Maximal oxygen uptake (VO2max), as demonstrated by the Fick Equation, is equal to maximal cardiac output multiplied by the arterial-venous difference, whereas muscle oxygen saturation (SmO2) measures the difference between oxygenated and deoxygenated hemoglobin in a muscle. SmO2 has previously demonstrated a strong inverse relationship to both VO2and Heart Rate (HR) for both running and cycling. Although previous research has examined the metabolic responses to both cycling and running, no studies have examined the responses of SmO2, VO2, and HR during a customized graded exercise test (GXT) with a verification phase (VP). Purpose: The purpose of these case studies was to examine the local and whole-body metabolic responses (SmO2, pulmonary VO2, and HR) to a customized GXT with a supramaximal VP while running on a treadmill and submaximal VP while cycling. Methods: Three subjects (see Table 1 for demographics) completed a customized GXT followed by a VP. After the customized GXT, 2 competitive distance runners performed a supramaximal square-wave VP at the subsequent stage of the initial test while a recreationally-active cyclist completed a submaximal VP at a fixed intensity of 2 stages minus the end-GXT power for the attainment of VO2max, HRmax, and SmO2min. Results: As VO2 and HR increased, reaching maximal values for both running and cycling, SmO2 demonstrated an inverse relationship by decreasing to a minimal value (SmO2min) on both the GXT and verification bouts (see Table 1 for results). Conclusions: The HR and SmO2 values remained consistent, with SmO2min values remaining within approximately 1% for the GXT and VP. Practical Applications: SmO2 may be used as an indicator of muscular exertion and used to monitor exercise intensity within various domains of intensity. By identifying SmO2min, one will have context to percentage of maximal muscular effort, without influences related to HR monitoring (e.g., heat, caffeine).
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