Plantarflexor Function Research Articles

Looking Beyond the Number of Repetitions: An Observational Cross-Sectional Study on Calf Raise Test Outcomes in Children Aged 10–17 Years

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

Alpha and beta/low-gamma frequency bands may have distinct neural origin and function during post-stroke walking.

Plantarflexors provide propulsion during walking and receive input from both corticospinal and corticoreticulospinal tracts, which exhibit some frequency-specificity that allows potential differentiation of each tract's descending drive. Given that stroke may differentially affect each tract and impair the function of plantarflexors during walking; here, we examined this frequency-specificity and its relation to walking-specific measures during post-stroke walking. Fourteen individuals with chronic stroke walked on an instrumented treadmill at self-selected and fast walking speed (SSWS and FWS, respectively) while surface electromyography (sEMG) from soleus (SOL), lateral gastrocnemius (LG), and medial gastrocnemius (MG) and ground reaction forces (GRF) were collected. We calculated the intermuscular coherences (IMC; alpha, beta, and low-gamma bands between SOL-LG, SOL-MG, LG-MG) and propulsive impulse using sEMG and GRF, respectively. We examined the interlimb and intralimb IMC comparisons and their relationships with propulsive impulse and walking speed. Interlimb IMC comparisons revealed that beta LG-MG (SSWS) and low-gamma SOL-LG (FWS) IMCs were degraded on the paretic side. Intralimb IMC comparisons revealed that only alpha IMCs (both speeds) exhibited a statistically significant difference to random coherence. Further, alpha LG-MG IMC was positively correlated with propulsive impulse in the paretic limb (SSWS). Alpha and beta/low-gamma bands may have a differential functional role, which may be related to the frequency-specificity of the underlying descending drives. The persistence of alpha band in plantarflexors and its strong positive relationship with propulsive impulse suggests relative alteration of corticoreticulospinal tract after stroke. These findings imply the presence of frequency-specific descending drives to walking-specific muscles in chronic stroke.

Acute microtubule changes linked to DMD pathology are insufficient to impair contractile function or enhance contraction-induced injury in healthy muscle.

Duchenne muscular dystrophy (DMD) is marked by the genetic deficiency of the dystrophin protein in striated muscle whose consequence is a cascade of cellular changes that predispose the susceptibility to contraction injury central to DMD pathology. Recent evidence identified the proliferation of microtubules enriched in post-translationally modified tubulin as a consequence of dystrophins absence that increases the passive mechanics of the muscle fiber and the excess mechanotransduction elicited reactive oxygen species and calcium signals that promote contraction injury. Motivated by evidence that acutely normalizing the disease microtubule alterations reduced contraction injury in murine DMD muscle ( mdx ), here we sought the direct impact of these microtubule alterations independent of dystrophins absence and the multitude of other changes consequent to dystrophic disease. To this end we used acute pharmacologic (epithiolone-D, EpoD; 4 hours) or genetic (vashohibin-2 and small vasohibin binding protein overexpression via AAV9; 2 weeks) strategies to effectively model the proliferation of detyrosination enriched microtubules in the mdx muscle. Quantifying in vivo nerve evoked plantarflexor function we find no alteration in peak torque nor contraction kinetics in WT mice modeling these DMD relevant MT alterations. Quantifying the susceptibility to eccentric contraction injury we show EpoD treatment proffered a small but significant protection from contraction injury while VASH/SVBP had no discernable impact. We conclude that the disease dependent MT alterations act in concert with additional cellular changes to predispose contraction injury in DMD.

Injury and performance related biomechanical differences between recreational and collegiate runners.

