Maximal Muscle Force Research Articles

The relationship between scapular dyskinesis and rotator cuff strength in adolescent baseball players

BACKGROUND: In overhead athletes, including adolescent baseball players, scapular dyskinesis is linked to rotator cuff muscle weakness. This relationship exists because the scapula provides a stable platform and maintains the optimal length – tension relationship essential for maximal rotator cuff muscle force. While the link between scapular dyskinesis and the isometric strength of the rotator cuff has been studied, the connection with dynamic strength, particularly isokinetic concentric and eccentric strength, and their effects on functional strength ratios (agonist concentric strength to antagonist eccentric strength ratio), remain less clear. OBJECTIVES: This study aimed to explore the association between scapular dyskinesis and the isokinetic concentric and eccentric strength of the rotator cuff muscles, functional strength ratios, and shoulder function, as well as to determine the differences in these parameters between the dominant shoulder with scapular dyskinesis and the non-dominant shoulder without dyskinesis in adolescent baseball players. METHODS: This study included 50 adolescent baseball players with scapular dyskinesis. Measurements included scapular movement patterns in the scapular dyskinesis test, scapular dyskinesis scores, isokinetic concentric and eccentric internal and external rotation torques (expressed as peak torque/body weight, %), functional strength ratios, and shoulder function. Correlations between scapular dyskinesis scores and various strength and functional measurements were analyzed, as well as differences between the dominant and non-dominant shoulders using the paired t-test. RESULTS: Internal and external rotation torques were reduced on the scapular dyskinesis side across all types of contractions. A weak negative correlation was observed between the scapular dyskinesis score and eccentric internal rotation torque, with no significant correlations seen for the other variables. A moderate negative correlation was found between concentric internal rotation torque and the eccentric external rotation/concentric internal rotation ratio. Additionally, concentric and eccentric external rotation torques showed a weak negative and a positive correlation with the eccentric internal rotation/concentric external rotation ratio, respectively. CONCLUSIONS: Reduced isokinetic strength was noted on the scapular dyskinesis side, correlating particularly with eccentric internal rotation torque. This study highlights the relationship between rotator cuff muscle strength and functional strength ratios, suggesting the need for targeted strategies to restore balance between scapular positioning and rotator cuff strength.

Biomechanical Profile after Dry Needling in Mixed Martial Arts.

The purpose of this study was to compare the effects of dry needling (DN) intervention on the responses of muscle tone, stiffness, and elasticity, as well as power, pressure pain thresholds, and blood perfusion of the flexor carpi radialis muscle in mixed martial arts (MMA) athletes. Thirty-two trained/developmental men MMA fighters (25.5±4.5 years; 24.5±3 body mass index) participated in a randomized crossover study. Participants underwent a single intervention, receiving both DN and placebo. Laser Doppler flowmetry measured blood perfusion, while a myotonometer assessed the mechanical characteristics of muscle tone, stiffness, and elasticity of the flexor carpi radialis muscle. Pressure pain thresholds (PPT) were measured using an algometer, and maximal forearm muscle force was measured using a hand dynamometer. Outcomes were assessed at baseline, immediately after, and 24 hours and 48 hours post-intervention. A two-way repeated-measures ANOVA revealed significant Intervention*Time interaction for all outcomes: perfusion unit (p<0.001), muscle tone (p<0.001), stiffness (p<0.001), elasticity (p<0.001), PPT (p<0.001) and maximal forearm muscle force (p<0.001). The current study suggests that a single session of DN enhances muscle recovery, increases muscle strength, and improved PPT in MMA athletes. These positive adaptations appear to last up to 48 hours in some variables.

Loss of FAM210A in Satellite Cell Drives Mitochondrial Dysfunction and Muscle Weakness in Experimental Peripheral Artery Disease

