On “Impact of Surface Type, Wheelchair Weight, and Axle Position on Wheelchair Propulsion by Novice Older Adults”

Sprigle S. On “Impact of surface type, wheelchair weight, and axle position on wheelchair propulsion by novice older adults.”

The mechanical efficiency of propelling manual wheelchairs is a very important topic. Wheelchair users, clinicians, manufacturers and payers would all benefit from better understanding of mechanical efficiency. However, the measurement of the mechanical efficiency is a nontrivial challenge. Cowan et al deserve a lot of credit for tackling such a difficult problem in their article “Impact of surface type, wheelchair weight, and axle position on wheelchair propulsion by novice older adults.”

The study demonstrated good internal validity in detecting a 4% difference in peak propulsion forces in wheelchairs that differed in mass by 9.1kg. However, the instrumentation used to measure forces altered both the mass and inertia of the wheelchair-occupant system—2 factors that directly affect system energy. This approach, therefore, affects external validity, and the results cannot be extended to infer differences across wheelchair codes. That said, this study adds important information to the body of work into mechanical efficiency of wheelchairs. We now have evidence to suggest that addition of 9kg and an 8cm posterior displacement of axle position adversely affects propulsion biomechanics in an elderly cohort. Improved methodology can lead to mechanical efficiency measurement of different wheelchair models and different wheelchair options.