Measurement of functional capacity requirements of police officers to aid in development of an occupation-specific cardiac rehabilitation training program

Abstract

This study was designed to measure the functional capacity of healthy subjects during strenuous simulated police tasks, with the goal of developing occupation-specific training for cardiac rehabilitation of police officers. A calibrated metabolic instrument and an oxygen consumption data collection mask were used to measure the oxygen consumption and heart rates of 30 Dallas Police Academy officers and cadets as they completed an 8-event obstacle course that simulated chasing, subduing, and handcuffing a suspect. Standard target heart rates (85% of age-predicted maximum heart rate, or 0.85 × [220 – age]) and metabolic equivalents (METs) were calculated; a matched-sample t test based on differences between target and achieved heart rate and MET level was used for statistical analysis. Peak heart rates during the obstacle course simulation were significantly higher than the standard target heart rates (those at which treadmill stress tests in physicians' offices are typically stopped) (t₂₉ = 12.81, P < 0.001) and significantly higher than the suggested maximum of 150 beats/min during cardiac rehabilitation training (t₂₉ = 17.84, P < 0.001). Peak MET levels during the obstacle course simulation were also significantly higher than the goal level (8 METs) that patients typically achieve in a cardiac rehabilitation program (t₂₉ = 14.73, P < 0.001). We conclude that police work requires a functional capacity greater than that typically attained in traditional cardiac rehabilitation programs. Rehabilitation professionals should consider performing maximal stress tests and increasing the intensity of cardiac rehabilitation workouts to effectively train police officers who have had a cardiac event.

Police work involves exposure to a broad range of emotionally harrowing incidents and is often cited as one of the most stressful occupations (1). Traumatic events such as shootings, severe motor vehicle accidents, and incidents involving the death of a child are all ranked as extremely stressful by law enforcement personnel (2–4). Given the overwhelming stress of events like these, coupled with the continual threat of physical danger, it is not surprising that police work has been linked to high rates of cardiovascular disease. In a report covering data from 1990 to 2000, heart attacks accounted for 22% of deaths among on-duty police officers and detectives (5).

A previous study of Dallas-area police officers found that middle-aged officers had below-average fitness levels compared with the average sedentary population of similar age and were at higher risk of coronary heart disease than their sedentary counterparts (6). Most of the time, police work is not physically demanding; however, physical tasks are invariably part of the job (7). Endurance and strength are needed for tasks such as chasing suspects on foot, climbing over fences, jumping across ditches or creek beds, and wrestling with individuals who resist being subdued (6, 7). Being in better-than-average physical condition is vital because police officers must often deal with perpetrators who are young and fit (6).

Patients (including police officers) who suffer a cardiac event are encouraged to enroll in a cardiac rehabilitation program. These programs are intended to help patients recover by restoring their “optimal physiological, psychological, social, vocational, and emotional status” (8). Unfortunately, the concept of occupation-specific training for those who have physically demanding jobs is nonexistent in the typical cardiac rehabilitation setting.

Our recently published study of firefighters found that the functional capacity needed for typical firefighting tasks greatly exceeded the level attained during typical cardiac rehabilitation training (9). To objectively measure the functional capacity required of police officers, we designed a study in which subjects completed an obstacle course that simulated the physical demands of chasing, subduing, and handcuffing a suspect. The study results will help rehabilitation professionals define appropriate cardiovascular functional capacity goals to use in occupation-specific training for police officers in a cardiac rehabilitation setting.

SUBJECTS AND METHODS

The institutional review board approved the study, and all subjects gave informed consent before participating. Career police officers and cadets from the Dallas Police Academy in Dallas, Texas, volunteered to complete an obstacle course while wearing a portable metabolic system (K4 b²) (Cosmed USA Inc., Chicago, IL). A laptop computer with K4 b² software was used to create subject data profiles at the testing site. Each subject's date of birth, height, weight, and body fat (obtained by the skinfold method) were recorded. Prior to testing, the metabolic system was calibrated as described previously (9). For safety, blood pressure and heart rate were measured before and after each subject completed the obstacle course.

