Effects of single-variable biofeedback on wheelchair handrim biomechanics.
To determine the effects of single-variable biofeedback on select wheelchair propulsion variables. Within-subject comparisons. Biomechanics laboratory. Manual wheelchair users (N=31). Biofeedback on braking moment, cadence, contact angle, peak force, push distance, and smoothness were presented on a large monitor during propulsion on a motor-driven treadmill. For each variable, subjects were asked to make a maximum improvement, as well as a targeted 10% improvement for cadence, contact angle, peak force, and push distance. Relative differences (%) in each variable between the normal propulsion trial and the biofeedback trials. Subjects were able to interpret and respond to the biofeedback successfully. For the maximum change conditions, significant improvements were made to all variables except smoothness, with individual improvements of 11% in peak force, 31% in contact angle, 44% in braking moment, 64% in cadence, and 255% in push distance. For the 10% target conditions, improvements were achieved to within 1% for all variables except peak force, which was a difficult variable for most subjects to control. Cross-variable interactions were found for most variables, particularly during the maximum change conditions. Minimizing cadence led to a 154% increase in peak force, suggesting the need for multi-variable feedback if multiple training objectives, such as reducing cadence and peak force simultaneously, are desired. While subjects were unable to significantly change smoothness, efforts to push more smoothly led to improvements across most outcome variables. Biofeedback can be used to improve specific aspects of wheelchair propulsion. Cadence, contact angle, and push distance are well controlled by wheelchair users, and may be useful for clinical propulsion training. Clinicians should be aware of and comfortable with any cross-variable effects resulting from single-variable biofeedback training.