Objective: To test whether concentric (CON)-only resistance training increases the vulnerability to eccentric (ECC) exercise-induced dysfunction and muscle injury.
Design: Before-after trial.
Setting: General community.
Patients or other participants: Nine men (77 +/- 3 kg body weight) who were not trained in resistance exercise.
Intervention: Nine weeks of CON-only training of the left quadriceps femoris (QF); performance of 10 sets of 10 ECC actions with each QF using a load equivalent to 85% of the posttraining CON 1-repetition maximum (1RM).
Main outcome measures: CON 1RM for the untrained and trained QF measured immediately after training, and again 1, 3, 8, and 10 days after the bout of ECC exercise; cross-sectional area and spin-spin relaxation time (T2) of each QF determined by magnetic resonance imaging (MRI) before and 3 days after the ECC exercise bout.
Results: As a result of the ECC bout, the CON 1RM was reduced by approximately 30% in the trained limb and 16% in the untrained limb. Strength did not return to normal in the trained limb even after 10 days of recovery; however, in the untrained limb strength was restored by day 8. As assessed by MRI, the trained limb showed a greater area of muscle injury compared with the untrained QF. The T2 of the injured area was similar in both limbs, suggesting that the intensity of injury was similar, but more widespread in the trained limb.
Conclusion: CON-only training increases the vulnerability to ECC exercise-induced dysfunction and muscle injury, probably by increasing the CON 1RM, thus allowing the individual to be exposed to greater ECC loading potential.