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Effect of Muscular Exercise on Dark Adaptation*
E F F E C T O F MUSCULAR E X E R C I S E ON DARK A D A P T A T I O N * W E I DLAND, M . D . Minneapolis Minnesota
J O H N P.
INTRODUCTION
Muscular exercise is one of the most im portant and most frequently encountered stress situations, and investigations of its effect on the dark-adaptation process is of considerable interest for various reasons. Muscular exercise, even of moderate inten sity, produces pronounced metabolic, circula tory, and respiratory changes and thus pre sents a useful method of studying the effect of these changes upon one of the most funda mental visual functions. Also, in situations where muscular exercise occurs in darkness, or prior to the entrance of an individual into darkness, the problem has obvious prac tical applications. In addition, any effect muscular exercise has on dark adaptation would be important in the standardization of dark-adaptation tests. In view of the large amount of research work performed during recent years on the effect of various factors influencing dark adaptation, one would expect a substantial number of publications dealing with the effects of muscular exercise. Actually, the literature is meager ; only two articles could be found dealing with this subject. Bodansky and Hendley 1 found that bi cycle ergometer exercise both in normal and methemoglobinemic individuals produced a rise in the rod thresholds after S to 10 min utes. However, the methemoglobinemic indi viduals showed an improvement in sensi tivity preceding the depression ; whereas, the normal individuals showed no improve ment at any time. There was no correlation between the amount of work done, which ranged from 20,000 to 35,000 foot pounds over a period of from 3 to 5 minutes, and the changes in threshold obtained. * From the Department of Physiological Hygiene and Division of Ophthalmology, University of Min nesota Medical School.
Kekcheev2 claimed that light muscular ex ercise reduced the duration of the darkadaptation process from 25 to 45 minutes to 5 to 6 minutes ; such a claim is surprising, as no other factor affecting dark adaptation has been noted to influence it to a compar able degree. His article is very brief, how ever, and does not give any details of his method. METHOD OF INVESTIGATION
A biophotometer was used but the tech nique of its use modified. The test area in this instrument normally consists of a quincunx of spots, the illumination of which may be varied by means of a rheostat ad justed by the examiner. Filters are present in the instrument which make the light in tensity of the two left-hand spots the high est, the central spot of medium intensity, and the two right-hand spots of least in tensity. The subject reports on any given threshold when he is able to distinguish the central and two left-hand spots of the quin cunx, but not the two on the right. Considerable justified criticism3"5 has been leveled at the results obtained with this in strument, as it has been used by various investigators. The major fault has been the lack of a fixation spot. This fault, however, is readily corrected by using the instrument according to the method first described by Sheard, 6 and this technique was followed in these experiments. All spots, except the upper-left and central spot, were covered with opaque adhesive tape. The subject fixes on the upper-left spot and reports on the ap pearance of the central spot as the brightness of both is increased. The change in wave length of the test light3 as the spots are dimmed is of no consequence in these studies since the same wave-length change is present both in the controls and in the tests follow ing exercise.
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1430
JOHN P. WENDLAND
The preadapting light incorporated in the biophotometer is of insufficient brightness to record the full extent of the visual adap tation curve. A brighter preadapting light, as mentioned below, was, therefore, used. The left eye was used in all determina-
which would increase the pulse rate by 25 to 30 beats per minute. SUBJECTS
The subjects were all college students be tween the ages of 17 and 29 years, with no
TABLE 1 SUMMARY OF METHODS OF TESTING THE EFFECT OF EXERCISE ON DARK ADAPTATION
Type of Exercise
Duration and Rate of Exercise
Procedure of Testing
Light Bicycle ergometer 35 min.; pulse increase Exercise started immediately of 25-30 beats per min. after preadaptation. Readings taken at 4, 8, ,12, 16, 20, 25, 30, and 35 min.
Rate of Dark Adap tation or Final Threshold
No. of Subjects; No. of Tests
Rate
9 subjects, 13 tests
Rate
8 subjects, 8 tests
Bicycle ergometer 10 min.; pulse increase Exercise started after full dark 25-30 beats per min. adaptation. Readings taken after exercise from 15 sec. to 13 to 15
Final threshold
5 subjects, 6 tests
Genuflexions
Final threshold
7 subjects, 7 tests
Rate
4 subjects, 4 tests
Genuflexions
2§—3 min.; pulse in Exercise started immediately crease of 25-30 beats after preadaptation. Readings taken at 4, 8, 12, 16, 20, 25, 30, per minute and 35 min.
