1. IE 571 OCCUPATIONAL
BIOMECHANIC SEMESTER LONG
GROUP PROJECT
Spring 2015
SOFT TISSUE DAMAGE CAUSED
BY POLICE DUTY BELTS
GROUP MEMBERS:
ARISTIZABAL XIMENA
JOSE DEAN
RAJANA KRISHNA LEELA
SCHNIEDERS THOMAS
SINGH ANUPAM
VIJAYARANGAN JAIPRAVIN
WANG XIN
2. INTRODUCTION
Police duty belts, and the weight and shape of the equipment carried on them, not only cause
discomfort and fatigue to the officers wearing them, but over the years of an officer’s career can
cause chronic physical problems. Some of the ailments include lower back problems and pain,
leg and hip problems, numbness and tingling of the fronts of the upper thighs, tissue ischemia,
sciatica and other nerve ailments in addition to skin irritations, cuts or abrasions caused by the
friction with the belt. Due to the conservative nature of the U.S. police community, and the
demand that officers present a traditional and sharp appearance in uniform, the solutions to these
problems most likely to be accepted are limited to duty belt or armor design that maintain a
minimalistic and unthreatening look of the police uniform.
Today, the police officer’s “duty belt” provides the foundation on which the officer’s tools are
supported. The paramount purpose of the duty belt is to allow the officer to carry his/her most
important items of equipment in a manner that will make them both secure, and readily
accessible when needed. The irregularity of belt shapes and sizes and the individual’s use of the
belt result in many variables affecting the officers’ health and resulting in injuries and soft tissue
damage. For example, placing the expandable baton or similar objects too far back on the belt
can make them press uncomfortably into the back of the car seat when the officer is seated in a
patrol car. Also conflicting with the need for equipment accessibility, any large object, such as a
holstered handgun may press intolerably into the officer’s stomach or ribs at the belt’s top edge,
and into the officer’s upper thighs at the bottom edge, when the officer is seated in a police car –
a problem that affects people differently based on height, weight and body dimensions.
Soft tissue damage results from the effects of the weight, friction, and stress and strain on the
officer’s body due to having to carry a duty belt. There are different biomechanical factors
contributing to the soft tissue damage. The duty belts exert a shear force on the skin because of
the different activities performed by the officers while on duty such as driving, getting in and out
of the car, and other various movements. Because of this shear force, force due to friction also
comes into the picture. The belts are tied above the shirt and during a movement; the shirt rubs
3. against the skin around the waist causing damage to the tissue. The equipment and duty belt
weight exert a downward load on the duty belts. The load distribution of these accessories is also
non-uniform because each of them weighs differently. Thus, the resultant load of the belt keeps
pulling the body down and to resist this, the officers need to constantly hitch it up from time to
time. The turning movement of the hips also results into a torque acting on the waist.
Soft tissue damage exacerbates over a period of time and its effect is not realized in the initial
stages. Soft tissue injuries are caused by damage to four different types of tissue: muscles,
ligaments, tendons or nerves.Soft tissue injury is caused by direct or indirect trauma. Direct
trauma may happen in connection with sports or other accidents, being struck by an object or
falling. Indirect trauma commonly stems from overuse of the tissue. The purpose of our project
is to understand the specifics of soft tissue damage on police officers due to the use of duty belts,
the biomechanical factors involved and to provide plausible solutions to mitigate the impact
through the modification of the belt.
4. PROJECT PLAN/OUTLINE
In order to understand specifics of soft tissue damage on police officers due to the use of duty
belts, the biomechanical factors involved and to provide plausible solutions to mitigate the
impact through the modification of the belt, the project team conducted the following steps:
1. Understand commonly used duty belt
○ history, uses, traditional structure, and materials
○ research conducted via online journal publications and inter-library loan
2. Understand duty belt effects on the body on sample population
○ survey ISU police officers
○ sample questions for survey found in the section below
3. Compile survey results and establish biomechanics metrics to be used
4. Design solution
○ Compile results will be considered in the design phase
5. Test solution
○ Compare biomechanical metrics and damage models looking for improvement
6. Make changes as necessary
7. Compare traditional duty belt to modified designs and metrics
8. Upon successful completion, submit final recommendation
The team will conduct a survey where the police officers will be asked to answer a few questions
based on their day to day experiences with regards to the activities performed. The following is a
sample list of questions for the officers:
1. What do you put on your belt?
2. Is there anything that can or cannot be removed from the belt and be relocated?
3. Which item (carried on your duty belt) bothers you the most, and why?
4. Does the belt cause you any discomfort and where?
5. 5. Which part of hip do you usually feel discomfort or painful when wearing the belt in
duty?
