Triceps Surae Muscle Activation Research Articles

Effects of ankle joint degree of freedom of knee–ankle–foot orthoses on loading patterns and triceps surae muscle activity on the paretic side in individuals with subacute severe hemiplegia: a retrospective study

BackgroundIndividuals with subacute severe hemiplegia often undergo alternate gait training to overcome challenges in achieving walking independence. However, the ankle joint setting in a knee–ankle–foot orthosis (KAFO) depends on trunk function or paralysis stage for alternate gait training with a KAFO. The optimal degree of ankle joint freedom in a KAFO and the specific ankle joint conditions for effective rehabilitation remain unclear. Therefore, this study aimed to investigate the effects of different degrees of freedom of the ankle joint on center-of-pressure (CoP) parameters and muscle activity on the paretic side using a KAFO and to investigate the recommended setting of ankle joint angle in a KAFO depending on physical function.MethodsThis study included 14 participants with subacute stroke (67.4 ± 13.3 years). The CoP parameters and muscle activity of the gastrocnemius lateralis (GCL) and soleus muscles were compared using a linear mixed model (LMM) under two ankle joint conditions in the KAFO: fixed at 0° and free ankle dorsiflexion. We confirmed the relationship between changes in CoP parameters or muscle activity under different conditions and physical functional characteristics such as the Fugl–Meyer Assessment of Lower Extremity Synergy Score (FMAs) and Trunk Impairment Scale (TIS) using LMM.ResultsAnterior–posterior displacement of CoP (AP_CoP) (p = 0.011) and muscle activity of the GCL (p = 0.043) increased in the free condition of ankle dorsiflexion compared with that in the fixed condition. The FMAs (p = 0.004) and TIS (p = 0.008) demonstrated a positive relationship with AP_CoP. A positive relationship was also found between TIS and the percentage of medial forefoot loading time in the CoP (p < 0.001).ConclusionsFor individuals with severe subacute hemiplegia, the ankle dorsiflexion induction in the KAFO, which did not impede the forward tilt of the shank, promotes anterior movement in the CoP and muscle activity of the GCL. This study suggests that adjusting the dorsiflexion mobility of the ankle joint in the KAFO according to improvement in physical function promotes loading of the CoP to the medial forefoot.

Increased muscle force does not induce greater stretch-induced damage to calf muscles during work-matched heel drop exercise

PurposeTo investigate the effect of muscle force during active stretch on quantitative and qualitative indicators of exercise-induced muscle damage (EIMD) in the medial gastrocnemius (MG) muscle.MethodsTwelve recreationally active volunteers performed two trials of an eccentric heel drop exercise. Participants performed a single bout of low-load (body weight) and high-load (body weight + 30% body weight) exercises on separate legs. The total mechanical work output for each condition was matched between legs. Before, two hours and 48 h after each bout of eccentric exercise, electrically stimulated triceps surae twitch torque, muscle soreness, MG active fascicle length at maximum twitch torque and muscle passive stiffness were collected. Triceps surae electromyographic (EMG) activity, MG fascicle stretch and MG muscle–tendon unit (MTU) length were measured during the eccentric tasks.ResultsThe high-load condition increased triceps surae muscle activity by 6–9%, but reduced MG fascicle stretch (p < 0.001). MTU stretch was similar between conditions. The greater muscle force during stretch did not give rise to additional torque loss (5 vs 6%) or intensify muscle soreness.ConclusionsAdding 30% body weight during eccentric contractions has a modest impact on exercise-induced muscle damage in the medial gastrocnemius muscle. These results suggest that muscle load may not be an important determinant of stretch-induced muscle damage in the human MG muscle. The muscle investigated does exhibit large pennation angles and high series elastic compliance; architectural features that likely buffer muscle fibres against stretch and damage.

Faster triceps surae muscle cyclic contractions alter muscle activity and whole body metabolic rate.

