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

This study examined the power output adjustments and subsequent shifts in metabolic (V̇O₂) demands as well as minute ventilation ( \({\dot{\text{V}}}_{{\text{E}}}\) ${\dot{\text{V}}}_{\text{E}}$ ), respiratory rate (RR), and rating of perceived exertion (RPE) responses during vigorous intensity (77–95% HR_peak) heart rate (HR)-clamp cycle ergometry.

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 (HR_L = 77% HR_peak), middle (HR_M = 86% HR_peak), and higher (HR_H = 95% HR_peak) end of the vigorous intensity range. Time course of changes were examined.

The times to exhaustion (T_lim) for the HR_L, HR_M, and HR_H trials were 56.05 ± 10.09, 44.22 ± 19.00, and 9.74 ± 7.54 min, respectively. There were significant decreases in power output, \({\dot{\text{V}}\text{O}}_{{2}}\) ${\dot{\text{V}}\text{O}}_2$ , and \({\dot{\text{V}}}_{{\text{E}}}\) ${\dot{\text{V}}}_{\text{E}}$ 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 HR_L than HR_M, and HR_L and HR_M were lower than HR_H. The mean \({\dot{\text{V}}\text{O}}_{{2}}\) ${\dot{\text{V}}\text{O}}_2$ (HR_L = 56.7 ± 3.8, HR_M = 68.1 ± 4.3, and HR_H = 90.5 ± 3.3% \({\dot{\text{V}}\text{O}}_{{{\text{2max}}}}\) ${\dot{\text{V}}\text{O}}_{\text{2max}}$ ) responses fell below the recommended \({\dot{\text{V}}\text{O}}_{{2}}\) ${\dot{\text{V}}\text{O}}_2$ range for vigorous exercise at 10%T_lim for HR_L, and at 90%T_lim for HR_M, but remained above the recommended V̇O₂ range for vigorous exercise until 70% of T_lim for HR_H.

Only the HR_M trial met the current guidelines of a vigorous intensity \({\dot{\text{V}}\text{O}}_{{2}}\) ${\dot{\text{V}}\text{O}}_2$ 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.