Running related injuries (RRI) are common, but factors contributing to running performance and RRIs are not commonly compared between different types of runners. We compared running biomechanics previously linked to RRIs and performance between 27 recreational and 35 collegiate runners. Participants completed 5 overground running trials with their dominant limb striking a force plate, while outfitted with standardised footwear and 3-dimensional motion capture markers. Post hoc comparisons revealed recreational runners had a larger vertical loading rate (194.5 vs. 111.5 BW/s, p < 0.001) and shank angle (6.80 vs. 2.09, p < 0.001) compared with the collegiate runners who demonstrated greater vertical impulse (0.349 vs. 0.233 BWs, p < 0.001), negative impulse (-0.022 vs. -0.013 BWs, p < 0.001), positive impulse (0.024 vs. 0.014 BWs, p < 0.001), and propulsive force (0.390 vs. 0.333 BW, p = 0.002). Adjusted for speed, collegiate runners demonstrated greater total support moment (TSM), plantar flexor moment, knee extensor moment, hip extensor moment, and had greater proportional plantar flexor moment contribution and less knee extensor moment contribution to the TSM compared with recreational runners. Unadjusted for speed, collegiate runners compared with recreational had greater TSM and plantar flexor moment but similar joint contributions to the TSM. Greater ankle joint contribution may be more efficient and allow for greater capacity to increase speed. Improving plantarflexor function during running provides a strategy to improve running speed among recreational runners. Moreover, differences in joint kinetics and ground reaction force characteristics suggests that recreational and collegiate runners may experience different types of RRI.

Effects of exercise treatment on functional outcome parameters in mid-portion achilles tendinopathy: a systematic review.

Exercise interventions are evident in the treatment of mid-portion Achilles tendinopathy (AT). However, there is still a lack of knowledge concerning the effect of different exercise treatments on improving a specific function (e.g., strength) in this population. Thus, this study aimed to systematically review the effect of exercise treatments on different functional outcomes in mid-portion AT. An electronic database of Pubmed, Web of Science, and Cochrane Central Register of Controlled Trials were searched from inception to 21 February 2023. Studies that investigated changes in plantar flexor function with exercise treatments were considered in mid-portion AT. Only randomized controlled trials (RCTs) and clinical controlled trials (CCTs) were included. Functional outcomes were classified by kinetic (e.g., strength), kinematic [e.g., ankle range of motion (ROM)], and sensorimotor (e.g., balance index) parameters. The types of exercise treatments were classified into eccentric, concentric, and combined (eccentric plus concentric) training modes. Quality assessment was appraised using the Physiotherapy Evidence Database scale for RCTs, and the Joanna Briggs Institute scale for CCTs. The search yielded 2,260 records, and a total of ten studies were included. Due to the heterogeneity of the included studies, a qualitative synthesis was performed. Eccentric training led to improvements in power outcomes (e.g., height of countermovement jump), and in strength outcomes (e.g., peak torque). Concentric training regimens showed moderate enhanced power outcomes. Moreover, one high-quality study showed an improvement in the balance index by eccentric training, whereas the application of concentric training did not. Combined training modalities did not lead to improvements in strength and power outcomes. Plantarflexion and dorsiflexion ROM measures did not show relevant changes by the exercise treatments. In conclusion, eccentric training is evident in improving strength outcomes in AT patients. Moreover, it shows moderate evidence improvements in power and the sensorimotor parameter "balance index". Concentric training presents moderate evidence in the power outcomes and can therefore be considered as an alternative to improve this function. Kinematic analysis of plantarflexion and dorsiflexion ROM might not be useful in AT people. This study expands the knowledge what types of exercise regimes should be considered to improve the functional outcomes in AT.

Surgically Repairing Achilles Tendon Ruptures Restores Plantar Flexor Function Better Than Non- Surgical Treatment in a Rat Model

