Measuring energy expenditure using heart rate to assess the effects of wheelchair tyre pressure

Objective: To investigate the effects of wheelchair tyre pressure on mechanics and energy and explore the use of heart rate as a measurement of energy expenditure. Design: A single factor repeated measures design was used. Four tyre pressures (100, 75, 50, 25 psi) represented a change of workload. Each subject wheeled at a constant self-selected wheeling velocity for 8 min. A total of four trials were completed with a 10-min rest between trials. Oxygen consumption, heart rate and distance travelled were collected during each trial. Subjects: Three women and I I men with spinal cord injury. The mean age for the whole group was 34.5 years. The range of lesion level was T4-L1. Results: There was a significant increase is energy expenditure when tyres were deflated to 50 psi from 100 psi. The mean correlation between heart rate and oxygen consumption was 0.74 for all subjects. For the subjects with lesions above T6 and T6 and below the correlations were 0.55 and 0.82, respectively. Conclusions: Tyre pressures below 50% inflation add an additional 25% increase in energy expenditure during wheeling. This could be detected using oxygen consumption or heart rate, as heart rate was shown to have a good correlation with oxygen consumption in the spinal cord injured with lesions below T5. Heart rate does have its limitations and it should only be used to measure within-subject differences.