Running training alters fiber type composition in spinal muscles.

The issue of whether exercise can induce changes in muscle fiber types has been long debated. Knowledge about the alterations in spinal muscle fiber types is scarce. In this study, the alterations initiated by long-distance running on spinal muscle fiber type distribution was studied. Ten young dogs were run on a treadmill for 55 weeks, 5 days a week, and ten dogs from the same litters served as controls. The daily running distance was gradually increased to 40 km and maintained at that level for the final 15 weeks. Histological sections were prepared from the cervical, thoracic, and lumbar multifidus muscles and the medial and lateral heads of triceps brachii and analyzed for the fiber type composition and cross-sectional area of fibers. In the lumbar multifidus, the numerical percentage of the muscle fibers with low oxidative capacity (type II) increased significantly in the running group. However, in the thoracic and cervical spine multifidus, the response to running resembled more of the significant shift from type II to type I fibers (with high oxidative capacity), which was also observed in the triceps brachii muscle. In these muscles, the quantitative image analysis of nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) reaction also demonstrated a shift towards a higher oxidative capacity within the type II fibers. The results show that training can induce changes in fiber type composition not only in limb muscles but also in the stabilizing spinal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)