AN AUTOMATED ATHLETE PERFORMANCE

EVALUATION SYSTEM

From Theory to Practice

Hugo Silva, Gonçalo Martins, Susana Palma

PLUX, Biosensor Engineering., Av. 5 de Outubro nº 70-8º, Lisbon, Portugal

Pedro Mil-Homens, Maria Valamatos

Faculty of Human Kinetics, Lisbon, Portugal

Keywords: Athletic Performance Evaluation, Wireless, Sensors, Real-Time, Automated signal processing.

Abstract: In order to obtain information on athletic performance, strength and power characteristics of the athlete are

generally evaluated. However, due to the large number of variables needed for the assessment, this kind of

evaluations is usually time consuming. Taking advantage of recent developments in the area of sensors and

acquisition systems and using signal processing algorithms reported in the literature, we developed a new

Athletic Performance Evaluation System. This system automatically determines evaluation parameters and

integrates them in ready-made reports, decreasing the time involved in the evaluation process. The system is

based on the installation of sensors and wireless acquisition systems at the assessment workstations of a

Sports Evaluation Laboratory. At present, Jump Platform, Leg Press and Multipower workstations are being

used. Strength and displacement data collected by the sensors at these workstations is automatically

processed in real time at the Central Base Station where standard force and power related evaluation

parameters are determined. Graphical representations of time evolution of the variables being measured by

the sensors are showed in real time on the screen. Each evaluation session is defined by a protocol that can

be specifically created by the coach for each athlete. The results of the evaluations are stored in an athletes'

database so that the historic performance of the athlete can be easily assessed. The resulting system presents

the deployment of sound theoretical evaluation metrics in a real time athlete performance evaluation system.

1 INTRODUCTION

Athletic performance can be assessed by analyzing

specific variables that provide information about the

physical condition of the athlete. Generally, strength

and power related variables are the gold standard for

athletic evaluation. For their assessment, specific

tests and procedures are used (Morrow et al, 2005).

Those tests are designed in accordance to

recommendations and guidelines that assist coaches

collecting valid and reliable data used to determine

the needed evaluation parameters (Brown et al,

2001).

Traditionally, and according to the assessment

guidelines, a large amount of evaluation variables

must be determined in order to obtain complete

information on the athlete's physical condition.

Usually, the data measured during the evaluation

tests is processed a posteriori and summarized in

reports that are analyzed a few hours or even days

after the tests are done, which also contributes to the

slowness of the evaluation. With the recent

technological advances, this situation can be

overcame. Besides introducing new levels of

objectivity, automation and usability into the

evaluation process, the use of new technological

tools may reduce markedly the time needed to

complete a performance evaluation session. The

training process itself is, nowadays, turning into a

process that uses the advantages of new technologies

(Liebermann et al, 2002): the use of sensors and

real-time presentation of the athlete's signals during

training provides athletes and coaches with

sophisticated objective information about the sport

performance evolution and it can also be used as a

real time feedback tool.

239

Silva H., Martins G., Palma S., Mil-Homens P. and Valamatos M. (2009).

AN AUTOMATED ATHLETE PERFORMANCE EVALUATION SYSTEM - From Theory to Practice.

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 239-244

DOI: 10.5220/0001548602390244

 SciTePress

This paper describes a new Athletic Performance

Evaluation System based on real-time measurement

and processing of signals generated by the athlete

during the assessment tests. Using wireless sensors

and acquisition systems installed on different

evaluation workstations, an athlete-focused system

that includes automated algorithms for determining

strength and power-related variables was developed.

Standard evaluation methods (Hori et al, 2006,

Linthorne et al, 2001; Dowling et al, 1993) used for

manual analysis of data in the traditional evaluation

laboratories were automated in order to obtain a

faster, integrated evaluation system. In this way, the

time involved in testing each athlete is decreased by

a factor of three.

The computed variables are summarized in a

ready-made report and may be used as performance

indicators for purposes such as the quantification of

the relative contribution of strength and power to

athletics events, the identification of specific

weaknesses and prescription of suitable

training/rehabilitation programs, the follow-up of

training/rehabilitation programs or even the

identification of athletic talented individuals.

2 GENERAL DESCRIPTION

The setup of the system involves both hardware and

software modules. Signal acquisition and

transmission is done by wireless signal acquisition

hardware and measurement sensors installed on the

evaluation devices of the laboratory. Data analysis

and reporting as well as management of athletes

database and evaluation protocols are performed by

the different software modules installed on a Central

Base Station.

The system works on a workstation/protocol

basis.