6. Any ideas to mitigate any pain it causes?
7. What are the worst types of injuries incurred due to the duty belts?
8. Are there any variations on your discomfort due different seasons?
9. Do you use an inner belt? If so, how is the duty belt attached?
10. What (in terms of layers of clothing and/or other equipment) is separating your skin from
the duty belt?
11. Typically, how many hours a day do you carry the belt? Do you take it off while you are
on duty? If yes, how often?
12. What percentage of your day is spent sitting?
13. Do you experience pain from your duty belt while sitting, and if so, where?
14. What percentage of your day is spent standing?
15. Do you experience pain from your duty belt while standing, and if so, where?
16. When does the duty belt cause the most discomfort?
17. Do you have any ideas for improving the belt over all?
Following the survey and data collection, the team moved into a design and analysis phase
keeping in mind information collected about officers habits, anthropometry and pain/injury
history. The following sections propose possible causes of the discomfort and a modified duty
belt design and tests to understand the benefits of the modifications.
6. BACKGROUND INFORMATION
Types of Soft tissue injuries
When you participate in sports and physical fitness activities, you can injure the soft tissues of
your body. These activities can damage ligaments, tendons, and muscles.
Some of the soft-tissue injuries you are most likely to experience include:
● sprains
● strains
● contusions
● tendonitis
● bursitis
● stress injuries
These can be the result of a single event, such as a fall, a sudden twist, or a blow to the body.
You might also sustain one or more of these injuries because of repeated overuse, such as in
ongoing athletic activities or activities that you perform on a daily basis. In this case, small
amounts of body stress accumulate slowly but steadily. The result can be damage and pain.
Sprains
The joints of your body are supported by ligaments. Ligaments are strong bands of connective
tissue that connect one bone to another. A sprain is a simple stretch or tear of the ligaments. The
areas of our body that are most vulnerable to sprains are our ankles, knees, and wrists. A
sprained ankle can occur when our foot turns inward. This can put extreme tension on the
ligaments of your outer ankle and cause a sprain. A sprained knee can be the result of a sudden
twist. A wrist sprain most often occurs when you fall on an outstretched hand. Most mild sprains
heal with "R.I.C.E." (Rest, ice, compression, and elevation) and exercise. Moderate sprains may
also require a period of bracing. The most severe sprains may require surgery to repair torn
ligaments.
7. Strains
Your bones are supported by a combination of muscles and tendons. Tendons connect muscles to
bones. A strain is the result of an injury to either a muscle or a tendon, usually in your foot or
leg. The strain may be a simple stretch in your muscle or tendon, or it may be a partial or
complete tear in the muscle-and-tendon combination. The recommended treatment for a strain is
the same as for a sprain: rest, ice, compression, and elevation. This should be followed by simple
exercises to relieve pain and restore mobility. For a serious tear, the soft tissues may need to be
repaired surgically.
Contusions
A contusion is a bruise caused by a blow to your muscle, tendon, or ligament. The bruise is
caused when blood pools around the injury and discolors the skin. They are mild and respond
well when you rest, apply ice and compression, and elevate the injured area. If symptoms persist,
medical care should be sought to prevent permanent damage to the soft tissues.
Tendonitis
Inflammation is a healing response to injury which is usually accompanied by swelling, heat,
redness, and pain. An inflammation in a tendon or in the covering of the tendon is called
tendonitis. Tendonitis is caused by a series of small stresses that repeatedly aggravate the tendon.
Professional baseball players, swimmers, tennis players, and golfers are susceptible to tendonitis
in their shoulders and arms. Tendonitis may be treated by rest to eliminate stress, anti-
inflammatory medication, steroid injections, splinting, and exercises to correct muscle imbalance
and improve flexibility.
