOTEWORTHY: The results of the present study highlight the importance of using electrical stimulation modalities that preferentially activate Ia afferents to take advantage of the superimposition of muscle lengthening to further enhance afferent pathways' contribution to evoked torque and, in turn, increase torque production. These results offer the opportunity to improve the efficacy of the wide-pulse high-frequency stimulation modality. [ABSTRACT FROM AUTHOR]

AbstractAimsMethodsResultsConclusionThe calf raise test (CRT) assesses plantarflexor strength and endurance, but normative data for children are scarce. Furthermore, contradictions exist on which factors are associated with total repetitions, with repetitions being the only metric considered. We quantified three of the main CRT outcomes (repetitions, total work, and peak height) in children 10–17 years and explored their relationship with various factors.Healthy children (n = 165, 50.3% female) completed single-legged calf raises on a 10° incline, once on each leg. Test outcomes were extracted using the valid and reliable Calf Raise application.CRT outcomes were not significantly different between legs (p ≥ .19). The only covariates significantly associated with outcomes based on stepwise quantile regressions were body mass index centile for repetitions, meeting physical activity recommendations for total work and peak height, and age for total work. Outcomes did not significantly differ based on sex or maturation. Median values were around 26 for repetitions, 640–1460 J for total work (age dependent), and 10.1 cm for peak height for children meeting physical activity recommendations.Children who were older, had lower body mass indices, and were more active exhibited superior CRT outcomes. Meeting physical activity recommendations appears beneficial for plantarflexor function and should continue to be prioritized in children. [ABSTRACT FROM AUTHOR]

Older adults have difficulty maintaining balance when faced with postural disturbances, a task that is influenced by the stiffness of the triceps surae and Achilles tendon. Age-related changes in Achilles tendon stiffness have been reported at matched levels of effort, but measures typically have not been made at matched loads, which is important due to age-dependent changes in strength. Moreover, there has been limited investigation into age-dependent changes in muscle stiffness. Here, we investigate how age alters muscle and tendon stiffness and their influence on ankle stiffness. We hypothesized that age-related changes in muscle and tendon contribute to reduced ankle stiffness in older adults and evaluated this hypothesis when either load or effort were matched. We used B-mode ultrasound with joint-level perturbations to quantify ankle, muscle, and tendon stiffness across a range of loads and efforts in seventeen healthy younger and older adults. At matched loads relevant to standing and the stance phase of walking, there was no significant difference in ankle, muscle, or tendon stiffness between groups (all p > 0.13). However, at matched effort, older adults exhibited a significant decrease in ankle (27%; p = 0.008), muscle (37%; p = 0.02), and tendon stiffness (22%; p = 0.03) at 30% of maximum effort. This is consistent with our finding that older adults were 36% weaker than younger adults in plantarflexion (p = 0.004). Together, these results indicate that, at the loads tested in this study, there are no age-dependent changes in the mechanical properties of muscle or tendon, only differences in strength that result in altered ankle, muscle, and tendon stiffness at matched levels of effort. [ABSTRACT FROM AUTHOR]

Objective: To compare clinical assessment findings between elite athletic populations with and without a clinical diagnosis of posterior ankle impingement syndrome (PAIS). Design: Cross-sectional case-control study. Setting: Elite ballet and sport. Participants: Ten male and female professional ballet dancers and athletes with a clinical diagnosis of PAIS and were matched for age, sex, and activity to 10 professional ballet dancers and athletes without PAIS. Independent variables: Posterior ankle pain on body chart and a positive ankle plantarflexion pain provocation test. Main outcome measures: Single-leg heel raise (SLHR) endurance test, range of motion testing for weight-bearing ankle dorsiflexion, passive ankle plantarflexion, and first metatarsophalangeal joint dorsiflexion, and Beighton score for generalized joint hypermobility. Participants also completed the Cumberland Ankle Instability Tool (CAIT) questionnaire. Results: The group with PAIS achieved significantly fewer repetitions on SLHR capacity testing ( P = 0.02) and were more symptomatic for perceived ankle instability according to CAIT scores ( P = 0.004). Conclusions: Single-leg heel raise endurance capacity was lower, and perceived ankle instability was greater in participants with PAIS. The management of this presentation in elite dancers and athletes should include the assessment and management of functional deficits. [ABSTRACT FROM AUTHOR]

Purpose: The Achilles tendon consists of three subtendons with the ability to slide relative to each other. As optimal intratendinous sliding is thought to reduce the overall stress in the tendon, alterations in sliding behavior could potentially play a role in the development of Achilles tendinopathy. The aims of this study were to investigate the difference in intratendinous sliding within the Achilles tendon during isometric contractions between asymptomatic controls and patients with Achilles tendinopathy and the effect of changing the horizontal foot position on intratendinous sliding in both groups. Methods: Twenty‐nine participants (13 Achilles tendinopathy and 16 controls) performed isometric plantarflexion contractions at 60% of their maximal voluntary contraction (MVC), in toes‐neutral, and at 30% MVC in toes‐neutral, toes‐in, and toes‐out positions during which ultrasound images were recorded. Intratendinous sliding was estimated as the superficial‐to‐middle and middle‐to‐deep relative displacement. Results: Patients with Achilles tendinopathy present lower intratendinous sliding than asymptomatic controls. Regarding the horizontal foot position in both groups, the toes‐out foot position resulted in increased sliding compared with both toes‐neutral and toes‐out foot position. Conclusion: We provided evidence that patients with Achilles tendinopathy show lower intratendinous sliding than asymptomatic controls. Since intratendinous sliding is a physiological feature of the Achilles tendon, the external foot position holds promise to increase sliding in patients with Achilles tendinopathy and promote healthy tendon behavior. Future research should investigate if implementing this external foot position in rehabilitation programs stimulates sliding within the Achilles tendon and improves clinical outcome. [ABSTRACT FROM AUTHOR]

Purpose: Understanding muscle-tendon forces (e.g., triceps surae and Achilles tendon) during locomotion may aid in the assessment of human performance, injury risk, and rehabilitation progress. Shear wave tensiometry is a noninvasive technique for assessing in vivo tendon forces that has been recently adapted to a wearable technology. However, previous laboratory-based and outdoor tensiometry studies have not evaluated running. This study was undertaken to assess the capacity for shear wave tensiometry to produce valid measures of Achilles tendon loading during running at a range of speeds. Methods: Participants walked (1.34 m⋅s-1) and ran (2.68, 3.35, and 4.47 m⋅s-1) on an instrumented treadmill while shear wave tensiometers recorded Achilles tendon wave speeds simultaneously with whole-body kinematic and ground reaction force data. A simple isometric task allowed for the participant-specific conversion of Achilles tendon wave speeds to forces. Achilles tendon forces were compared with ankle torque measures obtained independently via inverse dynamics analyses. Differences in Achilles tendon wave speed, Achilles tendon force, and ankle torque across walking and running speeds were analyzed with linear mixed-effects models. Results: Achilles tendon wave speed,Achilles tendon force, and ankle torque exhibited similar temporal patterns across the stance phase of walking and running. Significant monotonic increases in peak Achilles tendon wave speed (56.0-83.8 m⋅s-1), Achilles tendon force (44.0-98.7 N⋅kg-1), and ankle torque (1.72-3.68 N⋅m⋅(kg-1)) were observed with increasing locomotion speed (1.34-4.47 m⋅s-1). Tensiometry estimates of peak Achilles tendon force during running (8.2-10.1 body weights) were within the range of those estimated previously via indirect methods. Conclusions: These results set the stage for using tensiometry to evaluate Achilles tendon loading during unobstructed athletic movements, such as running, performed in the field. [ABSTRACT FROM AUTHOR]

