Effects of strength and endurance training on muscle fibrecharacteristics in elderly women

The effects of 18weeks’ intensive strength and endurance training on fibre characteristics of the vastuslateralis muscle were studied in 76- to 78-year-old women. Type I and type IIa fibresconstituted over 90% of the cell population and were almost equally represented. Nochanges were observed in the proportions of the different fibre types. When comparing thebaseline and the 18-week measurements within the groups, the strength group showed a meanincrease of 34% (P=0·028) in mean type I fibre area. Thefrequency histograms showed an increased proportion of larger type I fibres after strengthtraining and a decreased proportion of smaller type IIa fibres after endurance training. In thecontrol subjects, the proportion of smaller type I and type IIa fibres increased during theexperimental period. The results indicate that intensive strength training induces type I fibrehypertrophy, whereas the effects of endurance training are less evident. The considerablevariation found in the change in muscle fibre cross-sectional areas is also noteworthy.