2 §-3 min.; pulse in- Exercise started after full dark crease of 25-30 beats adaptation. Readings taken after per min. exercise from 15 sec. to 13 to 15 min.
Heavy Standing running subject ran "all out" until exhaustion which in no case was more than 2J-3 min.
Exercise started immediately after preadaptation. Readings taken at 4, 8, 12, 16, 20, 25, 30, and 35 min.
Standing running subject ran "all out" Exercise started after full dark until exhaustion which adaptation. Readings taken after in no case was more exercise from 15 sec. to 13 to 25 than 2^-3 min. min.
tions; the test spot subtended an angle of one degree, 6 degrees temporal and superior to the fovea. The influence of light and heavy muscu-. lar exercise on both the rate and final rod threshold of adaptation was studied. The experimental arrangement and testing pro cedure are summarized in Table 1. In the light-exercise experiments, in order to make the work load physiologically comparable in various subjects of unequal muscular ca pabilities, exercise was performed at a rate
Final threshold
19 subjects, 20 tests
ocular defects. They were well trained on the apparatus in order to eliminate learning as a possible factor in the results obtained. In the experiments on the rate of dark adaptation, successive tests were made with no exercise in between to establish controls. In the experiments on the final rod thresh old, numerous readings were taken until the subject reached a level constant except for the slight unavoidable normal variability found in repeated readings. Exercise was then performed using the preëxercise read-
EFFECT OF EXERCISE ON DARK ADAPTATION
ings as controls. Only values exceeding the normal preëxercise variability are con sidered in this paper. Statistical analysis of the results was ac complished by means of the "t-test" (Fisher 7 ). The subjects performed no ex ercise, other than walking to the laboratory, for several hours prior to the tests and rested in a room, illuminated with 2 footcandles, for 15 minutes before the control tests were begun. TESTS
In the tests concerning the effect of ex ercise on the rate of adaptation the subject
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was begun after full dark adaptation. The same forms of exercise were used as in the experiments on the rate of dark adaptation. RESULTS
In tabulating the effects of exercise on the rate of adaptation, the readings taken during the course of adaptation are divided into 3 intervals. Interval I includes the readings at 4, 8, and 12 minutes ; Interval II, the readings at 16, 20, and 25 minutes ; and Interval III, the readings at 30 and 35 min utes. The results of light exercise are shown in Table 2. Columns 5 and 9 represent the effect
TABLE 2 EFFECT OF LIGHT EXERCISE ON THE RATE OF DARK ADAPTATION
Genufle ixions
Ergometer Exercise Subject
Interval I
Interval II
Interval III
T.D.A.
Interval I
Interval II
Interval III
T.D.A.
D.M. M.H.
+0.05
+0.04
+0.10
+0.06
B.S. B.S. B.S. E.T. E.T. L.W. P.W. P.W. T.G. M.O. C.P.
+0.07 -0.03 -0.01 -0.07 -0.07 +0.01 +0.05 +0.12 +0.07 +0.01 -0.05 -0.03
+0.04 +0.05 0 -0.08 0 +0.04 +0.12 +0.11 -0.01 +0.01 -0.05 +0.07
+0.06 +0.02 +0.08 +0.02 0 0 +0.12 +0.22 -0.10 -0.02 0 +0.04
+0.06 +0.02 +0.02 -0.05 -0.03 +0.02 +0.14 +0.14 -0.01 +0.01 -0.04 +0.02
-0.05 +0.01 +0.04
-0.04 +0.04 -0.07
-0.02 +0.02 -0.06
-0.04 +0.02 -0.02
-0.03
+0.09
+0.06
+0.04
0 -0.04 -0.05 -0.07
-0.01 -0.07 +0.07 +0.07
-0.06 0 +0.10 -0.02
-0.02 +0.01 +0.04 +0.01
Mean
+0.01
+0.03
+0.04
+0.03
-0.02
+0.01
+0.002
+0.005
K.J.
J.A.
