title: Effects of resistance exercise intensity on extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase activation in men.
abstract: Extracellular signal-regulated kinase (ERK) 1/2 signaling has been shown to be increased after heavy resistance exercise and suggested to play a role in the hypertrophic adaptations that are known to occur with training. However, the role that ERK1/2 may play in response to lower intensities of resistance exercise is unknown. Therefore, the purpose of this study was to determine the effects of resistance exercise intensity on ERK1/2 activity in human skeletal muscle. Twelve recreationally active men completed separate bouts of single-legged resistance exercise with 8-10 repetitions (reps) at 80-85% 1 repetition maximum (1RM) (85%) and 18-20 reps at 60-65% 1RM (65%) in a randomized crossover fashion. For both resistance exercise sessions, vastus lateralis biopsies and blood draws were taken immediately before exercise (PRE) and at 30 minutes (30MPST), 2 hours (2HRPST), and 6 hours (6HRPST) post exercise, with an additional blood draw occurring immediately after exercise (POST). The phosphorylated levels of pIGF-1R, pMEK1, pERK1/2, and activated Elk-1 were assessed by phosphoELISA, and serum insulin-like growth factor 1 (IGF-1) was assessed via enzyme-linked immunosorbent assay. Statistical analyses used a 2 × 4 (muscle responses) and 2 × 5 (serum responses) multivariate analysis of variance on delta values from baseline (p < 0.05). Both exercise intensities significantly increased the activity of insulin-like growth factor 1 receptor (IGF-1R), mitogen-activated protein kinase 1, ERK1/2, and Elk-1, with peak activity occurring at 2HRPST (p < 0.001). However, 65% resulted in a preferential increase in IGF-1R and Elk-1 activation when compared with 85% (p < 0.05). No differences were observed for serum IGF-1 levels regardless of intensity and time. These findings demonstrate that resistance exercise upregulates ERK1/2 signaling in a manner that does not appear to be preferentially dependent on exercise intensity.
authors.affiliation: 1Department of Exercise and Sport Science, Human Performance Lab, University of Mary Hardin-Baylor, Belton, Texas, USA.
authors.forename: Lem W
authors.initials: LW
authors.lastname: Taylor
authors.forename: Colin D
authors.initials: CD
authors.lastname: Wilborn
authors.forename: Richard B
authors.initials: RB
authors.lastname: Kreider
authors.forename: Darryn S
authors.initials: DS
authors.lastname: Willoughby
mesh_terms: D018592:Cross-Over Studies; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000097:blood / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000097:blood / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000097:blood / Q000378:metabolism*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D055070:Resistance Training; D055815:Young Adult; D050807:ets-Domain Protein Elk-1 / Q000097:blood
chemical_list: D050807:ets-Domain Protein Elk-1; D007334:Insulin-Like Growth Factor I; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases