Plantar Flexor Muscle Group Research Articles

Children with cerebral palsy have larger Achilles tendon moment arms than typically developing children

The effectiveness of the plantarflexor muscle group to generate desired plantarflexion moments is modulated by the geometry of the Achilles tendon moment arm (ATMA). Children with cerebral palsy (CP) frequently have reduced plantarflexion function, which is commonly attributed to impaired muscle structure and function, however little attention has been paid to the potential contribution of ATMA geometry. The use of musculoskeletal modelling for the simulation of gait and understanding of gait mechanics, rely on accuracy of ATMA estimates. This study aimed to compare 3D in-vivo estimates of ATMA of adults, children with CP and typically developing (TD) children, as well as compare 3D in-vivo estimates to linearly scaled musculoskeletal model estimates. MRI scans for eight children with CP, 11 TD children and nine healthy adults were used to estimate in-vivo 3D ATMA using a validated method. A lower limb musculoskeletal model was linearly scaled to individual tibia length to provide a scaled ATMA estimate. Normalised in-vivo 3D ATMA for children with CP was 17.2% ± 2.0 tibia length, which was significantly larger than for TD children (15.2% ± 1.2, p = 0.013) and adults (12.5% ± 0.8, p < 0.001). Scaled ATMA estimates from musculoskeletal models significantly underestimated in-vivo estimates for all groups, by up to 34.7%. The results of this study show children with CP have larger normalised 3D ATMA compared to their TD counterparts, which may have implications in understanding reduced plantarflexor function and the efficacy of surgical interventions whose aim is to modify the musculoskeletal geometry of this muscle group.

Dynamic stretching is not detrimental to neuromechanical and sensorimotor performance of ankle plantarflexors.

The acute effects of two dynamic stretching (DS) protocols on changes in the ankle range of motion (RoM), neuromechanical, and sensorimotor properties of the plantarflexor muscle group were examined. Eighteen participants received slow (SDS) or fast dynamic stretching (FDS) on two separate days. Outcome measures were assessed pre‐ and 2 minutes post‐interventions, and included maximum dorsiflexion angle, maximum isometric torque at neutral ankle position, maximum concentric and eccentric torques, force matching capacity, joint position sense and medial gastrocnemius muscle and tendon strain. Possibly and likely small increases in dorsiflexion RoM were observed after SDS (mean ± 90% confidence intervals; 1.8 ± 1.2°) and FDS (2.1 ± 1.2°), respectively. Very likely moderate decreases in muscle strain after SDS (−38.0 ± 20.6%) and possibly small decrease after FDS (−13.6 ± 21.2%) were observed. SDS resulted in a likely beneficial small increase in tendon strain (25.3 ± 29.7%) and a likely beneficial moderate increase after FDS (41.4 ± 44.9%). Effects on strength were inconsistent. Possibly small effect on positional error after SDS (−27.1 ± 37.5%), but no clear effect after FDS was observed. Both DS protocols increased RoM, and this was more due to an increase in tendon elongation rather than the muscle. However, SDS showed greater improvement than FDS in both neuromechanical and sensorimotor performance, and hence, SDS can be recommended as part of warm‐up in sporting contexts.

Joint moment strategies during stair descent in patients with peripheral arterial disease and intermittent claudication

