Abstract
This study investigated the effect of respiratory muscle fatigue on cardiovascular function, locomotor muscle fatigue and exercise performance in young and master athletes, a model of successful ageing. Ten young male (YA, 27.4 ± 4.4 years) and 11 male master endurance athletes (MA, 65.0 ± 5.1 years) performed, on separate days, two constant workload cycling tests at 90% of peak power to exhaustion (CWT) following a fatiguing inspiratory loading task at 60% (ILT(60%)) and a sham task at 2% (ILT(2%)) of their maximal inspiratory pressure. On a third day, the sham task was replicated but CWT was interrupted at the time equal to that performed during CWT(ILT60%) (CWT(ILT2%-ISO)). Quadriceps fatigue was assessed by changes in maximal voluntary isometric contraction (MVC), potentiated twitch force (QT(SINGLE)) and voluntary activation (VA) from 15 s to 15 min post-exercise. Mean arterial pressure (MAP) was measured using finger pulse photoplethysmography. Blood flow (Q̇(L)) and limb vascular conductance (LVC) were measured using Doppler ultrasound. During ILT(60%), MA demonstrated reduced Q̇(L) (P = 0.036), a greater increase in MAP (P < 0.001) and a larger decrease in LVC (P = 0.044) compared to YA. During CWT(ILT60%), MA experienced a larger decrease in time to exhaustion (-39.7 ± 14.0%) than YA (-15.5 ± 13.9%, P = 0.010). Exercise-induced reductions in MVC and QT(SINGLE) (both P < 0.039) were also more pronounced during CWT(ILT60%) compared to CWT(ILT2%-ISO) in MA. Ageing exacerbates the adverse effects of respiratory muscle fatigue on limb vascular function and locomotor muscle fatigue during subsequent exercise, resulting in greater impairments in exercise performance.