Key result
A substantially lower cardiac output response to exercise did not result in altered ratings of perceived exertion or exercising muscle deoxygenation compared to a higher response (P>0.4).
Why the study?
Do interindividual differences in cardiac output during submaximal exercise explain differences in exercising muscle oxygenation and ratings of perceived exertion in healthy males?
Observational (n=31)
Do interindividual differences in cardiac output during submaximal exercise explain differences in exercising muscle oxygenation and ratings of perceived exertion in healthy males?
p-value: p=>0.4
Substantially lower cardiac output response to exercise does not alter exercising muscle deoxygenation, suggesting compensatory blood flow redistribution protects muscle oxygen delivery.
Lower cardiac output may not limit perceived exertion or muscle oxygenation during exercise; leaves open central hemodynamic determinants of exercise tolerance.
Considerable interindividual differences in the Q˙-V˙O2 relationship during exercise have been documented but implications for submaximal exercise tolerance have not been considered. We tested the hypothesis that these interindividual differences were associated with differences in exercising muscle deoxygenation and ratings of perceived exertion (RPE) across a range of submaximal exercise intensities. A total of 31 (21 ± 3 years) healthy recreationally active males performed an incremental exercise test to exhaustion 24 h following a resting muscle biopsy. Cardiac output (Q˙ L/min; inert gas rebreathe), oxygen uptake (V˙O2 L/min; breath-by-breath pulmonary gas exchange), quadriceps saturation (near infrared spectroscopy) and exercise tolerance (6-20; Borg Scale RPE) were measured. The Q˙-V˙O2 relationship from 40 to 160 W was used to partition individuals post hoc into higher (n = 10; 6.3 ± 0.4) versus lower (n = 10; 3.7 ± 0.4, P < 0.001) responders. The Q˙-V˙O2 difference between responder types was not explained by arterial oxygen content differences (P = 0.5) or peripheral skeletal muscle characteristics (P from 0.1 to 0.8) but was strongly associated with stroke volume (P < 0.05). Despite considerable Q˙-V˙O2 difference between groups, no difference in quadriceps deoxygenation was observed during exercise (all P > 0.4). Lower cardiac responders had greater leg (P = 0.027) and whole body (P = 0.03) RPE only at 185 W, but this represented a higher %peak V˙O2 in lower cardiac responders (87 ± 15% vs. 66 ± 12%, P = 0.005). Substantially lower Q˙-V˙O2 in the lower responder group did not result in altered RPE or exercising muscle deoxygenation. This suggests substantial recruitment of blood flow redistribution in the lower responder group as part of protecting matching of exercising muscle oxygen delivery to demand.
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Bentley et al. (2018) conducted an observational in Healthy (n=31). Lower cardiac output response (Q˙-V˙O2 relationship) vs. Higher cardiac output response was evaluated on Quadriceps deoxygenation during exercise (p=>0.4). A substantially lower cardiac output response to exercise did not result in altered ratings of perceived exertion or exercising muscle deoxygenation compared to a higher response (P>0.4).
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