Extracellular Matrix Content and Remodeling Does Not Differ Between Higher-Responders and Lower-Responders to Resistance Training.

Abstract

OBJECTIVE: To determine if markers of skeletal muscle extracellular matrix (ECM) content and ECM remodeling are indicators of hypertrophy in previously untrained collage aged males. HYPOTHESES: Higher-responders (HR) to resistance training would demonstrate more malleable changes in assayed ECM markers than lower-responders (LR). METHODS: Untrained, college-aged males (n=38, 21+/-3 years old) participated in 10 weeks of full-body progressive resistance training (2x weekly) which included the leg press, bench press, leg extension, deadlift, and lat pulldown exercises. Participants completed a pre-testing battery (DXA, ultrasound, pQCT and strength testing) and donated a vastus lateralis (VL) biopsy approximately one week prior to training. Participants completed post-testing 72 hours following their last training bout, and this mimicked pre-testing. Participants were then sorted into HR (n=10) and LR (n=10) based on changes in lean body mass, mid-thigh cross-sectional area (CSA), VL thickness, and deadlift strength changes. Muscle tissue from these 20 participants were processed for western blotting targeting MMP-2, MMP-9, MMP-14, TIMP-1, TIMP-2, collagen-1, and collagen-4 protein levels. Global MMP activity was also performed on whole tissue lysates, and fascial thickness was measured from ultrasound images. All dependent variables were analyzed in SPSS (v22.0) using two-way (group*time) repeated measures ANOVAs. RESULTS: No significant group*time interactions or main effects of time were detected for MMP-2, MMP-9, TIMP-1, TIMP-2, Collagen-1, or Collagen-4 protein levels (p > 0.05). MMP activity and VL fascial thickness also revealed no significant group*time interactions or main effects of time (p > 0.05). A significant main effect of time (p = 0.009) and group*time interaction (p = 0.007) was detected for MMP-14. Further analysis revealed a significant difference between HR and LR prior to training (p = 0.026) along with a significant decrease from pre to post in HR (p = 0.002) CONCLUSIONS: Our data suggest that skeletal muscle ECM markers did not differentiate higher-responders versus lower-responders to resistance training. However, MMP-14 was responsive to resistance training and significantly different between response clusters prior to resistance training, and this warrants further investigation.