ObjectiveTo determine the lower limb joint kinetic strategies during stair descent in claudicants with peripheral arterial disease (PAD-IC). DesignCross-sectional observation study. SettingUniversity laboratory. ParticipantsA total of 22 participants; 10 healthy controls and 12 patients diagnosed with PAD-IC. Main outcome measuresBetween-group comparisons of ground reaction force (GRF) and, hip, knee and ankle kinetics during steady-state stair descent. ResultsThe claudicating-limb group demonstrated reduced vertical and posterior GRF compared to healthy controls (ES = −1.46 [−2.32,−0.69] and ES = −1.08 [−0.42,−0.26]) as well as demonstrating an greater contribution to support moment from the ankle and trends towards a smaller hip contribution (42 ± 14% vs 28 ± 7%, P = .005 and Hip 16 ± 8% vs 21 ± 11%, P = .056, respectively). A unique sub-group was identified within the PAD-IC cohort demonstrating different hip moment strategies during weight acceptance: a novel hip extensor group (PAD-IC HExt) and stereotypical hip flexor group (PAD-IC HFlex). Compared to both healthy controls and the PAD-IC HFlex groups, the PAD-IC HExt group demonstrated increased hip extensor moment (ES = 3.05 [1.67,4.42] and ES = 3.62 [1.89,5.35]) and reduced knee extensor moment (ES = −2.00 [−3.15,−0.85] and ES = −1.36 [−2.60,−0.11] respectively) during weight acceptance. ConclusionsA novel hip extensor strategy was identified in a sub-group of claudicants which acts to reduce the demand on the knee extensors, but not the plantarflexors. Weakness in the knee extensors may prevent redistribution of the task demand, typically seen in older adults in stair descent, away from the functionally limited plantarflexor muscle group. Further investigation into multi-level joint strength and the relationship to functional tasks is warranted to inform targeted intervention programmes.

Effects of Ibuprofen on the Passive Properties of Musculotendinous Stiffness in the Plantar Flexor Muscle Group

Effects of Ibuprofen on the Passive Properties of Musculotendinous Stiffness in the Plantar Flexor Muscle Group

Does Blood Flow Restriction Enhance Exercise-mediated Changes In The Plantar Flexors?

The plantar flexor muscle group readily atrophies when exposed to an unloaded environment (i.e. microgravity). There is evidence that the plantar flexors are also resistant to exercise stimuli when compared to other musculature. A rather novel training method called Kaatsu, or blood flow restriction (BFR) training, may potentially provide a substantial resistance training stimulus to the plantar flexors. PURPOSE: To determine if there are differences in strength and body composition after five weeks of training utilizing fatiguing protocols with or without BFR. METHODS: Seven physically inactive subjects (6 male, 1 female) engaged in five weeks of resistance training for the plantar flexors. Each leg was randomly assigned to one of three protocols: 1) high intensity (HIT), 2) low intensity (LIT), or 3) low intensity with blood flow restriction (BFR). Exercise sessions consisted of three sets to fatigue with 1.5 minutes of rest between sets. Each repetition consisted of a maximal shortening contraction followed by a controlled lengthening contraction regulated audibly by a metronome. Exercise was conducted unilaterally on hack squat equipment. Sets were terminated when 80% of full ROM was not obtained for two consecutive repetitions. For BFR, pressure was applied just superior to the proximal patella at 1.3 x systolic blood pressure and was maintained through the duration of the protocol. RESULTS: No significant differences were found with isometric torque although % changes pre-post in peak power across isokinetic velocities ranging from 30 to 240 degrees were significantly greater with LIT. One repetition max (1RM) increased post-training in all groups with a trend towards increased strength at the mid-assessment for BFR only (p=0.0537). Total reps completed were significantly lower and total training volume higher with HIT. Session RPE was not different among protocols. There were no changes in lower leg lean or fat mass as assessed by DXA. CONCLUSIONS: In general, all three training protocols resulted in increased 1RM strength following five weeks of training with no changes in body composition. Supported by NIH grant UL1 TR00153 and the Undergraduate Research Opportunities Program at UCI.

Lower Extremity Strength Is Correlated with Walking Function After Incomplete SCI.

Lower extremity strength has been reported to relate to walking ability, however, the relationship between voluntary lower extremity muscle function as measured by isokinetic dynamometry and walking have not been thoroughly examined in individuals with incomplete spinal cord injury (iSCI). To determine the extent to which measures of maximal voluntary isometric contraction (MVIC) and rate of torque development (RTD) in the knee extensor (KE) and plantar flexor (PF) muscle groups correlate with self-selected overground walking speed and spatiotemporal characteristics of walking. Twenty-two subjects with chronic (>6 months) iSCI participated in a cross-sectional study. Values for MVIC and RTD in the KE and PF muscle groups were determined by isokinetic dynamometry. Walking speed and spatiotemporal characteristics of walking were measured during overground walking. MVIC in the KE and PF muscle groups correlated significantly with walking speed. RTD was significantly correlated with walking speed in both muscle groups, the more-involved PF muscle group showing the strongest correlation with walking speed (r = 0.728). RTD in the KE and PF muscle groups of the more-involved limb was significantly correlated with single support time of the more-involved limb. These data demonstrate that lower extremity strength is associated with walking ability after iSCI. Correlations for the muscle groups of the move-involved side were stronger compared to the less-involved limb. In addition, PF function is highlighted as a potential limiting factor to walking speed along with the importance of RTD.