Context: Strengthening of ankle plantar flexor muscles is one of the important components in the rehabilitation of many lower limb injuries and disorders. However, there are few simple methods to evaluate ankle plantar flexor strength in clinical situations without using equipment. The puipose of this study was to verify the intraexaminer and interexaminer reliability and the concurrent validity of a novel ankle isometric plantar flexion (PF) strength test (PF break test fPFBTj). Design: Case-control study. Methods: The intraexaminer and interexaminer reliabilities of the PFBT were evaluated in 57 orthopedic patients and 30 healthy adults. The range of motion of the ankle joint and the number of heel raises were compared between positive and negative PFBT cases. Then, isometric ankle PF torque (ankle PF of 0°, 15°, and 30°) was compared in knee extension and in the 50° flexion position between positive and negative PFBT cases in 30 healthy adults. Results: The intraexaminer reliability (κ) of the PFBT was .81 to .94, and the interexaminer reliability (κ) was .37 to .74. The PFBT positive group had a significantly smaller range of motion in the ankle joint (P < .05) and a significantly lower number of heel raises (P < .001) than the PFBT negative group in orthopedic patients, but no significant differences in healthy adults. The PFBT positive group had less ankle PF torque than the PFBT negative group at all ankle PF angles (P < .01). The isometric PF torque in the end range of ankle PF in knee extension could predict the results of the PFBT and correctly classified 90.0% of cases (P< .001). Conclusion: The PFBT is considered a simple and valid method to evaluate isometric ankle PF strength in the clinical setting. [ABSTRACT FROM AUTHOR]

The wide variation in muscle fibre type distribution across individuals, along with the very different energy consumption rates in slow versus fast muscle fibres, suggests that muscle fibre typology contributes to inter‐individual differences in metabolic rate during exercise. However, this has been hard to demonstrate due to the gap between a single muscle fibre and full‐body exercises. We investigated the isolated effect of triceps surae muscle contraction velocity on whole‐body metabolic rate during cyclic contractions in individuals a priori selected for their predominantly slow (n = 11) or fast (n = 10) muscle fibre typology by means of proton magnetic resonance spectroscopy (1H‐MRS). Subsequently, we examined their whole‐body metabolic rate during walking and running at 2 m/s, exercises with comparable metabolic rates but distinct triceps surae muscle force and velocity demands (walking: low force, high velocity; running: high force, low velocity). Increasing triceps surae contraction velocity during cyclic contractions elevated net whole‐body metabolic rate for both typology groups. However, the slow group consumed substantially less net metabolic energy at the slowest contraction velocity, but the metabolic difference between groups diminished at faster velocities. Consistent with the more economic force production during slow contractions, the slow group exhibited lower metabolic rates than the fast group while running, whereas metabolic rates were similar during walking. These findings provide important insights into the influence of muscle fibre typology on whole‐body metabolic rate and emphasize the importance of considering muscle mechanical demands to understand muscle fibre typology related differences in whole‐body metabolic rates. Key points: Muscle fibre typology is often suggested to affect whole‐body metabolic rate, yet convincing in vivo evidence is lacking.Using isolated plantar flexor muscle contractions in individuals a priori selected for their predominantly slow or fast muscle fibre typology, we demonstrated that having predominantly slow muscle fibres provides a metabolic advantage during slow muscle contractions, but this benefit disappeared at faster contractions.We extended these results to full‐body exercises, where we demonstrated that higher proportions of slow fibres associated with better economy during running but not when walking.These findings provide important insights into the influence of muscle fibre typology on whole‐body metabolic rate and emphasize the importance of considering muscle mechanical demands to understand muscle fibre typology related differences in whole‐body metabolic rate. [ABSTRACT FROM AUTHOR]

Previous training studies with comprehensive stretching durations have reported that an increase in range of motion (ROM) can be related to decreases in muscle stiffness. Therefore, the purpose of this study was to analyze the association between the passive muscle stiffness of three muscle groups (triceps surae, quadriceps, hamstrings) to the respective joint ROM. Thirty-six healthy male soccer players volunteered in this study. After a standardized warm-up, the muscle stiffness was tested via shear wave elastography in six muscles (gastrocnemius medialis and lateralis, rectus femoris, semitendinosus, semimembranosus, and biceps femoris long head). The hip extension, hip flexion, and ankle dorsiflexion ROM were also assessed with a modified Thomas test, a sit and reach test, and a standing wall push test, respectively. We found significant moderate to large correlations between hip flexion ROM and muscle stiffness for the semimembranosus (rP = -0.43; P = 0.01), biceps femoris long head (rP = -0.45; P = 0.01), and overall hamstring stiffness (rP = -0.50; P < 0.01). No significant correlations were found for triceps surae (rP = -0.12; P = 0.51 to 0.67) and rectus femoris muscle stiffness (rP = 0.25; P = 0.14) with ankle dorsiflexion and hip extension ROM, respectively. We conclude that muscle stiffness is an important contributor to hip flexion ROM, but less important for hip extension or ankle joint ROM. Additional contributors to ROM might be tendon stiffness or stretch/pain tolerance. [ABSTRACT FROM AUTHOR]

Introduction: In post-stroke patients with equinovarus foot deformity (EVFD), soft tissue rearrangements may contribute to muscle overactivity when a muscle is stretched or tension is applied. Therefore, we investigated the effects of surgically restoring the triceps surae (TS) length and lengthening ability on TS spasticity. Methods: This retrospective study included chronic post-stroke patients who underwent neuro-orthopedic surgery inclusive of TS lengthening. TS spasticity was measured using the Modified Tardieu Scale (MTS) before and 1 month after surgery, both with the knee extended (KE) and flexed (KF). MTS variations were analyzed using the Wilcoxon test. The time from stroke onset was compared between patients with and without post-surgical spasticity using the t-test. Statistical significance was set at 5%. Results: A total of 120 patients with EVFD, aged 57 (12) years, ranging from 1 to 36 years from stroke, were included in the study. The median MTS_KE score significantly decreased from 3 (range 0-4) to 2 (0-4) (p < 0.001) after surgery. The MTS score decreased by =1 point in more than half of the sample. Notably, 19 and 32 patients were completely relieved from spasticity (MTS = 0) in the KE and KF conditions, respectively. Post-surgical spasticity did not depend on the time since stroke onset (p = 0.560). Discussion: TS lengthening led to a short-term reduction of spasticity in 41% and 63% of chronic post-stroke patients in the gastro-soleus complex and soleus, respectively, with complete relief observed in 21% and 30% of the sample. Surgical lengthening can be considered an effective treatment that not only restores joint range of motion but also may reduce spasticity, even in chronic patients. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate torque production in response to the application of a brief muscle lengthening during neuromuscular electrical stimulation (NMES) applied over the posterior tibial nerve. Fifteen participants took part in three experimental sessions, where wide-pulse NMES delivered at 20 and 100 Hz (pulse duration of 1 ms applied during 15 s at an intensity evoking 5–10% of maximal voluntary contraction) was either applied alone (NMES condition) or in combination with a muscle lengthening at three distinct speeds (60, 180, or 300°/s; NMES + LEN condition). The torque-time integral (TTI) and the muscle activity following the stimulation trains [sustained electromyography (EMG)] were calculated for each condition. Results show that TTI and sustained EMG activity were higher for the NMES + LEN condition only when using 100-Hz stimulation, regardless of the lengthening speed (P = 0.029 and P = 0.007 for the two parameters, respectively). This indicates that superimposing a muscle lengthening to high-frequency NMES can enhance the total torque production, partly due to neural mechanisms, as evidenced by the higher sustained EMG activity. This finding has potential clinical relevance, especially when it comes to finding ways to enhance torque production to optimize the effectiveness of NMES training programs. NEW & NOTEWORTHY: This study showed, for the first time, that the combined application of a brief muscle lengthening and wide-pulse neuromuscular electrical stimulation (NMES) delivered over the posterior tibial nerve can entail increased torque production as compared with the sole application of NMES. This observation, present only for high stimulation frequencies (100 Hz) and independently of the lengthening speed, is attributed to neural mechanisms, most probably related to increased afferents' solicitation, although muscular phenomena cannot be excluded. [ABSTRACT FROM AUTHOR]

