Muscular Pain, Soreness and Stiffness

During and following strenuous muscular exercise, particularly in untrained objects, there may be muscular pain, soreness and stiffness.

Muscular pain commonly occurs during exercise, while soreness and stiffness usually appear some hours later. It is well known that when muscles are forced to work without adequate blood supply (for example, rapid flexion and extension of the fingers with the circulation occluded by a blood pressure cuff) severe pain results. The inadequate blood flow results in failure of complete removal of the products of muscle metabolism, and it is probable that the pain of strenuous exercise is due to accumulation of acid metabolites which irritate the receptor organs of pain located in the muscles.

Fluid collects in muscles during activity and a number of hours may be required for its reabsorption into the blood stream. The resulting swelling of the muscle causes it to become shorter and thicker and more resistant to stretching. This gives rise to a sensation of stiffness when the muscle is stretched during the contraction of antagonistic muscles.

The cause of muscle soreness is not completely understood. Two types of muscle soreness have been postulated:

(1) general soreness due to the presence of diffusible metabolic waste products which usually disappears within three or four hours after the cessation of exercise, and (2) localized soreness or lameness which appears eight to twenty-four hours after exercise and may persist for several days. The second type of soreness is probably due to the rupture of muscle fibers or of the sarcolemma which transmits the contraction to the tendon. The less frequently used fibers and the sarcolemma covering them are probably more susceptible to strain than are the fibers more frequently used in ordinary contractions. The generalized type of soreness is alleviated by light work which hastens the circulatory removal of the metabolic waste products, while the localized lameness, which is due to actual injury, needs rest with heat and only enough exercise to prevent adhesions between the injured muscle fibers.