Ratios of cross-sectional areas of muscles and their tendons in a healthy human forearm.

The muscles and tendons in the forearm and hand of a young man, amputated after an accident, have been weighed and measured. The physiological cross-sectional areas of those muscles that had long tendons were 35 +/- 9 (mean and standard deviation) times the cross-sectional areas of the tendons. The mean is very close to the optimum calculated from the theory of Ker, Alexander & Bennett (1988). It implies that the tendons experience stresses of about 11 MPa and strains of about 1.3%, when the muscles exert their maximum isometric forces. Very much larger forces would be needed to break the tendons.