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Objective: The aim of to analyze the feasibility of isometric wall squat exercise (IWSE) over a 12-week period as a method of breaking up sitting time during occupational activities in sedentary adults. Methods: This feasibility randomized study involved sedentary adults. Participants in the IWSE group (n = 12) performed isometric wall squats, while participants in the STAND group (n = 12) were recommended to stand up for 12 weeks. Feasibility was assessed through online questionnaires in the eighth week regarding adherence, safety, satisfaction, and acceptability. Results: Adherence toweekly breakswas similar between groups (P > 0.05). No serious side effects have been reported in the groups. Dropout rates (IWSE: 40% vs STAND: 40%, P = 1.000), satisfaction (IWSE +3.4 [1.2] vs STAND +3.0 [1.7], P = 0.709), and intention to continue with the intervention (IWSE: 75% vs STAND: 83%, P = 0.368) were similar between groups. Conclusions: The IWSE is as feasible as stand up as a strategy to breaking up sedentary time in workplace. [ABSTRACT FROM AUTHOR]

BACKGROUND: “Tendon off-position” is a disease name included in the International Classification of Diseases 11th Revision, and also a clinical indication of manipulation, acupuncture and other treatments. However, its specific mechanism is still unclear. It is urgent to establish an animal model that can reflect the clinical and pathological characteristics of “tendon off-position,” so as to further study the mechanism of effective clinical treatments. OBJECTIVE: To establish an animal model of “tendon off-position” in rats based on isometric contraction of skeletal muscles, and to explore the changes of skeletal muscle function and morphological phenotype after “tendon off-position.” METHODS: Sixty rats were randomly divided into control group, static-loading group and extra loading group, with twenty rats in each group. Rats in the control group were kept normally without treatment. In the latter two groups, the rats were fixed by the self-made static-loading modeling device and a static-loading (the body mass of each rats was applied as the static-loading) was applied to cause sustained isometric contraction of the upper limb muscles. Then, animal models of “tendon off-position” were successfully established. In the extra loading group, 50% of the body mass was added to the ankle joint after modeling. The skeletal muscle samples were harvested at 2 and 4 weeks after modeling. The changes of limb grip strength, wet mass of skeletal muscle, and serum levels of creatine kinase-muscle and lactate dehydrogenase A were measured, and the changes of skeletal muscle histomorphology and ultrastructure were observed. RESULTS AND CONCLUSION: At 2 weeks after modeling, the rats in the static-loading group and extra loading group showed significantly decreased grip strength and wet muscle mass, significantly increased serum levels of creatine kinase-muscle and lactate dehydrogenase A, and abnormal muscle fiber morphology and structure accompanied by a large number of deposited collagen fibers. Electron microscopy results showed that the structure of myofibrils was disordered, the Z-line was distorted, and the light and dark boundaries were blurred. At 4 weeks after modeling, the grip strength of the model rats was increased compared with that at 2 weeks, the serum creatine kinase-muscle and lactate dehydrogenase A levels were decreased, and the changes of muscle fiber morphology and ultrastructure were recovered to varying degrees. It is suggested that the rat skeletal muscle injury model based on continuous isometric contraction of skeletal muscle can well reflect the pathological characteristics of “tendon off-position” at 2 weeks, and can be used to study the mechanism of acupuncture and manipulation in the treatment of “tendon off-position.” [ABSTRACT FROM AUTHOR]

Purpose: The critical force (CF) concept, differentiating steady and non-steady state conditions, extends the critical power paradigm for sport climbing. This study aimed to validate CF for finger flexors derived from the 4 min all-out test as a boundary for the highest sustainable work intensity in sport climbers. Methods: Twelve participants underwent multiple laboratory visits. Initially, they performed the 4 min intermittent contraction all-out test for CF determination. Subsequent verification visits involved finger-flexor contractions at various intensities, including CF, CF −2 kg, CF −4 kg, and CF −6 kg, lasting for 720 s or until failure, while monitoring muscle-oxygen dynamics of forearm muscles. Results: CF, determined from the mean force of last three contractions, was measured at 20.1 ± 5.7 kg, while the end-force at 16.8 ± 5.2 kg. In the verification trials, the mean time to failure at CF was 440 ± 140 s, with only one participant completing the 720 s task. When the load was continuously lowered (−2 kg, −4 kg, and −6 kg), a greater number of participants (38%, 69%, and 92%, respectively) successfully completed the 720 s task. Changes of muscle-oxygen dynamics showed a high variability and could not clearly distinguish between exhaustive and non-exhaustive trials. Conclusions: CF, based on the mean force of the last three contractions, failed to reliably predict the highest sustainable work rate. In contrast, determining CF as the end-force of the last three contractions exhibited a stronger link to sustainable work. Caution is advised in interpreting forearm muscle-oxygen dynamics, lacking sensitivity for nuanced metabolic responses during climbing-related tasks. [ABSTRACT FROM AUTHOR]

Background: this study aimed to identify the influence of postural stability on upper-limb bilateral deficit (BLD), and to compare the assessment of strength generated during elbow flexion functionally vs. analytically in the dominant and nondominant arms. Methods: Twenty men participated in two sessions to evaluate the maximum isometric strength of elbow flexion. This evaluation was performed unilaterally with the dominant arm, unilaterally with the non-dominant arm, and bilaterally, both in the sitting position (SiP) and the standing position (StP). Results: The BLD when peak force was considered was lower for StP (−6.44 ± 5.58%) compared to SiP (−10.73 ± 6.17%) (p = 0.007). Regarding peak force, statistically significant differences were observed for comparisons between dominance (p < 0.001) and Position*Dominance (p = 0.02), but mean force differences were only observed for the dominance factor (p < 0.001). Greater mean and peak forces were always produced bilaterally compared to unilaterally (p < 0.001). Conclusions: a decrease in postural stability by performing elbow flexion exercises in a standing position accentuates BLD of peak force. [ABSTRACT FROM AUTHOR]

Background:Due to the crucial nature of knee joint stability in basketball players and the possible role of the rate of torque development hamstrings to quadriceps ratio for determining knee joint stability in the early phase of explosive movements, the purpose of this cross-sectional study was to explore the relationship between the rate of torque development hamstrings to quadriceps ratio and biomechanical parameters of hip and knee joints in the sagittal and frontal planes during the drop vertical jump test.Methods: Twenty healthy male recreational basketball players (aged 15-18) were recruited for this cross-sectional study. After measuring anthropometric data, the rate of torque development hamstrings to quadriceps ratio was assessed using an isokinetic Biodex system. Biomechanical variables were measured using a motion analysis system during the drop vertical jump test.Results: The rate of torque development hamstrings to quadriceps ratio (0-50 milliseconds) was negatively correlated with knee abduction angle (p = 0.028), knee adduction angle (p = 0.003), knee abduction moment (p = 0.023), and knee joint range of motion in the frontal plane (p = 0.01) during 17-50 ms after initial contact. Other biomechanical parameters did not significantly correlate with the rate of torque development hamstrings to quadriceps ratio.Conclusion: This study's results revealed that the torque development rate hamstrings to quadriceps ratio was negatively associated with knee kinematic and kinetic parameters. Based on the outcomes of this study and previous investigations, it can be acknowledged that the rate of torque development hamstrings to quadriceps ratio might be a useful tool to add to athlete injury screening.

