Skeletal muscle fibre types, physical performance, physical activity and attitude to physical activity in women and men. A follow-up from age 16 to 27.

Fifty-five men and 28 women were tested at age 16 and retested at age 27. Muscle biopsies were taken from m. vastus lateralis to analyse fibre types, fibre areas and enzyme contents. A cycle ergometer test to was used to estimate the maximal oxygen uptake. Physical performance was assessed in an endurance test, where the subjects had to run as far as possible in 9 min on a 400-m track, and in three strength tests designed to test maximal dynamic strength (Sargent jump) and maximal static strength (handgrip test, two-hand lift). The subjects answered a questionnaire concerning physical activity during their leisure time and an activity index was calculated from the answers. The relative proportion of type I fibres (type I%) tended to increase with age in women and decreased in men. At age 27, the type I% was higher in women than in men. Multiple regression analysis indicated that sex per se could explain some of the interindividual variation in the type I% at age 27 and in the changes with age in the type I%, but also factors as physical activity (increase in type I%) and smoking (decrease in type I%) probably contributed to the variation. VO2max (ml.kg-1.min-1) increased with age in women and was unchanged in men so that there was no significant sex difference in VO2max at age 27. Running performance remained unchanged from age 16 to age 27 in both sexes and men performed better than women at both ages. Running performance was directly related to the type I% for both women and men at age 27, a relationship which existed also for men at age 16, but not for women at that age. It seems that the age related changes in relationship between running performance and type I% may be related to the altered choice of physical activity from speed and strength to more endurance demanding activities and the increased VO2max in the women. This may allow an adaptation of the skeletal muscle towards type I fibres in the active ones. The sex differences in strength increased from age 16 to age 27. The relationship between strength and the type II% in the women changed with age from a positive correlation (Sargent jump only, partiell correlation after body dimensions were considered) to negative correlations for all the strength tests, i.e. the more type I fibres the stronger. A positive correlation between strength and activity index was revealed in the women at both ages.(ABSTRACT TRUNCATED AT 400 WORDS)

RCT Entities:   Population Interventions Outcomes