Kawakami Y, Muraoka T, Ito S, Kanehisa H, Fukunaga T

J. Physiol., 540: 635-646, 2002.

Six men performed a single ankle plantar flexion exercise in a supine position with the maximal effort with (CM, plantar flexion preceded by dorsiflexion) and without a counter-movement (NoCM, plantar flexion only) on a sliding table that controlled applied load to the ankle (40% of the maximal voluntary force). The reaction force at the foot and ankle joint angle were measured using a force-plate and a goniometer respectively. From real-time ultrasonogram of the gastrocnemius medialis muscle during the movement, the fascicle length was determined. The estimated peak force, average power, and work at the Achilles tendon during the plantar flexion phase in CM were significantly greater than those in NoCM. In CM, in the dorsiflexion phase, fascicle length initially increased with only little electromyographic activity, then remained constant while the whole muscle-tendon unit was still lengthened, before decreasing in the final plantar flexion phase. In NoCM, fascicle length decreased throughout the movement and the fascicle length at the onset of movement was longer than that of the corresponding phase in CM. It was concluded that during CM muscle fibres optimally work almost isometrically, by leaving to tendon the task of storing and releasing elastic energy for enhancing exercise performance.