Acute Signaling Responses To Resistance Exercise In Previously Trained And Untrained Skeletal Muscle

Abstract

It has been indicated that human skeletal muscle has a heightened sensitivity to exercise stimulus when it has been previously trained i.e. possess a “muscle memory”. While previous studies have been directed to the aspects of myonuclear content and epigenetic modifications, no previous study have explored the potential of a muscle memory concerning signaling responses related to acute resistance exercise. PURPOSE: The aim here was to study whether basal and acute resistance exercise induced cell signaling is influenced by previous strength training history in human skeletal muscle. METHODS: 19 training naïve women and men completed 10 weeks of hypertrophy inducing unilateral strength training followed by 20 weeks of detraining. Subsequently, an acute resistance exercise session involving leg press and knee extensions was performed alternated with both legs. Vastus lateralis biopsies taken at rest and 1 h post exercise in both the Control- and Memory-leg. Immunoblotting was used to assess total content and phosphorylation status of proteins in the mTORC1- and related pathways. RESULTS: Following detraining leg muscle hypertrophy had been reversed, but the Memory-leg was on average 19% stronger than the Control-leg. There were no differences between legs with regard to total protein content of all the signaling proteins analyzed. The phosphorylation of AMPKThr172 and eEF2Thr56 was 16%, respectively 21%, higher in the Memory-leg compared to the Control-leg at both time points. The effect on AMPKThr172 was attributed to changes in the women only, whereas the effect on eEF2Thr56 was present in both sexes. Exercise induced an increased phosphorylation of mTORSer2448 (26-36%), S6K1Thr389 (6- to 7-fold) and S6Ser235/236 (13- to 18-fold), that did not differ between the Control- and Memory-leg. In contrast, post exercise phosphorylation of 4E-BP1Thr46 and 4E-BP1Ser65 was 18%, respectively 31%, higher in the Memory-leg compared to the Control-leg. For 4E-BP1Ser65 the effects were attributed to changes in the male subjects only. CONCLUSION: In summary, we illustrate that both basal- and exercise induced cell signaling important for muscle adaptations to strength training can be altered by previous training history, and that some of the changes seem to be sex dependent.