The foot has been studied in walking, running and jogging using high speed cinema photography in the laboratory for gait analysis in the Shriner's Hospital for Crippled Children, San Francisco. During running, as well as in walking, the extrinsic toe flexors restrain progression of the tibia. The extrinsic extensors accelerate the tibia over the fixed foot. The intrinsic toe muscles function from mid-stance to lift-off when the subject runs on his toes. In sprinting, the intrinsics are active throughout the weight-bearing phase.