The effect of walking speed on superficial lower limb muscles, such as tibialis anterior and triceps surae, is well established. However, there are no published data available for tibialis posterior - a muscle that plays an important role in controlling foot motion. The purpose of this study was to characterise the electromyographic timing and amplitude of selected lower limb muscles across five walking speeds. Thirty young adults were instructed to walk barefoot while electromyographic activity was recorded from tibialis posterior and peroneus longus via intramuscular electrodes, and medial gastrocnemius and tibialis anterior via surface electrodes. At faster walking speeds, peak electromyographic amplitude increased systematically during the contact and midstance/propulsion phases. Changes in the time of peak amplitude were also observed for tibialis posterior, tibialis anterior and peroneus longus activity; however, these were muscle and phase specific. During contact phase, peak electromyographic amplitude for tibialis posterior and peroneus longus was similar across very slow to slow walking speeds. During midstance/propulsion phase, peak electromyographic amplitude for tibialis posterior and medial gastrocnemius was similar across very slow to slow walking speeds. These findings may reflect a relatively higher than expected demand for peroneus longus and tibialis posterior to assist with medio-lateral foot stability at very slow speeds. Similarly, peak amplitude of medial gastrocnemius was also relatively unchanged at the very slow speed, presumably to compensate for the reduced forward momentum. The data presented in this study may serve as a reference for comparing similarly matched participants with foot deformity and/or pathological gait.