In vivo behaviour of human muscle tendon during walking

In the present study we investigated in vivo length changes in the fascicle s and tendon of the human gastrocnemius medialis (GM) muscle during walking . The experimental protocol involved real-time ultrasound scanning of the G M muscle, recording of the electrical activity of the muscle, measurement o f knee- and ankle-joint rotations, and measurement of ground reaction force s in six men during walking at 3 km h(-1) on a treadmill. Fascicular length s Were measured from the sonographs recorded, Musculotendon complex length changes were estimated from anatomical and joint kinematic data. Tendon len gth changes were obtained combining the musculotendon complex and fascicula r length-change data. The fascicles followed a different length-change patt ern from those of the musculotendon complex and tendon throughout, the step cycle. Two important features emerged: (i) the muscle contracted near-isom etrically in the stance phase, with the fascicles operating at ca. 50 mm; a nd (ii) the tendon stretched by ca. 7 mm during single support and recoiled in push-off. The behaviour of the muscle in our experiment indicates consu mption of minimal metabolic energy for eliciting the contractile forces req uired to support and displace the body On the other hand, the spring-like b ehaviour of the tendon indicates storage and release of elastic-strain ener gy. Either of the two mechanisms would favour locomotor economy.