Background
Delayed onset muscle soreness (DOMS) is an overuse injury related to physical activity, considered one of the most common reasons for compromised sport performance. Some hypotheses have been suggested to explain this condition including lactate theory, muscle damage theory, and inflammation theory [1-3]. It is accepted that the main mechanism is related to eccentric exercise, as well as performance of unfamiliarized sporting activities. In fact, biopsy analysis of eccentric strained muscle tissue has shown loss of myofibrillar integrity and disruption of sarcomeres in the myofibrils, leading to local inflammatory response [1,4].
Clinical Perspective
Clinical signs and symptoms vary, including impaired muscular strength, soreness, stiffness or swelling, often accompanied by reduced motion range of the adjacent joints. Signs and symptoms normally begin 6-12 hours after exercise, peaking at 48-72 hours, decreasing until they disappear 5-7 days later [1,3]. Such clinical presentation represents the main key to diagnosis, differing from ordinary muscle strains, where the onset of pain is usually immediate. Increased CK levels may occur. There is usually no permanent damage to muscle function [3].
Imaging Perspective
Imaging features of DOMS may be similar to muscle strain, making it challenging to differentiate the two [3]. On ultrasound, it presents as well-defined hyperechoic regions within the muscle, and increased muscle size with minimal hyperemia [1,3].
On MRI, muscle edema is depicted as high signal intensity of the affected muscle in the fluid-sensitive sequences (T2 and STIR), and perifascial fluid may be present in the early phases. There is no macroscopic fiber disruption or tear associated with DOMS. A delay between the occurrence of severe symptoms and the maximum intensity of signal abnormalities seen on MR images has been described. Abnormal signal intensity on fluid-sensitive MR images may last up to 80 days [1,3].
Outcome
DOMS generally resolves after a few days or weeks. A variety of treatments have been described, such as cryotherapy, massage, active exercises, compression clothing, acupuncture, stretching, kinesio taping, foam roller and electro-stimulation [4].
Take Home Message / Teaching Points
The primary mechanism of DOMS is currently thought to be due to eccentric exercise and high intensity unfamiliarized physical activity. Signs and symptoms have a peak at 48-72 hours and generally resolve after a few days or weeks. MRI has been reported as the preferred imaging modality. Nevertheless, ultrasound can also provide useful imaging features for an adequate diagnosis in the right clinical setting.
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