Category: Basic Sciences/Biologics; Sports Introduction/Purpose: Achilles tendon ruptures cause long-term functional deficits in nearly 2 out of 3 patients. Our group has established a complex muscle-tendon pathology following isolated Achilles tendon ruptures. Our long-term goal is to determine how rehabilitation loads can simultaneously accomplish 2 competing objectives: (1) prevent muscle remodeling while (2) not overloading the healing tendon that causes permanent tendon elongation - unloading the muscle and stimulating muscle remodeling. To do this, we developed a novel experimental framework to test the potential therapeutic effectiveness of different loading paradigms on the healing muscle-tendon following surgically induced Achilles tendon ruptures in an established rat model. We hypothesized that overloading the healing tendon would lead to worse functional outcomes compared to unloaded immobilization. Methods: Achilles tendon rupture, repair, and immobilization. Male Sprague-Dawley rats underwent a surgically induced Achilles tendon rupture by blunt dissection followed by a modified Kessler repair in this IACUC approved study. The repaired limb was immobilized in either unloaded plantar flexion (n=7) to simulate the clinical standard of rehabilitative care or loaded dorsiflexion (n=5) to simulate clinically damaging rehabilitation. Structural analyses. Following 2 weeks of immobilization and 2 weeks of cage recovery, we sacrificed our study animals and measured tendon elongation and serial sarcomere count. Plantar flexor functional assessment. We developed an ankle dynamometer to quantify plantar flexor function that mirrored our clinical assessments in patients. To demonstrate the clinical- relevance of this device, we tested 1 animal that was immobilized in unloaded plantar flexion for 1 week and 1 animal that was immobilized in loaded dorsiflexion for 1 week - both then completed 2 weeks of unrestricted cage activity. Results: Muscle-tendon structural changes. Achilles tendon ruptures caused the tendon to heal in an elongated position with fewer sarcomeres in series (Fig. A). Tendon length increased by 73% following 2-weeks of loaded immobilization in dorsiflexion and 23% in unloaded immobilization in plantar flexion (p&lt;.001). We measured sarcomere length in a subset of these animals but found similar trends in serial sarcomere reductions, where unloaded immobilization in plantar flexion caused 14% reduced serial sarcomeres (p&lt;.01, n=4) and loaded immobilization in dorsiflexion caused 32% reduced serial sarcomeres (n=2). Plantar flexor function. Plantar flexor work was adversely impacted by the Achilles tendon ruptures (Fig. B). We found that unloaded immobilization in plantar flexion caused a 13% decrease in plantar flexor work with the detectable deficits occurring in ankle plantar flexion. Loaded immobilization in dorsiflexion caused greater plantar flexor work deficits (28%) with greater torque deficits in dorsiflexion and continuing through plantar flexion angles. Conclusion: Our exciting experimental findings are the first of their kind to directly link muscle-tendon structural deficits with plantar flexor functional deficits in an animal model of Achilles tendon rupture using a clinically relevant ankle dynamometer. We established preliminary evidence that supports our overarching hypothesis that joint immobilization, whether unloaded or loaded, causes detrimental muscle-tendon structural changes that impose functional constraints on plantar flexor work. Our preliminary findings suggest that rehabilitation loading is critical to structural and functional outcomes following surgically repairing the Achilles tendon. Too little loading promotes muscle remodeling while too much loading elongates the healing tendon.

A Comparison Of Lower Extremity Joint Kinetics During Walking Between Runners And Inactive Individuals.

Age-related changes affecting gait can begin as early as the third decade. Running requires greater plantarflexor involvement than walking, suggesting that running may provide a large enough benefit in retaining the plantar flexor function. In doing so, running may reduce or postpone the distal-to-proximal shift in joint kinetics that has been observed in aging individuals. PURPOSE The purpose of this study was to investigate walking mechanics and the presence of age-related gait adaptations in runners between the ages of 36-45 years old compared to inactive individuals of the same age. METHODS A total of 30 individuals aged 36-45 years old were included in this analysis (Table 1). Participants walked at a self-selected pace over a 17-m long runway with force platforms collecting kinetic data. Six successful walking trials were selected for analysis. Between-group differences were determined using independent t-tests and effect sizes. RESULTS Mean values for kinetic variables of interest are shown in Table 2. When normalized to body mass (BM), runners generated greater knee power than inactive individuals (p = 0.01). When normalized to fat-free mass (FFM), inactive individuals had a greater peak plantarflexor moment than runners (p = 0.01). CONCLUSION Knee power was no longer greater in runners than inactive individuals when normalized to FFM, suggesting this difference is a function of overall mass. However, when normalized to FFM, the greater plantarflexor torque exhibited by inactive individuals suggests their need to generate a greater relative torque than the runners to assist in propelling them forward. FUNDING: This research was co-funded by European union and Ministry of Education, Youth and Sports of the Czech Republic, grant number CZ.02.1.01/0.0/0.0/16_019/0000798 Program 4 Healthy Aging in Industrial Environment.

