Dynamic exercise training in foxhounds. II. Analysis of skeletal muscle.

The purpose of this study was to determine whether 8-12 wk of endurance training produces biochemical and histochemical adaptations in skeletal muscle in foxhounds. Analyses were performed on samples removed from gastrocnemius, triceps, and semitendinosus muscles of foxhounds before and after a treadmill running program. Biochemical analysis showed that training did not alter the activities of phosphofructokinase, beta-hydroxyacyl-CoA dehydrogenase, succinate dehydrogenase, or total phosphorylase. Histochemical analysis of myofibrillar actomyosin ATPase demonstrated three distinct classes of type II fibers and one type I fiber in the semitendinosus and triceps muscles and two type II and two type I fibers in the gastrocnemius muscle. Fiber type distribution and oxidative and glycolytic potentials, as indicated by nicotinamide adenine dinucleotide tetrazolium reductase or alpha-glycerophosphate dehydrogenase staining intensity, were unaltered by training. Similarly, capillary density, capillary-to-fiber ratios, and capillary area-to-fiber area ratios did not change with training. Thus, unlike humans and other mammals (i.e., rat), these foxhounds did not manifest biochemical or histochemical adaptations in skeletal muscle as the result of endurance training. This is consistent with the results of the study in which endurance training produced a 27% increase in maximal cardiac output and a 4% increase in maximal arteriovenous O2 extraction in foxhounds.