Intern. J. Neuroscience, 115:1043–1050, 2005 Copyright 2005 Taylor & Francis Inc. ISSN: 0020-7454 / 1543-5245 online DOI: 10.1080/00207450590898481
EFFECTS OF EXERCISE ON VISUAL EVOKED POTENTIALS
RECEP ÖZMERDIVENLI Physical Education and Sports Academy Firat University Elazig, Turkey SERPIL BULUT Department of Neurology Firat University Elazig, Turkey HALE BAYAR KURSAT KARACABEY Physical Education and Sports Academy Firat University Elazig, Turkey FIGEN CILOGLU GENLAB Medical Diagnostics and Research Laboratory Istanbul, Turkey ISMAIL PEKER Department of Chemical Engineering Marmara University Istanbul, Turkey Received 12 August 2004. Address correspondence to Dr. Recep Özmerdivenli, Sports Academy, Firat University, Elazig, Turkey. E-mail:
[email protected] 1043
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UNER TAN Department of Physiology Cukurova University Adana, Turkey
The aim of this study was to investigate the effects of acute or habitual exercise on visual evoked potentials (VEP). The study group consisted of 9 female and 7 male volleyball players and the control group contained 9 female and 7 male students who were not involved in any sportive activity. The N75, P100, and N145 latency and amplitudes were measured before and after exercise. Intragroup comparison was made to evaluate the acute effects and intergroup comparison for the chronic effects of exercise. Significant differences were noted between athletes and the sedentary subjects in terms of pre-exercise left-N145 latencies and amplitudes and left -P100 amplitudes. Right-eye N145 latencies of inactive female subjects obtained before and after exercise were also statistically different. The results suggest that acute and habitual exercise affects the VEP responses independent from the body temperature and other physiological parameters. Small sized pre-exercise P100 amplitudes in the athletes can be attributed to the effect of rapid visual-activity-demanding sports on the central nervous system. Visual evoked potentials maybe used as neurophysiological criteria in defining the performance of an athlete. Keywords brain, evoked potential, exercise, performance, volleyball
INTRODUCTION Visual evoked potentials (VEP) are used to assess the central visual pathways (Thomas et al., 1991). Some physiological factors are known to affect the VEPs (Allison et al., 1983; Sokol et al., 1981). The attention has been drawn to the correlation between the physical activity and evoked potential responses of the athletes in some studies that have reported that “time to reaction” is shorter in athletes than inactive people (Guthkelch et al., 1987; Michael, 1971; Chiou-Tan et al., 1998). The aim of this study was to investigate the effects of acute and regular exercise on the evoked potentials after the normalization for the body temperature and to validate the VEP responses as a parameter in classifying the performance of the athletes.
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MATERIALS AND METHODS Volunteers from the Firat University were selected as subjects in this study after being thoroughly informed about the details of the study and questioned about the length of their sports life, daily schedule of exercise, systemic diseases, and visual problems. From the volunteers, 10 female volleyball players devoid of systemic disease and similar duration of sports life, daily length of exercise, age, height, and head circumference were included in the 181 study group; 10 male volleyball players with similar features were enrolled in the 2nd study group. Ten inactive girls were included in group 3 and 10 inactive boys in group 4. Prior to the study, all subjects underwent a thorough neurological examination, nerve conduction studies for one upper and one lower extremity, and visual field and visual acuity tests. The visual evoked potential recordings were accomplished with eyeglasses in 4 subjects who had refraction defects. Body temperature was measured by using a mouth thermometer before, immediately, and every 10 min after exercise until it dropped to the preexercise level. A Dantec Keypoint Electromyography device (Denmark) was used for the study of evoked potentials. All subjects were seated comfortably in a dark room 115 cm away from the monitor giving out visual stimuli for VEP recordings. The active electrode was positioned at the Oz, and the reference electrode at the Cz point. Electrode impedance was adjusted below 5 kOhms. Right eye monocular recordings of all cases were obtained while the left eye was closed. A “chessboard pattern reversal” method was applied with a speed of 1.5 Hz. The subjects were instructed to gaze at the square-shaped white target in the middle of the screen, the filters were tuned at 0.5–1000 Hz, sweep velocity at 30/ms and 100 responses from each eye were averaged by automatic analysis and artifact rejection. N75, P100, and N145 latencies and amplitudes were measured as milliseconds (ms) and millivolts (mV), respectively. The subjects exercised 30 min on a treadmill (Star Track Tr 900) at 60– 70% of their maximum heart rate based on 70% of their indirectly calculated maxVO2 value by using the Karvonen protocol (Wilmore & Costill, 1999). SPSS for windows version 10.0-computer program was used for statistical analysis. Age, height, weight, length of sports life, head circumference, body temperature before and after exercise, and resting heart rate values of the groups were compared by Kruskall-Wallis One-Way Anova test. Visual evoked potential latencies and amplitudes for each group before and after
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exercise were evaluated by Wilcoxon–Rank test. The Mann Whitney U test was used in comparing the pre- and post-exercise values of the women (Groups 1 and 3) and men (Groups 2 and 4). p < .05 was accepted as being statistically significant.
