Ankle Plantar Flexors Research Articles

Differential behavior of distinct motoneuron pools that innervate the triceps surae.

It has been shown that when humans lean in various directions, the central nervous system (CNS) recruits different motoneuron pools for task completion; common units that are active during different leaning directions, and unique units that are active in only one leaning direction. We used high-density surface electromyography (HD-sEMG) to examine if motor unit (MU) firing behavior was dependent on leaning direction, muscle (medial and lateral gastrocnemius; soleus), limits of stability, or whether a MU is considered common or unique. Fourteen healthy participants stood on a force platform and maintained their center of pressure in five different leaning directions. HD-sEMG recordings were decomposed into MU action potentials and the average firing rate (AFR), coefficient of variation (CoVISI), and firing intermittency were calculated on the MU spike trains. During the 30°-90° leaning directions both unique units and common units had higher firing rates (F = 31.31, P < 0.0001). However, the unique units achieved higher firing rates compared with the common units (mean estimate difference = 3.48 Hz, P < 0.0001). The CoVISI increased across directions for the unique units but not for the common units (F = 23.65, P < 0.0001). Finally, intermittent activation of MUs was dependent on the leaning direction (F = 11.15, P < 0.0001), with less intermittent activity occurring during diagonal and forward-leaning directions. These results provide evidence that the CNS can preferentially control separate motoneuron pools within the ankle plantarflexors during voluntary leaning tasks for the maintenance of standing balance.NEW & NOTEWORTHY In this study, we demonstrate that the different subpopulations of motor units within the three muscles comprising the ankle plantarflexors behave differently during multidirectional leaning. Our results suggest that the central nervous system has the capability to control distinct subpopulations of motor units to meet the force requirements necessary for leaning. This may allow for a precise, efficient, and flexible control strategy for the maintenance of standing balance.

Use or lose: A case for normalizing neuromuscular clinical test for body weight in children

<h3>Research Objectives</h3> To compare and contrast relationships of contraction- and velocity-specific muscle strength of lower extremity muscles with clinical tests of neuromuscular performance such as lateral step up test (at heights of 0.05 m (LSUT0.05) and 0.15 m (LSUT0.15)) and sit-to-stand (STS) with and without normalization for body weight. Research scientists typically normalize tests of neuromuscular performance for body weight to understand qualitative aspect of neuromuscular performance. However, clinically no normalization of these tests are performed. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> University laboratory. <h3>Participants</h3> Typically developing children (n=15; male = 40%) 8-13 years of age. <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> After a familiarization, Knee extensors and ankle plantarflexors were assessed in random order for concentric (CONC) and eccentric (ECC) muscle strength at 2 different velocities (120°/s and 180°/s) for the knee extensors and ankle plantarflexors on Biodex3 device. We used LSUT0.05, LSUT0.15, and STS to determine neuromuscular performance. We assessed LSUT0.05, LSUT0.15 and STS in random order after familiarization. Maximum counts achieved during testing LSUT0.05, LSUT0.15 and STS were normalized for body mass. <h3>Results</h3> We noted positive spearman correlations for (i) LSUT0.05 and (a) ECC120knee, (b) CONC180ankle (ii), LSUT0.15 and (a) CONC120knee, (b) CONC180knee, and (iii) STS and CONC180ankle (all p < 0.05). However, after adjusting all the measures for body weight, positive spearman correlations were noted for LSUT0.05 and LSUT0.15 with CONC120, CONC180, ECC 120, and ECC180 of the knee and ankle while STS was positively related to CON180knee, ECC120knee, CON120ankle, CON180ankle, and ECC120ankle (all p < 0.05). Most of these relationships remained after adjusting for age, sex, and height. <h3>Conclusions</h3> Adjusting for body mass provides a greater insight on relationships of clinical tests of neuromuscular performance with contraction- and velocity-specific muscle strength of the lower extremity. This knowledge is vital for specific understanding of the role of muscles in clinical tests such as STS and LSUT in children. <h3>Author(s) Disclosures</h3> None.

