This study was designed to evaluate the dynamic support provided to the human longitudinal arch by the leg muscles active in the stance phase of gait and by the plantar aponeurosis. Ten fresh adult cadaveric specimens were mounted in a materials testing machine. The tendons of the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, peroneus brevis, and Achilles tendon were attached to force transducers. Plantar loads of 0, 350 and 700 N were applied, and the tendons were tensioned individually. The Achilles tendon was tensioned an amount equal to the plantar load; the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, and peroneus brevis were tensioned a fractional amount (depending on the proportion of the cross-sectional area to the gastrocsoleus complex). The angular relationships between the first metatarsal, navicular, and talus were recorded using a 3-dimensional movement analysis system. An additional series of measurements was obtained by positioning the ankle plantarflexed 10 degrees under a plantar load of 350 N. Dorsiflexing the toes with the ankle in a neutral position and loading the foot to 350 N and 700 N permitted an evaluation of the effect of the plantar aponeurosis. The plantar aponeurosis, via dorsiflexion of the toes, contributed the most significant arch support in the sagittal plane with a 3.6 degrees increase between the first metatarsal and talus at 350 N and a 2.3 degrees increase at 700 N. The posterior tibialis tendon consistently provided arch support at plantar loads of 350 N and 700 N. The peroneus longus consistently abducted the forefoot in the transverse plane at 350-N and 700-N load levels. The study provides further insight into the dynamic supporting and deforming forces of the longitudinal arch.