title: Polycythemia decreases fatigue in tetanic contractions of canine skeletal muscle.
abstract: OBJECTIVE
  The effects of an acute polycythemia on muscle fatigue development were investigated in the self-perfused canine gastrocnemius in situ.
  
  
  METHODS
  Following isolation of the gastrocnemius, dogs (N = 5) were made polycythemic through a bolus injection of packed erythrocytes (hematocrit (Hct) = 90-92%) to raise systemic Hct to 63.5 +/- 0.5%. Subsequently, the gastrocnemius was stimulated, through the sciatic nerve, to perform 20 min of isotonic tetanic contractions (60 x min(-1), 200 ms, 50Hz). Control (normocythemic) animals (N = 5) underwent an identical contraction regimen.
  
  
  RESULTS
  Although blood flow to the gastrocnemius was not different at any time, oxygen delivery was significantly increased during polycythemia (peak = 33.7 +/- 2.2 mL x 100 g(-1) x min-1) over control (peak = 25.1 +/- 2.1 mL x 100 g(-1)x min(-1)) at all times during contraction. Oxygen uptake by the gastrocnemius, although consistently increased, was not significantly different between the normocythemic and polycythemic conditions at any time. The rate of fatigue was significantly decreased over the first 6 min of contraction in polycythemic animals (3.5 +/- 0.6% x min(-1)) when compared with controls (5.8 +/- 0.7% x min(-1)). Subsequent fatigue development was not different between groups. As a result of the early rate differences in fatigue, however, the work production in polycythemic animals was significantly greater than in normocythemic dogs for the duration of the contraction period.
  
  
  CONCLUSIONS
  We conclude that during high metabolic rate isotonic tetanic contractions, muscle fatigue development is diminished by polycythemia, but the ergogenic effect appears to be transient.
authors.affiliation: Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada. jfrisbee@mcw.edu
authors.forename: J C
authors.initials: JC
authors.lastname: Frisbee
authors.forename: C L
authors.initials: CL
authors.lastname: Murrant
authors.forename: B A
authors.initials: BA
authors.lastname: Wilson
authors.forename: J K
authors.initials: JK
authors.lastname: Barclay
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004285:Dogs; D006400:Hematocrit; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D011086:Polycythemia / Q000503:physiopathology*
chemical_list: D010100:Oxygen