Muscle can be damaged by external factors (for example, in contact sports), or by internal factors (mechanical or biological factors, triggered by un unusual exercise that involve eccentric muscle actions, for example). An eccentric muscle contraction occurs when a muscle opposes a stronger force, which causes the muscle to lengthen as it contracts (let us just think, for example, about opening a heavy door with one arm). Muscle eccentric contractions are present in activities as normal as going from stand to sit, walking, or regaining balance, among others; and chronic eccentric exercise is important in the rehabilitation of some patients.
“Exercise-induced muscle injury” frequently occurs after unusual exercise involving a large amount of eccentric contractions, and its main symptoms are pain, swelling, stiffness, reduced strength and fatigue. In all dynamic sports (basketball, hockey, jogging, skating, tennis, etc.), which involve high-intensity eccentric contractions, these symptoms are most common when intense training is reintroduced after a period of relative inactivity. However, muscles that have been previously prepared with eccentric contractions, warm-up, and stretching are protected against damage. Besides, it has been observed in a recent study that a single high dose of EPA from fish oil (1 g per 10 kg body mass) might ameliorate the functional changes following exercise-induced muscle damage.
The intake of EPA in addition to perform specific routines: a few high-intensity eccentric contractions one to two weeks before returning to full activity, and performing specific stretching and warm-up exercises for the principal muscle groups immediately before the first few training sessions or games, may reduce the severity of the symptoms of muscle damage induced by exercise.