Bursitis
A bursa is a sac filled with fluid that is located between a bone and a tendon or muscle. A bursa
allows the tendon to slide smoothly over the bone. Repeated small stresses and overuse can cause
the bursa in the shoulder, elbow, hip, knee, or ankle to swell. This swelling and irritation is called
bursitis. Many people experience bursitis in association with tendonitis. Bursitis can usually be
relieved by rest and possibly with anti-inflammatory medication. Some orthopedic surgeons also
inject the bursa with additional medication to reduce the inflammation.
8. Stress Fractures
When one of your bones is stressed by overuse, tiny breaks in the bone can occur. The injury is
termed a stress fracture. Early symptoms may be pain and swelling in the region of the stress
fracture. The bones of the lower leg and foot are particularly prone to stress fractures. The
fracture may not be seen on initial routine X-rays, requiring a bone scan to obtain the diagnosis.
These injuries are treated by rest, activity modification, cast immobilization, and, rarely, by
surgery.
Tissue Damage for Police Officers Caused by Duty Belts
For police officers, dehydration, toxicity, poor dietary choices, inflammatory foods, and inability
to tolerate stress are associated with soft tissue damage. Due to the nature of police work,
systemic tightness or rigidity develops, resulting in the nervous system to become tight, making
it extremely difficult to relax. The use of duty belts acting creating friction with the skin and
adding loads to the mid-section of an officer’s body further make them prone to injuries.
Human skin is in permanent contact with textiles during the various activities of everyday life
when touching or wearing fabrics. For police officers, they are not only in contact with their
uniforms but also to their duty belts of stiff materials, variable sizes and weight loads creating
risks for tissue damage. When studying this particular group of police officers and from survey
data, it was found that officers experience high levels of discomfort from the friction of the belt
and from being struck by the varying sizes and shapes of the tools in their belts. When asked, the
officers responded that the tools could not be changed (removed from the belt or carried
differently) so as a group we have focused on what we can control- reducing the friction and pain
causing discomfort as a way to mitigate the subsequent tissue damage,
9. PROTOTYPE TRIALS/EXPERIMENTATION
Experimentation
Our research revealed that there is no standard way of how the accessories in a duty belt are
fitted, it varies from officer to officer or in some cases the accessories in a duty belt varied too.
Some duty belts had night-vision torch and pepper spray etc,. It is safe to assume that the officers
arrange the accessories in the sequence they wish but one standard rule is that the gun and the
baton are always kept easily accessible.
Setup
Various arrangement of accessories of duty belts since there is no one standard way, and decided
on the setup as shown in the picture below:
10. Tests were run by connecting the Flexiforce sensors to the duty belt for quantifying the force
exerted on the body. Data from the force sensors was taken, since it is difficult to perform an
actual skin abrasion and tissue damage tests which involve blood sampling.
The figure below shows a typical Flexiforce® sensor. A sensor of 25 lbf range was used, since
the predicted forces would be below the range. One end connects to the duty belt with Gorilla
tape® where the force reading has to be taken, and the other connects to the flexicomp® which
in turn is connected to the computer where the data is stored for data analysis later.
It took many trials to set up the force sensors and get a valid reading.
The figure below gives you an idea of how we connected the force sensors to the belt.
11. Testing
Pressure points were identified on the duty belt, and the force sensor were attached in these
points in the following sequence -
1A- magazine
1B- gun (position 1)
1C- gun (position 2)
1D- handcuffs
1E- taser
1F- baton
A series of activities as following was defined and each task was performed for a specific time
period. The following are the tasks and the time periods.
TASK TIME PERIOD(secs)
Twist left 10
Twist right 10
Sit 180
Stand 40
Bend forward 20
Running 30
Squat 40
Walk 40
The above defined activities were performed in the same order, and data collected
simultaneously. The pictures below depict the activities mentioned in the table above.
16. The tests were conducted without foam for the first trial, and with foam in the next trial.
A survey of the police officers revealed that majority of the officers experienced pain at
hips,which is why the foam is attached throughout the undershirt as shown in the figure below, to
see if it mitigates any pressure.
