Monitoring of the Functional State of Athletes by Pupillometry

N. N. Varchenko

, K. A. Gankin

and I. A. Matveev

2,3

Sambon Precision and Electronics Co.,LTD, B. Tatarskaya str., 21, Moscow, Russia

Computing Centre of Russian Academy of Sciences, Vavilov str., 40, Moscow, Russia

Iritech Inc. RnD Center, B.Tatarskaya str., 21, Moscow, Russia

Keywords:

Pupil Reaction, Functional State Evaluation, Binocular Pupillometry.

Abstract:

Method of binocular pupillometry is presented with an application to evaluation of the functional state of ath-

letes. The method is based on synchronous registration of both pupil reactions to a light ﬂash stimulus. Pupil

reaction reﬂects the state of sympathetic-parasympathetic balance of autonomic nervous system and serves as

an objective measurement of the body condition. The advantages of the method are: non-invasiveness, quick

operation, wide spectrum of measured characteristics, and the fact that pupil reaction to light ﬂash stimulus

is an unconditioned reﬂex and is not controlled by the cortex and consciousness. Results of the experiments

performed with various groups of athletes are presented. A possibility of using the pupillometry for evaluating

athletes’ state is shown. Comparison with traditional methods of functional state evaluation is done.

1 INTRODUCTION

Nowadays trainers, physicians, rehabilitation doctors

who are involved in sports of high achievements face

increasing negativeeffectsof sport to the human body.

Quite frequently this is connected with lack of infor-

mation on functional state of the athletes in the right

time. That is why it is necessary to enhance the meth-

ods of survey, diagnosis, and control in order to notice

deviations of health condition in time and to prevent

unwanted outcomes of training and competition loads

as well as to correct training process. One of actual

problems of modern sport medicine is development

of new methods of examination, allowing more com-

plete and reliable evaluation of the functional state of

an athlete.

One of such methods is pupillometry that is mea-

suring pupil response to a stimulus, typically light

ﬂash. Possibility to use pupil as an objective crite-

rion for estimating the condition of autonomic ner-

vous system and various connected characteristics

was persuasively proven by the works (Velhover

and Ananin, 1991; Apter, 1956; Shahnovich, 1964;

Smirnov, 1953). Pupillometry is especially attractive

since pupil reaction is unconditioned reﬂex, which

is not driven by cortex and thus is not controlled by

mind (Velhover and Ananin, 1991; Andreassi, 2000).

At the same time it is sensitive indicator of wide

spectrum of physiological processes connected with

sympathetic-parasympathetic balance.

Despite the seeming simplicity, registration and

processing of pupil reaction poses several difﬁcul-

ties due to its quickness and relatively small size of

an object to be measured. Pupillometry as a clini-

cal medicine method dates back more than 100 years:

in the end of 19-th century Du Bois-Reymond and

P. Garten made attempts to photograph the pupil for

diagnostic purposes. However necessity of speedy

recording and processing of vast data amount delayed

the development of the method. First versions of

pupillometer devices also faced problems connected

with bright background illumination necessary for

capturing the ﬁlm, which causes strong constriction

of the pupil. Due to modern means of image registra-

tion and processing these problems are now solved.

Recent development of informational technology al-

lowed to construct the systems, which register pupil

image stream with high speed and process it in real

time precisely and reliably. Basic informative fea-

ture of modern pupillometry systems is pupillogram,

which is a graph of pupil size during its reaction.

This paper presents a method of binocular pupil-

lometry in its application to athlete functional state

evaluation. Following section describes some pecu-

liarities of the method. In the third chapter results of

experiments are presented. The tests were performed

210

N. Varchenko N., A. Gankin K. and A. Matveev I..

Monitoring of the Functional State of Athletes by Pupillometry.

DOI: 10.5220/0005132102100215

In Proceedings of the 2nd International Congress on Sports Sciences Research and Technology Support (icSPORTS-2014), pages 210-215

ISBN: 978-989-758-057-4

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

on several groups of athletes before and after training

loads. Abilities of pupillometry in the evaluation of

their conditions are shown. The presented method is

compared with standard ones used for this purpose.

