[[{“type”:”media”,”view_mode”:”wysiwyg”,”fid”:”427886″,”attributes”:{“alt”:””,”class”:”media-image media-image-right”,”style”:”width: 350px; height: 257px; border-width: 4px; border-style: solid; margin: 4px; float: right; “,”title”:””,”typeof”:”foaf:Image”}}]]The eccentric portion of lifts causes more muscle damage—and growth! Fast-twitch muscle fibers contribute mostly to muscle strength and have greater potential for increases in mass. Explosive muscle contractions such as sprinting, Olympic lifting, and plyometrics activate more fast-twitch muscle fibers. The slow-twitch muscle fibers are more efficient at extended muscle contractions over a long period of time. Therefore, slow-twitch fibers are great at helping athletes run marathons and bicycle for hours. Eccentric contractions (i.e., lowering the weight) have been found to increase muscle mass and strength compared to concentric contractions (lifting the weight). The rationale is that as the muscle fiber is stretched during a contraction, more tension is placed on fewer muscle fibers and more damage occurs to the muscle fibers. Researchers examined both fast-twitch and slow-twitch muscle fibers after eccentric exercise. Eight men performed 210 eccentric contractions of the elbow flexors on an isokinetic dynamometer with one arm. Markers of muscle damage and strength were examined before and after exercise. Researchers observed that only fast-twitch muscle fibers were damaged, whereas the slow-twitch fibers were not. This may be the reason why eccentric exercise causes more muscle growth as noted in the study. – FLEX