The literature offers limited information on the effect of obesity on the rate of force development (RFD), a critical parameter for mobility in older adults. The objectives of this study were to explore the influence of obesity on the RFD in older adults and to examine the association between this neuromuscular parameter and walking speed. The participants (42 older adults) were classified into two groups: the control group (CG, n = 22; mean age = 81.13 ± 4.02 years; body mass index (BMI) = 25.13 ± 3.35 kg/m2), and the obese group (OG, n = 20; mean age = 77.71 ± 2.95 years; BMI = 34.46 ± 3.25 kg/m2). Walking speed (m/s) was measured using the 10 m walking test. Neuromuscular parameters of the plantar flexors were evaluated during a maximal voluntary contraction test using a dynamometer. The RFD was calculated from the linear slop of the force–time curve in the following two phases: from the onset of the contraction to 50 ms (RFD0–50) and from 100 to 200 ms (RFD100–200). The gait speed was lower in the OG compared to the CG (p < 0.001). The RFD50/100 and RFD100/200 were lower in the OG compared to the CG (p < 0.001). The RFD50/100 was found to be the predominant influencer on gait speed in the OG. In conclusion, obesity negatively impacts the RFD in older adults and RFD stands out as the primary factor among the studied parameters influencing gait speed. [ABSTRACT FROM AUTHOR]

The Achilles tendon exhibits anatomical variations in subtendon twist among individuals, and its compliance can change due to conditions like Achilles tendinopathy. However, current musculoskeletal models overlook these material and morphological variations. This study aimed to investigate the impact of altering Achilles subtendon insertion points and compliance on the triceps surae muscle forces, and therefore tendon loading, during dynamic exercises in one Achilles tendinopathy patient. First, subtendon insertion points were altered in the musculoskeletal model based on a subject-specific 3D freehand ultrasound model and for three types of subtendon twists: low, medium, and high. Second, tendon compliance was modeled based on experimental values, creating three musculoskeletal models: compliant, mean, and stiff. Results indicated that tendon compliance had a larger effect than tendon twist on triceps surae muscle forces. Altering subtendon insertion points to the three types of twist showed a maximal change of 2.3% in muscle force contribution compared to the no-twist model. During the eccentric rehabilitation exercise—a common exercise choice during rehabilitation—the compliant tendon model showed substantial differences compared to the generic (control) musculoskeletal model, resulting in decreased gastrocnemius medialis (−3.5%) and gastrocnemius lateralis (−3.2%) contributions and increased soleus contribution (+ 6.6%). Our study results highlight the necessity of incorporating tendon compliance in musculoskeletal models to accurately predict triceps surae muscle forces, especially in individuals with increased tendon compliance, such as patients with Achilles tendinopathy. Such findings contribute to more accurate predictions of muscle forces and hence, personalized rehabilitation strategies.

Previous training studies with comprehensive stretching durations have reported that an increase in range of motion (ROM) can be related to decreases in muscle stiffness. Therefore, the purpose of this study was to analyze the association between the passive muscle stiffness of three muscle groups (triceps surae, quadriceps, hamstrings) to the respective joint ROM. Thirty-six healthy male soccer players volunteered in this study. After a standardized warm-up, the muscle stiffness was tested via shear wave elastography in six muscles (gastrocnemius medialis and lateralis, rectus femoris, semitendinosus, semimembranosus, and biceps femoris long head). The hip extension, hip flexion, and ankle dorsiflexion ROM were also assessed with a modified Thomas test, a sit and reach test, and a standing wall push test, respectively. We found significant moderate to large correlations between hip flexion ROM and muscle stiffness for the semimembranosus (rP = –0.43; P = 0.01), biceps femoris long head (rP = –0.45; P = 0.01), and overall hamstring stiffness (rP = 0.50; P < 0.01). No significant correlations were found for triceps surae (rP = –0.12; P = 0.51 to 0.67) and rectus femoris muscle stiffness (rP = 0.25; P = 0.14) with ankle dorsiflexion and hip extension ROM, respectively. We conclude that muscle stiffness is an important contributor to hip flexion ROM, but less important for hip extension or ankle joint ROM. Additional contributors to ROM might be tendon stiffness or stretch/pain tolerance.

Chronic heat stress induces mitochondrial adaptation in skeletal muscle. However, the effect of chronic heat stress on the respiratory function per mitochondria in skeletal muscle has not been well studied. Here, the present study reports on the effect of 3-weeks heat stress on muscle mitochondrial respiration using male C57BL/6JJ mice at age 21 weeks. Mice were randomly assigned to either the control group (n = 6) or passive heat group (n = 6). After 3-weeks of heat stress, the right triceps surae was removed and used for biochemical analysis. Protein expression was assessed by immunoblotting. Mitochondrial respiratory function was measured by Oxygraph-2k. The study also shows the impact of the heat stress on daily feeding, body weight, muscle weight, and protein expression of heat shock proteins (heat-response marker).

Increasing the efficiency at which muscles generate mechanical power could improve running economy. A potential way to reduce muscle fiber shortening velocities and enhance energy storing of the Triceps Surae is changing their gear ratio at the ankle via optimization of shoe rollover profile. The aim of the current study was to individually optimize rollover profile of rocker shoes via human‐in‐the‐loop optimization to maximize positive ankle work to redistribute joint work from the hip and knee to the ankle and improve running economy. A total of 10 runners ran on a treadmill with experimental rocker shoes in which apex position and angle were optimized using an evolution algorithm to maximize positive ankle work. We compared experimental shoes with optimal settings, standard settings, and control shoes in terms of biomechanics and running economy. Optimal apex parameters differed considerably between participants. The optimal condition resulted in higher positive ankle work and a higher proportional share of the ankle in the total positive lower limb work compared to the standard condition. A difference in running economy between these conditions was not found. Human‐in‐the‐loop optimization can redistribute joint work from the hip and knee to the ankle by individually optimizing apex parameters. Although this did not improve running economy, the study showed that human‐in‐the‐loop optimization could improve the effectiveness of footwear with respect to the selected optimization parameter on an individual level. Highlights: Human‐in‐the‐loop optimization is able to individually optimize apex position and apex angle of running shoes to enhance ankle workThe increase in positive ankle work results in a redistribution of positive work generated around the lower limb joints from the hip and knee to the ankleThe increase ankle work did not result in an increased running economy and therefore it should be further investigated which factors confound the theoretical benefit [ABSTRACT FROM AUTHOR]

Introduction: Bioelectrical impedance analysis (BIA) can noninvasively and quickly assess electrical properties of the body, such as the phase angle. Phase angle is regarded as the quantity and/or quality of skeletal muscle and is associated with exercise performance, such as jump height and walking speed. Although the phase angle derived from BIA is assumed to be a useful way to assess muscle function, the relationship between the phase angle and neuromuscular properties has not been fully investigated. The purpose of this study was to investigate the association of phase angle with voluntary and evoked contractile properties in 60 adults (age, 21–83 years; 30 females and 30 males). Methods: The phase angle of the right leg at 50 kHz was evaluated using BIA. The twitch contractile properties (peak twitch torque [PTtwitch], rate of twitch torque development [RTDtwitch], and time-to-PTtwitch [TPTtwitch]) of the plantar flexors were measured using tibial nerve electrical stimulation. Maximal voluntary isometric contractions (MVICs) were performed to measure the maximal muscle strength and explosive muscle strength, from which the peak MVIC torque (PTMVIC) and rate of torque development (RTD) over a time interval of 0–200 ms were assessed, respectively. The root mean square (RMS) values of electromyographic (EMG) activity during the PTMVIC and RTD measurements (EMG-RMSMVIC and EMG-RMSRTD, respectively) were calculated. The RTD and EMG-RMSRTD were normalized using PTMVIC and EMG-RMSMVIC, respectively. Results and discussion: Phase angle significantly correlated with twitch contractile properties (|r| ≥ 0.444, p < 0.001), PTMVIC (r = 0.532, p < 0.001), and RTD (r = 0.514, p < 0.001), but not with normalized RTD (r = 0.242, p = 0.065) or normalized EMG-RMSRTD (r = −0.055, p = 0.676). When comparing measurement variables between the low- and high-phase angle groups while controlling for sex and age effects, the high-phase angle group showed greater PTtwitch, RTDtwitch, PTMVIC, and RTD (p < 0.001) and shorter TPTtwitch (p < 0.001) but not normalized RTD (p = 0.184) or normalized EMG-RMSRTD (p = 0.317). These results suggest that the leg phase angle can be an indicator of voluntary and evoked muscle contractile properties but not the neuromuscular activity of the plantar flexors, irrespective of sex and age. [ABSTRACT FROM AUTHOR]