BACKGROUND: The maximum muscle strength is typically used for evaluating the recovery of muscle function after anterior cruciate ligament reconstruction. Recent studies have suggested that neuromuscular function should also be considered, such as rate of force development, which measures the slope of the force time curve at different time intervals under conditions of isometric muscle contraction. OBJECTIVE: To elaborate on the current research status and shortcomings of muscle isometric rate of force development in patients undergoing anterior cruciate ligament reconstruction surgery, and analyze the degree of defects in quadriceps femoris and hamstring isometric rate of force development at different times after surgery; to analyze the effect of isometric rate of force development on postoperative functional performance, thereby providing important information for optimizing postoperative rehabilitation following anterior cruciate ligament reconstruction, reducing secondary injury to patients, and reducing the incidence of knee osteoarthritis. METHODS: Literature retrieval of CNKI, VIP, WanFang and PubMed was performed using “anterior cruciate ligament, rate of force development” as Chinese search terms and “anterior cruciate ligament, rate of force development, rate of torque development” as English search terms. Finally, 69 articles were included according to inclusion and exclusion criteria. RESULTS AND CONCLUSION: Most studies have found defects in bilateral muscle isometric rate of force development in patients undergoing anterior cruciate ligament reconstruction within 6 months. Early isometric rate of force development of the bilateral hamstring muscles (i.e. the slope of the force time curve at any time interval during muscle contraction of 100 ms) showed significant improvement after 6 months. However, long-term defects in early isometric rate of force development of the bilateral quadriceps indicate long-term damage to the neuromuscular function of the quadriceps after surgery. There is limited research on late isometric rate of force development (the slope of the force time curve at any time interval after 100 ms of muscle contraction), and conclusions cannot be drawn. Regarding landing exercises (jumping to the ground, lateral cutting, etc.) and daily activities (walking, running), early isometric rate of force development of the quadriceps is more correlated with isometric peak torque. Abnormal biomechanical changes during exercise are considered an important risk factor for secondary injury and traumatic knee osteoarthritis in patients. Actively improving early isometric rate of force development of the quadriceps may reduce the incidence of secondary injury and traumatic knee osteoarthritis. Currently, there is limited evidence to suggest that wholebody vibration training can improve early isometric rate of force development of the quadriceps femoris in patients undergoing anterior cruciate ligament reconstruction. It is recommended to use neuromuscular electrical stimulation to intervene in the quadriceps and hamstring in the early postoperative stage and implement explosive force and high resistance training in the late postoperative stage, which may improve the isometric rate of force development in patients. Generating sufficient muscle strength in a short period of time is necessary to effectively protect the anterior cruciate ligament, while the relationship between isometric rate of force development in the hamstring muscle and functional performance is still unclear, which may provide information on preventing secondary injury in patients. It is recommended to use the isometric rate of force development as one of the evaluation indicators for guiding rehabilitation and restoring movement. In addition to focusing on improving symmetry and differences from normal individuals, the hamstring to quadriceps strength ratio should also be considered. An appropriate range of ratios can ensure the balance of muscles during rapid muscle exertion, which may reduce the occurrence of secondary injuries. However, the normal range of ratios is not yet clear. Future research should consider the effects of graft type and knee flexion angle on isometric rate of force development, in order to identify neuromuscular dysfunction in patients as much as possible and help them recover better. [ABSTRACT FROM AUTHOR]

Background: The peroneus longus (PL) and peroneus brevis (PB) function as the primary muscles of eversion, a movement closely associated with tibial external rotation for ankle mor-tise stability. Ankle motion and tibial rotation vary based on different ankle and knee positions. Objects: This study aimed to investigate the PL, PB, and biceps femoris (BF) muscle activation and eversion strength during side-lying isometric eversion exercise based on different ankle positions (neutral [N] and plantarflexion [PF]) and knee positions (90° flexion [KF] and exten-sion [KE]). Methods: Thirty healthy adults with an Ankle Joint Functional Assessment Tool score of ≥ 22 were recruited (mean age = 24.8 ± 3.1 years). Maximal isometric eversion strength and submaximal muscle activation of the PL, PB and BF were measured during isometric eversion exercise in side-lying. A 2 × 2 repeated measures analysis of variance was performed to inves-tigate differences in muscle activation and strength. Results: The PL and PB muscle activation showed significant main effects with the knee and ankle positions (p < 0.05); activation was greater in the KE and PF positions than in the KF and N positions. The BF muscle activation showed a significant interaction effect with knee and ankle positions, which was greater in knee extension and ankle plantarflexed (KEPF) posi-tion than in knee flexion and ankle plantarflexed (KFPF) position (p < 0.05). Eversion strength showed a significant main effect only in ankle position (p < 0.05) and was greater in the N position than in the PF position. Conclusion: The results of this study indicate that the KEPF position can be recommended to facilitate contraction of the PL and PB during side-lying eversion exercise. Furthermore, the effects of the knee-ankle positions should be considered for measuring ankle eversion strength and implementing the isometric submaximal side-lying eversion exercise.

Copyright of Firat Universitesi Sağlik Bilimleri Tip Dergisi is the property of Firat Universitesiu, Saglik Bilimleri Enstitusu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We investigated the acute effects of different whole-body vibration (WBV) interventions on the jump height of highly trained karate practitioners. Fifteen male karate club athletes (age: 20.0 ± 3.8 years; stature: 177.3 ± 4.7 cm; body mass: 76.9 ± 11.2 kg; % body fat: 9.2 ± 4.3) performed six randomized interventions: [a] static half-squat (SHS); [b] SHS with external loads at 30% of the body weight (SHS + 30%BW); [c] WBV at frequency (f) 25 Hz, and 2 mm amplitude (A) (WBV 25/2); [d] WBV 25/2 with external loads of 30% of the body weight (WBV 25/2 + 30% BW); [e] WBV at f = 50 Hz, and A = 4 mm (WBV 50/4), and [f] WBV 50/4 with external loads of 30% of the body weight (WBV 50/4 + 30% BW). Each intervention was performed for 5 sets at 60 s/set, with a rest interval of 30 s between sets. Countermovement jump (CMJ) data were collected at 2, 4, 6, 8 and 10 min after each preconditioning intervention. Two-way repeated-measures ANOVA revealed a non-significant main effect of intervention [F(5, 10) = 1.44, η2 = 0.42, p = 0.29)] and a significant main effect of the rest interval [F(4, 11) = 3.51, η2 = 0.56, p = 0.04)] on CMJ height. A rest interval of 4 min resulted in significantly higher CMJ values than a rest interval of 2 min (p = 0.031). In conclusion, utilizing a 4-min rest interval irrespective of the intervention schemes may have potential for enhancing jumping performance among highly trained karate athletes. [ABSTRACT FROM AUTHOR]

Copyright of Firat Universitesi Saglik Bilimleri Veteriner Dergisi is the property of Firat Universitesiu, Saglik Bilimleri Enstitusu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revija Šport is the property of Sport: Revija Za Teoreticna in Praticna Vprasanja Sporta and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: Low back pain (LBP) is common in elite athletes. Several peripheral and central factors have been identified to be altered in non-athletic LBP populations, however whether these alterations also exist in elite athletes with LBP is unknown. The aim of this study was to determine whether elite basketballers with a history of persistent LBP perform worse than those without LBP at a lumbar muscle endurance task, a lumbar extension peak-torque task, and a lumbar motor imagery task. Method: An observational pilot study. Twenty junior elite-level male basketballers with (n = 11) and without (n = 9) a history of persistent LBP were recruited. Athletes completed a lumbar extensor muscle endurance (Biering-Sorensen) task, two lumbar extensor peak-torque (modified Biering-Sorensen) tasks and two motor imagery (left/right lumbar and hand judgement) tasks across two sessions (48 hours apart). Performance in these tasks were compared between the groups with and without a history of LBP. Results: Young athletes with a history of LBP had reduced lumbar extensor muscle endurance (p < 0.001), reduced lumbar extension peak-torque (p < 0.001), and were less accurate at the left/right lumbar judgement task (p = 0.02) but no less accurate at a left/right hand judgement task (p = 0.59), than athletes without a history of LBP. Response times for both left/right judgement tasks did not differ between groups (lumbar p = 0.24; hand p = 0.58). Conclusions: Junior elite male basketballers with a history of LBP demonstrate reduced lumbar extensor muscle endurance and lumbar extension peak-torque and are less accurate at a left/right lumbar rotation judgement task, than those without LBP. [ABSTRACT FROM AUTHOR]

This study investigated associations of fatigue resistance determined by an exercise-induced decrease in neuromuscular power with prefatigue neuromuscular strength and power of the knee extensors in 31 older men (65–88 years). A fatigue task consisted of 50 consecutive maximal effort isotonic knee extensions (resistance: 20% of prefatigue isometric maximal voluntary contraction torque) over a 70° range of motion. The average of the peak power values calculated from the 46th to 50th contractions during the fatigue task was normalized to the prefatigue peak power value, which was defined as neuromuscular fatigue resistance. Neuromuscular fatigue resistance was negatively associated with prefatigue maximal power output (r = −.530) but not with prefatigue maximal voluntary contraction torque (r = −.252). This result highlights a trade-off between prefatigue maximal power output and neuromuscular fatigue resistance, implying that an improvement in maximal power output might have a negative impact on neuromuscular fatigue resistance. [ABSTRACT FROM AUTHOR]