* Values are expressed in log units. Plus ( + ) denotes a lowering of threshold, minus (—) denotes a rise compared to the control. T.D.A. = total dark-adaptation curve.
was preadapted for a period of one minute to a light of 2,400 millilamberts subtending an angle of 41 degrees at the subject's eye. For light exercise two forms of exercise (bicycle ergometer and genuflexions) per formed as indicated in Table 1 were used. For heavy exercise but one form of exer cise (standing running all out) was used. In the tests concerning the effect of ex ercise on the final rod threshold, exercise
on the "total dark adaptation curve" (T.D.A.). The effect on the T.D.A. was arrived at by averaging the values of indi vidual readings taken during the entire course of dark adaptation as given in Table 1. A plus value denotes an increase in sensitivity (lowering of threshold), and a minus value a decrease in sensitivity (rise in threshold), compared to control values. It will be noted that most of the changes
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JOHN P. WENDLAND TABLE 3 EFFECT OF HEAVY EXERCISE ON THE RATE OF DARK ADAPTATION*
Subject
Heavy Exercise Inter val I
Inter val II
Inter T.D.A. val III
D.M. L.C. M.H. J.A.
+0.04 -0.07 0 -0.50
+0.01 +0.03 -0.08 -0.07
-0.10 +0.02 -0.16 -0.06
-0.02 -0.01 -0.02 -0.06
Mean
-0.01
-0.02
-0.06
-0.02
* Values are expressed in log units. Plus ( + ) de notes a lowering of the threshold, minus ( —) de notes a rise compared to the control. T.D.A. =total dark adaptation curve.
are of small magnitude and that they are both plus and minus. The statistical analysis of the results shows that light muscular ex ercise has no effect upon the rate of dark adaptation. The effects of heavy exercise on the rate of dark adaptation are represented in Table
3. It will be seen here that, under Intervals I and II, the values fall fairly equally on both the plus and minus sides. In Interval III, however, all the values are minus ex cept one and, in the column T.D.A., all values are minus. Statistical analysis shows that, although there is a tendency to a de crease in sensitivity in Interval III, which represents final rod thresholds, and in the T.D.A., none of the changes are of suffi cient magnitude to reach statistical signifi cance. Table 4 represents the results of the experiments with the effect of light exercise on the final rod threshold·—that is, on the threshold of the fully dark-adapted eye. It will be noted that there is a tendency to both a lowering and a raising of the threshold. The lowering of the threshold occurs imme diately after exercise and is of compara tively short duration as shown in Column 3 ; it is followed by a rise in the threshold of
TABLE 4 EFFECT OF LIGHT EXERCISE ON THE FINAL ROD THRESHOLD*
Subject
Lowering of Threshold
Time of Lowering Threshold
Duration of Lowered Threshold
Rise of Threshold
Time of Rise of Threshold
Duration of Rise of Threshold
ERGOMETER
s.c. s.c. W.P.
+0.16
CG.
+0.04
Mean
+0.04
B.S.
J.E.
0
+0.08 0
0
o-u 0 0-1 0
ο-έ 0
U
0 1 0 1
0 1
-0.08 -0.08 -0.04 -0.04 -0.12 0
3-5
5-15 6-8
31-41; 8-10 1-15 0
2 10 2 2* 15 0 11
-0.06
GENUFLEXIONS
W.P. D.M. B.S. O.G. CG.
0 0 0
+0.08 +0.08
L.H. W.N.
+0.04
Mean
+0.03
0
0 0 0
0-3*
2 f -2|; 3|-4i
0 0 0 3§
-0.04
0 1
0 0
0 0 0
i
-0.08
2 Ϊ
-0.02
9-11
0 0 0
2§-3;4-5;6-9 0 0
2 0 0 0 44 0 0 A
* Threshold changes are expressed in arbitrary log units and represent maximum changes. Plus ( + ) de notes a lowering of the threshold, minus (—) denotes a rise compared to values before exercise. Time inter vals are given in minutes and include the entire time any lowering or elevation of the threshold occurred.
