Regional regulation of focal adhesion kinase after concentric and eccentric loading is related to remodelling of human skeletal muscle

AimsWe assessed focal adhesion kinase (FAK) response to concentric (CON) vs eccentric (ECC) resistance training (RT) at two vastus lateralis (VL) sites, and the relationships between FAK, muscle protein synthesis (MPS) and morphological remodelling. MethodsSix young males trained both legs unilaterally 3times/week for 8weeks; one leg performed CON RT, the contralateral performed ECC RT. Muscle biopsies were collected after training from VL mid-belly (MID) and distal (distal) sites at 0, 4, 8weeks. Focal adhesion kinase content and activation were evaluated by immunoblotting. MPS was assessed by deuterium oxide tracer; morphological adaptations were evaluated by ultrasound and DXA. ResultspY397-FAK 8weeks levels were 4-fold greater after ECC at the distal site compared to CON (P<.05); pY397FAK to total FAK ratio was greater in ECC vs CON at 4 (2.2-fold, P<.05) and 8weeks (9-fold, P<.001) at the distal site. Meta-vinculin was found transiently increased at 4weeks at the distal site only after ECC RT. ECC presented greater fascicle length (Lf) increases (10.5% vs 4%), whereas CON showed greater in pennation angle (PA) changes (12.3% vs 2.1%). MPS did not differ between exercise types or muscle sites at all time points. distal pY397-FAK and pY397-FAK/FAK values correlated to changes in Lf at 8weeks (r=.76, P<.01 and r=.66, P<.05 respectively). ConclusionFocal adhesion kinase phosphorylation was greater at 8weeks after ECC RT and was muscle region-specific. FAK activity correlated to contraction-dependent architectural remodelling, suggesting a potential role of FAK in orienting muscle structural changes in response to distinct mechanical stimuli.