Lower limb injury prevention in the New Zealand Army : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Sport and Exercise at Massey University, Wellington, New Zealand

Abstract

Background The mobility of the New Zealand Defence Force (NZDF) and its ability to deploy personnel at short notice is compromised by the high number of musculoskeletal injuries, particularly to the lower limbs. Literature searches indicated footwear may be the issue. The aim of this research is to examine the extent of the problem, which injuries and anatomical structures are most affected, the aetiology involved, and finally, the effects of a possible remedial intervention. Methodology Information from 11 years of NZDF injury records were examined. Chi square analysis was used to determine most affected joint(s), injury type and activities (sporting or military). The ankle joint appeared most vulnerable to injury, particularly during sporting or military activities involving running. Traumatic ankle sprains and strains were the most prolific injuries and this occurred when not wearing the military boot. This information was used to determine the subsequent investigations of the biomechanical and neurological aetiology underlying habitual boot-wear that might give rise to these injuries. Ankle range of motion (ROM), endurance strength, power and fatigue were measured using an isokinetic dynamometer (Biodex) in new recruits and repeated after one year of military boot-wear. Muscle activation of tibialis anterior and both the medial and lateral gastrocnemius were also measured during quiet standing on a force platform to measure postural sway. The same measures of aetiology were conducted on 65 habitual boot wearing regular force military male personnel pre and post-introduction of a low-cut flexible shoe. These 65 personnel all had served greater than two years in the NZDF. At 10 weeks, the effects of pre- and post- flexible shoe wear were measured to determine if the effects of habitual boot-wear could be reversed. Results After 12 months of habitual military boot-wear, ankle ROM was decreased in all planes of movement, endurance strength and power were significantly reduced and fatigue onset increased after one year of boot-wear. Muscle activation was increased in tibialis anterior and both the medial and lateral gastrocnemius, which coincided with significantly increased sway patterns indicating poor postural stability. After 10 weeks of transitioning from habitual military boot-wear to a flexible shoe, ankle ROM, and strength significantly increased, while fatigue, muscle activation and postural sway decreased. Conclusion Chronic military boot-wear causes mal-adaptations and is associated with the high number of ankle injuries in the NZDF, however the effects can be reversed. It was advised that when not on military manoeuvres that personnel wear a low-cut flexible garrison shoe.