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Purpose: While muscle mass and skeletal muscle fibers phenotype have been shown atypical in constitutional thinness (CT), force production capacities and its architectural determinants have never been explored. The present study compared muscle functionality and architecture between participants with CT and their normal-weight (NW) counterparts. Methods: Anthropometry, body composition (Dual-X-ray Absorptiometry), physical activity/sedentary behavior (ActiGraph wGT3X-BT), ultrasound recording of the Vastus Lateralis (2D-ultrasound system), and functional capacities at maximal isometric and isokinetic voluntary contractions (MVCISO and MVCCON) during knee extension (isokinetic dynamometer chair Biodex) have been measured in 18 women with CT (body mass index < 17.5 kg/m2) and 17 NW women. Results: A lower fat-free mass (ES: −1.94, 95%CI: −2.76 to −1.11, p < 0.001), a higher sedentary time, and a trend for a lower time spent at low-intensity physical activity, were observed in CT vs NW participants. While absolute MVCISO, MVCCON, rate of torque development (RTD), and torque work were all markedly lower in CT, these differences disappeared when normalized to body or muscle mass. Muscle thickness and fascicle length were found lower in CT (ES: −1.29, 95%CI: −2.03 to −0.52, p < 0.001; and ES: −0.87, 95%CI: −1.58 to −0.15, p = 0.02, respectively), while pennation angle was found similar. Conclusion: Despite lower absolute strength capacities observed in CT, present findings support the hypothesis of physiological adaptations to the low body and muscle mass than to some intrinsic contractile impairments. These results call for further studies exploring hypertrophy-targeted strategies in the management of CT. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the effect of unmodulated low-frequency superficial neuromuscular electrical stimulation (NMES) for 30 and 60 min/day during 7 weeks on muscle contractile functions. Many studies have examined the effect of training intensity during NMES on maximal voluntary isometric strength (MVIS). However, no study has assessed the effect of NMES duration per day and per week on changes in muscle functions. Ten healthy volunteers (23.2 ± 3.2 years; age range 18–28 years) participated in the study and were randomly assigned to group 1 (30 min NMES) and group 2 (60 min NMES) five times a week. The influence of NMES training was estimated by changes in MVIS and speed-strength properties of foot extensors before electrical training and in the beginning of each week of a 7-week training period for all subjects. Contractile abilities were recorded with a Biodex isokinetic dynamometer. After a 7-week training period, MVIS and voluntary maximal explosive strength differed significantly between groups. Referring to electrical stimulation parameters and healthy subjects of this study, electrical training caused an increase in foot extensor muscle strength and a gradient in voluntary explosive strength when used for five trainings per week for 30 min for 7 weeks. [ABSTRACT FROM AUTHOR]

This study aimed (i) to investigate the role of regional characteristics of the knee extensors muscles (vastus lateralis: VL, vastus intermedius: VI and rectus femoris: RF) in determining maximum-voluntary force (MVF); and (ii) to understand which regional parameter of muscle structure would best predict MVF. Muscle architecture (e.g., pennation angle and fascicle length), muscle volume (Vol), anatomical (ACSA) and physiological cross-sectional-area (PCSA) were measured in the proximal (0–33% of the muscle length), middle (33–66% of the muscle length) and distal (66–100% of the muscle length) portions of each muscle in fifteen healthy males using ultrasound and Magnetic Resonance Imaging (MRI). Knee extensors force was calculated in isometric condition at a single knee joint angle of 90 degrees. Regional ACSA, Vol and PCSA were correlated with MVF production. Regional muscle geometry showed no significant correlations with MVF. Among regions, the middle portion of each muscle was largely correlated with MVF compared to all the other regions (distal and proximal). To understand which regional structural parameter best predicted MVF, a stepwise multiple linear regression was performed. This model showed a significant explanatory power (P < 0.001, R2 = 0.76, adjusted R2 = 0.71), including muscle Vol collected in the mid portions of VL and RF. Even if no significant differences were reported between Vol, PCSA and ACSA in determining MVF, our results showed that the RF and VL volume collected in the middle portion of the muscle length are strong determinants of MVF produced by the knee extensors at 90 degrees joint angle. [ABSTRACT FROM AUTHOR]

Technological advances have enabled the development of a novel technique of dissection, digitization and three-dimensional modelling of skeletal muscle and other tissues including neurovascular structures as in situ over the last 25 years. Meticulous serial dissection followed by digitization is used to collect Cartesian coordinate data of the contractile and connective tissue elements throughout the entire muscle volume. The Cartesian coordinate can then be used to construct high-fidelity three-dimensional models that capture the spatial arrangement of the contractile and connective tissue elements as in situ enabling detailed studies of the arrangement of the fiber bundles and their attachment sites to aponeuroses, tendon, and bone. In the laboratory, we have concurrently developed a computational methodology to quantify architectural parameters, including fiber bundle length, pennation angle, volume, physiological cross-sectional area in three-dimensional space. In this paper, a flexor digitorum superficialis specimen will be used to demonstrate the high-fidelity outcomes of dissection, digitization, and three-dimensional modelling. This three-step methodology provides a unique opportunity to study muscle architecture in three dimensions, as in situ. Knowledge translation from the anatomy laboratory to the clinical setting has been highly successful. [ABSTRACT FROM AUTHOR]

Purpose: Assessing muscle flexibility and architecture is important for hamstring strain injury (HSI) prevention. We investigated the relationship between shear modulus and passive force in hamstring muscles at different sites and the effect of muscle architecture on the slope of the shear modulus–passive force using shear wave elastography (SWE). Methods: The biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles were dissected from nine Thiel-embalmed cadavers and fixed to a custom-made mechanical testing machine. Calibrated weights (0−1800 g) were applied gradually in 150-g increments. The shear modulus and anatomical cross-sectional area (ACSA) were measured at proximal, central, and distal points using SWE. The muscle mass and length were measured before the loading test. The shear modulus–passive load relationship of each tested muscle region was analyzed by fitting a least-squares regression line. The increase in shear modulus slope per unit load was calculated and compared between the muscles before and after normalization by the muscle mass, length, and ACSA. Results: The shear modulus and passive force for all hamstring muscles in each region showed a statistically significant linear correlation. Furthermore, the increase in shear modulus slope was greater for BFlh and ST than for SM (P < 0.05), but after normalization by the muscle length and ACSA, there were no significant differences among the muscles. Conclusion: The local mechanical properties of individual hamstring muscles can be indirectly estimated using SWE, and the slope of increase in shear modulus reflects characteristics of the muscle architecture. [ABSTRACT FROM AUTHOR]

Musculotendon parameters are key factors in the Hill-type muscle contraction dynamics, determining the muscle force estimation accuracy of a musculoskeletal model. Their values are mostly derived from muscle architecture datasets, whose emergence has been a major impetus for model development. However, it is often not clear if such parameter update indeed improves simulation accuracy. Our goal is to explain to model users how these parameters are derived and how accurate they are, as well as to what extent errors in parameter values might influence force estimation. We examine in detail the derivation of musculotendon parameters in six muscle architecture datasets and four prominent OpenSim models of the lower limb, and then identify simplifications which could add uncertainties to the derived parameter values. Finally, we analyze the sensitivity of muscle force estimation to these parameters both numerically and analytically. Nine typical simplifications in parameter derivation are identified. Partial derivatives of the Hill-type contraction dynamics are derived. Tendon slack length is determined as the musculotendon parameter that muscle force estimation is most sensitive to, whereas pennation angle is the least impactful. Anatomical measurements alone are not enough to calibrate musculotendon parameters, and the improvement on muscle force estimation accuracy will be limited if the source muscle architecture datasets are the only main update. Model users may check if a dataset or model is free of concerning factors for their research or application requirements. The derived partial derivatives may be used as the gradient for musculotendon parameter calibration. For model development, we demonstrate that it is more promising to focus on other model parameters or components and seek alternative strategies to further increase simulation accuracy. [ABSTRACT FROM AUTHOR]

