Increases in Integrin-ILK-RICTOR-Akt Proteins, Muscle Mass, and Strength after Eccentric Cycling Training.

PURPOSE Recently it has been suggested that a cellular pathway composed of integrin, integrin-linked kinase (ILK), rapamycin-insensitive companion of mTOR (RICTOR), and Akt may facilitate long-term structural and functional adaptations associated with exercise, independent of the mTORC1 pathway. Therefore, we examined changes in integrin-ILK-RICTOR-Akt protein in vastus lateralis (VL) before and after 8 weeks of eccentric cycling training (ECC) which was expected to increase muscle function and VL cross-sectional area (CSA). METHODS Eleven men (23 ± 4 years) completed 24 sessions of ECC with progressive increases in intensity and duration, resulting in a 2-fold increase in work from the first three (75.4 ± 14.1 kJ) to the last three sessions (150.7 ± 28.4 kJ). Outcome measures included lower-limb lean mass, VL CSA, static strength, and peak and average cycling power output. These measures and VL samples were taken before and 4-5 days after the last training session. RESULTS Significant (P < 0.05) increases in integrin-β1 (1.64-fold) and RICTOR (2.99-fold) protein as well as the phosphorylated-to-total ILK ratio (1.70-fold) were found, but integrin-α7 and Akt did not change. Increases in lower-limb, thigh, and trunk lean mass (2.8-5.3%, P < 0.05) and CSA (13.3 ± 9.0%, P < 0.001) were observed. Static strength (18.1 ± 10.8%) and both peak (8.6 ± 10.5%) and average power output (7.4 ± 8.3%) also increased (P < 0.05). However, no significant correlations were found between the magnitude of increases in protein and the magnitude of increases in CSA, static strength, or power output. CONCLUSION In addition to increased muscle mass, strength, and power, we demonstrate that eccentric cycling training increases integrin-β1 and RICTOR total protein and p-ILK/t-ILK, which may play a role in protection against muscle damage as well as anabolic signaling to induce muscle adaptations.