Succinate dehydrogenase (SDH) and NADH tetrazolium reductase (NADHTR) as well as 6-phosfofructokinase (PFK) and a-glycerophosphate dehydrogenase (a-GPD) were measured in biopsies from Quadriceps muscles. 84 healthy young soccer players were measured before and after immobilization in a plaster cast as treatment for a ruptured knee ligament. Significant decrease in SDH activity was found especially in the immobilized muscle (3.44 to 2.22 umol/g/min) whereas the NADHTR activity was found unchanged. The PFK activity was unaffected of immobilisation (22.5 to 24.7 umol/g/min) whereas a significant increase was found in a-GPD especially in type II fibres of the immobilized muscles. Surgical repair of the ligament prior to immobilization did not influence these enzymatic changes. The immobilization-induced enzymatic changes were unaffected of electrostimulation with 10Hz and 50 Hz and also unaffected of Quadriceps settings during the immobilization. Only weak correlations were found between the biochemical and histochemical enzyme analysis of the different metabolic pathways. The variation in fibre composition in the human skeletal muscle seems to be an important reason for the variation in the enzyme analysis. It is concluded that the SDH activity is sensitive to reduced physical demand of human skeletal muscle, and that isometric exercise (quadriceps settings) seems insufficient as prevention.

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