Decreased dorsiflexion range of motion (DROM) can be modified using static stretching and joint mobilizations and may attenuate known knee anterior cruciate ligament injury risk factors. It is not known how these interventions compare to each other and how they improve knee landing mechanics. This study's purpose was to determine the immediate effects of static stretching and joint mobilization interventions on DROM measurement changes and right-leg drop jump knee landing mechanics. Eighteen females and 7 males, all recreationally active, completed 2 study sessions. Active and passive DROM, the weight-bearing lunge test, the anterior reach portion of the Star Excursion Balance Test, and a right-leg drop jump landing task were completed before and after the intervention. Change in DROM (ΔDROM) was calculated for DROM assessments between preintervention and postintervention. Pairwise dependent t tests determined no differences in ΔDROM between interventions, and statistical parametric mapping determined increased knee flexion (P =.004) and decreased anterior shear force (P =.015) during landing after both interventions. Increased DROM improves sagittal plane displacement and loading at the knee. Stretching may be a more feasible option in a healthy population for those wanting to maintain range of motion and decrease knee injury risk without physical therapist involvement. [ABSTRACT FROM AUTHOR]

To examine the strength of the relationship between plantarflexor power and strength-endurance metrics and 10-m sprint times in male Rugby Union players. A secondary aim was to examine the strength of the relationship within calf muscle metrics. Observational cross-sectional correlational. Field-based. Sixteen male Rugby Union players in the National Provincial Championship. Participants completed three single-leg calf muscle tests: bodyweight power, weighted power, and strength-endurance. Data were recorded using the Calf Raise application. Three-to-four days later, average and best 10-m sprint performances were collected using timing lights. There were large significant correlations between 10-m sprint performances (average and best times) and calf muscle power (weighted) and strength-endurance (total displacement and work) metrics (r = −0.503 to −0.628). There were large significant correlations between bodyweight and weighted power, weighted power and strength-endurance (total displacement and work), and most strength-endurance metrics (r = 0.520 to 0.943). Our findings emphasise the importance of triceps surae muscle power and strength-endurance for maximal-effort accelerations and sprint performances in Rugby Union. Our data indicate that weighted power and total work from strength-endurance tests are the most useful metrics for further investigation in the context of short sprints and acceleration. • We tested the relationship between plantarflexor function and 10-m sprint performance in rugby. • Plantarflexor power (weighted) and strength-endurance largely related to 10-m sprint times. • Plantarflexion function is a key indicator of acceleration ability in Rugby Union. • Our findings have performance implications for team sport athletes. [ABSTRACT FROM AUTHOR]

The Achilles tendon consists of three subtendons that transmit force from the triceps surae muscles to the calcaneus. Individual differences have been identified in Achilles subtendon morphology and twist in cadavers, which may have implications for triceps surae mechanics and function. High‐field magnetic resonance imaging (MRI) can be used to identify boundaries within multi‐bundle tissues, which could then enable studies of subtendon structure−function relationships in humans. The objective of this study was to use high‐field MRI (7T) to image and reconstruct Achilles subtendons arising from the triceps surae muscles. We imaged the dominant lower leg of a cohort of healthy human subjects (n = 10) using a tuned musculoskeletal sequence (double echo steady state sequence, 0.4 mm isotropic voxels). We then characterized the cross‐sectional area and orientation of each subtendon between the MTJ and calcaneal insertion. Image collection and segmentation was repeated to assess repeatability. Subtendon morphometry varied across subjects, with average subtendon areas of 23.5 ± 8.9 mm2 for the medial gastrocnemius, 25.4 ± 8.9 mm2 for the lateral gastrocnemius, and 13.7 ± 5.9 mm2 for the soleus subtendons. Repeatable subject‐specific variations in size and position of each subtendon were identified over two visits, expanding on prior knowledge that high variability exists in Achilles subtendon morphology across subjects. [ABSTRACT FROM AUTHOR]

Whether there is an optimal range of motion (ROM) to induce muscle hypertrophy remains elusive, especially for gastrocnemius. This study aimed to compare the changes in gastrocnemius muscle thickness between calf raise exercise performed with full ROM (FULLROM), partial ROM performed in the initial (INITIALROM), and final (FINALROM) portions of the ROM. Forty-two young women performed a calf training program for 8 weeks, 3 days⋅week-1, with differences in the calf raise ROM configuration. The calf raise exercise was performed in a pin-loaded, horizontal, leg-press machine, in 3 sets of 15-20 repetition maximum. The subjects were randomly assigned to 1 of the 3 groups: FULLROM (ankle: -25° to +25°), INITIALROM (ankle: -25° to 0°), and FINALROM (ankle: 0°to +25°), where 0° was defined as an angle of 90° of the foot with the tibia. The muscle thickness measurements of medial and lateral gastrocnemius were taken by means of B-mode ultrasound. INITIALROM elicited greater medial gastrocnemius increases than FULLROM and FINALROM (INITIALROM = +15.2% vs. FULLROM = +6.7% and FINALROM = +3.4%; p ≤ 0.009). Furthermore, INITIALROM elicited greater lateral gastrocnemius increases than FINALROM (INITIALROM = +14.9% vs. FINALROM = +6.2%; p < 0.024) but did not significantly differ from FULLROM (FULLROM = +7.3%; p = 0.060). The current results suggest that calf training performed at longer muscle lengths may optimize gastrocnemius muscle hypertrophy in young women. Therefore, when prescribing hypertrophy-oriented training, the inclusion of the calf raise exercise performed with partial ROM in the initial portion of the excursion should be considered. [ABSTRACT FROM AUTHOR]

The acute rupture of the Achilles tendon is an increasingly common injury due to an active lifestyle and participation in sports, especially in the middle-aged group. We conducted a focused review of the literature and found that the acute rupture of the Achilles tendon leaves long-term changes in the structure of the triceps surae muscle, regardless of whether it was treated surgically or conservatively. Significant elongation of the Achilles tendon and atrophy of the triceps surae can be observed on the injured leg, even 4 years or more after the injury. The injury also has long-lasting consequences on movement patterns of walking, running and jumping. These compensatory strategies place stress on other musculoskeletal structures, which are then at greater risk for injury.

