Morphological Adaptations of the Rectus Femoris and Biceps Femoris to EccentricIsometric Training and Their Relationship with Range of Motion

I .Subashka

Abstract: Objective: The aim of the study was to determine the effectiveness of flexibility training that incorporates eccentric and isometric muscle contractions performed at end ranges of motion by examining the resulting morphological and functional adaptations. Joint outcomes focused on the hip, including active and passive hip flexion and hip extension as well as front-split performance. Material and methods: Forty-four recreationally active adults (10 men, 34 women; 35.91 ± 6.84 years) completed a six-month training protocol. Participants were randomly assigned to an experimental group (n = 23) and a control group (n=21). Ultrasonography was used to assess fascicle length and pennation angle of m. rectus femoris and m. biceps femoris. Range of motion was measured using a goniometer, and flexibility was evaluated through active and passive front split tests. Results: he experimental group demonstrated greater improvements in flexibility - 25.5% in the left leg and 23.5% in the right - compared to the control group. Fascicle length increased by 35.4% in rectus femoris dextra and 22.9% in rectus femoris sinistra. These structural adaptations were accompanied by enhanced range of motion and strength at end ranges. Conclusion: Eccentric and isometric muscle contractions performed at end ranges of motion produce significant morphological adaptations—elongation of fascicles and increased pennation angle - that contribute to improved flexibility and functional performance.

Series on Biomechanics, Vol.39, No. 4 (2025), 3-14
DOI: 10.7546/SB.01.04.2025

Keywords: fascicle length; Muscle architecture; pennation angle; range of motion

DOI: 10.7546/SB.01.04.2025

Date published: 2025-12-12