For the first 100+ million years of their evolutionary history, the majority of mammals were very small, and many exhibited relatively generalized locomotor ecologies. Among extant mammals, small-bodied, generalist species share similar hindlimb bone morphology and locomotor mechanics, but details of their musculature have not been investigated. To examine whether hindlimb muscle architecture properties are also similar, we dissected hindlimb muscles of the gray short-tailed opossum (Monodelphis domestica) and aggregated muscle properties from the literature for three other small-bodied mammals (Mus musculus, Rattus norvegicus, Cavia porcellus). We then studied hindlimb musculature from a whole-limb perspective and by separating the limb into nine anatomical regions. The region analysis explained substantially more variance in the data (r2: 0.601 > 0.074) but only detected six statistically significant pairwise species differences in muscle architecture properties. This finding suggests either deep conservation of therian hindlimb muscle properties or, more likely, a biomechanical constraint imposed by small body size. In addition, we find specialization for either large force production (i.e., PCSA) or longer active working ranges (i.e. long muscle fascicles) in proximal limb regions but neither specialization in more distal limb regions. This functional pattern may be key for small mammals to traverse across uneven and shifting substrates, regardless of environment. These findings are particularly relevant for researchers seeking to reconstruct and model soft tissue properties of extinct mammals during the early evolutionary history of the clade. [ABSTRACT FROM AUTHOR]

Manipulating resistance training variables is crucial to plan the induced stimuli correctly. When reporting the exercise variables in resistance training protocols, sports scientists and practitioners often refer to the load lifted and the total number of repetitions. The present conceptual review explores all within-exercise variables that may influence the strength and hypertrophic gains, and the changes in muscle architecture. Together with the (1) load and (2) the number of repetitions, (3) performing repetitions to failure or not to failure, (4) the displacement of the load or the range of movement (full or partial), (5) the portion of the partial movement to identify the muscle length at which the exercise is performed, (6) the total time under tension, the duration of each phase and the position of the two isometric phases, (7) whether the concentric, eccentric or concentric-eccentric phase is performed, (8) the use of internal or external focus and (9) the inter-set rest may all have repercussions on the adaptations induced by each resistance exercise. Manipulating one or more variable allows to increase, equalize or decrease the stimuli related to each exercise. Sports scientists and practitioners are invited to list all aforementioned variables for each exercise when reporting resistance training protocols. [ABSTRACT FROM AUTHOR]

Purpose: Due to its eccentric nature, downhill running (DR) training has been suggested to promote strength gains through neuromuscular adaptations. However, it is unknown whether short-term chronic DR can elicit such adaptations. Methods: Twelve untrained, young, healthy adults (5 women, 7 men) took part in 4 weeks' DR, comprising 10 sessions, with running speed equivalent to 60–65% maximal oxygen uptake ( V ˙ O2max, assessed at weeks 0 and 4). Isometric and isokinetic knee-extensor maximal voluntary torque (MVT), vastus lateralis (VL) muscle morphology/architecture (anatomical cross-sectional area, ACSA; physiological CSA, PCSA; volume; fascicle length, Lf; pennation angle, PA) and neuromuscular activation (VL EMG) were assessed at weeks 0, 2 and 4. Results: MVT increased by 9.7–15.2% after 4 weeks (p < 0.01). VL EMG during isometric MVT increased by 35.6 ± 46.1% after 4 weeks (p < 0.05) and correlated with changes in isometric MVT after 2 weeks (r = 0.86, p = 0.001). VL ACSA (+2.9 ± 2.7% and +7.1 ± 3.5%) and volume (+2.5 ± 2.5% and +6.6 ± 3.2%) increased after 2 and 4 weeks, respectively (p < 0.05). PCSA (+3.8 ± 3.3%), PA (+5.8 ± 3.8%) and Lf (+2.7 ± 2.2%) increased after 4 weeks (p < 0.01). Changes in VL volume (r = 0.67, p = 0.03) and PCSA (r = 0.71, p = 0.01) correlated with changes in concentric MVT from 2 to 4 weeks. V ˙ O2max (49.4 ± 6.2 vs. 49.7 ± 6.3 mL·kg−1·min−1) did not change after 4 weeks (p = 0.73). Conclusion: Just 4 weeks' moderate-intensity DR promoted neuromuscular adaptations in young, healthy adults, typically observed after high-intensity eccentric resistance training. Neural adaptations appeared to contribute to most of the strength gains at 2 and 4 weeks, while muscle hypertrophy seemed to contribute to MVT changes from 2 to 4 weeks only. [ABSTRACT FROM AUTHOR]

Even under isometric conditions, muscle contractions are associated with some degree of fiber shortening. The effects of muscle shortening on extracellular electromyographic potentials have not been characterized in detail. Moreover, the anatomical, biophysical, and detection factors influencing the muscle-shortening effects have been neither identified nor understood completely. Herein, we investigated the effects of muscle shortening on the amplitude and duration characteristics of single-fiber, motor unit, and compound muscle action potentials. We found that, at the single-fiber level, two main factors influenced the muscle-shortening effects: (1) the electrode position and distance relative to the myotendinous zone and (2) the electrode distance to the maxima of the dipole field arising from the stationary dipole created at the fiber-tendon junction. Besides, at the motor unit and muscle level, two additional factors were involved: (3) the overlapping between the propagating component of some fibers with the non-propagating component of other fibers and (4) the spatial spreading of the fiber-tendon junctions. The muscle-shortening effects depend critically on the electrode longitudinal distance to the myotendinous zone. When the electrode was placed far from the myotendinous zone, muscle shortening resulted in an enlargement and narrowing of the final (negative) phase of the potential, and this enlargement became less pronounced as the electrode approached the fiber endings. For electrode locations close to the myotendinous zone, muscle shortening caused a depression of both the main (positive) and final (negative) phases of the potential. Beyond the myotendinous zone, muscle shortening led to a decrease of the final (positive) phase. The present results provide reference information that will help to identify changes in MUPs and M waves due to muscle shortening, and thus to differentiate these changes from those caused by muscle fatigue. [ABSTRACT FROM AUTHOR]

Purpose: Respiratory and musculoskeletal function decline with age, irrespective of physical activity levels. Previous work has suggested that the age-related rate of decline in function of these two systems might be similar, but it is not known to what extent each system contributes to decreasing performance in ageing master cyclists. Therefore, the purposes of this study are (1) whether the age-related rate of decline in respiratory function, respiratory muscle strength, muscle architecture, muscle function, haemoglobin concentration, haematocrit and performance in master cyclists is uniform and (2) which parameters contribute most to the reduction in performance with age. Methods: Master cyclists were recruited during the Track Cycling Masters World Championship 2019 in Manchester. Respiratory function and respiratory muscle strength were determined using spirometry and a mouth pressure device, respectively. Muscle architecture was determined using ultrasonography, and muscle function by countermovement jump. Results: Forced expiratory volume in the first second, forced vital capacity, fascicle length, muscle thickness, take-off velocity, jump power, jump power per body mass, handgrip strength, haemoglobin concentration and performance correlated negatively with age (p ≤ 0.043). The age-related rate of decline did not differ significantly between parameters (p = 0.124), but it was slower for haemoglobin concentration (p = 0.041). Take-off velocity was the major determinant of performance in 200, 500 and 2000 m track cycling disciplines (R2adj = 0.675, 0.786 and 0.769, respectively; p < 0.001). Conclusion: Age-related decline in respiratory and muscle system is accompanied by a similar rate of decline in performance. The major contribution to the age-related decline of performance is reduced muscle function, specifically take-off velocity. [ABSTRACT FROM AUTHOR]

Muscle architecture, which includes parameters like fascicle length, pennation angle, and physiological cross-sectional area, strongly influences skeletal muscles' mechanical properties. During maturation, the muscle architecture has to adapt to a growing organism. This study aimed to develop an architectural model capable of predicting the complete 3D fascicle architecture for primarily unipennate muscles of an arbitrary age, based on fascicle data for an initial age. For model development, we collected novel data on 3D muscle architecture of the rabbit (Oryctolagus cuniculus) M. plantaris of eight animals ranging in age from 29 to 106 days. Experimental results show that plantaris muscle belly length increases by 73%, whereas mean fascicle length and mean pennation angle increases by 39 and 14%, respectively. Those changes were incorporated into the model. In addition to the data collected for M. plantaris the predictions of the model were compared to existing literature data of rabbit M. soleus and M. gastrocnemius medialis. With an error of −1.0 ± 8.6% for relative differences in aponeurosis length, aponeurosis width, muscle height, and muscle mass, the model delivered good results matching interindividual differences. For future studies, the model could be utilized to generate realistic architectural data sets for simulation studies. [ABSTRACT FROM AUTHOR]

