Relating cardiorespiratory responses to work rate during incremental ramp exercise on treadmill in children and adolescents: sex and age differences

PURPOSE: Evaluation of cardiopulmonary exercise testing (CPET) slopes such as [Formula: see text] (cardiac/skeletal muscle function) and [Formula: see text] (O(2) delivery/utilization), using treadmill protocols is limited because the difficulties in measuring the total work rate ([Formula: see text] ). To overcome this limitation, we proposed a new method in quantifying [Formula: see text] to determine CPET slopes. METHODS: CPET’s were performed by healthy patients, (n = 674, 9–18 year) 300 female (F) and 374 male (M), using an incremental ramp protocol on a treadmill. For this protocol, a quantitative relationship based on biomechanical principles of human locomotion, was used to quantify the [Formula: see text] of the subject. CPET slopes were determined by linear regression of the data recorded until the gas exchange threshold occurred. RESULTS: The method to estimate [Formula: see text] was substantiated by verifying that: [Formula: see text] for treadmill exercise corresponded to an efficiency of muscular work similar to that of cycle ergometer; [Formula: see text] (mL min(−1) W(−1)) was invariant with age and greater in M than F older than 12 years old (13–14 years: 9.6 ± 1.5(F) vs. 10.5 ± 1.8(M); 15–16 years: 9.7 ± 1.7(F) vs. 10.6 ± 2.2(M); 17–18 years: 9.6 ± 1.7(F) vs. 11.0 ± 2.3(M), p < 0.05); similar to cycle ergometer exercise, [Formula: see text] was inversely related to body weight (BW) (r = 0.71) or [Formula: see text] (r = 0.66) and [Formula: see text] was not related to BW (r = − 0.01), but had a weak relationship with [Formula: see text] (r = 0.28). CONCLUSION: The proposed approach can be used to estimate [Formula: see text] and quantify CPET slopes derived from incremental ramp protocols at submaximal exercise intensities using the treadmill, like the cycle ergometer, to infer cardiovascular and metabolic function in both healthy and diseased states.