Coordination of hamstrings is individual specific and is related to motor performance

Abstract

The torque-sharing strategies between synergistic muscles may have important functional consequences. This study involved two experiments. The first experiment ( n = 22) aimed 1) to determine the relationship between the distribution of activation and the distribution of torque-generating capacity among the heads of the hamstring, and 2) to describe individual torque-sharing strategies and to determine whether these strategies are similar between legs. The second experiment ( n = 35) aimed to determine whether the distribution of activation between the muscle heads affects endurance performance during a sustained submaximal knee flexion task. Surface electromyography (EMG) was recorded from biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) during submaximal isometric knee flexions. Torque-generating capacity was estimated by measuring muscle volume, fascicle length, pennation angle, and moment arm. The product of the normalized EMG amplitude and the torque-generating capacity was used as an index of muscle torque. The distributions of muscle activation and of torque-generating capacity were not correlated significantly (all P> 0.18). Thus, there was a torque imbalance between the muscle heads (ST torque > BF and SM torque; P < 0.001), the magnitude of which varied greatly between participants. A significant negative correlation was observed between the imbalance of activation across the hamstring muscles and the time to exhaustion ( P < 0.001); i.e., the larger the imbalance of activation across muscles, the lower the muscle endurance performance. Torque-sharing strategies between the heads of the hamstrings are individual specific and related to muscle endurance performance. Whether these individual strategies play a role in hamstring injury remains to be determined. NEW & NOTEWORTHY The distribution of activation among the heads of the hamstring is not related to the distribution of torque-generating capacity. The torque-sharing strategies within hamstring muscles vary greatly between individuals but are similar between legs. Hamstring coordination affects endurance performance; i.e., the larger the imbalance of activation across the muscle heads, the lower the muscle endurance.

Hamstring muscle elasticity differs in specialized high‐performance athletes

“…Importantly, this methodological issue does not explain the higher shear modulus values obtained for BF and SM compared to ST, as the maximal shear wave velocity is reached when the probe is along the fibers . Therefore, this influence is likely marginal between SM and BF which present close pennation angle . Thus, the lower shear modulus values for ST compared to SM and BF could result from the variance in biomechanical loads for each hamstring muscle.…”

“…30 Therefore, this influence is likely marginal between SM and BF which present close pennation angle. 31 Thus, the lower shear modulus values for ST compared to SM and BF could result from the variance in biomechanical loads for each hamstring muscle. During running, Schache et al 32 showed that BF exhibits the largest peak strain while SM produced the highest peak force and performed the largest amount of work.…”

Mechanisms of Hamstring Strain Injury: Interactions between Fatigue, Muscle Activation and Function

“…In conclusion, the hamstring muscles generate large opposing forces during high-speed running [96] while also playing a role in the production of dynamic stability at the knee [82]. Based on the present research, the possibility exists that changes in muscle coordination strategies may cause one or more hamstring muscles to be disproportionately activated [70], possibly increasing metabolic demand and thus prematurely fatiguing the overactive muscles [70]. With fatigue it appears that lower limb stiffness decreases [85], which could cause the adoption of a "Groucho" running pattern, associated with reduced movement efficiency and greater joint moments of force.…”

“…In accordance with this, Avrillon et al [70] observed individual-specific differences in hamstring muscle coordination strategies and hypothesized that these individual muscle coordination strategies might have functional consequences. For example, if one muscle is activated to a greater extent than required by the task, which is inevitably the case when activation between synergists is imbalanced, its metabolic demand would be higher and fatigue would develop sooner, which the authors suggested could increase injury risk [70]. Conversely, fatigue influences muscle activation patterns during maximum sprint running [71] so that neuromuscular coordination is altered under fatiguing conditions.…”

“…Given that the BF and ST muscle bellies share a common proximal tendon origin, differences in activation patterns and the timing of peak activation between these muscles may exert significant influence on HSI risk [57]. In accordance with this, Avrillon et al [70] observed individual-specific differences in hamstring muscle coordination strategies and hypothesized that these individual muscle coordination strategies might have functional consequences. For example, if one muscle is activated to a greater extent than required by the task, which is inevitably the case when activation between synergists is imbalanced, its metabolic demand would be higher and fatigue would develop sooner, which the authors suggested could increase injury risk [70].…”