Purpose: To examine whether unilateral multifidus damage could promote degeneration at the L5-6 facet joint (FJ) and compensatory changes in lumbo-pelvic muscles in rats. Methods: 12 facet clamp, 12 facet sham and 7 control rats were studied. Facet clamp and sham animals had the left L5-6 FJ exposed, and the clamp group had a mild compressive clamp applied using hemostatic forceps to model post-traumatic arthritis. Both groups then had the left multifidus detached from the L1–L6 spinous processes. Animals were euthanized 28 days post-surgery. Muscle mass and fascicle length were evaluated bilaterally for the paraspinal muscles, gluteal muscles and biceps femoris. Intra-muscular collagen of the paraspinal muscles was measured histologically. FJ transverse plane angles were measured from micro-computed tomography scans. L5-6 FJ degeneration was evaluated through the 24-point OARSI scale. Results: Differences, compared to control, were observed in the detached multifidus from both facet clamp and sham groups; namely decreased mass and fascicle length and increased collagen content. However, no between group differences were found for any other muscle. Further, mild FJ degeneration was more prevalent in the groups that had experienced multifidus injury but was not exacerbated by the mild compressive clamping of the FJ. Conclusion: Unilateral multifidus injury with or without FJ compressive clamping does not have a clear impact on the characteristics of surrounding spinal musculature within 28 days post-surgery in rats. Mild FJ degeneration was present in some animals from all three groups, and the impact of multifidus injury on this degeneration is inconclusive. [ABSTRACT FROM AUTHOR]

Callitrichidae are small, arboreal New World primates that utilize a variety of locomotor behaviors including trunk-to-trunk leaping (TTL) and horizontal locomotion which involve differential functional demands. Little is known about the relationship between the preferred locomotor behavior and musculoskeletal architecture of these primates. In this study, we compared the musculoskeletal architecture of selected shoulder muscles in two cadavers each of the trunk-to-trunk leaper Cebuella pygmaea and the mainly pronograde quadrupedally moving Saguinus imperator subgrisescens. Contrast-enhanced microfocus computed tomography (µCT) was used to virtually dissect the cadavers, produce muscle maps, and create 3D reconstructions for an image-based analysis of the muscles. Muscle lengths, muscle volumes, and osteological muscle moment arms were measured, and the anatomical cross-sectional areas (ACSA) were calculated. We expected the muscles of the forelimb of S. imperator to be larger in volume and to be relatively shorter with a larger ACSA due to a higher demand for powerful extension in the forelimbs of this horizontally locomoting species. For C. pygmaea, we expected relatively larger moment arms for the triceps brachii, supraspinatus, infraspinatus and subscapularis, as larger moment arms present an advantage for extensive vertical clinging on the trunk. The muscles of S. imperator were relatively larger in volume than in C. pygmaea and had a relatively larger ACSA. Thus, the shoulder muscles of S. imperator were suited to generate relatively larger forces than those of C. pygmaea. Contrary to our expectations, there were only slight differences between species in regard to muscle lengths and moment arms, which suggests that these properties are not dependent on the preferred locomotor mode. The study of this limited dataset demonstrates that some but not all properties of the musculoskeletal architecture reflect the preferred locomotor behavior in the two species of Callitrichidae examined. [ABSTRACT FROM AUTHOR]

Aquatic birds show a great diversity of locomotion styles and wing morphologies, from penguins that are fully specialized for an aquatic life to species of aerial flyers that also use their wings for underwater propulsion (e.g. auks and shearwaters). Moving between the air–water interface exerts conflicting pressures on the body and wing anatomy of diving birds. In this work, we investigated the functional morphology of the forelimb musculature of 18 species of aquatic birds that display a variety of flight and foraging styles. Muscle architecture was related to function, with special emphasis on muscle mass. Dissections of one of the forelimbs of 20 specimens of waterbirds were performed to obtain numerical data of muscle architecture. Total wing muscle mass scaled isometrically to body mass1.0, whereas fascicle length scaled to muscle mass0.284, which is consistent with previous results of scaling in wings of raptors. A principal component analysis (PCA) of normalised muscle masses resulted in a biplot where three main morphological groups can be distinguished. Anatids (ducks and geese) occupy a space represented by muscles that are activated during downstroke. Auks and penguins clustered together in a region dominated by muscles that assist in wing elevation and showed a degree of hypertrophy. The rest of the species grouped together in the lower limits of both PCs where muscles that facilitate wing flexion–extension and stabilisation are loaded. The distribution of mass in the wing muscles of the aquatic birds seemed to be related to flight and foraging style and showed non-significant influence of shared phylogenetic history (Kmult: 0.71, p value: 0.083, 10,000 permutations). [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effects of 12 weeks of passive static stretching training (PST) on force-generating capacity, passive stiffness, muscle architecture of plantarflexor muscles.Methods: Thirty healthy adults participated in the study. Fifteen participants (STR, 6 women, 9 men) underwent 12-week plantarflexor muscles PST [(5 × 45 s-on/15 s-off) × 2exercises] × 5times/week (duration: 2250 s/week), while 15 participants (CTRL, 6 women, 9 men) served as control (no PST). Range of motion (ROM), maximum passive resistive torque (PRTmax), triceps surae architecture [fascicle length, fascicle angle, and thickness], passive stiffness [muscle-tendon complex (MTC) and muscle stiffness], and plantarflexors maximun force-generating capacity variables (maximum voluntary contraction, maximum muscle activation, rate of torque development, electromechanical delay) were calculated Pre, at the 6th (Wk6), and the 12th week (Wk12) of the protocol in both groups.Results: Compared to Pre, STR ROM increased (P < 0.05) at Wk6 (8%) and Wk12 (23%). PRTmax increased at Wk12 (30%, P < 0.05), while MTC stiffness decreased (16%, P < 0.05). Muscle stiffness decreased (P < 0.05) at Wk6 (11%) and Wk12 (16%). No changes in triceps surae architecture and plantarflexors maximum force-generating capacity variables were found in STR (P > 0.05). Percentage changes in ROM correlated with percentage changes in PRTmax (ρ = 0.62, P = 0.01) and MTC stiffness (ρ = - 0.78, P = 0.001). In CTRL, no changes (P > 0.05) occurred in any variables at any time point.Conclusion: The expected long-term PST-induced changes in ROM were associated with modifications in the whole passive mechanical properties of the ankle joint, while maximum force-generating capacity characteristics were preserved. 12 weeks of PST do not seem a sufficient stimulus to induce triceps surae architectural changes. [ABSTRACT FROM AUTHOR]

Purpose: Neural drive and contractile properties are well-defined physiological determinants of explosive strength, the influence of muscle architecture and related morphology on explosive strength is poorly understood. The aim of this study was to examine the relationships between Quadriceps muscle architecture (pennation angle [ΘP] and fascicle length [FL]) and size (e.g., volume; QVOL), as well as patellar tendon moment arm (PTMA) with voluntary and evoked explosive knee extension torque in 53 recreationally active young men. Method: Following familiarisation, explosive voluntary torque at 50 ms intervals from torque onset (T50, T100, T150), evoked octet at 50 ms (8 pulses at 300-Hz; evoked T50), as well as maximum voluntary torque, were assessed on two occasions with isometric dynamometry. B-mode ultrasound was used to assess ΘP and FL at ten sites throughout the quadriceps (2–3 sites) per constituent muscle. Muscle size (QVOL) and PTMA were quantified using 1.5 T MRI. Result: There were no relationships with absolute early phase explosive voluntary torque (≤ 50 ms), but θP (weak), QVOL (moderate to strong) and PTMA (weak) were related to late phase explosive voluntary torque (≥ 100 ms). Regression analysis revealed only QVOL was an independent variable contributing to the variance in T100 (34%) and T150 (54%). Evoked T50 was also related to QVOL and θP. When explosive strength was expressed relative to MVT there were no relationships observed. Conclusion: It is likely that the weak associations of θP and PTMA with late phase explosive voluntary torque was via their association with MVT/QVOL rather than as a direct determinant. [ABSTRACT FROM AUTHOR]

