Mielke, M., Housh, T. J., Malek, M. H., Beck, T. W., Hendrix, C. R., Zuniga, J. M., Camic, C. L., Schmidt, R. J., & Johnson, G. O. (2009). A test for determining critical heart rate using the critical power model. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 2795.

"The critical power test relates the amount of work accomplished at exhaustion and the time to exhaustion and, theoretically, estimates the maximum power output that can be maintained for an extended period of time without fatigue. However, the critical power test overestimates the exercise intensity that can be sustained over time and a significant, progressive increase in the metabolic intensity is observed until exhaustion."

This study applied the critical power model to heart rate data to propose a heart-rate based analog of the critical power test called the critical heart rate test. The critical heart rate test was compared to the heart rate values at critical power, ventilatory threshold, and the respiratory compensation point. Adults (N = 10) performed an incremental (30 W increase every two minutes) test to exhaustion on an electronically braked cycle ergometer for the determination of VO2peak, ventilatory threshold, and respiratory compensation point. Ss also performed four randomly ordered exercises to exhaustion at different power outputs (ranging from 100 to 246 W) for the determination of critical power and critical heart rate. For each power output, the total number of heart beats was calculated. The total number of heart beats and work for each of the four power outputs were plotted as a function of the time to exhaustion at each power output. The critical heart rate and critical power were defined as the slope coefficients of the regression lines between total number of beats or work accomplished at exhaustion and time to exhaustion, respectively. The heart rate values from the incremental test were plotted against power output or VO2 values and the regression equations derived were used to determine the heart rate that corresponded to critical power, ventilatory threshold, and respiratory compensation point.

Critical heart rate was not significantly different from the respiratory compensation point heart rate, but was significantly higher than critical power heart rate and the ventilatory threshold heart rate.

Implication. The relationship between heart rate and time to exhaustion derived from the critical heart rate test can be described by the critical power model. The critical heart rate test may be a practical method for estimating the respiratory compensation point, but not critical power or ventilatory threshold.

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