The predictive validity of functional screening tests for lower extremity overuse injuries in miltary recruits of the armed forces of Malta

Abstract

Objectives: Basic military training is physically demanding with recruits suffering mostly from overuse-related lower extremity injuries, resulting in loss of training days, increased medical costs, discharges and dropouts. Hence, the study aimed at investigating risk factors and predictive validity of three functional tests, namely, the single leg hop test, weight-bearing lunge test and Y-excursion balance test, to identify military recruits with increased risk of lower extremity overuse injuries during basic military training. Design: Prospective cohort design. Setting: The Armed Forces of Malta training school, medical centre and Luqa’s barracks. Participants: All 84 invited recruits who started their basic military training in August 2015 agreed to participate in the study. Eight participants terminated their training prematurely, resulting in a final cohort of 76, consisting of 73 males and 3 females with a mean age of 22 ± 2.41 years. Main Outcome Measures: All lower extremity overuse injuries were recorded using the Orchard Sports Injury Classification System. These injuries were analysed for associations with risk factors including: age, height, leg length, body mass index and fitness score, and with functional tests including: single leg hop test, weight-bearing lunge test and Y-excursion balance test for their predictive validity. Results: A total of 29 recruits sustained 42 lower extremity overuse injuries. The only risk factor associated with lower extremity overuse injuries was pre-basic military training fitness level (p=0.04), with lower fitness level being related to a higher risk of sustaining LEOI. Functional tests valid for predicting lower extremity overuse injuries in recruits included the normalized single leg hop test for distance (p=0.04) with a cut-off score of 86%, indicating recruits jumping a lesser distance being at an increased risk of sustaining LEOI; and the composite right-left lower extremity asymmetry of the Y-excursion balance test (p=0.04) with a cut-off score of 12cm, indicating a higher risk of LEOI in those with an increased asymmetry. Conclusion: This study indicated fitness level as a risk factor for lower extremity overuse injuries in military recruits suggesting adjustments to selection and the use of prevention strategies including pre-conditioning to maintain high fitness level before initiation of basic military training. The normalized single leg hop test for distance and the Y-excursion balance test composite reach limb difference, valid predictors of lower extremity overuse injuries might be implemented and used as part of the pre-recruitment screening procedure in order to identify military recruits possessing specific deficits in the lower extremities rendering them vulnerable to such injuries. Such implementation might lead to significant benefits in terms of reduced injury rates.

Keywords: Basic military training, lower extremity overuse injuries, risk factors, fitness level, screening, predictive validity, functional tests, single leg hop test, weight-bearing lunge test, Y-excursion balance test.