Downhill walking training with and without exercise-induced muscle damage similarly increase knee extensor strength

This study examined whether avoiding or experiencing exercise-induced muscle damage (EIMD) influences strength gain after downhill walking training. Healthy young males performed treadmill downhill walking (gradient: -28%, velocity: 5kmh(-1) and load: 10% of body mass) 1 session per week for four weeks using either a ramp-up protocol (n=16), where exercise duration was gradually increased from 10 to 30, 50 and 70min over four sessions, or a constant protocol (n=14), where exercise duration was 40min for all four sessions. Indirect markers of EIMD were measured throughout the training period. Maximal knee extension torque in eccentric (-1.05 rads(-1)), isometric and concentric (1.05 rads(-1)) conditions were measured at pre- and post-training. The ramp-up group showed no indications of EIMD throughout the training period (e.g., plasma creatine kinase (CK) activity: always <185UL(-1)) while EIMD was evident after the first session in the constant group (CK: peak 485UL(-1)). Both groups significantly increased maximal knee extension torque in all conditions with greater gains in eccentric (ramp-up: +19%, constant: +21%) than isometric (+16%, +15%) and concentric (+12%, +10%) strength without any significant group-difference. The current results suggest that EIMD can be avoided by the ramp-up protocol and is not a major determinant of training-induced strength gain.