Introduction: Peripheral artery disease (PAD) affects approximately 200 million people globally. Chronic limb-threatening ischemia (CLTI) represents the most advanced clinical phenotype of PAD. Mitochondrial metabolism defects are apparent in the satellite cells of CLTI patients, and the muscle regeneration process demands increased energy, with satellite cell mitochondrial metabolism and dynamics playing a crucial role. However, our current understanding of the role of satellite cells and muscle regeneration in PAD pathology is notably inadequate. Recent studies have shown that the absence of FAM210A, a newly identified mitochondrial protein, can trigger morphological and energetic abnormalities in mitochondria, resulting in muscle function deterioration and promoting muscle wasting. Given the impaired mitochondrial function in satellite cells in CLTI patients and the heightened energy demand regulated by mitochondrial dynamics during muscle regeneration in satellite cell, it is therefore essential to exploring the role of FAM210A in satellite cells in CLTI limb pathology. The objective of this study was to investigate the impact of the loss of FAM210A in satellite cells in mice with experimental PAD. Methods: Male and female conditional FAM210A satellite cell knock out (FAM210ASCKO) and FAM210A floxed (FAM210Afl/fl) mice (N=3-5) were used for this project. Femoral artery ligation surgery was performed to induce PAD. Tamoxifen was administered for 5 days intraperitoneally one week prior to the surgery. Mice were euthanized twenty-eight days after surgery. Outcome measures included limb perfusion assessment, muscle weight, muscle force production, and mitochondrial respiration. Results: FAM210ASCKO mice had significantly decreased muscle mass of the tibialis anterior and extensor digitorum longus ( p&lt;0.0001 and p=0.0004 respectively). More importantly, maximal muscle force with in-situ contraction in tibialis anterior was significantly lower in FAM210ASCKO mice compared to FAM210Afl/fl mice (FAM210Afl/fl mice: 1085.16 ± 331.08 mN; FAM210ASCKO mice: 430.77 ± 467.91 mN; p=0.0139). Furthermore, analysis of mitochondrial oxidative phosphorylation (OXPHOS) revealed that FAM210ASCKO mice had a significant reduction compared to FAM210Afl/fl mice (48%) in skeletal muscle mitochondrial bioenergetic function at various levels of energy demand mimicking from resting to maximal exercise when carbohydrate was used to energize mitochondria ( p=0.034). Importantly, the analysis of mitochondrial membrane potential consistently reveals a substantial reduction in FAM210ASCKO mice compared to FAM210Afl/fl mice, which can partially explain the diminished mitochondrial bioenergetic function observed in ischemic FAM210ASCKO mice. Conclusion: The results of this study indicate that the loss of FAM210A in satellite cells exacerbates ischemic muscle pathology evidenced by muscle weakness and mitochondrial failure in FAM210ASCKO mice with PAD. Future work is needed to elucidate the mechanisms by which FAM210A regulate ischemic satellite cell function and the therapeutic potential of preventing ischemia-induced loss of FAM210A in PAD. This study was supported by National Institutes of Health (NIH) grant R01-HL149704 (to Dr Ryan). Mr Thome was supported by NIH grant F31-DK128920. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Age-specific comparisons in the rate of force development of toe pressure strength and its association with the timed up and go test.

It has recently been recommended that Rate of Force Development (RFD) be evaluated in addition to maximal muscle strength. There are no studies on RFD of toe pressure strength, and its importance in older adults and the extent to which it is associated with aging needs to be clarified. This study purpose was to examine the association between the RFD of toe pressure strength and timed up and go test (TUG) in an age-specific study. This study is a cross-sectional study. Participants in the study included 159 younger adults (26.3 ± 13.1years, 52% male) and 88 older adults (75.0 ± 6.2years, 26% male). The RFD of toe pressure strength was determined from the force-time curve obtained during the toe pressure strength assessment, and the ability to exert maximum muscle force in the shortest possible time was assessed. Regression analysis was performed for each group to test the association between RFD of toe pressure strength and TUG by age. Younger adults showed no association between TUG and RFD of toe pressure strength, and significant association between TUG and RFD of toe pressure strength was found only in the older adults (standard regression coefficient = - 0.19, p = 0.048). This study showed a significant association between TUG and RFD of toe pressure strength in older adults. These findings show that RFD is one of the functions that should be assessed, particularly in older adults. Furthermore, it was suggested that approaching RFD could improve gait, standing, and sitting movements.

Impaired muscle parameters in adults with mild to severe types of osteogenesis imperfecta: a cross-sectional study.