The literature offers limited information on the effect of obesity on the rate of force development (RFD), a critical parameter for mobility in older adults. The objectives of this study were to explore the influence of obesity on the RFD in older adults and to examine the association between this neuromuscular parameter and walking speed. The participants (42 older adults) were classified into two groups: the control group (CG, n = 22; mean age = 81.13 ± 4.02 years; body mass index (BMI) = 25.13 ± 3.35 kg/m2), and the obese group (OG, n = 20; mean age = 77.71 ± 2.95 years; BMI = 34.46 ± 3.25 kg/m2). Walking speed (m/s) was measured using the 10 m walking test. Neuromuscular parameters of the plantar flexors were evaluated during a maximal voluntary contraction test using a dynamometer. The RFD was calculated from the linear slop of the force–time curve in the following two phases: from the onset of the contraction to 50 ms (RFD0–50) and from 100 to 200 ms (RFD100–200). The gait speed was lower in the OG compared to the CG (p < 0.001). The RFD50/100 and RFD100/200 were lower in the OG compared to the CG (p < 0.001). The RFD50/100 was found to be the predominant influencer on gait speed in the OG. In conclusion, obesity negatively impacts the RFD in older adults and RFD stands out as the primary factor among the studied parameters influencing gait speed.

Objective: To compare the efficacy of botulinum toxin injections using ultrasound-guidance vs electrical-stimulation-guidance in triceps surae (soleus and gastrocnemius) spasticity after stroke. Design: A clinical, single-centre, prospective, interventional, single-blind, cross-over, randomized trial, with outpatients in the tertiary care hospital. After randomization, subjects received electrical-stimulation-guided, followed by ultrasound-guided abobotulinumtoxinA injection (n = 15), or the same 2 procedures in the reverse order (n = 15) with the same operator, 4 months apart. The primary endpoint was the Tardieu scale with the knee straight at 1 month after injection. Results: The 2 groups did not differ in Tardieu scale score (effect size = 0.15, 95% confidence interval (95% CI) –0.22 to 0.51, p = 0.43). In addition, the muscle localization technique used had no influence on walking speed, pain on injection or spasticity, assessed at 1 month after the injection, using the modified Ashworth scale. Ultrasound-guided injections were faster to administer than electrical-stimulation-guided injections. Conclusion: In agreement with previous research, no differences were found in the efficacy of ultrasound-guided or electrical-stimulation-guided abobotulinumtoxinA injections in triceps surae spasticity after stroke. Both techniques are of equal use in guiding muscle localization for botulinum toxin injections in spastic triceps surae. LAY ABSTRACT This study compared the efficacy of 2 techniques used to localize botulinum toxin (BoNT-A) injections in triceps surae (soleus and gastrocnemius) spasticity after stroke: ultrasound-guidance vs electrical-stimulation-guidance. The results show that electrostimulation guidance and ultrasound guidance have the same efficacy for BoNT-A injections in triceps surae spasticity. The technique used had no influence on spasticity, walking speed, or pain on injection. Administration of ultrasound-guided injections was faster than electrical-stimulation-guided injections.

Purpose: The combination of motor imagery (MI) and neuromuscular electrical stimulation (NMES) can increase the corticospinal excitability suggesting that such association could be efficient in motor performance improvement. However, differential effect has been reported at spinal level after MI and NMES alone. The purpose of this study was to investigate the acute effect on motor performance and spinal excitability following MI, NMES and combining MI and NMES. Methods: Ten participants were enrolled in three experimental sessions of MI, NMES and MI + NMES targeting plantar flexor muscles. Each session underwent 60 imagined, evoked (20% MVC) or imagined and evoked contractions simultaneously. Before, immediately after and 10 min after each session, maximal M-wave and H-reflex were evoked by electrical nerve stimulation applied at rest and during maximal voluntary contraction (MVC). Results: The MVC decreased significantly between PRE-POST (− 12.14 ± 6.12%) and PRE-POST 10 (− 8.1 ± 6.35%) for NMES session, while this decrease was significant only between PRE-POST 10 (− 7.16 ± 11.25%) for the MI + NMES session. No significant modulation of the MVC was observed after MI session. The ratio Hmax/Mmax was reduced immediately after NMES session only. Conclusion: The combination of MI to NMES seems to delay the onset of neuromuscular fatigue compared to NMES alone. This delay onset of neuromuscular fatigue was associated with specific modulation of the spinal excitability. These results suggested that MI could compensate the neuromuscular fatigue induced acutely by NMES until 10 min after the combination of both modalities. [ABSTRACT FROM AUTHOR]

Neuromusculoskeletal models can be used to evaluate aberrant muscle function in cerebral palsy (CP), for example by estimating muscle and joint contact forces during gait. However, to be accurate, models should include representative musculotendon parameters. We aimed to estimate personalised parameters that capture the mechanical behaviour of the plantarflexors in children with CP and typically developing (TD) children. Ankle angle (using motion capture), torque (using a load-cell), and medial gastrocnemius fascicle lengths (using ultrasound) were measured during slow passive ankle dorsiflexion rotation for thirteen children with spastic CP and thirteen TD children. Per subject, the measured rotation was input to a scaled OpenSim model to simulate the torque and fascicle length output. Musculotendon model parameters were personalised by the best match between simulated and experimental torque–angle and fascicle length-angle curves according to a least-squares fit. Personalised tendon slack lengths were significantly longer and optimal fibre lengths significantly shorter in CP than model defaults and than in TD. Personalised tendon compliance was substantially higher in both groups compared to the model default. The presented method to personalise musculotendon parameters will likely yield more accurate simulations of subject-specific muscle mechanics, to help us understand the effects of altered musculotendon properties in CP. [ABSTRACT FROM AUTHOR]

Achilles tendon lengthening (ATL) is frequently used in the treatment of foot deformities. However, there is currently no objective method to determine the optimal muscle length during surgery. We developed an intraoperative approach to evaluate the passive and active forces of the triceps surae muscle group before and after ATL and aimed to test the following hypotheses: 1) the ankle passive range of motion (ROM) increases, 2) passive muscle forces decrease post-ATL, and 3) forces measured from patients with non-neurological and neurological conditions demonstrate different characteristics. Passive forces at various ankle joint positions were measured in ten patients (11.3 ± 3.0 years old) pre- and post- ATL using a force transducer attached to the Achilles tendon. In six patients, active isometric forces were measured by stimulating the triceps surae supramaximally. Passive forces decreased by 94.3% (p < 0.0001), and ROM increased by 89.4% (p < 0.0001) post-ATL. The pre-ATL passive forces were 70.8% ± 15.1% lower in patients with idiopathic foot deformities than in patients with neurological conditions (p < 0.001). The peak active force of 209.8 ± 114.3 N was achieved at an ankle angle of 38.3° ± 16.0°, where the passive force was 6.3 ± 6.7 N. The inter-individual variability was substantial in both groups. In conclusion, the hypotheses posed were supported. The present findings suggest that muscle passive and active force production as well as the inter-individual variability should be considered when planning further treatment. [ABSTRACT FROM AUTHOR]

Objectives: Deficits in muscle performance could be a consequence of a reduced ability of a motor neuron to increase the rate in which it discharges. This study aimed to investigate motor unit (MU) discharge properties of each triceps surae muscle (TS) and TS torque steadiness during submaximal intensities in runners with Achilles tendinopathy (AT). Methods: We recruited runners with (n = 12) and without (n = 13) mid-portion AT. MU discharge rate was analysed for each of the TS muscles, using high-density surface electromyography during 10 and 20% isometric plantar flexor contractions. Results: MU mean discharge rate was lower in the gastrocnemius lateralis (GL) in AT compared to controls. In AT, GL MU mean discharge rate did not increase as torque increased from 10% peak torque, 8.24 pps (95% CI 7.08 to 9.41) to 20%, 8.52 pps (7.41 to 9.63, p = 0.540); however, in controls, MU discharge rate increased as torque increased from 10%, 8.39 pps (7.25–9.53) to 20%, 10.07 pps (8.89–11.25, p < 0.001). There were no between-group difference in gastrocnemius medialis (GM) or soleus (SOL) MU discharge rates. We found no between-group differences in coefficient of variation of MU discharge rate in any of the TS muscles nor in TS torque steadiness. Conclusion: Our data demonstrate that runners with AT may have a lower neural drive to GL, failing to increase MU discharge rate to adjust for the increase in torque demand. Further research is needed to understand how interventions focussing on increasing neural drive to GL would affect muscle function in runners with AT. [ABSTRACT FROM AUTHOR]