Unique Joint And Neuromuscular Characteristics Dictate Loss Of Stretch-Shortening Cycle Potentiation In Older Adults

<h3>Research Objectives</h3> To compare the rate of force development (RFD) and the stretch-shortening cycle (SSC) potentiation of eccentric-preloaded concentric contraction between young and older populations at 3 different velocities: 120°/s, 180°/s, and 240°/s for 3 different range of motions (ROMs): small (ROM for walking), medium, and large (ROM for balance recovery from moderate to severe large-intensity perturbations, respectively) at the ankle. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> University laboratory. <h3>Participants</h3> 23 participants (12 young adults and 11 older adults). <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> Ankle plantarflexors were measured randomly for concentric only and eccentric-preloaded concentric muscle strength at 3 different velocities (120°/s, 180°/s, and 240°/s) at 3 different ROMs (small, medium, and large) on an isokinetic device. Body-mass normalized differences between eccentric-preloaded concentric torque and concentric torque without any preloading was calculated as SSCpotentiation. Average RFD (slope of eccentric-preloaded maximum concentric torque-time curve) was calculated for all the conditions in young and older adults. <h3>Results</h3> SSCpotentiation at the ankle in older adults was lower than young adults at 120°/s for the middle ROM (p ≤ 0.05, d = 0.3), and at 240°/s for the large ROM (p = 0.035, d = 0.3). Older adults had significantly lower RFD of eccentric-preloaded concentric torque at the ankle at 120°/s and 240°/s (p ≤ 0.05, d = 0.8 - 1.8) for the middle ROM, and at 120°/s, and 180°/s for the large ROM (p < 0.05, d = 1.0 - 2.6) than young. <h3>Conclusions</h3> SSCpotentiation and RFD of eccentric-preloaded concentric torque at the ankle are lower in older adults than young adults. The degree of deficit of RFD is markedly higher than SSCpotentiation in older adults. Whether these deficits with aging explain a greater risk of mobility-loss and falls remains unknown. <h3>Author(s) Disclosures</h3> No conflict of interest.

Enhanced Torque Due to Eccentric Preloading Relates to Greater Ease and Lower O2 Cost of Movement

<h3>Research Objectives</h3> To examine relationships of stretch-shortening cycle potentiation (SSCP) with ease of movement and oxygen cost of walking at 120°/s, 180°/s, and 240°/s for 3 different ranges of movements (ROMs): small, medium and large. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> University laboratory. <h3>Participants</h3> Young adults; n=10; Older adults, n = 10. <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> Ankle plantarflexors were assessed in random order for concentric only and eccentric-preloaded concentric muscle strength at 3 different velocities (120°/s, 180°/s, and 240°/s) at 3 different ROMs (small, medium, and large). Body-mass normalized SSCP (difference between eccentric-preloaded-concentric torque and concentric torque) was calculated for all the conditions. O2 consumption and heart rate (HR) were measured at the patient's steady state at 0.89 m/s and 1.34 m/s. <h3>Results</h3> In young adults, SSCP for the middle ROM was negatively related to O2 consumption at 0.89 m/s and HR at 1.34 m/s at all velocities (p < 0.05). Additionally in the middle ROM at 240°/s, SSCP was negatively related to HR at 0.89 m/s in younger adults (p < 0.05). For the small ROM, SSCP at 180°/s was negatively related to HR at 0.89 m/s in younger adults (p < 0.05). Whereas in older adults for the small ROM, SSCP at 240°/s was positively related to HR at 1.34 m/s. <h3>Conclusions</h3> Enhanced torque after eccentric loading is related to greater ease and lower O2 cost of movement in young adults. Our data suggests differential mechanisms exist for enhanced torque after eccentric loading in older adults. Whether enhanced torque after eccentric loading affects physical activity in adults remains unknown. <h3>Author(s) Disclosures</h3> No disclosures to report.

