Muscle fiber distribution, capillary density, and enzymatic activities in the lumbar paravertebral muscles of young men. Significance for isometric endurance.

The aim of this work is to expand the knowledge about fiber distribution, capillarization, and metabolic potential in different anatomic sections of the left and right human lumbar paravertebral muscles and further to investigate whether a relationship between these parameters and trunk muscle endurance exists. Lumbar (L3) paravertebral muscle samples were taken bilaterally from six young male cadavers (study 1) and from 10 normal young healthy men (study 2). The main findings are that the paravertebral muscles are dominated by slow twitch fibers with small fiber areas and a well-developed capillary network. This is most pronounced in the longissimus muscle. Glycogen concentration and enzyme activities (glycogen phosphorylase, lactate dehydrogenase, citric synthetase and 3-hydroxyacyl-CoA-dehydrogenase) in both aerobic and anaerobic metabolic pathways are large compared to other muscles. No obvious bilateral differences in the histochemical and biochemical results were present. The isometrical trunk extensor endurance time is markedly increased compared to other human skeletal muscles.