2 BINOCULAR PUPILLOMETRY

METHOD

Method of pupil reﬂex registration and processing is

implemented by HW/SW complex. Images of right

and left eyes are registered simultaneously and syn-

chronously during 2.5 seconds. Light ﬂash stimu-

lus is outputted after 200ms after start of registra-

tion. Light intensity of 145lux was used in examina-

tions described herein. Images are registered by two

CCD/NTSC cameras with interlacing. Frame rate is

60 frames per second, thus 150 pairs of frames are

captured in one registration session. Frame period is

1/60 = 16.67ms. Image resolution is 640 ∗ 480 pix-

els, grayscale 8 bit. Infrared illumination with wave-

lengths of 880nm and 940nm is used. Frame scan and

light ﬂash output are synchronized. Examination in-

cludes registration of three series split by 1-minute

pauses for pupil recovery. Thus total duration of ex-

amination does not exceed three minutes. Apart from

images age of testee is input since normal behaviour

of pupil depends on the age of person.

Figure 1 shows a sample of eye images obtained

in pupillometry examination. Images with maximum

pupil size (before ﬂash) and in the moment of maxi-

mum pupil constriction are presented.

Figure 1: Sample of pupil reaction. (a) — ﬁrst image in se-

quence, original pupil size; (b) — 55-th (from 150) image,

minimal pupil size.

Pupillogram is determined as a ratio of pupil and

iris sizes, dependent on time, expressed in percent:

R(t) =

pupil

(t)

iris

(t)

100% , (1)

where r

pupil

(t) and r

iris

(t) are measured radii or pupil

and iris in the moment t. One should note that it is

necessary to measure iris radius in all frames of the

sequence since the testee can move and scale of image

may change. Radii of pupil and iris are determined in

frames by the iris segmentation algorithms (Gankin

et al., 2014) that give higher precision compared to

photometric methods (Shahnovich, 1964) and sub-

stantially higher speed compared to manual process-

ing (Velhover and Ananin, 1991), which were used

earlier.

First phase of pupillogram reﬂects the state of

pupil sphincter innervated by parasympathetic ner-

vous system. Second phase reveals the state of pupil

dilator innervated by sympathetic nervous system.

Hence pupillogram characterizes interaction of these

two compounds of autonomic nervous system and

gives an opportunity to judge about them. Figure 2

represents the typical appearance of the pupillogram.

Abscissa axis uses time in milliseconds, ordinate axis

gives relative pupil radius (1).

Figure 2: Scheme of the pupillogram and some of its pa-

rameters.

From mathematical point of view pupillogram is

a series of 150 numbers: {r(t)}

150

t=1

each belonging to

an interval from 10 to 80 (minimal and maximal pos-

sible relative pupil radius). Using time series analysis

methods (Hamilton, 1994) the following characteris-

tic points are located in pupillogram: B — moment of

reaction start; M — middle of the plateau, which is

a ﬂat segment of minimum pupillogram values; F —

control point lying in a distance of 667ms from M;

E — control point lying in a distance of 1167ms from

M. Various parameters describing person’s functional

state can be extracted from pupillogram. We present

nine of them, which are used for functional state mon-

itoring and easily interpretable.

1. R

— original relative pupil size, measured in

percent. It is calculated as an average relative radius

in several beginning frames:

∑

t=0

R(t) , T ≈ 5 . (2)

2. T

lat

— duration of latent period of pupil con-

MonitoringoftheFunctionalStateofAthletesbyPupillometry

211

striction, i.e. time elapsed from light ﬂash till the start

of pupil reaction. It is measured in milliseconds. This

parameter is numerically equal tot coordinate of point

B: T

lat

= t(B). It characterizes the agility of nervous

processes.

3. T

para

— duration of parasympathetic phase of

pupil reaction i.e. time passed from start of pupil re-

action to the middle of plateau. T

para

= t(M) −t(B).

4. S

para

— criterion of pupil constriction activ-

ity, which is an angle between the BM segment and

ordinate axis.

5. A — reaction amplitude, measured as a con-

striction of pupil relative to iris radius:

A =

pupil

(B) − r

pupil

(M)

iris

(0)

, (3)

where r

pupil

(B) and r

pupil

(M) are absolute pupil sizes

in B and M points.

