Minyoung Kwak1, Pasquale J. Succi1, Taylor K. Dinyer-McNeely2, Caleb C. Voskuil3, Brian Benitez1, Haley C. Bergstrom1. 1University of Kentucky, Lexington, KY. 2Oklahoma State University, Stillwater, OK. 3Texas Christian University, Fort Worth, TX.

BACKGROUND: Fatigue thresholds provide information about unique physiological or perceptual responses to exercise that are used to develop individualized cardiorespiratory endurance prescriptions. The ventilatory threshold (VT) and respiratory compensation point (RCP) estimate the demarcation of the moderate and heavy, and the heavy and severe exercise intensity domains, respectively. The physical working capacity at the rating of perceived exertion thresholds (PWCRPE) estimates the maximal power output that can be sustained for an extended period of time without an increase in RPE. The critical heart rate (CHR) is the highest heart rate (HR) that can be sustained for an extended period of time. This study compared the PWCRPE, power output (P) at the CHR (PCHR), P at respiratory compensation point (PRCP), and P at ventilatory threshold (PVT). METHODS: Eleven subjects (Mean ± SD: Age 25 ± 4 yrs) completed a graded exercise cycle ergometer test (GXT) to determine PVT, PRCP, and the P at V O2 peak (PP). The PWCRPE and PCHR were determined from 4 constant P trials (85 - 100% PP), and time to exhaustion (TLim), HR, and RPE were recorded. The PWCRPE was determined from the slope coefficients for the RPE versus time relationship for 4 constant P rides that were plotted as a function of P. The CHR was determined from the total heart beats (HBlim) versus TLim, and PCHR was estimated from linear regression of the P versus HR. RESULTS: The PWCRPE (195 ± 51W; 74 ± 4% PP), PRCP (204 ± 55W; 78 ± 5% PP), and PCHR (207 ± 65W; 78 ± 10% PP) were not different from each other, but each threshold was greater (p = 0.019 - 0.025) than the PVT (160 ± 34W; 62 ± 8% PP). The PWCRPE, PRCP, PCHR, and PVT were all moderately to highly correlated (r = 0.735 - 0.959). CONCLUSIONS: Based on their proximity to the PRCP, it is likely that the PWCRPE and PCHR are at the higher end of the heavy intensity domain. PWCRPE is likely influenced by afferent responses from the working respiratory and skeletal muscles. The PCHR provides an initial P associated with the CHR in the heavy domain, however, it is possible that the reductions in P required to maintain the CHR would result in a transition from the heavy to moderate intensity domain. The moderate to strong relationships among each threshold suggested that ventilatory, cardiovascular, and perceptual thresholds are sensitive to distinguish cardiorespiratory fitness level.

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