Impaired muscle parameters may further compromise the already compromised skeleton in individuals with OI. This cross-sectional study aimed to compare muscle function and body composition in adults with various OI types and healthy controls. Sixty-eight adults with OI (mean age 42.2yr; 27 men) and 68 healthy age- and sex-matched controls were recruited. Maximal isometric muscle force was assessed by handheld dynamometry (hand grip, hip flexors, shoulder abductors, and ankle dorsiflexors), muscle endurance by posture maintenance tests (shoulder abduction, hip flexion, and wall sit), and functional lower limb strength by 30-s chair rise test. In a sub cohort, dynamic muscle function (peak power and force) was assessed by a ground reaction force plate, and lean and fat mass, muscle and fat cross-sectional area (CSA), and muscle density by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Multiple linear regression models were fitted with group (OI type I, III, IV/V, or controls), country, sex, and age in the fixed effects part. Overall, adults with various types of OI had lower isometric, endurance, and functional muscle strength (mean difference [MD] = OI type I: 19-43%, OI type IV/V: 25-68%, OI type III: 20-72%) compared to controls. Furthermore, adults with OI type I had lower dynamic muscle function (peak force [MD = 25-29%] and power [MD = 18-60%]), lean mass (MD = 10-17%), muscle CSA (MD = 9-21%), and muscle density (MD = 2-3%) but higher adiposity indices (MD = 24-42%) compared to controls. Functional lower limb strength and maximal muscle force were significantly different between OI types, whereas muscle endurance was not. To conclude, adults with OI present with markedly impaired muscle function which may partially be explained by their altered body composition. Our findings emphasize the need for proper assessment of various muscle parameters and (research into) appropriate and safe muscle strengthening approaches in this population.

Investigating the biomechanics of the biceps brachii muscle during dumbbell curl exercise: A comprehensive approach

Investigation of the mechanical behavior of the biceps brachii (BB) muscle at different dynamic forces is essential to improve training techniques, prevent sports injuries and optimize rehabilitation results. In previous studies, researchers studied mechanical changes during muscle contraction using various mathematical methods and simulation models. The models adopted by the majority of these studies assumed a constant value for muscle force. However, variable muscle force has different effects on muscle mechanics. In this study, an inverse dynamic simulation model was initially utilized to determine the dynamic muscle forces generated in the BB while performing the dumbbell curl exercise with 5 kg and 10 kg weights. Subsequently, the finite element method (FEM) was used to calculate the stress and strain changes experienced by BB as a consequence of the applied forces. Moreover, simultaneous analysis through electromyography (EMG) was carried out to investigate muscle contraction during the dumbbell curl exercise. Consequently, it was concluded that the average BB force during the dumbbell curl exercise with 5 kg and 10 kg weights was 433.9 N and 695.0 N, respectively. The maximum stresses in the BB during exercise were calculated to be 960.5 Pa and 1484.9 Pa, respectively. Additionally, the maximum displacements were determined to be 102.30 μm and 158.28 μm, respectively. According to the findings of muscle force 100% increase in dumbbell weight increases the maximum muscle force by 83.13% and the average muscle force by 60.17%. Therefore, it is understood that there was no linear correlation between weight gain and muscle force.

Speed-specific optimal contractile conditions of the human soleus muscle from slow to maximum running speed.

The soleus is the main muscle for propulsion during human running but its operating behavior across the spectrum of physiological running speeds is currently unknown. This study experimentally investigated the soleus muscle activation patterns and contractile conditions for force generation, power production and efficient work production (i.e. force-length potential, force-velocity potential, power-velocity potential and enthalpy efficiency) at seven running speeds (3.0 m s-1 to individual maximum). During submaximal running (3.0-6.0 m s-1), the soleus fascicles shortened close to optimal length and at a velocity close to the efficiency maximum, two contractile conditions for economical work production. At higher running speeds (7.0 m s-1 to maximum), the soleus muscle fascicles still operated near optimum length, yet the fascicle shortening velocity increased and shifted towards the optimum for mechanical power production with a simultaneous increase in muscle activation, providing evidence for three cumulative mechanisms to enhance mechanical power production. Using the experimentally determined force-length-velocity potentials and muscle activation as inputs in a Hill-type muscle model, a reduction in maximum soleus muscle force at speeds ≥7.0 m s-1 and a continuous increase in maximum mechanical power with speed were predicted. The reduction in soleus maximum force was associated with a reduced force-velocity potential. The increase in maximum power was explained by an enhancement of muscle activation and contractile conditions until 7.0 m s-1, but mainly by increased muscle activation at high to maximal running speed.

The Functional and Anatomical Impacts of Healthy Muscle Ageing.