The acute rupture of the Achilles tendon is an increasingly common injury due to an active lifestyle and participation in sports, especially in the middle-aged group. We conducted a focused review of the literature and found that the acute rupture of the Achilles tendon leaves long-term changes in the structure of the triceps surae muscle, regardless of whether it was treated surgically or conservatively. Significant elongation of the Achilles tendon and atrophy of the triceps surae can be observed on the injured leg, even 4 years or more after the injury. The injury also has long-lasting consequences on movement patterns of walking, running and jumping. These compensatory strategies place stress on other musculoskeletal structures, which are then at greater risk for injury. [ABSTRACT FROM AUTHOR]

Forward propulsion depends on the forces generated by the triceps surae muscles and transmitted through the muscles' subtendons, which merge and twist to form the Achilles tendon (AT). As people age, the AT may undergo structural changes that could alter the subtendons' ability to transmit forces or function with some independence; prominent changes include increased tendon compliance and a proliferation of interfascicular adhesions compared to younger tendon. However, the effects of age-related changes on the subtendons are difficult to isolate in vivo. Here, we used a Hill-type musculoskeletal model of the triceps surae muscle-subtendon units to simulate the effects of age-related changes on gastrocnemius (GAS) and soleus (SOL) muscle contractile dynamics across a range of physiological force levels during fixed-end contractions. We simulated individual and dual muscle excitations with altered tendon compliance (ε o = 3 %, 6 %, 9 %) and inclusion of a shared tendon. Consistent with fundamental muscle mechanics, compared to stiffer tendons, increased tendon compliance elicited more than three times the GAS and SOL fiber shortening and greater muscle excitation – effects that increased with requisite force demand. However, our model results also suggest combinatory effects of increased tendon compliance and interfascicle adhesions in the aging AT that deleteriously amplify redistribution from the GAS to the SOL which may be functionally detrimental during gait. [ABSTRACT FROM AUTHOR]

Abstract Background We aimed to investigate the association of age-related differences in the intracellular-to-total water ratio with explosive strength of the plantar flexors. Methods A total of 60 young (21–33 years) and older (64–83 years) individuals were recruited. Intracellular- (ICW) and total-water (TW) content within the right leg was evaluated by bioelectrical impedance spectroscopy as indicators of muscle cell mass and whole muscle mass within the segment, respectively. ICW divided by TW (ICW/TW) was calculated as an index of the occupancy of muscle cells within whole muscle. Rate of torque development (RTD) and electromyography (EMG) activity during maximal voluntary isometric plantar flexion were measured as indicators of explosive muscle strength and neuromuscular activity, respectively. RTD was calculated from three time windows of 0–50, 50–100, and 100–200 ms. Time-to-peak torque (TPT) was assessed from evoked twitch contraction. Results Compared with young participants, older participants showed lower ICW/TW (−7%, P < 0.001), RTD (−25 to −40%, P = 0.003 to 0.001), and longer TPT (+11%, P < 0.001). ICW/TW associated positively with RTD (r = 0.377 to 0.408, P = 0.004 to 0.001) and negatively with TPT (r = −0.392, P = 0.002), but not with EMG activity. RTD was associated positively with EMG for each time window (r = 0.527 to 0.607, P < 0.001). Conclusions These results indicate that ICW/TW may be a useful predictor of the age-related decrease in RTD, and that the decrease in ICW/TW with age may reflect age-associated changes in intrinsic contractile properties.

Achilles tendon lengthening (ATL) is frequently used in the treatment of foot deformities. However, there is currently no objective method to determine the optimal muscle length during surgery. We developed an intraoperative approach to evaluate the passive and active forces of the triceps surae muscle group before and after ATL and aimed to test the following hypotheses: 1) the ankle passive range of motion (ROM) increases, 2) passive muscle forces decrease post-ATL, and 3) forces measured from patients with non-neurological and neurological conditions demonstrate different characteristics. Passive forces at various ankle joint positions were measured in ten patients (11.3 ± 3.0 years old) pre- and post-ATL using a force transducer attached to the Achilles tendon. In six patients, active isometric forces were measured by stimulating the triceps surae supramaximally. Passive forces decreased by 94.3% (p < 0.0001), and ROM increased by 89.4% (p < 0.0001) post-ATL. The pre-ATL passive forces were 70.8% ± 15.1% lower in patients with idiopathic foot deformities than in patients with neurological conditions (p < 0.001). The peak active force of 209.8 ± 114.3 N was achieved at an ankle angle of 38.3° ± 16.0°, where the passive force was 6.3 ± 6.7 N. The inter-individual variability was substantial in both groups. In conclusion, the hypotheses posed were supported. The present findings suggest that muscle passive and active force production as well as the inter-individual variability should be considered when planning further treatment.

During human running, the soleus, as the main plantar flexor muscle, generates the majority of the mechanical work through active shortening. The fraction of chemical energy that is converted into muscular work (enthalpy efficiency) depends on the muscle shortening velocity. Here, we investigated the soleus muscle fascicle behaviour during running with respect to the enthalpy efficiency as a mechanism that could contribute to improvements in running economy after exercise-induced increases of plantar flexor strength and Achilles tendon (AT) stiffness. Using a controlled longitudinal study design (n = 23) featuring a specific 14-week muscle–tendon training, increases in muscle strength (10%) and tendon stiffness (31%) and reduced metabolic cost of running (4%) were found only in the intervention group (n = 13, p < 0.05). Following training, the soleus fascicles operated at higher enthalpy efficiency during the phase of muscle–tendon unit (MTU) lengthening (15%) and in average over stance (7%, p < 0.05). Thus, improvements in energetic cost following increases in plantar flexor strength and AT stiffness seem attributed to increased enthalpy efficiency of the operating soleus muscle. The results further imply that the soleus energy production in the first part of stance, when the MTU is lengthening, may be crucial for the overall metabolic energy cost of running. [ABSTRACT FROM AUTHOR]

Purpose: Human muscle–tendon units (MTUs) are highly plastic and undergo changes in response to specific diseases and disorders. To investigate the pathological changes and the effects of therapeutic treatments, the use of valid and reliable examination methods is of crucial importance. Therefore, in this study, a simple 3D ultrasound approach was developed and evaluated with regard to: (1) its validity in comparison to magnetic resonance imaging (MRI) for the assessment of the gastrocnemius medialis (GM) MTU, muscle belly, and Achilles tendon lengths; and (2) its reliability for static and dynamic length measurements. Methods: Sixteen participants were included in the study. To evaluate the validity and reliability of the novel 3D ultrasound approach, two ultrasound measurement sessions and one MRI assessment were performed. By combining 2D ultrasound and 3D motion capture, the tissue lengths were assessed at a fixed ankle joint position and compared to the MRI measurements using Bland–Altman plots. The intra-rater and inter-rater reliability for the static and dynamic length assessments was determined using the coefficient of variation, standard error of measurement (SEM), minimal detectable change (MDC95), and intraclass correlation coefficient (ICC). Results: The 3D ultrasound approach slightly underestimated the length when compared with MRI by 0.7%, 1.5%, and 1.1% for the GM muscle belly, Achilles tendon, and MTU, respectively. The approach showed excellent intra-rater as well as inter-rater reliability, with high ICC (≥ 0.94), small SEM (≤ 1.3 mm), and good MDC95 (≤ 3.6 mm) values, with even better reliability found for the static length measurements. Conclusion: The proposed 3D ultrasound approach was found to be valid and reliable for the assessment of the GM MTU, muscle belly, and Achilles tendon lengths, as well as the tissue lengthening behavior, confirming its potential as a useful tool for investigating the effects of training interventions or therapeutic treatments (e.g., surgery or conservative treatments such as stretching and orthotics). Level of evidence: Level II. [ABSTRACT FROM AUTHOR]

