ABSTRACT
It is well known that extreme repetitive stress on the apophysis without considering the physical characteristics of children induces a growth disorder of the growing skeleton. However, only a few studies have evaluated the indexes of the muscle-tendon complex as a risk factor of apophysitis. The purpose of this study was to investigate the relationship between the elastic properties of the Achilles tendon, physical characteristics, muscle tightness (MT) and general joint laxity score (GLP), and tenderness from typical apophysitis (calcaneal tubercle, tibial tuberosity and iliac spine) in kindergarten and elementary school students. Body and lower leg size, and MT of the calf muscle increased ; while GLP decreased significantly with age. The Elastic index of the Achilles tendon and its standard deviations were greater among 5<sup>th</sup> and 6<sup>th</sup> graders than among 3<sup>rd</sup> and 4<sup>th</sup> graders. Point tenderness was more frequent in older age groups (4<sup>th</sup>-6<sup>th</sup> graders) than in younger age groups (kindergartren-3<sup>rd</sup> graders) and was greatest in 4<sup>th</sup> graders. When subjects were categorized into groups with and without point tenderness, no significant differences were found between GLP, muscle tightness of gastrocnemius, quadriceps and iliopsoas. However subjects who showed point tenderness had a higher Elastic index (p=0.07). Considering the pathomechanics of apophysitis, repetitive traction of the apophysis by a stiffer muscle-tendon unit lead to injury of the apophysis and growth plate. Tendon properties appear to be more sensitive to the pathomechanics of apophysitis.