Inhibition of Activin A Ameliorates Skeletal Muscle Injury and Rescues Contractile Properties by Inducing Efficient Remodeling in Female Mice

Activin A, a member of the transforming growth factor-β superfamily, provides pleiotropic regulation of fibrosis and inflammation. We aimed at determining whether selective inhibition of activin A would provide a regenerative benefit. The introduction of activin A into normal muscle increased the expression of inflammatory and muscle atrophy genes Tnf, Tnfrsf12a, Trim63, and Fbxo32 by 3.5-, 10-, 2-, and 4-fold, respectively. The data indicate a sensitive response of muscle to activin A. Two hours after cardiotoxin-induced muscle damage, local activin A protein expression increased by threefold to ninefold. Neutralization of activin A with a specific monoclonal antibody in this muscle injury model decreased the muscle protein levels of lymphotoxin α and Il17a by 32% and 42%, respectively. Muscle histopathological features showed that activin A antibody-treated mice displayed an increase in muscle degradation, with the concomitant 9.2-fold elevation in F4/80-positive cells 3 days after injury. At the same time, the number of Pax7/Myod1-positive cells also increased, indicative of potentiated muscle precursor activation. Ultimately, activin A inhibition resulted in rapid recovery of muscle contractile properties indicated by a restoration of maximum and specific force. In summary, selective inhibition of activin A with a monoclonal antibody in muscle injury leads to the early onset of tissue degradation and subsequent enhanced myogenesis, thereby accelerating muscle repair and functional recovery.

Effects of a Fall Prevention Exercise Program on Muscle Strength and Balance of the Old-old Elderly.

[Purpose] The purpose of this study was to investigate the effects of an 8-week balance exercise and elastic-resistance exercise program on muscle strength and balance of the old-old elderly (over the age of 75). [Subjects and Methods] Fifty-five elderly persons were recruited from the community and assigned to three groups for convenience: balance exercise (intervention group 1; INT 1), resistance exercise (intervention group 2; INT 2), and control (CON) groups. The intervention was performed twice a week at a senior center and three times a week at home for 8 weeks. Muscle strength and balance were evaluated before and at the end of the trial, using a PowertrackIIand Tetrax. [Results] There were significant improvements in the strength of all seven muscle groups and balance in the INT 2 group. In the INT 1 group, there were significant improvements in the strength of all muscle groups except for the knee flexor and ankle plantar flexor muscle groups. [Conclusion] This study demonstrated that an intervention using balance exercises or elastic-resistance exercises is effective at improving the muscle strength and balance of the old-old elderly. These type of exercises should be appropriate for the physical characteristics of the subjects.

Muscle volume as a predictor of maximum force generating ability in the plantar flexors post‐stroke

Post-stroke muscle weakness is commonly thought to be the result of a combination of decreased voluntary activation and decreased maximum force generating ability (MFGA). We assessed the ability of muscle volumes obtained using MRI to estimate the MFGA of the plantar flexor muscle group in individuals post-stroke. MRI was used to measure muscle volume of the plantar flexor muscle group in 17 individuals with post-stroke hemiparesis. A modified burst superimposition test was used to measure force of volitional contraction and predict the MFGA of the plantar flexors. While muscle volume obtained by means of MRI provided information on the overall size of muscle, it overestimated the force generating ability of the paretic plantar flexors. Results suggest that MRI-derived muscle volume underestimates the functional impairment in individuals post-stroke. Interestingly, the central activation ratio had a strong relationship with the maximum volitional force of contraction.

