A, the treadmill speed at which the highest percentage of stepping was seen is shown for 8 of the 9 infants as a function of the infant's age. One subject did not have sufficiently long trials to make an accurate estimate. B, 6 of these 9 subjects stepped at an intermediate treadmill speed of 0.2 m s−1. At this constant speed, infants of all ages showed similar step cycle durations, r = 0.13, P > 0.05.