Effects of ammonium chloride ingestion on phosphocreatine metabolism during moderate- and heavy-intensity plantar-flexion exercise.

This study examined the effects of NH(4)Cl ingestion on phosphocreatine (PCr) metabolism during 9 min of moderate- (MOD) and heavy- (HVY) intensity constant-load isotonic plantar-flexion exercise. Healthy young adult male subjects (n = 8) completed both a control (CON) and NH(4)Cl ingestion (ACID) trial. Phosphorus-31 magnetic resonance spectroscopy was used to monitor changes in intracellular pH (pHi), [Pi], [PCr], and [ATP]. During the Middle (3-6 min) and Late (6-9 min) stages of HVY, ACID was associated with a higher (P < 0.05) intracellular hydrogen-ion concentration ([H(+)]i) [Middle: 246 (SD 36) vs. 202 (SD 36) mmol/l]; [Late: 236 (SD 35) vs. 200 (SD 39) mmol/l]. In addition, ACID was associated with a lower (P < 0.05) [PCr] relative to CON during the Early (0-3 min) [18.1 (SD 5.1) vs. 20.4 (SD 5.4) mmol/l] and Middle stages [14.1 (SD 5.4) vs. 16.7 (SD 6.0) mmol/l] of HVY. The amplitude of the primary component of PCr breakdown during the transition to HVY was greater in ACID than CON [14.5 (SD 5.8 vs. 11.3 (SD 4.8) mmol/l], however, the PCr slow component (continued slow decline in [PCr]) showed no difference (P > 0.05). The time constant for PCr breakdown (tauPCr) was greater in HVY than MOD for both conditions [58 (SD 22) vs. 28 (SD 15) s ACID; 51 (SD 20) vs. 29 (SD 14) s CON] (P < 0.05). In summary, ACID increased PCr breakdown during the transition from MOD to HVY, but did not increase the magnitude of the PCr slow component.