Each workstation is composed of an evaluation

device instrumented with measurement sensors and

a wireless acquisition unit which collects the signals

measured by the sensors. The acquired data is

transmitted in real time to a Central Base Station via

Bluetooth, where it is automatically processed and

represented on a screen. For the moment, three

workstations are predefined: (a) Leg Press: for

evaluation of force production characteristics of the

lower members; (b) Jump Platform: for evaluation of

reactive force of the inferior members and (c)

Multipower: for evaluation of force production

characteristics of the superior members and dynamic

parameters such as power, velocity and muscular

resistance (Figure 1).

Figure 1: Schematic Representation of powerPlux athletic

performance evaluation system setup.

Each evaluation session is defined by a protocol

that is previously designed by the coach for the

athlete. To build a protocol, the coach chooses the

set and sequence of evaluations the athlete will

execute as well as the respective details. In the end

of each evaluation session a report is produced that

summarizes it and presents the best results, allowing

also the introduction of comments by the coach. If

several sessions of a same evaluation protocol are

performed, a comparative report may be produced.

Given the wireless connectivity between the

workstations and the Central Base Station, the coach

can easily follow the athlete's work, in three simple

steps: (a) connect: communicate wirelessly with the

workstation; (b) acquire: automatically access the

main performance indicators in real-time; and (c)

visualize: session and historic reporting and analysis,

with graphical curves representation and gain

indicators.

Simultaneously the athlete has real-time

feedback about his/her performance during the

evaluations, with automated visual and acoustic aids

to support the protocol execution. The fact that this

feedback information is given in real-time to the

athlete provide conditions for him/her to improve

significantly the process of skill acquisition and

sport performance (Schmidt et al, 1999; Liebermann

et al, 2002).

Besides the automated data acquisition,

processing and analysis module, powerPlux also has

a management module which includes an Athlete

Database to store relevant information for each

athlete, each evaluation session and corresponding

final reports.

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3 HARDWARE

The recent technological developments in the area of

hardware design and integration offer appropriate

tools for the development of compact, miniaturized

and versatile systems with a large range of

applications in the areas of real-time signal

acquisition and processing (Silva et al, 2005).

At a Sports Evaluation Laboratory, space needs

to be clear of obstacles and evaluation tools should

not interfere with athletes' performance, so that

parameters such as wireless connectivity,

miniaturization, versatility and usability are

desirable features when one thinks of a sports

assessment tool. Taking advantage of the new

acquisition hardware solutions (Silva et al, 2005),

we developed powerPlux Athletic Evaluation

System, which gathers the features referred above.

Each Workstation is instrumented with a 12bit,

1000Hz bioPlux8 wireless acquisition system and

suitable sensors for measuring the signals produced

by the athlete at those workstations (Table 1). In this

way, the analog data measured by the sensors are

converted to digital data by the bioPlux8 uint that

communicates via Bluetooth with the Central Base

Station, where the data is processed (Figure 2).

Table 1: Sensors used in the Workstations.

Workstation Sensors

Leg Press Load Cell

Jump Platform Force Platform

Multipower Load Cell; Displacement sensor

Figure 2: Schematic representation of powerPlux

hardware.

4 SOFTWARE

Signals measured by the sensors of each

workstations are managed by powerPlux Software

Application. It consists of five internal modules: (a)

device and sensor configuration; (b) acquisition and

display; (c) automatic signal processing; (d)

reporting; and (e) database. These modules receive

the signals collected at the different workstations in

order to determine evaluation parameters, present

them in real time and store them in the database.

The architecture of powerPlux software is

intentionally simple. A Home Screen allows to

choose between the Configuration and the Database

sections. The Configuration section is where the

coach manages the evaluation devices, protocols,

and evaluations. The database section is reserved for

accessing athletes’ profiles: viewing the historic of

evaluations’ results and performing new evaluation

sessions.

In order to obtain an objective quantification of

the athlete’s physical condition, reliable and valid

data needs to be collected. The design of evaluation

protocols may be guided by procedures

recommendations published by exercise science

experts (Brown et al, 2001). However, the ideal

evaluation protocol is not yet defined. Sports

scientists and coaches in evaluation laboratories

follow distinct recommendations and rules in order

to design their own evaluation protocols. Taking this

situation into account, we designed a versatile

software application that allows the coach to define

several parameters for his evaluation protocol and

sessions. In this way, a protocol may be costumized

according to the athletes' needs and according to the

different assessment guidelines. This is done in the

Protocol Configuration screen, where the coach may

choose the kind and sequence of the evaluations the

athlete needs to perform (Reactive Force, Isometric

Force or Velocity-Power) as well as a variety of

factors that need to be considered when testing: joint

angle at which to perform the testing, the rest

interval between consecutive repetitions, the number

of repetitions to perform (trials and definitives) or

the duration of each test. Other evaluation-specific

parameters may also be configured for each

evaluation protocol.