Hundred years ago, Fenn demonstrated that when a muscle shortens faster, its energy liberation increases. Fenn's results were the first of many that led to the general understanding that isometric muscle contractions are energetically cheaper than concentric contractions. However, this evidence is still primarily based on single fiber or isolated (ex vivo) muscle studies and it remains unknown whether this translates to whole body metabolic rate. In this study, we specifically changed the contraction velocity of the ankle plantar flexors and quantified the effects on triceps surae muscle activity and whole body metabolic rate during cyclic plantar flexion (PF) contractions. Fifteen participants performed submaximal ankle plantar flexions (∼1/3 s activation and ∼2/3 s relaxation) on a dynamometer at three different ankle angular velocities: isometric (10° PF), isokinetic at 30°/s (5-15° PF), and isokinetic at 60°/s (0-20° PF) while target torque (25% MVC) and cycle frequency were kept constant. In addition, to directly determine the effect of ankle angular velocity on muscle kinematics we collected gastrocnemius medialis muscle fascicle ultrasound data. As expected, increasing ankle angular velocity increased gastrocnemius medialis muscle fascicle contraction velocity and positive mechanical work (P < 0.01), increased mean and peak triceps surae muscle activity (P < 0.01), and considerably increased net whole body metabolic rate (P < 0.01). Interestingly, the increase in triceps surae muscle activity with fast ankle angular velocities was most pronounced in the gastrocnemius lateralis (P < 0.05). Overall, our results support the original findings from Fenn in 1923 and we demonstrated that greater triceps surae muscle contraction velocities translate to increased whole body metabolic rate.NEW & NOTEWORTHY Single muscle fiber studies or research on isolated (ex vivo) muscles demonstrated that faster concentric muscle contractions yield increased energy consumption. Here we translated this knowledge to muscle activation and whole body metabolic rate. Increasing ankle angular velocity increased triceps surae contraction velocity and mechanical work, increasing triceps surae muscle activity and substantially elevating whole body metabolic rate. Additionally, we demonstrated that triceps surae muscle activation strategy depends on the mechanical demands of the task.

Effects of Heel Raising Exercise whith Kinesio Taping on Triceps Surae Muscle Activity and Balance in 20s Adults

Effects of Heel Raising Exercise whith Kinesio Taping on Triceps Surae Muscle Activity and Balance in 20s Adults

Triceps surae muscle force potential and force demand shift with altering stride frequency in running.

While it is well recognized that the preferred stride frequency (PSF) in running closely corresponds to the metabolically optimal frequency, the underlying mechanisms are still unclear. Changes in joint kinematics when altering stride frequency will affect the muscle-tendon unit lengths and potentially the efficiency of muscles crossing these joints. Here, we investigated how fascicle kinematics and forces of the triceps surae muscle, a highly energy consuming muscle, are affected when running at different stride frequencies. Twelve runners ran on a force measuring treadmill, adopting five different frequencies (PSF; PSF ± 8%; PSF ± 15%), while we measured joint kinematics, whole-body energy expenditure, triceps surae muscle activity, and soleus (SOL; N=10) and gastrocnemius medialis (GM; N=12) fascicle kinematics. In addition, we used dynamic optimization to estimate SOL and GM muscle forces. We found that SOL and GM mean muscle fascicle length during stance followed an inverted U-relationship with the longest fascicle lengths occurring at PSF. Fascicle lengths were shortest at frequencies lower than PSF. In addition, average SOL force was greater at PSF-15% compared with PSF. Overall, our results suggest that reduced SOL and GM muscle fascicle lengths, associated with reduced muscle force potential, together with greater SOL force demand, contribute to the increased whole-body energy expenditure when running at lower than PSF. At higher stride frequencies, triceps surae muscle kinematics and force production were less affected suggesting that increased energy expenditure is rather related to higher cost of leg swing and greater cost of force production.

Corticospinal excitability remains unchanged in the presence of residual force enhancement and does not contribute to increased torque production.

