Selective recruitment of the triceps surae muscles with changes in knee angle

The muscles of the triceps surae group are important for performance in most sports and in the performance of activities of daily life. In addition, hypertrophy and balance among these muscles are integral to success in bodybuilding. The purpose of this study was to compare the muscle utilization patterns of the 2 major muscles of the triceps surae group, the soleus (SOL) and gastrocnemius (lateral head = LG and medial head = MG), and the tibialis anterior (TA) as an antagonist muscle to the group. Their electromyographic (EMG) signals were compared during 50 constant external resistance contractions at a level established before the testing session. Eleven experienced subjects contributed data during plantar flexion at 3 different knee angles (90, 135, and 180 degrees ). Both root mean square amplitude and integrated signal analyses of the EMGs revealed that the MG produced significantly greater activity than either the SOL or TA at 180 degrees, whereas the LG was not different from the SOL at any knee angle measured. Data also revealed that the SOL produced less electrical activity at 180 degrees than at the other knee angles, whereas the MG produced greater electrical activity. As would be expected, the TA produced lower EMG values than any of the triceps surae muscles at all angles tested. These data indicate that selective targeting of the SOL and MG is possible through the manipulation of knee angle. This targeting appears to be controlled by the biarticular and monoarticular structures of the MG and SOL, respectively. The LG appears less affected by knee position than the MG. Results suggest that the SOL can be targeted most effectively with the knee flexed at 90 degrees and the MG with the leg fully extended. The LG appears to also be more active at 180 degrees; however, it is not as affected as the MG or SOL by knee angle.     

Intermuscular force transmission between human plantarflexor muscles in vivo

The exact mechanical function of synergist muscles within a human limb in vivo is not well described. Recent studies indicate the existence of a mechanical interaction between muscle actuators that may have functional significance and further play a role for injury mechanisms. The purpose of the present study was to investigate if intermuscular force transmission occurs within and between human plantarflexor muscles in vivo. Seven subjects performed four types of either active contractile tasks or passive joint manipulations: passive knee extension, voluntary isometric plantarflexion, voluntary isometric hallux flexion, passive hallux extension, and selective percutaneous stimulation of the gastrocnemius medialis (MG). In each experiment plantar- and hallux flexion force and corresponding EMG activity were sampled. During all tasks ultrasonography was applied at proximal and distal sites to assess task-induced tissue displacement (which is assumed to represent loading) for the plantarflexor muscles [MG, soleus (SOL), and flexor hallucis longus (FHL)]. Selective MG stimulation and passive knee extension resulted in displacement of both the MG and SOL muscles. Minimal displacement of the triceps surae muscles was seen during passive hallux extension. Large interindividual differences with respect to deep plantarflexor activation during voluntary contractions were observed. The present results suggest that force may be transmitted between the triceps surae muscles in vivo, while only limited evidence was provided for the occurrence of force transfer between the triceps surae and the deeper-lying FHL.     

Fatigue-induced changes in synergistic muscle force do not match tendon elongation

This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min×5 times: interval 30 s, intensity: 20–30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles. The tendon elongation of MG and SOL in post-fatigue ramp was similar, although evoked MG forces dropped nearly to zero. In addition, for a given torque output, the tendon elongation of SOL significantly decreased while that of LG did not, although the activation levels of both muscles had increased. Results suggest that the fatigue-induced changes in force of the triceps surae muscles do not match their tendon elongation. These results imply that the tendons of the triceps surae muscles are mechanically coupled even after selective fatigue of a single muscle.     

An assessment of the reliability and standardisation of tests used to elicit reference muscular actions for electromyographical normalisation

Prior to implementing a normalisation method, the standardisation and reliability of the method needs to be examined. This investigation aimed to assess the reliability of EMG amplitudes and test outputs from proposed normalisation methods for the triceps surae. Sixteen participants completed isometric (maximum and sub-maximum); isokinetic (1.05 rad/s, 1.31 rad/s and 1.83 rad/s) squat jump and 20 m sprint conditions, on 3 separate occasions over 1 week. The EMG data was collected from the medial and lateral gastrocnemius (MG and LG) and soleus (SOL). Log transformed typical error measurements (TEM_CV%) assessed EMG signal and test output reliability across the three sessions. Only the squat jump provided acceptable EMG reliability for all muscles both between days (SOL: 13%; MG: 14.5%; LG: 11.8%) and between weeks (SOL: 14.5%; MG: 12.9%; LG: 8.9%), with the sprint only showing poor reliability in the LG between days (16.3%). Acceptable reliability for the isometric and isokinetic conditions were muscle and re-test period dependant. Reliable output was found for the squat jump (4.1% and 3.6%), sprint (0.8% and 0.6%) and 1RM plantar flexion test (2.8% and 3.5%) between days and weeks, respectively. Isokinetic plantar flexion displayed poor reliability at all velocities between days and weeks. It was concluded that the squat jump provides a standardised and reproducible reference EMG value for the triceps surae for use as a normalisation method.     