6. C

max

— maximum speed of pupil constriction,

expressed in percent per millisecond.

max

= max

t∈[B

]



−

dR(t)



. (4)

Values of T

para

, S

para

, A, C

max

characterize strength

and stability of nervous and muscular excitations.

7. T

plato

— duration of latent period of recovery,

time from stopping constriction till starting dilation.

This is the width of the plateau. This value as well

as T

lat

characterizes agility of nervous processes, i.e.

speed of switching between excitation and inhibition.

For sportive achievements it is optimal to have this

parameter in minimum of normal range.

8. S

simp

— criterion of activity of pupil recovery,

which is an angle between FM segment and ordinate

axis.

9. V — ratio of pupil sizes after certain period of

recovery (control point E). It characterizes recovery

abilities of the body. It is expressed in percent:

V =

R(E)

100% , (5)

If this parameter falls below 50%, chronic fatigue

syndrome may take place (Ananin, 1982). With ath-

letes it means over-training.

Average, minimal and maximal values are deter-

mined for each parameter statistically. These values

vary according to age of the testee. Parameters are

normalized so as to ﬁt in range [−100%;+100%]:

P =











P− P

norm

− P

min

100%, P 6 P

norm

P− P

norm

max

− P

norm

100%, P > P

norm

(6)

where P

norm

, P

min

, P

max

are average, minimal and

maximal norms of P. By this normalization param-

eters become dimensionless and their substantial de-

pendence from age is eliminated.

Synchronous binocular pupillometry obtains two

pupil reactions and hence gives an opportunity to re-

veal and examine bilateral asymmetry of nervous sys-

tem, particularly hemisphere asymmetry. One of ba-

sic asymmetry manifestations is anisocoria i.e. rela-

tive difference in radii of two pupils, deﬁned here as:

An = 2

(D)

−

(S)

(D)

| + |

(S)

, (7)

where

(D)

and

(S)

are normalized parameter R

(2)

for right and left eyes respectively. Due to limita-

tions of iris segmentation methods precision of aniso-

coria value is 2%. Thus hemisphere asymmetry is

detected if An /∈ [−0.02;0.02]. For athletes presence

of hemisphere asymmetry ﬁrst of all means possible

mismatch in coordination.

3 COMPARISON WITH OTHER

METHODS

Pupillometry abilities were veriﬁed in comparative

tests with standard methods. 30 professional volley-

ball players were tested. Age of the athletes ranges

22-24 years, sport experience is 5-6 years. Con-

trol group was formed from 30 healthy men of same

age, not athletes. Tests were performed in natu-

ral conditions, i.e. in the sports hall. Pupillogram

was registered in rest (before the load) and after the

load (training or competition). Complex estimation

of functional condition of the testees was done in-

cluding studies of cardiovascular, somatic and auto-

nomic nervous systems, operability, emotional and

volitional qualities. Cardiovascular system was eval-

uated by conventional sports medicine methods: heart

rate (HR), blood pressure (BP) and electrocardiogram

(ECG) (Dolmatova et al., 2001). Operability was

determined by a common European test PWC-170.

Maximal oxygen consumption (MOC) calculated by

the method (Karpman et al., 1988). State of condi-

tioned reﬂex activity was determined by the latent pe-

riod of the motor response (visual-motor test). Senso-

rimotor coordination (tremor of hands, strength and

endurance of individual muscle groups hands) was

determined by labyrinth tremor-meter as the number

of errors made in 30 seconds. Emotional and voli-

tional qualities and status of major organs and sys-

tems were determined by electro-puncture reﬂex di-

agnosis (Nacatani and Yarnashita, 1985). The ath-

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212

letes were divided into two groups according to their

performance in competitions: I — high professional

group, II — middle level group.

As shown in Table 1, indicatorsHR and BP in both

groups of athletes have the same value, and the value

of these indicators point to a good recovery of the car-

diovascular system. However, the performance of the

MOC and PWC in group I was signiﬁcantly above

the rate of group II and correlated with the level of

professional training of athletes. Control group has

signiﬁcantly lower MOC and PWC, and indicators of

the cardiovascular system showing that these testees

are above their limits of adaptation at this test load.

