The Effect of Arm Restriction on Dynamic Stability and Upper Body Responses to Lateral Loss of Balance During Walking: An Observational Study

Background When losing balance, arm movements serve as a mechanical aid to regain stability. However, it remains unclear how arm movements contribute to dynamic stability during recovery from a lateral loss of balance while walking. Our objectives were to 1) quantify the effect of arm restriction on gait stability and upper body velocities; 2) test the association between gait stability and upper body velocities; 3) analyze upper body kinematics and strategies in response to lateral surface translations under different arm-restriction conditions. Methods Fourteen young adults (age 35±2.3; 7 female) experienced unexpected lateral surface translations while walking on a computerized treadmill under three conditions: ‘free arms’, ‘1-arm restricted’ and, ‘2-arms restricted’. Full-body kinematic data were used to extract dynamic stability parameters (measured as the margin of stability in the mediolateral (MoS\_ML) and anterior-posterior (MoS\_AP) directions), and velocity profiles of the head, trunk and shoulders (measured as the area under the curve) for the first step after perturbation onset. Mixed-effect models were used to test our hypotheses. Results A significant main effect for the ‘arm restriction condition’ indicated lower MoS\_AP and higher trunk velocity in the ‘2-arm restricted’ condition compared to the ‘free arms’ condition. MoS\_AP was positively correlated with head velocity and negatively correlated with trunk and shoulder velocities. Additionally, head and trunk movements in the mediolateral (ML) plane were either ‘coupled’ (i.e., their velocities were in the same direction, 55.69% of responses) or ‘decoupled’ (i.e., their velocities were in opposite directions, 44.31% of responses). Furthermore, head and trunk velocities were greater in the ML direction compared to the anterior-posterior (AP) direction. Conclusions Increased upper body velocities contribute to balance responses following lateral perturbations while walking with arm constraints. The greater the arm constraint, the more pronounced the effect on dynamic stability in the AP direction and upper body velocities. The 2-arm restricted condition may be utilized as a method for targeted perturbation-based balance training, focusing on head and trunk responses during walking. ### Competing Interest Statement The authors have declared no competing interest.