A preliminary model for estimating mass-specific oxygen uptake during manual wheelchair propulsion from mechanical power and heart rate.

Manual wheelchair users may have reduced physical activity and total energy expenditure, while wearable devices may not adequately capture external mechanical demand during wheelchair propulsion. This pilot study examined whether wheel-level mechanical power combined with heart rate could estimate mass-specific oxygen uptake (V̇O2/kg) during manual wheelchair propulsion. Ten long-term manual wheelchair users aged 29-38 years completed 3-min trials under three progressively loaded conditions on a wheelchair ergometer. Wheel velocity and braking torque were measured, mechanical power was calculated from trial-mean torque and angular velocity, and metabolic variables were assessed using a wearable respiratory gas analyzer. A two-predictor linear regression model was developed, with participant-clustered standard errors and leave-one-participant-out cross-validation (LOPO-CV) for internal evaluation. V̇O2/kg increased across conditions despite lower velocity under the highest load. The final model was V̇O2/kg = 5.5738 + 0.2444P + 0.03587HR. Mechanical power (95% CI: 0.1330-0.3558) and heart rate (95% CI: 0.01342-0.05833) were significant positive predictors. The model explained 72.2% of the variance (R2 = 0.722; adjusted R2 = 0.701). LOPO-CV yielded an RMSE of 1.128 mL O2·kg-1·min-1, an MAE of 0.917 mL O2·kg-1·min-1, and R2 = 0.575. Repeated-measures Bland-Altman analysis of LOPO-CV predictions showed a mean bias of -0.156 mL O2·kg-1·min-1 (95% CI: -0.6259 to 0.2022), with limits of agreement from -2.389 (95% CI: -3.1667 to -1.7711) to 2.077 mL O2·kg-1·min-1 (95% CI: 1.6096 to 2.6636). Mechanical power and heart rate may provide complementary information for estimating metabolic demand during manual wheelchair propulsion. However, the model was developed in a small exploratory sample, was only internally evaluated, and requires external validation before practical application.