Abstract Background Knee osteoarthritis (KOA) progression is often influenced by biomechanical factors. Biomechanical interventions, such as Trunk stabilization exercise (TSE) and Mulligan joint mobilization (MWM), may offer relief from KOA symptoms and potentially slow disease progression. However, the comparative efficacy of these therapies remains uncertain. This study aimed to compare the efficacy of TSE, Mulligan joint mobilization, and isometric knee strengthening (KSE) on disability, pain severity, and aerobic exercise capacity in patients with KOA. Methodology A randomized controlled trial (RCT) with three intervention groups was conducted between September 2020 to February 2021. The study enrolled adults aged between 40 and 60 years with a confirmed KOA diagnosis recruited from the physical therapy clinic of the Sindh Institute of Physical Medicine and Rehabilitation, Pakistan. Participants were randomly assigned to receive 24 sessions of either TSE, MWM, or KSE. The knee’s functionality was assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS), pain on a visual analogue scale (VAS), and two objective functional tests—the 6-minute walk test (6MWT) and the 11-stair climb test (SCT). These assessments were conducted at baseline, the third week, and the sixth week. Changes in outcome measures were analyzed using a mixed-design ANOVA with Bonferroni post-hoc analysis, with statistical significance set at a p-value

Background: Knee osteoarthritis (KOA) progression is often influenced by biomechanical factors. Biomechanical interventions, such as Trunk stabilization exercise (TSE) and Mulligan joint mobilization (MWM), may offer relief from KOA symptoms and potentially slow disease progression. However, the comparative efficacy of these therapies remains uncertain. This study aimed to compare the efficacy of TSE, Mulligan joint mobilization, and isometric knee strengthening (KSE) on disability, pain severity, and aerobic exercise capacity in patients with KOA. Methodology: A randomized controlled trial (RCT) with three intervention groups was conducted between September 2020 to February 2021. The study enrolled adults aged between 40 and 60 years with a confirmed KOA diagnosis recruited from the physical therapy clinic of the Sindh Institute of Physical Medicine and Rehabilitation, Pakistan. Participants were randomly assigned to receive 24 sessions of either TSE, MWM, or KSE. The knee's functionality was assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS), pain on a visual analogue scale (VAS), and two objective functional tests—the 6-minute walk test (6MWT) and the 11-stair climb test (SCT). These assessments were conducted at baseline, the third week, and the sixth week. Changes in outcome measures were analyzed using a mixed-design ANOVA with Bonferroni post-hoc analysis, with statistical significance set at a p-value < 0.05. Result: Of the 60 participants, 22 (36.7%) were females, and 38 (63.3%) were males. Within-group analysis revealed a significant improvement in all outcome measures at the third week (p < 0.05) and sixth week (p < 0.05). Notably, the TSE group exhibited a greater reduction in mean difference (M.D) in VAS scores than the MWM and KSE groups across various measures in the third week. At rest, during stair ascent, and descent, the TSE group showed significant improvements in VAS scores: MWM (-2.05; -1.94; -1.94), TSE (-2.38; -2.5; -2.5), KSE (-1.05; -0.63; -0.63). Additionally, during sub-maximal exercise capacity assessment, the TSE group showed greater improvement (MWM 12.89; TSE 22.68; KSE 7.89), as well as in Knee Injury and Osteoarthritis Outcome Score for activities of daily living (KOOS-ADL) (MWM 20.84; TSE 28.84; KSE 12.68), and KOOS-pain (MWM 24.84; TSE 27.77; KSE 5.77) at the third-week assessment (p < 0.05). The TSE group demonstrated significant improvements (p < 0.05) across various measures in the sixth week. Specifically, improvements were observed in VAS scores at rest (MWM − 4.15; TSE − 4.42; KSE − 3.78), during stair ascent (MWM − 3.89; TSE − 4.88; KSE − 3.56) and descent (MWM − 3.78; TSE − 4.05; KSE − 2.94). Furthermore, significant improvements were noted in the stair climb test (MWM − 7.05; TSE − 7.16; KSE − 4.21), 6-minute walk test (6MWT) (MWM 22.42; TSE 37.6; KSE 13.84), KOOS-pain (MWM 41.47; TSE 49.11; KSE 28.73), and KOOS-ADL (MWM 40.31; TSE 50.57; KSE 26.05). Conclusion: In this study in patients with KOA, TSE had greater efficacy compared to MWM and KSE in enhancing functional levels, reducing pain, improving sub-maximal exercise capacity, and performance on the stair climb test. Importantly, mean scores between the groups, particularly in the TSE group, reached the minimally important level, particularly in key areas such as pain, functional levels, sub-maximal exercise capacity, and stair climb performance. Clinicians should consider the significant pain reduction, improved functionality, and enhanced exercise capacity demonstrated by TSE, indicating its potential as a valuable therapeutic choice for individuals with KOA. Trial no: ClinicalTrials.gov = NCT04099017 23/9/2019. [ABSTRACT FROM AUTHOR]

Skeletal muscles are living tissues that can undergo large deformations in short periods of time and that can be activated to produce force. In this paper we use the principles of continuum mechanics to propose a dynamic, fully nonlinear, and three-dimensional model to describe the deformation of these tissues. We model muscles as a fiber-reinforced composite and transversely isotropic material. We introduce a flexible computational framework to approximate the deformations of skeletal muscle to provide new insights into the underlying mechanics of these tissues. The model parameters and mechanical properties are obtained through experimental data and can be specified locally. A semi-implicit in-time, conforming, finite element in space scheme is used to approximate the solutions to the governing nonlinear dynamic model. We provide a series of numerical experiments demonstrating the application of this framework to relevant problems in biomechanics and also discuss questions around model validation. [ABSTRACT FROM AUTHOR]

Background The benefit of performing the Nordic Hamstring Exercise (NHE) on an inclined board has been described, however, isometric hamstring activation in different knee and hip angles has not yet been thoroughly explored. Purpose This study investigated the effect of variations in knee and hip angles during the isometric performance of the NHE on electromyographic activity of the hamstring muscles. Study design Crossover study Methods Thirteen male volunteers performed isometric contractions during the NHE with the knee (30°, 50°, 60°) and the hip (0°, 30°, and 45°) in various angles of flexion on a leg support platform which was inclined at 30°. An electrical goniometer was used to monitor the knee and hip joint angles during 5-s isometric contractions. A multivariate analysis of variance with repeated measures was used to compare normalized electromyographic values of each muscle across different knee and hip angles, followed by pairwise comparisons. Results The electromyographic activity of the biceps femoris, semitendinosus, and semimembranosus at a knee angle of 30° and hip angle of 0° were significantly higher than those observed with a knee angle of 50° and hip angle of 0°, or a knee angle of 60° and hip angle of 0° (p<0.05). The electromyographic activity of the semimembranosus at a knee angle of 60° and hip angle of 45° was significantly higher than values obtained with knee and hip angles of 60° and 0°, respectively (p<0.05). Conclusions The results indicate that using a knee flexion of 30° and a hip flexion of 0°, while isometrically performing the NHE on a platform inclined at 30°, may optimize electromyographic activity of the hamstrings. Level of Evidence 3 [ABSTRACT FROM AUTHOR]

This study explores the important role of assessing force levels in accurately controlling upper limb movements in human–computer interfaces. It uses a new method that combines entropy to improve the recognition of force levels. This research aims to differentiate between different levels of isometric contraction forces using electroencephalogram (EEG) signal analysis. It integrates eight different entropy measures: power spectrum entropy (PSE), singular spectrum entropy (SSE), logarithmic energy entropy (LEE), approximation entropy (AE), sample entropy (SE), fuzzy entropy (FE), alignment entropy (PE), and envelope entropy (EE). The findings emphasize two important advances: first, including a wide range of entropy features significantly improves classification efficiency; second, the fusion entropy method shows exceptional accuracy in classifying isometric contraction forces. It achieves an accuracy rate of 91.73% in distinguishing between 15% and 60% maximum voluntary contraction (MVC) forces, along with 69.59% accuracy in identifying variations across 15%, 30%, 45%, and 60% MVC. These results illuminate the efficacy of employing fusion entropy in EEG signal analysis for isometric contraction detection, heralding new opportunities for advancing motor control and facilitating fine motor movements through sophisticated human–computer interface technologies. [ABSTRACT FROM AUTHOR]