Even "healthy" muscle ageing is often associated with substantial changes in muscle form and function and can lead to increased injury risks and significant negative impacts on quality of life. However, the impacts of healthy muscle ageing on the fibre architecture and microstructure of different muscles and muscle groups throughout the lower limb, and how these are related to their functional capabilities, are not fully understood. Here, a previously established framework of magnetic resonance and diffusion tensor imaging was used to measure the muscle volumes, intramuscular fat, fibre lengths and physiological cross-sectional areas of 12 lower limb muscles in a cohort of healthily aged individuals, which were compared to the same data from a young population. Maximum muscle forces were also measured from an isokinetic dynamometer. The more substantial interpopulation differences in architecture and functional performance were located within the knee extensor muscles, while the aged muscles were also more heterogeneous in muscle fibre type and atrophy. The relationships between architecture and muscle strength were also more significant in the knee extensors compared to other functional groups. These data highlight the importance of the knee extensors as a potential focus for interventions to negate the impacts of muscle ageing.

SEMG-based prediction of human forearm movements utilizing a biomechanical model based on individual anatomical/ physiological measures and a reduced set of optimization parameters.

For assistive devices such as active orthoses, exoskeletons or other close-to-body robotic-systems, the immediate prediction of biological limb movements based on biosignals in the respective control system can be used to enable intuitive operation also by untrained users e.g. in healthcare, rehabilitation or industrial scenarios. Surface electromyography (sEMG) signals from the muscles that drive the limbs can be measured before the actual movement occurs and, hence, can be used as source for predicting limb movements. The aim of this work was to create a model that can be adapted to a new user or movement scenario with little measurement and computing effort. Therefore, a biomechanical model is presented that predicts limb movements of the human forearm based on easy to measure sEMG signals of the main muscles involved in forearm actuation (lateral and long head of triceps and short and long head of biceps). The model has 42 internal parameters of which 37 were attributed to 8 individually measured physiological measures (location of acromion at the shoulder, medial/lateral epicondyles as well as olecranon at the elbow, and styloid processes of radius/ulna at the wrist; maximum muscle forces of biceps and triceps). The remaining 5 parameters are adapted to specific movement conditions in an optimization process. The model was tested in an experimental study with 31 subjects in which the prediction quality of the model was assessed. The quality of the movement prediction was evaluated by using the normalized mean absolute error (nMAE) for two arm postures (lower, upper), two load conditions (2 kg, 4 kg) and two movement velocities (slow, fast). For the resulting 8 experimental combinations the nMAE varied between nMAE = 0.16 and nMAE = 0.21 (lower numbers better). An additional quality score (QS) was introduced that allows direct comparison between different movements. This score ranged from QS = 0.25 to QS = 0.40 (higher numbers better) for the experimental combinations. The above formulated aim was achieved with good prediction quality by using only 8 individual measurements (easy to collect body dimensions) and the subsequent optimization of only 5 parameters. At the same time, just easily accessible sEMG measurement locations are used to enable simple integration, e.g. in exoskeletons. This biomechanical model does not compete with models that measure all sEMG signals of the muscle heads involved in order to achieve the highest possible prediction quality.

Application of numerical simulation studies to determine dynamic loads acting on the human masticatory system during unilateral chewing of selected foods.

Introduction: This paper presents its kinematic-dynamic computational model (3D) used for numerical simulations of the unilateral chewing of selected foods. The model consists of two temporomandibular joints, a mandible, and mandibular elevator muscles (the masseter, medial pterygoid, and temporalis muscles). The model load is the food characteristic (i), in the form of the function Fi = f(Δhi)-force (Fi) vs change in specimen height (Δhi). Functions were developed based on experimental tests in which five food products were tested (60 specimens per product). Methods: The numerical calculations aimed to determine: dynamic muscle patterns, maximum muscle force, total muscle contraction, muscle contraction corresponding to maximum force, muscle stiffness and intrinsic strength. The values of the parameters above were determined according to the mechanical properties of the food and according to the working and non-working sides. Results and Discussion: Based on the numerical simulations carried out, it can be concluded that: (1) muscle force patterns and maximum muscle forces depend on the food and, in addition, the values of maximum muscle forces on the non-working side are 14% lower than on the working side, irrespective of the muscle and the food; (2) the value of total muscle contraction on the working side is 17% lower than on the non-working side; (3) total muscle contraction depends on the initial height of the food; (4) muscle stiffness and intrinsic strength depend on the texture of the food, the muscle and the side analysed, i.e., the working and non-working sides.