Introduction. Bodybuilding is a sport that requires all muscle groups to be similarly developed, bringing an aesthetic physique to the observers. The development of the triceps surae may be a difficult goal to achieve for some athletes. Considering this, we chose to focus on a new training method that induces less stress in muscle groups: the time under tension. Objective. The purpose of the study was to compare exercises used for calf hypertrophy using the time under tension method and to identify the optimal situations in which this method could be used. Methods. Ten subjects, 6 male and 4 female, age of 25.7±4.9 years old, height 174.7±9.5 centimeters, body weight 82±17.8 kg and with varied levels of fitness, participated in the study. The plantar flexions were done with body weight only on one and both feet. The exercises we tested were done on a 3 second cycle: 3 seconds on the upwards movement and 3 seconds for the downwards one. The subjects performed a total of 10 repetitions for each exercise. Results. A significant statistical difference was found between the types of plantar flexion measured. This indicates that the analysis of time under tension plantar flexion should take into account the actual type of movement done. Conclusions. Time under tension method for calf muscle hypertrophy should take into consideration the movement characteristics for the focused muscle group. Our results showed that postural balance and body position can influence the force and power output of plantar flexion. [ABSTRACT FROM AUTHOR]

This study compared the acute responses of three neuromuscular electrical stimulation (NMES) methods on muscle torque‐time integral (TTI) and neuromuscular fatigue. Narrow‐pulse (0.2 ms; NP), wide‐pulse (1 ms; WP), and tendon vibration superimposed onto wide‐pulse (WP + VIB)‐NMES conditions were applied to sixteen healthy individuals (n = 16) in three separate sessions in a randomized order. Stimulation intensity was set to elicit 20% of maximal voluntary contraction (MVC); the stimulus pattern comprised four sets of 20 repetitions (5 s On and 5 s Off) with a one‐minute inter‐set interval. TTI was measured for each NMES condition and MVC, voluntary activation (VA), peak twitch torque (Peaktwitch), and peak soleus (EMGSOL), medial (EMGMG), and lateral gastrocnemius (EMGLG) electromyography were measured before and immediately after each NMES condition. TTI was higher during WP + VIB (19.63 ± 6.34 MVC.s, mean difference = 3.66, p < 0.001, Cohen's d = 0.501) than during WP (15.97 ± 4.79 MVC.s) condition. TTI was higher during WP + VIB (mean difference = 3.79, p < 0.001, Cohen's d = 0.626) than during NP (15.84 ± 3.73 MVC.s) condition. MVC and Peaktwitch forces decreased (p ≤ 0.001) immediately after all conditions. No changes were observed for VA (p = 0.365). EMGSOL amplitude reduced (p = 0.040) only after NP, yet EMGLG and EMGMG amplitudes decreased immediately after all conditions (p = 0.003 and p = 0.013, respectively). WP + VIB produced a higher TTI than WP and NP‐NMES, with similar amounts of neuromuscular fatigue across protocols. All NMES protocols induced similar amounts of peripheral fatigue and reduced EMG amplitudes. [ABSTRACT FROM AUTHOR]

Mounting evidence suggests that motor evoked potentials (MEPs) recorded in upper limb muscles with postural support roles following transcranial magnetic stimulation receive contributions from both corticospinal and non-corticospinal descending pathways. We tested the hypothesis that neural structures responsible for regulating upright balance are involved in transmitting late portions of TMS-induced MEPs in a lower limb muscle. MEPs were recorded in the medial gastrocnemius muscles of each leg, while participants supported their upright posture in five postural conditions that required different levels of support from the target muscles. We observed that early and late portions of the MEP were modulated independently, with early MEP amplitude being reduced when high levels of postural support were required from a target muscle. Independent modulation of early and late MEPs by altered postural demand suggests largely separable transmission of each part of the MEP. The early component of the MEP is likely generated by fast-conducting corticospinal pathways, whereas the later component may be primarily transmitted along a polysynaptic cortico-reticulospinal pathway. [ABSTRACT FROM AUTHOR]

This study aims to analyze the effects of Dry Needling (DN) for the release of myofascial trigger points (MTrPs) in the triceps surae muscles (TSM). A systematic review was performed up to February 2022 in PubMed, PEDro, Scopus, CENTRAL, and Web of Science. Selection criteria were studies involving subjects older than 18 years presenting MTrPs in the TSM, without any concomitant acute or chronic musculoskeletal conditions; DN interventions applied to the MTrPs of the TSM; and results on pain, range of motion (ROM), muscle strength, muscle stiffness, and functional outcomes. The PEDro scale was used to assess the methodological quality of the studies, and the Risk of Bias Tool 2.0 to assess risk of bias. A total of 12 studies were included in the systematic review, involving 426 participants. These results suggest that DN of MTrPs in TSM could have a positive impact on muscle stiffness and functional outcomes. There are inconclusive findings on musculoskeletal pain, ROM, and muscle strength. Significant results were obtained in favor of the control groups on pressure pain thresholds. Despite the benefits obtained on muscle stiffness and functional performance, the evidence for the use of DN of MTrPs in the TSM remains inconclusive. [ABSTRACT FROM AUTHOR]

We examined the validity and reliability of biomechanical outcomes extracted using the Calf Raise application of three calf muscle tests. We then established normative calf muscle function values for male rugby union players accounting for rugby-related factors (position, level) alone and together with clinical factors (age, leg dominance, BMI, previous injury). In total, 120 athletes performed three single-leg calf muscle tests. Twenty athletes participated in application validation; 18 in test–retest reliability; and all in establishing normative equations. Validity of application outcomes against 3D motion and force plate data was good-to-excellent (CV ≤ 6.6%, ICC ≥0.84). Test–retest reliability was good across outcomes following familiarisation (CV < 10%, ICC ≥0.83). Forwards produced superior power than backs during the bodyweight (59 W, p = 0.007) and weighted (73 W, p < 0.001) power tests. Playing level influenced power outcomes (p < 0.009). Super Rugby players were more powerful than Club (both power tests), Provincial (both power tests), and International (bodyweight power). Backs completed more repetitions (3 repetitions, p = 0.001) and positive displacement (30 cm, p = 0.001) than forwards during endurance testing. When accounting for clinical factors; BMI, age, and previous injury explained some of the differences observed between positions and levels. This study provides initial benchmark values of calf muscle function in rugby union. [ABSTRACT FROM AUTHOR]

This randomised crossover study with repeated measures examined the influence of the three most common foot starting positions used in conducting the calf raise test (CRT) on test outcomes. This study also accounted for the potential influence of gender, age, body mass index (BMI), and level of physical activity on test outcomes. Forty-nine healthy individuals (59 % female, 21 ± 4 years) performed single-leg calf raise repetitions in a human movement laboratory in three randomised foot starting positions: flat, 10° incline, and step. The validated Calf Raise application was used to track the vertical displacement of a marker placed on the foot using computer vision. The application extracted the following CRT outcomes from the vertical displacement curve: number of repetitions, peak vertical height, total vertical displacement, and total positive work. Data were analysed using mixed-effects models and stepwise regression. There was a significant main effect (P < 0.001) of foot starting position on all outcomes, with all paired comparisons being statistically significant (P ≤ 0.023). Repetitions, total vertical displacement, and total positive work were greatest in flat and lowest in step, whereas peak vertical height was greatest in incline and lowest in step. Gender (P = 0.021; males>females) and BMI (P = 0.002; lower BMI>higher BMI) significantly influenced the number of repetitions. Gender (P < 0.001; males>females) also influenced total positive work. Age and physical activity levels did not significantly influence CRT outcomes. CRT foot starting position mattered and significantly affected all CRT outcomes. CRT foot starting position needs consideration when contrasting data in research and practice. • Varying foot starting position significantly affected calf raise test outcomes. • Repetitions, peak height, total displacement, and total work were greater from flat than 10° incline and step. • Gender and body mass index were significant predictors of calf raise test outcomes. • This study provides information useful for clinicians in implementing evidence-based practice. [ABSTRACT FROM AUTHOR]

