Prevalence of cardio-respiratory factors in the occurrence of the decrease in oxygen uptake during supra-maximal,...

Area of Science:

• Exercise Physiology
• Cardiorespiratory Function
• Sports Science

Background:

• The physiological mechanisms behind the decline in oxygen uptake (V̇O2) at the end of strenuous exercise are not fully understood.
• Previous research has explored various factors, but a definitive explanation remains elusive, particularly in trained athletes.

Purpose of the Study:

• To investigate the physiological reasons for the decrease in oxygen uptake (V̇O2) observed at the cessation of strenuous, constant-power exercise.
• To differentiate between cardio-respiratory and blood metabolic contributions to this end-exercise phenomenon in trained cyclists.

Main Methods:

• Eleven trained cyclists performed exhaustive supramaximal cycling exercise.
• Continuous monitoring of oxygen uptake (V̇O2), ventilation, stroke volume (SV), and heart rate.
• Analysis of arterialized capillary blood for pH, oxygen saturation, lactate, and bicarbonate levels pre- and post-exercise.

Main Results:

• Over 5% decrease in V̇O2 and/or SV occurred in 6 subjects, with 5 showing both.
• V̇O2 decrease correlated with SV reduction, end-tidal O2, and resting forced expiratory volume in 1s (FEV1).
• No significant correlation was found between V̇O2 decrease and blood metabolic markers; reduced lung function suggested respiratory muscle fatigue.

Conclusions:

• The end-exercise decrease in V̇O2 in trained cyclists during strenuous exercise is primarily driven by cardio-respiratory factors.
• Stroke volume limitation and potential respiratory muscle fatigue, rather than blood metabolic responses like acidosis, are key contributors.
• These findings highlight the complex interplay of the cardiovascular and respiratory systems in limiting exercise performance.