Lactate and Contractile Force in Frog Muscle During Development of Fatigue and Recovery
American Physiological Society
American Journal of Physiology
The relationship between lactic acid concentration and twitch tension was reevaluated in electrically stimulated frog sartorius muscle. If muscles stimulated under anaerobic conditions at a rate of 30 stimuli/min, contractile force decreased to 36% of the initial value in 15 min. Concomitantly lactate increased from 3.3 to 18.7 μmol/g of muscle. The correlation between the increase in lactate and the decrease in contractile force was significant (r = -0.99, P < 0.000001). Recovery occurred in two phases. A rapid increase in contractile force, which represented 20% of the total recovery, took place during the first 15 s and occurred concomitantly with an increase in ATP from 3.9 to 4.6 μmol/g. Lactate concentration did not change significantly during this period. The second phase of recovery of contractile force was complete in 50 min. Lactate concentration and contractile force were significantly correlated during recovery (r = -0.92, P < 0.00001). However, recovery of contractile force lagged behind the decrease in lactate; a given concentration of muscle lactate was associated with a higher contractile force early during development of fatigue than late during recovery.