Ventilatory responses to dynamic exercise elicited by intramuscular sensors.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 277-286, 1999.Purpose:Eight subjects, aged 27.0 ± 1.6 yr, performed incremental workload cycling to investigate the contribution of skeletal muscle mechano- and metaboreceptors to ventilatory control during dynamic exercise.Methods:Each subject performed four bouts of exercise: exercise with no intervention (CON); exercise with bilateral thigh cuffs inflated to 90 mm Hg (CUFF); exercise with application of lower-body positive pressure (LBPP) to 45 torr (PP); and exercise with 90 mm Hg thigh cuff inflation and 45 torr LBPP (CUFF+PP). Ventilatory responses and pulmonary gas exchange variables were collected breath-by-breath with concomitant measurement of leg intramuscular pressure.Results:Ventilation (&OV0312;E) was significantly elevated from CON during PP and CUFF+PP at workloads corresponding to ≥ 60% CON peak oxygen uptake (&OV0312;O2peak) and during CUFF at workloads ≥ 80% CON &OV0312;O2peak,P< 0.05. The &OV0312;O2at which ventilatory threshold occurred was significantly reduced from CON (2.17 ± 0.28 L·min−1) to 1.60 ± 0.19 L·min−1, 1.45 ± 0.15 L·min−1, and 1.15 ± 0.11 L·min−1during CUFF, PP, and CUFF+PP, respectively. The slope of the linear regression describing the &OV0312;E/CO2output relationship was increased from CON by approximately 22% during CUFF, 40% during PP, and 41% during CUFF+PP.Conclusions:As intramuscular pressure was significantly elevated immediately upon application of LBPP during PP and CUFF+PP without a concomitant increase in &OV0312;E, it seems unlikely that LBPP-induced increases in &OV0312;Ecan be attributed to activation of the mechanoreflex. These findings suggest that LBPP-induced reductions in perfusion pressure and decreases in venous outflow resulting from inflation of bilateral thigh cuffs may generate a metabolite sensitive intramuscular ventilatory stimulus.