![]() The onset of this plateau is typically demarcated by a breakpoint ( bp) in the signal, which has been shown to be a repeatable physiological phenomenon ( 30) that occurs at similar metabolic rates (i.e., V̇ o 2) as other markers of exercise intensity generally measured during RI test ( 31) and constant-load tests ( 31, 32, 35). However, the profile of the near-infrared spectroscopy (NIRS)-derived deoxygenated hemoglobin () signal, a proxy index of local O 2 extraction ( 25), measured at the level of the vastus lateralis (VL) muscle generally shows a linear increase up to a point (i.e., ~75%–85% of the RI test) at which a plateau in the response begins ( 22, 46, 57). When evaluated at the systemic level, the increase in V̇ o 2 is the result of a linear increase in cardiac output (Q̇) and a hyperbolic increase in arteriovenous O 2 difference ( 5, 53). These results suggest that the bp response is not dependent of O 2 driving pressure and that other physiological mechanisms might determine its occurrence.ĭuring a ramp-incremental (RI) test to exhaustion, the rate of oxygen uptake (V̇ o 2) increases linearly to support the increasing metabolic demand until V̇ o 2max is attained ( 5, 27, 36). HYPER and HYPER SWITCH resulted in greater St O 2 and S p O 2 compared with NORM. The PO associated with the bp in HYPER SWITCH (240 ± 23) was not different compared with NORM. ![]() 247 ± 24 W), but it was lower in HYPO (198 ± 31 W) than NORM and HYPER. ![]() The PO associated with bp was not different between NORM and HYPER (246 ± 23 vs. Peak PO was significantly lower in HYPO (290 ± 21 W) and higher in HYPER (321 ± 22 W) and HYPER SWITCH (320 ± 19 W) compared with NORM (311 ± 18 W). PO,, tissue O 2 ( St O 2), and pulse O 2 saturation ( S p O 2) were recorded continuously. Ten physically active male participants reported to the laboratory on four separate occasions to perform an RI test to exhaustion in NORM, HYPO, and HYPER and an RI test to exhaustion with an abrupt increase in F I O 2 (30% HYPER SWITCH) 15 W before the power output (PO) associated with bp in normoxia. This study investigated if 1) the bp is affected by different fractions of inspired O 2 ( F I O 2) and 2) an abrupt change to hyperoxic-inspired gas just before the occurrence of the bp (HYPER SWITCH) would affect the plateau-like response. ![]() During ramp-incremental (RI) exercise to exhaustion, the near-infrared spectroscopy-derived deoxygenated hemoglobin () signal in the vastus lateralis muscle shows a linear increase up to a point at which a plateau-like response is manifested ( bp). ![]()
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