Once an evaluation protocol is designed and

chosen for an athlete, it is saved in the respective

page of the athletes’ database. The athlete may

execute as many evaluation sessions of that protocol

as needed.

The evaluation process is guided by visual

instructions. A graphic representation of the signal is

showed on the screen while the athlete is performing

the evaluations, which gives him real time visual

feedback of his performance.

In the end of an evaluation session a report os

produced with graphic representations of the best

execution with companion tables where the results

determined automatically by the signal processing

algorithms are shown. All the Session Reports are

saved to the Database and identified by date and

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241

time. For printing purposes, a printable format of the

Report may also be generated. In this way, the

historic performance progress of the athlete can be

easily accessed, allowing follow-up as well as

performance gains comparison throughout different

evaluation sessions.

4.1 Evaluations

From the analysis of the signals recorded at the

different workstations, powerPlux processing

algorithms determine standard performance

evaluation variables. The fact that the determination

of those variables is automated, introduces a new

level of objectivity into the evaluation process,

allowing a better characterization of the performance

of the athlete.

4.1.1 Reactive Force

Jumping is frequently used as a method of

evaluation of reactive and explosive force in lower

members. The measurement and monitoring of

variables such as the jump height, contact time,

impulse or vertical velocity are used to study these

characteristics.

At the Jumping Workstation, the athlete

performs vertical jumps while standing on a force

platform that collects the vertical force signal. The

processing of this data allows the computation of the

standard variables related with the evaluation of

lower members reactive force.

Before the evaluation takes place, the coach may

configure some specific Evaluation Parameters,

namely the kind of jumps the athlete will perform

(Squat-jump, Counter-movement Jump or Drop

Jump) (Linthorne, 2001), the number of trial and

definitive collections and the duration of each

collection.

Introduction of algorithm configuration values is

also possible. As an example, the force value above

which the algorithm will detect the beginning of a

jump or the force value for the detection of invalid

squat jumps due to the an initial downward

movement may be different in distinct evaluation

sessions.

powerPlux software automatically processes the

force signal measured during the jumps and

determinates the performance indicator variables in

real time: (a) contact time, (b) gravity center

elevation, (c) vertical velocity and (f) impulse

achieved in each of the repetitions. These

parameters, determined according to standard

methods in the literature (Dowling et al, 1993;

Linthorne, 2001), are presented while the athlete is

jumping (Figure 3) and are stored in the Evaluation

Session Report. The squat jump must always be

performed in a Reactive Force Evaluation Session in

order to assess the relative enhancements in jump

performance due to the effect of stretching the

muscle/tendon complex prior to contracting.

(Linthorne, 2001; Brown et al, 2001). The elevation

of the center of gravity achieved in this jump is

taken as base value with which the values achieved

in counter-movement and drop jump are compared.

Figure 3: Evaluation screen showing the results of a

counter movement jump evaluation.

4.1.2 Isometric Force

Isometric assessment of muscular function requires

the athlete to push maximally against a resistance,

where a measurement sensor is placed, without

movement taking place. This test is one of the oldest

methods used in sports science.

powerPlux allows the evaluation of isometric

force of both superior and inferior members. The test

is done at the Multi-Power and Leg-Press

workstations, respectively. The devices are

instrumented with load cells to measure force data.

The algorithms are applied in real time to this data

and determine, directly from the force-time curve,

the evaluation variables. Figure 4 shows a screen

shot of an evaluation of suprior members' isometric

force.

Maximum Strength (Maximum Voluntary

Contraction) and the speed with which force can be

developed (Rate of Force Production) are important

variables of the isometric force evaluation

(Abernethy et al, 1995; Wilson et al, 1996). These

variables are determined by powerPlux software for

both superior and inferior members by automatic

analysis of the force-time curve and respective

derivative. Other important variables are also

determined: the percentage of the Maximum Force

at the instant when the Maximum Rate of Force

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Production is achieved, the Rate of Force Production

at 50, 150, 250 and 350ms and the Percentage of

Maximum Force at 50, 150, 250 and 350ms.

The evaluation may be unilateral or bilateral,

allowing the comparison between both left and right

members' performances.

Isometric assessments usually display high

test/retest reliabilities (Abernethy et al, 1995).