Overexpression of insulin‐like growth factor‐1 attenuates skeletal muscle damage and accelerates muscle regeneration and functional recovery after disuse

Skeletal muscle is a highly dynamic tissue that responds to endogenous and external stimuli, including alterations in mechanical loading and growth factors. In particular, the antigravity soleus muscle experiences significant muscle atrophy during disuse and extensive muscle damage upon reloading. Given that insulin-like growth factor-1 (IGF-1) has been implicated as a central regulator of muscle repair and modulation of muscle size, we examined the effect of virally mediated overexpression of IGF-1 on the soleus muscle following hindlimb cast immobilization and upon reloading. Recombinant IGF-1 cDNA virus was injected into one of the posterior hindlimbs of the mice, while the contralateral limb was injected with saline (control). At 20 weeks of age, both hindlimbs were immobilized for 2 weeks to induce muscle atrophy in the soleus and ankle plantarflexor muscle group. Subsequently, the mice were allowed to reambulate, and muscle damage and recovery were monitored over a period of 2-21 days. The primary finding of this study was that IGF-1 overexpression attenuated reloading-induced muscle damage in the soleus muscle, and accelerated muscle regeneration and force recovery. Muscle T2 assessed by magnetic resonance imaging, a non-specific marker of muscle damage, was significantly lower in IGF-1-injected compared with contralateral soleus muscles at 2 and 5 days reambulation (P<0.05). The reduced prevalence of muscle damage in IGF-1-injected soleus muscles was confirmed on histology, with a lower fractional area of abnormal muscle tissue in IGF-1-injected muscles at 2 days reambulation (33.2±3.3 versus 54.1±3.6%, P<0.05). Evidence of the effect of IGF-1 on muscle regeneration included timely increases in the number of central nuclei (21% at 5 days reambulation), paired-box transcription factor 7 (36% at 5 days), embryonic myosin (37% at 10 days) and elevated MyoD mRNA (7-fold at 2 days) in IGF-1-injected limbs (P<0.05). These findings demonstrate a potential role of IGF-1 in protecting unloaded skeletal muscles from damage and accelerating muscle repair and regeneration.

Understanding compensatory strategies for muscle weakness during gait by simulating activation deficits seen post-stroke

Musculoskeletal simulations have been used to explore compensatory strategies, but have focused on responses to simulated atrophy in a single muscle or muscle group. In a population such as stroke, however, impairments are seen in muscle activation across multiple muscle groups. The objective of this study was to identify available compensatory strategies for muscle weakness during gait by simulating activation deficits in multiple muscle groups. Three dimensional dynamics simulations were created from 10 healthy subjects (48.8±13.3 years, self-selected speed 1.28±0.17m/s) and constraints were set on the activation capacity of the plantar flexor, dorsiflexor, and hamstrings muscle groups to simulate activation impairments seen post-stroke. When the muscle groups are impaired individually, the model requires that the plantar flexor, dorsiflexor, and hamstrings muscle groups are activated to at least 55%, 64%, and 18%, respectively, to recreate the subjects’ normal gait pattern. The models were unable to recreate the normal gait pattern with simultaneous impairment of all three muscle groups. Other muscle groups are unable to assist the dorsiflexor muscles during early swing, which suggests that rehabilitation or assistive devices may be required to correct foot drop. By identifying how muscles can interact, clinicians may be able to develop specific strategies for using gait retraining and orthotic assistance to best address an individual's needs.

Subject-Specific Tendon-Aponeurosis Definition in Hill-Type Model Predicts Higher Muscle Forces in Dynamic Tasks