Table 1: Indicators of cardiovascular and performance after

the load test

Indicator

Groups

Group I Group II Control

HR, beats/min 54− 74 56− 71 110− 118

BP, mm Hg 130/60 130/75 150/90

MOC, ml·kg/min 60± 1 51± 6.8 33± 5.2

PWC-170, kgm/kg 21.8± 1 17.3± 2.13 11.4± 1.7

The effects of exercise on the somatic nervous

system and the coordination of movements are pre-

sented in Table 2. Columns ’A’ and ’B’ show the

results in tests before and after exercise, respec-

tively. As the table shows, the reaction rate (based on

reﬂex-meter) and sensorimotor coordination (in terms

tremor-meter) before exercise are same in both groups

of athletes, but after training indicators of Group I are

much better.

Table 2: Indicators of reaction speed and tremor before and

after the load.

Indicator

Groups

Control Group I Group II

A B A B A B

Reﬂex, ms 380 495 126 96 129 128

Tremor, errors 30 52 30 10 30 25

In the control group, the rate of reaction and sen-

sorimotor coordination worsens after a load test, that

indicates the deterioration of conditioned reﬂex activ-

ity and inadequate physical load, which led to fatigue.

Pupillometry results are presented in Tables 3 and

4. Columns ’A’ and ’B’ show test results before and

after exercise, respectively. For athletes columns ’C’

and ’D’ show results before and after the competition.

As shown in Table 3, latent period of pupil reac-

tion T

lat

in Group I before exercise is much shorter

(at 48ms), than in the control group. For Group I T

lat

becomes shorter after a training and is reduced even

more before compatition, that can be explained by

emotion tension. After the competition T

lat

increases

to the level observed after training, but does not reach

Table 3: Dynamics of pupillometry parameters for Group I

and Control.

Parameter

Groups

Control Group I

A B A B C D

lat

, ms 283 306 235 224 216 223

para

,ms 408 401 441 453 483 508

A,% 8 6 12 14 15 16

V,% 65 57 76 82 84 90

the values that characterize the state of rest. Thus, the

readiness of athletes in Group I, characterized by T

lat

increases during exercise, peaking before the compe-

tition. Observed dynamics of T

lat

in this group of ath-

letes is positive and indicates an adequate adaptation.

Dynamics of T

para

for Group I is characterized

by a progressive increase. It is minimum in the

state of rest, grows after training, grows more be-

fore competition, reaching a maximum after compe-

tition. This demonstrates high functionality of ath-

letes in Group I. Maintaining a high level indicator

after the event shows that the functional reserves of

the athletes in this group have not been exhausted by

psycho-emotional and physical stress even till the end

of the competition.

A similar pattern is observed for the reaction am-

plitude A. For Group I the indicator increases during

exercise, increases even more before the competition

and reaches a maximum by the end of the competi-

tion. This behavior shows that the potential perfor-

mance of athletes by the end of the competition is not

exhausted, but due to the inertia of energy mobiliza-

tion processes remained at a high level even after the

competition.

Recovery criterion V for Group I is also signiﬁ-

cantly higher than in control group. After training,

V value is signiﬁcantly higher than before training

and remains approximately same before the compe-

tition. After the competition the recovery process is

strengthened. Thus, the pupillometry study of Group I

conﬁrms a known phenomenon of overcompensation

after exercise for well-trained athletes. Pupillometry

analysis allows to conclude that in this group of vol-

leyball players a high level of adaptation of the auto-

nomic nervous system to physical activity is achieved.

For these athletes psycho-emotional load during com-

petition stimulates the adaptive mechanisms.

Table 4: Dynamics of pupillometry parameters for Group

II.

Parameter

Group II

A B C D

lat

, ms 251 253 246 274

para

, ms 427 432 442 421

A, % 10 10 12 9

V, % 74 77 80 68

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213

As can be seen by comparing the tables 3 and

4, value and dynamics of pupillogram parameters of

Group II signiﬁcantly differ from Group I. Parameters

of Group II show higher activity than that of control

group, but lower than in Group I.

The latent period of the reaction T

lat

is longer.

