Relationship between pre-exercise muscle stiffness and muscle damage induced by eccentric exercise

Abstract

This study aimed to determine whether pre-exercise muscle stiffness is related to the amount of muscle damage induced by an eccentric exercise and to determine whether the post-exercise increase in stiffness is homogenously distributed between the synergist muscles. Fifty healthy participants were randomly assigned to an eccentric exercise group or a control group. The shear modulus (an index of stiffness) of rectus femoris (RF), vastus lateralis (VL) and vastus medialis oblique (VMO) was measured before, immediately after and at 48 h after eccentric exercise. The maximal isometric voluntary knee extension (MVC) torque was also measured. Significant reduction in MVC torque was observed in the eccentric group both at post and 48 H when compared with pre-exercise (both p < .001). RF shear modulus increased significantly when assessed at 90° of knee flexion at post and 48 H after the eccentric exercise (p = .004 and .005, respectively). Slight but significant decrease in VL shear modulus was observed at post-exercise for the eccentric group (p = .002). No change was observed in VMO. The decrease in MVC at 48 H was negatively correlated with the RF shear modulus measured at 90° of knee flexion before the exercise. Eccentric exercise induced a wide range of peak torque reduction and muscle-head specific modulation on muscle stiffness. Participants with stiffer RF muscles exhibited greater decrease in force generating capacity at 48 H after eccentric exercise.

Keywords:

• Elastography
• muscle tension
• muscle damage
• quadriceps femoris
• ultrasound

Acknowledgements

The authors thank Mr Siu Sik Cheung (Department of Rehabilitation Science, the Polytechnic University) for making the synchronizer between the Cybex dynamometer and the SSI machine. Special thanks to Dr Lui Che Woo and Mrs Lui Chui Kam Ping for their generous donation of the Aixplorer elastography scanner.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Jingfei Xu http://orcid.org/0000-0002-6430-4180