Our knowledge of the age and sex associated changes in strength during childhood and adolescence is relatively limited compared to other physiological parameters. However, those studies available on the age and sex associated change in strength are relatively consistent, especially for the lower limbs. Caution must be taken when transferring this knowledge to other muscle joints as the development in strength appears to be both muscle action and joint specific. Strength appears to increase in both boys and girls until about the age of 14 y where it begins to plateau in girls and a spurt is evident in boys. By 18 y there are few overlaps in strength between boys and girls. The exact age in which sex differences become apparent appears to be both muscle group and muscle action specific and there is a suggestion that sex differences in upper body strength occur earlier than lower body strength. What is less clear is the complex factors that contribute to the production of strength during childhood and adolescence. There are few well controlled longitudinal studies that have concurrently examined the influence of known variables using appropriate statistical techniques. Most studies have shown that maturation does not exert an independent effect when other factors, such as stature and body mass are accounted for. Also, the assumption that muscle cross-sectional area is the most important parameter in strength production does not hold when examined with other known variables. Consistently, stature appears to play a key role in strength development and this may be attributed to the strength spurt that has been linked to peak height velocity, and the muscle moment arm. Advances in technology have provided us with more accurate techniques to examine these explanatory variables but the complex interaction of neural, mechanical and muscular remains to be clearly identified from well controlled longitudinal studies.