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). 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 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 Lacat a given intensity of exercise. That such a decrease in Lac 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 are not ascribable to a substantial increase in the 'lactate threshold'.