Focal Application of Neurotrophic Factors Augments Outcomes of Nerve-Muscle-Endplate Grafting Technique for Limb Muscle Reinnervation.

We have developed a novel muscle reinnervation technique called "nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ)." This study aimed to augment the outcomes of the NMEG-NMZ (NN) by focal application of exogenous neurotrophic factors (ENFs) for limb reinnervation. Adult rats were used to conduct NN plus ENF (NN/ENF) and autologous nerve grafting (ANG, technique control). The nerve innervating the left tibialis anterior (TA) muscle was resected and the denervated TA was immediately treated with NN/ENF or ANG. For NN procedure, an NMEG pedicle was taken from the lateral gastrocnemius muscle and transferred to the NMZ of the denervated TA. For ANG, the nerve gap was bridged with sural nerve. Three months after treatment, the extent of functional and neuromuscular recovery was assessed by measuring static toe spread, maximal muscle force, wet muscle weight, regenerated axons, and innervated motor endplates (MEPs). NN/ENF resulted in 90% muscle force recovery of the treated TA, which is far superior to ANG (46%) and NN alone (79%) as reported elsewhere. Toe spread recovered up to 89 and 49% of the control for the NN/ENF and ANG groups, respectively. The average wet muscle weight was 87 and 52% of the control for muscles treated with NN/ENF and ANG, respectively. The mean number of the regenerated axons was 88% of the control for the muscles treated with NN/ENF, which was significantly larger than that for the ANG-repaired muscles (39%). The average percentage of the innervated MEPs in the NN/ENF-treated TA (89%) was higher compared with that in the ANG-repaired TA (48%). ENF enhances nerve regeneration and MEP reinnervation that further augment outcomes of NN. The NN technique could be an alternative option to treat denervated or paralyzed limb muscles caused by traumatic nerve injuries or lesions.

Decrements of mobility and power in recreationally active septuagenarians is related to loss of force, but not slowing of the muscle: a 5-year longitudinal study

A lesser 6-min walk distance (6MWD) and timed up-and-go (TUG) in old compared with young adults was previously linked to slowing of muscle contractile properties. The purpose of the present study was to determine whether any further reductions in 6MWD and TUG over a 5-year period in septuagenarians are associated with further slowing of muscle contractile properties. We measured muscle function by a countermovement jump, isometric maximal knee extensor strength (MVC) on a dynamometer and quadriceps muscle size by magnetic resonance imaging (MRI) in 17 older women (71.1 ± 2.8 y) and 17 older men (71.3 ± 4.1y). Performance in TUG and 6MWD were reduced over the 5-year period, irrespective of sex (P < 0.001), and both were correlated with power at both baseline and follow-up (R ≥ 0.53; P ≤ 0.001). Jump take-off velocity (VCMJ) was slower at follow-up (P < 0.01) and correlated with 6MWD and TUG at both baseline and follow-up in both sexes (R ≥ 0.54; P ≤ 0.001). However, the relationship between ‘body mass: maximal muscle force ratio’ with VCMJ was not significantly changed, indicating that the lower VCMJ was attributable to muscles working at a higher relative load, hence a lower part of the force–velocity relationship, due to a reduction in MVC (body mass had not changed significantly), rather than slowing of the muscle. The lower VCMJ in women than men (P < 0.001) was likewise attributable to a lower MVC rather than slower contractile properties in women. In conclusion, the decrement in 6MWD and TUG in septuagenarians is due to a loss of muscle mass, rather than further loss of muscle quality.

Neuromusculoskeletal model calibration accounts for differences in electromechanical delay and maximum isometric muscle force

