The effects of controlled voluntary hyperventilation (Hyp) on phosphocreatine (PCr) kinetics and muscle deoxygenation were examined during moderate-intensity plantar flexion exercise. Male subjects (n = 7) performed trials consisting of 20-min rest, 6-min exercise, and 10-min recovery during a control (Con; P_ET,CO₂ ~ 33 mmHg) and Hyp (P_ET,CO₂ ~ 17 mmHg) condition. Phosphorus-31 magnetic resonance and near-infrared spectroscopy were used simultaneously to monitor intramuscular acid-base status, high-energy phosphates, and muscle oxygenation. Resting intracellular hydrogen ion concentration ([H⁺]_i) was lower (P<0.05) in Hyp (90 nM (SD 3)) than Con (96 nM (SD 4)), however, at end-exercise, [H⁺]_i was greater (P < 0.05) in Hyp (128 nM (SD 19)) than Con (120 nM (SD 17)). At rest, [PCr] was not different between Con (36 mM (SD 2)) and Hyp (36 mM (SD 1)). The time constant (tau;) of PCr breakdown during transition from rest to exercise was greater (P < 0.05) in Hyp (39-s (SD 22)) than Con (32-s (SD 22)), and the relative PCr amplitude was greater (P < 0.05) in Hyp (26% (SD 4)) versus Con (22% (SD 6)). The of deoxyhaemoglobin/myoglobin (HHb) was similar between Hyp (13-s (SD 8)) and Con (10-s (SD 3)), however the amplitude was greater (P < 0.05) in Hyp (40 a.u. (SD 23)) than Con (26 a.u. (SD 17)). In conclusion, our results indicate that hyperventilation-induced hypocapnia enhanced substrate-level phosphorylation during moderate-intensity exercise. In addition, the increased amplitude of the HHb response suggests a reduced local muscle perfusion in Hyp compared to Con.