Sports that demand repetitive overhead activity (e.g. baseball, softball, tennis, swimming, volleyball) often cause compensatory changes in the shoulder musculature.

• Stress fractures distal to the elbow, shoulder girdle & ribs are more common in female athletes. 
• Rotator cuff tendonitis is often related to shoulder laxity & muscle imbalance while the overuse injury is the result of excessive repetition combined with insufficient recovery. Growth plate trauma (associated with repetitive compressive forces combined with load bearing) may lead to its premature closure.

The prevalence of most upper body injuries increases with time in the sport & the intensity of involvement.

Prior to puberty, there are no differences in body composition between boys & girls, yet with the onset of pubertal events, muscle mass accrues in young boys at a faster rate. Strength gains occur more quickly in boys.