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

Abstract

ObjectiveTo determine if markers of skeletal muscle extracellular matrix (ECM) content and ECM remodeling are indicators of hypertrophy in previously untrained collage aged males.HypothesesHigher‐responders (HR) to resistance training would demonstrate more malleable changes in assayed ECM markers than lower‐responders (LR).MethodsUntrained, 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.ResultsNo 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)ConclusionsOur 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.