Motor unit firing rates of the gastrocnemii during maximal brief steady-state contractions in humans

The human triceps surae (soleus, medial (MG) and lateral (LG) gastrocnemii) is complex and important for posture and gait. The soleus exhibits markedly lower motor unit firing rates (MUFRs; ∼16 Hz) during maximal voluntary isometric contraction (MVC) than other limb muscles, but this information is unknown for the MG and LG. During multiple visits, subjects performed a series of 5–7, ∼7-s plantar flexor MVCs with tungsten microelectrodes inserted into the MG and LG. During a separate testing session, another group of subjects performed submaximal isometric contractions at 25%, 50%, and 75% MVC with inserted fine-wires in the MG, LG and soleus. Maximum steady-state MUFRs for MG and LG (∼23 Hz) were not different, but faster than prior reports for the soleus. No differences between the three triceps surae components were detected for 25% or 50% MVC, but at 75% MVC, the MG MUFRs were 31% greater than soleus. The triceps surae exhibit similar torque modulation strategies at <75% MVC, but to achieve higher contraction intensities (>75% MVC) the gastrocnemii rely on faster rates to generate maximal torque than the soleus. Therefore, the MG and LG exhibit a larger range of MUFR capacities.     

Changes in human skeletal muscle architecture and function induced by extended spaceflight

The aim of this study was to quantitatively describe the relationships between joint angles and muscle architecture (lengths (L_f) and angles (Θ_f) of fascicles) of human triceps surae [medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles] in vivo for three men-cosmonaut after long-duration spaceflight. Sagittal sonographs of MG, LG, SOL were taken at ankle was positioned at 15° (dorsiflexion), 0° (neutral position), +15°, and +30° (plantarflexion), with the knee at 90° at rest and after a long-duration spaceflight. At each position, longitudinal ultrasonic images of the MG and LG and SOL were obtained while the cosmonauts was relaxed from which fascicle lengths and angles with respect to the aponeuroses were determined. After space flight plantarflexor force declined significantly (26%; p < 0.001). The internal architecture of the GM, and LG, and SOL muscle was significantly altered. In the passive condition, L_f changed from 45, 53, and 39 mm (knee, 0°, ankle, −15°) to 26, 33, and 28 mm (knee, 90° ankle, 30°) for MG, LG, and SOL, respectively. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses. The three heads of the triceps surae muscle substantially differ in architecture, which probably reflects their functional roles. Differences in fiber length and pennation angle that were observed among the muscles and could be associated with differences in force production and in elastic properties of musculo-tendinous complex and aponeuroses.     

Contributions of slow and fast muscles of triceps surae to a cyclic movement

The relative contribution of synergistic muscles has been studied during pedalling on a bicycle. The electromyographic (EMG) activity of the different components of triceps surae (namely soleus or SOL and medial gastrocnemius or MG) has been recorded and analyzed for increasing pedalling speed performed against increasing resistance. The results indicate that SOL IEMG (integrated EMG) increases linearly (y = 2x-12.1; r = 0.98) with increasing load (10-70 N) at constant speed (60 rpm), whereas no change is noted in MG IEMG below 40 N. In contrast, when the pedalling speed is increased (from 30 to 170 rpm) at constant load, MG IEMG shows the largest increase. Furthermore, although in both muscles EMG activity appears earlier in the movement with increases in load and/or speed, the delay between the onset of both EMGs remains unchanged at constant speed and synchronization of MG with SOL is only observed when speed is increased above 140 rpm. These results suggest that the different muscles of the triceps surae make specific contributions to the development of the mechanical tension required to maintain or increase the speed of movement.     

