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.

Changes in phosphocreatine concentration of skeletal muscle during high-intensity intermittent exercise in children and adults

“…Comparing children and adults at similar intense exercise, convective or diffusive oxygen supply may contribute to the greater proportion of oxidative energy provision during contraction and recovery in children than in adults. A previous study conducted with adults showed that an improved blood and oxygen supply by means of lower body negative pressure significantly enhances oxidative ATP formation and fatigue resistance during intensive interval exercise compared to control conditions (Zange et al 2008). Since adult muscle becomes ischaemic under high load contraction, the initial PCr decrease was the same with and without lower body negative pressure.…”

“…The visibility of deoxymyoglobin for about 45 s after exhaustive exercise (Tran et al 1999) indicates a rather slow reoxygenation of the sarcoplasma. Also the effects of lower body negative pressure on PCr recovery after intensive exercise, previously mentioned (Zange et al 2008) only makes sense if oxygen was rate limiting for oxidative phosphorylation during recovery at least for some seconds. Therefore, the borderline difference in s between adults and children in this study may not hint to differences in the capacity of oxidative phosphorylation, but is more likely the result of a temporary inhibition of oxidative phosphorylation in adults, starting PCr recovery at lower pH values and very low oxygen levels.…”

“…Dynamic plantar flexion exercise. During fatiguing exercise and subsequent recovery, depletion and recovery of PCr, ATP, inorganic phosphate (P i ), and phosphomonoesters (PME, sugar phosphates), were measured in the right calf muscle by 31 P-MRS, following the methods of Zange et al (2008). Subjects were lying on a treatment table, in a supine position, with their legs in the 40 cm diameter bore of the magnetic resonance (MR) magnet.…”

“…The footplate of the pedal could be turned between 70°and 40°relative to the horizontal position. The lift of the load was optically measured using a striated tape and a photoelectric relay, in order to calculate the forcetime integral (FTI) and FTI per kg of body mass (FTI/ kg bm) as well as the range of motion (ROM) per lift (Zange et al 2008).…”

Electromyography activity across gait and incline: The impact of muscular activity on human morphology

“…In those situations where we do not see substantial increases in muscular activity level or variability, we might expect those activities to cost less metabolic energy and thus be more efficient [c.f. (Zange et al, 2008; Hepple et al, 2010)]. In general, individuals able to negotiate variations in slope and speed with minimal increases in muscular activity will require less locomotor-related metabolic energy (Reilly et al, 2007), leading to an increase in their reproductive fitness (Gibson and Mace, 2006).…”