Improving Ankle Muscle Recruitment via Plantar Pressure Biofeedback during Robot Resisted Gait Training in Cerebral Palsy.

Neurological impairment from stroke or cerebral palsy often presents with diminished ankle plantar flexor function during the propulsive phase of gait. This deficit often results in slow, energy-expensive walking patterns that limit community mobility. Robotic gait training interventions may prove effective in improving functional outcomes, including exoskeleton resistance used to provide targeted neuromuscular recruitment. However, these interventions to date have required regular verbal cues and coaching for proper plantar flexor engagement with resistance, particularly for pediatric applications. In this validation study, we sought to address the need for automating and improving the effectiveness of facilitating user engagement with robotic resistance. Specifically, our main goal was to compare changes in plantar flexor activity between walking with plantar flexor resistance alone vs plantar flexor resistance combined with plantar pressure biofeedback in individuals with cerebral palsy. We recruited 8 ambulatory adolescents with cerebral palsy between the ages of 11-18 years old to participate in this cross-sectional feasibility study. Supporting our hypothesis, we observed a 36 ± 36% and 46 ± 39% increase in mean and peak soleus activity, respectively, between resistance plus biofeedback vs resistance alone (both p < 0.05). Compared to other biofeedback sensing modalities like assessment of muscle activity via surface electrodes, integrating the plantar pressure-based system within the wearable robotic devices minimizes barriers to clinical implementation by reducing cost, complexity, and setup time. With these positive feasibility results, our future work will explore longer-term training effects of ankle resistance combined with plantar pressure biofeedback.

Sex differences in central and peripheral fatigue induced by sustained isometric ankle plantar flexion

The main aim of this study was to determine sex differences in central and peripheral fatigue produced by a sustained isometric exercise of ankle plantar flexors in healthy young adults. Ten males and fourteen females performed a sustained isometric ankle exercise until task failure. Maximal voluntary isometric contraction (MVIC) torque (plantarflexion), voluntary activation level (using the twitch interpolation technique), and resting twitch contractile properties [twitch peak torque (ST), twitch half relaxation time, and low frequency fatigue (LFF) ratio] were measured before, immediately after, and throughout a recovery period (1, 2, 5, and 10 min) following the exercise protocol in order to characterize neuromuscular fatigue. Fatigue had effects (p≤ 0.05) on all dependent variables (reduction in MVIC, VA and twitch torque and slowing of relaxation time). However, no significant differences in performance fatigability markers (MVIC torque decline and time to fatigue) and only minor differences in the variables reflecting central and peripheral fatigue mechanisms were found between males and females. A regression analysis did suggest a somewhat greater role of central fatigue in males compared with females. Females also showed a slightly greater and more prolonged decline in ST and LFF after exercise compared with males. The presence of only minor differences in central and peripheral fatigue mechanisms between males and females in the present study could be explained by the lack of important sex differences in performance fatigability, which could be due to lesser sex differences in the relative area of type I muscle fibers and in contractile function (muscle strength) of ankle plantar flexors as compared with other muscle groups.

