Specificity and sensitivity of visual evoked potentials P100 latency to different events exercise

doi:10.4236/health.2009.11009

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HEALTH, 20

09, 1, 47-50

Published Online June 2009 in SciRes. http://www.scirp.org/journal/health

Specificity and sensitivity of visual evoked

potentials P100 latency to different events exercise

Jing-Guo Zhao1, Shu-Juan Pang1, Guang-Wei Che2

1Physical Education College, Shandong Normal University, Jinan, 250014, P. R. China; 2Physical Education College, Shandong

University of Traditional Chinese Medicine, Jinan, 250014, P. R. China.

Email: [email protected]

Received 6 April 2009; revised 26 April 2009; accepted 29 April 2009.

ABSTRACT

Visual evoked potentials (VEPs) are a series of

signals about visual occipital cortex in response

to visual stimuli and can be used as one of ob-

jective non-invasive neuro-physiological pa-

rameters to reflect the visual organs and central

visual pathway’s functional integrity. Previous

studies have shown that acute and chronic ex-

ercise could affect VEPs independent from body

temperature and other physiological parameters.

VEPs may well be used as neuro-physiological

criteria in defining the performances of the ath-

letes. Different sports training have different

effects on VEPs, but the results are not consis-

tent. P100 latency is the representative compo-

nent of VEPs and it is of high, steady amplitude

and of slight intra- and inter-individual variabil-

ity so that the index is most commonly used.

The purpose of this study was to investigate the

specificity and sensitivity of P100 latency to dif-

ferent physical activities. The neural electricity

device of NDI-200 was used to measure the

pattern reversal VEPs of all subjects, including

the values of the resting state before and after

different events exercise. Different events exer-

cise contained an aerobic cycloergometric ex-

ercise (7 subjects were conducted to a Bruce

Graded Exercise Test on the Monark Ergomedic

839E cycloergometer, THR (target heart rate) =

85% HRmax, 3 times/week, about 10 minutes

once time, 6 weeks), tennis training (16 volun-

teers, 2 hours/day, 3 days/week, 8 weeks),

aerobic Latin exercise (7 subjects, 1 hour/day, 3

days/week, 6 weeks) and the Baduanjin of

Health Qigong training (6 subjects, 1 hour/day, 3

days/week, 6 weeks). The VEPs recordings of

the control groups obtained synchronized with

the experimental groups. SPSS 11.5 for win-

dows was used for statistical analysis. A level of

P﹤0.05 was accepted as statistically significant.

The VEPs P100 latency of post-exercise of all

experimental groups except Baduanjin group

became shorter significantly compared with

those of pre-exercise (P﹤0.05). No significant

difference was found between pre-and post-

exercise for the control groups. This study

showed that exercise could shorten the P100 la-

tency significantly. Moreover, it also indicated

that VEPs were sensitive to exercise to a certain

extent. We concluded that VEPs might well be

used as neuro-physiological criteria in defining

the performances of the athletes. It was found

that the VEPs P100 latency became shorter after

most training programs; furthermore, it demon-

strated that P100 latency of VEPs had little

specificity to different events.

Keywords: visual evoked potentials; P100 latency;

specificity; sensitivity

1. INTRODUCTION

Visual evoked potentials (VEPs) are a series of signals

representing the responses of the visual occipital cortex

to visual stimuli including flash and pattern stimuli, and

can be used as one of the objective non-invasive neuro-

physiological parameters in the assessment of the func-

tions of visual organs, visual pathways and the optical

central nervous system [1]. Previous studies have shown

that both acute and regular/chronic exercise could affect

VEPs independent from body temperature and other

physiological parameters. But all the results are not con-

sistent [2,3,4,5,6,7]. P100 latency is the representative

component of VEPs and the most commonly used index

for its high, steady amplitude and slight intra- and in-

ter-individual variability. In order to investigate the

specificity and sensitivity of P100 latency to different

physical activities, we recorded the efficacy of an aero-

bic cycloergometric exercise, tennis training, aerobic

Latin exercise and Baduanjin of Health Qigong training

for 6 to 8 weeks [8].

