Title : Bracing of the Trunk and Neck has a Differential Effect on Head Control during Gait

1 During gait, the trunk and neck are believed to play an important role in dissipating the transmission 2 of forces from the ground to the head. This attenuation process is important to ensure head control is 3 maintained. The aim of the current study was to assess the impact of externally restricting the motion of 4 the trunk and/or neck segments on acceleration patterns of the upper body and head and related trunk 5 muscle activity. Twelve healthy adults performed 3 walking trials on a flat, straight 65 m walkway, under 6 four different bracing conditions: (1) Control-no brace, (2) Neck-braced, (3) Trunk-braced, and (4) Neck-7 trunk braced. 3D acceleration from the head, neck (C7) and lower trunk (L3) were collected as were 8 muscle activity from trunk. Results revealed that, when the neck and/or trunk were singularly braced, an 9 overall decrease in the ability of the trunk to attenuate gait related oscillations was observed which led to 10 increases in the amplitude of vertical acceleration for all segments. However, when the trunk and neck 11 were braced together, acceleration amplitude across all segments decreased in line with increased 12 attenuation from the neck to the head. Bracing was also reflected by increased activity in erector spinae, 13 decreased abdominal muscle activity and lower trunk muscle co-activation. Overall, it would appear that 14 the neuromuscular system of young, healthy individuals was able to maintain a consistent pattern of head 15 acceleration irrespective of the level of bracing and that priority was placed over the control of vertical 16 head accelerations during these gait tasks.