BackgroundFollowing stretch of an active muscle, muscle force is enhanced, which is known as residual force enhancement (rFE). As earlier studies found apparent corticospinal excitability modulations in the presence of rFE, this study aimed to test whether corticospinal excitability modulations contribute to rFE.MethodsFourteen participants performed submaximal plantar flexion stretch-hold and fixed-end contractions at 30% of their maximal voluntary soleus muscle activity in a dynamometer. During the steady state of the contractions, participants either received subthreshold or suprathreshold transcranial magnetic stimulation (TMS) of their motor cortex, while triceps surae muscle responses to stimulation were obtained via electromyography (EMG), and net ankle joint torque was recorded. B-mode ultrasound imaging was used to confirm muscle fascicle stretch during stretch-hold contractions in a subset of participants.ResultsFollowing stretch of the plantar flexors, an average rFE of 7% and 11% was observed for contractions with subthreshold and suprathreshold TMS, respectively. 41–46 ms following subthreshold TMS, triceps surae muscle activity was suppressed by 19–25%, but suppression was not significantly different between stretch-hold and fixed-end contractions. Similarly, the reduction in plantar flexion torque following subthreshold TMS was not significantly different between contraction conditions. Motor evoked potentials, silent periods and superimposed twitches following suprathreshold TMS were also not significantly different between contraction conditions.DiscussionAs TMS of the motor cortex did not result in any differences between stretch-hold and fixed-end contractions, we conclude that rFE is not linked to changes in corticospinal excitability.

The effects of triceps surae muscle stimulation on localized Achilles subtendon tissue displacements.

The triceps surae muscle-tendon unit is composed of the lateral and medial gastrocnemius (MG) and soleus (SOL) muscles and three in-series elastic 'subtendons' that form the Achilles tendon. Comparative literature and our own in vivo evidence suggest that sliding between adjacent subtendons may facilitate independent muscle actuation. We aim to more clearly define the relationship between individual muscle activation and subtendon tissue displacements. Here, during fixed-end contractions, electrical muscle stimulation controlled the magnitude of force transmitted via individual triceps surae muscles while ultrasound imaging recorded resultant subtendon tissue displacements. We hypothesized that MG and SOL stimulation would elicit larger displacements in their associated subtendon. Ten young adults completed four experimental activations at three ankle angles (-20, 0 and 20deg) with the knee flexed to approximately 20deg: MG stimulation (STIMMG), SOL stimulation (STIMSOL), combined stimulation, and volitional contraction. At 20deg plantarflexion, STIMSOL elicited 49% larger tendon non-uniformity (SOL-MG subtendon tissue displacement) than that of STIMMG (P=0.004). For STIMSOL, a one-way post hoc ANOVA revealed a significant main effect of ankle angle (P=0.009) on Achilles tendon non-uniformity. However, peak tendon non-uniformity decreased by an average of 61% from plantarflexion to dorsiflexion, likely due to an increase in passive tension. Our results suggest that localized tissue displacements within the Achilles tendon respond in anatomically consistent ways to differential patterns of triceps surae muscle activation, but these relations are highly susceptible to ankle angle. This in vivo evidence points to at least some mechanical independence in actuation between the human triceps surae muscle-subtendon units.

Classification of Walking Environments Using Deep Learning Approach Based on Surface EMG Sensors Only.

Classification of terrain is a vital component in giving suitable control to a walking assistive device for the various walking conditions. Although surface electromyography (sEMG) signals have been combined with inputs from other sensors to detect walking intention, no study has yet classified walking environments using sEMG only. Therefore, the purpose of this study is to classify the current walking environment based on the entire sEMG profile gathered from selected muscles in the lower extremities. The muscle activations of selected muscles in the lower extremities were measured in 27 participants while they walked over flat-ground, upstairs, downstairs, uphill, and downhill. An artificial neural network (ANN) was employed to classify these walking environments using the entire sEMG profile recorded for all muscles during the stance phase. The result shows that the ANN was able to classify the current walking environment with high accuracy of 96.3% when using activation from all muscles. When muscle activation from flexor/extensor groups in the knee, ankle, and metatarsophalangeal joints were used individually to classify the environment, the triceps surae muscle activation showed the highest classification accuracy of 88.9%. In conclusion, a current walking environment was classified with high accuracy using an ANN based on only sEMG signals.