The subjects wore a standard police uniform (pants, shirt, police belt, and boots) and carried a flashlight. Before beginning the obstacle course, each subject was fitted with a mask for collecting oxygen consumption data. The mask sealed tightly around the mouth and was kept in place by a head cap. Attached to the front of the mask was the optoelectronic reader, which contained the turbine, wind cover, and sampling plug. A chest strap was used to monitor the heart rate, and all data were transmitted to the laptop computer.

The obstacle course—confirmed by Dallas Police Academy instructors as representing the tasks performed in a typical police situation—was explained and demonstrated to all subjects to ensure uniform performance. The eight events were as follows:

1. 150-foot sprint (simulates a foot chase). From a standing position, the subject sprinted 150 feet.

2. Stair climb (simulates a chase through an apartment complex). The subject climbed up five stairs and descended them 12 times (equivalent to five floors).

3. Wall scale (simulates climbing over a fence or wall during a foot chase). The subject scaled a 5-foot wooden wall.

4. Serpentine/cone sprint (simulates a diversion run during a foot chase). The subject sprinted a total of 450 feet, with 100 feet being serpentine through cones and 50 feet involving turning around cones.

5. Ditch (simulates crawling through a small space during a foot chase). The subject dropped to his or her knees and crawled through a 3.5-foot ditch.

6. Culvert jump (simulates traversing a creek bed or ditch during a foot chase). The subject sprinted 100 feet and jumped over a culvert.

7. Fight (simulates a fight during a foot chase). The subject kicked and punched a dummy fighter three times.

8. Takedown (simulates wrestling with and handcuffing a suspect). The subject dropped to his or her knees, rolled the 145-lb dummy three times one way and three times back, and then simulated a behind-the-back arm cuff.

After each subject completed the obstacle course, a study coordinator removed the monitoring equipment and harness and took the subject to a rest area. Healthy snacks, water, and a chair were provided, and the recovery blood pressure and heart rate were measured.

The average working heart rate and MET level were determined for each subject, as were the peak heart rate and MET level. The calculated age-predicted maximum heart rate (220 – age) was multiplied by 85% to obtain the standard target heart rate (the intensity level at which a treadmill stress test in a physician's office is typically stopped). A matched-sample t test based on differences between target and achieved heart rate and MET level was used for statistical analysis, with P < 0.05 (conventional type I error rate) considered significant. The sample size was empiric, as these were first-in-kind pilot data.

RESULTS

Thirty career police officers and cadets, aged 21 to 59 years, volunteered as subjects for this study from a pool of 50 qualified candidates. All completed the obstacle course without adverse events, and none were taking medication that lowered heart rate and thus could have affected the physiologic variables during testing. Demographic characteristics are summarized in Table 1. For the group, the mean working heart rate was 170 beats/min (SD, 18) and the mean working MET level was 10.5 (SD, 3.2) during performance of the obstacle course; the mean peak values were 180 beats/min (SD, 9) and 14.0 METs (SD, 2.2), respectively. Detailed data for each of the 30 subjects are listed in Table 2.

Table 1.

Summary of demographic characteristics

Variable	Mean	SD	Minimum	Maximum
Age (yrs)	31	9	21	59
Height (cm)	170	2	166	175
Weight (lb)	185	24	151	246
Body fat (%)	18.6	4.1	10.4	27.2

Table 2.

