Data are presented on stress fracture patterns at the Commando Training Center Royal Marines. To reduce the high number of training injuries, including stress fractures, a complete review of the training syllabus was undertaken. Following recommendations from this review, a newly designed, physiologically progressive training program was introduced. The result of this revised training syllabus was a statistically significant reduction in stress fracture incidence. The causes of stress fractures are discussed with particular reference to skeletal adaptation to physical loading and the role of muscular support of the axial skeleton.