Metabolic Cost of Wheelchair Propulsion Using an Ergonomic Hand Drive Mechanism

Abstract

Conventional manual wheelchair (CMW) use is associated with a high prevalence of shoulder and wrist pain, which may interfere with mobility and lead to increased risk of cardiovascular problems. Previous lever-activated propulsion designs have been shown to shift and reduce shoulder muscular demands, decreasing the risk of incurring repetitive strain injuries. However, these designs do not consider the anthropometrics of the user (height, arm length, etc.). The novel ergonomic hand drive mechanism (EHDM) used in this study was designed to shift awkward postures while accommodating different users without additional metabolic cost. PURPOSE: To evaluate metabolic cost (VO2 and HR) while using an EHDM. METHODS: Eight adult full-time manual wheelchair users participated (46.8±21.8 yrs, 74.0±12.7 kg, 174.6±13.6 cm). All participants were medically and functionally stable and at least six months post injury. Participants propelled around a circuit for three and a half minutes at a self-selected pace in a CMW and then again in the same chair fitted with the hand drive mechanism for a total of two trials. VO2 and HR were recorded using a portable device while distance, velocity and push frequency were measured manually. Velocity, distance traveled, push frequency, VO2 per meter, and heart rate were compared by wheelchair condition for the last 30 seconds of each trial using paired t-tests (α=0.05). RESULTS: The CMW condition resulted in more distance traveled (28.7±15.1 m vs. 20.0±8.7 m, p=0.049) as well as greater velocity (0.957±0.5 m/s vs. 0.667±0.3 m/s, p=0.049) than the EHDM condition. No significant differences were found between the two conditions for number of pushes (26.3±5.8 vs. 27.0±5.3, p=0.683), VO2 efficiency (0.24±0.1 ml/kg/min/m vs. 0.31±0.1 ml/kg/min/m, p=0.08), or HR (102.6±14.2 bpm vs. 105.5±15.7 bpm, p=0.635). CONCLUSION: The results demonstrate that participants avoided additional metabolic costs although performance (velocity and distance) was sacrificed with the EHDM. Modifications to the EHDM (e.g. addition of gearing) could rectify the performance decrement. Supported by the Clinical and Translational Science Institute Pilot & Collaborative Research Projects (NIH). The hand drive mechanism used in this study is the intellectual property of Shands Healthcare.