Characterization of aging-associated deficits of rate of force development of eccentric preloaded concentric torque

<h3>Research Objectives</h3> To compare average rate of force development (RFD) of eccentric-preloaded concentric torque (Ecccon-Torque) at 120°/s, 180°/s, and 240°/s for 3 different range of movements (ROMs) (corresponding to muscle length used for walking (small) and balance recovery from moderate (medium) to severe (large) perturbations) at the knee and ankle. Although stretch-shortening induced potentiation of Ecccon-Torque is a positive contributor to physical activity in older adults, a knowledge on joint-specific RFD of the Ecccon-Torque is unknown. Further, it is unknown if movement velocities and ROMs would affect RFD of the Ecccon-Torque. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> University laboratory. <h3>Participants</h3> Young adults, n=12; Older adults, n=11. <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> Knee extensors and ankle plantarflexors were assessed in random order for concentric only and eccentric-preloaded concentric muscle strength at 3 different velocities (120°/s, 180°/s, and 240°/s) at 3 different ROMs (small, medium, and large) on Biodex3 device. Average RFD (slope of eccentric-preloaded maximum concentric torque-time curve) was calculated for all the velocities and ROMs, <h3>Results</h3> RFD of Ecccon-Torque of older adults was significantly lower than young adults for i) the ankle at all velocities at medium ROMs (p < 0.05, d from 0.8 to 1.8) and 180°/s large ROM (p < 0.05, d = 1); and ii) the knee at 240°/s at all ROMs (p < 0.05, d from 0.3 to 0.6), 180°/s at large ROM (p < 0.05, d = 0.7), and 120°/s at middle ROM (p < 0.05, d = 0.5). <h3>Conclusions</h3> Aging-associated lower RFD of Ecccon-Torque is evident at the ankle and knee. Further, these deficits are movement velocity-, and ROM-specific. Whether RFD of Ecccon-Torque dictates ease, economy, and degree of physical activity in older adults is unknown. <h3>Author(s) Disclosures</h3> No conflict of interest

Differences in Muscle Demand and Joint Contact Forces Between Running and Skipping

Skipping has been proposed as a viable cross-training exercise to running due to its lower knee contact forces and higher whole-body energy expenditure. However, how individual muscle forces, energy expenditure, and joint loading are affected by differences in running and skipping mechanics remains unclear. The purpose of this study was to compare individual muscle forces, energy expenditure, and lower extremity joint contact forces between running and skipping using musculoskeletal modeling and simulations of young adults (n = 5) performing running and skipping at 2.5m·s-1 on an instrumented treadmill. In agreement with previous work, running had greater knee and patella contact forces than skipping which was accompanied by greater knee extensor energetic demand. Conversely, skipping had greater ankle contact forces and required greater energetic demand from the uniarticular ankle plantarflexors. There were no differences in hip contact forces between gaits. These findings further support skipping as a viable alternative to running if the primary goal is to reduce joint loading at the commonly injured patellofemoral joint. However, for those with ankle injuries, skipping may not be a viable alternative due to the increased ankle loads. These findings may help clinicians prescribe activities most appropriate for a patient's individual training or rehabilitation goals.

Eight-week virtual reality training improves lower extremity muscle strength but not balance in adolescents with intellectual disability: A randomized controlled trial.

Purpose: This study aims to assess the effects of 8-week virtual reality (VR) training on balance and lower extremity muscle strength in adolescents with intellectual disability (ID). Methods: Thirty adolescents with intellectual disability were randomly divided into the virtual reality group and control group. The participants in the virtual reality group and the control group received the virtual reality training and the physical education (PE) course, respectively, for 8weeks. The Berg Balance Scale (BBS), Timed Up and Go (TUG) test and lower extremity muscle strength were measured before and after the training. Results: The between-group results showed that the participants in the virtual reality group increased the muscle strength of hip flexors (p < 0.001), hip extensors (p = 0.002), hip abductors (p < 0.001), knee flexors (p < 0.001), knee extensors (p = 0.002) and ankle plantar flexors (p = 0.042) significantly after training, compared to the control group. However, no significant improvement was found in the berg balance scale and timed up and go scores between the virtual reality group and control group after training (p > 0.05). The within-group results showed that the strength of all the muscle groups significantly increased after training in the virtual reality group (p < 0.05) compared to the baseline. However, no significant difference was found in the muscle strength in the control group before and after training. The within-group berg balance scale and timed up and go scores showed no significant improvements in both groups. Conclusion: Virtual reality training intervention might be effective in improving the lower extremity muscle strength, but no significant improvement was found on balance ability in adolescents with intellectual disability.

