Exercise training comprised of predominantly eccentric muscle contractions (eccentric exercise) is supposed to elicit higher gains in muscle mass and strength than standard resistance training. Mechanisms of eccentric exercise are not yet fully understood; it is assumed that microtrauma plays a key role in triggering subsequent reinforcement of tissue. The purpose is to review published evidence on the influence of eccentric exercise on skeletal muscle structure in humans. Methods: We searched for research reports published in English language in PubMed and Cochrane Library databases. The review was limited to studies performed on healthy adult human subjects. Results: Nine articles reporting structural changes of skeletal muscles after either a single bout of eccentric exercise or prolonged training programme were included in the review. Significant changes in muscle cross-section area, thickness, fascicle length and angle, oedema, anabolism of muscle proteins and changes in T-system structure were reported. Conclusions: A single bout of eccentric muscle overload causes microtrauma to the cells, whereas prolonged eccentric training leads to lasting improvements in skeletal muscle structure and hypertrophy. More methodologically comparable studies conducted on larger samples are needed to draw definite conclusions in this regard.
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