Study aim: To assess spine flexibility and possible muscle contractures at shoulder and hip joints in boys practicing football and in their untrained mates.Material and methods: Two groups of boys aged 10 - 13 years were studied: football players (n = 176) and untrained boys (n = 137). Warm-up stretching exercises were applied at every training session. Spine mobility was determined by measuring differences between standing and bent postures in the forward (thoracic and lumbar regions), backward and lateral bends and in axial rotation (body twist). Muscle contractures were detected by applying Thomas', Dega's (wall test) and pseudo-Laseque's (for sciatic-tibial muscles) tests.Results: Boys training football had significantly (p<0.01 - 0.001) better mobility of the thoracic spine and in the transversal plane, that latter being age-related. Muscle contractures (by pseudo-Laseque's test) were significantly (p<0.05) less frequent in football players than in untrained boys, especially in the older ones.Conclusions: Stretching exercises ought to be recommended as elements of warm-ups and of physical education classes in order to improve spine flexibility and reduce the incidence of muscle contractures (thoracic and sciatictibial muscles and hip flexors).