Purpose: This study examined whether additional external load during the eccentric phase of lower limb strength training exercises led to greater adaptations in knee extensor strength, muscle architecture, and patellar tendon properties than traditional concentric–eccentric training in already-trained men. Methods: Twenty-eight men accustomed to strength training were randomized to undertake 10 weeks of supervised traditional (TRAD) or accentuated eccentric loading (AEL) or continue their habitual unsupervised (CON) strength training. TRAD and AEL trained 2∙week−1 with a six-repetition maximum (RM) session and a ten-RM session. TRAD used the same external load in both concentric and eccentric phases, while AEL used 40% greater load during the eccentric than concentric phase. Tests were performed at pre- and post-training, including: maximum unilateral isokinetic (30°·s−1) concentric, eccentric and isometric torques by isokinetic dynamometry, unilateral isometric ramp contractions with muscle–tendon ultrasound imaging to measure tendon stiffness and hysteresis, and resting vastus lateralis and medialis fascicle angle and length measured by extended-field-of-view ultrasound. Results: After training, both TRAD and AEL significantly increased maximum concentric and isometric torque (p < 0.05), but only AEL increased eccentric torque (AEL: + 10 ± 9%, TRAD: + 4 ± 9%) and vastus lateralis (AEL: + 14 ± 14%, TRAD: + 1 ± 10%) and medialis (AEL: + 19 ± 8%, TRAD: + 5 ± 11%) fascicle length. Conclusion: Both TRAD and AEL increased maximum knee extensor strength but only AEL increased VL and VM fascicle length. Neither training program promoted changes in fascicle angle or changes in patellar tendon properties in our already-trained men. [ABSTRACT FROM AUTHOR]

Purpose: The aponeurosis, a sheet of fibrous tissue, is the deep and superficial fascia where muscle fibers attach in pennate muscles. It is quite possible that the aponeurosis size increases in response to resistance training-induced fiber hypertrophy due to an increase in connection area. As a result, it leads to an increase in anatomical muscle cross-sectional area. However, attention has not been paid to aponeurosis area changes. This review sought to determine whether muscle hypertrophy changes aponeurosis width following short-term resistance training using an equation we modified [post/pre changes in aponeurosis width (AWpost/pre) = post/pre changes in anatomical cross-sectional area (CSApost/pre) ÷ post/pre changes in pennation angle (PApost/pre) ÷ post/pre changes in fascicle length (FLpost/pre)].Methods: A search using two electronic databases (PubMed and Google Scholar) was conducted. Nine studies measured CSApost/pre, PApost/pre, and FLpost/pre of the vastus lateralis muscle by ultrasound and magnetic resonance imaging.Results: There was a statistically significant 2.73 [95% CI 1.11, 4.36; p = 0.009] cm2 increase in CSApost/pre along with a statistically significant 1.21° [95% CI 0.44, 1.97; p = 0.002] increase in PApost/pre and a statistically significant 0.36 cm [95% CI 0.19, 0.54; p = 0.0002] increase in FLpost/pre. These results yield an estimated 1% reduction in aponeurosis width.Conclusion: Our results suggest that while muscle CSA, pennation angle, and fascicle length all increase following short-term resistance training, the aponeurosis width is not altered. [ABSTRACT FROM AUTHOR]

Nutritional alterations are highly prevalent in older rather than adult hospitalized patients. In these subjects, a loss of physical performance is dependent on the impairment of muscle architecture. This study aimed to investigate the association between the nutritional status and muscle architecture in elderly patients hospitalized in internal medicine wards. 68 aged patients admitted in internal medicine wards were consecutively enrolled and stratified in three groups based on the Mini Nutritional Assessment (MNA) score: well-fed (WF), at risk of malnutrition (RM), and malnourished (M). Biochemical indices and anthropometric parameters were sampled at hospital admission. Furthermore, all patients were assessed at admission and after 7 days of hospitalization for muscle strength (hand-grip test), mass (bioimpedentiometry), and architecture (ultrasonography of vastus lateralis). At hospital admission, M patients showed lower percentage of fat free mass and muscle mass with respect to WF and RM. Furthermore, M group presented with lower muscle thickness and pennation angle, as compared to WF and RM. At admission, the MNA score was positively related to the pennation angle and muscle strength. Multivariate linear regression analysis showed that the nutritional status at admission was the only significant factor influencing pennation angle. Finally, during the first 7 days of hospitalization, a decrease of pennation angle occurred in all the groups studied. We conclude that malnutrition at admission is associated with impaired muscle architecture in elderly patients hospitalized in internal medicine wards. Moreover, muscle architecture is impacted by early hospitalization, irrespective of nutritional status. [ABSTRACT FROM AUTHOR]

In the present study we calculated the muscle fascicle length (MFL) and the physiological cross-sectional area (PCSA) in the elbow flexor muscles of five Homo sapiens and five Pan troglodytes. We also assessed the expression of the myosin heavy chain (MyHC) isoforms with real-time quantitative polymerase chain reaction in the same muscles and, finally, we analyzed the muscle insertion sites in the proximal epiphyses of the ulna and the radius with 3D geometric morphometrics. Our main objective is to identify quantitative differences in the elbow flexor muscles of Homo sapiens and Pan troglodytes in terms of muscle architecture, expression of MyHC isoforms, and bone insertion sites and to explore the association of these differences with the types of locomotion developed by these two species of hominoid primates. We observed that the elbow flexor muscles had a greater PCSA and a higher expression of the fast MyHC-II isoforms in Pan troglodytes, while they had a greater MFL and a higher expression of the slow MyHC-I isoform in Homo sapiens. The insertion site of the brachialis was larger in Pan troglodytes, while that of the biceps brachii was larger in Homo sapiens. Our findings may be related to the greater capacity of force generation in the elbow flexor muscles of Pan troglodytes, as an adaptation to vertical climbing, and to the greater contraction speed and resistance to fatigue of the muscles in Homo sapiens, as an adaptation to the manipulative function of the upper extremities. [ABSTRACT FROM AUTHOR]

In individuals of similar body mass representing closely related species with different lifestyles, muscle architectural properties can be assumed to reflect adaptation to differing, lifestyle-related functional demands. We here employ a fibre recognition algorithm on contrast-enhanced micro-computed tomography (μCT) scans of one specimen each of an arboreal (Sciurus vulgaris) and a fossorial (Spermophilus citellus) sciuromorph rodent. The automated approach accounts for potential heterogeneity of architectural properties within a muscle by analysing all fascicles that compose a muscle. Muscle architectural properties (volume, fascicle length and orientation, and force-generating capacity) were quantified in 14 hindlimb (hip, knee, and ankle) extensor muscles and compared between specimens. We expected the arboreal squirrel to exhibit greater force-generating capacity and a greater capacity for length change allowing more powerful hindlimb extension. Generally and mostly matching our expectations, the S. vulgaris specimen had absolutely and relatively larger extensor muscles than the S. citellus specimen which were thus metabolically more expensive and demonstrate the relatively larger investment into powerful hindlimb extension necessary in the arboreal context. We conclude that detailed quantitative data on hindlimb muscle internal structure as was gathered here for a very limited sample further lends support to the notion that muscle architecture reflects adaptation to differential functional demands in closely related species with different locomotor behaviours and lifestyles. [ABSTRACT FROM AUTHOR]

Objectives: To investigate any differences in muscle architecture (fascicle angle, fascicle length, and muscle thickness) and muscle strength in people of different ages with and without knee osteoarthritis (OA). Methods: This is a cross-sectional study conducted with 40 individuals with and 40 without knee OA. Four groups were analyzed, middle-aged OA group (KL II/III) aged 40–50 years (n = 20), middle-aged healthy (H) group aged 40–50 years (n = 20), older OA group (KL II/III) aged 70 years and over (n = 20), and older H group, aged 70 years and over (n = 20). Outcomes analyzed were isometric and isokinetic peak torque of knee extensors, level of physical activity, self-reported pain level, and vastus lateralis fascicle length, fascicle angle, and muscle thickness assessed by ultrasound. One-way ANOVA was used to identify differences between groups, followed by the Tukey post hoc test. Results: There were no differences between the middle-aged OA group and older H group for any variables. The older OA group presented the smallest muscle architecture parameters and worst isometric and concentric peak torques compared to the other three groups (p < 0.001). In contrast, the middle-aged H group presented the largest muscle architecture parameters and was the strongest group compared to the others (p < 0.001). Conclusions: The presence of knee OA is associated with early muscular changes and seems to intensify these thigh changes that are similar to the effects of the aging process. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to determine the effect of a 15-week partial range of motion (ROM) resistance training program on the vastus lateralis (VL) architecture and mechanical properties, when the time under tension (TUT) was equalized.Methods: Nineteen untrained male subjects were randomly assigned to a control (Control; n = 8) or training (TG; n = 11) group. In the TG, the dominant and nondominant legs were randomly selected to be trained with a full ROM (FULL) or a partial ROM (PART) in an isokinetic dynamometer. Training volume was equalized based on the TUT by manipulating sets and repetitions. The VL muscle architecture was assessed by B-mode ultrasonography at rest and during maximal isometric knee extension contractions (MVCs) at ten knee angles. The VL fascicle force and specific tension were calculated from the MVCs with superimposed stimuli, accounting for the moment arm length, muscle architecture, and antagonist coactivation.Results: The FULL training induced changes in fascicle length (FL) (4.9 ± 2.0%, P < 0.001) and specific tension (25.8 ± 18.7%, P < 0.001). There was a moderate effect of PART training on the physiological cross-sectional area (PCSA) (7.8 ± 4.0%, P < 0.001, dav = 0.6) and torque-angle adaptations (average increase 17.7 ± 3.9%, P < 0.05).Conclusions: These results provide evidence that crucial architectural and mechanical muscle adaptations are dependent on the ROM used in strength training. It seems that muscle FL and specific tension can be increased by pure concentric training if greater ROM is used. Conversely, restricting the ROM to shorter muscle lengths promotes a greater PCSA and angle-specific strength adaptations. [ABSTRACT FROM AUTHOR]

