The effect of additional mass by body armor on police specific performance

IntroductionIn most police specific tasks, the body must be accelerated or resist external forces. Since acceleration equals force divided by mass, increased body mass needs more force to move the body. An increase in mass by 10 to 40% means a decrease in acceleration at a given force by 9 to 29%. Because police personnel often wear body armor (BA) for protection against punches and shots, the additional mass of BA (Germany 21±1 kg) potentially reduces a) physical performance on the one hand, but 2) enhances officer’s resistance against impacts (e.g. by offender’s tackling) on the other hand. The objectives of the present study were to analyze individuals on their physical performance with and without body armor and their resistance against external forces.MethodsThirty two physical active (5.3±2.8 hrs/week) women were divided into two groups by body mass (group 1: n=16, 1.57±0.03 m, 55.7±4.5 kg, 25.4±4.7 yrs, BMI 22.6±1.5; group 2: n=16, 1.79±0.02 m, 72.2±7.8 kg, 24.5±5.5 yrs, BMI 22.4±2.5). Two tests (Fig. 1) with and without body armor (m=21 kg) were obtained: 1.) Center of mass (COM) height and mechanical power during countermovement jumps; 2.) Acceleration of the body (Vicon, Oxford, UK) after impact of an oscillating pendulum (Ekin=126 J): Simulation of 80 kg heavy offender, who bumps or jolts an officer with a fast walking speed (e.g. body check against officer). Statistics: Kolmogorov-Smirnov test, two-factor ANOVA with Bonferroni's post-hoc test (α = 5%).
ResultsThe mass fraction of the BA in relation to the group’s mean body masses amounted to 38% for group 1 and 29% for group 2. BA reduced sig. (P<0.05) jump height and mechanical power (Tab. 1). There were no sig. differences (P>0.05) between the groups in jumping. BA reduced body acceleration after impact sig. (P<0.05) in group 1 (57%) and 2 (66%). There were no sig. differences (P>0.05) between group 1 and 2 without BA. With BA, body acceleration was sig. (P<0.05) lower in group 2 than in group 1. 
DiscussionExercise performance of fit, light- and normal-weighted individuals decreased with increasing additional mass [1]. BA has clearly exceeded the critical weight limits for external loads of less than 15% [2], but the additional mass helped to resist external forces. As additional mass had positive as well as negative effects on exercise performance, fitness tests for the evaluation of job applicants and future employees have to consider police specific tasks. Therefore, precise requirement profiles are needed for the evaluation of police specific work and the choice of fitness tests.
References1.Cureton et al., Med & Sci Sports, 10:194-199, 1978. 2.Robertson et al., Eur J Appl Physiol, 49:69-78, 1982. 
AcknowledgementsWe would especially like to thank the Police of North Rhine Westphalia, Germany for providing equipment and body armor.