MUSCLE STRENGTH FROM ADOLESCENCE TO ADULTHOOD - RELATIONSHIP TO MUSCLE-FIBER TYPES

The aim of the present study was to reinvestigate muscle strength and the relationship to muscle fibre and the level of physical activity in adult men and women previously studied during adolescence. A group of 55 men and 26 women were tested for maximal strength (handgrip, Sarge nt jump and two-hand lift) and completed a questionnaire concerning ph ysical activity during their leisure time (activity index) at the ages of 16 and 27 years. Biopsy specimens were taken from the vastus later alis and analysed for fibre type (percentage of I, IIA, IIB) and fibre area (area I, area IIA, area IIB). The sex differences in strength in creased from age 16 to 17 years. Body dimension, sex, percentage of ty pe II, mean fibre area and the activity index contributed to explainin g 50-75% of the strength at both ages. Different changes in relationsh ip between fibre type composition and strength in women and men was se en with increasing age. In the women, the relationship between strengt h and the percentage of type II fibres changed with age (from 16 to 27 years of age) from a positive correlation (only Sargent jump) to nega tive correlations for all the strength tests, i.e. the more type I fib res the stronger the subject. A positive correlation between strength and the level of physical activity during leisure time was revealed in the women at both ages. The positive correlation between strength and type II fibres in the 16-year-old men had disappeared at age 27. No s ystematic relationships between strength and the level of physical act ivity were seen in the men at either 16 or 27 years of age. It is sugg ested that women may be more dependent on physical activity than adult men to develop strength and the percentage of type I fibres reflects the degree of physical activity among adult women but not among adoles cent women.