The effect of whole-body vibration on spasticity in post-stroke hemiplegia: A prospective, randomized-controlled study.

This study aims to investigate whether whole-body vibration (WBV) has an anti-spastic effect on the ankle plantar flexors. This single-blind, prospective, randomized-controlled clinical study included a total of 48 patients with chronic stroke (33 males, 15 females; mean age: 60.7±10.9 years; range, 25 to 80 years) between May 2019 and February 2020. They were randomized into two groups: WBV group (n=24) and sham WBV group (n=24). A training program of 12 sessions (three days a week for four weeks) was applied regularly in both groups. The spasticity degree of the plantar flexors was evaluated by using both a subjective assessment method (modified Ashworth scale [MAS]) and several objective assessment methods (Hmax/Mmax, homosynaptic post-activation depression [HPAD], and torque) before and after the training program. There were no significant changes in the torque values, Hmax/Mmax, and HPAD level after the training program in both groups (p>0.05). However, the MAS score in the WBV group significantly decreased (-9.0%), but no change in the control group was observed (0.7%) (p=0.027, effect size = 0.32). The objective assessment methods for spasticity show that WBV has no anti-spastic effect.

Swing-phase pelvis perturbation improves dynamic lateral balance during walking in individuals with spinal cord injury.

The purpose of this study was to determine whether the control of lateral balance can be improved by applying repeated lateral perturbation force to the pelvis during swing versus stance phase walking in individuals with spinal cord injury (SCI). Fourteen individuals with incomplete SCI were recruited in this study. Each participant visited the lab once and was tested in two experimental sessions that consisted of (1) treadmill walking with bilateral perturbation force applied to the pelvis in the lateral direction during either swing or stance phase of each leg and (2) overground walking pre- and post-treadmill walking. Applying the swing-phase perturbation during walking induced a greater increase in the muscle activation of hip abductors and ankle plantar flexors and a greater improvement in lateral balance control after the removal of perturbation force, in comparison to the results of the stance-phase perturbation condition (P ≤ 0.03). Participants also exhibited a greater reduction in overground step width and a greater improvement in overground walking speed after a session of treadmill walking practice with the swing-phase perturbation, compared with the result of the stance-phase perturbation (P = 0.01). These findings suggest that applying perturbation force to the pelvis during the swing phase of gait while walking may enhance muscle activities of hip abductors and improve lateral balance control in individuals with SCI. A walking practice with the swing-phase pelvis perturbation can be used as a rehabilitation approach to improve the control of lateral balance during walking in people with SCI.

A kinetic analysis of the judo osoto-gari technique: relationship to sweeping leg velocity

ABSTRACT The present study characterised supporting leg kinetics (sweeping and pivot legs) during osoto-gari and investigated the relationship between kinetic variables and sweeping leg velocity at sweep contact. Fifteen black belt judoka performed osoto-gari. Motion data were recorded using a Mac3D motion analysis system (250 Hz), and ground reaction force (GRF) data were collected using four force plates (1,000 Hz). During the swing phase, the peak anterior (r = −0.535, p = 0.040) and upward (r = −0.693, p = 0.005) GRFs generated by the sweeping leg and the peak plantar flexion moment (r = 0.548, p = 0.034) and power (r = −0.700, p < 0.005) of the sweeping leg ankle joint significantly correlated with the sweeping leg velocity at sweep contact. During the throwing phase, the peak clockwise moment (r = −0.604, p = 0.017) correlated with the peak sweeping leg velocity. The peak knee extension moment (r = 0.602, p = 0.018), hip flexion moment (r = −0.589, p = 0.021) and knee power (r = −0.618, p = 0.016) of the pivot leg also correlated with the sweeping leg velocity at sweep contact. The results indicated that exertion of the sweeping leg ankle plantar flexors positively contributed to the sweeping velocity. Increasing whole-body rotation by contracting the pivot leg knee extensors is a crucial biomechanical factor in accelerating the sweeping leg at sweep contact.

Modulation of Achilles tendon force with load carriage and exosuit assistance.