The relationship between quantitative magnetic resonance imaging of the ankle plantar flexors, muscle function during walking and maximal strength in people with neuromuscular diseases

BackgroundProgression of plantar flexor weakness in neuromuscular diseases is usually monitored by muscle strength measurements, although they poorly relate to muscle function during walking. Pathophysiological changes such as intramuscular adipose tissue affect dynamic muscle function independent from isometric strength. Diffusion tensor imaging and T2 imaging are quantitative MRI measures reflecting muscular pathophysiological changes, and are therefore potential biomarkers to monitor plantar flexor functioning during walking in people with neuromuscular diseases. MethodsIn fourteen individuals with plantar flexor weakness diffusion tensor imaging and T2 scans of the plantar flexors were obtained, and the diffusion indices fractional anisotropy and mean diffusivity calculated. With a dynamometer, maximal isometric plantar flexor strength was measured. 3D gait analysis was used to assess maximal ankle moment and power during walking. FindingsFractional anisotropy, mean diffusivity and T2 relaxation time all moderately correlated with maximal plantar flexor strength (r > 0.512). Fractional anisotropy and mean diffusivity were not related with ankle moment or power (r < 0.288). T2 relaxation time was strongly related to ankle moment (r = −0.789) and ankle power (r = −0.798), and moderately related to maximal plantar flexor strength (r < 0.600). InterpretationIn conclusion, T2 relaxation time, indicative of multiple pathophysiological changes, was strongly related to plantar flexor function during walking, while fractional anisotropy and mean diffusivity, indicative of fiber size, only related to maximal plantar flexor strength. This indicates that these measures may be suitable to monitor muscle function and gain insights into the pathophysiological changes underlying a poor plantar flexor functioning during gait in people with neuromuscular diseases.

Runners with mid‐portion Achilles tendinopathy have greater triceps surae intracortical inhibition than healthy controls

This study aimed to investigate short-interval intracortical inhibition (SICI) and muscle function in the triceps surae of runners with mid-portion Achilles tendinopathy (AT). Runners with (n=11) and without (n=13) AT were recruited. Plantar flexor isometric peak torque and rate of torque development (RTD) were measured using an isokinetic dynamometer. Triceps surae endurance was measured as single-leg heel raise (SLHR) to failure test. SICI was assessed using paired-pulse transcranial magnetic stimulation during a sustained contraction at 10% of plantar flexor isometric peak torque. Triceps surae SICI was 14.3% (95% CI: -2.1 to 26.4) higher in AT than in the control group (57.9%, 95% CI: 36.2 to 79.6; and 43.6% 95% CI: 16.2 to 71.1, p=0.032) irrespective of the tested muscle. AT performed 16 (95% CI: 7.9 to 23.3, p<0.001) fewer SLHR repetitions on the symptomatic side compared with controls, and 14 (95% CI: 5.8 to 22.0, p=0.004), fewer SLHR repetitions on the non-symptomatic compared with controls. We found no between-groups differences in isometric peak torque (p=0.971) or RTD (p=0.815). Our data suggest greater intracortical inhibition for the triceps surae muscles for the AT group accompanied by reduced SLHR endurance, without deficits in isometric peak torque or RTD. The increased SICI observed in the AT group could be negatively influencing triceps surae endurance; thus, rehabilitation aiming to reduce intracortical inhibition should be considered to improve patient outcomes. Furthermore, SLHR is a useful clinical tool to assess plantar flexor function in AT patients.

Understanding the effects of quantitatively prescribing passive-dynamic ankle-foot orthosis bending stiffness for individuals after stroke.