48 J. G. Zhao et al. / HEALTH 1 (2009) 47-50

2. MATERIALS AND METHODS

2.1 Subjects

All subjects filled out the PARQ (Physical Activity

Readiness Questionnaire) & YOU questionnaire and

they have no optic or other systematic disease or other

history of neurological disease or exercise taboos. Writ-

ten consent was obtained from all subjects. The experi-

ment was approved by the local ethics committee.

3. EXPERIMENTAL DESIGN

3.1 The Aerobic Cycloergometric Exercise

11 healthy volunteers [(average age, (24±1) years)] from

Shandong Normal University were selected for this

study from October to December, 2007. Of these, 8 stu-

dents participated in the exercise including 4 boys and 4

girls. Meanwhile the 1st control group was consisted of

3 girls. This exercise was completed using the Monark

Ergomedic 839E cycloergometer with Bruce Graded

Exercise Test, THR (target heart rate) at 85% HRmax,

and 10 min a time, 3 times/week, for 6 weeks. The 1st

control group was measured synchronized with the ex-

perimental group.

3.2 The Tennis Training

45 healthy volunteers from Shandong Normal University

were selected for this study from April to June, 2007. 31

of them were majored in physical education. There were

21 male students [average age, (26±3) years; height,

(177±6) cm; weight, (74±8) kg; sports life, (8±4) years]

and 10 female students [average age, (24±1) years,

height, (165±6) cm, weight, (59±10) kg; sports life, (5±3)

years]. Of these, 11 males and 5 females participated in

the tennis training for 8 weeks. The remained 14 stu-

dents of them were studying as usual and had no profes-

sional sports history. There were 9 males [average age,

(23±1) years; height, (170±3) cm; weight, (65±8) kg]

and 5 females [average age (23±1) years; height, (157±3)

cm; weight, (50±5) kg]. According to that whether they

were majored in physical education or not, and whether

they took part in tennis training, the students were di-

vided into 3 groups: a tennis group of physical education

students (n =16), the 2nd control group (a non-tennis

group of physical education students, n =15), the 3rd

control group (a non-tennis group of non-physical edu-

cation students, n =14). Although there were differences

in age among the three groups, it could be overlooked,

because some previous studies have reported that the

latencies and amplitudes of VEPs are stable from the age

of 18 to 49.

3.3 The Aerobic Latin Exercise and Baduan-

jin of Health Qigong Training

27 healthy girls from Shandong Normal University were

selected to perform this experimental protocol. They

were randomly divided into three groups. The aerobic

Latin group contained 7 girls, the Baduanjin Health

Qigong group included 6 volunteers and the 4th control

group was consisted of 7 students. Both the aerobic

Latin and Baduanjin Health Qigong group took exercise

1 hour/day, 3 days/week, for 6 weeks, respectively. In

the experimental duration, the 4th control group was

examined synchronized with the two exercise groups.

3.4 Instrument

VEPs in response to middle check stimuli were recorded

and analyzed using an NDI-200 neural electricity tester,

which was produced by Shanghai Haishen Medical

Electronic Instrument Co., Ltd. This instrument is a kind

of 4-channel, anti-shock-type neural electrophysiological

system, which is safe and reliable, and which can be

used for clinical application to record electromyograms

and visual-, brainstem auditory-, and somatosensory-

evoked potentials.

3.5 Measurement of VEPs

Prior to the study, all subjects were thoroughly informed

about the details of the study to eliminate their fears, and

they were comfortably settled in a quiet and dark room

waiting for testing for 5 minutes.

3.5.1 Recording Conditions

The sites where the electrodes were to be placed were

cleaned with 75% alcohol, and then the electrodes were

smeared with conductive paste and placed on the skin.

The VEPs recordings were performed using bipolar

electrodes on the head; the recording electrode was posi-

tioned 1.5 cm above the occipital bone, the reference

electrode was placed on the middle forehead and the

ground electrode was placed on the vertex. After the

electrode impedance test, the electrode impedance was

kept below 5kΩ.