Exosuits have the potential to assist locomotion in both healthy and pathological populations, but the effect of exosuit assistance on the underlying muscle-tendon tissue loading is not yet understood. In this study, we used shear wave tensiometers to characterize the modulation of Achilles tendon force with load carriage and exosuit assistance at the ankle. When walking (1.25 m/s) unassisted on a treadmill with load carriage weights of 15 and 30% of body weight, peak Achilles tendon force increased by 11 and 23%, respectively. Ankle exosuit assistance significantly reduced peak Achilles tendon force relative to unassisted, although the magnitude of change was variable across participants. Peak Achilles tendon force was significantly correlated with peak ankle torque for unassisted walking across load carriage conditions. However, when ankle plantarflexor assistance was applied, the relationship between peak tendon force and peak biological ankle torque was no longer significant. An outdoor pilot study was conducted in which a wearable shear wave tensiometer was used to measure Achilles tendon wave speed and compare across an array of assistance loading profiles. Reductions in tendon loading varied depending on the profile, highlighting the importance of in vivo measurements of muscle and tendon forces when studying and optimizing exoskeletons and exosuits.

Neuromechanical adaptations of foot function when hopping on a damped surface.

To preserve motion, humans must adopt actuator-like dynamics to replace energy that is dissipated during contact with damped surfaces. Our ankle plantar flexors are credited as the primary source of work generation. Our feet and their intrinsic foot muscles also appear to be an important source of generative work, but their contributions to restoring energy to the body remain unclear. Here, we test the hypothesis that our feet help to replace work dissipated by a damped surface through controlled activation of the intrinsic foot muscles. We used custom-built platforms to provide both elastic and damped surfaces and asked participants to perform a bilateral hopping protocol on each. We recorded foot motion and ground reaction forces, alongside muscle activation, using intramuscular electromyography from flexor digitorum brevis, abductor hallucis, soleus, and tibialis anterior. Hopping in the Damped condition resulted in significantly greater positive work and contact-phase muscle activation compared with the Elastic condition. The foot contributed 25% of the positive work performed about the ankle, highlighting the importance of the foot when humans adapt to different surfaces.NEW & NOTEWORTHY Adaptable foot mechanics play an important role in how we adjust to elastic surfaces. However, natural substrates are rarely perfectly elastic and dissipate energy. Here, we highlight the important role of the foot and intrinsic foot muscles in contributing to replacing dissipated work on damped surfaces and uncover an important energy-saving mechanism that may be exploited by the designers of footwear and other wearable devices.

Isokinetic Resistance Training for Ankle Plantarflexor Spasticity and Muscle Weakness in People With Multiple Sclerosis: A Proof-of-Concept Case Series.

To the best of the authors' knowledge, no data are available about the use of isokinetic resistance training for managing ankle plantarflexor spastic hypertonia in people with multiple sclerosis (MS). The aim of this proof-of-concept study was to explore the feasibility and effects of concentric contractions on spasticity-related resistance to passive motion, strength, and mobility in people with MS and ankle plantarflexor spasticity. In this pretest/posttest case series, 5 people with MS (mean age = 53.6 [SD = 8.8] years; median Expanded Disability Status Scale score = 5; Modified Ashworth Scale range = 1-4) received 6weeks of isokinetic resistance training of the spastic plantarflexors. Before and after the intervention, the following outcomes were assessed: average peak torque during passive robotic mobilization, isometric strength, surface electromyography (sEMG) from the spastic muscles, time to complete the 10-m Walk Test, and the Timed "Up & Go" Test. The standardized effect size was used to test pretest and posttest effects at the individual level. Group-level analyses were also performed. Following the training, the average peak torque recorded from the plantarflexors during passive motion at a velocity of 150 degrees per second was found to be decreased by at least 1 SD in all participants but 1, with a significant reduction at the group level of 23.8%. Conversely, no changes in sEMG activity were detected. Group-level analyses revealed that the maximal strength of the trained plantarflexors increased significantly (31.4%). Fast walking speed increased and time to complete the Timed "Up & Go" Test decreased in 4 participants, although not significantly at the group level. Isokinetic resistance training proved safe and feasible in people who had MS and ankle plantarflexor spasticity. The observed reductions in resistance to passive motion from the spastic plantarflexors in the absence of sEMG changes might suggest a mechanical rather than a neural effect of the training. Based on these preliminary findings, isokinetic resistance training does not exacerbate hypertonia in people with MS and ankle plantarflexor spasticity and could be safely used to manage muscle weakness in this population.