Neuromusculoskeletal models are a common method to estimate muscle forces. Developing accurate neuromusculoskeletal models is a challenging task due to the complexity of the system and large inter-subject variability. The estimation of muscles force is based on the mechanical properties of tendon-aponeurosis complex. Most neuromusculoskeletal models use a generic definition of the tendon-aponeurosis complex based on in vitro test, perhaps limiting their validity. Ultrasonography allows subject-specific estimates of the tendon-aponeurosis complex’s mechanical properties. The aim of this study was to investigate the influence of subject-specific mechanical properties of the tendon-aponeurosis complex on a neuromusculoskeletal model of the ankle joint. Seven subjects performed isometric contractions from which the tendon-aponeurosis force-strain relationship was estimated. Hopping and running tasks were performed and muscle forces were estimated using subject-specific tendon-aponeurosis and generic tendon properties. Two ultrasound probes positioned over the muscle-tendon junction and the mid-belly were combined with motion capture to estimate the in vivo tendon and aponeurosis strain of the medial head of gastrocnemius muscle. The tendon-aponeurosis force-strain relationship was scaled for the other ankle muscles based on tendon and aponeurosis length of each muscle measured by ultrasonography. The EMG-driven model was calibrated twice - using the generic tendon definition and a subject-specific tendon-aponeurosis force-strain definition. The use of subject-specific tendon-aponeurosis definition leads to a higher muscle force estimate for the soleus muscle and the plantar-flexor group, and to a better model prediction of the ankle joint moment compared to the model estimate which used a generic definition. Furthermore, the subject-specific tendon-aponeurosis definition leads to a decoupling behaviour between the muscle fibre and muscle-tendon unit in agreement with previous experiments using ultrasonography. These results indicate the use of subject-specific tendon-aponeurosis definitions in a neuromusculoskeletal model produce better agreement with measured external loads and more physiological model behaviour.

Consistency of rapid muscle force characteristics: Influence of muscle contraction onset detection methodology

The purpose of this study was to investigate the consistency of commonly reported rapid force characteristics utilizing both automated and manual muscle contraction onset detection methods. Twenty-four healthy volunteers performed isometric strength testing of the plantar flexor muscle group on two nonconsecutive days. Test–retest reliability was evaluated using intraclass correlation coefficients (ICCs), standard errors of measurement (SEM), and the SEM as a percentage of the mean (SEM%) for rate of force development (RFD), relative RFD, contractile impulse, and absolute force–time values at various epoch durations using automated and manual onset detection methods. For all rapid force variables, ICC and SEM% values ranged from 0.52 to 0.96 and 7.56% to 37.56%, respectively. For the majority of these variables (20 of 23), the automated onset detection method resulted in higher ICC and lower SEM% values compared to the manual onset detection method. Regardless of onset detection methodology, the consistency of relative RFD values declined following 50% of MVC. Collectively, these findings indicated that commonly evaluated rapid muscle force variables demonstrated acceptable relative and absolute consistency values. However, these values were generally superior for the automated onset detection methodology. Additionally, the consistency of relative RFD values declines following 50% MVC and therefore should be evaluated with caution.

Leg Muscle Strength, Area And Contraction Velocity In Young, Old And Very Old Women

Healthy adult aging is associated with a loss of muscle mass, known as sarcopenia, and functional alterations within the neuromuscular system. As a result, older adults exhibit less strength and slower voluntary contractile velocity. However, these parameters have not been studied fully in older women. PURPOSE: To determine the effect of aging on voluntary isometric strength and contraction velocity of the leg muscles of young (Y), old (O) and very old (VO) women. METHODS: Cross-sectional areas (CSAs) of the anterior and posterior compartments of the right leg were assessed with 3T magnetic resonance (MR) imaging in seven Y (23±2y), five O (65±4y) and six VO (76±3y) women. Maximal voluntary isometric contraction (MVC) torque and maximal contraction velocity (at a fixed load of ∼1Nm) of the dorsiflexors and plantar flexors were determined using a Biodex dynamometer. To determine normalized strength, MVC torque was expressed relative to muscle CSA. RESULTS: Anterior compartment CSA was ∼27% and ∼19% less in the VO compared with the Y and O, respectively, but there was no difference between the Y and O women. The VO had a ∼16% lower dorsiflexor MVC torque than the Y, but neither group differed significantly from the O women. No differences existed among groups for normalized dorsiflexor strength. Maximal voluntary contraction velocity was ∼15% less in the VO than the Y with no other group differences. In the posterior compartment, CSA was 25% less in the VO compared with the Y, but the O did not differ from either Y or VO. Similarly, plantar flexor MVC torque was ∼32% less in the VO compared with the Y women but not different between Y and O, or O and VO. Normalized plantar flexor strength was equivalent among the groups. The VO were 13% slower than the Y for plantar flexor maximal contraction velocity with no other differences between groups. CONCLUSIONS: Lower maximal strength observed in the dorsiflexors and plantar flexors of the VO women can be accounted for by an age-related decrease in muscle mass. Also, contraction velocity did not slow until the 8th decade of life and was similar for both the dorsiflexor and plantar flexor muscle groups. Supported by NSERC.