3.5.2 Recording Methods

All subjects were seated comfortably in a dark room 100

cm away from the monitor. After 5 min of dark adapta-

tion, they were instructed to gaze at a fixed point in the

middle of the screen with one eye (the advantage eye,

that is the better visual acuity one), with natural pupil,

but they couldn’t blink throughout the test, while the

other eye which was not tested was covered. In order to

make the waveform reliable, we measured each subject

two times and took the average of the two measure-

ments.The VEPs recordings were accomplished using

eyeglasses in subjects who were myopic.

3.5.3 Stimulation

A chessboard pattern reversal method in middle check

(25×25) mm2 was displayed on a 12-inch screen. The

stimulation frequency was at a speed of 2 Hz, lightness

of 90 cd/m2, contrast of 80%.

J. G. Zhao et al. / HEALTH 1 (2009) 47-50 49

3.5.4 Wave Recording

The range of filters was 1-100 Hz, the sensitivity was 10

μV/div. In order to improve the SNR 100 responses were

averaged.

3.5.5 Wave Recognition

Tests were performed strictly according to the require-

ments for recording stable VEPs. VEPs were three-phase

composite waves. The first was a smaller negative wave,

and its peak time was at about 75 ms, the second wave

was a large and stable positive wave, which peaked at

about 100 ms, and the last was a negative wave peaking

at about 145 ms, which was not only unstable, but also

be influenced easily by many other factors. This three-

wave compound is also named the NPN complex, and it

is the main waveform used for clinical observation. The

waves were named separately as N75, P100 and N145,

according to both their peak times and that whether they

were negative or positive waves.

3.5.6 Index Analysis

The latencies of N75, P100 and N145 waves were tested

separately. Measurements of the latencies were made

from the beginning of stimulation to the peak response

time.

3.5.7 Reliability of VEPs Measurements

All the subjects took part in the exercise according to the

coach strictly and completed the examinations actively.

The operator of this study had regular special training

and operated the procedure seriously.

4. STATISTICAL ANALYSIS

The experimental data were analyzed by SPSS for win-

dows 11.5. The Independent-Samples and Paired-Sam-

ples T Test were used for testing the significant differ-

ences of inter-group and intra-group. A level of P<0.05

was accepted as being statistically significant. Meas-

urement data are expressed as Mean±SD.

5. RESULTS

Comparisons of VEP P100 latencies before and after dif-

ferent events are shown in Table 1.

Obviously, P100 latency shortened significantly after

the aerobic cycloergometric exercise for 6 weeks, tennis

training for 8 weeks and aerobic Latin exercise for 6

weeks compared with those of pre-exercise (P<0.05)

except Baduanjin of Health Qigong program for 6 weeks.

However, no significant difference was found in corre-

sponded control group between the first and the second

measurement (P>0.05).

6. DISCUSSION

VEPs are a family of signals induced in response to vis-

ual stimuli (flashed or patterned stimulus) within the

visual occipital cortex; they mainly reflect the conduc-

tive function from retinal nerve cells to the optic central

system. Pattern-reversal VEPs (also named PR-VEPs)

were adopted by this study; they were acquired to use

stimuli with the same brightness, namely a black and

white checkerboard (25mm×25mm), which was reversed

at a certain frequency. In the visual pathway, the retina

makes a rough analysis of stimuli information; while the

lateral geniculate body is the relay station of the central

visual pathway. P100 latency is the typical component of

VEPs NPN complexes and it is the most commonly used

index for its high, steady amplitude and slight intra- and

inter-individual variability. The P100 latency is measured

from the beginning of stimulation to the peak response

time and it could reflect the information processing and

conduction velocity from ganglion cells to optic center

of visual system. Previous studies demonstrated that

VEPs latencies of athletes’ were significantly shorter

than those of non-athletes. Many factors could influence

VEPs, such as stimuli, recording parameters and indi-

vidual differences between subjects [9]. Visual reaction

time has been shown to be much shorter in athletes

training in the types of sports that demand rapid eye ac-

tivity (such as tennis, volleyball and squash) than other

types of sports (for example, cycling) [2]. Recent studies

have shown that both acute and chronic exercise could

affect VEPs independently of body temperature and

other physiological parameters. The capability and level

of visual function are important to athletes so that VEPs

can well be used as neuro-physiological criteria in clas-

sifying the performances of the athletes [2,3,11,12].

