Muscle metabolism in dog skeletal muscle during fatiguing work with altered arterial oxygen tensions

These experiments were conducted to determine whether changes in arterial O₂ tension are related to changes in muscle metabolism during fatiguing contractions. Arterial and venous circulation to the gastrocnemius muscle (n=8) was isolated and the calcanean tendon was attached to a force transducer. Each muscle was electrically stimulated through the sciatic nerve for three 2-min periods of fatiguing contractions separated by 8 min of rest. The arterial O₂ tensions were altered for each work period (mean P O₂ =44, 72, 391 Torr). Arterial and venous samples were drawn to measure lactate, O₂ and C O₂ concentrations (Van Slyke analysis) and [H⁺] — while muscle biopsies were taken to measure muscle [H⁺] (homogenate method) and lactate. Fatigue was evaluated as the decline in tension from peak initial tension. At rest, arterial [H⁺] was significantly different (p < 0.05) among treatments (low arterial O₂ tension=39 nM ± 1 SE, high arterial O₂ tension=47 ± 2). At the end of the contraction periods, values (mean ± SE) were significantly different (p < 0.05) between the low arterial O₂ tension and the high for flow (84± 6 vs. 70 ± 8 ml/100g per min), muscle lactate concentration (44 ± 10 vs. 26 ± 4 mmol/kg dry wt) and lactate release (122 ± 12 vs. 57 ± 14 umol/100g per min). Oxygen uptake and fatigue were not different among treatments during contractions. Muscle [H⁺] increased (work [H⁺] minus rest [H⁺]) to a significantly greater extent during low arterial O2 tensions as compared to high (p < 0.05).

I concluded that altering the arterial O₂ tensions during fatiguing contractions induces changes in blood and muscle acid-base status and in muscle metabolism. The mechanisms for these alterations cannot be determined from this investigation. Although the rate of fatigue was not different among treatments in this study, I hypothesize that these changes in muscle metabolism may be responsible for performance differences measured during hypoxic and hyperoxic work.