Effect of different ankle- and knee-joint positions on gastrocnemius medialis fascicle length and EMG activity during isometric plantar flexion

The purpose of this study was to provide evidence on the fact that the observed decrease in EMG activity of the gastrocnemius medialis (GM) at pronounced knee flexed positions is not only due to GM insufficiency, by examining muscle fascicle lengths during maximal voluntary contractions at different positions. Twenty-two male long distance runners (body mass: 78.5+/-6.7 kg, height: 183+/-6 cm) participated in the study. The subjects performed isometric maximal voluntary plantar flexion contractions (MVC) of their left leg at six ankle-knee angle combinations. To examine the resultant ankle joint moments the kinematics of the left leg were recorded using a Vicon 624 system with 8 cameras operating at 120 Hz. The EMG activity of GM, gastrocnemius lateralis (GL), soleus (SOL) and tibialis anterior (TA) were measured using surface electromyography. Synchronously, fascicle length and pennation angle values of the GM were obtained at rest and at the plateau of the maximal plantar flexion using ultrasonography. The main findings were: (a) identifiable differences in fascicle length of the GM at rest do not necessarily imply that these differences would also exist during a maximal isometric plantar flexion contraction and (b) the EMG activity of the biarticular GM during the MVC decreased at a pronounced flexed knee-joint position (up to 110 degrees ) despite of no differences in GM fascicle length. It is suggested that the decrease in EMG activity of the GM at pronounced knee flexed positions is due to a critical force-length potential of all three muscles of the triceps surae.     

Mechanomyographic and electromyographic responses of the triceps surae during maximal voluntary contractions.

The objective of this study was to examine the effect of joint angle on the electromyogram (EMG) and mechanomyogram (MMG) during maximal voluntary contraction (MVC). Eight subjects performed maximal isometric plantar flexor torque productions at varying knee and/or ankle angles. Maximal voluntary torque, EMG, and MMG from the soleus (Sol), medial (MG) and lateral gastrocnemius (LG) muscles were measured at different joint angles. At varying knee angles, the root mean squared (rms) MMG amplitude of the MG and LG increased with knee joint extension from 60 degrees to 180 degrees (full extension) in steps of 30 degrees, whereas that of the Sol was constant. At varying ankle angles, the rms-MMG of all muscles (Sol, MG, and LG) decreased with torque as ankle joint extending from 80 degrees (10 degrees dorsiflexion position) to 120 degrees (30 degrees plantar flexion position) in steps of 10 degrees. In each case, changes in the rms-MMG of the three muscles were almost parallel to those in torque. In contrast, there were no significant differences in the rms-EMG of all muscles among all joint angles. Our data suggest that the MMG amplitudes recorded from individual muscles during MVCs can represent relative torque-angle relationships that cannot be represented by the EMG signals.     

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.     

Functional and clinical significance of the architecture of human skeletal muscles

The architectural properties of the triceps surae muscle were studied in vivo in groups of healthy subjects (eight men) and patients with locomotor function disorders (four men and four women) with the ankle joint positioned at a plantar flexion 0° and the knee set at 90° (neutral position). In this position, using ultrasonic scanning, longitudinal ultrasonic images of the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (Sol) muscles were obtained when the subject was relaxed (the passive state) or performed isometric plantar flexion (50% of the maximum voluntary contraction (MVC), the active state). The fascicle lengths, fascicle angles, and muscle thickness were determined. In the passive state, the fascicle lengths of the MG, LG, and Sol muscles in the group of healthy subjects were 33, 35, and 30 mm and the pennation angle, 25°, 19°, and 25°; in the group of patients with motor disorders, 38, 39, and 29 mm and 21°, 19°, and 24°, respectively. The MG, LG, and Sol thicknesses in the group of healthy subjects were 15, 13, and 12 mm, and in the group of patients with motor disorders, 14, 12, and 14 mm, respectively. In the active state (50% of the MVC), the MG, LG, and Sol fiber lengths in the group of healthy subjects shortened by 31, 24, and 18%; the fiber pennation angle increased by 60, 41, and 41%, respectively. In the group of patients with motor disorders, the fiber lengths shortened by 28, 14, and 18% and the fiber pennation angle decreased by 28, 26, and 36%, respectively. The MG, LG, and Sol thicknesses in the group of healthy subjects increased by 9, 22, and 18%, while in the group of patients with motor disorders the thickness decreased by 4% in the MG and increased by 11 and 4% in the LG and Sol muscles, respectively. Different fiber lengths and pennation angles and their changes upon contraction might be related to differences in the force-producing capabilities of the muscles and the viscoelastic properties of muscle tendons and aponeuroses.     

