Gretebeck, R. J., Sutton, J. L., Karapetian, G. K., & Engels, H. J. (2004). Use of heart rate variability to estimate lactate threshold. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 293.

"Ventilatory threshold (VT), the point at which pulmonary ventilation increases disproportionately in its relationship to oxygen consumption during exercise, often coincides with lactate threshold (LT). Heart rate variability (HRV) is a measure of the variability from one heart beat to the next, is mainly vagally mediated, and has been found to change significantly during the aerobic-anaerobic transition of exercise. The purpose of this study [was] to examine the relationship between LT, V, and HRV and to determine whether changes in heart rate variability can accurately estimate LT" (p. S43).

Ss (N = 24) performed a graded maximal cycle ergometry test to volitional fatigue. Metabolic gas and ventilatory parameters were measured every 30 seconds, and blood lactate was measured every three minutes. Lactate threshold and VT were measured. Heart rate variability was determined using time domain indexes including standard deviation, coefficient of variation, and mean successive difference. Time domain changes were used to establish a heart rate variability threshold (HRVT).

A marked R-R interval deflection point of heart rate in the region of LT was found and identified as the HRVT. There was no significant difference between HRVT and LT or between HRVT and VT. A small but significant difference between VT and LT was found. The average VO2 at LT and HRVT were similar.

Implication. Heart rate variability threshold coincides with lactate threshold during graded exercise and can be used for detecting lactate threshold.

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