Key result
Higher aerobic fitness (VO2peak) was significantly correlated with breakpoints in muscle oxygenation, muscle activation, and respiratory compensation point occurring at a higher relative exercise intensity.
Cross-Sectional (n=64)
No
During incremental ramp exercise, muscle oxygenation, activation, and pulmonary oxygen uptake occur in a specific cascade of events that is shifted to higher relative intensities in individuals with higher aerobic fitness.
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Higher fitness may shift exercise breakpoints; hypothesis-generating for training effects on oxygenation thresholds.
We investigated whether muscle and ventilatory responses to incremental ramp exercise would be influenced by aerobic fitness status by means of a cross-sectional study with a large subject population. Sixty-four male students (age: 21.2 ± 3.2 years) with a heterogeneous peak oxygen uptake (51.9 ± 6.3 mL·min(-1)·kg(-1), range 39.7-66.2 mL·min(-1)·kg(-1)) performed an incremental ramp cycle test (20-35 W·min(-1)) to exhaustion. Breath-by-breath gas exchange was recorded, and muscle activation and oxygenation were measured with surface electromyography and near-infrared spectroscopy, respectively. The integrated electromyography (iEMG), mean power frequency (MPF), deoxygenated [hemoglobin and myoglobin] (deoxy[Hb+Mb]), and total[Hb+Mb] responses were set out as functions of work rate and fitted with a double linear function. The respiratory compensation point (RCP) was compared and correlated with the breakpoints (BPs) (as percentage of peak oxygen uptake) in muscle activation and oxygenation. The BP in total[Hb+Mb] (83.2% ± 3.0% peak oxygen uptake) preceded (P < 0.001) the BP in iEMG (86.7% ± 4.0% peak oxygen uptake) and MPF (86.3% ± 4.1% peak oxygen uptake), which in turn preceded (P < 0.01) the BP in deoxy[Hb+Mb] (88.2% ± 4.5% peak oxygen uptake) and RCP (87.4% ± 4.5% peak oxygen uptake). Furthermore, the peak oxygen uptake was significantly (P < 0.001) positively correlated to the BPs and RCP, indicating that the BPs in total[Hb+Mb] (r = 0.66; P < 0.001), deoxy[Hb+Mb] (r = 0.76; P < 0.001), iEMG (r = 0.61; P < 0.001), MPF (r = 0.63; P < 0.001), and RCP (r = 0.75; P < 0.001) occurred at a higher percentage of peak oxygen uptake in subjects with a higher peak oxygen uptake. In this study a close relationship between muscle oxygenation, activation, and pulmonary oxygen uptake was found, occurring in a cascade of events. In subjects with a higher aerobic fitness level this cascade occurred at a higher relative intensity.
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Boone et al. (2015) conducted a cross-sectional in Healthy (Physically active) (n=64). Aerobic fitness level (VO2peak) vs. Lower aerobic fitness was evaluated on Correlation between VO2peak and the breakpoint in deoxygenated hemoglobin/myoglobin (deoxy[Hb+Mb]) as %VO2peak (r=0.76, p=<0.001). Higher aerobic fitness (VO2peak) was significantly correlated with breakpoints in muscle oxygenation, muscle activation, and respiratory compensation point occurring at a higher relative exercise intensity.
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