PROTEIN-METABOLISM IN RAT TIBIALIS ANTERIOR MUSCLE AFTER STIMULATED CHRONIC ECCENTRIC EXERCISE

In another study (J. Appl. Physiol. 69: 1709-1717, 1990) we reported that gastrocnemius (GAST) muscle enlargement failed to occur after 10 wk of 192 contractions performed every 3rd or 4th day. This result was surprising because increased protein synthesis rates were determined after an initial acute exercise bout with the same paradigms. In the same set of animals, tibialis anterior (TA) muscles were enlarged 16-30% compared with sedentary control muscles after the same chronic training regimen. This indicated that the regulation of protein expression may be different between the GAST and TA muscles. The present experiment attempted to define and explain these differences by comparing changes in various indexes of protein metabolism in TA with the same parameters determined in the accompanying study for the GAST. As in the GAST, results showed that TA protein synthesis rates are increased by acute exercise and principally regulated by translational and possibly posttranslational mechanisms. The differential response in muscle mass between the GAST and TA muscles after training may be due, in part, to greater relative resistances imposed on the TA than on the GAST that result in a more-prolonged effect on protein synthesis rates, with lower numbers of stimulated contractions required to stimulate increases in protein synthesis. Data also revealed that although as little as 1 min of total contractile duration (24 repetitions) increased TA protein synthesis rate by 30%, 8 min of total contractile duration (192 repetitions) further increased TA protein synthesis rates to only 45% above control.