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 wk of eccentric cycling training (ECC), which was expected to increase muscle function and VL cross-sectional area (CSA).

Methods: Eleven men (23 ± 4 yr) completed 24 sessions of ECC with progressive increases in intensity and duration, resulting in a twofold 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 d 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.

Conclusions: In addition to increased muscle mass, strength, and power, we demonstrate that ECC 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.