Demographic characteristics and test results

Subject	Age (yrs)	Height (cm)	Weight (lb)	Body fat (%)	Average working HR	Peak HR	Standard target HR∗	Average working METs	Peak METs
1	59	168	181	25.4	142	162	137	9.4	13.8
2	47	171	200	20.3	178	185	147	9.7	13.0
3	46	168	190	24.3	160	172	148	10.9	14.9
4	46	169	158	18.9	155	163	148	9.2	12.8
5	41	170	196	16.7	157	163	152	12.0	15.6
6	39	170	204	18.1	169	179	154	11.4	14.5
7	39	169	192	23.5	157	183	154	12.0	17.8
8	35	168	195	15.9	170	179	157	10.4	13.3
9	32	173	175	19.3	163	175	160	10.5	14.6
10	31	172	219	18.0	176	183	161	9.4	13.1
11	30	170	180	10.4	160	175	162	12.3	16.0
12	30	172	225	20.6	159	168	162	7.8	9.8
13	28	172	187	18.0	175	184	163	11.0	15.1
14	28	171	206	25.3	180	192	163	8.6	10.6
15	28	168	195	23.1	176	193	163	9.1	11.9
16	28	175	187	13.6	171	180	163	12.2	16.4
17	27	171	206	12.8	192	198	164	11.1	13.2
18	27	168	164	17.2	156	173	164	8.9	11.0
19	26	170	246	21.1	174	187	165	8.9	11.2
20	25	173	166	14.3	181	193	166	11.6	18.8
21	25	169	155	27.2	175	181	166	9.9	14.3
22	24	170	159	15.8	172	179	167	11.2	14.1
23	24	169	214	15.8	166	176	167	9.6	13.9
24	23	169	151	17.2	180	193	167	12.5	17.1
25	22	166	162	17.8	181	186	168	10.8	12.7
26	22	167	159	16.4	171	181	168	12.9	17.6
27	22	168	160	16.4	180	188	168	10.9	13.8
28	22	172	191	15.0	162	172	168	11.5	14.3
29	22	167	176	24.2	173	182	168	8.8	10.4
30	21	171	163	15.0	177	187	169	11.9	14.9

∗Calculated as 0.85 × (220 − age).

HR indicates heart rate in beats/min; METs, metabolic equivalents.

Peak heart rates during the obstacle course simulation were significantly higher than the standard target heart rates (t₂₉ = 12.81, P < 0.001) and the suggested heart rate at which patients would typically be stopped during cardiac rehabilitation training, 150 beats/min (t₂₉ = 17.84, P < 0.001). Likewise, the peak MET levels during the obstacle course simulation were significantly higher than the goal level (8 METs) that patients would typically achieve in a cardiac rehabilitation program (t₂₉ = 14.73, P < 0.001).

DISCUSSION

Two aspects of contemporary cardiac rehabilitation programs hinder the appropriate training of police officers and others who have physically demanding jobs. First, there is no accurate assessment of the patient's starting functional capacity. Physicians tend to be reluctant to perform maximal stress testing on the general population because of fear of producing cardiac or musculoskeletal injury (10). Consequently, the stress test that many patients receive in their physician's office before entering a cardiac rehabilitation program is usually terminated at a predetermined heart rate (often 85% of age-predicted maximum heart rate [10]). Because insurance carriers generally will not cover multiple stress tests over a short period, rehabilitation staff lack the maximal stress test data that would help them initiate a safe and effective exercise program that is challenging enough to meet the patient's occupational requirements.

Second, the standard activities in cardiac rehabilitation programs—walking on a treadmill, riding an exercise bike, and lifting 1- to 5-lb hand weights (11, 12)—have not been updated for more than 30 years and are not vigorous or intense enough to help those with physically demanding jobs return to work safely. In contemporary cardiac rehabilitation programs, for example, the commonly recommended exercise intensity produces a heart rate of 110 to 150 beats/min (12).

If the youngest subject in this study (a 21-year-old) were to have a heart event, his age-adjusted stress test endpoint would likely be calculated as 169 beats/min. Upon entering cardiac rehabilitation classes, he would probably be asked, for safety reasons, to decrease his exercise intensity if his heart rate exceeded 150 beats/min. The mean peak heart rate of the police officers and cadets performing the obstacle course, however, was 180 beats/min. We believe that the common practices of stopping the stress test too early and undertraining this type of heart patient during cardiac rehabilitation should be considered inappropriate, even unethical.

In summary, the subjects on the obstacle course were working at levels that are higher than those at which stress tests in physicians' offices are usually stopped and much higher than the levels reached during typical cardiac rehabilitation training. Thus, it is necessary that we clinicians reexamine our current practices and consider performing maximal stress tests and increasing the intensity of cardiac rehabilitation workouts to effectively train police officers for the level of physical exertion that their challenging and crucial job demands.

Acknowledgments

We thank the Dallas Police Academy in Dallas, Texas, for allowing us to perform research on their police officers and cadets. We also thank Beverly Peters, MA, ELS, for her help in formulating the manuscript.