Electromechanical delay (EMD) and maximum isometric muscle force (FoM) are important parameters for joint contact force calculation with EMG-informed neuromusculoskeletal (NMS) models. These parameters can vary between tasks (EMD) and individuals (EMD and FoM), making it challenging to establish representative values. One promising approach is to personalise candidate parameters to the participant (e.g., FoM by regression equation) and then adjust all parameters within a calibration (i.e., numerical optimisation) to minimise error between corresponding pairs of experimental measures and model-predicted values. The purpose of this study was to determine whether calibration of an NMS model resulted in consistent joint contact forces, regardless of EMD value or personalisation of FoM. Hip, knee, and ankle contact forces were predicted for 28 participants using EMG-informed NMS models. Differences in joint contact forces with EMD were examined in six models, calibrated with EMD from 15 to 110 ms. Differences in joint contact forces with personalisation of FoM were examined in two models, both calibrated with the same initial EMD (50 ms), one with generic and one with personalised values for FoM. For all models, joint contact force peaks during the first and second halves of stance were extracted and compared using a repeated-measures analysis of variance. Calibrated models with EMD set between 35 and 70 ms produced similar magnitude and timing of peak joint contact forces. Compared with generic values, personalising and then calibrating FoM resulted in comparable peak contact forces at hip, but not knee or ankle, while also producing muscle-specific tensions similar to reported literature. Overall, EMD between 35 and 70 ms and personalised initial values of FoM before calibration are advised for EMG-informed NMS modelling.

Mitochondria transplant therapy improves regeneration and restoration of injured skeletal muscle.

Injection of exogenous mitochondria has been shown to improve the ischaemia-damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle function after injury. BaCl2 was injected into the gastrocnemius muscle of one limb of 8-12-week-old C57BL/6 mice to induce damage without injury to the resident stem cells. The contralateral gastrocnemius muscle was injected with phosphate-buffered saline (PBS) and served as the non-injured intra-animal control. Mitochondria were isolated from donor mice. Donor mitochondria were suspended in PBS or PBS without mitochondria (sham treatment) and injected into the tail vein of BaCl2 injured mice 24h after the initial injury. Muscle repair was examined 7, 14 and 21days after injury. MTT did not increase systemic inflammation in mice. Muscle mass 7days following injury was 21.9±2.1% and 17.4±1.9% lower (P<0.05) in injured as compared with non-injured intra-animal control muscles in phosphate-buffered saline (PBS)- and MTT-treated animals, respectively. Maximal plantar flexor muscle force was significantly lower in injured as compared with uninjured muscles of PBS-treated (-43.4±4.2%, P<0.05) and MTT-treated mice (-47.7±7.3%, P<0.05), but the reduction in force was not different between the experimental groups. The percentage of collagen and other non-contractile tissue in histological muscle cross sections, was significantly greater in injured muscles of PBS-treated mice (33.2±0.2%) compared with MTT-treated mice (26.5±0.2%) 7days after injury. Muscle wet weight and maximal muscle force from injured MTT-treated mice had recovered to control levels by 14days after the injury. However, muscle mass and force had not improved in PBS-treated animals by 14days after injury. The non-contractile composition of the gastrocnemius muscle tissue cross sections was not different between control, repaired PBS-treated and repaired MTT-treated mice 14days after injury. By 21days following injury, PBS-treated mice had fully restored gastrocnemius muscle mass of the injured muscle to that of the uninjured muscle, although maximal plantar flexion force was still 19.4±3.7% (P<0.05) lower in injured/repaired gastrocnemius as compared with uninjured intra-animal control muscles. Our results suggest that systemic mitochondria delivery can enhance the rate of muscle regeneration and restoration of muscle function following injury.

Prolonged static stretching increases the magnitude and decreases the complexity of knee extensor muscle force fluctuations.

Static stretching decreases maximal muscle force generation in a dose-response manner, but its effects on the generation of task-relevant and precise levels of submaximal force, i.e. force control, is unclear. We investigated the effect of acute static stretching on knee extensor force control, quantified according to both the magnitude and complexity of force fluctuations. Twelve healthy participants performed a series of isometric knee extensor maximal voluntary contractions (MVCs) and targeted intermittent submaximal contractions at 25, 50 and 75% MVC (3 x 6 seconds contraction separated by 4 seconds rest, with 60 seconds rest between each intensity) prior to, and immediately after, one of four continuous static stretch conditions: 1) no stretch; 2) 30-second stretch; 3) 60-second stretch; 4) 120-second stretch. The magnitude of force fluctuations was quantified using the standard deviation (SD) and coefficient of variation (CV), while the complexity of fluctuations was quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. These measures were calculated using the steadiest 5 seconds of the targeted submaximal contractions at each intensity (i.e., that with the lowest SD). Significant decreases in MVC were evident following the 30, 60 and 120-second stretch conditions (all P < 0.001), with a significant correlation observed between stretch duration and the magnitude of decrease in MVC (r = -0.58, P < 0.001). The 120-second stretch resulted in significant increases in SD at 50% MVC (P = 0.007) and CV at 50% (P = 0.009) and 75% MVC (P = 0.005), and a significant decrease in ApEn at 75% MVC (P < 0.001). These results indicate that the negative effects of prolonged static stretching extend beyond maximal force generation tasks to those involving generation of precise levels of force during moderate- to high-intensity submaximal contractions.

