Potential Mechanisms for the Occurrence of Tibial Stress Fractures, Metatarsal Stress Fractures and Ankle Inversion Injuries in Royal Marine Recruits
Thesis or dissertation
University of Exeter
Lower limb injury incidence is high amongst Royal Marine recruits. Tibial and metatarsal stress fractures are particularly problematic. The regular load carriage activities undertaken throughout training have been implicated, but mechanisms by which these injuries develop are poorly understood. The aim of this thesis was to improve understanding of the mechanisms by which the most prevalent Royal Marine training injuries develop. The first experimental chapter was a prospective study of 1065 Royal Marine recruits. Anthropometric and dynamic biomechanical variables (during barefoot running at 3.6 m.s-1) were recorded at the start of training. A smaller calf girth and bimalleolar breadth were found to predispose recruits to tibial stress fractures and ankle inversion injuries. Recruits who sustained tibial stress fractures demonstrated greater heel loading than those who remained injury-free. Recruits who sustained metatarsal stress fractures demonstrated later peak metatarsal pressures than those who remained injury-free. A review of the 32-week Royal Marine recruit training programme found an association between prolonged load carriage activities and injury occurrence. The second experimental study identified gait changes following a prolonged load carriage activity (12.8 km, 35.5 kg load). Biomechanical variables were recorded during barefoot running (3.6 m.s-1) in 32 recruits pre- and post-activity. Recruits demonstrated increased rearfoot loading, and later peak metatarsal pressures post-activity, indicative of a reduced ability to push-off. The final study examined the influence of the same load carriage activity on gait changes during walking (1.4 m.s-1) in 32 recruits, allowing assessment of the independent influence of load carriage. Kinetic and electromyographic variables provided further explanation of changes observed in the previous study. During load carriage there were increased plantar flexor and knee extensor moments and corresponding increases in muscle activity. There were reduced knee extensor moments, and evidence of plantar flexor muscle fatigue post-activity. A reduced ability to push off during stance due to muscular fatigue was suggested as a key contributor to tibial and metatarsal stress fracture development. This may explain the association between a smaller calf girth and tibial stress fracture development.
Institute of Naval Medicine
PhD in Sport and Health Sciences