Eccentric ergometry: increases in locomotor muscle size and strength at low training intensities

Lengthening (eccentric) muscle contractions are characterized by several un usual properties that may result in unique skeletal muscle adaptations. In particular, high forces are produced with very little energy demand. Eccent rically trained muscles gain strength, but the specific nature of fiber siz e and composition is poorly known. This study assesses the structural and f unctional changes that occur to normal locomotor muscle after chronic eccen tric ergometry at training intensities, measured as oxygen uptake, that do not influence the muscle when exercised concentrically. Male subjects train ed on either eccentric or concentric cycle ergometers for 8 wk at a trainin g intensity starting at 54% and ending at 65% of their peak heart rates. Th e isometric leg strength increased significantly in the eccentrically train ed group by 36%, as did the cross-sectional area of the muscle fiber by 52% , but the muscle ultrastructure remained unchanged. There were no changes i n either fiber size, composition, or isometric strength in the concentrical ly trained group. The responses of muscle to eccentric training appear to b e similar to resistance training.