Acute effects of very low-volume high-intensity interval training on muscular fatigue and serum testosterone level vary according to age and training status.

Abstract

To compare the acute physiological responses of three different very low-volume cycling sessions (6 × 5s, 3 × 30s, and 3 × 60s) and their dependence on age and training status. Subjects were untrained young men (mean ± SD; age 22.3 ± 4.6years, VO2peak 42.4 ± 5.5ml/kg/min, n = 10), older untrained men (69.9 ± 6.3years, 26.5 ± 7.6ml/kg/min, n = 11), and endurance-trained cyclists (26.4 ± 9.4years, 55.4 ± 6.6ml/kg/min, n = 10). Maximal voluntary contraction (MVC) and electrically stimulated knee extension torque, and low-frequency fatigue, as ratio of stimulation torques at 20-100Hz (P20/100), were measured only 24h after exercise. Serum testosterone (Te) and blood lactate concentrations were measured only 1h after exercise. All protocols increased the blood lactate concentration and decreased MVC and P20/100 in young men, but especially young untrained men. In old untrained men, 6 × 5s decreased P20/100 but not MVC. Te increased after 3 × 30s and 3 × 60s in young untrained men and after 3 × 60s in older untrained men. The increase in Te correlated with responses of blood lactate concentration, MVC, and P20/100 only in old untrained men. As little as 6 × 5s all-out cycling induced fatigue in young and old untrained and endurance-trained cyclists. Slightly higher-volume sessions with longer intervals, however, suppressed contractile function more markedly and also transiently increased serum testosterone concentration in untrained men.