Maximum force production: why are crabs so strong?

Durophagous crabs successfully hunt hard-shelled prey by subjecting them to extremely strong biting forces using their claws. Here I show that, for a given body mass; six species of Cancer crabs (Cancer antennarius, Cancer br anneri, Cancer gracilis, Cancer magister, Cancer oregonensis and Cancer pro ductus) were able to exert mean maximum biting forces greater than the forc es exerted in any other activity by most other animals. These strong biting forces were in part a result of the high stresses (740-1350kNm(-2)) genera ted by the claw closer muscle. Furthermore, the maximum muscle stress incre ased with increasing mean resting sarcomere length (10-18 mu m) for the clo ser muscle of the claws of these six Cancer species. A more extensive analy sis incorporating published data on muscle stresses in other animal groups revealed that stress scales isometrically with the resting sarcomere length among species, as predicted by the sliding filament model of muscle contra ction. Therefore, muscle or filament traits other than a very long mean sar comere length need not be invoked in explaining the high stresses generated by crustacean claws.