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

AIMS We assessed focal adhesion kinase (FAK) response to concentric (CON) versus eccentric (ECC) resistance training (RT) at two vastus lateralis (VL) sites, and the relationships between FAK, muscle protein synthesis (MPS), and morphological remodeling. METHODS Six young males trained both legs unilaterally 3 times/week for 8 weeks; one leg performed CON RT, the contralateral performed ECC RT. Muscle biopsies were collected after training from VL midbelly (MID) and distal (Distal) sites at 0, 4, 8 weeks. FAK content and activation were evaluated by immunoblotting. MPS was assessed by deuterium-oxide tracer; morphological adaptations were evaluated by ultrasound and DXA. RESULTS pY397-FAK 8 weeks levels were ~4-fold greater after ECC at the Distal site compared to CON (p<0.05); pY397FAK to total FAK ratio was greater in ECC versus CON at 4 (~2.2 fold, p<0.05) and 8 weeks (~9fold, p<0.001) at the Distal site. Meta-vinculin was found transiently increased at 4 weeks 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=0.76, p<0.01 and r=0.66, p<0.05, respectively). CONCLUSION FAK phosphorylation was greater at 8-wks after ECC RT and was muscle region-specific. FAK activity correlated to contraction-dependent architectural remodeling, suggesting a potential role of FAK in orienting muscle structural changes in response to distinct mechanical stimuli. This article is protected by copyright. All rights reserved.