Efficacy of Cryo-compression on Shin Splints in Female Amateur Marathon Runners

Background: Medial tibial stress syndrome (MTSS) or Shin splints is exercise-induced lower leg pain along the distal posterior-medial aspect of tibia caused by repetitive loading stress during running and jumping. It is one of the most common lower leg sports injury. Cryotherapy is the most commonly used treatment during immediate care of athletic injuries and acute soft tissue injuries and is also included as part of RICE (rest, ice, compression and elevation). Cryotherapy is helpful in reducing swelling as well as it exerts analgesic effect. The external compression is also used during immediate care phase and it helps in decrease tissue temperature and prevent oedema formation. Cryotherapy in combination with intermittent pneumatic compression hypothetically help in reducing the physiologic effects of traumatic tissue damage which is based on the models of cryotherapy and static compression therapy. This study aims to establish the efficacy of cryo-compression on shin splints in female amateur marathon runners. Methods: A total 30 subjects diagnosed with shin splints were selected for study. Subjects received cryo-compression for reducing pain and swelling and exercises to strengthen the muscles. Each session was conducted for 45 minutes duration, 5 days per week for 4 weeks. Outcome measure used was Numerical Pain Rating Scale (NPRS), Goniometry for ROM and Manual muscle testing (MMT). Results: According to statistical analysis, the results of the study demonstrate that there was a significant effect of the use of cryo-compression on numerical pain rating scale (p&lt;0.0001), range of motion (ankle plantarflexion, dorsiflexion, eversion and inversion) (p&lt;0.0001), manual muscle testing – ankle plantarflexors (p=0.0028) and ankle dorsiflexors (p&lt;0.0001) during the pre and post intervention assessment. Conclusion: The conducted study shows that efficacy of cryo-compression on shin splints in female amateur marathon runners is very effective in reducing pain, increasing range of motion (ROM) and strength of muscles along with other treatment program. KEYWORDS: Cryo-compression, shin splints, numerical pain rating scale (NPRS), range of motion, ankle plantarflexion, ankle dorsiflexion, ankle eversion, ankle inversion, manual muscle testing, ankle plantarflexors, ankle dorsiflexors.

Relationship between spatiotemporal parameters and clinical outcomes in children with bilateral spastic cerebral palsy: Clinical interpretation proposal

BackgroundUnderstanding the links between gait disorders, impairments, and activity limitations is essential for correctly interpreting the instrumented gait analysis. We aimed to evaluate the relationships between spatiotemporal parameters and clinical outcomes in children with bilateral spastic cerebral palsy, and find out whether spatiotemporal parameters provide clinical information regarding gait pattern and walking. MethodsData from 19 children with bilateral spastic cerebral palsy (nine males, ten females, 9.6 ± 2.8 years old) were collected retrospectively. All children underwent an instrumented gait analysis and a standardized clinical assessment. Seven spatiotemporal parameters were calculated: non-dimensional cadence, stride length, step width, gait speed, first double support, single support, and time of toe off. Clinical outcomes included measures of two different components of the International Classification of Functioning, Disability and Health - Children and Youth version: body functions and structures (spasticity, contractures and range of motion, and deformities), and activities and participation (gross motor function, and walking capacity). Pearson correlation, ANOVA, Student’s t, Mann–Whitney U, and Kruskal–Wallis tests were used to analyze relationships. Spatiotemporal parameters related to clinical outcomes of body functions and structures were interpreted as outcome measures of gait pattern, while those related to clinical outcomes of activities and participation were interpreted as outcome measures of walking. ResultsNon-dimensional cadence, stride length, and gait speed showed relationships (p < 0.05) with hip flexors spasticity and hindfoot deformity, ankle plantar flexors spasticity, and hindfoot deformity, respectively. All spatiotemporal parameters except non-dimensional cadence showed correlation (p < 0.05) with gross motor function and walking capacity. ConclusionsSpatiotemporal parameters provide clinical information regarding both gait pattern and walking.

