Skeletal muscle adaptations in elastic resistance-trained young men and women.

Skeletal muscle adaptations (fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarity) were assessed in the vastus lateralis muscle of young men and women after 8 weeks of training with the Sportcord, an elastic resistance device. Ten men [mean (SD) age 20 (1.1) years] and 13 women [20 (1.2) years] performed two sets each to failure of single leg squats and leg extensions at approximately 50 repetitions x min(-1). Biopsy samples were taken from the right vastus lateralis muscle before and after training. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using myofibrillar ATPase histochemistry. Training with the Sportcord caused a small, but significant, increase in one-repetition maximum using free weights and a large increase in repetitions to failure. In addition, elastic resistance training caused an increase in the percentage of fibers classified as type IIAB for both men and women, and a decrease in the percentage of type IIB fibers in the men. MHC analysis supported these findings (a significant increase in the percentage of MHCIIa for the men). The cross-sectional areas ofboth the type I and IIAB + IIB fibers increased after training for the men, whereas no area changes were found for the women. The capillary:fiber ratio and capillary contacts per fiber type increased significantly for the men, and similar trends were noted for the women. Capillary density did not change in either the men or the women. These data suggest minor changes in fiber type composition (IIB-->IIAB), fiber size, and capillarization following short-term training with elastic resistance. Although muscular changes did occur using the Sportcord, the extent of these changes was less than those reported previously for short-term resistance-training programs using free weights.