Quantifying the Effect of Trunk Postural Control on Reaching with Progressive Shoulder Abduction Loading in Hemiparetic Stroke

Background: Adults post hemiparetic stroke exhibit motor deficits in both the trunk and arm that impact function. In the paretic arm, involuntary coupling of torques in the fingers, wrist, and elbow during shoulder abduction, known as the flexion synergy, reduces reaching function. While there have been deficits shown to exist at the trunk such as weakness and altered coordination, it remains unclear if active trunk control compounds reaching deficits. This study examined if active trunk control with progressive shoulder abduction loading impacts reaching function in stroke and control participants. Methods: Thirteen adults, 9 post hemiparetic stroke (64.11 {+/-} 6.57 years) and 4 age matched controls (66.25 {+/-} 0.96 years), completed seated reaching tasks with the trunk restrained and unrestrained while reaching with their arm coupled to the ACT-3D robotic device on a frictionless table, lifting against 25% MVT, and 50% MVT. A linear mixed effects model was used with limb as a random factor, and group, trunk restraint, and shoulder abduction load as fixed factors for quantifying changes in reaching distance expressed percent limb length (% LL). Findings: Across limbs (paretic, non-paretic, control), when the trunk was un-restrained, reaching distance was reduced (p<.05). Further reduction in reaching distance was observed in the paretic compared to the non-paretic and control (p< .05) limbs. Reaching velocity was fastest for controls (3.26 {+/-} 1.52 m/s) compared to non-paretic (3.24 {+/-} 1.19 m/s) and paretic (1.59 {+/-} 1.32 m/s) limbs in stroke. Shoulder abduction loading had an effect on reaching distance in the paretic limb (p<.05) Table: .83 {+/-} .13 % LL, 25% MVT: .77 {+/-} .14 % LL, 50% MVT: .76 {+/-} .15 %LL). Greater shoulder excursion occurred during non-paretic limb reaching compared to the paretic limb with an increase of 14.80 mm (p<.05). Conclusion: Active trunk control impacted reaching function and further reduced reaching distance in chronic hemiparetic stroke participants. However, the primary driver of reduced reaching distance was the flexion synergy. While reaching speed increased the demand at the trunk, excursions were comparable during paretic and non-paretic limb reaching, suggesting that overall trunk function was intact during this paradigm.