The highest antagonistic coactivation of the vastus intermedius muscle among quadriceps femoris muscles during isometric knee flexion

Although the possibility that the vastus intermedius (VI) muscle contributes to flexion of the knee joint has been suggested previously, the detail of its functional role in knee flexion is not well understood. The purpose of this study was to examine the antagonist coactivation of VI during isometric knee flexion. Thirteen men performed 25–100% of maximal voluntary contraction (MVC) at 90°, 120°, and 150° knee joint angles. Surface electromyography (EMG) of the four individual muscles in the quadriceps femoris (QF) was recorded and normalized by the EMG signals during isometric knee extension at MVC. Cross-talk on VI EMG signal was assessed based on the median frequency response to selective cooling of hamstring muscles. Normalized EMG of the VI was significantly higher than that of the other synergistic QF muscles at each knee joint angle (all P < 0.05) with minimum cross-talk from the hamstrings to VI. There were significant correlations between the EMG signal of the hamstrings and VI (r = 0.55–0.85, P < 0.001). These results suggest that VI acts as a primary antagonistic muscle of QF during knee flexion, and that VI is presumably a main contributor to knee joint stabilization.     

Motor unit firing patterns of lower leg muscles during isometric plantar flexion with flexed knee joint position

The ankle flexor and extensor muscles are essential for pedal movements associated with car driving. Neuromuscular activation of lower leg muscles is influenced by the posture during a given task, such as the flexed knee joint angle during car driving. This study aimed to investigate the influence of flexion of the knee joint on recruitment threshold-dependent motor unit activity in lower leg muscles during isometric contraction. Twenty healthy participants performed plantar flexor and dorsiflexor isometric ramp contractions at 30 % of the maximal voluntary contraction (MVC) with extended (0°) and flexed (130°) knee joint angles. High-density surface electromyograms were recorded from medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) muscles and decomposed to extract individual motor units. The torque-dependent change (Δpps /Δ%MVC) of the motor unit activity of MG (recruited at 15 %MVC) and SOL (recruited at 5 %MVC) muscles was higher with a flexed compared with an extended knee joint (p < 0.05). The torque-dependent change of TA MU did not different between the knee joint angles. The motor units within certain limited recruitment thresholds recruited to exert plantar flexion torque can be excited to compensate for the loss of MG muscle torque output with a flexed knee joint.     

Can pennation angles be predicted from EMGs for the primary ankle plantar and dorsiflexors during isometric contractions?

Ultrasonography was used to measure pennation angle and electromyography (EMG) to record muscle activity of the human tibialis anterior (TA), lateral gastrocnemius (LG), medial gastrocnemius (MG), and soleus (SOL) muscles during graded isometric ankle plantar and dorsiflexion contractions done on a Biodex dynamometer. Data from 8 male and 8 female subjects were collected in increments of approximately 25% of maximum voluntary contraction (MVC) ranging from rest to MVC. A significant positive linear relationship (p<0.05) between normalized EMG and pennation angle for all muscles was observed when subject specific pennation angles at rest and MVC were included in the analysis. These were included to account for gender differences and inter-subject variability in pennation angle. The coefficient of determination, R(2), ranged between 0.76 for the TA and 0.87 for the SOL. The EMG-pennation angle relationships have ramifications for use in EMG-driven models of muscle force. The regression equations can be used to characterize fiber pennation angle more accurately and to determine how it changes with contraction intensity, thus providing improved estimates of muscle force when using musculoskeletal models.     

Difference in aftereffects following prolonged Achilles tendon vibration on muscle activity during maximal voluntary contraction among plantar flexor synergists.

