Vigorous intensity heart rate-clamp exercise does not elicit recommended oxygen consumption rates

Purpose This study examined the power output adjustments and subsequent shifts in metabolic (VO2) demands as well as minute ventilation ((VE)-E-center dot), respiratory rate (RR), and rating of perceived exertion (RPE) responses during vigorous intensity (77-95% HRpeak) heart rate (HR)-clamp cycle ergometry. Methods Fifteen males (mean +/- SD age = 25.9 +/- 4.4 years) performed a graded exercise test to exhaustion to determine peak parameters and three, randomly ordered, HR-clamp trials to exhaustion, up to 60 min, at the lower (HRL = 77% HRpeak), middle (HRM = 86% HRpeak), and higher (HRH = 95% HRpeak) end of the vigorous intensity range. Time course of changes were examined. Results The times to exhaustion (T-lim) for the HRL, HRM, and HRH trials were 56.05 +/- 10.09, 44.22 +/- 19.00, and 9.74 +/- 7.54 min, respectively. There were significant decreases in power output, V(center dot)O2, and (VE)-E-center dot across time for each trial, but no changes in RR, and increases in RPE (p < 0.05). Responses were intensity specific for all variables such that mean values were lower for HRL than HRM, and HRL and HRM were lower than HRH. The mean V(center dot)O2 (HRL = 56.7 +/- 3.8, HRM = 68.1 +/- 4.3, and HRH = 90.5 +/- 3.3%V(center dot)O2max) responses fell below the recommended V(center dot)O2 range for vigorous exercise at 10%T-lim for HRL, and at 90%T-lim for HRM, but remained above the recommended VO2 range for vigorous exercise until 70% of T-lim for HRH. Conclusions Only the HRM trial met the current guidelines of a vigorous intensity V(center dot)O2 sustained for at least 20 min. This study indicated that HR-clamp exercise cannot be consistently used to prescribe a desired metabolic stimulus for exercise performed in a single session.