Muscle metabolic responses during 16 hours of intermittent heavy exercise

• Published in: Canadian journal of physiology and pharmacology 2007-06, Vol.85 (6), p.634-645
• Main Authors: Green, H.J, Duhamel, T.A, Holloway, G.P, Moule, J, Ouyang, J, Ranney, D, Tupling, A.R
• Format: Article
• Language: English
• Subjects: activité répétitive; adaptation; Adenine Nucleotides - metabolism; Adenosine; Adenosine Triphosphate - metabolism; Adult; AMP; Bicycling - physiology; Biological and medical sciences; Chromatography, High Pressure Liquid; Creatine - metabolism; Electron transport; Electron Transport Complex IV - metabolism; Evaluation; Exercise; Exercise - physiology; Female; Fructosephosphates - metabolism; Fundamental and applied biological sciences. Psychology; Glucose-6-Phosphate - metabolism; Glycogen; Glycogen - metabolism; Glycolysis - physiology; Health aspects; Humans; Inosine monophosphate; Inosine Monophosphate - metabolism; Lactates - metabolism; Lactic acid; Male; Metabolic response; Metabolism; Metabolites; Mitochondria; mitochondrial sensitivity; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Muscles; métabolisme; Oxidative phosphorylation; Oxygen consumption; Oxygen Consumption - physiology; Phosphocreatine; Phosphocreatine - metabolism; Phosphorylation; phosphorylation oxydative; Physical Exertion - physiology; Physical fitness; Physiological aspects; Physiology; Pyruvates - metabolism; repetitive activity; Respiration; Rest - physiology; sensibilité mitochondriale; Short term; Succinate Dehydrogenase - metabolism; Time Factors; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0008-4212; 1205-7541
• DOI: 10.1139/Y07-039

The alterations in muscle metabolism were investigated in response to repeated sessions of heavy intermittent exercise performed over 16 h. Tissue samples were extracted from the vastus lateralis muscle before (B) and after (A) 6 min of cycling at approximately 91% peak aerobic power at repetitions one (R1), two (R2), nine (R9), and sixteen (R16) in 13 untrained volunteers (peak aerobic power = 44.3 ± 0.66 mL·kg -1 ·min -1 , mean ± SE). Metabolite content (mmol·(kg dry mass) -1 ) in homogenates at R1 indicated decreases (p < 0.05) in ATP (21.9 ± 0.62 vs. 17.7 ± 0.68) and phosphocreatine (80.3 ± 2.0 vs. 8.56 ± 1.5) and increases (p < 0.05) in inosine monophosphate (IMP, 0.077 ± 0.12 vs. 3.63 ± 0.85) and lactate (3.80 ± 0.57 vs. 84.6 ± 10.3). The content (µmol·(kg dry mass) -1 ) of calculated free ADP ([ADP f ], 86.4 ± 5.5 vs. 1014 ± 237) and free AMP ([AMP f ], 0.32 ± 0.03 vs. 78.4 ± 31) also increased (p < 0.05). No differences were observed between R1 and R2. By R9 and continuing to R16, pronounced reductions (p < 0.05) at A were observed in IMP (72.2%), [ADP f ] (58.7%), [AMP f ] (85.5%), and lactate (41.3%). The 16-hour protocol resulted in an 89.7% depletion (p < 0.05) of muscle glycogen. Repetition-dependent increases were also observed in oxygen consumption during exercise. It is concluded that repetitive heavy exercise results in less of a disturbance in phosphorylation potential, possibly as a result of increased mitochondrial respiration during the rest-to-work non-steady-state transition.