Introduction and hypothesis: Obstetrical external anal sphincter (EAS) injury and subsequent dysfunction are leading risk factors for female fecal incontinence (FI). Limited knowledge of the EAS structure-function relationship hinders treatment optimization. We directly measured functionally relevant intrinsic parameters of human EAS and tested whether vaginal delivery alters the EAS structure-function relationship.Methods: Major predictors of in vivo EAS function were compared between specimens procured from vaginally nulliparous (VN, n = 5) and vaginally parous (VP, n = 7) cadaveric donors: operational sarcomere length (Ls), which dictates force-length relationship; physiological cross-sectional area (PCSA), which determines isometric force-generating capacity; fiber length (Lfn), responsible for muscle excursion and contractile velocity; and muscle stiffness. Data were analyzed using unpaired and paired t tests, α < 0.05. Results are presented as mean ± SEM.Results: The VN and VP (median parity 3) groups were similar in age and BMI. No gross anatomical defects were identified. EAS Ls (2.36 ± 0.05 μm) was shorter than the optimal Lso (2.7 μm), at which contractile force is maximal, P = 0.0001. Stiffness was lower at Ls than Lso (5.4 ± 14 kPa/μm vs 35.3 ± 12 kPa/μm, P < 0.0001). This structural design allows active and passive tension to increase with EAS stretching. EAS relatively long Lfn (106 ± 24.8 mm) permits rapid contraction without decreased force, whereas intermediate PCSA (1.3 ± 0.3 cm2) is conducive to maintaining resting tone. All parameters were similar between groups.Conclusions: This first direct examination of human EAS underscores how EAS intrinsic design matches its intended function. Knowledge of the EAS structure-function relationship is important for understanding the pathogenesis of FI and the optimization of treatments for EAS dysfunction. [ABSTRACT FROM AUTHOR]

Introduction and hypothesis: Animal models are essential to further our understanding of the independent and combined function of human pelvic floor muscles (PFMs), as direct studies in women are limited. To assure suitability of the rhesus macaque (RM), we compared RM and human PFM architecture, the strongest predictor of muscle function. We hypothesized that relative to other models, RM best resembles human PFM. Methods: Major architectural parameters of cadaveric human coccygeus, iliococcygeus, and pubovisceralis (pubococcygeus + puborectalis) and corresponding RM coccygeus, iliocaudalis, and pubovisceralis (pubovaginalis + pubocaudalis) were compared using 1- and 2-way analysis of variance (ANOVA) with post hoc testing. Architectural difference index (ADI), a combined measure of functionally relevant structural parameters predictive of length-tension, force-generation, and excursional muscle properties was used to compare PFMs across RM, rabbit, rat, and mouse. Results: RM and human PFMs were similar with respect to architecture. However, the magnitude of similarity varied between individual muscles, with the architecture of the most distinct RM PFM, iliocaudalis, being well suited for quadrupedal locomotion. Except for the pubovaginalis, RM PFMs inserted onto caudal vertebrae, analogous to all tailed animals. Comparison of the PFM complex architecture across species revealed the lowest, thus closest to human, ADI for RM (1.9), followed by rat (2.0), mouse (2.6), and rabbit (4.7). Conclusions: Overall, RM provides the closest architectural representation of human PFM complex among species examined; however, differences between individual PFMs should be taken into consideration. As RM is closely followed by rat with respect to PFM similarity with humans, this less-sentient and substantially cheaper model is a good alternative for PFM studies. [ABSTRACT FROM AUTHOR]

The common marmoset, Callithrix jacchus, is a small New World monkey that has recently gained attention as an important experimental animal model in the field of neuroscience as well in rehabilitative and regenerative medicine. This attention reflects the closer phylogenetic relationship between humans and common marmosets compared to that between humans and other experimental animals. When studying the neuronal mechanism behind various types of neurological motor disorders using the common marmoset, possible differences in muscle parameters (e.g., the force-generating capacity of each of the muscles) between the common marmoset and other animals must be taken into account to permit accurate interpretation of observed motor behavior. Differences in the muscle architectural properties are expected to affect biomechanics, and hence to affect neuronal control of body movements. Therefore, we dissected the forelimbs and hind limbs of two common marmosets, including systematic analysis of the muscle mass, fascicle length, and physiological cross-sectional area (PCSA). Comparisons of the mass fractions and PCSA fractions of the forelimb and hind limb musculature among the common marmoset, human, Japanese macaque, and domestic cat demonstrated that the overall muscle architectural properties of the forelimbs and hind limbs in the common marmoset are very similar to those of the Japanese macaque, a typical quadrupedal primate. However, muscle architectural properties of the common marmoset differ from those of the domestic cat, which has relatively larger hamstrings and pedal digital flexor muscles. Compared to humans, the common marmoset exhibits relatively smaller shoulder protractor, retractor, and abductor muscles and larger elbow extensor and rotator-cuff muscles in the forelimb, and smaller plantarflexor muscles in the hind limb. These differences in the muscle architectural properties must be taken into account when interpreting motor behaviors such as locomotion and arm-reaching movements in the common marmoset. [ABSTRACT FROM AUTHOR]

Introduction and Hypothesis: Pelvic floor muscle rehabilitation is a widely utilized, but often challenging therapy for pelvic floor disorders, which are prevalent in older women. Regimens involving the use of appendicular muscles, such as the obturator internus (OI), have been developed for strengthening of the levator ani muscle (LAM). However, changes that lead to potential dysfunction of these alternative targets in older women are not well known. We hypothesized that aging negatively impacts OI architecture, the main determinant of muscle function, and intramuscular extracellular matrix (ECM), paralleling age-related alterations in LAM. Methods: OI and LAM were procured from three groups of female cadaveric donors (five per group): younger (20 - 40 years), middle-aged (41 - 60 years), and older (≥60 years). Architectural predictors of the excursional (fiber length, L ), force-generating (physiological cross-sectional area, PCSA) and sarcomere length ( L ) capacity of the muscles, and ECM collagen content (measure of fibrosis) were determined using validated methods. The data were analyzed using one-way ANOVA and Tukey's post-hoc test with a significance level of 0.05, and linear regression. Results: The mean ages of the donors in the three groups were 31.2 ± 2.3 years, 47.6 ± 1.2 years, and 74.6 ± 4.2 years ( P < 0.005). The groups did not differ with respect to parity or body mass index ( P > 0.5). OI L and L were not affected by aging. Age >60 years was associated with a substantial decrease in OI PCSA and increased collagen content ( P < 0.05). Reductions in OI and LAM force-generating capacities with age were highly correlated ( r = 0.9). Conclusions: Our findings of age-related decreases in predicted OI force production and fibrosis suggest that these alterations should be taken into consideration, when designing pelvic floor fitness programs for older women. [ABSTRACT FROM AUTHOR]

