Quantitative Assessment of a Functional Movement Screen in

Athletes using a Wireless Body Area Sensor Network

Suryadip Chakraborty

, Saibal K. Ghosh

, Anagha Jamthe

, Dharma P. Agrawal

, Robert Mangine

Angelo Colosimo

and Joe Rauch

Center of Distributed and Mobile Computing Laboratory, Department of Electrical Engineering and Computing Systems,

University of Cincinnati, Cincinnati, OH, 45220-0008, U.S.A.

Athletic Department, University of Cincinnati, Cincinnati, OH, 45220-0008, U.S.A.

Keywords: Sports Medicine, Functional Movement Screen, Wireless Body Area Sensor Network, Force Sensor.

Abstract: Technological solutions enabling the monitoring of human motion during sports and exercise by collecting

quantifiable measurements are gaining increased attention as tools for evaluating progress in rehabilitation.

Wireless technologies employing small sensors are particularly useful since they allow monitoring of

kinematic data without affecting individuals in executing their motions. Advances in miniaturized and

wireless technology will push capturing and clearly illustrate measurements in real time game situations.

This will eventually eliminate capturing forces from simulated situations in the training room and tell us

what actually happens on the playing field.

1 INTRODUCTION

Whenever any college athlete sustains an injury, one

of the main concerns is how soon can he or she

return to play. The answer to this question is not

always straightforward because each athlete suffers

from a unique injury. Returning to play too soon can

increase the risk of re-injury or lead to a chronic

problem, resulting in a longer recovery period.

However, waiting too long can lead to unnecessary

deconditioning and poor performance. Return-to-

play decisions are fundamental to the practice of

sports medicine. But the method used to make the

decision varies greatly between different sports

medicine programs. Although there are published

articles that clearly identify individual components

that go into these decisions, a quantitative

assessment of functional movements is not currently

used as an integral part of the medical decision-

making process. There is a need to have an objective

decision-based model developed for clinical use by

sports medicine practitioners that take into account

quantification of defined outcomes of players before

allowing them to return to play.

Our project took one functional movement

screen, the overhead squat, to look at how to access

an athlete’s ability to perform the squat

quantitatively. To begin this process, we looked at

the use of a Wireless Body Area Sensor Network

(WBASN) that measures forces on the soles of the

feet during an overhead squat exercise. The

WBASN is a wireless network of wearable

computing devices including medical body sensors

that capture and transmit force data wirelessly to a

monitoring base station like a laptop. This provides

real time information about an athlete performing a

functional movement in a non-invasive way The

primary objective of this feasibility study was to

build an inexpensive and highly reliable force

measuring system using a WBASN designed and

developed by memebers of the Center of Distributed

and Mobile Computing Laboratory in the College of

Engineering and Applied Sciences at the University

of Cincinnati, Cincinnati, OH, United States.

The purpose of our study is to demonstrate the

ability of collecting force data by using our WBASN

in athletes performing an overhead squat exercise.

2 BACKGROUND

The NCAA and the National Athletic Trainers'

Association have an injury surveillance system that

collects injury reports submitted by trainers for

roughly 380,000 male and female college athletes. It

has been in operation since 1988 and through 2004

Chakraborty S., K. Ghosh S., Jamthe A., Agrawal D., Mangine R., Colosimo A. and Rauch J..

Quantitative Assessment of a Functional Movement Screen in Athletes using a Wireless Body Area Sensor Network.

DOI: 10.5220/0004638200950102

In Proceedings of the International Congress on Sports Science Research and Technology Support (icSPORTS-2013), pages 95-102

ISBN: 978-989-8565-79-2

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

there were 200,000 injury reports. An injury report

is filed when an athlete misses a day or more of

practice or competition and this equates to about

12,500 injuries per year, a number that has been

rrelatively consistent over the years. Functional

movement screens are evaluation tools used to

assess the fundamental movement patterns of an

individual. The screens can be used to determine

whether an athlete has the essential movement and

flexibility needed to participate in his/her sport.

The overhead squat is one of the key functional

movement screens that can be used to determine an

athlete's lower body flexibility, providing a visual

indicator for the trainer in predicting the

performance of an athlete during regular play or

returning to play after an injury. Several joints and

muscles are involved in performing an overhead

squat. Currently our athletic trainers employ the

squat test to note the degree of deficiency of postural

balance in an athlete. Pressure data from the feet

could help them to more accurately determine the

extent of postural balance deterioration. To date, we

have not found any report of a study measuring the

forces on different parts of the soles of the feet

during the overhead squat.