Long-term assessments of lower leg muscle forces in ambulant patients with distal myopathies. Over a five-year period, we measured involuntary, nerve-stimulated, isometric torques of the ankle dorsiflexors in a group of ambulant patients with myopathies and compared results with voluntary Manual Muscle Tests (MMT). From ten recruited patients, five could finish the five-year protocol. Twenty-seven force measurements sessions (one per year; 1,5 hours duration each) were performed. These patients exhibited low, stable torques or increased minimally (0.2 Newtonmeter, versus 0.1 Nm, ns; 0.7 vs. 1.0, ns; 3.4 vs. 3.5, ns; 0.2 vs. 0.1, ns; 0.8 vs. 1.5, P 0.0004 initial values vs. 5-year values, [norm: 3.9–5.7 Nm]). A 6th patient, eliciting low torque values (0.1 Nm) early passed away. Contraction times inversely correlated with MMT. MMT provided similar overall force abilities. Long-term monitoring of lower leg muscle forces in ambulant patients is limited by the patient's health status. In a small group of patients, stimulated lower leg forces did not worsen over many years relative to their diagnosed myopathies. Tracking involuntary forces, could be a useful monitoring providing phenotypic information, in addition to MMT. Future devices should be small and be simply self-applying, designed for subjects' domestic use and web-based data transfer. ClinicalTrials.gov NCT00735384. [ABSTRACT FROM AUTHOR]

Although attentional focus affects motor performance, whether corticospinal excitability and intracortical modulations differ between focus strategies depending on the exercise patterns remains unclear. In the present study, using single- and paired-pulse transcranial magnetic stimulation and peripheral nerve stimulation, we demonstrated changes in the cortical and spinal excitability under external focus (EF) and internal focus (IF) conditions with dynamic or static exercise. Participants performed the ramp-and-hold contraction task of right index finger abduction against an object (sponge or wood) with both exercises. They were asked to concentrate on the pressure on the sponge/wood induced by finger abduction under the EF condition, and on the index finger itself under the IF condition. Motor-evoked potential (MEP) and F-wave in the premotor, phasic, or tonic phase, and short- and long-interval intracortical inhibition (SICI and LICI, respectively), and intracortical facilitation (ICF) in the premotor phase were examined by recording surface electromyographic activity in the right first dorsal interosseous muscle. Increments in the MEP amplitude were larger under the EF condition than under the IF condition in the dynamic, but not static, exercise. The F-wave, SICI, and LICI did not differ between focus conditions in both exercises. In the dynamic exercise, interestingly, ICF was greater under the EF condition than under the IF condition and positively correlated with the MEP amplitude. These results indicate that corticospinal excitability and intracortical modulations to attentional focus differ depending on exercise patterns, suggesting that attentional focus differentially affects the central nervous system responsible for diverse motor behaviors. NEW & NOTEWORTHY: We investigated attentional focus-dependent corticospinal and intracortical modulations in dynamic or static exercise. The corticospinal excitability was modulated differentially depending on the focus of attention during dynamic, but not static exercise. Although the reduction of intracortical GABAergic inhibition was comparable between focus conditions in both exercises, intracortical facilitation was smaller when focusing on the internal environments in the dynamic exercise, resulting in lower activation of the corticospinal tract. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to evaluate whether motor–respiratory coupling exists in rhythmic isometric handgrip exercises and its effect on endurance performance. In addition, the mechanism underlying observed effects was to be investigated if higher motor–respiratory coupling rate could enhance endurance performance. Methods: Eleven subjects completed three rhythmic isometric handgrip trials to task failure in a randomized manner. After one pretraining session to determine personal grip frequency, one trial was performed without respiration requirement (CON), and two trials were performed with inspiration–motor coupling (IMC) or expiration–motor coupling. Changes in maximal voluntary contraction (MVC) and EMG were used to measure neuromuscular fatigue. Force data during test were used to assess exercise intensity. Another 10 subjects completed electrical stimulation-induced finger flexion and extension during normal inspiration, normal expiration, fast inspiration, fast expiration, and breath holding. Force changes of different breathing conditions were compared. Results: Normalized exercise time to exhaustion was significantly longer in IMC (1.27 ± 0.23) compared with expiration–motor coupling (0.82 ± 0.18) and CON (0.91 ± 0.18, P < 0.001). ΔMVC, grip frequency, force, and EMG indices were not different among conditions (all P > 0.05). Electrical stimulation-induced finger extensor force was significant higher during fast inspiration (1.11 ± 0.09) than normal respiration (1.00 ± 0.05) and fast expiration (0.94 ± 0.08, P < 0.05). Conclusions: IMC is an effective way to improve endurance performance of rhythmic handgrip exercise. This is likely due to a reduction in the energy consumption of motion control, as evidenced by similar peripheral fatigue in different conditions and modulation of corticospinal excitability by respiration. [ABSTRACT FROM AUTHOR]

Purpose: When exercising above the lactic threshold (LT), the slow component of oxygen uptake ( V ˙ O 2sc ) appears, mainly ascribed to the progressive recruitment of Type II fibers. However, also the progressive decay of the economy of contraction may contribute to it. We investigated oxygen uptake ( V ˙ O 2 ) during isometric contractions clamping torque (T) or muscular activation to quantify the contributions of the two mechanisms. Methods: We assessed for 7 min T of the leg extensors, net oxygen uptake ( V ˙ O 2net ) and root mean square (RMS) from vastus lateralis (VL) in 11 volunteers (21 ± 2 yy; 1.73 ± 0.11 m; 67 ± 14 kg) during cyclic isometric contractions (contraction/relaxation 5 s/5 s): (i) at 65% of maximal voluntary contraction (MVC) (FB-Torque) and; (ii) keeping the level of RMS equal to that at 65% of MVC (FB-EMG). Results: V ˙ O 2net after the third minute in FB-Torque increased with time ( V ˙ O 2net = 94 × t + 564; R2 = 0.99; P = 0.001), but not during FB-EMG. V ˙ O 2net /T increased only during FB-Torque ( V ˙ O 2net /T = 1.10 × t + 0.57; R2 = 0.99; P = 0.001). RMS was larger in FB-Torque than in FB-EMG and significantly increased in the first three minutes of exercise to stabilize till the end of the trial, indicating that the pool of recruited MUs remained constant despite V ˙ O 2sc . Conclusion: The analysis of the RMS, V ˙ O 2 and T during FB-Torque suggests that the intrinsic mechanism attributable to the decay of contraction efficiency was responsible for an increase of V ˙ O 2net equal to 18% of the total V ˙ O 2sc . [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the sensitivity of different methods of partialization, in terms of different body component indices in relation to indicators of strength and explosiveness. The research involved 187 subjects who were divided into two groups based on sex. This research consisted of measuring body composition characteristics by multichannel bioimpedance analysis (BIA) InBody 720, as well as contractile characteristics of different muscle groups with tenziometric Dinamometry method. Based on the results of the factor analysis we found that regardless of the sex the most sensitive variable for partialization of absolute body isometric strength variable (ABiS) is partialization by allometric scaling (0.964 for females and 0.947 for males explained factor variance). However, in the case of absolute body isometric explosiveness (ABiE), the results of this study have demonstrated that partialization relative to skeletal muscle mass according to the body longitudinality – skeletal muscle mass index (SMMI) is the methodological choice disregarding the sex (0.982 for females and 0.980 for males explained factor variance). The results of the study have shown that for the purpose of scaling the maximal strength relative to body composition, the allometric method can be considered as a choice, while for the partialization of maximal isometric explosiveness skeletal muscle mass index is the best choice insensitive of the sex. [ABSTRACT FROM AUTHOR]