RESULTS AND DISCUSSION From the initial 40 subjects, 4 students did not participate, another 2 had elevated body temperatures before exercise (>37.5 C), and 2 students could not finish the exercise program and therefore were excluded from the study. No significant difference was noted among all 4 groups in terms of age, head circumference, or body temperature taken before and after exercise. Significant differences were found between women and men in terms of height and weight (p < .05). Resting heart rates were found to be significantly higher in the inactive groups (Groups 3 and 4) as compared to the athletes (p < .05) (Table 1). In order to eliminate the effects of the physiological factors on evoked potentials, groups similar in demographic features were compared with each other (group 1–3 and group 2–4). Comparing the pre-exercise VEP latencies and amplitudes of inactive and athletic women (Groups 1 and 3), left N145 latency and amplitudes was found to be significantly different (p < .05). No difference was noted in post-exercise VEP values (Table 2). Likewise, there was a significant difference in pre-exercise P100 amplitudes of inactive and
Table 1. Demographic characteristics of the groups (mean ± standard deviation) Group 1 (n = 9) Age (years) Height (cm) Weight (kg) HC (cm) LSL (years) RHR BT (pre-ex) BT (post-ex) Max VO 2 (ml/kg/mm)
21.11 162.33 57.6 57.2 4.5 55.3 36.5 36.4 38.75
± ± ± ± ± ± ± ± ±
1.90 5.63 4.3 1.2 2.4 3.2 0.4 0.6 3.55
Group 2 (n = 7) 20.22 162.66 63.4 58.8 6.1 50.5 36.3 36.6 51.25
± ± ± ± ± ± ± ± ±
1.3 5.14 7.1 1.0 2.1 4.7 0.7 0.8 2.17
Group 3 (n = 9) 21.42 ± 180.42 ± 58.2 ± 57.4 ± — 75.4 ± 36.6 ± 36.7 ± 30.35 ±
0.97 4.15 3.5 1.3 5.7 0.5 0.3 3.09
Group 4 (n = 7) 19.57 ± 172.71 ± 66.2 ± 59.1 ± — 72.7 ± 36.5 ± 36.6 ± 44.18 ±
0.97 3.09 3.1 0.8 4.3 0.6 0.3 1.05
HC = head circumference, LSL = length of sports life, RHR = resting heart rate, BT = body temperature.
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Table 2. Comparison of pre- and post-exercise VEP responses in groups 1 and 3 (mean ± standard deviation) Group 1 (female athletes) (n = 9) Pre-exercise
Post-exercise
Group 3 (sedentary females) (n = 9) Pre-exercise
Post-exercise
Right N75 latency (ms) 67.31 ± 3.24 68.61 ± 3.55 69.40 ± 4.68 70.04 ± 3.22 Right P100 latency (ms) 96.32 ± 6.95 95.94 ± 5.08 99.01 ± 5.91 98.48 ± 3.69 Right N145 latency (ms) 136.31 ± 11.44 141.40 ± 7.89 140.81 ± 4.61 143.40 ± 4.30 Right N75 amplitude (mV) 2.30 ± 0.75 2.81 ± 1.29 3.54 ± 2.04 2.65 ± 1.04 Right P100 amplitude (mV) 5.80 ± 1.19 5.99 ± 1.22 6.95 ± 2.38 5.48 ± 1.65 Right N145 amplitude (mV) 3.47 ± 1.41 4.02 ± 1.44 4.40 ± 1.94 3.74 ± 1.53 Left N75 latency (ms) 63.73 ± 3.47 69.81 ± 5.17 69.51 ± 50.4 70.71 ± 3.17 Left P100 latency (ms) 97.03 ± 6.76 97.35 ± 5.40 100.07 ± 5.08 99.21 ± 3.49 Left N145 latency (ms) 136.55 ± 10.27b 141.11 ± 8.21 a 146.24 ± 6.83 b 144.10 ± 4.40 Left N75 amplitude (mV) 2.16 ± 1.02 2.63 ± 1.88 2.99 ± 1.74 70.71 ± 3.17 Left P100 amplitude (mV) 5.81 ± 0.78 5.98 ± 1.95 6.51 ± 2.39 6.77 ± 2.27 Left N145 amplitude (mV) 3.48 ± 1.18b 3.42 ± 1.75 5.98 ± 1.57b 4.09 ± 1.61 a
Intergroup; bintragroup.