3 METHODS AND SYTEM

DESIGN

Our invention is designed to wirelessly monitor

athletes during an overhead squat test using wireless

transducers and force sensors beneath the feet of an

athlete. We conducted a pilot test of our system

using both male and female athletes from the

University of Cincinnati football and volleyball

teams and all athletes were free of injuries at the

time of the testing. Demographic data recorded for

the subjects included age, weight and number of

years of experience playing their primary sport.

Figure 1: Current system design.

Force sensors are transducers capable of

determining the amount of difference in forces

exerted on them. These sensors can be connected to

an integrated circuit capable of wirelessly

transmitting the sensed data to a monitoring station,

which can either be a personal computer, laptop or a

portable device such as tablet or smart phone. Figure

1 shows the prototype for monitoring performance

using force sensors beneath the feet.

The athlete repeated the prescribed squat for a

defined number of times and the system

continuously analyzed the performance throughout.

We can train the system to do intelligent analysis

based on the history of an athlete performing squat.

The received data will determine the relation of the

force between heel and toes and will be displayed

graphically in a format easily readable by the trainer.

During the first stage of our investigation, we aimed

to look at the relationships between the parameters

discussed above with the force values that athlete's

exert on their feet during an overhead squat. The

output is a graphical display of the force in the toes

versus the ones in the heels. This output was then

evaluated from the perspective of weight, gender,

age, and the number of years playing their sport.

3.1 Force and Pressure Sensors

Our system employs FlexiForce™ force sensors

(Phidgets, Inc., Calgary, Alberta, Canada) beneath

the soles of athletes for measuring the distribution of

force in the feet. In an individual, not suffering from

any injuries and having normal postural balance, the

force exerted by the body on the feet is roughly

equally distributed between the two legs.

Figure 2: Flexiforce sensors arranged in shoe sole.

A diagram depicting the arrangement of such

sensors is shown in Figure 2.

The flexiforce sensors used in our system are

thin, flexible piezoresistive sensors that change

resistance as the applied force changes. This

resistance change is converted to voltage by the

Phidgets™ adapter board that plugs into the

Phidgets™ interface kit.

icSPORTS2013-InternationalCongressonSportsScienceResearchandTechnologySupport

3.2 the Phidgets Interface Kit

The Phidgets interface kit provides a means to attach

the force sensors and interface them to a computer

for data acquisition and display. It consists of eight

analog inputs that can be used to measure

continuous quantities such as temperature, humidity,

pressure, position etc. The force sensors can be

attached to the analog inputs provided in the

interface kit. Phidgets provides a mechanism to tune

the sampling rates for the analog sense lines. The

sampling rates can be set at 1ms, 2ms, 4ms, 8ms, up

to 1000ms in steps of 8ms. The interface kit also

provides a series of digital inputs in order to sense

the states of certain devices such as push buttons,

relays and logic gates. The kit incorporates a digital

input hardware filter in order to eliminate false

triggering from the ambient electric noise. The

digital outputs provided from the kit can be used to

drive LEDs and transistors. A diagram of the

interface kit is shown in Figure 3.

Figure 3: The Phidgets Interface Kit (Phidgets, Inc.,

Calgary, Alberta, Canada).

3.3 The Raspberry Pi

The Raspberry Pi is a system on a chip computer

megabytes of onboard RAM which is shared with a

GPU. The whole device is just the size of a credit

card and requires only 5 volts of power. This makes

an appropriate choice for our system as its modest

power requirements mean that the device can be

battery powered. The system also has two USB

ports. We use one port as the input from the Phidgets

interface kit that sends the data from the force

sensors in the shoe soles. The other USB port would

be used to connect a Wi-Fi dongle that would ensure

that the Pi is able to connect to a wireless network

and transmit data to the server. This port can also be

used to attach GSM/LTE dongles that would provide

connectivity to cellular networks thereby ensuring a

higher transmission rate and provides ability to be

used in places without any Wi-Fi coverage. The Pi

runs Raspbian which is a Linux distribution derived

from Debian stable and is optimized for soft-floating

point operations since the Pi does not support the

hard floating point operands yet.

Figure 4: The Raspberry Pi (Raspberry Pi Foundation,

UK).