This study aimed to narrow down the possible mechanisms of Post-Activation Performance Enhancement (PAPE), especially if they are exclusively found in the muscle. It was therefore investigated whether (1) the PAPE effect is influenced by neural factors and (2) if Post-Activation-Potentiation (PAP) influences PAPE. Thirteen strength-trained participants (26.5 ± 3.2 years) took part in at least one of three interventions (PAP, PAPE-Electrical (PAPEE), and PAPE-Voluntary (PAPEV)). Conditioning contractions (CC) and testing involved isometric knee extensions performed on an isokinetic device at an 80° knee flexion angle. The CC was either performed voluntarily (PAP, PAPEV) or was evoked through electrical stimulation (PAPEE). Testing was performed at baseline and after two seconds, four minutes, eight minutes, and twelve minutes of the CC. Maximum voluntary isometric contractions (MVIC) for the PAPE trials and supramaximal twitches for the PAP trial were used for testing. Parameters of interest were peak torque and rate of torque development (RTD), and electromyography (EMG) amplitude of the quadriceps (only PAPE). Repeated measures ANOVA and simple contrast comparisons were used for statistical analysis. Peak torque (p < 0.001, ηp² = 0.715) and RTD (p = 0. 005, ηp² = 0.570) increased significantly during the PAP protocol immediately two seconds after the CC and decreased to near baseline values for the following time points (p > 0.05). Peak torque, RTD, and peak EMG showed no significant differences during PAPEE and PAPEV trials (p > 0.05). Due to the lack of a visible PAPE effect, the question of whether neural mechanisms influence PAPE cannot be answered. Due to the time course of the PAP analysis, it is questionable if these mechanisms play a role in PAPE. The assumption that the PAP mechanism influences PAPE cannot be confirmed for the same reason. [ABSTRACT FROM AUTHOR]

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Background and aim: This research aimed to compare the effect of six weeks of electrical stimulation and isometric contraction of the quadriceps muscle on the pain and performance of male athletes with knee osteoarthritis. Methods: thirty-two male soccer players with at least 2 years of playing experience in the provincial league and suffering from mild to moderate knee osteoarthritis with an average age of 45-50 years participated in this research. Eligible people were randomly divided into 4 groups of 8 people including electrical stimulation, isometric contraction, electrical stimulation+isometric contraction and control. Interventions were implemented in the target groups for six weeks. The intensity of knee pain was determined according to VAS (Visual Analogue Scale), 6-minute walking test (6MWT), SCD test and fast walking test of 10 x 4 meters were evaluated to measure the performance of patients with osteoarthritis. After ensuring the normality of the data distribution, analysis of covariance statistics was used to determine inter-group changes and despite the significance of Tukey's test. Results: Six weeks of electrical stimulation, isometric and combined contraction (electrical stimulation and isometric contraction) caused a significant decrease in changes in pain index levels (vas) and functional indices in patients with knee osteoarthritis compared to the control group (p≤0.05) and No significant difference was observed between the experimental groups (p>0.05). Conclusion: According to the results of the research, it is recommended to use both treatment methods or a combination of them to reduce pain and improve the performance of athletes with knee osteoarthritis. [ABSTRACT FROM AUTHOR]

Isometric exercise is a non-pharmacologic intervention to improve muscle hemodynamic responses and blood pressure in humans. However, the effects of intensity, duration, and muscle mass factors of isometric exercise on local muscle hemodynamic responses and systemic blood pressure regulation have not been studied. The purpose of this study was to assess whether various modes of isometric exercise could induce various levels of muscle hemodynamic responses that are related to the blood pressure changes. Near-infrared spectroscopy was used to assess muscle hemodynamic responses after 4 isometric exercise protocols in 20 healthy adults. One-way analysis of variance (ANOVA) with repeated measures was used to assess the effect of factors of isometric exercise on oxyhemoglobin, deoxy-hemoglobin, blood volume, and oxygenation. For oxygenation, the lowest mean was recorded for the unilateral isometric handgrip exercise at 30% of MVC for 2 min (−0.317 ± 0.379 μM) while the highest mean was observed for the isometric wall squat (1.496 ± 0.498 μM, P < 0.05). Additionally, both the bilateral isometric handgrip exercise at 30% MVC for 1 min (1.340 ± 0.711 μM, P < 0.05) and the unilateral isometric handgrip exercise at 20% MVC for 3 min (0.798 ± 0.324 μM, P < 0.05) are significantly higher than 30% of MVC for 2 min. Blood pressure showed an inverse trend with oxygenation changes of the forearm muscle. The study indicates that the duration and muscle mass of isometric exercise are more effective on oxygenation responses and systematic blood pressure regulation, and suggests that the local muscle oxygenation factor following isometric contractions may mediate systematic blood pressure regulation.

Objectives Low back pain (LBP) is common in elite athletes. Several peripheral and central factors have been identified to be altered in non-athletic LBP populations, however whether these alterations also exist in elite athletes with LBP is unknown. The aim of this study was to determine whether elite basketballers with a history of persistent LBP perform worse than those without LBP at a lumbar muscle endurance task, a lumbar extension peak-torque task, and a lumbar motor imagery task. Method An observational pilot study. Twenty junior elite-level male basketballers with (n = 11) and without (n = 9) a history of persistent LBP were recruited. Athletes completed a lumbar extensor muscle endurance (Biering-Sorensen) task, two lumbar extensor peak-torque (modified Biering-Sorensen) tasks and two motor imagery (left/right lumbar and hand judgement) tasks across two sessions (48 hours apart). Performance in these tasks were compared between the groups with and without a history of LBP. Results Young athletes with a history of LBP had reduced lumbar extensor muscle endurance (p

Background: this study aimed to identify the influence of postural stability on upper-limb bilateral deficit (BLD), and to compare the assessment of strength generated during elbow flexion functionally vs. analytically in the dominant and nondominant arms. Methods: Twenty men participated in two sessions to evaluate the maximum isometric strength of elbow flexion. This evaluation was performed unilaterally with the dominant arm, unilaterally with the non-dominant arm, and bilaterally, both in the sitting position (SiP) and the standing position (StP). Results: The BLD when peak force was considered was lower for StP (−6.44 ± 5.58%) compared to SiP (−10.73 ± 6.17%) (p = 0.007). Regarding peak force, statistically significant differences were observed for comparisons between dominance (p < 0.001) and Position*Dominance (p = 0.02), but mean force differences were only observed for the dominance factor (p < 0.001). Greater mean and peak forces were always produced bilaterally compared to unilaterally (p < 0.001). Conclusions: a decrease in postural stability by performing elbow flexion exercises in a standing position accentuates BLD of peak force.

The shot performance of female soccer players is one of the most critical factors in winning a soccer match. It is essential to thoroughly clarify the kinetic factors that can improve shot performance. This study explores the connections between ball velocity post-shooting and isokinetic knee extension (EXT) and flexion (FLX) strength performances among female soccer players. Thirteen voluntary players from professional leagues took part in the research study. The study analyzed the average and peak concentric (Con) and eccentric (Ecc) torques, isometric (Iso) strength performances at angular velocities of 60°/s, 180°/s and 300°/s, the time required to reach peak torque, and ball velocities during shooting. The relationships among these variables were investigated separately for the dominant (D) and non-dominant (ND) legs. The analysis unveiled significant correlations between ball velocities and D-EXT (Absolute) peak torque at an angular velocity of 60°/s (r = 0.597; p < 0.05), D-%IPS (r = −0.580; p < 0.05), and ND-FLX (Absolute) average torque (r = 0.559; p < 0.05). Moreover, notable associations were observed between ball velocities and ND-EXT (Absolute) (r = 0.581; p < 0.05), as well as ND-FLX (Absolute) (r = 0.602; p < 0.05) average torques at an angular velocity of 180°/s. Additionally, significant relationships were found between ball velocities and peak (r = 0.664; p = 0.013) and average (r = 0.660; p = 0.014) torques generated during ND-EXT (Absolute) at an angular velocity of 300°/s. However, the connections between the time to reach peak torque, eccentric and isometric forces, and ball velocities were not statistically significant (p > 0.05). The results of the study indicate that enhancing concentric isokinetic strength development at 60°/s, 180°/s, and 300°/s angular velocities, along with balanced strengthening of the ND extremity, holds paramount importance in elevating shot performance among female soccer players, particularly in the context of rapid shot strategies. [ABSTRACT FROM AUTHOR]

