title: Prior exercise delays the onset of acidosis during incremental exercise.
abstract: The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (approximately 0.6 W/min) to volitional fatigue (Ramp); 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT; Mod-Ramp); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT (Hvy-Ramp); the constant-load and incremental exercise periods were separated by 6 min of rest. (31)P-magnetic resonance spectroscopy was used to continuously monitor intracellular pH, phosphocreatine concentration ([PCr]), and inorganic phosphate concentration ([P(i)]). No differences in exercise performance or the metabolic response to exercise were observed between Ramp and Mod-Ramp. However, compared with Ramp, a 14% (SD 10) increase (P < 0.01) in peak power output (PPO) was observed in Hvy-Ramp. The improved exercise performance in Hvy-Ramp was accompanied by a delayed (P = 0.01) onset of intracellular acidosis [Hvy-Ramp 60.4% PPO (SD 11.7) vs. Ramp 45.8% PPO (SD 9.4)] and a delayed (P < 0.01) onset of rapid increases in [P(i)]/[PCr] [Hvy-Ramp 61.5% PPO (SD 12.0) vs. Ramp 45.1% PPO (SD 9.1)]. In conclusion, prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.
authors.affiliation: School of Kinesiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7.
authors.forename: Graydon H
authors.initials: GH
authors.lastname: Raymer
authors.forename: Sean C
authors.initials: SC
authors.lastname: Forbes
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: R Terry
authors.initials: RT
authors.lastname: Thompson
authors.forename: Greg D
authors.initials: GD
authors.lastname: Marsh
mesh_terms: D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control*; D000328:Adult; D015444:Exercise; D005528:Foot; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D010807:Physical Endurance; D013997:Time Factors
chemical_list: D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine