The effect of inspiratory muscle training upon maximum lactate steady-state and blood lactate concentration

Several studies have reported that improvements in endurance performance following respiratory muscle training (RMT) are associated with a decrease in blood lactate concentration ([Lac](B)). The present study examined whether pressure threshold inspiratory muscle training (IMT) elicits an increase in the cycling power output corresponding to the maximum lactate steady state (MLSS). Using a double-blind, placebo-controlled design, 12 healthy, non-endurance-trained male participants were assigned in equal numbers to an experimental (IMT) or sham training control (placebo) group. Cycling power output at MLSS was initially identified using a lactate minimum protocol followed by a series of constant power output rides (2.5% increments) of 29.5 min duration; MLSS was reassessed following six weeks of IMT or sham IMT. Maximum inspiratory mouth pressure increased significantly (26%) in the IMT group, but remained unchanged in the placebo group. The cycling power output corresponding to MLSS remained unchanged in both groups after the intervention. After IMT, [Lac](B) decreased significantly at MLSS power in the IMT group [-1.17 (1.01) mmol l(-1) after 29.5 min of cycling; mean (SD)], but remained unchanged in the placebo group [+0.37 (1.66) mmol l(-1)]. These data support previous observations that IMT results in a decrease in [Lac](B )at a given intensity of exercise. That such a decrease in [Lac](B) was not associated with a substantial (>2.5%) increase in MLSS power is a new finding suggesting that RMT-induced increases in exercise tolerance and reductions in [Lac](B) are not ascribable to a substantial increase in the 'lactate threshold'.