Passive-dynamic ankle-foot orthosis (PD-AFO) bending stiffness, which assists plantar flexor function, can be prescribed to improve poststroke gait. However, outcomes with PD-AFOs are variable likely because of improper personalization. We implemented a prescription model that objectively personalizes PD-AFO bending stiffness based on each individual's level of plantar flexor weakness (quantitatively prescribed PD-AFO). To evaluate whether a quantitatively prescribed PD-AFO improves peak paretic plantar flexion moment compared with the original AFO for individuals after stroke and to examine the immediate effects of wearing a quantitatively prescribed PD-AFO. This is a repeated-measures study. PD-AFO bending stiffness was personalized for 10 individuals after stroke through the previously developed prescription model. Participants underwent an instrumented gait analysis while wearing their original AFO and the quantitatively prescribed PD-AFO. Participants' peak paretic plantar flexion moment significantly increased while wearing the quantitatively prescribed PD-AFO compared with the original AFO. In addition, participants showed different levels of improvements in a series of other key biomechanical and walking performance parameters with PD-AFO use. Some participants showed improvements in all parameters, whereas others showed moderate to no improvements. Quantitatively prescribed PD-AFO bending stiffness resulted in inconsistent improvements in biomechanical and walking performance parameters, which warrants further investigation. Future work should investigate whether more consistent benefits are seen with faster walking speeds and longer-term PD-AFO use. In addition, future work should conduct larger-scale studies that aim to understand and optimize orthosis-patient matching for all AFO designs/characteristics.

Novel isodamping dynamometer accurately measures plantar flexor function

Isokinetic dynamometers are the gold standard tools used to assess in vivo joint and muscle function in human subjects, however, the large size and high cost of these devices prevents their widespread use outside of traditonal biomechanics labs. In this study, we developed a mobile dynamometer to allow for field measurements of joint level function. To ensure subject safety, we designed a new “isodamping” dynamometer that acted as passive energy sink which constrains velocity by forcing incompressible oil through an orifice with an adjustable diameter. We validated the performance of this device by testing plantar flexor function in six healthy adults on both a commercial isokinetic dynamometer and this novel device at three velocities/damper settings and at three different effort levels. During maximal effort contraction, measurements of peak moment and velocity at peak moment of the novel device and the commercial device were strongly correlated along the predicted quadratic line (R2 > 0.708, p ≤ 0.008). The setting of the damper prescribed the relationship between peak moment and velocity at peak moment across all subjects and effort levels (R2 > 0.910, p < 0.001). The novel device was significantly smaller (0.75 m2 footprint), lighter (30 kg), and lower cost (~$2,200 US Dollars) than commercial devices compared to commercially-available isokinetic dynamometers (5.95 m2 footprint, 450 kg, and ~$40,000 US Dollars respectively).

Mechanisms of reduced plantarflexor function in Cerebral palsy: smaller triceps surae moment arm and reduced muscle force

Both muscle forces, and moment arm (MA) could contribute to reduced muscle moment in people with Cerebral Palsy (CP). Current reports in CP are conflicting. The tendon travel method of estimating MA requires constant force, but passive force is high and variable in CP, and range of motion is limited. Therefore, the purpose of this study was to examine triceps surae muscle MA in 12 subjects with mild to moderate CP (15–32 years) and 10 typically developing peers (TD, 17–26 years) by tendon travel and by visually measuring the apparent MA. MA was calculated at 90° and at a reference angle (∼106°) with zero net passive moment. The tendon travel (28.8 ± 5.6 mm) and visual methods (29.1 ± 5.5 mm) yielded similar MA in CP (p = 0.94) at the reference angle. TD had significantly larger triceps surae muscle MA than CP subjects (p = 0.002), 35.4 ± 4.1 mm at the reference angle for tendon travel and 35.4 ± 3.6 mm by the visual method. Test/retest revealed less bias (0.8 mm) using the visual method. Calculated active peak isometric force was significantly less in CP (1983.8 ± 887.0 N) than TD (4104.9 ± 1154.9 N, p < 0.001). There are challenges in estimating MA in CP, but the visual method is more reliable. Although a shorter moment arm would reduce the joint moment, joint angular velocity for a given velocity of muscle shortening would be enhanced. Strength training may mitigate the effects of the smaller moment arm and reduced joint moment generated in those with CP.

Plantar Flexor Function in Adults with and without Prader-Willi Syndrome.

