Relationship between muscle swelling and stiffness after eccentric exercise

The time courses of muscle compartmental swelling and passive stiffness change were measured to determine whether muscle compartmental swelling accounted for increased stiffness.

Eleven untrained female college students exercised eccentrically by lowering a weight with their elbow flexors. Measurements of muscle compartment volume, stiffness, relaxed elbow angle, circumference, and pain were recorded before exercise, immediately after exercise, and 1-5, 7, 9, and 11 d after exercise. Muscle compartment volume was calculated from cross-sectional ultrasound images taken along the upper arm. Stiffness was measured using a device that extended the elbow and recorded the torque required to hold the forearm at successive angles.

Elbow flexor volume increased gradually to peak on the fourth day (26.1 +/- 4.3%, P < 0.05) and then decreased to baseline values over days 7-11. Stiffness increased immediately after exercise (59.9 +/- 14.1%, P < 0.05) and remained at or above this level until decreasing to pre-exercise levels over days 7-11.

This suggests that muscle swelling does not account for the sudden increase in stiffness of the elbow flexor muscles within the first 48 h after exercise but may play a role in the subsequent time course of stiffness.