Background: The prevalence, indications, and preferred methods for gastrocnemius recession and tendo-Achilles lengthening—grouped as triceps surae lengthening (TSL) procedures—in foot and ankle trauma are supported by a scarcity of clinical evidence. We hypothesize that injury, practice environment, and training heritage are significantly associated with probability of performing adjunctive TSL in the operative management of foot and ankle trauma. Methods: A survey was distributed to members of the American Orthopaedic Foot & Ankle Society and the Orthopaedic Trauma Association. Participants rated how likely they would be to perform TSL at initial management, definitive fixation, and after weightbearing in the presence and absence of a positive Silfverskiöld test in 10 clinical scenarios of closed foot and ankle trauma. Results: A total of 258 surgeons with median 14 years' experience responded. Eighty-five percent reported foot and ankle fellowship training, 24% reported traumatology fellowship training, 13% both, and 4% no fellowship. Ninety-nine percent reported performing TSL with a median 25 TSL procedures per year, 72% open gastrocnemius recession, and 17% percutaneous tendo-Achilles lengthening). Across all scenarios, we observed low overall 8% probability with fair agreement (κ = 0.246) of performing TSL (range, 1% at initial management of an unstable Weber B bimalleolar ankle fracture with negative contralateral Silfverskiöld test to 29% at definitive fixation of tongue-type calcaneus fracture with positive contralateral Silfverskiöld test). Silfverskiöld testing significantly influenced TSL probability at all time points. University of Washington training (β = 1.5, P =.007) but not trauma vs foot fellowship training, years in practice, academic practice, urban setting, or facility trauma designation were significantly associated with likelihood of performing TSL. Conclusion: Orthopaedic traumatology and foot and ankle surgeons report similar indications, methods, and low perceived propensity to use TSL in the management of foot and ankle trauma. We found that graduates of 1 fellowship training site were more likely to perform TSL in the setting of acute trauma potentially indicating the need for better scientific data to support this practice. Level of Evidence: Level V, therapeutic. [ABSTRACT FROM AUTHOR]

BACKGROUND: Stretching exercises increase the joint range of motion (ROM) and depend on the skeletal tissues' exposition-time to stretch. However, it is unclear how a long stretching time affects the muscle-tendon unit's passive mechanical properties. AIM: This study aimed to analyze changes in the triceps surae muscle-tendon unit’s passive mechanical properties before and after a 10-minute passive stretching protocol. METHOD: Thirty healthy participants (26.57 ± 3.82 years old) were allocated into a control group (n=15), who did not perform any intervention, and to an experimental group (n=15), who performed one bout of a 10-minute ankle plantar flexor passive static stretching. Ankle ROM, plantar flexor passive torque, and myotendinous junction displacement were evaluated pre-intervention, immediately after, and 15, 30, 45, and 60 minutes after the end of the intervention. The stiffnesses of the muscle-tendon unit, muscle, and tendon were calculated for all moments. A generalized estimating equation test was performed to compare groups and moments. RESULTS: The experimental group increased the ROM (p<0.001) from pre- to post-intervention and remained augmented up to 60 minutes. The myotendinous junction displacement decreased at post-30 and post-45 moments compared to pre-intervention. Muscular stiffness increased immediately after stretching and post-45 and post-60 minutes. Passive torque and musculotendinous unit stiffness decreased over time, with trivial, small, and moderate effect sizes, respectively. CONCLUSION: Passive static stretching (10 min) generates an acute ROM increase associated with muscletendon unit passive mechanical properties reduction, which lasts up to one-hour post-intervention. [ABSTRACT FROM AUTHOR]

BACKGROUND: Assessment of the plantar flexion (PF) isokinetic performance has been greatly diverse and based on personal preferences rather than standardized guidelines. OBJECTIVE: To examine the performance of the plantar flexors under different settings including knee joint angle and subject position. METHODS: Thirteen women and 20 men took part in this study. The isokinetic protocol (60 ∘ /s) was set to ankle movement between 10 ∘ dorsiflexion to 30 ∘ PF. Participants performed three repetitions of concentric PF in randomly-ordered knee angles; 15 ∘ , 45 ∘ and 90 ∘ , and in seated and supine positions. Surface electromyography (EMG) data were collected from the Soleus (SOL) and Gastrocnemius. RESULTS: Knee angle impacted the PF moment (P ⩽ 0.001–0.026) and work (P ⩽ 0.05) measures in both genders. The moment and work measures were significantly less in the 90 ∘ than those in the 45 ∘ and 15 ∘ positions. The 45 ∘ position had the highest values, particularly in sitting in the male participants. Only the GL EMG data was significantly impacted (P = 0.017) by the subject position. However, the difference was trivial (1.6%). The SOL muscle showed a consistent pattern of increased activity when the knee was in flexion. CONCLUSION: The 45 ∘ position seems to be optimal for obtaining the highest isokinetic PF scores. [ABSTRACT FROM AUTHOR]

Equinus deformity is a common cause of foot and ankle pathology. The purpose of our study was to evaluate the role of the plantaris in equinus. Secondary aims were to describe the role of the plantaris in intramuscular gastrocnemius recession and to determine the prevalence of the plantaris in our patient population. We measured ankle dorsiflexion during the steps of a Baumann-type intramuscular gastrocnemius recession. Eighty-nine patients were enrolled in our study. Fourteen of 89 (15.7%) patients did not have a plantaris. A mean dorsiflexion of 9 (interquartile range 6-12)° was obtained after transection of the plantaris tendon and an additional mean 8 (interquartile range 5-10)° was obtained after recession of the gastrocnemius aponeurosis. There was a strong positive correlation (rs = 0.842) of dorsiflexion increase after plantaris transection and dorsiflexion increase after gastrocnemius recession (p <.00). Linear regression showed that for every one-degree of dorsiflexion increase with plantaris transection, there was a predicted dorsiflexion increase of 0.69° with gastrocnemius recession. These results indicate that the plantaris is a component of equinus deformity. [ABSTRACT FROM AUTHOR]

The aim of this review was to report on the imaging modalities used to assess morphological and architectural properties of the m. triceps surae muscle in typically developing children, and the available reliability analyses. Scopus and MEDLINE (Pubmed) were searched systematically for all original articles published up to September 2020 measuring morphological and architectural properties of the m. triceps surae in typically developing children (18 years or under). Thirty eligible studies were included in this analysis, measuring fibre bundle length (FBL) (n = 11), pennation angle (PA) (n = 10), muscle volume (MV) (n = 16) and physiological cross‐sectional area (PCSA) (n = 4). Three primary imaging modalities were utilised to assess these architectural parameters in vivo: two‐dimensional ultrasound (2DUS; n = 12), three‐dimensional ultrasound (3DUS; n = 9) and magnetic resonance imaging (MRI; n = 6). The mean age of participants ranged from 1.4 years to 18 years old. There was an apparent increase in m. gastrocnemius medialis MV and pCSA with age; however, no trend was evident with FBL or PA. Analysis of correlations of muscle variables with age was limited by a lack of longitudinal data and methodological variations between studies affecting outcomes. Only five studies evaluated the reliability of the methods. Imaging methodologies such as MRI and US may provide valuable insight into the development of skeletal muscle from childhood to adulthood; however, variations in methodological approaches can significantly influence outcomes. Researchers wishing to develop a model of typical muscle development should carry out longitudinal architectural assessment of all muscles comprising the m. triceps surae utilising a consistent approach that minimises confounding errors. [ABSTRACT FROM AUTHOR]