Prader-Willi Syndrome (PWS) is a form of congenital obesity characterized by excessive body fat, hypotonia, muscle weakness, and physical/cognitive disability. However, the sources of muscle dysfunction and their contribution to mobility are unclear. The purposes of this study were to 1) compare plantar flexor function between adults with and without PWS; and 2) to examine the relationship between plantar flexor function and gait speed in adults with PWS. Participants included 10 adults with PWS, 10 adults without PWS and with obesity, and 10 adults without PWS and without obesity (matched on age and sex). Plantar flexor function was assessed using isokinetic dynamometry (peak torque [PT], early/late rate of torque development [RTD]), Hoffman reflex (H/M ratio), ultrasound imaging (cross-sectional area [CSA], echo intensity, pennation angle, and fascicle length), and peak propulsive force and plantar flexor moment during gait. Outcomes were compared between groups using one-way MANOVA. Associations between plantar flexor outcomes and gait speed were assessed using Pearson correlation in the PWS group. Adults with PWS had lower absolute and normalized early RTD, and lower H/M ratio than controls with and without obesity; lower absolute PT and late RTD than controls with obesity (all P < 0.05). Cross-sectional area, propulsive force, and plantarflexor moment were lower, and echo intensity was higher, in adults with PWS compared with controls without obesity (all P < 0.05). Greater absolute PT (r = 0.64), absolute early RTD (r = 0.62), absolute late RTD (r = 0.64), gastrocnemii CSA (r = 0.55), and propulsive force (r = 0.58) were associated with faster gait speed (all P < 0.05). Adults with PWS have impaired plantar flexor function likely attributable to reduced neuromuscular function and altered muscle morphology, which are associated with slower gait speeds.

Adaptive Ankle Resistance from a Wearable Robotic Device to Improve Muscle Recruitment in Cerebral Palsy.

Individuals with cerebral palsy can have weak and poorly coordinated ankle plantar flexor muscles that contribute to inefficient walking patterns. Previous studies attempting to improve plantar flexor function have had inconsistent effects on mobility, likely due to a lack of task-specificity. The goal of this study was to develop, validate, and test the feasibility and neuromuscular response of a novel wearable adaptive resistance platform to increase activity of the plantar flexors during the propulsive phase of gait. We recruited eight individuals with spastic cerebral palsy to walk with adaptive plantar flexor resistance provided from an untethered exoskeleton. The resistance system and protocol was safe and feasible for all of our participants. Controller validation demonstrated our ability to provide resistance that proportionally- and instantaneously-adapted to the biological ankle moment (R = 0.92 ± 0.04). Following acclimation to resistance (0.16 ± 0.02Nm/kg), more-affected limbs exhibited a 45 ± 35% increase in plantar flexor activity (p = 0.02), a 26 ± 24% decrease in dorsiflexor activity (p < 0.05), and a 46 ± 25% decrease in co-contraction (tibialis anterior and soleus) (p = 0.02) during the stance phase. This adaptive resistance system warrants further investigation for use in a longitudinal intervention study.

Gastrocnemius Muscle Structure Remodels Within the First Month Following Acute Achilles Tendon Rupture