3.4 System Architecture

The ultimate goal of our project is to build a

comprehensive, portable system for acquiring data

from individuals, transmit them securely to a server

and develop tools and interfaces for subsequent

analysis and visualization. The data acquisition

module of our system is totally battery powered and

Wi-Fi enabled, thereby making it portable to be

deployed anywhere. The analysis module of the

system would run on a dedicated server enabling

faster computation of the acquired data and support

of a rich GUI that would make use of the system

easier for users. Data pertaining to a particular

individual would be time stamped and stored in the

database. The system would enable various

statistical computations to be performed on the

gathered data. The system would also employ Fuzzy

Logic and distributed consensus protocols to analyse

patterns of injuries and recovery rates of various

individuals and aid doctors and medical personnel in

making appropriate decisions for patients

recuperating from the injuries. A schematic diagram

of our proposed system is shown in Figure 5.

Figure 5: The proposed system architecture.

QuantitativeAssessmentofaFunctionalMovementScreeninAthletesusingaWirelessBodyAreaSensorNetwork

Our system will employ multiple force sensors

on the shoe soles to be used by the athletes. This

data can be gathered by the interface kit on its

analog input lines.

However, the interface kit does not have any

processing power. Therefore, we are employing a

Raspberry Pi to provide the required processing

power to the system. The interface kit and the Pi

would be battery powered in order to make it

portable. The Raspberry Pi would be equipped with

a USB Wi-Fi dongle that would provide it with

wireless capabilities and allow it to be connected to

the campus network. Our system would also allow

the Pi to be equipped with GSM/LTE dongles that

would give it a larger range and increased data rates.

Here, we also propose that the Raspberry Pi would

run an HTTP server that would post the gather data

over a web service to a database server. The goal is

to enable the wireless transmission of the pressure

data to a central repository for storage.

3.5 Experimental Set up

Each athlete has to undergo an assessment of their

body posture during an overhead squat. Below are

the standardized instructions they followed for

performing the overhead squat (Butler et al., 2010).

1. Stand tall with feet approximately shoulder width

apart in a comfortable position and toes pointing

forward.

2. Grasp the rod in both hands.

3. Press the rod so that it is directly above the head.

4. While maintaining an upright torso, and keeping

heels in contact with the ground and the rod in

position, descend as deep as possible.

5. Hold the descended position for a count of two,

then return to the starting position.

Figure 6: Experimental WBASN set-up for the overhead

squat.

We drew an “X” on the floor to mark the center

of mass for each subject. Athletes were instructed to

put their feet in a comfortable position around the

“X”. We put our video cameras in the following set-

up: the front camera at 300cm from “X”, the side

camera – 350cm from “X”, camera height in front –

153cm, and the camera height on side – 103.5cm.

We instructed the athletes to perform 3

repetitions of overhead squats. The only specific

instruction was how to place the feet on the sensors.

Verbal instruction included “3 repetitions of

overhead squats slowly with a two second pause at

the bottom”.

The 3 male players are identified below as

subject1, subject2 and subject3 and the 3 female

volleyball players by subject4, subject5 and

subject6.

Table 1: Demographics.

SUBJECT AGE EXPERIENCE WEIGHT SPORTS

1 (Male) 21 14 yrs 177 lbs Football

2 (Male) 21 14 yrs 209 lbs Football

3 (Male) 21 8 yrs 250 lbs Football

4 (Female) 19 7 yrs 177 lbs

Volleyba

5 (Female) 20 7 yrs 160 lbs

Volleyba

6 (Female) 19 9 yrs 162 lbs

Volleyba

We conducted experiments by placing force

sensors beneath the athlete’s feet in two distinct

areas of foot - the heel and toes. Then, we asked

each player to perform three iterations of squats and

we recorded the force values every second. We

captured the force data of both the toe and heel

during the front-overhead and back-overhead squats.

We also video recorded the overhead squat testing

session so that the subject’s performance could be

analyzed by the athlete’s trainers and their analysis

could be correlated with the force data that the

WBASN system captured wirelessly.

4 RESULTS AND DISCUSSION

We captured the force data in our experimental set-

up and retrieved it to generate the graphical display

for the athletic trainers. Based on the variations in

the force values, we identified three main different

postures which lead to significant changes in the

corresponding force values on their feet as shown

below.

icSPORTS2013-InternationalCongressonSportsScienceResearchandTechnologySupport

Figure 7a: Overhead squat position 1 (Kiesel et al., 2007).

