Modulation of muscle-tendon interaction in the human triceps surae during an energy dissipation task

Abstract

The compliance of elastic elements allows muscles to dissipate energy safely during eccentric contractions. This buffering function is well documented in animal models but our understanding of its mechanism in humans is confined to non-specific tasks, requiring a subsequent acceleration of the body. The present study aimed to examine the behaviour of the human triceps surae muscle-tendon unit (MTU) during a pure energy dissipation task, under two loading conditions. Thirty-nine subjects performed a single-leg landing task, with and without added mass. Ultrasound measurements were combined with three-dimensional kinematics and kinetics to determine instantaneous length changes of MTUs, muscle fascicles, Achilles tendon and combined elastic elements. Gastrocnemius and soleus MTUs lengthened during landing. After a small concentric action, fascicles contracted eccentrically during most of the task, whereas plantar flexor muscles were activated. Combined elastic elements lengthened until peak ankle moment and recoiled thereafter, whereas no recoil was observed for the Achilles tendon. Adding mass resulted in greater negative work and MTU lengthening, which were accompanied by a greater stretch of tendon and elastic elements and a greater recruitment of the soleus muscle, without any further fascicle strain. Hence, the buffering action of elastic elements delimits the maximal strain and lengthening velocity of active muscle fascicles and is commensurate with loading constraints. In the present task, energy dissipation was modulated via greater MTU excursion and more forceful eccentric contractions. The distinct strain pattern of the Achilles tendon supports the notion that different elastic elements may not systematically fulfil the same function.

Interactions between fascicles and tendinous tissues in gastrocnemius medialis and vastus lateralis during drop landing

“…In addition, the peak of fascicle lengthening was notably delayed according to the lengthening of tendinous tissues. This decoupling mechanism between the muscle‐tendon unit, muscle fascicle, and tendinous tissues is consistent with previous animal and human studies . In accordance with our first hypothesis, GM tendinous tissues lengthened more when the loading increased allowing for a constant fascicle lengthening amplitude and peak velocity during landing.…”

“…The behavior of GM fascicle during drop landing presented a clear turning point (Figure B) from shortening to lengthening following the impact with a small delay of shortening between the foot‐ground contact and the onset of fascicle lengthening (ranged from 3 to 12 ms). Our patterns of fascicle lengthening were similar to those reported during the landing phase of a step‐down . In the current study, although stretching of the GM muscle‐tendon unit was greater as landing height increased, muscle fascicle lengthening and peak lengthening velocity remained unchanged.…”

“…First, we defined “force rise” as the phase between the ground contact (ie, 0% of landing phase) and the time of peak vertical GRF. “Force decay” corresponded to the phase between the peak vertical GRF and the end of the landing phase . It must be noted that the phases we used are based on the vertical GRF and differ from the method initially proposed by Konow & Roberts based on the muscle‐tendon unit force of turkeys.…”

“…“Force decay” corresponded to the phase between the peak vertical GRF and the end of the landing phase . It must be noted that the phases we used are based on the vertical GRF and differ from the method initially proposed by Konow & Roberts based on the muscle‐tendon unit force of turkeys. Fascicle lengthening amplitudes and AGR of the GM and VL muscles were calculated for these two phases.…”

“…Most of previous studies explored fascicle‐tendon interactions in eccentric conditions during monoarticular tasks or low‐intensity exercises . A recent study examined the fascicle‐tendon interactions of the human triceps surae during a pure energy dissipation task of step landing . These authors elegantly demonstrated that both gastrocnemius medialis and soleus muscles displayed quite similar fascicle lengthening during step landing irrespective of the loading condition (ie, body weight vs body weight with added mass) thanks to a buffering action of tendinous tissues.…”