Muscle length influence on rectus femoris damage and protective effect in knee extensor eccentric exercise

• Published in: Scandinavian journal of medicine & science in sports Vol. 31; no. 3; pp. 597 - 609
• Main Authors: Ema, Ryoichi, Nosaka, Kazunori, Kawashima, Ryosuke, Kanda, Akihiro, Ikeda, Koya, Akagi, Ryota
• Format: Journal Article
• Language: English
• Published: Denmark Blackwell Publishing Ltd 01-03-2021; John Wiley and Sons Inc
• Subjects: Electromyography; hip flexion; Hypotheses; Knee; maximal voluntary contraction; muscle soreness; Original; repeated bout effect; shear modulus; maximal voluntary contraction; hip flexion; muscle soreness; shear modulus; repeated bout effect
• ISSN: 0905-7188; 1600-0838
• DOI: 10.1111/sms.13890

This study tested the hypothesis that the magnitude of rectus femoris (RF) damage and the repeated bout effect (RBE) would be greater after knee extensor eccentric exercise performed in a supine (long RF lengths) than a sitting (short RF lengths) position, and the muscle length effects would be more prominent at the proximal than distal RF. Young untrained men were placed to one of the two groups (n = 14 per group). S group performed the knee extensor eccentric exercise in the sitting position for the first bout and the supine position for the second bout, and L group performed the exercise in the supine position for two bouts, with 4 weeks between bouts. Dependent variables included evoked and maximal voluntary isometric contraction (MVC) torque, electromyography (EMG) during MVC, muscle soreness, and shear modulus, which were measured before and 1‐3 days after each exercise bout. After the first bout, L group in comparison with S group showed greater (P < .05) changes in hip flexor MVC torque (average of 1‐3 days post‐exercise: −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 evident for any of other variables after the first bout including knee extensor MVC torque, and for the changes in all variables after the second bout. These results supported the hypothesis that RF damage would be greater for the spine than sitting position especially at the proximal region, but did not support the hypothesis about the RBE.