Purpose: Whilst neural and morphological adaptations following resistance training (RT) have been investigated extensively at a group level, relatively little is known about the contribution of specific physiological mechanisms, or pre-training strength, to the individual changes in strength following training. This study investigated the contribution of multiple underpinning neural [agonist EMG (QEMGMVT), antagonist EMG (HEMGANTAG)] and morphological variables [total quadriceps volume (QUADSVOL), and muscle fascicle pennation angle (QUADSθ p)], as well as pre-training strength, to the individual changes in strength after 12 weeks of knee extensor RT.Methods: Twenty-eight healthy young men completed 12 weeks of isometric knee extensor RT (3/week). Isometric maximum voluntary torque (MVT) was assessed pre- and post-RT, as were simultaneous neural drive to the agonist (QEMGMVT) and antagonist (HEMGANTAG). In addition QUADSVOL was determined with MRI and QUADSθ p with B-mode ultrasound.Results: Percentage changes (∆) in MVT were correlated to ∆QEMGMVT (r = 0.576, P = 0.001), ∆QUADSVOL (r = 0.461, P = 0.014), and pre-training MVT (r = -0.429, P = 0.023), but not ∆HEMGANTAG (r = 0.298, P = 0.123) or ∆QUADSθ p (r = -0.207, P = 0.291). Multiple regression analysis revealed 59.9% of the total variance in ∆MVT after RT to be explained by ∆QEMGMVT (30.6%), ∆QUADSVOL (18.7%), and pre-training MVT (10.6%).Conclusions: Changes in agonist neural drive, quadriceps muscle volume and pre-training strength combined to explain the majority of the variance in strength changes after knee extensor RT (~60%) and adaptations in agonist neural drive were the most important single predictor during this short-term intervention. [ABSTRACT FROM AUTHOR]

Purpose: During resistance training, volume and load can be altered either gradually (traditional periodization: TP) or with frequent changes between subsequent sessions (daily undulating periodization: DUP). We hypothesized that the periodization model employed would not impact upon training-induced adaptations when exercise variables are equated.Methods: Nineteen females (22.0 years, moderate resistance training experience of 27.9 months) performed 6 weeks of knee extensor training with 3 weekly sessions exercising one leg using TP and the contralateral leg using DUP. Training load varied between 40, 60, and 80% of one repetition maximum (1RM). Volume, range of motion, and time under tension were equated for each leg with a biofeedback software. Dynamometry, surface EMG and ultrasonography were used to determine temporal changes of knee extensor maximum voluntary strength (MVC), neural drive of the M. quadriceps femoris (QF) and vastus lateralis (VL) and rectus femoris (RF) muscle architecture.Results: Significant (P < 0.05) gains for isometric (TP 15%, DUP 13%) and isokinetic-concentric (TP 8%, DUP 10%) MVC and knee extensor 1RM (TP 18%, DUP 24%) occurred post training. VL and RF-muscle thickness showed significant (P < 0.05) increases ranging from 12 to 20% for TP and from 13 to 19% for DUP. Furthermore, significant (P < 0.05) increases in VL-pennation angle and VL-fascicle length occurred in both legs while QF EMG remained unchanged. No significant temporal differences were found between both models, displaying similar small to large effect sizes.Conclusion: Periodization is no adaptation trigger during short-term resistance training with equated exercise variables. [ABSTRACT FROM AUTHOR]

Introduction: Currently, little attention is given to the muscle architecture reliability studies of the hamstring using a robust statistical. Our purpose was to determine the reliability of ultrasound measurements of muscle thickness, fascicle length and pennation angle of the biceps femoris and semitendinosus muscles, including heteroskedasticity and internal consistency analyses. Methods: Two images of biceps femoris and semitendinosus at 50% of the thigh length were acquired from 21 volunteers, in two visits. The parameters were measured three times in each image, and for each muscle. The reliability was analyzed by the intraclass correlation coefficient (ICC) and Cronbach's alpha (αCronbach). The relative standard error of the measurements (%SEM) were calculated and Bland-Altman plots were generated. Results: All parameters presented excellent ICC for the three repeated measurements (ICC from 0.93 – 0.99) and moderate to excellent reliability intraday (ICC from 0.70 – 0.95) for both muscles. The present study indicates that ultrasound is a reliable tool to estimate the biceps femoris fascicle length (ICC = 0.97, αCronbach = 0.98, %SEM = 7.86) and semitendinosus (ICC = 0.90, αCronbach = 0.95, %SEM = 7.55), as well as the biceps femoris muscle thickness (ICC = 0.89, αCronbach = 0.94, %SEM = 10.23) and semitendinosus muscle thickness (ICC = 0.87, αCronbach = 0.93, %SEM = 1.35). At last, biceps femoris pennation angle (ICC = 0.93, αCronbach = 0.96 and %SEM = 4.36) and semitendinosus (ICC = 0.96, αCronbach = 0.98 and %SEM = 4.25) also had good repeatability. Conclusion: Ultrasonography show good repeatability in estimating of muscle architecture parameters. [ABSTRACT FROM AUTHOR]

The aim of this study was to concurrently assess the effect of age on neuromuscular and mechanical properties in 24 young (23.6 ± 3.7 years) and 20 older (66.5 ± 3.8 years) healthy males and females. Maximal strength of knee extensors (KE) and flexors (KF), contractile rate of torque development (RTD) and neural activation of agonist-antagonist muscles (surface EMG) were examined during maximal voluntary isometric contraction (MVIC). Tissue stiffness (i.e. musculo-articular stiffness (MAS) and muscle stiffness (MS)) was examined via the free-oscillation technique, whereas muscle architecture (MA) of the vastus lateralis and subcutaneous fat were measured by ultrasonography. Males exhibited a greater age-related decline for KE (47.4 %) and KF (53.1 %) MVIC, and RTD (60.4 %) when compared to females (32.9, 42.6 and 34.0 %, respectively). Neural activation of agonist muscles during KE MVIC falls markedly with ageing; however, no age and sex effects were observed in the antagonist co-activation. MAS and MS were lower in elderly compared with young participants and in females compared with males. Regarding MA, main effects for age (young 23.0 ± 3.3 vs older 19.5 ± 2.0 mm) and sex (males 22.4 ± 3.5 vs females 20.4 ± 2.7 mm) were detected in muscle thickness. For fascicle length, there was an effect of age (young 104.6 ± 8.8 vs older 89.8 ± 10.5 mm), while for pennation angle, there was an effect of sex (males 13.3 ± 2.4 vs females 11.5 ± 1.7°). These findings suggest that both neuromuscular and mechanical declines are important contributors to the age-related loss of muscle strength/function but with some peculiar sex-related differences. [ABSTRACT FROM AUTHOR]

In the ageing muscle, many changes occur. Some are on an architectural level, like alterations in muscle composition, or modifications in the characteristics of the muscle fiber itself, where muscle fiber length, orientation and type change. Other changes are neuronal, which occur on all levels, from the central activation over the spinal properties down to the level of the motor unit and the neuromuscular junction. There are also hormonal factors that undergo agerelated concentration variations. All these alterations in the muscle have an effect on both strength and function. In this matter, they contribute to the process of sarcopenia. Although many different components are identified, it is still unclear to what degree these components contribute to the loss of muscle mass, strength and function. This review summarizes the occurring physiological and anatomical changes within the ageing muscle and links them to outcomes such as strength and function. [ABSTRACT FROM AUTHOR]

Purpose: This study compared the adaptive responses to two concurrent training programmes frequently used in professional soccer.Methods: Fifteen youth soccer players (17.3 ± 1.6 years, 1.82 ± 0.06 m, 77.0 ± 7.3 kg; VO2 peak, 62.0 ± 4.7 ml(-1) kg(-1) min(-1)) who compete in the English Premier League volunteered for this study. In addition to completing their habitual training practices, the participants were asked to alter the organisation concurrent training by performing strength (S) training either prior to (S + E, n = 8) or after (E + S, n = 7) soccer-specific endurance training (E) 2d wk(-1) for 5 wk(-1).Results: With the exception of 30 m sprint, IMVC PF, quadriceps strength (60°/s(CON), 180°/s(CON), 120°/s(ECC)) pooled data revealed training effects across all other performances measures (P < 0.05). Whilst ANCOVA indicated no significant interaction effects for training condition, the difference between the means divided by the pooled standard deviation demonstrated large effect sizes in the E + S condition for in HBS 1-RM [S + E vs E + S; -0.54 (9.6 %) vs -1.79 (19.6 %)], AoP-M [-0.72 (7.9 %) vs -1.76 (14.4 %)], SJ [-0.56, (4.4 %), vs -1.08, (8.1 %)], IMVC-LR; [-0.50, (20.3 %) vs -1.05 (27.3 %)], isokinetic hamstring strength 60°/s (CON) [-0.64, (12.2 %) vs -0.95 (19.2 %)], 120°/s(ECC) [-0.78 (27.9 %) vs -1.55 (23.3 %)] and isokinetic quadriceps strength 180°/s (CON) [-0.23 (2.5 %) vs -1.52 (13.2 %)].Conclusion: Results suggest the organisation of concurrent training, recovery time allocated between training bouts and the availability nutrition may be able to modulate small but clinically significant changes in physical performance parameters associated with match-play. This may have practical implications for practitioners who prescribe same day concurrent training protocols. [ABSTRACT FROM AUTHOR]

