Justin X. Nicoll1, Adam J. Sterczala1, and Andrew C. Fry1. 1Dept. of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS; e-mail: Justin.nicoll@ku.edu

Mitogen-activated protein kinases (MAPK) modulate the hypertrophic, apoptotic, and metabolic resistance exercise (RE) adaptations of muscle tissue. Several studies have described the acute MAPK response to RE, yet few have reported their expression following RE used during maintenance training. Furthermore, there is a paucity of research concerning MAPK following the cessation of RE training. PURPOSE: The purpose of this study was to describe MAPK expression after short-term “maintenance” RE, and after the complete cessation of training. METHODS: Male subjects (n=6; age: 24.2±4.6yrs; body mass: 76.6±8.4kg, bodyfat: 10.1±6.7%) performed three weeks of RE training. Subjects participated in preparatory training the first two weeks (wk 1+2) and performed 3 sets of 5 repetitions of barbell back squats at 70% 1-RM load for all training sessions two times per week. After two weeks, subjects performed two sessions of “maintenance training” during week 3, which utilized the same training load and scheme as the preparatory period. Following the maintenance period, subjects ceased all training for one week (wk 4). Resting muscle biopsies were collected at the end of preparatory training (T1), the end of maintenance training (T2), and one week after the complete cessation of training (T3). Biopsy samples were analyzed for total and ratio (pMAPK/totalMAPK) of extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38 via western blotting. Non-parametric Freidman’s test determined differences in MAPK expression between T1, T2, and T3. Cohen’s d effect sizes were calculated anchoring on T1. Significance was set at p<0.05. RESULTS: There were no significant differences in total- or pMAPK/totalMAPK for ERK1/2, JNK, or p38 among any timepoint (p>0.05). There were large and moderate effect sizes for total- and pJNK/totalJNK respectively. Resting total JNK displayed a large effect size at T2 (68% increase; d=0.8). Resting pJNK/totalJNK displayed a moderate effect size at T3 (27% decrease; d=0.5). CONCLUSION: Expression of most MAPK (i.e. ERK and p38) remain stable following short-term maintenance RE. Furthermore, total and pJNK/totalJNK may differentially alter their resting expression depending on the phase and training stresses (or lack thereof) placed on muscle tissue.

Funding provided by Nutricia.

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