Changes in Running Kinematics, Kinetics, and Spring-Mass Behavior over a 24-h Run

This study investigated the changes in running mechanics and spring-mass behavior over a 24-h treadmill run (24TR). Kinematics, kinetics, and spring-mass characteristics of the running step were assessed in 10 experienced ultralong-distance runners before, every 2 h, and after a 24TR using an instrumented treadmill dynamometer. These measurements were performed at 10 km·h, and mechanical parameters were sampled at 1000 Hz for 10 consecutive steps. Contact and aerial times were determined from ground reaction force (GRF) signals and used to compute step frequency. Maximal GRF, loading rate, downward displacement of the center of mass, and leg length change during the support phase were determined and used to compute both vertical and leg stiffness. Subjects' running pattern and spring-mass behavior significantly changed over the 24TR with a 4.9% higher step frequency on average (because of a significantly 4.5% shorter contact time), a lower maximal GRF (by 4.4% on average), a 13.0% lower leg length change during contact, and an increase in both leg and vertical stiffness (+9.9% and +8.6% on average, respectively). Most of these changes were significant from the early phase of the 24TR (fourth to sixth hour of running) and could be speculated as contributing to an overall limitation of the potentially harmful consequences of such a long-duration run on subjects' musculoskeletal system. During a 24TR, the changes in running mechanics and spring-mass behavior show a clear shift toward a higher oscillating frequency and stiffness, along with lower GRF and leg length change (hence a reduced overall eccentric load) during the support phase of running.

Ageing, but not yet senescent, rats exhibit reduced muscle quality and sarcoplasmic reticulum function

Reduced muscle force greater than expected from loss of muscle mass has been reported in ageing muscles. Impaired sarcoplasmic reticulum (SR) Ca(2+) release has been implicated as a possible mechanism, and attributed to several factors, including loss of ryanodine receptor (RYR) expression and protein binding. The aim of this study was to evaluate muscle quality and SR Ca(2+) release in ageing rats that were not so old that major atrophy had occurred. We collected in situ force data from the plantarflexor muscle group and muscle mass from the constituent muscles to determine muscle quality (force/mass) in adult (6-8 months) and ageing (24 months) rats (n=8/group). We evaluated SR Ca(2+) uptake and release, and determined expression of key proteins associated with Ca(2+) release [RYR and FK506 binding protein (FKBP)] and uptake (SERCA, parvalbumin, calsequestrin). Plantarflexor force and muscle quality were reduced with ageing (approx. 28 and 34%, respectively), but atrophy was limited, and significant only in the medial gastrocnemius (approx. 15%). The fast phase of SR Ca(2+) release was reduced with ageing in both gastrocnemii, as was FKBP expression and FKBP-RYR binding, but RYR expression was not affected. Similar, but non-significant changes were present in the plantaris, but the soleus muscle generally showed no ageing-related changes. These data suggest a possible role for impaired SR Ca(2+) release in ageing-related loss of muscle quality, although not through loss of RYR expression.

