Estimation of energy expenditure during treadmill exercise via thermal imaging

PURPOSE: Non-invasive imaging of oxygen uptake may provide a useful tool for quantification of energy expenditure during human locomotion. A novel thermal imaging method (optical flow) was validated against indirect calorimetry for estimation of energy expenditure during human walking and running. METHODS: Fourteen endurance-trained subjects completed a discontinuous incremental exercise test on a treadmill. Subjects performed 4-min intervals at 3, 5 and 7 kmhr (walking) and at 8, 10, 12, 14, 16 and 18 kmhr (running) with 30 s of rest between intervals. Heart rate, gas exchange and mean accelerations of ankle, thigh, wrist and hip were measured throughout the exercise test. A thermal camera (30 framess) was used to quantify optical flow, calculated as the movements of the limbs relative to the trunk (internal mechanical work), and vertical movement of the trunk (external vertical mechanical work). RESULTS: Heart rate, gross oxygen uptake (mLkg min) together with gross and net energy expenditure (Jkg min) rose with increasing treadmill velocities, as did optical flow measurements and mean accelerations (g) of ankle, thigh, wrist and hip. Oxygen uptake was linearly correlated with optical flow across all exercise intensities (R = 0.96, P