Mild to moderate damage in knee extensor muscles accumulates after two bouts of maximal eccentric contractions

PurposeThis study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days.MethodsThirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24 h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course.ResultsTwo days after the initial eccentric session, participants from EXP had a higher strength deficit (- 14.5 & PLUSMN; 10.6%) than CON (- 6.6 & PLUSMN; 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 & PLUSMN; 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%).ConclusionAlthough the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24 h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage.

Automated summary

The purpose of this study was to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days. The results showed that two days after the initial eccentric session, the experimental group had a higher strength deficit and an increase in muscle shear modulus compared to the control group.