Muscle chemoreflex elevates muscle blood flow and O-2 uptake at exercise onset in nonischemic human forearm

We tested the hypothesis that increases in forearm blood flow (FBF) during the adaptive phase at the onset of moderate exercise would allow a more rap id increase in muscle O-2 uptake ((V) over dot O-2mus). Fifteen subjects co mpleted forearm exercise in control (Con) and leg occlusion (Occ) condition s. In Occ, exercise of ischemic calf muscles was performed before the onset of forearm exercise to activate the muscle chemoreflex evoking a 25-mmHg i ncrease in mean arterial pressure that was sustained during forearm exercis e. Eight subjects who increased FBF during Occ compared with Con in the ada ptation phase by >30 ml/min were considered "responders." For the responder s, a higher (V) over dot O-2 mus accompanied the higher FBF only during the adaptive phase of the Occ tests, whereas there was no difference in the ba seline or steady-state FBF or (V) over dot O-2 mus between Occ and Con. Sup plying more blood flow at the onset of exercise allowed a more rapid increa se in (V) over dot O-2 mus supporting our hypothesis that, at least for thi s type of exercise, O-2 supply might be limiting.