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