Polycythemia decreases fatigue in tetanic contractions of canine skeletal muscle

Purpose: The effects of an acute polycythemia on muscle fatigue development were investigated in the self-perfused canine gastrocnemius in situ. Metho ds: Following isolation of the gastrocnemius, dogs (N = 5) were made polycy themic through a bolus injection of packed erythrocytes (hematocrit (Hct) = 90-92%) to raise systemic Hct to 63.5 +/- 0.5%. Subsequently, the gastrocn emius was stimulated, through the sciatic nerve, to perform 20 min of isoto nic tetanic contractions (60.min(-1), 200 ms, 50Hz). Control (normocythemic ) animals (N = 5) underwent an identical contraction regimen. Results: Alth ough blood flow to the gastrocnemius was not different at any time, oxygen delivery was significantly increased during polycythemia (peak = 33.7 +/- 2 .2 mL.100 g(-1).min(-1)) over control (peak = 25.1 +/- 2.1 mL.100 g(-1).min (-1)) at all times during contraction. Oxygen uptake by the gastrocnemius, although consistently increased, was not significantly different between th e normocythemic and polycythemic conditions at any time. The rate of fatigu e was significantly decreased over the first 6 min of contraction in polycy themic animals (3.5 +/- 0.6%.min(-1)) when compared with controls (5.8 +/- 0.7%.min(-1)). Subsequent fatigue development was not different between gro ups. As a result of the early rate differences in fatigue, however, the wor k production in polycythemic animals was significantly greater than in norm ocythemic dogs for the duration of the contraction period. Conclusion: We c onclude that during high metabolic rate isotonic tetanic contractions, musc le fatigue development is diminished by polycythemia, but the ergogenic eff ect appears to be transient.