EFFECTS OF STRENGTH AND ENDURANCE TRAINING ON MUSCLE-FIBER CHARACTERISTICS IN ELDERLY WOMEN

The effects of 18 weeks' intensive strength and endurance training on fibre characteristics of the vastus lateralis muscle were studied in 7 6- to 78-year-old women. Type I and type IIa fibres constituted over 9 0% of the cell population and were almost equally represented. No chan ges were observed in the proportions of the different fibre types. Whe n comparing the baseline and the 18-week measurements within the group s, the strength group showed a mean increase of 34% (P=0.028) in mean type I fibre area. The frequency histograms showed an increased propor tion of larger type I fibres after strength training and a decreased p roportion of smaller type IIa fibres after endurance training. In the control subjects, the proportion of smaller type I and type IIa fibres increased during the experimental period. The results indicate that i ntensive strength training induces type I fibre hypertrophy, whereas t he effects of endurance training are less evident. The considerable va riation found in the change in muscle fibre cross-sectional areas is a lso noteworthy.