Estimation of oxygen uptake during fast running using accelerometry and heart rate

Previous investigations have reported that accelerometer counts plateau during running at increasingly faster speeds. Purpose: To assess whether biomechanical and/or device limitations cause this phenomenon and the feasibility of generating oxygen uptake (VO2) prediction equations from the combined use of accelerometry and heart rate during walking and running. Methods: Sixteen endurance-trained subjects completed two exercise tests on a treadmill. The first was a continuous incremental test to volitional exhaustion to determine ventilatory threshold and peak VO2. The second was a discontinuous incremental exercise test while walking (3, 5, and 7 km(.)h(-1)) and running (8, 10, 12, 14, 16, 18, and 20 km(.)h(-1), or until volitional exhaustion). Subjects completed 3 min of exercise at each speed, followed by 3-5 min of recovery. Activity counts from uni- and triaxial accelerometers, heart rate, and gas exchange were measured throughout exercise. Results: All accelerometer outputs rose linearly with speed during walking. During running, uniaxial accelerometer outputs plateaued, whereas triaxial output rose linearly with speed up to and including 20 km(.)h(-1). Prediction of VO2 during walking and running using heart rate (R-2 = 0.42 and 0.59, respectively), accelerometer counts (R 2 = 0.48-0.83 and 0.76, respectively), the combined methodologies (R-2 = 0.54-0.85 and 0.80, respectively), and the combined methodologies calibrated with individual data (R-2 = 0.99-1.00 and 0.99, respectively) was completed by linear regression. Conclusions: Uni- and triaxial accelerometer outputs have a linear relationship with speed during walking. During running, uniaxial accelerometer outputs plateau because of the biomechanics of running, whereas triaxial accelerometer output has a linear relationship. The combined methodologies predict VO2 better than either predictor alone; a subject's individually calibrated data further improves VO2 estimation.