Redefining the Manual Wheelchair Stroke Cycle: Identification and Impact of Nonpropulsive Pushrim Contact

Objectives: To create a comprehensive definition of the manual wheelchair stroke cycle, which includes multiple periods of pushrim contact, and to show its improved clinical benefit to wheelchair propulsion analyses. Design: Cross-sectional biomechanics study. Setting: Three motion analysis laboratories. Participants: Persons (N=54) with paraplegia who use a manual wheelchair. Interventions: Not applicable. Main Outcome Measures: Pushrim forces, axle moments, and contact angles measured during wheelchair propulsion. Results: Total force on the pushrim was used to define pushrim contact and positive axle moment was used to identify the included period of propulsive contact. During most strokes, periods of nonpropulsive contact existed before and after propulsive contact. Within these periods, braking moments were applied to the pushrim, resulting in negative power output, or power loss. Including nonpropulsive data decreased mean stroke moment and power. The magnitude and the angle over which braking moments and power loss occurred increased with wheel speed. Mean braking moment and power loss within the initial contact period were significantly (P<.001) related to stroke pattern. Conclusions: The proposed definition of the stroke cycle provides a thorough and practical description of wheelchair propulsion. Researchers and clinicians should use this definition to understand and minimize the impact of nonpropulsive contact throughout the stroke.