The static flexibility of the gleno-humeral joint of fourteen experienced male weight lifters was determined. Further the subjects performed a series of quasistatic muscular actions of the deltoid/pectoralis musculature during which a brief perturbation was applied. The damped oscillations resulting from such a procedure provided data pertaining to the stiffness of each subject's musculature. A significant correlation (r = -0.544, p less than 0.05) between maximal stiffness and static flexibility was observed. This relationship is discussed with reference to the popular belief that flexibility is related to the incidence of muscular injury. It is proposed that the injury-reducing benefits associated with a high degree of flexibility can be effectively explained through the relationship between flexibility and stiffness.