STRESSES IN HUMAN LEG MUSCLES IN RUNNING AND JUMPING DETERMINED BY FORCE PLATE ANALYSIS AND FROM PUBLISHED MAGNETIC-RESONANCE IMAGES

Calculation of the stresses exerted by human muscles requires knowledg e of their physiological cross-sectional area (PCSA). Magnetic resonan ce imaging (MRI) has made it possible to measure PCSAs of leg muscles of healthy human subjects, which are much larger than the PCSAs of cad averic leg muscles that have been used in previous studies, We have us ed published MRI data, together with our own force-plate records and f ilms of running and jumping humans, to calculate stresses in the major groups of leg muscles. Peak stresses in the triceps surae ranged from 100 kN m(-2) during take off for standing high jumps to 150 kN m(-2) during running at 4 m s(-1). In the quadriceps, peak stresses ranged f rom 190 kN m(-2) during standing long jumps to 280 kN m(-2) during sta nding high jumps, Similar stresses were calculated from published meas urements of joint moments, These stresses are lower than those previou sly calculated from cadaveric data, but are in the range expected from physiological experiments on isolated muscles.