title: Muscle metabolic status and acid-base balance during 10-s work:5-s recovery intermittent and continuous exercise.
abstract: Gastrocnemius muscle phosphocreatine ([PCr]) and hydrogen ion ([H(+)]) were measured using (31)P-magnetic resonance spectroscopy during repeated bouts of 10-s heavy-intensity (HI) exercise and 5-s rest compared with continuous (CONT) HI exercise. Recreationally active male subjects (n = 7; 28 yr ± 9 yr) performed on separate occasions 12 min of isotonic plantar flexion (0.75 Hz) CONT and intermittent (INT; 10-s exercise, 5-s rest) exercise. The HI power output in both CONT and INT was set at 50% of the difference between the power output associated with the onset of intracellular acidosis and peak exercise determined from a prior incremental plantar flexion protocol. Intracellular concentrations of [PCr] and [H(+)] were calculated at 4 s and 9 s of the work period and at 4 s of the rest period in INT and during CONT exercise. [PCr] and [H(+)] (mean ± SE) were greater at 4 s of the rest periods vs. 9 s of exercise over the course of the INT exercise bout: [PCr] (20.7 mM ± 0.6 vs. 18.7 mM ± 0.5; P < 0.01); [H(+)] (370 nM ± 13.50 vs. 284 nM ± 13.6; P < 0.05). Average [H(+)] was similar for CONT vs. INT. We therefore suggest that there is a glycolytic contribution to ATP recovery during the very short rest period (<5 s) of INT and that the greater average power output of CONT did not manifest in greater [H(+)] and greater glycolytic contribution compared with INT exercise.
authors.affiliation: University of Western Ontario, London, Ontario, Canada. gbelfry@uwo.ca
authors.forename: Glen R
authors.initials: GR
authors.lastname: Belfry
authors.forename: Graydon H
authors.initials: GH
authors.lastname: Raymer
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Marsh
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
authors.forename: R Terry
authors.initials: RT
authors.lastname: Thompson
authors.forename: Scott G
authors.initials: SG
authors.lastname: Thomas
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010725:Phosphocreatine / Q000032:analysis / Q000502:physiology; D055815:Young Adult
chemical_list: D010725:Phosphocreatine