Bilateral in vivo neuromechanical properties of the triceps surae and Achilles tendon in runners and triathletes

Inter-limb differences in Achilles tendon mechanical, material and morphological properties have previously been described in non-athletes and attributed to the preferential use of a given limb. Achilles tendon overuse tendon injury generally initiate unilaterally and alters triceps surae activation and Achilles tendon properties. The investigation of inter-limb differences in muscle activation and tendon properties may provide directions for injury prevention in habitual runners. In this study triceps surae and Achilles tendon properties were investigated bilaterally in habitual runners during unilateral maximal isometric contractions. Morphological, mechanical and material Achilles tendon properties were assessed using isokinetic dynamometry, motion capture and ultrasonography while triceps surae activation strategies were assessed using electromyography. Lower limb preference was assessed for inter-limb comparisons using the Waterloo questionnaire. Zero and one-dimensional statistical analysis and Cohen’s d were employed to investigate possible inter-limb differences. Inter-limb associations in Achilles tendon properties and intra-limb associations between triceps surae activations were assessed using Pearson’s correlation coefficients. No differences were observed between the preferred and non-preferred limb in terms of triceps surae muscle activation amplitude and Achilles tendon properties. However, intra-limb association among triceps surae activation ratios were not identical between limbs. Runners and triathletes present similar Achilles tendons properties between limbs, and thus initial observations of unilateral changes in the Achilles tendon properties might be used as a strategy to prevent the onset of overuse tendon injury. The non-similar associations within activation ratios between limbs should be further explored since triceps surae activation strategies may alter loading of the Achilles tendon.

Applying Stretch to Evoke Hyperreflexia in Spasticity Testing: Velocity vs. Acceleration.

In neurological diseases, muscles often become hyper-resistant to stretch due to hyperreflexia, an exaggerated stretch reflex response that is considered to primarily depend on the muscle's stretch velocity. However, there is still limited understanding of how different biomechanical triggers applied during clinical tests evoke these reflex responses. We examined the effect of imposing a rotation with increasing velocity vs. increasing acceleration on triceps surae muscle repsonse in children with spastic paresis (SP) and compared the responses to those measured in typically developing (TD) children. A motor-operated ankle manipulator was used to apply different bell-shaped movement profiles, with three levels of maximum velocity (70, 110, and 150°/s) and three levels of maximum acceleration (500, 750, and 1,000°/s2). For each profile and both groups, we evaluated the amount of evoked triceps surae muscle activation. In SP, we evaluated two additional characteristics: the intensity of the response (peak EMG burst) and the time from movement initiation to onset of the EMG burst. As expected, the amount of evoked muscle activation was larger in SP compared to TD (all muscles: p < 0.001) and only sensitive to biomechanical triggers in SP. Further investigation of the responses in SP showed that peak EMG bursts increased in profiles with higher peak velocity (lateral gastrocnemius: p = 0.04), which was emphasized by fair correlations with increased velocity at EMG burst onset (all muscles: r > 0.33–0.36, p ≤ 0.008), but showed no significant effect for acceleration. However, the EMG burst was evoked faster with higher peak acceleration (all muscles p < 0.001) whereas it was delayed in profiles with higher peak velocity (medial gastrocnemius and soleus: p < 0.006). We conclude that while exaggerated response intensity (peak EMG burst) seems linked to stretch velocity, higher accelerations seem to evoke faster responses (time to EMG burst onset) in triceps surae muscles in SP. Understanding and controlling for the distinct effects of different biological triggers, including velocity, acceleration but also length and force of the applied movement, will contribute to the development of more precise clinical measurement tools. This is especially important when aiming to understand the role of hyperreflexia during functional movements where the biomechanical inputs are multiple and changing.

Older Adults Overcome Reduced Triceps Surae Structural Stiffness to Preserve Ankle Joint Quasi-Stiffness During Walking.

Ankle joint quasi-stiffness is an aggregate measure of the interaction between triceps surae muscle stiffness and Achilles tendon stiffness. This interaction may be altered due to age-related changes in the structural properties and functional behavior of the Achilles tendon and triceps surae muscles. The authors hypothesized that, due to a more compliant of Achilles' tendon, older adults would exhibit lower ankle joint quasi-stiffness than young adults during walking and during isolated contractions at matched triceps surae muscle activations. The authors also hypothesized that, independent of age, triceps surae muscle stiffness and ankle joint quasi-stiffness would increase with triceps surae muscle activation. The authors used conventional gait analysis in one experiment and, in another, electromyographic biofeedback and in vivo ultrasound imaging applied during isolated contractions. The authors found no difference in ankle joint quasi-stiffness between young and older adults during walking. Conversely, this study found that (1)young and older adults modulated ankle joint quasi-stiffness via activation-dependent changes in triceps surae muscle length-tension behavior and (2)at matched activation, older adults exhibited lower ankle joint quasi-stiffness than young adults. Despite age-related reductions during isolated contractions, ankle joint quasi-stiffness was maintained in older adults during walking, which may be governed via activation-mediated increases in muscle stiffness.

