Low effective mechanical advantage of giraffes’ limbs during walking reveals trade-off between limb length and locomotor performance

A giraffe's long legs can work against its muscles. The same limbs that lift its mouth towards high leaves give forces from the ground a long lever to turn its joints. Muscles must oppose that turning force, and their own leverage does not necessarily increase enough to match it.

Christopher Basu and John Hutchinson combined a computer model built from a giraffe forelimb with fourteen recorded walking steps from one adult reticulated giraffe. Cameras tracked the movement while a force platform measured the push against the ground. They then compared simplified models of a giraffe, an okapi and the large, extinct giraffe relative Sivatherium.

The walking giraffe's estimated limb leverage meant roughly three units of muscle force were required for each unit of ground force. That was substantially worse than expected by extending the pattern seen in smaller mammals. The extinct relative's shorter, more robust limbs offered better leverage in the models. Because the measurements concerned walking, a restriction on running performance remains an interpretation rather than a direct result. Height gives giraffes access to food, but supporting that height creates a mechanical demand with every step.