Abstract

Three different training regimens were performed to study the influence of eccentric muscle actions on skeletal muscle adaptive responses to heavy resistance exercise. Middle-aged males performed the leg press and leg extension exercises 2 d/wk. The resistance was selected to induce failure within 6 to 12 repetitions of each set. Group CON/ECC performed coupled concentric and eccentric actions while group CON used concentric actions only. They did 4 or 5 sets of each exercise. Group CON/CON performed twice as many sets with only concentric actions. 8 subjects did not train and served as controls. Tissue samples were obtained from m. vastus lateralis using the biopsy technique before and after 19 wk of training, and after 4 wk of detraining. Histochemical analyses were performed to assess fibre type composition, fibre area and capillarization. Training increased Type IIA and decreased Type IIB fibre percentage. Only group CON/ECC increased Type I area (14). Type II area increased 32 and 27, respectively, in groups CON/ECC and CON/CON, but not in group CON. Mean fibre area increased 25 and 20 in groups CON/ECC and CON/CON, respectively. Capillaries per fibre increased equally for Type I and Type II fibres. Capillaries per fibre area for both fibre types, however, increased only in groups CON and CON/CON. The changes in fibre type composition and capillary frequency were manifest after detraining. At this time only group CON/ECC showed mean fibre hypertrophy, while capillary density was elevated in CON/CON and CON. Verf.-Referat