However, reliability varies between the muscle

groups, the parameter being assessed (Maximum

Force or Rate of Maximum Force Production) and

the posture at which the testing is performed (joint

angle). In order to facilitate the performance of a

comprehensive evaluation and follow-up of the

athlete, these parameters are recorded in the report

as well as the parameters configured before the

evaluation takes place.

Algorithm configuration parameters is also

possible for isometric force evaluation Workstations:

the Initial Force Value, the range of the derivative

and the Acquisition Frequency are configurable

parameters which the coach may adapt for different

evaluations.

Figure 4: Evaluation screen showing the results of a

Isometric Force Evaluation (unilateral).

4.1.3 Velocity-Power

The measurement of power output during exercise

gives useful information to evaluate athletes’ speed

strength (Hori et al, 2006), which can be used as an

indicator of performance in most athletic activities.

This evaluation can be done with an isotonic test that

consists of moving a sub-maximal load against

gravity as fast as possible.

Weightlifting exercises are effective training

methods to improve speed strength, which makes the

measurement of the power output in this kind of

exercises a helpful tool for coaches

powerPlux system integrates a Multipower

device instrumented with a sensor that measures the

time variation of the load displacement when the

athlete does the weightlifting. An algorithm

determines the velocity and acceleration of the

lifting exercise from the displacement data recorded

by the sensor mounted on the device (Hori et al,

2006). With this data, Force/Velocity and

Force/Power relations can be determined for

muscles under the isotonic situation, namely

regression equations for force and load as function

of velocity.

The maximum amount of weight that can be

lifted in one repetition, i.e., the One-Repetition

Maximum (1RM) is the most common measure of

isotonic strength. 1RM testing involves a trial and

error procedure in which progressively heavier

weights are lifted until the weight exceeds the

subject's ability. The standard procedure involves

starting from a percentage of a (estimated) reference

1 RM value and then lifting progressively heavier

loads until the heaviest successful lift is reached

(Brown, 2001). Before the evaluation takes place,

the coach indicates the estimated 1 RM. The lifting

evaluation starts with a load of 20% of the reference

1RM and continues with equally spaced increases of

loads until the maximum is reached. For each lifted

load, the following variables are automatically

computed and presented in the report: (a) Mean

Power; (b) Mean strength; (c) Mean and Maximum

Velocity of the lifted load; (d) Displacement of the

load; (f) Time to reach the Maximum Force and (g)

Strength Deficit.

Graphical representations of time variation of

displacement, force, force/velocity, force/power and

force deficit are also presented in real time, giving

the athlete feedback of his own work. At the end of

each evaluation session Full Power, ratio between 1

RM and Body Weight (1 RM/BW) and ratio

between the lifted load and Body Weight (W/BW)

are determined and presented in the report which can

be used for follow-up purposes.

Some evaluation parameters of the velocity-

power workstation may be configured, namely the

duration of each test (15s , 30 s, 45 s or 60 s), the

time until the start of the test and the type of

evaluation (unilateral or bilateral). The Acquisition

Frequency is also configurable.

4.2 Reports and Athletes' Database

At the end of the evaluation session, the results and

configuration parameters used are stored in the

Report. Results are organized in tables and

represented graphically for a better understanding

and analysis. When several sessions of the same

AN AUTOMATED ATHLETE PERFORMANCE EVALUATION SYSTEM - From Theory to Practice

243

evaluation protocol are performed, additional

comparative data, including gain indicators, is

generated and added to the summary tables. The

several evaluation session's reports are organized by

date and time, in order to allow a simple and easy

view of the historic evolution of each athlete for

follow-up purposes.

The Database is the key point of athletes'

management since all the data concerning

evaluations and results can be consulted or edited. It

includes the athletes' profiles, where personal data as

well as reports of previous evaluation sessions are

stored.

5 CONCLUSIONS

This paper describes an intergrated, athlete-focused

system for automatic athletic performance

monitoring and evaluation. Making use of the recent

advances in technology, we installed wireless

measurement sensors and data acquisition systems in

the devices traditionally used for physical condition

assessment and designed a specific software that

integrates and automatically processes the data

recorded by the sensors in real time. The signal

processing algorithms are based on standard

methods available in the literature and have some

configurable parameters that make them adaptable to

the specific characteristics of an athlete or group of

athletes.

Thanks to the automatic processing of data and

generation of reports the amount of time needed for

a coach to build and execute an evaluation session is

markedly reduced in contrast to the traditional

methods.

Each evaluation session is defined by a protocol

that is specifically created by the coach for the

athlete. In this way, a comprehensive athletic

evaluation can be made, showing the weaknesses

and strengths of the athelte and helping in the design

of a specific and optimized training program.

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