Fig : With foam
The figure below shows the impression created on the foam after the test. The impressions were only
created on one side of the foam showing an increased stress in this area. This is part where the gun and
magazines are kept.
Fig : Foam with impression
17. DATA ANALYSIS
Without Foam
The average force, in lbf, applied to the body without protective foam in the various activities
can be seen below. The abbreviation LT in the figure below stands for Linear Transform and
represents the conversion of data to pounds force. The force sensor readings are as follows : 1A -
Magazine, 1B - Gun in position 1, 1C - Gun in position 2, 1D - Handcuffs, 1E - Taser, and 1F -
Baton.
Figure X : Average Force (lbf) Without Foam
The handcuffs essentially applied no force on the body and therefore no friction on the skin. The
magazine adds a near constant 39.5lbf against the body but no average change in force implying
that there will be little to no frictional force.
The baton and the gun in position 2 have changing forces at every time step ranging [1:13]lbf
which will result in frictional force against the body. While there is change in force against the
body for the taser, the values are extremely small indicating negligible friction force.
With Foam
The average forces for the activities can be seen in the figure below.
18. Figure X: Average Force (lbf) With Foam
There is little to no change in force for 1A, 1B, 1D, and 1F which implies little to no frictional
force on the body. There is minor change in force for 1C which is the gun in position 2. The most
fluctuation in force readings come from the taser implying frictional force acting on the body.
Comparison
For the charts below, WLT represents the data without the foam insert and FLT represents the
data with the foam insert.
While the average force due to the magazine is higher with the addition of the foam, the average
change in force, which leads to friction, is approximately the same.
19. Here we see that the foam has little impact on the force or change in force for gun position 1.
It can be seen that the foam again increases the average force loading on the body, however this
time, the average change is greater. This implies that adding foam for gun position 2 could
increase the amount of friction on the skin. The evaluators recommend keeping the gun in
position 1.
20. Again we see an increase in average force on the body with the addition of foam in the taser area as well
as a larger change for different activities.
Finally, the average force from the baton is drastically lessened by the addition of the foam insert.
21.
22. RESULTS
It is interesting to note that in 3 of the 6 categories the foam increased the average force loading
on the body instead of reducing it. However, a number of unforeseen variables could come into
play during the evaluation. It might be because of the tightness of the duty belt. The duty belt
was kept at the same level of tightness even after adding the foam insert which would have
resulted in more force on the body. The duty belt just fit the subject, and when the foam was
inserted it was a better fit, this might be another factor that might have caused the increase in the
average force after the foam is inserted. The subject reported a dramatic increase in the level of
comfort with foam, and felt a reduction in force acting on the body.
23. RECOMMENDED PROTOTYPE &
CONCLUSION
There were two possible solutions that were investigated for reducing skin tissue damage.
1. Attaching a foam to the undershirt at the points of high pressure.
2. Attaching the foam throughout the undershirt at the belt region.
The first solution was considered infeasible since there is no singular set up of the duty belt for
officers, and it was impossible to adjust the foam at the exact pressure points , since it would
vary by every fit of the duty belt for the same person and on a large scale from officer to officer.
The second solution which was designed on the basis of experimentation and subjective report of
the increase in level of comfort of the subject.
The prototype of our design is made with the help of an apparel merchandising graduate student.
Fig: Prototype with foam attached
The foam that was used had more bending stiffness in relation to the highly stretchable knit
fabric of the vest and the lining, making it difficult to blend the two together as a singular
garment. Also, the distance between the pressure foot to the fabric had to be increased
24. In conclusion, the second solution of attaching the foam throughout the undershirt is feasible and
easy to manufacture. From our results, it can be said a foam with lower bending stiffness would
be a better solution for the officers’ problems with the skin tissue damage.
25. REFERENCES
1. Impact of police body amour and equipment on mobility
http://www.ncbi.nlm.nih.gov/pubmed/23668780-
2. Ergonomic Load Bearing Systems- https://www.ncjrs.gov/pdffiles1/nij/grants/229710.pdf
3. Low Back Pain in Police Officers-
http://scholarworks.gvsu.edu/cgi/viewcontent.cgi?article=1641&context=theses
4. Selection and Application Guide to police body armor https://www.ncjrs.gov/pdffiles/169587.pdf