Early Observations of the Effects of Lateral Wedge Orthoses on Lower Limb Muscle Length and Potential for Exacerbating Spasticity

Lateral wedge orthoses are often prescribed to correct varus deformity after stroke. Spasticity is implicated in varus deformity and is caused by velocity-related muscle length changes, so a lateral wedge may affect spasticity by manipulating foot and ankle kinematics which, in turn, may alter the length of these muscles. We sought to test this theory in healthy participants. Eight volunteers walked with no wedge and with lateral wedges of 5 and 8.5 degrees in both shoes. Qualysis motion capture system collected kinematic data and SIMM musculoskeletal modeling software calculated muscle tendon length of plantarflexor and peroneal muscle groups using 3-D ankle and knee joint angle data. The wedges increased ankle eversion (p < 0.0001) and total excursion of tibialis posterior, peroneus longus and brevis by 13-29% (p < 0.05). Muscle length of peroneus longus and brevis increased by <1% (p < 0.005). Potentially clinical meaningful effects were found for tibialis posterior (15%), peroneus brevis (23%) and peroneus tertius (13%). Further research is required to be conclusive and to explore the effects of lateral wedge orthoses in patients with stroke. If such changes are seen in people with stroke, a change in orthotic prescription practice could be indicated as lateral wedge orthoses may exacerbate spasticity.

Mouse Plantar Flexor Muscle Size and Strength After Inactivity and Training

Losses in muscle mass and strength may affect an astronaut's safety; therefore, it is of utmost importance to optimize countermeasures to minimize atrophy and strength loss during spaceflight. The main purpose of this study was to determine if high force eccentric or isometric contractions performed by the plantar flexor group during hind limb suspension would preserve muscle mass and strength. Plantar flexor muscles of mice were trained with either eccentric or isometric contractions every other day during a 10-d hind limb suspension period. Pre- and post-suspension stimulation frequency- and angular velocity-dependent measurements of torque of the plantar flexors, soleus twitch (Pt) and tetanic (Po) force, bodyweight, and muscle wet weight measurements were made. The 19 and 26% losses in gastrocnemius and soleus muscle wet weights, respectively, were not attenuated with eccentric or isometric contractions. Neither eccentric nor isometric contractions attenuated the soleus muscle's 30% isometric force loss after hind limb suspension. Despite losses in muscle mass, there was no decrease in the force produced by the plantar flexor muscle group after hind limb suspension. Hind limb suspension decreased both gastrocnemius and soleus mass, and in vitro soleus force production. However, in vivo force production of the plantar flexor muscle group did not decrease, which may be explained by a shift in the isometric torque: ankle angle relationship. The use of eccentric or isometric contractions as a countermeasure to offset muscle mass and strength requires further investigation as neither was capable of maintaining soleus muscle force production, or gastrocnemius and soleus muscle mass during hind limb suspension.

Factors Associated with the Timed Up and Go Test Score in Elderly Women

[Purpose] The purpose of this study was to determine the relationship between the Timed Up and Go (TUG) test score and the physical performance of women aged 75 years and over according to orthopedic status. [Subjects] The participants were 832 elderly women (mean age, 78.6 ± 2.7 years) who carried out their daily activities independently in their own homes and did not have histories of stroke or osteoarthritis of the hip. [Methods] Maximal voluntary contractions of the knee extensor and ankle plantar flexor muscle groups were measured using a hand-held dynamometer. One-leg standing time and usual walking speed were assessed as balance and walking performances. [Results] The TUG score was more strongly correlated with walking speed (r = -0.776) than the other measures of physical performance (r = -0.228 to -0.399). Correlations between the TUG score and walking speed were strongest for participants with knee osteoarthritis (r = -0.824) and fractures after 60 years of age (r = -0.809). A linear regression model of data from all participants showed that all performance scores and age were determinants of the TUG score (R2 = 0.634). The determinants of the TUG score for participants with osteoarthritis or fractures were walking speed and one-leg standing score, and age (R2 = 0.701) and walking speed, age, and knee strength (R2 = 0.688). Beta estimates of walking speed for all participants and for the subgroups were higher (-0.69 to -0.76) than those for the other determinants (-0.06 to 0.14). [Conclusion] Walking speed is a stronger determinant of the TUG score than muscle strength or balance for elderly women.

Newton's force as countermeasure for disuse atrophy

the observation that disuse leads to muscle atrophy is an old one, but we still lack a good mechanistic description of what is going on to cause wasting in conditions as diverse as bed rest and spaceflight. In fact, much of the current descriptions of the superficial mechanisms of atrophy come from