Methods for determining three-dimensional wheelchair pushrim forces and moments: a technical note

Area of Science:

• Biomechanics
• Rehabilitation Engineering
• Human Movement Science

Background:

• Manual wheelchair propulsion lacks standardized analysis systems for pushrim forces and moments.
• Variability in reported wheelchair propulsion data may stem from differing calculation methods for key variables.

Purpose of the Study:

• To present novel tools and analytical techniques for direct measurement and calculation of upper limb biomechanics during manual wheelchair propulsion.
• To establish a framework for accurate analysis of wheelchair propulsion forces and moments.

Main Methods:

• Development of a system for direct measurement of global coordinate forces (Fx, Fy, Fz) and moments.
• Implementation of analytical techniques to calculate radial (Fr) and tangential (Ft) forces, point of force application (PFA), and hand moment (Mhz).

Main Results:

• The point of force application (PFA) can be accurately calculated from kinetic data.
• Averaged 0.2 radian difference observed when comparing PFA from kinetic data versus kinematic data (second metacarpophalangeal joint).
• Using PFA provides a more accurate tangential force measurement compared to previous methods assuming negligible hand-moment contribution.

Conclusions:

• The presented methods offer a standardized framework for analyzing wheelchair propulsion forces and moments.
• Improved accuracy in calculating PFA and tangential forces enhances the reliability of wheelchair biomechanics research.
• Direct measurement and refined analytical techniques address inconsistencies in wheelchair propulsion studies.