ERK1/2 Phosphorylation in Human Skeletal Muscle of Elite and Recreationally Weight Trained Men

Abstract

Muscle readily adapts to resistance exercise, but to date, little data is available linking the MAPK signaling pathways to these adaptations. PURPOSE: This study was designed to quantify the relative activation via phosphorylation of the ERK1/2 MAPK pathway in human skeletal muscle in subjects with varied weight training backgrounds. METHODS: Subjects were national and international caliber competitive weightlifters (WL, n=6) or powerlifters (PL, n=5), recreationally trained men with 10 wks of circuit weight training experience (CWT, n=8), or sedentary controls (CON, n=3). All subjects provided muscle biopsies from the vastus lateralis muscle. Samples were lysed and ERK1/2 and phosphorylated ERK (ERK-P) were determined via SDS-PAGE and western blots using infrared markers. Data were analyzed via one-way ANOVA and LSD post-hoc tests. RESULTS: WL & PL had less total ERK1/2 than CWT or CON (p<0.05; OD [arbitrary units]; WL=1385 ± 202, PL=1957 ± 142, CWT=4401 ± 723, CON= 3733 ± 600; X ± SE), with a moderate effect size observed for the CWT group when compared to CON (Cohen's D= 0.64). Similar patterns were observed for ERK-P (OD; WL=474 ± 34, PL=1148 ± 89, CWT=2284 ± 372, CON= 2228 ± 178). When expressed as % of total ERK1/2 phosphorylated (%ERK-P), no significant differences were observed (%; WL=39.3 ± 7.6, PL=59.3 ± 4.2, CWT=51.9 ± 3.5, CON=63.0 ± 10.9), although a large effect size was apparent for the WL when compared to CON (D=1.25). CONCLUSIONS: Chronic weight training appears to influence resting levels of ERK1/2 MAPK pathway activity. Total ERK1/2 is modestly increased in recreationally trained individuals, while elite lifters with training histories of >10 yrs exhibit attenuated total ERK 1/2. This response pattern suggests increased ERK1/2 as an initial response to resistance exercise, while long-term training experience and elite-level performances may result in either a more efficient ERK1/2 MAPK pathway, or simply reduced activation of this system. The absolute levels of ERK-P appear to simply reflect total ERK1/2 levels, with ERK-P decreasing with total ERK 1/2. In summary, elite lifters exhibit altered activation of the ERK 1/2 MAPK pathway primarily by altering total ERK1/2 available. Additionally, elite lifters appear to require less ERK activation, perhaps reflective of a more efficient signal or less stimulus for ERK activation. Funded by The University of Memphis FedEx Institute of Technology Research Investment Fund and the National Strength and Conditioning Association