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The functional capacity of the cervical spine plays a central role in healthy living. The aim of this study was to examine the sex-related effect on cervical strength, range of motion (ROM), and the musculoskeletal pain profile in young physically active individuals. A total of 30 males and 30 females (21.53 ± 1.15 years old), without injury or chronic pain at the cervical joint, participated in the study. ROM (forward flexion, extension, lateral flexion-rotation), maximal isometric strength (forward flexion, extension, lateral flexion), and musculoskeletal pain were assessed using an electronic goniometer, a handheld dynamometer, and the Nordic questionnaire, respectively. The results revealed that: (a) females had higher ROM during extension and lateral flexion than males (p < 0.05); (b) males had higher absolute strength than females in all movement directions, and higher relative strength/body mass (at forward flexion) and flexion/extension ratio (p < 0.05); (c) ROM and strength were not significantly different between right and left sides (p > 0.05); (d) a large proportion (43.3%) of the participants had cervical pain; and (e) cervical strength showed a significant small negative correlation with pains (p < 0.05; r = −0.225 to −0.345). In conclusion, the derived reference values may be used by health and fitness professionals to extensively evaluate the cervical spine and to design specific exercise programs for injury prevention and rehabilitation. [ABSTRACT FROM AUTHOR]

Introduction: Under isometric conditions, the increase in muscle force is accompanied by a reduction in the fibers' length. The effects of muscle shortening on the compound muscle action potential (M wave) have so far been investigated only by computer simulation. This study was undertaken to assess experimentally the M-wave changes caused by brief voluntary and stimulated isometric contractions. Methods: Two different methods of inducing muscle shortening under isometric condition were adopted: (1) applying a brief (1 s) tetanic contraction and (2) performing brief voluntary contractions of different intensities. In both methods, supramaximal stimulation was applied to the brachial plexus and femoral nerves to evoke M waves. In the first method, electrical stimulation (20 Hz) was delivered with the muscle at rest, whereas in the second, stimulation was applied while participants performed 5-s stepwise isometric contractions at 10, 20, 30, 40, 50, 60, 70, and 100% MVC. The amplitude and duration of the first and second M-wave phases were computed. Results: The main findings were: (1) on application of tetanic stimulation, the amplitude of the M-wave first phase decreased (~ 10%, P < 0.05), that of the second phase increased (~ 50%, P < 0.05), and the M-wave duration decreased (~ 20%, P < 0.05) across the first five M waves of the tetanic train and then plateaued for the subsequent responses; (2) when superimposing a single electrical stimulus on muscle contractions of increasing forces, the amplitude of the M-wave first phase decreased (~ 20%, P < 0.05), that of the second phase increased (~ 30%, P < 0.05), and M-wave duration decreased (~ 30%, P < 0.05) as force was raised from 0 to 60–70% MVC force. Conclusions: The present results will help to identify the adjustments in the M-wave profile caused by muscle shortening and also contribute to differentiate these adjustments from those caused by muscle fatigue and/or changes in Na+–K+ pump activity. [ABSTRACT FROM AUTHOR]

BACKGROUND: Adequate normalization methodology to establish maximum voluntary isometric contraction (MVIC) is needed to compare %MVIC values for core exercise completed until discontinuation. Clinicians can use %MVIC classifications to guide their preventative and rehabilitative exercise interventions. OBJECTIVE: The aim of this study was to compare %MVIC of the external oblique (EO) between normalization techniques of side-lying lateral trunk flexion and Roman chair lateral trunk flexion. METHODS: Twenty-two participants completed two MVIC techniques followed by one repetition of the prone bridge plank (PBP), torso elevated side plank (TESP), foot elevated side plank (FESP), dead bug and bird dog. The average %MVIC during the first 5-seconds, last 5-seconds and overall duration of exercise were included for analysis. ANOVA was used to compare normalized %MVIC from each of the 5 exercises between MVIC techniques. Alpha set a priori p = 0.05. RESULTS: The side-lying table technique yielded no %MVIC values above 100%, while the Roman chair technique produced 7 values above 100%. The largest mean difference between techniques was during the last 5-seconds of the torso elevated side plank (57.87 ± 38.51%MVIC, p < 0.001). CONCLUSION: The side-lying table technique likely provides the optimal methodology of %MVIC determination. [ABSTRACT FROM AUTHOR]

BACKGROUND: The reason that participants develop pain episodes during the Sorensen test remains unclear. Lumbar lordosis and trunk muscle are important for dynamic stability of the spine; however, their role in pain episodes during the Sorensen test has not yet been discussed. OBJECTIVE: To investigate the effects of muscular morphology and lumbar curvature on pain development during the Sorensen test in patients with non-specific low back pain (LBP). METHODS: Ninety-one patients diagnosed with chronic non-specific LBP and underwent the Sorensen test were enrolled. Lumbar lordosis, cross-sectional area and fat infiltration rate of trunk muscle and centroid line of psoas major (dividing into three types: anterior arc, linear and posterior arc) were measured using ImageJ software. All recruited patients were grouped into pain episode and exhaustion groups and were matched for the confounders based on propensity scores. The above parameters were compared between groups and further adjusted for confounding bias. RESULTS: After adjustment , the mean differences in lumbar lordosis of 12.1 ± 2.3 ∘ between the two groups in the complete cohort and of 13.9 ± 2.5 ∘ in the matching cohort remained significant, the exhaustion group had a 0.22-fold and 0.08-fold risk of presenting as linear and posterior arc types, respectively, compared with the pain episode group in the complete cohort (p = 0.008, p = 0.004), the corresponding values were 0.19-fold and 0.05-fold, respectively, in the matching cohort (p = 0.014, p = 0.010). Logistic regression demonstrated that lumbar lordosis, the linear and posterior arc types were significantly associated with pain episode during the test (OR = 0.78, p < 0.001; OR = 4.50, p = 0.038; OR = 9.93, p = 0.033). CONCLUSIONS: Lower lumbar lordosis and linear and posterior arc types of the psoas major centroid line were possibly relevant to the pain episode during Sorensen test in patients with chronic non-specific LBP. [ABSTRACT FROM AUTHOR]

Aims: To compare the postactivation potentiation effects of isometric contraction until failure in double- and single-leg tasks on older women's balance. Methods: The one-legged balance test was performed before and immediately after a rise-to-toes task until the task failure. Older women were divided into two groups: a group performed the task with double leg (n = 43) and the other group with single-leg support (n = 55). Results: The single-leg group showed slower velocity of sway post rise-to-toes task (pre = 4.02 ± 1; post = 3.78 ± 1.15 m/s; p =.04) without differences for the center of pressure path length (pre = 79 ± 21; post = 75 ± 23 cm; p =.08). In the double-leg group, faster velocity of sway (pre = 4 ± 1.22; post = 4.25 ± 1.13; p =.03) and increased center of pressure path length (pre = 80 ± 24; post = 85 ± 23 cm; p =.03) were observed after the task. Conclusions: The single-leg group showed improved balance outcomes due to postactivation potentiation, while the double-leg group showed worsened balance consistent with muscle fatigue. [ABSTRACT FROM AUTHOR]

Context: Elastic taping has been widely used for either to facilitate or to inhibit muscle contraction. The efficacy of elastic taping is allegedly ascribed to physiological mechanisms related to subcutaneous tissue and muscle stimulation as a result of tape tension and direction. However, the underlying mechanisms that support the use of elastic taping are still unclear. Objective: To investigate changes in electrophysiological responses after 48 hours of tape application in different directions on the calf muscles of healthy individuals. Design: Within-subjects design. Setting: Research laboratory. Participants: Twenty-seven physically active males (age 18.0 [4.2] y, height 1.65 [0.07] m, body mass 62.3 [10.3] kg) participated. Interventions: Soleus H-reflex responses were evoked through stimulation of the tibial posterior nerve with 2- to 4-second interval between stimuli (32 sweeps) for each condition (baseline: without tape; facilitation: tape applied from muscle origin to insertion; inhibition: tape applied from muscle insertion to origin). Main outcome measures: The H-reflex amplitude values were normalized by the maximal direct response (Mmax). Parameters were estimated from a sigmoidal fit of the H-reflex recruitment curve (ascending limb). Results: No significant differences were found for the parameters derived from the recruitment curve of the H-reflex among the conditions (P > .05). Conclusions: The authors' findings showed that, irrespective of the direction of tape application, the elastic tape applied over the triceps surae does not generate any significant alteration on the excitability of the reflex pathway for different subpopulations of motor units. The authors therefore suggest a re-examination of the current recommendations on taping direction in clinical and sports activities. [ABSTRACT FROM AUTHOR]