Toward the definition of a minimum input model for an EMG analysis in clinics

Neuro-musculoskeletal (NMS) modeling based on electromyographic (EMG) signals allows for a better understanding of the principles of human movement [1]. Through appropriate modeling software (CEINMS) it is possible to estimate the muscular forces and joint moments calibrated on the single individual. The possibility of having highly subject-specific models allows an improvement in the treatment of a great variety of neurodegenerative diseases and can be fundamental for the general understanding of the neuro-mechanics of human locomotion. Fifteen walking trials of four able body subjects (mean age = 60 ± 2.16, mean BMI = 26.66 ± 4.13) were acquired with a motion capture system (BTS, 60 Hz), synchronized with a force plate (Bertec, 960 Hz) and a 15 channels surface electromyography (sEMG) system (FreePocketEMG, 1000 Hz). The CAST protocol was adopted as marker set, while the following muscles were acquired: Gluteus Maximus, Gluteus Medius, Tensor Fasciae Latae, Sartorius, Adductor Longus, Rectus Femoris, Biceps Femoris, Semitendinosus, Vastus Lateralis, Vastus Medialis, Tibialis Anterior, Peroneus Longus, Gastrocnemius Lateralis, Gastrocnemius Medialis and Soleus. The data were processed in MatLab for the extraction of four muscle synergies by applying the ‘Non-negative Matrix Factorization’ method [2]. Then, 'Statistical Parametric Mapping' [3] and 'Cosine Similarity' were used as metrics to assign each synergy to the EMG signals of just one muscle for each different muscle groups (Ankle Plantar-flexors, Ankle Dorsi-flexors, Knee Extensors and Knee Flexors). Afterwards data were processed in OpenSim; scaling, inverse kinematics, inverse dynamics, muscle analysis were run. Finally, CEINMS was executed to calculate muscle activations and torques first by informing the model with a complete setup of experimental EMGs data then with a reduced setup (the foru EMGs that best matched with muscle synergies). Activation signals of the muscle-tendon units and the angular moments of the knee and ankle obtain from models developed by CEINMS were compared for different setup with the experimental EMG signals. Comparison was done for both different muscle setups for each subject. In Fig. 1a are shown the values of cosine similarities of the muscles able to better approximate each primitive for one subject. In Fig. 1 b-e are displayed the pattern of primitives and the chosen experimental EMG signals for the same subject during one walking trial. The implemented methodology allowed the analysis of the muscular forces developed during walking with an acquisition protocol that includes a reduced number of EMG signals, and a sensitivity analysis for the adoption of NMS models based on a limited number of inputs was conducted. Results seem promising but a validation on a wider sample of subjects including pathological subjects is needed.

Postural Sway and Muscle Activity Dynamics of Upright Standing on Sloped Surfaces.

During upright standing, individuals often use co-contraction muscle activity at the ankle joint when encountering increased postural difficulty; however, this strategy has been shown to be maladaptive. The purpose of the current investigation was to examine the effect of sloped standing on postural sway and muscle co-contraction at the ankle joint as a function of postural difficulty. Twelve young (21.67 ± 1.11years) adults performed upright standing on flat, declined, and inclined support surfaces. Center of pressure displacements indexed postural sway while electromyography data were collected for the tibialis anterior and gastrocnemius medialis muscles. A co-contraction index and a nonlinear coupling metric (cross-approximate entropy) were computed between ankle dorsiflexor and plantar flexor muscles (tibialis anterior/gastrocnemius medialis) activity. The results showed that higher degrees of postural difficulty led to increased amounts of sway as well as increased sway regularity. Lower co-contraction index was observed for higher degrees of postural difficulty; however, increased dynamic coupling occurred with deviations from the flat standing condition. Overall, increased postural difficulty as manipulated by sloped standing (in either inclined or declined conditions) resulted in individuals adopting a more regular sway trajectory that may be due, in part, to a stronger dynamic coupling strategy occurring at the neuromuscular level.

The effect of footwear on mechanical behaviour of the human ankle plantar-flexors in forefoot runners.

