Assessment and interpretation of isokinetic muscle strength during growth and maturation.

The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions. There are numerous methodological issues in the isokinetic testing of paediatric populations that require further investigation. However, several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions. Most paediatric studies have examined the knee joint and more data are needed to elucidate the reliability of upper body isokinetic strength testing. The age- and sex-associated development of isokinetic strength is less well understood. Studies have indicated that isokinetic strength increases with age but the mechanisms associated with this increase require further investigation. Current data are also conflicting regarding the age at which sex differences become apparent in isokinetic strength. More work is needed to examine the influence of maturation on isokinetic strength development, but available data suggest that maturation is a non-significant contributory factor once stature and body mass are accounted for. Most studies have demonstrated a significant relationship between stature, body mass and isokinetic strength during growth and maturation. The importance that changes in body composition during growth have on isokinetic strength has been investigated using fat-free mass and muscle cross-sectional area. Data have shown that although fat-free mass and muscle cross-sectional area are important contributors to isokinetic strength, other unexplained factors also influence isokinetic strength development. Additional work needs to investigate possible qualitative changes in muscle during growth and maturation. More work is also needed to examine changes in eccentric strength with age and to investigate sex differences in upper body isokinetic strength. Future studies should preferably be longitudinal in nature and examine known covariates simultaneously using appropriate statistical techniques.