Comparison of biomechanical effects of eccentric and concentric exertions

Research Trainee: Amrish Chourasia, PhD Student in Biomedical 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

Work place exertions may include muscle shortening (concentric), muscle lengthening (eccentric) or constant muscle length (isometric) contractions. Muscle injury may occur for any of these types of exertions depending upon the magnitude, repetition rate and duration of the contractions. However, eccentric contractions have been associated with higher damage than similar concentric contractions. Onset of muscle soreness, increased passive muscle stiffness, force decrements several days after intense eccentric contractions have been reported but not after concentric contractions of similar magnitude, repetition and duration. Changes in signal intensity and T2 relaxation time in MRI images have been seen after eccentric exercise but not after concentric exercise.

The human hand and arm have been modeled as a single degree of freedom mechanical torsional system and represented as a single mass, spring and damper. An instrument was developed in the Occupational Ergonomics and Biomechanics laboratory at the University of Wisconsin-Madison to quantify the dynamic properties of (stiffness, inertia and damping) of the hand-arm system. Previous studies have shown that the dynamic mechanical properties are dependent on the posture of the operator and location of the workspace. Reduced stiffness can cause greater reaction forces and handle displacement when using a power tool, adversely affecting the ability of a worker to operate one. Long-term effects of these findings in repetitive exercise are not yet known.

This study investigates the upper limb mechanical properties and magnetic resonance images (MRI) of the involved muscles following submaximal eccentric and concentric exertions. Twelve participants were randomly assigned to perform at 30° per second eccentric or concentric forearm supination exertions at 50% isometric maximum voluntary contraction (MVC) for 30 minutes. Measurement of mechanical stiffness, isometric MVC, localized discomfort and MRI supinator: extensor signal intensity ratio was done before, immediately after, 1 hour after and 24 hours after the bout of exercise. A 53% average decrease in mechanical stiffness after 1 hour was observed for the eccentric group (p< 0.05) compared to a 1% average decrease for the concentric group (p> 0.05). Both groups had significant reduction (p<0.05) in static strength following exercise but both groups had recovered to within 5% of pre exercise static strength. Edema, indicative of swelling, was observed 24 hrs after exercise, with an average increase in the MRI supinator: extensor signal intensity ratio of 36% for the eccentric group and less than 10% for the concentric group (p<0.05).

 

Research trainee’s current position:
Amrish Chourasia completed his PhD in 2010 and is currently a Human Factors Engineer at Design Concepts.