Pasquale J. Succi1, Taylor K. Dinyer-McNeely2, Caleb C. Voskuil3, Brian Benitez1, Minyoung Kwak1, Mark G. Abel1, Jody L. Clasey, FACSM1, Haley C. Bergstrom1. 1University of Kentucky, Lexington, KY. 2Oklahoma State University, Stillwater, OK. 3Texas Christian University, Fort Worth, TX.

BACKGROUND: The current recommendations for improving cardiorespiratory endurance (CE) are based on percentages of VO2 or heart rate (HR) maximum or reserve. However, these intensities are often based on estimation equations that are extrapolated to power outputs (P) or velocities. The recent application of the critical power model to a physiological parameter in HR provides an individualized threshold which has demonstrated a dissociation of typical responses that have previously been described during constant P exercise. Therefore, the purpose of this study was to examine the patterns in physiological (VO2, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO2]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP,MMG AMP] and mean power frequency [EMG MPF,MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise anchored at critical heart rate (CHR) versus the P associated with CHR (PCHR). METHODS: On separate days, nine participants (Age 26±3y) performed a graded exercise test (GXT), 4 constant P trials at 85%-100% of peak power output (PP) to derive CHR and PCHR from the total heartbeats vs time to exhaustion (Tlim) and P vs HR relationships, respectively. The physiological, neuromuscular, and perceptual responses were recorded during trials at CHR (173±9b·min-1,TLim=45.5±20.2min) and PCHR (198±58W,TLim=21.0±17.8min) and normalized in 10% intervals to their respective values at PP. RESULTS: There were significant mode (CHRvsPCHR) x normalized time (10%-100%TLim) interactions for all variables (p=0.00-0.036) except MMG AMP (p>0.05). Follow-up one-way ANOVAs and Student Newman-Keuls tests indicated differences among the time points for CHR VO2 (mean±SD %change=-19±12%), PCHR VO2 (25±10%), PCHR HR (23±6%), CHR RR (24±23%), PCHR RR (105±53%), CHR P (-33±11%), CHR RPE (22±14%), PCHR RPE (65±26%), CHR %SmO2 (41±33%), PCHR %SmO2(-7±30%), CHR EMG AMP (-13±15%), PCHR EMG AMP (18±21%), CHR EMG MPF (9±8%), CHR MMG MPF (7±11%), and PCHR MMG MPF (1±11%). CONCLUSIONS: Exercise at CHR was more sustainable than exercise at PCHR due to decreases in P required to maintain HR. As a result, participants demonstrated a dissociation of the predictable responses seen in constant P exercise. These differences at CHR may indicate that exercise anchored by a physiological parameter provides a more sustainable exercise modality that can be used to improve CE.

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