Abstract
Summary – The aim of the study was to evaluate the adaptative cardiodynamic adjustment to 4 days of prolonged exercises by the alterations of oxygen pulse and to examine the role of plasma volume (PV) in this adaptative response. Methods and results – Thirty healthy males (aged 24 ± 2 yrs) exercised 5 h per day on cycle ergometer alternately with treadmill, at moderate intensity (58–63 % VO 2max). From the 1st to the 4th day, oxygen pulse was increased by 3 ± 2 ml O 2.beat –1 (cycle p < 0.0001) and 1 ± 1 (treadmill, p = 0.02). Heart rate (HR) decreased (14 ± 4 ± beats min –1, cycle p < 0.0001 and 10 ± 4, treadmill p = 0.001) since VO 2, external mechanical output and running speed were unchanged. The decrease in HR is significantly correlated with PV expansion (+ 8.5 ± 4.7 %) ( p = 0.02, r 2 = 0.403). Conclusion – PV expansion is an important factor in cardiac adaptation to prolonged and repeated exercises. Oxygen pulse drift must be taken into account for exercise intensity and energy expenditure calculation to avoid under estimation.
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