Gait analysis after total hip arthroplasty by direct minimally invasive anterolateral approach: A controlled study

IntroductionClinical and functional improvement after minimally invasive total hip arthroplasty (THA) has become increasingly controversial. The minimally invasive anterolateral approach (MIALA) allows rapid recovery resulting in a reduced need for rehabilitation. Alterations in muscle and static balance have previously been demonstrated. Results in the context of quantified gait analysis (QGA) and MIALA compared to an asymptomatic population remain unknown beyond one year postoperatively. Thus, the main objective of this controlled study was to compare the spatiotemporal parameters of gait, obtained using a QGA, beyond one year postoperatively in subjects operated on for THA by MIALA, with a group of asymptomatic subjects of the same age. The secondary objectives of the study were to compare the other QGA and EMG data acquired in operated subjects with asymptomatic subjects. HypothesisWe hypothesized that QGA and EMG parameters would not normalize beyond one year postoperatively. Patients and methodsThirty-one subjects were recruited, including 16 patients (68 years old; IQR: 65–70) who underwent MIALA, at 15.5 months postoperatively (IQR: 13–17) and 15 asymptomatic subjects (62 years old; IQR: 61–71). Subjects underwent QGA and maximal isometric muscle force tests on the gluteus medius, gluteus maximus, Tensor Fascia Lata (TFL) and Sartorius muscles. Spatiotemporal gait parameters were the primary endpoint. The other QGA parameters: kinetics (characteristic values of vertical ground reaction forces, peak hip moments) and kinematics (hip joint amplitudes and pelvic mobility in the frontal and sagittal plane) constituted the secondary criteria. ResultsFive subjects were excluded for unrestored offset. Walking speed was lower in operated patients (1.03m/s versus 1.18m/s, p=0.005). Maximal isometric muscle force moments were lower in patients operated on for the gluteus maximus and medius as well as the TFL (p<0.005). The vertical ground reaction forces were lower for the operated patients for the loading phase (FzFCmax, p=0.001), the single stance phase (FzSPmin, p=5.05.10−2) and the swing phase (FzTOmax, p=0.0002). The moments were lower in the sagittal plane for the operated patients (0.6N.m for the operated versus 1.1N.m for the asymptomatic, p=0.02). The pelvic amplitudes in the sagittal plane were lower for operated patients (3.3° versus 7.2°, p=0.05). DiscussionOur hypothesis appears to be validated. Gait deficits persisted beyond one year postoperatively after THA with MIALA. A decrease in walking speed, maximal isometric muscle force of the gluteus medius and gluteus maximus and TFL was observed, as well as a decrease in propulsive force and peak hip moment. Functionally, these results could signify muscle damage following surgery, requiring rehabilitation for improved muscle function. Level of proofIII: Non-randomized controlled trial.

Stress-Strain Response of Muscle Fibers in Biceps Brachii under Dynamic Force: An Analysis of Biceps Curl Exercise

One of the most important features of endurance training was to increase the weight of the dumbbells between sets. According to the relationship of the contractile force in the muscles, the porpuse was to increase muscle growth by gaining more contractile force. Previous studies had generally examined muscle behavior under maximum force. However, the relationship between increased dumbbell weight and muscle contraction was not fully investigated. The aim of this study was to investigate the mechanical behaviors resulting from the application of dynamic forces that occur during the dumbbell curl exercise on muscle fibers. In this study, biceps brachii muscle force during biceps curl exercise performed with two different weights (5kg and 10kg) was calculated. Then, a finite element model was developed and mechanical behaviors in the biceps muscle fiber during exercise were investigated. It was achieved that there was no linear correlation between dumbbell weight and muscle force. It was observed that when dumbbell weights were doubled (100%), the maximum muscle force and deformation increased by 83.13% and 84.92%, respectively. The results showed that increasing excessive weight during exercises will not be as beneficial for muscle development as expected.

