Abstract
Stepping on ground can be evoked in human neonates, though it is rather irregular and stereotyped heel-to-toe roll-over pattern is lacking. Such investigations can provide insights into the role of contact- or load-related proprioceptive feedback during early development of locomotion. However, the detailed characteristics of foot placements and their association with motor patterns are still incompletely documented. We elicited stepping in 33 neonates supported on a table. Unilateral limb kinematics, bilateral plantar pressure distribution and EMG activity from up to 11 ipsilateral leg muscles were recorded. Foot placement characteristics in neonates showed a wide variation. In ~25% of steps, the swinging foot stepped onto the contralateral foot due to generally small step width. In the remaining steps with separate foot placements, the stance phase could start with forefoot (28%), midfoot (47%), or heel (25%) touchdowns. Despite forefoot or heel initial contacts, the kinematic and loading patterns markedly differed relatively to toe-walking or adult-like two-peaked vertical force profile. Furthermore, while the general stepping parameters (cycle duration, step length, range of motion of proximal joints) were similar, the initial foot contact was consistently associated with specific center-of-pressure excursion, range of motion in the ankle joint, and the center-of-activity of extensor muscles (being shifted by ~5% of cycle toward the end of stance in the “heel” relative to “forefoot” condition). In sum, we found a variety of footfall patterns in conjunction with associated changes in motor patterns. These findings suggest the potential contribution of load-related proprioceptive feedback and/or the expression of variations in the locomotor program already during early manifestations of stepping on ground in human babies.
Highlights
Different types of stepping-like responses can be evoked in human neonates
In remaining 75% of separated foot placements (1078 steps), the initial foot contact at touchdown occurred at heel (25%), midfoot (47%), and forefoot (28%) (Figure 1B, right panel)
We aimed to classify the neonatal steps in relation to the initial foot contact (Figure 1) in order to describe the detailed characteristics of foot placements, plantar pressure distribution and their possible relation to motor patterns
Summary
Different types of stepping-like responses can be evoked in human neonates. Visual stimulation can elicit stepping-like leg movements in the air, whose features depend on the specific characteristics of the visual stimuli (Barbu-Roth et al, 2014). Neonatal Stepping on ground.This typically involves alternating limb movements at relatively slow speeds and exaggerated foot lift, and it is rather irregular. Other substantial differences relative to mature gait are excessive co-contraction of many leg muscles (Forssberg, 1985; Okamoto et al, 2001; Dominici et al, 2011; Teulier et al, 2012) and co-activation of motoneuron pools at both lumbar and sacral levels of the spinal cord (Ivanenko et al, 2013). Functional sensory-motor circuitry, adult-like footfall pattern and transition to coordinated activity of motoneurons emerge with specific timing during development (Thelen and Cooke, 1987; Lacquaniti et al, 2012; Yang et al, 2015)
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