Figure 7b: Overhead squat position 2 (Kiesel et al., 2007).

Figure 7c: Overhead squat position 3 (Kiesel et al., 2007)

We noticed that the force values collected using

our experimental set-up in a wireless environment

changes a lot during the three different postures of

the squat test. The graphical interface we developed

helped in comparing the performance among

different players and the two genders. We plotted the

time (seconds) on the X-axis and the force value

(pounds) on the Y-axis. A few of the performances

of the athletes are shown in Figure 8.

Figure 8: Squat force value of toe and heel of female

subject 4.

We collected data from the player’s heel and toe

as he/she performed the squat. This data is plotted in

Figure 8 for female subject4 and Figure 9 for the

male subject3. A good squat should have high values

of force for the heel since the heel takes the bulk of

his weight while the force values at the toe should be

less since as they do not need to support the weight.

From the graph we can see that the force values

show three large spikes that correspond to the athlete

performing the three squats. For male subject3, his

heel force data shows the three spikes. However, his

toe has also registered some large values which

show that he did not perform the squat properly.

Female subject4’s force values in the heel show

three well defined spikes while her toe values have

zero values corresponding to the actual squats. This

can be considered as an ideal squat force value. We

also discuss some of the other performance

characteristics which lead to some important

observations by the trainers as they correlated the

graphical values with on-field performances of the

athletes affected by prior injuries.

Figure 9: Force value of toe and heel of male subject 3.

QuantitativeAssessmentofaFunctionalMovementScreeninAthletesusingaWirelessBodyAreaSensorNetwork

We observed the following:

a) In order to distinguish a good squat from a bad

one, the player should exert more pressure in the

heel than the toes.

b) Figure 10 indicates that pressure exerted on left

heel is comparatively more that of right heel,

thus the balance is biased towards the left side.

c) Figure 10 also illustrates the comparison of force

between heel and toe of each leg of male

subject1. We observe that the force exerted on

left heel is more than left toe, which indicates a

good squat initially. The peak indicates a descent

during the squat where more pressure is exerted

on the heel during all the three iterations.

Comparing our results in Figure 9, we find

somewhat similar results, as well some

dissimilarity where the pressure exerted on the

heel at any instant is more than that of the toe,

which is an indication of a good squat, as also

confirmed by the trainers.

Another important aspect is to compare the

performance of two different athletes playing the

same game. According to the trainers, this

comparison really helps to understand the capability

of the players in playing continuously during the

sport season. Our WBASN experimental set-up gave

the trainers an opportunity to distinguish between

player squat performances, providing a robust means

of evaluating the athlete’s performance.

Figure 10: Squat force value of toe and heel of male

subject 1.

We compared the force squat values between male

subject1 and male subject3, both from the football

team and found the following observations as shown

in Figure11:

a) During the three repetitions of the overhead

squat performance, male subject3 seems to do

good squat with an appropriate postures as

compared to his team member male subject1.

The heel force values remain consistent over the

time progression for male subject3. For an ideal

squat, the heel takes the bulk of the body weight

during and the force values should remain at a

higher peak in a consistent fashion. For male

subject1, both the left and right heel values are

not consistent and change frequently indicating

poor form during the test. This correlates with

the athlete’s relatively poorer performance on the

field. The control on body weight during the

squat testing has always been an important

criterion to determine good, average and poor

athletes. Therefore our WBASN experimental

set-up is relevant and can help a trainer to

categorize the players based on quantifiable

performance metrics.

b) Unlike the right heel, the force value exerted by

the male subject3 on the right heel is continuous

which is more discrete. This leads to an inference

that the male subject1 could not maintain the

balance of his body while maintaining an upright

torso, and keeping his heels and the rod in

position, while descending as deep as possible,

as shown in Figure7a. We compared the force

values in the toe for both the athletes to

distinguish their athletic conditions based on

their performance.

Figure 11: Difference in squat force value of heel part

between male subject 1 and male subject 3.

Figure 12: Difference in squat force value of toe part

between male subject 1 and male subject 3.

icSPORTS2013-InternationalCongressonSportsScienceResearchandTechnologySupport

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In an ideal squat, the athlete should distribute the

weight through with equal pressure on their entire

foot from the heels through the toes and maintain

this foot position throughout the overhead squat as

they complete the exercise with their shoulders back

and their back straight (Tolliver). The weight should

be kept distributed on their upper thighs and the

heels or balls of your feet, neither on the toes nor

their knees. It’s more to get the athlete to get off

his/her toes than to literally squat only on the heels.