This study explores the important role of assessing force levels in accurately controlling upper limb movements in human–computer interfaces. It uses a new method that combines entropy to improve the recognition of force levels. This research aims to differentiate between different levels of isometric contraction forces using electroencephalogram (EEG) signal analysis. It integrates eight different entropy measures: power spectrum entropy (PSE), singular spectrum entropy (SSE), logarithmic energy entropy (LEE), approximation entropy (AE), sample entropy (SE), fuzzy entropy (FE), alignment entropy (PE), and envelope entropy (EE). The findings emphasize two important advances: first, including a wide range of entropy features significantly improves classification efficiency; second, the fusion entropy method shows exceptional accuracy in classifying isometric contraction forces. It achieves an accuracy rate of 91.73% in distinguishing between 15% and 60% maximum voluntary contraction (MVC) forces, along with 69.59% accuracy in identifying variations across 15%, 30%, 45%, and 60% MVC. These results illuminate the efficacy of employing fusion entropy in EEG signal analysis for isometric contraction detection, heralding new opportunities for advancing motor control and facilitating fine motor movements through sophisticated human–computer interface technologies.

Context: Strength assessment is essential to prescribe exercise in sports and rehabilitation. Low-cost valid equipment may allow continuous monitoring of training. Objective: To examine the validity of a very low-cost hanging scale by comparing differences in the measures of peak force to a laboratory grade load cell during shoulder abduction, flexion, extension, and internal and external rotations. Design: Analytical study. Participants: Thirty-two healthy subjects (18 women, age 26 [10] y, height 172 [8] cm, mass 69 [13] kg, body mass index 23 [4] kg/m2). Main Outcome Measures: The dependent variable was the maximal peak force (in kilogram-force). The independent variable was the instrument (laboratory grade load cell and hanging scale). Results: No differences were observed while comparing the results. The intraclass correlation coefficients1,1 ranged from.96 to.99, showing excellent results. The Cronbach alpha test also returned >.99 for all comparisons. The SEM ranged from 0.02 to 0.04 kgf, with an averaged SD from 0.24 to 0.38 kgf. The correlation was classified as high for all tested movements (r >.99; P <.001), with excellent adjusted coefficients of determination (.96 < r2 <.99). Bland–Altman results showed high levels of agreement with bias ranging from 0.27 to 0.48. Conclusions: Hanging scale provides valid measures of isometric strength with similar output measures as laboratory grade load cell. [ABSTRACT FROM AUTHOR]

This study contrasted the stochastic force component between young and older adults, who performed pursuit tracking/compensatory tracking by exerting in-phase/antiphase forces to match a sinusoidal target. Tracking force was decomposed into the force component containing the target frequency and the nontarget force fluctuations (stochastic component). Older adults with inferior task performance had higher complexity (entropy across time; p =.005) in total force. For older adults, task errors were negatively correlated with force fluctuation complexity (pursuit tracking: r = −.527 to −.551; compensatory tracking: r = −.626 to −.750). Notwithstanding an age-related increase in total force complexity (p =.004), older adults exhibited lower complexity of the stochastic force component than young adults did (low frequency: p =.017; high frequency: p =.035). Those older adults with a higher complexity of stochastic force had better task performance due to the underlying use of a richer gradation strategy to compensate for impaired oscillatory control. [ABSTRACT FROM AUTHOR]

IntroductionIt is acknowledged that training during recovery periods after injury involves reducing both volume and intensity, often resulting in losses of sport-specific fitness. Therefore, this study aimed to compare the effects of high-intensity training (HIT) and low-intensity training with blood flow restriction (LIT + BFR) of the finger flexors in order to preserve climbing-specific strength and endurance.MethodsIn a crossover design, thirteen intermediate climbers completed two 5-week periods of isometric finger flexors training on a hangboard. The trainings consisted of ten LIT + BFR (30% of max) or HIT sessions (60% of max without BFR) and were undertaken in a randomized order. The training session consisted of 6 unilateral sets of 1 min intermittent hanging at a 7:3 work relief ratio for both hands. Maximal voluntary contraction (MVC), force impulse from the 4 min all out test (W), critical force (CF) and force impulse above the critical force (W') of the finger flexors were assessed before, after the first, and after the second training period, using a climbing-specific dynamometer. Forearm muscle oxidative capacity was estimated from an occlusion test using near-infrared spectroscopy at the same time points.ResultsBoth training methods led to maintaining strength and endurance indicators, however, no interaction (P > 0.05) was found between the training methods for any strength or endurance variable. A significant increase (P = 0.002) was found for W, primarily driven by the HIT group (pretest—25078 ± 7584 N.s, post-test—27327 ± 8051 N.s, P = 0.012, Cohen's d = 0.29). There were no significant (P > 0.05) pre- post-test changes for MVC (HIT: Cohen's d = 0.13; LIT + BFR: Cohen's d = −0.10), CF (HIT: Cohen's d = 0.36; LIT + BFR = 0.05), W` (HIT: Cohen's d = −0.03, LIT + BFR = 0.12), and forearm muscle oxidative capacity (HIT: Cohen's d = −0.23; LIT + BFR: Cohen's d = −0.07).ConclusionsLow volume of BFR and HIT led to similar results, maintaining climbing-specific strength and endurance in lower grade and intermediate climbers. It appears that using BFR training may be an alternative approach after finger injury as low mechanical impact occurs during training.

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Duchenne muscular dystrophy is a genetic muscle‐wasting disorder characterized by progressive muscle weakness and easy fatigability. Here we examined whether high‐intensity interval training (HIIT) in the form of isometric contraction improves fatigue resistance in skeletal muscle from dystrophin‐deficient mdx52 mice. Isometric HIIT was performed on plantar flexor muscles in vivo with supramaximal electrical stimulation every other day for 4 weeks (a total of 15 sessions). In the non‐trained contralateral gastrocnemius muscle from mdx52 mice, the decreased fatigue resistance was associated with a reduction in the amount of peroxisome proliferator‐activated receptor γ coactivator 1‐α, citrate synthase activity, mitochondrial respiratory complex II, LC3B‐II/I ratio, and mitophagy‐related gene expression (i.e. Pink1, parkin, Bnip3 and Bcl2l13) as well as an increase in the phosphorylation levels of Src Tyr416 and Akt Ser473, the amount of p62, and the percentage of Evans Blue dye‐positive area. Isometric HIIT restored all these alterations and markedly improved fatigue resistance in mdx52 muscles. Moreover, an acute bout of HIIT increased the phosphorylation levels of AMP‐activated protein kinase (AMPK) Thr172, acetyl CoA carboxylase Ser79, unc‐51‐like autophagy activating kinase 1 (Ulk1) Ser555, and dynamin‐related protein 1 (Drp1) Ser616 in mdx52 muscles. Thus, our data show that HIIT with isometric contractions significantly mitigates histological signs of pathology and improves fatigue resistance in dystrophin‐deficient muscles. These beneficial effects can be explained by the restoration of mitochondrial function via AMPK‐dependent induction of the mitophagy programme and de novo mitochondrial biogenesis. Key points: Skeletal muscle fatigue is often associated with Duchenne muscular dystrophy (DMD) and leads to an inability to perform daily tasks, profoundly decreasing quality of life.We examined the effect of high‐intensity interval training (HIIT) in the form of isometric contraction on fatigue resistance in skeletal muscle from the mdx52 mouse model of DMD.Isometric HIIT counteracted the reduced fatigue resistance as well as dystrophic changes in skeletal muscle of mdx52 mice.This beneficial effect could be explained by the restoration of mitochondrial function via AMP‐activated protein kinase‐dependent mitochondrial biogenesis and the induction of the mitophagy programme in the dystrophic muscles. [ABSTRACT FROM AUTHOR]

