Stance Stability And Reports Of Previous Back Injury In Special Boat Operators

Abstract

We are investigating a variety of motor performance tasks to help identify measures that can be used to monitor the musculoskeletal health of US Navy Special Warfare personnel. One of these measures is postural stability, which has been linked to falling injury in older persons. PURPOSE To determine whether or not a previous back injury was associated with changes in stance stability. METHODS Stance stability was measured and reports of previous back injury gathered in a group of 34 US Navy Special Warfare Combatant-craft Crewmen (SWCC): age 28.7(5.8)y, stature 176.9(7.4)cm, weight 85.3(11.3)kg, and 17.5(4.9)%fat, and a group of 34 US Navy personnel entering SWCC training (STU): age 23.8(3.8)y, stature 177.9(7.7) cm, weight 78.1(8.3)kg, and 16.1(4.4)%fat. Stance stability was determined from movements of the center of pressure (COP), measured using a pressure-sensitive mat, while standing for 30 seconds on either the right or left foot with the eyes open. Two measures of stability were calculated for both left and right foot stance:(1) the total distance (DIST) represented by the movement of the COP, and (2) the mean deviation (DEV) of the COP from its average position for the 30-second period. Presence of a previous low-back injury was determined from questionnaire responses. Differences in mean stability values between those reporting a previous back injury (INJ, N = 24) and those reporting no previous back injury (NINJ, N = 44) were assessed using t-tests. Construction of models to predict back injury group membership was carried out using logistic regression. RESULTS Only DEV for the right leg stance (RDEV) differed significantly between injury groups: RDEV = 0.75 (0.14) cm for NINJ and 0.87 (0.21) cm for INJ, t (df, 66)= 2.76, P = 0.007. All 4 stability measures and occupational group membership (OCCGRP: SWCC vs. STU) were entered in stepwise fashion into the logistic regression. The resulting model was one in which OCCGRP and RDEV were significant predictors of INJ. The Nagelkierke R-squared value for the model was 0.404 and the model correctly classified 79.4% of the cases. CONCLUSION These findings suggest that back injury is associated with measurable functional impairment in stance. More work needs to be done to replicate these findings, and to determine the features of OCCGRP membership that result in its inclusion in this predictive model. Supported by US Special Operations Command MEDTECH Program award MIPR04180238.