This observation is clearly visible from Figure 12

where male subject3 put a majority of the force on

the right toe as compared to the same in the left toe,

indicating the trainer that the subject cannot balance

his body weight due to inflexibility. Force values on

both the heel and toes are very important when

determining the potential performance of the athletes

as they can be indicative of postural balance, body

flexibility and other cognitive factors which affect

the performance of athletes.

4.1 Decisions by the Athletic Trainers

Based on previous subjective analysis of the trainers,

and the past history of injuries, the additional force

value information can significantly help trainers and

healthcare professionals to prescribe exercises for an

increased flexibility.

Sports medicine personnel will be able to

determine progression of rehabilitation based on the

graphical force values and it will help them to

determine return-to-play estimates.

Figure 13: Classification of three different groups in squat.

A healthcare professional will be able to advise

the athletes to discontinue any exercise depending

on their medical history and the graphical output

analysis of the WBASN that we have developed.

The initial results in the form of graphical display

have been helpful in classifying 6 athletes in three

groups of overhead squat performance as being

shown in Figure 13.

The result of our study suggests that squat

performances judged mainly on the force values on

both the heels and the toes in the athletes totally

differs among athletes in group1, group2 and

group3. The overhead squat performance in the

group3 is thought to be better than the others, as

subjectively classified by the sports medicine

professionals.

4.2 Future Work

Another feature that will be incorporated into the

system is the measurement of sway in an athlete

while he/she is performing the overhead squat. An

athlete without injuries will perform the squat

following a certain gesticulation. However, athletes

with injuries will deviate from expected motions.

Our system will incorporate gyroscopes and three

axis accelerometers on the chest and two shoulders

to determine the degree of deviation from the

expected motion. As before, data can be stored and

analyzed to provide the coach with a complete

picture of an athlete’s fitness.

Additional work will be carried out to develop a

system to enhance the security of the

communications channel from the data acquisition

device to the application server. Public Key

Cryptography using Elliptic Curve Cryptography

maybe a viable option since it gives a reasonable

amount of security without a lot of computational

overhead. A caching server may also be

incorporated in the system so as to reduce the load

on the database/analysis server for data that is most

frequently requested and/or that needs not be

computed in real time. The applications running in

the devices may also be enhanced to enable the

running of various what-if scenarios that can give an

estimate of the time required for an individual to

recover completely.

Most of these systems in WBASN employ

wireless devices to provide an unobtrusive

experience for the users. Therefore, most of these

systems are also inherently susceptible to the delays

and failures that are common in wireless systems.

For a system to be effective in healthcare, it must be

robust and provide mechanisms to ensure the

reliable delivery of medical data in case of an

emergency. Therefore, we need to explore the

problem and importance of reliability in a WBASN

and develop a framework for ensuring the

guaranteed delivery of data packets.

QuantitativeAssessmentofaFunctionalMovementScreeninAthletesusingaWirelessBodyAreaSensorNetwork

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Questions that will have to be investigated in the

future include:

a) Can the sensors be placed in the shoes and/or

attached to the athletes for both training and in-

game situations?

b) Will measured forces on soles indicate weakness

in the ankles?

c) If we determine deviation in the movement of an

athlete when standing up from the overhead

squat can the degree of deviation give us an idea

of the degree of injury?

5 CONCLUSIONS

We were successful in quantifying some of the

movement of an athlete performing an overhead

squat. Our long term goal is to develop a means of

quantifying the movement in even more detail so

numerical scores can be measured to quantitatively

access the degree of flexibility of an athlete based on

their performance of an overhead squat.

REFERENCES

Butler, R. J., Plisky, P. J., Scoma, C., Kiesel, K. B., 2010,

"Biomechanical analysis of the different classifications

of the Functional Movement Screen deep squat test,"

Sports Biomechanics 9(4), 270-280.

Kiesel, K., Plisky, P. J., Voight, M. L., 2007, “Can serious

injury in professional football be predicted by a

preseason functional movement screen?” N Am J

Sports Phys Ther 2(3):147–158.

Tolliver, K. D.: “Front squat foot position.

http://healthyliving.azcentral.com/front-squat-foot-pos

ition-3410.html

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