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 (V̇O 2) demands as well as minute ventilation ( V ˙ E ), respiratory rate (RR), and rating of perceived exertion (RPE) responses during vigorous intensity (77-95% HR peak) 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 (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.

RESULTS: 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, V ˙ O 2 , and V ˙ 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 V ˙ O 2 (HR L  = 56.7 ± 3.8, HR M  = 68.1 ± 4.3, and HR H  = 90.5 ± 3.3% V ˙ O 2max ) responses fell below the recommended V ˙ 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 V̇O 2 range for vigorous exercise until 70% of T lim for HR H.

CONCLUSIONS: Only the HR M trial met the current guidelines of a vigorous intensity V ˙ 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.