Heavy cycling exercise at fixed heart rate prevent the decline of stroke volume and delay time to exhaustion in trained adolescents

Abstract

Summary Previous studies showed an interaction between the response over time of oxygen uptake ( V ˙ O 2 ), the drift of heart rate (HR) and the drop of stroke volume (SV) during constant workload exercise. Objective To compare the responses of oxygen uptake ( V ˙ O 2 ) and stroke volume (SV) in exhaustive exercises performed at a constant workload or at heart rate steady state. Methods Nine well-trained adolescents (14.6 ± 1.1 years, 1.7 ± 0.1 m and 59.7 ± 14.8 kg) performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with V ˙ O 2 max ( p V ˙ O 2 max ) and the power inducing SVmax (pSVmax). Two days later, they performed two continuous exercises at pSVmax (tlimpSVmax: 10 min 10 s ± 6 min 41 s) and at a heart rate steady state associated with SVmax (tlimHR@SVmax: 21 min 04 s ± 13 min 20 s, P V ˙ O 2 , HR and SV values were continuously measured by impedance. Results Maximal values of blood lactate and V ˙ O 2 were not different between the three exercises, but maximal cardiac output and SV values were higher in tlimHR@SVmax (21.3 ± 8.6 L·min−1 and 112 ± 46 mL·beat−1) compared to tlimpSVmax (19.8 ± 7.6 L·min−1 and 102 ± 40 mL·beat−1, P V ˙ O 2 values significantly fell before both exercise exhaustions (P Conclusion According to the exercise modalities, the interactive effects of increased HR or SV are responsible of the V ˙ O 2 max attainment during exhaustive exercise.