Swaying slower reduces the destabilizing effects of a compliant surface on voluntary sway dynamics.

The ability to control weight shifting (voluntary sway) is a crucial factor for stability during standing. Postural tracking of an oscillating visual target when standing on a compliant surface (e.g. foam) is a challenging weight shifting task that may alter the stability of the system and the muscle activation patterns needed to compensate for the perturbed state. The purpose of this study was to examine the effects of surface stability and sway frequency on the muscle activation of the lower limb, during visually guided voluntary postural sway. Seventeen volunteers performed a 2-min voluntary sway task in the anterior-posterior direction following with their projected center of pressure (CoPAP) a periodically oscillating visual target on a screen. The target oscillated at a frequency of 0.25 Hz or 0.125 Hz, while the participants swayed on solid ground (stable surface) or on a foam pad (unstable surface), resulting in four experimental conditions. The electromyogram (EMG) of 13 lower limb muscles was measured and the target-CoPAP coupling was evaluated with coherence analysis, whereas the difference in the stability of the system between the conditions was estimated by the maximum Lyapunov exponent (MLE). The results showed that slower oscillations outperformed the faster in terms of coherence and revealed greater stability. On the other hand, unstable ground resulted in an undershooting of the CoPAP to the target and greater MLE. Regarding the EMG data, a decreased triceps surae muscle activation at the low sway frequency compared to the higher was observed, whereas swaying on foam induced higher activation on the tibialis anterior as well. It is concluded that swaying voluntarily on an unstable surface results in reduced CoPAP and joint kinematics stability, that is accomplished by increasing the activation of the distal leg muscles, in order to compensate for this perturbation. The reduction of the sway frequency limits the effect of the unstable surface, on the head and upper body, improves the temporal component of coherence between CoP and target, whereas EMG activity is decreased. These findings might have implications in rehabilitation programs.

Impact of seated and standing positions on triceps surae muscle activation in unilateral Achilles tendon rupture.

Heel-rises are commonly used in the rehabilitation of individuals following Achilles tendon rupture, however, the impact of tendon elongation on triceps surae activation in seated versus standing positions has not been investigated. The purpose of this study was to investigate changes in triceps surae activation during seated compared to standing heel-rises in individuals with Achilles tendon rupture and its relationship to tendon elongation. Ten individuals with a history of Achilles tendon rupture were included in this study. Muscle activity using electromyography was examined during a heel-rise task in seated (unilateral) and standing (bilateral) positions. Soleus activity was not significantly different between sitting and standing on both the ruptured and uninjured side. On the ruptured, side there were no differences in medial or lateral gastrocnemius activity between sitting and standing; however, on the uninjured side medial and lateral gastrocnemius activity was lower in sitting compared to standing. The results of this study suggest that neuromuscular changes in triceps surae activation occur following Achilles tendon rupture. The seated heel-rise position can be used to strengthen all muscles of the triceps surae and is useful when the patient is unable to perform a standing heel-rise.

Soleus single motor units show stronger coherence with Achilles tendon vibration across a broad bandwidth relative to medial gastrocnemius units while standing

