Development of strength during childhood: Louise Wood and Mark De Ste Croix
The development of equipment, technology and an increased understanding of growth and maturation issues have recently provided new insights into paediatric strength development. Measurement of muscle force is certainly not a new concept, and the development of force production during childhood has been studied for decades. Despite this acknowledgement of the importance of strength to both physical performance and health and well-being, our understanding of the age-and sex-associated changes in strength is relatively limited compared to other physiological parameters. Nevertheless, those studies that are available describing the age-and sex-associated change in dynamic strength are relatively consistent, especially for the lower limbs. However, the complex interactions of factors that explain the differences in strength during childhood and adolescence are still poorly understood (De Ste Croix 2007). This may be due in part to the fact that there are few well-controlled longitudinal strength studies that have concurrently examined the influence of known explanatory variables using appropriate statistical techniques (Wood et al. 2004, 2006). There are a number of excellent reviews describing force production during childhood (e.g. De Ste Croix 2007, 2009), but few have focused predominantly on the measurement of muscle size and biomechanical changes during childhood. Therefore, the main purpose of this chapter is to explore the age-and sex-associated changes in muscle strength from a biomechanical position, focusing on physiological muscle cross-sectional area (CSA) and muscle moment arms. We will briefly describe the age-and sexassociated development in strength, but concentrate primarily on the biomechanical factors that may contribute towards this development. We will then derive clinical and practical applications based on biomechanical factors that influence age-and sex-associated changes in strength.