Exercise-induced hypoalgesia (EIH) is characterized by an increase in pain threshold following acute exercise. EIH is reduced in some individuals with chronic musculoskeletal pain, although the mechanisms are unknown. It has been hypothesized that this may relate to whether exercises are performed in painful or non-painful body regions. The primary aim of this randomized experimental crossover study was to investigate whether the presence of pain per se in the exercising muscles reduced the local EIH response. The secondary aim was to investigate if EIH responses were also reduced in non-exercising remote muscles. Pain-free women (n=34) participated in three separate sessions. In session 1, the maximal voluntary contraction (MVC) for a single legged isometric knee extension exercise was determined. In sessions 2 and 3, pressure pain thresholds (PPT) were assessed at the thigh and shoulder muscles before and after a 3-min exercise at 30 % of MVC. Exercises were performed with or without thigh muscle pain, which was induced by either a painful injection (hypertonic saline, 5.8 %) or a non-painful injection (isotonic saline, 0.9 %) into the thigh muscle. Muscle pain intensity was assessed with an 11-point numerical rating scale (NRS) at baseline, after injections, during and after exercises. PPTs increased at thigh and shoulder muscles after exercise with painful (14.0–24.9 %) and non-painful (14.3–19.5 %) injections and no significant between-injection EIH differences were observed (p>0.30). Muscle pain intensity was significantly higher following the painful injection compared to the non-painful injection (p<0.001). Exercising painful muscles did not reduce the local or remote hypoalgesic responses, suggesting that the pain-relieving effects of isometric exercises are not reduced by exercising painful body regions. S-20210184. NCT05299268. [ABSTRACT FROM AUTHOR]

Static stretching (SS) and dynamic stretching (DS) in combination with foam rolling (FR) have been attracting attention as warm-up routines in sports. However, the combined and intervention order effects of SS or DS and FR on flexibility, muscle strength, and jump performance are still unclear. Therefore, this study aimed to compare the combined effects of FR and SS or DS with the various intervention orders (i.e., SS + FR, DS + FR, FR + SS, DS + FR) on the function and properties of the knee extensors. Using a crossover, random allocation design, 17 male university students (21.0 ± 1.1 y) performed four conditions combining FR and SS or DS. The measurement included knee flexion range of motion (ROM), pain pressure threshold (PPT), tissue hardness, maximum voluntary isometric contraction (MVC-ISO), maximum voluntary concentric contraction (MVC-CON) torque, and single-leg countermovement jump (CMJ) height of the knee extensors. All interventions significantly (p < 0.01) increased knee flexion ROM (SS + FR: d = 1.29, DS + FR: d = 0.45, FR + SS: d = 0.95, FR + DS: d = 0.49), and significantly (p < 0.01) decreased tissue hardness (SS + FR: d = -1.11, DS + FR: d = -0.86, FR + SS: d = -1.29, DS + FR: d = -0.65). There were no significant changes in MVC-ISO, MVCCON, and CMJ height in all conditions, but a near significant, small magnitude (p = 0.056, d = -0.31) decrease of MVC-ISO was observed in the FR + SS condition. Our results showed that all the combinations of SS or DS and FR effectively decreased tissue hardness and increased ROM without decreasing muscle strength. Also, effect sizes indicated the largest increase in ROM and decrease in tissue stiffness after SS + FR without decreasing muscle strength and jump performance. [ABSTRACT FROM AUTHOR]

The hamstring muscle shortness is the primary risk factor for sports-related injuries. Numerous treatments are available for lengthening of hamstring muscle. The main purpose of this study was to compare the immediate effect of modified hold-relax, muscle energy technique (MET), and instrument assisted soft tissue mobilization-Graston techniques (IASTM-GT) on length of hamstring muscle in young healthy athletes. 60 athletes comprising of 29 females and 31 males were recruited in the present study. Participants were allocated to 3 groups of IASTM-GT (N = 20, 13 male, 7 female), Modified Hold-relax (N = 20, 8 male, 12 female), and MET (N = 20, 7 male, 13 female). Active knee extension and passive straight leg raising (SLR), and toe touch test were performed before and immediately after the intervention by a blinded assessor. For the comparison of dependent variables across time, 3*2 repeated measure ANOVA was utilized. Interaction of group by time was significant for passive SLR (P < 0.001). Interaction of group by time was not significant for active knee extension (P = 0.17). The results showed that dependent variables increased significantly in all groups. The effect size (Cohen's d) in the groups of IASTM-GT, modified Hold-relax, and MET was 1.7, 3.17, and 3.12, respectively. Although the measures were improved in all groups, it seems that IASTM-GT can be used as a safe and efficient treatment, which can be a suitable candidate alongside modified hold-relax and MET for increasing the hamstrings muscle length in healthy athletes. [ABSTRACT FROM AUTHOR]

There are no studies that have simultaneously examined muscle strength of high- and low-level athletes in each of the two competitive styles in wrestling. The purpose of this study was to clarify the characteristics of muscle strength by style and level of competition in lightweight athletes specializing in freestyle (FS) and Greco-Roman style (GS) in wrestling. Thirty-seven male collegiate lightweight wrestlers (age, 20.3±1.2 years; height, 165.3±3.7 cm; weight, 63.6±2.9 kg; competition career, 12.7±3.7 years) participated in this study. Participants were divided into 4 groups as follows: high-level GS (HGS, n＝9), low-level GS (LGS, n＝8), high-level FS (HFS, n＝8), and low-level FS (LFS, n＝12) . Isometric and isokinetic muscle extension and flexion torque of elbow, knee, and trunk as muscle strength were measured by biodex system 4. The main results of this study showed that isometric and isokinetic (60, 180, and 300 deg/sec) elbow extension strength were higher in high-level athletes than in low-level athletes, regardless of competitive style (all P<0.05), and that HGS was higher than HFS and LGS in isometric knee flexion muscle strength (P＝0.001, P＝0.023, respectively), and that GS was higher than FS in isometric knee and trunk extension muscle strength (P＝0.029, P＝0.014, respectively) . The results of this study suggest the importance of upper extremity extensor strength in wrestling competitions and the need for strength improvement programs based on competition style. [ABSTRACT FROM AUTHOR]

BACKGROUND: The dependence of fascicle length on complex interactions with joint angle and force challenges the interpretation of in vivo joint mechanics, muscle mechanical properties, contractile behavior, and muscle function. AIM: The purpose of this study was to determine the complex interaction between muscle activation, joint angle, and fascicle length for isometric contractions of the human vastus lateralis muscle (VL). METHOD: Knee extensor torques, joint angles, EMG activation, and fascicle lengths were determined in nine healthy subjects during maximal and submaximal isometric contractions. RESULTS: Fascicle shortening during isometric contractions depended on muscle-tendon unit length/joint angle and activation, reaching a maximum between angles where VL had its maximum force potential and minimum resistance to fascicle shortening. Maximal fascicle shortening shifted to shorter muscle-tendon unit lengths with decreasing activation. CONCLUSION: Fascicle shortening upon activation depends crucially on the force generating potential and stiffness of the muscle and can reach 30% of the resting fascicle length. Not accounting for the complex interactions between muscle length, force potential, muscle structure, and muscle stiffness has led to erroneous interpretations of the function and properties of healthy and diseased muscles. [ABSTRACT FROM AUTHOR]

This study investigated whether muscle contraction induces expression of regulated in development and DNA damage 1 (REDD1), a potent inhibitor of mTORC1, in mice muscle. Gastrocnemius muscle was unilaterally and isometrically contracted with electrical stimulation, and changes in muscle protein synthesis, mTORC1 signaling phosphorylation, and REDD1 protein, and mRNA were measured at time points of 0, 3, 6, 12, and 24 h after the contraction. At time point 0 and 3 h, muscle protein synthesis was blunted by the contraction, accompanied by a decrease in phosphorylation of 4E‐BP1 at time point 0 h, suggesting suppression of mTORC1 was involved in blunting of muscle protein synthesis during and shortly after the contraction. REDD1 protein was not increased in the contracted muscle at these time points, but at time point 3 h, both REDD1 protein and mRNA were increased in the contralateral non‐contracted muscle. The induction of REDD1 expression in the non‐contracted muscle was attenuated by RU‐486, an antagonist of the glucocorticoid receptor, suggesting that glucocorticoids are involved in this process. These findings suggest that muscle contraction induces temporal anabolic resistance in non‐contracted muscle, potentially increasing the availability of amino acids for contracted muscle, allowing for the synthesis of muscle protein. [ABSTRACT FROM AUTHOR]