Category:Sports, Trauma, Achilles TendonIntroduction/Purpose:Two out of three patients Achilles tendon ruptures have limited plantarflexor function 1-year following Achilles tendon rupture. While tendon elongation has been reported as a possible mechanism of functional deficits, the effects of rupture on plantarflexor muscle structure has not been as rigorously investigated. A recent study found that gastrocnemius fascicle length was decreased 6-months following Achilles tendon rupture compared to the uninjured limb. However, the changes in muscle structure following the first month of injury – when the healing tendon is most susceptible to elongation – has not yet been established. The purpose of this study was to quantify the structural changes to the medial gastrocnemius in patients who suffered acute Achilles tendon ruptures and were treated non-operatively.Methods:To test our hypothesis that plantarflexor structure would undergo rapid remodeling following Achilles tendon rupture, we quantified muscle structure in ten patients (9 male, Age: 44 ± 12; BMI: 28.6 ± 6.5) who provide informed written consent in this IRB approved study. We acquired B-mode ultrasound images of the medial gastrocnemius muscle at the initial presentation (week 0), two weeks, and four weeks following the injury. The same investigator acquired all the ultrasound images and measured fascicle length, pennation angle, muscle thickness, and echo intensity. These measurements had a coefficient of variation less than 10%. We compared these structural measurements of the injured muscle at each time point with the contralateral muscle scans at the initial presentation using paired t-tests.Results:Gastrocnemius muscle structure following an acute Achilles tendon rupture differed with the healthy-contralateral muscle throughout the first four weeks following injury (Figure). Fascicle length was 15% shorter (P < 0.001) and pennation angle was 21% greater (P < 0.001) at the presentation of injury (week 0). These differences in fascicle length (P < 0.001) and pennation angle persisted throughout the 4 weeks after the injury (P < 0.008). Muscle thickness changes were not detected at any of the post-injury visits. Muscle quality, measured as mean echo intensity, was 8% lower in the injured limb immediately (P= 0.008) and 11% lower 2 weeks following injury (P < 0.001). At week 4 muscle quality had returned to within 1% of the contralateral limb (P = 0.393).Conclusion:Our findings support our hypothesis that the gastrocnemius muscle fascicles of the affected side would demonstrate shorter length and greater pennation angle than the contralateral control muscle. These findings are a preliminary set of data from a larger clinical cohort of patients that were enrolled in an ongoing 1-year long prospective study. Achilles tendon ruptures elicit rapid changes in the configuration and quality of the medial gastrocnemius, which may explain long-term functional deficits.

Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading

Introduction: Differences between male and female muscle-tendon units have been previously observed. It is unknown if a sex-related difference exists in the plantarflexor response to repeated stretch-shortening cycles, as occurs during activities of daily living such as walking and running. Methods: An adapted force sledge was used with three dimensional motion analysis to investigate the response of the plantarflexors of 34 age and training-matched males and females during stretchshortening cycle impacts. Results: Contact times and flight times were found to be similar between groups. Statistically significant differences in absolute peak force and rates of force development were observed during loading. With normalisation to plantarflexor muscle volume, small and moderate effect sizes were observed for all force and rate of force development variables but only peak force remained statistically significant. Differences in absolute stiffness, peak negative and positive power and work were statistically significant with moderate effect size, but with normalisation only differences in peak negative power and work remained statistically significant with a moderate effect size. Conclusion: These results show females have lower force, rate of force production and force absorption capabilities, which are of relevance in injury prevention and rehabilitation, and informing personalised engineering design. Level of evidence: III b (individual case-control study).

Relationship between the architecture and function of ankle plantar flexors with Achilles tendon morphology in ballet dancers

Achilles tendinopathy is the most frequent foot overuse injury in ballet dancers and knowledge of clinically modifiable factors related to tendon structure in a population at risk, such as ballet dancers, would be important for the development of preventive programs. Therefore, the present study aimed to assess relationships of gastrocnemius muscle architecture and ankle plantar flexors function with Achilles tendon morphology in ballet dancers. Fifty-four measures from 27 ballet dancers were collected. Tendon morphology (thickness, echogenicity, hypoechoic areas and neovascularisation) and muscle architecture (thickness, pennation angle and fascicle length) were evaluated using ultrasonography; ankle plantar flexors torque was evaluated using hand-held dynamometry, flexibility was evaluated in maximal weight-bearing ankle dorsiflexion position using inclinometer, and endurance was evaluated using the heel rise test. Ankle plantar flexors torque and medial gastrocnemius muscle architecture (thickness, pennation angle and fascicle length) are associated with Achilles tendon thickness in ballet dancers (r2 = 0.24, p = 0.008). Ankle plantar flexors torque and medial gastrocnemius muscle fascicle length are also associated with the echogenicity of the Achilles tendon (r2 = 0.13, p = 0.03). These findings call attention to the potential importance of ankle plantar flexors muscle force in healthy ballet dancers for the prevention of alterations in Achilles tendon structure.

Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading

Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading