The effects of sensory stimulation and arousal on stepping in newborns

Humans produce step-like movements from birth. Stepping has been successfully utilised in treadmill training for infants at risk of developmental delay. Previous studies examining optimal training contexts focused on infants from one month of age: a knowledge gap exists for newborn stepping. This thesis explored stepping in three-day-old newborns and investigated whether tactile-proprioceptive and visual stimuli can improve stepping, whilst also controlling for and examining the effects of arousal. Experiment 1 examined if treadmill stimulation alone would improve stepping. Twenty-one newborns were supported, in four one-minute sessions, on a static or moving treadmill. In Experiment 2, 20 newborns were supported over a frictionenhanced treadmill with four different optic flow conditions: no optic flow, optic flow moving congruent or faster than the treadmill, or in random directions. Video footage, three-dimensional kinematic data (Experiment 2) and electromyography were recorded. Treadmill movement stimulated forward steps but not vertical flexionextension cycles. Cycle durations and muscle burst lengths decreased on the moving treadmill, without showing a linear relationship with treadmill speed. Optic flow on the moving treadmill did not affect step rate or coordination, although random optic flow increased pump rate, inter-joint coupling and hip extension. Fastest optic flow deactivated muscles during the stance phase. Arousal improved step rate, swing and stance definition and interlimb alternation in Experiment 1. In Experiment 2, arousal increased hip extension, inter-joint coupling and muscle activation ratio, without changing temporal and spatial muscle patterns. Improved belt friction may have caused the differences between experiments. In summary, newborns tolerated stepping on the treadmill and with optic flow. Step rate, coordination, kinematics and neuromuscular behaviour were highly variable but could be modified by tactileproprioceptive and visual stimulation. Arousal universally stimulated stepping, likely through increased muscular activity. Findings support the use of treadmill training from birth, although long term effects require further investigation.