To probe the frequency characteristics of somatosensory responses in the triceps surae muscles, we previously applied suprathreshold noisy vibration to the Achilles tendon and correlated it with ongoing triceps surae muscle activity (recorded via surface EMG) during standing. Stronger responses to tendon stimuli were observed in soleus (Sol) relative to medial gastrocnemius (MGas) surface EMG; however, it is unknown whether differences in motor unit activity or limitations of surface EMG could have influenced this finding. Here, we inserted indwelling EMG into Sol and MGas to record the activity of single motor units while we applied noisy vibration (10-115 Hz) to the right Achilles tendon of standing participants. We analyzed the relationship between vibration acceleration and the spike activity of active single motor units through estimates of coherence, gain, phase, and cross-covariance. We also applied sinusoidal vibration at frequencies from 10 to 100 Hz (in 5-Hz increments) to examine whether motor units demonstrate nonlinear synchronization or phase locking at higher frequencies. Relative to MGas single motor units, Sol units demonstrated stronger coherence and higher gain with noisy vibration across a bandwidth of 7-68 Hz, and larger peak-to-peak cross-covariance at all four stimulus amplitudes examined. Sol and MGas motor unit activity was modulated over the time course of the sinusoidal stimuli across all frequencies, but their phase-locking behavior was minimal. These findings suggest Sol plays a prominent role in responding to disturbances transmitted through the Achilles tendon across a broad frequency band during standing.NEW & NOTEWORTHY We examined the relationship between Achilles tendon stimuli and spike times of single soleus (Sol) and medial gastrocnemius (MGas) motor units during standing. Relative to MGas, Sol units demonstrated stronger coherence and higher gain with noisy stimuli across a bandwidth of 7-68 Hz. Sol and MGas units demonstrated minimal nonlinear phase locking with sinusoidal stimuli. These findings indicate Sol plays a prominent role in responding to tendon stimuli across a broad frequency band.

Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training.

Previously published studies on the effect of short-term endurance training on neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after 8 weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100, 100–200 ms) and iMVC of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that cycling endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance.

Effect of balance training on neuromuscular function at rest and during isometric maximum voluntary contraction.

This study was directed to investigate the neuromuscular function of the plantar flexors and tibialis anterior (TA) before and after 8 weeks of balance training. Twenty-six young adult subjects were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development (RTD), isometric maximum voluntary torque (iMVT) and muscle activation were measured. Triceps surae muscle activation and TA muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100, 0-200 ms) and maximum voluntary contraction (MVC) of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave), peak twitch torques induced by electrical stimulation at rest and balance performance were evaluated. We found a significant difference between groups in RTD of the plantar flexors during MVC in the time interval 0-100 ms [37.0 N m s(-1) (4.2-69.9 N m s(-1), P = 0.029)]. This change was accompanied by reduced antagonistic muscle co-activity. The normalized H-reflex of the soleus muscle at rest as well as the sway of the center of pressure during balance performance assessment were significantly lower for the intervention group compared with controls. The training intervention had no effect on iMVT, normalized muscle activity of the plantar flexors, normalized muscle activity of TA, normalized V-wave and normalized H-reflex evoked during MVC. Data suggest that balance training reduced antagonistic muscle co-activity at the onset of triceps surae contraction and, in turn, increased isometric explosive voluntary strength of the plantar flexors.

Alteration in neuromuscular function of the plantar flexors following caffeine ingestion.

The aim of this study was to compare the neuromuscular function of the plantar flexors following caffeine or placebo administration. Thirteen subjects (25 ± 3 years) ingested caffeine or placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after caffeine or placebo intake. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque, and neural drive to the muscles were measured. Triceps surae muscle activation was assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100 ms, 100-200 ms) and maximal voluntary contraction (MVC). Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave) and peak twitch torques were evaluated. The isometric maximum voluntary torque and evoked potentials were not different. However, we found a significant difference between groups for rate of torque development in the time intervals 0-100 ms [41.1 N · m/s (95% CI: 8.3-73.9 N · m/s, P = 0.016)] and 100-200 ms [32.8 N · m/s (95% CI: 2.8-62.8 N · m/s, P = 0.034)]. These changes were accompanied by enhanced neural drive to the plantar flexors. Data suggest that caffeine solely increased explosive voluntary strength of the triceps surae because of enhanced neural activation at the onset of contraction whereas MVC strength was not affected.

