Reliability Of The Microvascular Oxygenation Recovery Response: Halftime Analysis Versus Monoexponential Curve Fitting Analysis

PURPOSE: Mitochondrial function and skeletal muscle endurance characteristics can be noninvasively assessed by analyzing tissue oxygen saturation (StO2) recovery responses using near-infrared spectroscopy (NIRS). This may be of interest to practitioners to offer objective data during rehabilitation regarding return to sport decisions. The purpose of the study was to establish within session and between session reliability of two analysis techniques, halftime (t1/2) and monoexponential curve fitting (mono), when assessing StO2 recovery metrics. METHODS: 17 healthy, active subjects (4 female, 13 male; 24 ± 3 years; 1.74 ± 0.08 m; 72.2 ± 11.7 kg) completed a YMCA submaximal cycling test and a 6-minute active cool-down at 25 W on 2 separate occasions. The cycling protocol was completed twice during session 1 (bout 1 & 2) and once during session 2 (bout 3). StO2 data were collected via NIRS from the vastus lateralis of a randomized leg. The StO2 response from the cool-down was then analyzed using t1/2 and mono methods. The within (bout 1 & 2) and between (bout 1 & 3) session test-retest reliability of 3 microvascular oxygenation recovery response variables were tested by mixed, absolute agreement intraclass correlation coefficients. Statistical significance was set a priori at p < 0.05. RESULTS: Good-excellent within session reliability was found for end exercise StO2 (0.899), StO2 recovery time (0.772), and StO2 recovery amplitude (0.926) using t1/2. Mono revealed moderate-good within session reliability for StO2 recovery time (0.720), end exercise StO2 (0.845), and StO2 recovery amplitude (0.834). When using t1/2, between session reliability was good for end exercise StO2 (0.788) and StO2 recovery amplitude (0.803), and poor for StO2 recovery time (0.411). Between session reliability was moderate for end exercise StO2 (0.729) and StO2 recovery amplitude (0.697), and poor for StO2 recovery time (0.095) when using mono. CONCLUSION: Results of this study suggest both analysis techniques provide reliable within session measures; however, the t1/2 analysis provides slightly better between session reliability. Practitioners are encouraged to use t1/2 analysis when noninvasively assessing mitochondrial function and skeletal muscle endurance. This research was funded by the InQuery Collaborative Research Grant.