Effects of prior exercise or ammonium chloride ingestion on muscular strength and endurance

Previous studies linked muscular fatigue with a decrease in blood pH. This study investigated if the means of altering pH affected the extent of muscular fatigue. Drug-induced and exercise-induced acidosis were compared to test the hypothesis that exercise-induced acidosis impairs subsequent muscular performance more than chemically induced acidosis. In eight male subjects acidosis was induced by ingesting 0.3 g.kg-1 ammonium chloride (AC) for one trial, by upper body exercise (UBE) for another trial, and after placebo (PL) treatment. They then completed a performance test (PT) of 50 maximal, bilateral isokinetic knee extensions. Whole blood pH before (pHpre) and after (pHpost) the PT was 7.412, 7.264, and 7.261 for PL, UBE, and AC, respectively; both AC and UBE decreased pH similarly compared with PL. Peak torque and total work during the PT were similar for PL and AC, and were significantly greater than after UBE. Six subjects performed a fourth trial after combined AC and UBE treatments causing a pHpre of 7.081, but there was no greater performance impairment than that caused by UBE alone. The results dissociate the extent of the impairment from the magnitude of the disruption in blood pH.