Effect of Unweighting Assistance on Sit-to-Stand Mechanics in Healthy Older Adults

Aims: To assess the specificity of assistance provided by a sit-to-stand training device compared to unassisted sit-to-stand by quantifying the change in kinematic strategies and joint kinetic demands with decreasing assistance. Methods: Participants completed the sit-to-stand transfer at 5 randomized assistance levels (unassisted; 40%, 50%, 60%, and 70% body mass) using a sit-to-stand trainer while kinematic and ground reaction force data were collected. Results: Increasing assistance significantly increased total movement time (P =.009, 95% CI_diff =.46 to1.2s), shifted key events earlier (P <.002, 95% CI_diff = 2.0 to10.4%), decreased joint flexion angles (P <.001, 95% CI_diff = 2.4 to 8.2°), and decreased trunk flexion angular momentum (P <.001, 95% CI_diff =.01 to.09 kg•m²/s).). Increasing assistance had the greatest effect on the hip joint, with decreases in peak net joint moment (P <.001, d = 1.8) and angular work (P <.001, d = 2.2). Conclusions: As assistance decreased, mechanics while using the device became more similar to an unassisted sit-to-stand, suggesting promising use for progressive rehabilitation.