Triceps surae activation is altered in male runners with Achilles tendinopathy

Achilles tendinopathy is a common injury in running sports however the exact etiology of Achilles injury is still unclear. In recent years, altered neuromotor recruitment patterns of the triceps surae have been hypothesized to create differential intra-tendinous loads leading to pathology; however, this hypothesis has not been investigated. Further, the effect foot orthoses may have on neuromotor recruitment of the triceps surae in Achilles tendinopathy has not been investigated. Methods: The electromyographic activity of the triceps surae was recorded during an over-ground running task. Fifteen Achilles injured participants and 19 asymptomatic controls were assessed in a footwear only condition. The Achilles injured participants were also assessed running in a pre-fabricated foot orthoses. Results: In Achilles injured participants, there was a significant difference between soleus and lateral gastrocnemius offset times during running compared to the asymptomatic controls (p<0.05). There were no significant differences in triceps surae muscle activity between the footwear only and footwear and orthoses condition in the Achilles injured participants. Conclusions: The finding that triceps surae activity is altered in participants with Achilles tendinopathy may have clinical importance as it suggests that intra-tendinous loads are altered which may contribute to pathological changes. Further, foot orthoses have no immediate effect on the neuromotor control of the triceps surae.

Efficacy of current and novel electromyographic normalization methods for lower limb high-speed muscle actions

The aim of this study was to assess the efficacy of electromyography (EMG) normalization methods for a high-speed 20-m sprint. Comparisons were based on intra-individual reliability and magnitude of normalized EMG signals from three repeat sessions separated by 1 day (between days) and 1 week (between weeks) from the initial test. Surface EMGs were recorded (n=16) from the medial and lateral gastrocnemius and soleus during the normalization methods (isometric: maximum/sub-maximum/body weight; isotonic: maximum/sub-maximum/body weight; isokinetic: 1.05 rad · s–1, 1.31 rad · s–1, 1.83 rad · s–1; squat jump). The EMG data from the 20-m sprint were normalized using each method and using the within-sprint peak EMG (sprint peak). Intra-individual reliability of the EMG was assessed using typical error of measurement as a percentage of intra-individual coefficient of variance (TEMCV%). Sprint peak normalization improved intra-individual reliability of EMG (soleus: <4.91CV%; medial gastrocnemius: <6.2CV%; lateral gastrocnemius: <7.1CV%) compared with un-normalized EMG (soleus: <13.3CV%; medial gastrocnemius: <16.5CV%; lateral gastrocnemius: <16.3CV%) both between days and between weeks. Squat jump normalization improved the soleus (<11.2CV%) and medial gastrocnemius (<15.7CV%) reliability between days and weeks and provided a representative measure of triceps surae muscle activation. The intra-individual reliability of the medial gastrocnemius EMG data was improved both between days and weeks when using isotonic normalization. Isometric and isokinetic normalization showed no improvement in intra-individual reliability either between days or weeks for any muscle. The method of normalization influenced the between-stride muscle interaction during the 20-m sprint. The results of this study suggest that peak normalization can be used to normalize high-speed muscle actions, while normalizing EMG to a squat jump may provide an alternative method to represent relative muscle activation.

Peak triceps surae muscle activity is not specific to knee flexion angles during MVIC

There is limited research on peak activity of the separate triceps surae muscles in select knee flexion (KF) positions during a maximum voluntary isometric contraction (MVIC) used to normalize EMG signals. The aim of this study was to determine how frequent peak activity occurred during an MVIC for soleus (SOL), gastrocnemius medialis (GM), and gastrocnemius lateralis (GL) in select KF positions, and if these peaks were recorded in similar KF positions. Forty-eight healthy individuals performed unilateral plantar-flexion MVIC in standing with 0°KF and 45°KF, and in sitting with 90°KF. Surface EMG of SOL, GM, and GL were collected and processed in 250 ms epochs to determine peak root-mean-square amplitude. Peak activity was most frequently captured in standing and rarely in sitting, with no position selective to SOL, GM or GL activity. Peak GM and GL activity was more frequent in 0°KF than 45°KF, and more often in similar KF positions than not. Peak SOL activity was just as likely in 45°KF as 0°KF, and more in positions similar to GM, but not GL. The EMG amplitudes were at least 20% greater in positions that captured peak activity over those that did not. The overall findings support performing an MVIC in more than one KF position to normalize triceps surae EMG. It is emphasized that no KF position is selective to SOL, GM, or GL alone.