Introduction and hypothesis: Pelvic floor muscles (PFM) are deleteriously affected by vaginal birth, which contributes to the development of pelvic floor disorders. To mechanistically link these events, experiments using animal models are required, as access to human PFM tissue is challenging. In choosing an animal model, a comparative study of PFM design is necessary, since gross anatomy alone is insufficient to guide the selection. Methods: Human PFM architecture was measured using micromechanical dissection and then compared with mouse ( n = 10), rat ( n = 10), and rabbit ( n = 10) using the Architectural Difference Index (ADI) (parameterizing a combined measure of sarcomere length-to-optimal-sarcomere ratio, fiber-to-muscle-length ratio, and fraction of total PFM mass and physiological cross-sectional area (PCSA) contributed by each muscle). Coccygeus (C), iliocaudalis (IC), and pubocaudalis (PC) were harvested and subjected to architectural measurements. Parameters within species were compared using repeated measures analysis of variance (ANOVA) with post hoc Tukey's tests. The scaling relationships of PFM across species were quantified using least-squares regression of log-10-transformed variables. Results: Based on the ADI, rat was found to be the most similar to humans (ADI = 2.5), followed by mouse (ADI = 3.3). When animals' body mass was regressed against muscle mass, muscle length, fiber length, and PCSA scaling coefficients showed a negative allometric relationship or smaller increase than predicted by geometric scaling. Conclusion: In terms of muscle design among commonly used laboratory animals, rat best approximates the human PFM, followed by mouse. Negative allometric scaling of PFM architectural parameters is likely due to the multifaceted function of these muscles. [ABSTRACT FROM AUTHOR]

Purpose: Whilst skeletal muscle hypertrophy is considered an important adaptation to resistance training (RT), it has not previously been found to explain the inter-individual changes in strength after RT. This study investigated the contribution of hypertrophy to individual gains in isometric, isoinertial and explosive strength after 12 weeks of elbow flexor RT. Methods: Thirty-three previously untrained, healthy men (18-30 years) completed an initial 3-week period of elbow flexor RT (to facilitate neurological responses) followed by 6-week no training, and then 12-week elbow flexor RT. Unilateral elbow flexor muscle strength [isometric maximum voluntary force (iMVF), single repetition maximum (1-RM) and explosive force], muscle volume ( V), muscle fascicle pennation angle ( θ) and normalized agonist, antagonist and stabilizer sEMG were assessed pre and post 12-week RT. Results: Percentage gains in V correlated with percentage changes in iMVF ( r = 0.527; P = 0.002) and 1-RM ( r = 0.482; P = 0.005) but not in explosive force ( r ≤ 0.243; P ≥ 0.175). Percentage changes in iMVF, 1-RM, and explosive force did not correlate with percentage changes in agonist, antagonist or stabilizer sEMG (all P > 0.05). Percentage gains in θ inversely correlated with percentage changes in normalized explosive force at 150 ms after force onset ( r = 0.362; P = 0.038). Conclusions: We have shown for the first time that muscle hypertrophy explains a significant proportion of the inter-individual variability in isometric and isoinertial strength gains following 12-week elbow flexor RT in healthy young men. [ABSTRACT FROM AUTHOR]

Introduction and hypothesis: Skeletal muscle architecture is the strongest predictor of a muscle's functional capacity. The purpose of this study was to define the architectural properties of the deep muscles of the female pelvic floor (PFMs) to elucidate their structure-function relationships. Methods: PFMs coccygeus (C), iliococcygeus (IC), and pubovisceral (PV) were harvested en bloc from ten fixed human cadavers (mean age 85 years, range 55-102). Fundamental architectural parameters of skeletal muscles [physiological cross-sectional area (PCSA), normalized fiber length, and sarcomere length (L)] were determined using validated methods. PCSA predicts muscle-force production, and normalized fiber length is related to muscle excursion. These parameters were compared using repeated measures analysis of variance (ANOVA) with post hoc t tests, as appropriate. Significance was set to α = 0.05. Results: PFMs were thinner than expected based on data reported from imaging studies and in vivo palpation. Significant differences in fiber length were observed across PFMs: C = 5.29 ± 0.32 cm, IC = 7.55 ± 0.46 cm, PV = 10.45 ± 0.67 cm ( p < 0.001). Average L of all PFMs was short relative to the optimal L of 2.7 μm of other human skeletal muscles: C = 2.05 ± 0.02 μm, IC = 2.02 ± 0.02 μm, PC/PR = 2.07 ± 0.01 μm ( p = <0.001 compared with 2.7 μm; p = 0.15 between PFMs, power = 0.46). Average PCSA was very small compared with other human muscles, with no significant difference between individual PFMs: C = 0.71 ± 0.06 cm, IC = 0.63 ± 0.04 cm, PV = 0.59 ± 0.05 cm ( p = 0.21, power = 0.27). Overall, C had shortest fibers, making it a good stabilizer. PV demonstrated the longest fibers, suggesting that it functions to produce large excursions. Conclusions: PFM design shows individual muscles demonstrating differential architecture, corresponding to specialized function in the pelvic floor. [ABSTRACT FROM AUTHOR]

Muscle-tendon gearing is the ratio of the muscle-tendon unit velocity to the fascicle velocity and can be expressed as the product of the gearing within the muscle belly and the gearing due to tendon stretch. Previous studies have shown that gearing is variable and increases at higher velocities. Changes in the muscle activation levels and force development have been suggested to affect tendon gearing and thus muscle-tendon unit gearing. However, the role of belly gearing as a part of muscle-tendon gearing and its associations with structural aspects of muscle and thus movement performance are important facets that need to be studied. The two gastrocnemii of twenty young adults were tested during isokinetic and isotonic contractions on an ankle dynamometer. Ultrasound images of both muscles were collected during contractions and were later digitised. Gearing was also predicted using a 2-dimensional panel model of these muscles. The results from experimental and models tests showed increases in gearing with greater torque levels at slower contraction velocities. However, in the isotonic models there was a substantial increase in gearing at faster contraction velocities. The level of muscle-tendon unit gearing is largely determined by the belly gearing, but its variability is driven by changes in tendon gearing that in turn is a factor of the muscle activation and coordination. The belly thickness of the medial gastrocnemius decreased during contractions, but increased for the lateral gastrocnemius. It is likely that changes to the belly shape and 3-dimensional structure are important to the gearing of the muscle. [ABSTRACT FROM AUTHOR]

Macaques have been used as an important paradigm for understanding the neural control mechanisms of human precision grip capabilities. Therefore, we dissected the forearms and hands of two male Japanese macaques to systematically record the muscle mass, fascicle length and physiological cross-sectional area (PCSA). Comparisons of the mass fractions and PCSA fractions of the hand musculature among the Japanese macaque, chimpanzee, and human demonstrated that the sizes of the thenar and hypothenar eminence muscle groups are more balanced in the macaque and chimpanzee, but those of the thenar eminence group are much larger in the human, indicating that the capacity to generate force at the tip of the thumb is more restricted in macaques, despite their high manual dexterity. In the macaque, however, the extrinsic flexor muscles are much larger, possibly to facilitate weight bearing by the forelimbs in pronograde quadrupedal locomotion and forceful grasping of arboreal supports in gap-crossing movements such as leaping. Taking such anatomical differences imposed on the hand musculoskeletal system into consideration seems to be an important method of clarifying the mechanisms of precision grip in macaques. [ABSTRACT FROM AUTHOR]

A new musculoskeletal model for the lumbar spine is described in this paper. This model features a rigid pelvis and sacrum, the five lumbar vertebrae, and a rigid torso consisting of a lumped thoracic spine and ribcage. The motion of the individual lumbar vertebrae was defined as a fraction of the net lumbar movement about the three rotational degrees of freedom: flexion-extension lateral bending, and axial rotation. Additionally, the eight main muscle groups of the lumbar spine were incorporated using 238 muscle fascicles with prescriptions for the parameters in the Hill-type muscle models obtained with the help of an extensive literature survey. The features of the model include the abilities to predict joint reactions, muscle forces, and muscle activation patterns. To illustrate the capabilities of the model and validate its physiological similarity, the model's predictions for the moment arms of the muscles are shown for a range of flexion-extension motions of the lower back. The model uses the OpenSim platform and is freely available on to other spinal researchers interested in analyzing the kinematics of the spine. The model can also be integrated with existing OpenSim models to build more comprehensive models of the human body. [ABSTRACT FROM AUTHOR]