athletic men (groups 2 and 4) (p < .05) whereas no difference was noted for post-exercise values (Table 3). VEP latencies and amplitudes of all groups recorded before and after exercise when body temperature normalized were compared with each other (Table 2). Statistically significant difference (p < .05) was noted among the pre- and post-exercise N145 latencies recorded in the right eye of the sedentary women. No differences were noted in Group 1, 2, and 4 pre- and postexercise VEP latencies and amplitudes Evoked potential responses have been shown to be influenced by some physiological factors (Magnie et al., 1998; Bhanot, & Sidhu 1980; Thomas et al., 1991; Huttunen & Homberg, 1991; Nishihira et al., 1996). Shortening of “time to reaction,” improvement of muscle strength, and the enhancement of physical capacity in athletes are the clinical evidence of the effects of exercise on neuro-physiological parameters. Contradictory results have been obtained in studies investigating the effects of acute and habitual exercise on evoked potentials. Thomas, Jones, and Caramia (1991) evaluated the pre- and post-exercise auditory evoked potential (AER) responses in the bicycle riders and concluded that post-exercise 3 and 4 wave latencies were relatively shortened and correlated with the post-
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Table 3. Comparison of pre- and post-exercise VEP responses in groups 2 and 4 (mean ± standard deviation) Group 1 (male athletes) (n = 7) Pre-exercise
Post-exercise
Right N75 latency (ms) 68.88 ± 4.76 67.72 ± 3.52 Right P100 latency (ms) 96.15 ± 3.55 96.21 ± 4.52 Right N145 latency (ms) 140.30 ± 7.85 140.31 ± 6.42 Right N75 amplitude (mV) 1.80 ± 1.11 1.97 ± 1.77 Right P100 amplitude (mV) 4.53 ± 1.56 3.78 ± 1.20 Right N145 amplitude (mV) 3.20 ± 1.81 3.17 ± 1.48 Left N75 latency (ms) 68.97 ± 4.74 70.34 ± 3.53 Left P100 latency (ms) 97.64 ± 4.94 97.11 ± 3.08 Left N145 latency (ms) 143.21 ± 7.01 41.65 ± 3.99 Left N75 amplitude (mV) 2.23 ± 1.28 71.97 ± 1.65 Left P100 amplitude (mV) 4.14 ± 1.26a 3.77 ± 0.88 Left N145 amplitude (mV) 3.39 ± 0.69 3.15 ± 1.51
Group 3 (sedentary males) (n = 7) Pre-exercise
Post-exercise
69.75 ± 5.57 70.04 ± 3.22 98.52 ± 6.4 98.48 ± 3.69 145.58 ± 7.69 143.40 ± 4.30 2.66 ± 1.51 2.65 ± 1.04 4.72 ± 2.19 5.48 ± 1.65 3.45 ± 1.65 3.74 ± 1.53 70.54 ± 3.77 70.71 ± 3.17 98.64 ± 6.17 99.21 ± 3.49 147.11 ± 13.6 144.10 ± 4.40 2.13 ± 1.37 70.71 ± 3.17 7.09 ± 2.12a 6.77 ± 2.27 5.10 ± 2.79 4.09 ± 1.61
a
Intragroup (all others are intergroup).
exercise body temperature elevation (see Rossini et al., 1996). On the other hand, Magni found no difference between pre-exercise VEP and AER recordings and post-exercise recordings taken after the normalization of the body temperature and stated that there was no specific effect of exercise on evoked potentials (see Thomas et al., 1991). In this study volleyball players and inactive people with similar demographic features were compared to find if there is a physiological effect of acute and chronic exercise on evoked potentials independent from the body temperature elevation. Significant differences were noted between pre-exercise P100 amplitudes of male athletes and inactive men and pre-exercise N145 latency and amplitudes of female athletes and inactive women. Visual reaction time has been shown to be much shorter in the athletes training in the types of sports that demand rapid eye activity (tennis, volleyball, squash, etc.) than the other type of sports (athletics, bicycle riding, etc.) (Guthkelch et al., 1987; Monis & Kreighbaum, 1977; Michael, 1971). In this study, smaller pre-exercise P100 amplitudes recorded in the athletes may be explained by their branch of sports that requires rapid visual activity. Similar results were noted with squash players in another study (Bhanot & Sidhu, 1980). A correlation between P100 wave latency and head circumference was
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noted in some other studies (Allison et al., 1983). The N145 and P100 waves in this study were not correlated with the head circumference measurements. Post-exercise right N145 latencies of the sedentary women were shorter than the preexercise values whereas no difference was noted between preand post-exercise VEPs of the men that can be due to daily high activity of the men, thus being less influenced, by exercise. N9 and N20 amplitudes were evaluated by median nerve stimulation of the inactive subjects in order to prove the effects of isometric muscle contractions on SEPs at cortical level. N9 amplitude recorded at periphery was shown to increase after contraction, whereas N20 amplitude obtained at cortical level shortened significantly (Kjaer, 1980). Many authors have pointed out the depression of SEP amplitudes during muscle contraction recordings but failed to explain the mechanism (Delpont et al., 1981; Psatta & Matei, 1988; Parker et al., 1971; Chuang et al., 1999; Jones et al., 1989). VEP response differences between sportsmen and inactive subjects can be explained by likely changes of neuro-physiological and neuroendocrine factors caused by the increased exercise capacity. In conclusion, this study reveals that acute and habitual exercise affects VEP values independent from body temperature or other physiological parameters. Additionally, VEP potentials may well be used as neuro-physiological criteria in defining the performances of the athletes.
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