Muscle strength, rate of torque development and neuromuscular activation of the upper arm muscles in children and adolescents with spina bifida

BackgroundThe use of locomotive devices requires sufficient levels of upper limb strength. Therefore, it is important to evaluate the maximal isometric torque, rate of torque development and neuromuscular activation in youth with spina bifida. The objective was to investigate these parameters in the elbow muscles of youth with spina bifida versus healthy age-matched peers. MethodsForty-eight participants (8–17 years) were recruited: Spina Bifida (n = 23) and non-affected Controls (n = 25). Maximal isometric elbow flexor/extensor contractions were performed to assess maximal muscle strength (peak torque) and rate of torque development, along with synchronized electromyography recording in the biceps and triceps brachii muscles. FindingsDuring elbow flexor contractions, Spina Bifida showed reduced rate of torque development in the early contraction phase (0–50 ms) along with lowered relative rate of torque development in the later rate of torque development phase (0–100/200/300 ms) compared to controls. Spina Bifida showed reduced rate of torque development for the elbow extensors in the later phase of rising muscle force (0–200/300 ms) compared to controls. Lower isometric peak torque and smaller triceps brachii electromyography amplitudes (0–200/300 ms) were observed during elbow extensor contractions in Ambulatory spina bifida participants vs. controls. InterpretationAlthough a majority of peak torque and rate of torque development parameters did not differ, significant impairments in maximal and rapid elbow muscle force characteristics were noted in Spina Bifida compared to non-affected Controls. Ambulatory and Non-ambulatory spina bifida participants demonstrated similar rate of torque development in their upper arm muscles.

The Neuromuscular Fatigue-Induced Loss of Muscle Force Control.

Neuromuscular fatigue is characterised not only by a reduction in the capacity to generate maximal muscle force, but also in the ability to control submaximal muscle forces, i.e., to generate task-relevant and precise levels of force. This decreased ability to control force is quantified according to a greater magnitude and lower complexity (temporal structure) of force fluctuations, which are indicative of decreased force steadiness and adaptability, respectively. The "loss of force control" is affected by the type of muscle contraction used in the fatiguing exercise, potentially differing between typical laboratory tests of fatigue (e.g., isometric contractions) and the contractions typical of everyday and sporting movements (e.g., dynamic concentric and eccentric contractions), and can be attenuated through the use of ergogenic aids. The loss of force control appears to relate to a fatigue-induced increase in common synaptic input to muscle, though the extent to which various mechanisms (afferent feedback, neuromodulatory pathways, cortical/reticulospinal pathways) contribute to this remains to be determined. Importantly, this fatigue-induced loss of force control could have important implications for task performance, as force control is correlated with performance in a range of tasks that are associated with activities of daily living, occupational duties, and sporting performance.

Anatomically grounded estimation of hindlimb muscle sizes in Archosauria.

In vertebrates, active movement is driven by muscle forces acting on bones, either directly or through tendinous insertions. There has been much debate over how muscle size and force are reflected by the muscular attachment areas (AAs). Here we investigate the relationship between the physiological cross-sectional area (PCSA), a proxy for the force production of the muscle, and the AA of hindlimb muscles in Nile crocodiles and five bird species. The limbs were held in a fixed position whilst blunt dissection was carried out to isolate the individual muscles. AAs were digitised using a point digitiser, before the muscle was removed from the bone. Muscles were then further dissected and fibre architecture was measured, and PCSA calculated. The raw measures, as well as the ratio of PCSA to AA, were studied and compared for intra-observer error as well as intra- and interspecies differences. We found large variations in the ratio between AAs and PCSA both within and across species, but muscle fascicle lengths are conserved within individual species, whether this was Nile crocodiles or tinamou. Whilst a discriminant analysis was able to separate crocodylian and avian muscle data, the ratios for AA to cross-sectional area for all species and most muscles can be represented by a single equation. The remaining muscles have specific equations to represent their scaling, but equations often have a relatively high success at predicting the ratio of muscle AA to PCSA. We then digitised the muscle AAs of Coelophysis bauri, a dinosaur, to estimate the PCSAs and therefore maximal isometric muscle forces. The results are somewhat consistent with other methods for estimating force production, and suggest that, at least for some archosaurian muscles, that it is possible to use muscle AA to estimate muscle sizes. This method is complementary to other methods such as digital volumetric modelling.