SKELETAL-MUSCLE BIOCHEMICAL ADAPTATIONS TO EXERCISE TRAINING IN MINIATURE SWINE

The primary purpose of this study was to test the hypothesis that endu rance exercise training induces increased oxidative capacity in porcin e skeletal muscle. To test this hypothesis, female miniature swine wer e either trained by treadmill running 5 days/wk over 16-20 wk (Trn; n = 35) or pen confined (Sed; n = 33). Myocardial hypertrophy, lower hea rt rates during submaximal stages of a maximal treadmill running test, and increased running time to exhaustion during that test were indica tive of training efficacy. A variety of skeletal muscles were sampled and subsequently assayed for the enzymes citrate synthase (CS), 3-hydr oxyacyl-CoA dehydrogenase; and lactate dehydrogenase and for antioxida nt enzymes. Fiber type composition of are presentative muscle was also determined histochemically. The largest increase in CS activity (62%) was found in the gluteus maximus muscle (Sed, 14.7 +/- 1.1 mu mol.min (-1).g(-1); Tm, 23.9 +/- 1.0; P < 0.0005). Muscles exhibiting increase d CS activity, however, were located primarily in the forelimb; ankle and knee extensor and respiratory muscles were unchanged with training . Only two muscles exhibited higher 5-hydroxyacyl-CoA dehydrogenase ac tivity in Tm compared with Sed. Lactate dehydrogenase activity was unc hanged with training, as were activities of antioxidant enzymes. Histo chemical analysis of the triceps brachii muscle (long head) revealed l ower type IIB fiber numbers in Trn (Sed, 42 +/- 6%; Tm, 10 +/- 4; P < 0.01) and greater type IID/X fiber numbers (Sed, 11 +/- 2; Tm, 22 +/- 3; P < 0.025). These findings indicate that porcine skeletal muscle ad apts to endurance exercise training in a manner similar to muscle of h umans and other animal models, with increased oxidative capacity. Spec ific muscles exhibiting these adaptations, however, differ between the miniature swine and other species.