It has been suggested that a suppression of maximal voluntary contraction (MVC) induced by prolonged vibration is due to an attenuation of Ia afferent activity. The purpose of the present study was to test the hypothesis that aftereffects following prolonged vibration on muscle activity during MVC differ among plantar flexor synergists owing to a supposed difference in muscle fiber composition. The plantar flexion MVC torque and surface electromyogram (EMG) of the medial head of gastrocnemius (MG), the lateral head of gastrocnemius (LG), and the soleus (Sol) were recorded in 13 subjects before and after prolonged vibration applied to the Achilles tendon at 100 Hz for 30 min. The maximal H reflexes and M waves were also determined from the three muscles, and the ratio between H reflexes and M waves (H/Mmax) was calculated before and after the vibration. The MVC torque was decreased by 16.6 +/- 3.7% after the vibration (P < 0.05; ANOVA). The H/Mmax also decreased for all three muscles, indicating that Ia afferent activity was successfully attenuated by the vibration in all plantar flexors. However, a reduction of EMG during MVC was observed only in MG (12.7 +/- 4.0%) and LG (11.4 +/- 3.9%) (P < 0.05; ANOVA), not in Sol (3.4 +/- 3.0%). These results demonstrated that prolonged vibration-induced MVC suppression was attributable mainly to the reduction of muscle activity in MG and LG, both of which have a larger proportion of fast-twitch muscle fibers than Sol. This finding suggests that Ia-afferent activity that reinforces the recruitment of high-threshold motor units is necessary to enhance force exertion during MVC.     

Load-dependent muscle strategy during plantarflexion in humans

This study analyses the relative contribution of the triceps surae and tibialis anterior (TA) muscles to tension development with reference to voluntary plantarflexion at two articular positions of the knee joint (extended and flexed at 90°) for various inertial loads. Subjects were instructed to perform plantarflexions at various sub-maximal and maximal velocities with no intention of stopping the movement. Whereas in one series of experiments the subjects were informed of the load countering the movement, in the other they were not. The average electromyographic (EMG) activity of the different muscles was recorded. The main results were that with loading: (a) greater maximal plantarflexion velocities were recorded in flexed as compared to extended-knee positions; (b) greater durations and amplitudes of agonist and antagonist EMG bursts were recorded; (c) the co-activation of the TA and triceps surae muscles was enhanced; (d) unexpected sub-maximal loads induced greater EMG activity and speed of movement. It is concluded that increasing the load during plantarflexion in humans brings about changes in neuromuscular strategies that contribute to the efficiency of contractile activity during rapid movements. The results also indicate that unexpected sub-maximal loading induces a potentiated neuromuscular activity which increases the speed of movement.     

Architectural and functional features of human triceps surae muscles during contraction

Architecturalproperties of the triceps surae muscles were determined in vivo for sixmen. The ankle was positioned at 15° dorsiflexion (15°)and 0, 15, and 30° plantar flexion, with the knee set at 0, 45, and90°. At each position, longitudinal ultrasonic images of the medial(MG) and lateral (LG) gastrocnemius and soleus (Sol) muscles wereobtained while the subject was relaxed (passive) and performed maximalisometric plantar flexion (active), from which fascicle lengths andangles with respect to the aponeuroses were determined. In the passivecondition, fascicle lengths changed from 59, 65, and 43 mm (knee,0°; ankle, 15°) to 32, 41, and 30 mm (knee, 90°ankle, 30°) for MG, LG, and Sol, respectively. Fascicle shorteningby contraction was more pronounced at longer fascicle lengths. MG hadgreatest fascicle angles, ranging from 22 to 67°, and was in a verydisadvantageous condition when the knee was flexed at 90°,irrespective of ankle positions. Different lengths and angles offascicles, and their changes by contraction, might be related todifferences in force-producing capabilities of the muscles and elasticcharacteristics of tendons and aponeuroses.

     

Velocity-dependent muscle strategy during plantarflexion in humans

This work examines the relative contribution of the triceps surae heads and the tibialis anterior (TA) to tension development with reference to voluntary plantarflexion at various velocities and at two articular positions of the knee joint (extended and flexed at 90 °). Subjects were instructed to perform plantarflexion at various submaximal and maximal velocities with no intention of stopping the movement. Voluntary electromyographic (EMG) activity was recorded and the amplitude, duration and integral were analysed. Integrated EMG (IEMG) was normalized with respect to duration. The maximal M wave and the Hoffmann (H) reflex elicited by electrical stimulation of the tibial nerve were recorded in the triceps surae to estimate the effects in gastrocnemii (G) length and motoneuron excitability differences, respectively, in the two knee positions. The results indicate that: (a) although the largest EMG activity was recorded in the extended limb, the greatest maximal velocities were performed in the flexed knee position; (b) with increasing velocity of movement, all triceps surae muscles showed enhanced IEMG activities; (c) at a low velocity of movement the soleus (So1)/G IEMG ratio was larger in the flexed compared to the extended knee; and (d) with increasing velocity, co-activation of agonist and antagonist muscles appeared. It is concluded that the larger maximal velocity of movement observed in the flexed compared to the extended knee was not primarily related to the neural command of the different triceps surae components, but rather to their mechanical properties. Furthermore, co-activation of agonist and antagonist muscles may contribute to the performance of the contractile strategy during rapid movements.     