Whereas in Group I duration of the latent period de-

creased after training and before the competition, in-

dicating the improvement of readiness, no signiﬁcant

differences of T

lat

is found for Group II, and after the

competition the latency signiﬁcantly increases. This

marks a decline of starting readiness for these athletes

and slower decision making.

Level of reaction revealed by duration of parasym-

pathetic phase T

para

generally follows the dynamics

of T

lat

. Under the inﬂuence of emotional tension be-

fore the competition, the durability of reaction in-

creases, but after the event it becomes worse than be-

fore training. Such dynamics indicates an insufﬁcient

degree of ﬁtness and lower potential performance of

athletes in Group II compared with Group I.

Reaction amplitude A is signiﬁcantly lower in

Group II compared to Group I and does not change

under the inﬂuence of physical load during training.

Before the competition, under the inﬂuence of emo-

tional stress, these athletes demonstrate an increase of

the amplitude, but after the contest reaction strength

declines.

Distinct differences between two sportsmen

groups exist also in recovery. Characteristic of Group

I is a positive trend of all pupillogram parameters dur-

ing training and competition. Characteristic of Group

II is the lack of positive dynamics after exercise com-

pared with the resting state, the trend toward improve-

ment in these areas before the competition and a sig-

niﬁcant decline after the competition. Apparently, in

this group of athletes at the time of tests reached the

limit of adaptation capabilities of autonomic regula-

tion. This yields slight improvement in performance

under the inﬂuence of emotional stress before com-

petition, but then frustration during the competition.

Evidence of this frustration is the deterioration of all

pupillogram parameters after the competition.

4 COMPARISON OF SPORTS

SPECIALIZATIONS

Apart from monitoring of training process

pupillometry-based estimation may be applied

in other aspects. One of them is evaluation of the

appropriateness of the athlete to this or that sport

specialization. Different specializations require

different physical and psychical characteristics. A

study of athletes from different sport specializations

was performed in order to determine whether such

differences can be revealed by pupillometry.

Male athletes were tested from three different spe-

cializations: power (boxing), game (volleyball) and

endurance (skiing) in the age group under 25 years.

The control group consisted of men of the same age

who were not athletes. All participants in the study

period were healthy. Each groups included at least 20

persons. Table 5 key indicators for groups of athletes

are shown. The groups are designated as ’P’, ’G’, ’E’

(power, game, endurance). Control group indicators

are taken as 100%.

Table 5: Pupillogram parameters for athletes of different

specializations.

Parameter

Groups

P G E

lat

89% 78% 87%

para

69% 72% 73%

A 164% 165% 151%

V 150% 175% 172%

In general, the reaction of athletes of different spe-

cializations differ: reduced amplitude response in a

group of endurance, which is associated with the need

to save power and distribute it over a longer period.

The reaction time is less for the Game group that re-

ﬂects the focus on making quick decisions. Degree of

recovery is higher for Game and Endurance groups.

These indicators are lower for Power group, and it

is logical, because these sports suppose high perfor-

mance in short time periods, whereas recovery may

be slow.

5 CONCLUSION

Binocular pupillometry is an objective method of as-

sessing the state of the autonomic nervous system and

an important additional method for complex evalua-

tion of the functional state of the athletes. Studies

of pupil reﬂex in persons involved in various sports

revealed a signiﬁcant correlation between the time

of pupil constriction and overall reactivity of human.

Data obtained by pupillometry correlate with analyses

of reﬂex-meter, tremor measurements, latent periods

of somatic motor responses.

Binocular pupillometry method allows estimating

the degree of athlete’s adaptation to the physical and

psycho-emotional stress. Absence of positive dy-

namics of pupillogram parameters after exercise com-

pared with the resting level indicates tension in adap-

tation processes and the threat of failure of adap-

tation during the competition. Analysis of the dy-

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namics pupillogram parameters allows to effectively

adjust the training process of athletes, analyze their

functional ﬁtness and health, optimize and personal-

ize training loads at various stages of preparation, as

well as to identify athletes with limited reserves of

adaptation and make the selection of athletes for com-

petitions.

Method of computer binocular pupillometry is

easy to use, requires no special training and can be

utilized for mass screening.

ACKNOWLEDGEMENTS

Supported by the RFBR grant 12-07-00778.

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