The aims of this study were to determine the effects of plyometric training on both active and passive parts of the series elastic component (SEC) stiffness, and on geometrical parameters [i.e., muscle architecture, muscle and tendon cross-sectional area (CSA)] of the plantarflexors muscle-tendon complex to assess possible specific adaptations of the elastic properties. Nineteen subjects were randomly divided into a trained group and a control group. Active and passive components of the SEC stiffness were determined using a fast stretch during submaximal voluntary isometric plantarflexor activity. Geometrical parameters of the triceps surae muscles and the Achilles tendon were determined using ultrasonography. A significant increase in the passive component of the SEC stiffness was found (p < 0.05). In contrast, a significant decrease in the active part of the SEC stiffness was observed (p < 0.05). No significant changes in plantarflexor muscles CSA, architecture and Achilles tendon CSA were seen (p > 0.05). Thus, plyometric training led to specific adaptations within each part of the SEC. Theses adaptations could increase both the efficiency of the energy storage-recoil process and muscular tension transmission leading to an increase in jump performances. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop a muscle architecture model able to account for the observed distributions of innervation ratios and fiber densities of different types of motor units in a muscle. A model algorithm is proposed and mathematically analyzed in order to obtain an inverse procedure that allows, by modification of input parameters, control over the output distributions of motor unit fiber densities. The model’s performance was tested with independent data from a glycogen depletion study of the medial gastrocnemius of the rat. Results show that the model accurately reproduces the observed physiological distributions of innervation ratios and fiber densities and their relationships. The reliability and accuracy of the new muscle architecture model developed here can provide more accurate models for the simulation of different electromyographic signals. [ABSTRACT FROM AUTHOR]

Computer models that estimate the force generation capacity of lower limb muscles have become widely used to simulate the effects of musculoskeletal surgeries and create dynamic simulations of movement. Previous lower limb models are based on severely limited data describing limb muscle architecture (i.e., muscle fiber lengths, pennation angles, and physiological cross-sectional areas). Here, we describe a new model of the lower limb based on data that quantifies the muscle architecture of 21 cadavers. The model includes geometric representations of the bones, kinematic descriptions of the joints, and Hill-type models of 44 muscle–tendon compartments. The model allows calculation of muscle–tendon lengths and moment arms over a wide range of body positions. The model also allows detailed examination of the force and moment generation capacities of muscles about the ankle, knee, and hip and is freely available at . [ABSTRACT FROM AUTHOR]

We present a statistical evaluation and comparison of the simulation outcomes of nine different motor unit architecture modeling approaches, which derive from combinations of four motor unit territory placement algorithms with two innervation pattern algorithms (one of the combinations allows for a double approach). We test how well the outcomes of these models agree with well-established physiological principles. Our results show that algorithms based on independent and uniformly distributed territory placement always lead to an unwanted edge effect consisting in a decay of the number of overlapping motor unit territories toward the edge of the muscle cross section. This edge effect interferes with the properties of the simulated motor units. On the other hand, controlled placement of motor units, so as to minimize the spatial variance of muscle fiber density (MFD), can result in simulated motor units which better reflect the empirical evidence currently available about motor unit architecture. [ABSTRACT FROM AUTHOR]

It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F (t)) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F (t) by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 +/- 5 N cm(-2)) was similar to and correlated with that of Method 2 (29 +/- 5 N cm(-2); R (2) = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited. [ABSTRACT FROM AUTHOR]

The most important anatomical determinants of in vivo joint moment magnitude have yet to be defined. Relationships between maximal knee extensor moment and quadriceps muscle volume, anatomical (ACSA) and physiological (PCSA) cross-sectional area, muscle architecture and moment arm (MA) were compared. Nineteen untrained men and women performed maximal isokinetic knee extensions under isometric conditions (90 degrees joint angle) and at 30 degrees and 300 degrees s(-1). Magnetic resonance and ultrasound imaging techniques were used to measure vastus lateralis PCSA and fascicle length (FL), quadriceps ACSA, volume and patellar tendon MA. Muscle volume was the best predictor of extensor moment measured isometrically (R(2) = 0.60) and at 30 degrees s(-1)(R (2) = 0.74). PCSA x FL was the best predictor of moment at 300 degrees s(-1) (R(2) = 0.59). MA was not an important predictor. ACSA was the second best predictor at all three speeds and could be recommended as an ideal measure given its relative ease of measurement. [ABSTRACT FROM AUTHOR]

We dissected the left upper limb of a female orangutan and systematically recorded muscle mass, fascicle length, and physiological cross-sectional area (PCSA), in order to quantitatively clarify the unique muscle architecture of the upper limb of the orangutan. Comparisons of the musculature of the dissected orangutan with corresponding published chimpanzee data demonstrated that in the orangutan, the elbow flexors, notably M. brachioradialis, tend to exhibit greater PCSAs. Moreover, the digital II–V flexors in the forearm, such as M. flexor digitorum superficialis and M. flexor digitorum profundus, tend to have smaller PCSA as a result of their relatively longer fascicles. Thus, in the orangutan, the elbow flexors demonstrate a higher potential for force production, whereas the forearm muscles allow a greater range of wrist joint mobility. The differences in the force-generating capacity in the upper limb muscles of the two species might reflect functional specialization of muscle architecture in the upper limb of the orangutan for living in arboreal environments. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the influence of changing elastic properties of tendon and aponeuroses on force production and muscle geometry. A three-dimensional, structural, continuum mechanics model of the cat medial gastrocnemius was used for this purpose. Increasing compliance in tendon and aponeuroses caused a decrease in the peak isometric force and a shift of the force–length relationship to the right of the length axis (i.e. toward greater muscle lengths). This result can be explained with the stability condition of the force–length relationship which produced a history dependence of force production that is conceptually in agreement with experimental observations. [ABSTRACT FROM AUTHOR]

This study investigated the contribution of muscle architecture to the differences in the torque–velocity and power–velocity relationships between older (OM n = 9, aged 69–82 years) and younger men (YM n = 15, aged 19–35 years). Plantarflexors’ (PF) maximal isometric and concentric torques were recorded at 0.87, 1.75, 2.62, 3.49 and 4.36 rad s−1. Physiological cross-sectional area (PCSA) was calculated as the ratio of muscle volume (determined by magnetic resonance imaging) to muscle fascicle length ( L f, measured by ultrasonography). GM PCSA and L f of the OM were, respectively, 14.3% ( P < 0.05) and 19.3% ( P < 0.05) smaller than of the YM. In the OM, GM maximum isometric torque and maximum contraction velocity ( V max), estimated from Hill’s equation were, respectively, 48.5 and 38.2% lower ( P < 0.001) than in the YM. At all contraction velocities, the OM produced less torque than the YM (46.3% of YM at 0.87 rad s−1 to 14.7% at 4.36 rad s−1, P < 0.001). Peak power (PP) of the OM was 80% lower than that of the YM and normalisation of PP to muscle volume only reduced this difference by 10%. Normalisation of torque to PCSA reduced, but did not eliminate, differences in torque between YM and OM (9.6%) and differences in torque/PCSA increased with contraction velocity ( P < 0.05). After normalisation of velocity to L f, the difference in V max between the OM and the YM was reduced to 15.9%. Thus, although muscle architecture contributes significantly to the differences in the torque– and power–velocity properties of OM and YM, other contractile factors, intrinsic to the muscle, seem to play a role. It is noteworthy that the deficit in PP between OM and YM is far greater than that of muscle torque, even after normalisation of PP to muscle volume. This finding likely plays an important role in the loss of mobility in old age. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the differences in the viscoelastic properties of human tendon structures (tendon and aponeurosis) in the medial gastrocnemius muscle between men (n=16) and women (n=13). The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle was measured directly by ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) and tendon elongation (L) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the Fm-L loop to the area beneath the curve during the ascending phase was calculated as hysteresis. The L values at force production levels beyond 50 N were significantly greater for women than for men. The maximum strain (100×ΔL/initial tendon length) was significantly greater in women [9.5 (1.1)%] than in men [8.1 (1.6)%]. The stiffness and Young's modulus were significantly lower in women [16.5 (3.4) N/mm, 277 (25) MPa] than in men [25.9 (7.0) N/mm, 356 (32) MPa]. Furthermore, the hysteresis was significantly lower in women [11.1 (5.9)%] than in men [18.7 (8.5)%, P=0.048]. These results suggest that there are gender differences in the viscoelastic properties of tendon structures and that these might in part account for previously observed performance differences between the genders. [ABSTRACT FROM AUTHOR]