Muscle length influence on rectus femoris damage and protective effect in knee extensor eccentric exercise.
Level 2 - randomized trial
Parallel controlled trial in young untrained men
PubMed 33249658 · doi:10.1111/sms.13890
What was done
Twenty-eight young untrained men were assigned to two groups (n = 14 each) to test rectus femoris (RF) damage and the repeated bout effect (RBE). The S group performed knee extensor eccentric exercise in a sitting position (short RF lengths) for bout 1 and a supine position (long RF lengths) for bout 2. The L group performed both bouts in the supine position, separated by 4 weeks. Evoked and maximal voluntary isometric contraction (MVC) torque, electromyography (EMG) during MVC, muscle soreness, and shear modulus were measured before and 1-3 days after each bout.
What was found
After bout 1, the L group showed significantly greater (P < .05) changes than the S group in hip flexor MVC torque (-11.1 ± 9.4% vs -5.0 ± 7.5%), proximal RF EMG (-22.4 ± 16% vs -9.0 ± 21.9%), and proximal RF shear modulus (33.2 ± 22.8% vs 16.9 ± 13.5%). No significant differences between groups were found for other variables after the first bout (including knee extensor MVC torque), and no significant between-group differences were observed for changes in any variable after the second bout.
Why it matters
This study shows that eccentric exercise at longer muscle lengths selectively increases damage in the proximal region of the biarticular rectus femoris muscle. However, greater initial damage did not enhance the magnitude of the repeated bout protective effect.
Limits
The study was conducted in a small sample of young untrained men only. The abstract does not specify whether group assignment was randomized or if outcome assessors were blinded.
Cited by
- supports Exercises that load muscles in a stretched position or emphasize the eccentric phase create more muscle damage than exercises loaded in shortened positions.