Purpose: The purpose of this study was to investigate the effects of inspiratory threshold loading (ITL) and inspiratory muscle training (IMT) on blood lactate concentration ([lac−]B) and acid-base balance after maximal incremental cycling.
Methods: Eighteen subjects were divided into a control (n = 9) or an IMT group (n = 9). Before and after a 6-wk intervention, subjects completed two maximal incremental cycling tests followed by 20 min of recovery with (ITL) or without (passive recovery (PR)) a constant inspiratory resistance (15 cm H2O). The IMT group performed 6 wk of pressure threshold IMT at 50% maximal inspiratory mouth pressure. Throughout recovery, acid-base balance was quantified using the physicochemical approach by measuring the strong ion difference ([SID] = [Na+] + [K+] − [Cl−] + [lac−]), the total concentration of weak acids ([Atot−]), and the partial pressure of carbon dioxide (PCO2).
Results: After the intervention, maximal inspiratory mouth pressure increased in the IMT group only (+34%). No differences in lactate clearance were observed between PR and ITL before the intervention in both groups and after the intervention in the control group. After IMT, relative to PR, [lac−]B was reduced throughout ITL (minutes 2-20) by 0.66 ± 1.28 mmol·L−1 (P < 0.05), and both the fast (lactate exchange) and the slow (lactate clearance) velocity constants of the lactate recovery kinetics were increased (P < 0.05). Relative to pre-IMT, ITL reduced plasma [H+], which was accounted for by an IMT-mediated increase in [SID] due almost exclusively to a 1.7-mmol·L−1 reduction in [lac−]B.
Conclusions: After maximal exercise, ITL affected lactate recovery kinetics only after IMT. Our data support the notion that the inspiratory muscles are capable of lactate clearance that increases [SID] and reduces [H+]. These effects may facilitate subsequent bouts of high-intensity exercise.