MUSCULAR ADAPTATIONS AND INSULIN-LIKE GROWTH FACTOR-1 RESPONSES TO RESISTANCE TRAINING ARE STRETCH-MEDIATED

Introduction: Modulation of muscle characteristics was attempted through altering muscle stretch during resistance training. We hypothesized that stretch would enhance muscle responses. Methods: Participants trained for 8 weeks, loading the quadriceps in a shortened (SL, 0-50 degrees knee flexion; n=10) or lengthened (LL, 40-90 degrees; n=11) position, followed by 4 weeks of detraining. Controls (CON; n=10) were untrained. Quadriceps strength, vastus lateralis architecture, anatomical cross-sectional area (aCSA), and serum insulin-like growth factor-1 (IGF-1) were measured at weeks 0, 8, 10, and 12. Results: Increases in fascicle length (29 +/- 4% vs. 14 +/- 4%), distal aCSA (53 +/- 12% vs. 18 +/- 8%), strength (26 +/- 6% vs. 7 +/- 3%), and IGF-1 (31 +/- 6% vs. 7 +/- 6%) were greater in LL compared with SL muscles (P<0.05). No changes occurred in CON. Detraining decrements in strength and aCSA were greater in SL than LL muscles (P<0.05). Conclusions: Enhanced muscle in vivo (and somewhat IGF-1) adaptations to resistance training are concurrent with muscle stretch, which warrants its inclusion within training. Muscle Nerve49: 108-119, 2014