OXYGEN DELIVERY LIMITS MAXIMAL EXERCISE
McMillan, D. W., Edmunds, R. M., Sanchez, E., & Astorino, T. A. (2014). Central hemodynamic response to various maximal exercise protocols. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 1317.
“During incremental exercise to volitional exhaustion, it is evident that stroke volume (SV) increases and plateaus at submaximal work rates, although a linear increase in stroke volume has been revealed in trained athletes progressively to maximal oxygen uptake (VO2max). However, some data show that at near-maximal intensities, stroke volume declines before attainment of VO2max. This phenomenon has been observed in trained individuals completing traditional incremental protocols (RAMP) and supramaximal constant-load exercise. The effect of exercise structure, such as the self-paced and decremental protocols which have been shown to augment VO2max, on central hemodynamics remains unknown. Furthermore, the influence of fitness level on the stroke volume response to maximal exercise tests has not been examined.”
This study observed hemodynamic responses to completion of a traditional incremental and two novel maximal exercise protocols in Ss of various fitness levels (M+F = 30). Ss initially completed incremental protocols followed by a decremental test on a subsequent day. Over the next two sessions, which were randomized and separated by 48 hours, Ss performed a self-paced and an additional decremental test. During exercise, gas exchange data were measured via indirect calorimetry and hemodynamic function was assessed via thoracic impedance. Differences in oxygen uptake, heart rate, stroke volume, and cardiac output during exercise and across protocols were examined.
The self-paced protocol elicited a significantly higher maximum cardiac output and maximum heart rate when compared to the incremental protocols. Although there was no effect of protocol on maximum stroke volume, Ss with VO2max >45 mL/kg/min displayed a significant decline in stroke volume prior to attainment of VO2max across all protocols. Increased maximum cardiac output in the self-paced trial mediated a significantly greater VO2max compared to the incremental protocols.
Implication. Stroke volume declined suddenly prior to the attainment of VO2max in persons of moderate- to high-fitness levels. Protocol-induced increases in cardiac output augmenting VO2max suggest that oxygen delivery is a key limitation to maximal exercise.
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