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

Background: Individuals who have experienced a hemiparetic stroke often demonstrate motor deficits in both their trunk and arm, which can affect their overall functionality. In the affected arm, an involuntary coupling of torques in the fingers, wrist, and elbow during shoulder abduction, referred to as the flexion synergy, further diminishes reaching capabilities.

Although previous research has identified deficits in the trunk, such as weakness and altered coordination, the impact of active trunk control on reaching performance in stroke patients remains unclear. This study aimed to investigate whether the active engagement of trunk control, coupled with progressive shoulder abduction loading, influences reaching performance in both stroke and control participants.

Methods: The research involved 13 adults: 9 who had suffered a hemiparetic stroke (with an average age of 64.11 {+/-} 6.57 years) and 4 age-matched control participants (with an average age of 66.25 {+/-} 0.96 years). All participants engaged in seated reaching tasks using the ACT-3D robotic device on a frictionless table. The tasks included lifting against 25% and 50% maximum voluntary tone (MVT) while the trunk was either restrained or unrestrained.

A linear mixed effects model was utilized, incorporating limb as a random factor, and group, trunk restraint, and shoulder abduction load as fixed factors to analyze changes in reaching distance, expressed as a percentage of limb length (% LL).