Methods: Weight was taken (Befour model 6600 scale) in a fully uniformed officer, to the 1/10 lb. Height was taken in work boots, using a Holtain stadiometer to the nearest millimeter. Range of Motion was measured with a Leighton Flexometer for Hip Flexion and Extension, Trunk Flexion and Extension, Lateral Trunk Flexion, Hip Abduction, and Shoulder Flexion and Extension. Aerobic capacity was assessed and allometrically scaled using a Sensormedics 800s ergometer using the testing protocol of Astrand and Von Doblen. Shoulder Press and Pulldown and Squat exercises were assessed using a Ariel Dynamics Isokinetic CES system at 20 in/sec. Leg power (foot/lbs *sec-1), was assessed with a switch mat assembly made by Lafayette Instruments, and recording the subjects vertical jump. Lastly, the temperature and humidity measurements were collected using a thermometer/hygrometer gauge made by Acumen both pre and post exercise, worn inside the officers vest at the level of the mid-sternum.
Statement of the Problem: Duty belts distribute weight, (approximately 20 – 25 lbs), of a police officers equipment at the level of the hips, and has been associated with lower back, hip and knee strain. Recent technology has found that Ergometrically designed load-bearing vests have been increasingly effective at evenly distributing the weight of the officer’s equipment in a safer more risk aversive manner.
The purpose of this case study was to perform a comparison of physical performance parameters with duty belt versus the load-bearing vests on a Fircrest police officer. Objective and subjective data on performance of strength, power, range of motion, and temperature regulation will be examined.
Results: Range of motion showed a reduced range of motion across all measurements as displayed in table 1. Standard deviations from the average flexibility of a subject his age and sex was -.89 with the duty belt, and +.20 standard deviations above the mean wearing the load bearing vest.
Initial Temperature and Humidity measurement were recorded in the ambient conditions of the laboratory environment with a combination hygrometer-thermometer sensor. The sensor was then clipped onto inside the subject’ uniform at the level of the mid-sternum. Temperature and Humidity measurements were then recorded at the conclusion of the study exercise assessment portion. Temperature changes wearing the duty belt versus the load bearing vest are shown below. It was apparent the load-bearing vests showed an increased ability to attenuate the effects of body temperature and humidity with exercise.
Aerobic Capacity was measured using a 6 minute bicycle protocol designed to extrapolate the submaximal relationship of a heart rate workload line to an estimated maximum effort. The results indicated a virtually identical result in aerobic capacity estimates between trials (duty belt vs load-bearing vest), at 9.07 METs versus 9.09 METs respectively.
Strength Measurements were obtained as an average of a 5 repetition maximum on the shoulder press, pulldown and squat exercise (Table 3). Although there was no substantial losses in upper body strength between the duty belt and the load-bearing vests, the squat strength curves showed a marked lack of strength in the initial phase of the squat lift, as depicted in Figure 1.
The subject subjectively assessed a 6 on a pain scale of 1-10, (10 being the most pain), and showed a bruise in the anterior surface of the lower hip some 9 days later. There was no reported pain when performing a squat using the load bearing vest.
Figure 1: Strength curve of the squat lift with the duty belt versus load-bearing vest. Curves show the loss of strength at the initial range of motion due to the side arm impinging the initiation of the hip flexors.
Maximal leg Power estimates showed a loss of power with the duty vest versus the load bearing vest of 411 ft/lbs per sec, and 453 ft/lbs per sec respectively. This translated to a 10.2% increase in leg power output with the load-bearing vest in the performance of a vertical jump maneuver.
Discussion: The results showed, primarily, an increased range of motion for the officers wearing the load-bearing vests. This seemed to be more apparent throughout the lumbar and in particular the thoracic vertebrae. Strength measurements were similar in the upper body, with deficits noted in lower body strength and power wearing the duty vests. The performance of the squat exercise appeared to represent the most discomfort during the evaluation, as the officers sidearm was positioned in such a way as to “dig into” the hip. This painful placement of the sidearm also contributed to the officer’s decrease in leg power (vertical jump test), of nearly 10%.
Another advantage is that the load-bearing vests allowed some room for air circulation coming from under the officer’s arm and neck line, while the duty belts require the officers to wear their Kevlar vests bound tightly to the torso. The result was the temperature changes inside the officer’s uniforms were approximately 49% less when the load-bearing vest was worn, and a noted 33% lower humidity. The enhanced heat dissipation with the vests did not appear to contribute to an increase in aerobic performance seen in the aerobic bicycle assessment, possibly due to the shortened time interval for exercise of 6 minutes.
Conclusion: The case study showed the clear advantages in range of motion and temperature regulation in the officers using the load-bearing vests versus the duty belts as a part of their standard uniforms. Furthermore, the impingements noted in flexibility could adversely affect leg power and strength in the performance of their assigned duties. Lastly, the more even distribution of the weight of the police equipment (approximately 20 – 25 lbs) throughout the torso of the officer using the load-bearing vests, has the potential of minimizing back, hip and knee issues throughout the career of the officers.
The Exercise Science Center would like to express our appreciation to Officer Vic Celis and the Fircrest Police Department for making this study possible.