Effect of an Acute β-Adrenergic Blockade on the Relationship Between Ventilatory and Plasma Lactate Threshold

The present study assesses interobserver variability and day-to-day reproducibility of ventilatory threshold T(ven) and lactate threshold T(lac) in healthy young men. The data were obtained before and after acute β-adrenergic blockade with meto-prolol (100 mg/d p.o.). Fifteen healthy young men underwent progressively increased treadmill ergometry tests on two separate days (day 1, 2). Ten out of fifteen subjects participated in a third exercise test under an acute β-adrenergic blockade (day 3). Interobserver variability of oxygen uptake at T(ven) (8 %; ± 0.136 l/min) and T(lac) (5 %; ± 0.984 l/min) was small and day-to-day reproducibility of T(ven) (7 %; ±0.131 l/min) and T(lac) (7 %; ± 0.133 l/min) high. Under acute β-adrenergic blockade T(ven) occurred at a significantly lower work load (360 ± 117 s) as compared with T(ven) of days 1 and 2 (477 ± 153 s; p < 0.05), and T(lac) of day 3 after β-adrenergic blockade (456 ± 76 s; p < 0.05). Therefore, a significantly lower oxygen uptake (1.409±0.29 l/min) could be observed at T(ven) of day 3 as compared with T(ven) of days 1 and 2 (1.852 ± 0.30; p < 0.001), and T(lac) of days 1 and 2 (1.724 ± 0.22; p < 0.001). There was a significant linear correlation between oxygen uptake at T(ven) and T(lac) before β-adrenergic blockade (r = 0.86; p < 0.001). This correlation, however, was lost following an acute β-adrenertic blockade (r = 0.56; n.s.). The results of this study suggest that T(ven) is a noninvasive index of functional capacity with high day-to-day reproducibility and low interobserver variability, significantly correlated with exercise-induced lactate accumulation in the blood during incremental exercise tests. The discrepancy of oxygen uptake at T(ven) and T(lac) after acute β-adrenergic blockade, however, implies that T(ven) and T(lac) are not causally linked.

Key words

Anaerobic threshold - exercise testing - β-adrenergic blockade