Influence of knee flexion angle and age on triceps surae muscle fatigue during heel raises

ABSTRACT: Hébert-Losier, K, Schneiders, AG, García, JA, Sullivan, SJ, and Simoneau, GG. Influence of knee flexion angle and age on triceps surae muscle fatigue during heel raises. J Strength Cond Res 26(11): 3134-3147, 2012-The triceps surae (TS) muscle-tendon unit is 1 of the most commonly injured in elite and recreational athletes, with a high prevalence in middle-aged adults. The performance of maximal numbers of unilateral heel raises is used to assess, train, and rehabilitate TS endurance and conventionally prescribed in 0° knee flexion (KF) for the gastrocnemius and 45° for the soleus (SOL). However, the extent of muscle selectivity conferred through the change in the knee angle is lacking for heel raises performed to volitional fatigue. This study investigated the influence of knee angle on TS muscle fatigue during heel raises and determined whether fatigue differed between middle-aged and younger-aged adults. Forty-eight healthy individuals aged 18-25 and 35-45 years performed maximal numbers of unilateral heel raises in 0° and 45° KF. Median frequencies and linear regression slopes were calculated from the SOL, gastrocnemius medialis (GM), and gastrocnemius lateralis (GL) surface electromyographic signals. Stepwise mixed-effect regressions were used for analysis. The subjects completed an average of 45 and 48 heel raises in 0° and 45° KF, respectively. The results indicated that the 3 muscles fatigued during testing as all median frequencies decreased, and regression slopes were negative. Consistent with muscle physiology and fiber typing, fatigue was greater in the GM and GL than in the SOL (p < 0.001). However, knee angle did not influence TS muscle fatigue parameters (p = 0.814), with similar SOL, GM, and GL fatigue in 0° and 45° KF. These findings are in contrast with the traditionally described clinical use of heel raises in select knee angles for the gastrocnemius and the SOL. Furthermore, no difference in TS fatigue between the 2 age groups was able to be determined, despite the reported higher prevalence of injury in middle-aged individuals.     

Influence of knee flexion angle and age on triceps surae muscle activity during heel raises

ABSTRACT: Hébert-Losier, K, Schneiders, AG, García, JA, Sullivan, SJ, and Simoneau, GG. Influence of knee flexion angle and age on triceps surae muscle activity during heel raises. J Strength Cond Res 26(11): 3124-3133, 2012-Triceps surae and Achilles tendon injuries are frequent in sports medicine, particularly in middle-aged adults. Muscle imbalances and weakness are suggested to be involved in the etiology of these conditions, with heel-raise testing often used to assess and treat triceps surae (TS) injuries. Although heel raises are recommended with the knee straight for gastrocnemius and bent for soleus (SOL), the extent of muscle selectivity in these positions is not clear. This study aimed to determine the influence of knee angle and age on TS muscle activity during heel raises. Forty-eight healthy men and women were recruited from a younger-aged (18-25 years) and middle-aged (35-45 years) population. All the subjects performed unilateral heel raises in 0° and 45° knee flexion (KF). Soleus, gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) surface electromyography signals were processed to compute root-mean-square amplitudes, and data were analyzed using mixed-effects models and stepwise regression. The mean TS activity during heel raises was 23% of maximum voluntary isometric contraction when performed in 0° KF and 21% when in 45°. Amplitudes were significantly different between TS muscles (p < 0.001) and KF angles (p < 0.001), with a significant interaction (p < 0.001). However, the age of the population did not influence the results (p = 0.193). The findings demonstrate that SOL activity was 4% greater when tested in 45° compared with 0° KF and 5% lower in the GM and GL. The results are consistent with the recommended use of heel raises in select knee positions for assessing, training, and rehabilitating the SOL and gastrocnemius muscles; however, the 4-5% documented change in activity might not be enough to significantly influence clinical outcome measures or muscle-specific benefits. Contrary to expectations, TS activity did not distinguish between middle-aged and younger-aged adults, despite the higher injury prevalence in middle age.