Table 1. Comparisons of VEPs P100 latencies of pre- and post-exercise.

Events N Weeks The P100 latencies (ms)

Pre-exercise Post-exercise P

Aerobic Cycloergometric Group

The 1st Control Group

The tennis Group

The 2nd Control Group

The 3rd Control Group

The Aerobic Latin Group

Baduanjin Group

The 4th Control Group

96.0±4.8

94.5±8.8

97.9±3.9

99.3±10.8

99.4±6.1

98.4±5.7

97.9±2.5

99.4±6.1

92.7±7.6

95.4±10.4

96.3±3.7

101.2±11.0

99.7±5.5

97.3±5.7

96.2±2.4

99.7±5.5

＜0.05

＞0.05

＜0.05

＞0.05

＜0.05

＞0.05

50 J. G. Zhao et al. / HEALTH 1 (2009) 47-50

In order to use VEPs as an index in evaluating physi-

cal training and classifying the performance of athletes,

especially the P100 latency, it is necessary to investigate

both the sensitivity and specificity to different exercise.

Therefore, we observed the efficacy of an aerobic cyclo-

ergometric exercise, tennis training, aerobic Latin exer-

cise and Baduanjin of Health Qigong training for 6 to 8

weeks in the basis of our previous studies [10,11,12].

It is known to all that VEPs P100 latency is sensitive

to physical exercise. Considerable studies have revealed

that an acute exercise could shorten the P100 latency

significantly but the values returned to the basal level

after exercise [3,11,12]. In this study, the VEPs P100

latency shortened significantly compared with those of

pre-exercise (P<0.05) after an aerobic cycloergometric

exercise for 6 weeks, tennis training for 8 weeks and

aerobic Latin exercise for 6 weeks, but no statistical dif-

ference was found between the values measured firstly

and secondly in all the control subjects corresponding to

the experimental groups. These results indicated that not

only an acute exercise but also a period time of exercise

(6 to 8 weeks) could shorten the VEPs P100 latency sig-

nificantly. The results further supported the viewpoint

that VEPs may well be used as neuo-physiological crite-

ria in classifying the performances of the athletes. How-

ever, there were no reports about correlation between

VEPs P100 latency and the athletes’ performances. Fur-

ther studies should be done in the future about feature of

VEPs P100 latency in athletes of different training level.

Some studies have reported that VEPs were different

among different events athletes, but all the findings are

not consistent [2,3,4,5,6,7]. In this study, we mainly

examined the representative component of VEPs NPN

complexes-the P100 latency of inter-and intra-subjects.

Our results showed that the P100 latency was shorter

significantly after an aerobic cycloergometric exercise

for 6 weeks, a tennis training for 8 weeks and an aerobic

Latin exercise for 6 weeks compared with those values

of pre-exercise (P<0.05) except the Baduanjin of Health

Qigong exercise for 6 weeks. We thought that the dif-

ference might be due to its lower intensity of the

Baduanjin of Health Qigong exercise. This demonstrated

that VEPs P100 latency was sensitive to most physical

exercise, which was to say that its specificity to different

training programs was poor. As a result, it was difficult

to reflect the feature of different sports training with a

single VEPs examination. Our findings suggested that

both transversal and longitudinal studies should be done

so as to investigate the VEPs specificity to different

events, including the VEPs P100 waveforms, amplitudes

and latencies.

7. CONCLUSIONS

The present study demonstrated that VEPs P100 latency

became shorter significantly after most physical exercise.

That was to say VEPs P100 latency was sensitive to dif-

ferent events training to a certain extent, but its specific-

ity is very poor.

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