Relating Cardiorespiratory Responses to Work Rate During Incremental Ramp Exercise on Treadmill in Children and Adolescents: Sex and Age Differences

Evaluation of cardiopulmonary exercise testing (CPET) slopes such as $$d\mathrm{H}\mathrm{R}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ (cardiac/skeletal muscle function) and $${d \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ (O2 delivery/utilization), using treadmill protocols is limited because the difficulties in measuring the total work rate ( $${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ ). To overcome this limitation, we proposed a new method in quantifying $${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ to determine CPET slopes. 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 $${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ of the subject. CPET slopes were determined by linear regression of the data recorded until the gas exchange threshold occurred. The method to estimate $${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ was substantiated by verifying that: $$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ for treadmill exercise corresponded to an efficiency of muscular work similar to that of cycle ergometer; $$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ (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, $$dHR/d{WR}_{tot}$$ was inversely related to body weight (BW) (r = 0.71) or $$\dot{V}{\text{O}}_{{2,{\text{~peak}}}}$$ (r = 0.66) and $$d{ \dot{V}{\text{O}} }_{2}/d{\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ was not related to BW (r = − 0.01), but had a weak relationship with $$\dot{V}{\text{O}}_{{2,{\text{~peak}}}}$$ (r = 0.28). The proposed approach can be used to estimate $${\mathrm{W}\mathrm{R}}_{\mathrm{t}\mathrm{o}\mathrm{t}}$$ 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.