PurposeTo compare the ankle plantar-flexor muscle-tendon mechanical behaviour during barefoot and shod forefoot running.MethodsThirteen highly trained forefoot runners performed five overground steady-state running trials (4.5 ± 0.5 m.s-1) while barefoot and shod. Three-dimensional kinematic and ground reaction force data were collected and used as inputs for musculoskeletal modelling. Muscle-tendon behaviour of the ankle plantar-flexors (soleus; medial gastrocnemius; and lateral gastrocnemius) were estimated across the stance phase and compared between barefoot and shod running using a two-way multivariate analysis of variance.ResultsDuring barefoot running peak muscle-tendon unit (MTU) power generation was 16.5% (p = 0.01) higher compared to shod running. Total positive MTU work was 18.5% (p = 0.002) higher during barefoot running compared to shod running. The total sum of tendon elastic strain energy was 8% (p = 0.036) greater during barefoot compared to shod running, however the relative contribution of tendon and muscle fibres to muscle-tendon unit positive work was not different between conditions.ConclusionBarefoot forefoot running demands greater muscle and tendon work than shod forefoot running, but the relative contribution of tendon strain energy to overall muscle-tendon unit work was not greater.

The Influence of Footwear Longitudinal Bending Stiffness on Running Economy and Biomechanics in Older Runners

ABSTRACTPurpose: This study assessed the effects of footwear longitudinal bending stiffness on running economy and biomechanics of rearfoot striking older runners. Methods: Nine runners over 60 years of age completed two running bouts at their preferred running pace in each of three footwear conditions: low (4.4 ± 1.8 N·m-1), moderate (5.7 ± 1.7 N·m-1), and high (6.4 ± 1.6 N·m-1) bending stiffness. Testing order was randomized and a mirror protocol was used (i.e., A,B,C,C,B,A). Expired gases, lower limb kinematics, and ground reaction forces were collected simultaneously and lower limb joint kinetics, running economy (i.e., VO2), leg stiffness, and spatio-temporal variables were calculated. Results: Running economy was not different among stiffness conditions (p = 0.60, p = 0.53 [mass adjusted]). Greater footwear stiffness reduced step length (p = 0.046) and increased peak vertical ground reaction force (p = 0.019) but did not change peak ankle plantarflexor torque (p = 0.65), peak positive ankle power (p = 0.48), ankle positive work (p = 0.86), propulsive force (p = 0.081), and leg stiffness (p = 0.46). Moderate footwear stiffness yielded greater peak negative knee power compared to low (p = 0.04) and high (p = 0.03) stiffness. Conclusions: These novel findings demonstrate that increasing footwear longitudinal bending stiffness using flat carbon fiber inserts does not improve running economy and generally does not alter lower limb joint mechanics of rearfoot strike runners over 60 years. Future studies should investigate how other footwear characteristics (e.g., midsole material, plate location, and sole curvature) influence economy and biomechanics in this population.

Effect of electromyostimulation and plyometrics training on sports-specific parameters in badminton players

Badminton is one of the world's most popular racquet sports, demanding motor skills such as agility and vertical jump mainly for striking a shuttlecock. This study compared the effects of four weeks of plyometric training and electromyostimulation of knee extensor and ankle plantar flexor muscles on agility, 30-m sprint, lower limb explosive power and jumping ability amongst badminton players. State-level badminton players (n ​= ​90) were randomly allocated into three groups: plyometric (PG), electromyostimulation (EG) and control group (CG), each with 30 players. Randomized-to-Groups Pretest-Posttest Design with two experimental (plyometric and electromyostimulation) groups and a control group was used. The plyometric training was carried out two times/week while the EMS training was four times/week for four weeks. The control group did not receive any intervention. All three groups continued their general badminton training throughout the study. Players were assessed for agility, a 30-m sprint, a standing broad jump and a vertical jump height before and after four weeks. A significant improvement (p ​= ​0.01) in 30-m sprint time was observed (3.83%) in PG as compared to controls. Jumping ability was significantly improved in both the PG and EG in comparison to the controls (4.45%, p ​= ​0.003 for PG and 3.95%, p ​= ​0.048 for EG). No significant improvement was found in agility and lower limb explosive power in either of the PG or EG groups in comparison to the controls. Plyometric training showed significant improvement in sprint time and jumping ability, whereas electromyostimulation training showed significant improvement only in jumping ability.