Movement Strategies for Maintaining Standing Balance 3 during Arm Tracking in People with Multiple Sclerosis 4 5 Matthew

21 The purpose of this study was to quantify hip and ankle movement strategies during a standing, 22 arm tracking task in people with multiple sclerosis (MS). Full body kinematics and kinetics were 23 assessed using motion analysis cameras and force plates in 9 MS and 9 age-matched controls. 24 While standing, participants used their dominant hand to track a target moving around a large 25 horizontal or vertical figure-eight on a screen in front of them. The target moved at constant 26 speed, or linearly increasing speeds, with a frequency between 0.05 Hz and 0.35 Hz. Hip and 27 ankle moments and angles during tracking were calculated from kinematic and kinetic 28 measurements. The ratio of peak-to-peak (PP) hip/ankle moments (kinetics) and angles 29 (kinematics) were calculated to determine the strategies of the hips and ankles used to maintain 30 balance during arm movements. The center-of-mass (CoM) root mean square (RMS) 31 acceleration was calculated as a measure of overall balance performance. The MS group 32 produced larger PP hip/ankle moments at all speeds, compared with the control group (p<0.05). 33 The CoM RMS acceleration increased with tracking speed for both groups but was not 34 significantly different between groups. Additionally, the ratios of hip/ankle moments were 35 highly correlated with the Berg Balance Scale during horizontal steady speed tracking in MS. 36 These results suggest that people with MS increase the use of the hip during standing arm 37 tracking compared to age-matched controls. This adapted strategy might allow people with MS 38 to achieve similar balance performance to controls, possibly increasing the importance of the hip 39 in maintaining balance during voluntary movements. 40