title: Energy metabolism in intensively exercising calf muscle under a simulated orthostasis.
abstract: We conducted non-invasive methods to investigate the mechanisms how an orthostasis improves fatigue resistance in human calf muscle during intense exercise. Eleven healthy volunteers performed two series of ten intervals of maximum dynamic exercise (15 s) and recovery (45 s) at almost horizontal body position under both, control conditions (CON) and lower body negative pressure (LBNP, -40 mbar). As from the second work interval, LBNP significantly improved fatigue resistance shown as a lower reduction in work and in contraction velocity (P < 0.01). During each work interval, EMG showed a small increase in amplitude (P < 0.01) and a steep drop by 20% in median frequency (P < 0.01). Under LBNP, both EMG parameters completely recovered during subsequent rest, whereas under CON recovery was incomplete (P < 0.01). During the first work interval, consumption of phosphocreatine (PCr) was almost the same for both conditions. In periods of recovery under LBNP, resynthesis of PCr and inorganic phosphate were significantly faster. PCr reached 10 to 20% higher levels (P < 0.01). LBNP caused an initial increase in intracellular pH (0.08 U (P < 0.01)). The subsequent time courses of pH were similar for CON and LBNP. During work, pH steeply increased by about 0.3 U. During subsequent recovery, pH dropped to values between 6.3 and 6.5. LBNP caused significantly higher levels of total haemoglobin and oxy-haemoglobin (P < 0.05). A simulated orthostasis increased fatigue resistance during high intense interval exercise because of a faster PCr resynthesis and may be because of improvements in the maintenance of motoneuronal activity.
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR e.V.), 51170 Köln (Cologne), Germany. Jochen.Zange@dlr.de
authors.forename: Jochen
authors.initials: J
authors.lastname: Zange
authors.forename: Mareike
authors.initials: M
authors.lastname: Beisteiner
authors.forename: Klaus
authors.initials: K
authors.lastname: Müller
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shushakov
authors.forename: Norbert
authors.initials: N
authors.lastname: Maassen
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D018592:Cross-Over Studies; D004576:Electromyography; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006019:Glycolysis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007700:Kinetics; D007866:Leg / Q000098:blood supply / Q000502:physiology; D008150:Lower Body Negative Pressure; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism* / Q000502:physiology*; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D011187:Posture / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D016683:Supine Position / Q000502:physiology
chemical_list: D010725:Phosphocreatine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate