IN-VIVO ACHILLES-TENDON LOADING DURING JUMPING IN HUMANS

Elastic behaviour of the human tendomuscular system during jumping was investigated by determination of the in vivo Achilles tendon force. A buckle-type transducer was implanted under local anaesthesia around t he right Achilles tendon of an adult subject. After calibration, the A chilles tendon force was recorded together with the triceps surae musc le electromyogram activity and high speed filming and ground reaction force during: a maximal vertical jump from a squat position, a maximal vertical jump from an erect standing position with a preliminary coun termovement, and repetitive submaximal hopping on the spot. Jumping he ights were 33, 40 and 7 cm in the squat, the counter movement, and the hopping positions, respectively. The peak Achilles tendon force and m echanical work by the calf muscles were 2233 N and 34 J in the squat j ump, 1895 N and 27 J in the counter movement jump, and 3786 N and 51 J when hopping. The changes in tendon length were estimated assuming a stiffness constant calculated from the tendon architecture. The percen tages of elastic energy stored in the Achilles tendon during jumping w ere 23%, 17% and 34% of the total calf muscle work in the squat jump, the counter movement jump, and hopping, respectively.