The Effects of Eccentric Contractions on Muscle Mechanical Properties

Research Trainee: Mary Sesto, PhD Student in Industrial and Systems Engineering at the University of Wisconsin at Madison

Faculty Researcher: Robert G. Radwin, PhD, Professor of Industrial and Systems Engineering and Biomedical Engineering at the University of Wisconsin at Madison

This study investigated changes in human muscle mechanical properties due to eccentric activities, similar to exertions associated with operation of impulsive vibrating hand tools. Specifically, the study tested the hypothesis that mechanical changes following eccentric muscle contractions endure longer than changes associated with static muscle exertions.

Eighteen subjects (9 male, 9 female) were randomly assigned to one of three treatments in a laboratory study. Six performed static isometric exertions, six performed eccentric exertions, and six served as controls. All subjects were tested using an apparatus designed to measure mechanical properties of muscles, including stiffness and mass moment inertia. Forearm supination strength was also measured. Subjects were tested prior to a bout of exercise, immediately following exercise, and 24 hours later.

Forearm supination strength decreased 19% immediately post-exercise and 7% after 24 hours in the isometric exercise group, compared to 34% post-exercise and 14% after 24 hours in the eccentric exercise group (p < .001). The percent change is stiffness from pre-exercise to post-exercise in the isometric exercise and control groups was less than 1%, compared to an 11% decrease in stiffness in the eccentric exercise group (p < .01). After 24 hours, the change in stiffness in the isometric and control groups stayed below 1%, compared to an 8% decrease in the eccentric exercise group. There was also a post-exercise decrease in mass moment inertia in the eccentric group compared to the control and isometric exercise groups (p < .01).

The consequences of reduction in stiffness and mass moment inertia following eccentric exertions include reduced capacity to react against torque reaction forces when operating power hand tools. This reduction in capacity may have adverse long-term effects on safety. Future research will investigate the magnitude of mechanical changes for different levels of eccentric exertions and different dynamic velocities.

 

Publications resulting from this project:
Sesto ME, Radwin RG, Best TM, Richard TG. Upper limb mechanical changes following short duration repetitive eccentric exertions. Clin Biomech (Bristol, Avon). 2004;19(9):921-928. doi:10.1016/j.clinbiomech.2004.06.005.

Sesto ME, Radwin RG, Block WF, Best TM. Anatomical and mechanical changes following repetitive eccentric exertions. Clin Biomech (Bristol, Avon). 2005;20(1):41-49. doi:10.1016/j.clinbiomech.2004.09.002.

Sesto ME, Radwin RG, Block WF, Best TM. Upper limb dynamic responses to impulsive forces for selected assembly workers. J Occup Environ Hyg. 2006;3(2):72-79. doi:10.1080/15459620500471239.

Sesto ME, Radwin R G, Richard TG. Short-term changes in upper extremity dynamic mechanical response parameters following power hand tool use. Ergonomics. 2005;48(7):807-20.

Grants resulting from this project:
NIOSH/CDC. 1R01 OH007793. Biomechanical Effects of Industrial Eccentric Exertions (PI: Radwin). 2002-2003.

NIOSH/CDC. K01 OH008640-01. Functional Limitations in Lateral Epicondylitis (PI:Sesto).

 

Research trainee’s current position:
Mary Sesto received her PhD in 2003 and she is currently an Associate Professor in the Department of Orthopedics and Rehabilitation at the University of Wisconsin School of Medicine and Pubic Health.