Heart rate variability (HRV) is used to assess the autonomic nervous system’s (ANS) activity on the heart, while skeletal muscle oxygenation (SmO2) measures how well muscles uptake oxygen from the blood. Both measurements have demonstrated strong associations with cardiorespiratory fitness and are altered with increased exercise workloads. Both have been used to assess athletic performance. While the gold standard for assessing cardiorespiratory fitness is VO2 max testing, several situations preclude the usage of a true VO2 max. Purpose: To determine if HRV and SmO2 possess predictive qualities to accurately assess cardiorespiratory fitness levels. Methods: Thirty-six healthy fit individuals (n = 22 men; n = 14 women; age 37.6 + 12.4 yr; BF% 19.2 + 7.1%; VO2max 41.8 + 7.4 ml/kg/min) completed a single VO2 max ramp protocol treadmill test while wearing an infrared oxyhemoglobin (MOXY) Sensor to assess SmO2 while HRV was assessed via Polar (Bluetooth monitor (Polar H7)) heart rate (HR) monitor. The MOXY Sensor was placed on the lateral-posterior belly of the gastrocnemius while the Polar HR monitor was placed on the distal third of the sternum using an elastic belt. The data was analyzed using a Pearson Correlation to compare SmO2, HRV indices, and VO2max associations. In addition, a multiple linear regression analysis was performed to examine the relationship between HRV indices and SmO2 to VO2 max. All analyses were performed using SPSS (v. Results: There was a significant correlation between VO2 max, mean of RR intervals (mRR) (r = 0.440, p = 0.007), and THb Max (r = 0.509, p = 0.002). mRR and THb Max were able to significantly predictive (r2 = 0.365, p = 0.001) VO2 max outcomes. Conclusion: The combination of SmO2 measurements and HRV can assist in predicting VO2 max levels, but further research is needed to determine the accuracy at which it will predict. This can be a useful and simple method for predicting cardiorespiratory fitness when a VO2 max test is unavailable, or an individual is unfit to perform one. This can aid in better exercise prescription for chronic diseased individuals.



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