EFFECT OF EXERCISE ON DARK ADAPTATION somewhat longer duration (column 6 ) . However, the changes again are not statistic ally significant. The effect of heavy exercise on the final rod threshold is seen in Table 5. In the ma jority of subjects, the reaction is biphasic; that is, there is a temporary improvement
1433
ment immediately following exercise; whereas, all showed a reduction in sensi tivity beginning in 1 to 5^4 minutes follow ing exercise and lasting from 1 to 16 min utes. The improvement immediately follow ing exercise varied from none to 0.2 log units; the elevation of the threshold from
TABLE S E F F E C T OF HEAVY EXERCISE ON T H E FINAL ROD THRESHOLD*
Subject
L.C. E.B.
Lowering of Threshold
D.K. E.T, L.H.
+0.08 0 0 +0.04 +0.16 +0.20 +0.12 +0.12 +0.16 +0.04 +0.08 +0.04 0 +0.20 +0.04 +0.12 +0.12 0 +0.04 +0.08
Mean
+0.08
J.K. J.B.
M.O.
J.P.
H.S.
F.J.t
M.H. D.M. D.M. L.W. L.W.t J.P.W.Î H.W. P.W.
K.J.
Time of Lowering of Threshold Following Exercise
0-1 0 0
0-1
0-1 i; 2-Λ
Duration of Lowered Threshold
Time of Rise of Threshold Following Exercise
2-3; 7i-8i li-12 U-2J; 6 i - 7 i 2-3; 3i-4i; 7-12 7Wi li-6;10i-ll 2i-S;Si-7 lf-2i; 3 H 1-1i; 2J-8 3J-4; 7f-8i; 9^-10 l«-U;3-3i;4i-5i;7i-7i l i - 9 ; 12-13 2-2i;3f-ll 2-16 5 i - 7 ; 8 i - 9 i ; 11-12
14 3i
1
-0.24 -0.36 -0.32 -0.20 -0.08 -0.24 -0.20 -0.12 -0.28 -0.24 -0.16 -0.40 -0.44 -0.56 -0.24 -0.28 -0.28 -0.20 -0.12 -0.20
Si-5i; 6-14 Si-8 4-20 4-15
81 2i 16 11
2 3
-0.26
1 4
0 0
1
3*
o-i
i
ο-έ i-l
iA
o-i î
i-i\ n-n
o-i o-i
li 2
i *
1 4
0 0-1
0 1
0-1i; 2i-21 0-1Î 0
4,
o-i
o-i
0-1
Duration of Rise in Threshold
Rise of Threshold
1
U H
0
i
5H
2 Hi 1* 7 1 Si 4
i 51 21 U 7!
n U
Si
* Threshold changes are expressed in arbitrary log units and represent maximum changes. Plus ( + ) de notes a lowering of t h e threshold, minus ( —) denotes a rise compared t o values before exercise. Time inter vals are given in minutes and include the entire time any lowering or elevation of threshold occurred. t Artificial pupil used. î Pilocarpine fixation of the pupil.
in sensitivity of short duration, followed by a decrease in sensitivity often of con siderable magnitude and duration. Treated statistically the tendency shown in light ex ercise has here become highly significant. Superimposed upon the overall biphasic change are wavelike fluctuations of the threshold especially marked during the de pression phase. These fluctuations are evi dent in Columns 3 and 6, Table 5. There was no difference in the reactions between men and women. Sixteen out of 20 subjects showed some transitory improve-
0.08 to 0.56 log units. Thus, considerable individual variability was present. The maxi mum decrease in sensitivity of 0.56 log units represents almost a fourfold change in sensitivity. The mean lowering of the thresh old was 0.08 log units with a mean duration of 2/z minutes; the mean rise of threshold was 0.26 log units with a mean duration of 5J4 minutes. In two subjects, pilocarpine fixation of the pupil was used and in one, an artificial pupil. Control of pupillary size in this manner in no way influenced the response of the subject to the exercise.
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JOHN P. WENDLAND
Therefore, pupillary reactions cannot play a part in the results found. Figure 1 represents graphically the re sponse to heavy exercise. It will be seen that
0
I
2 3
actual average magnitude, for it was com puted by averaging the values of all the sub jects at given time intervals following the exercise. As the subjects showed consider-
4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 TIME IN MINUTES AFTER EXERCISE
Fig. 1 (Wendland). Effect of heavy exercise on the final rod threshold. "O" represents the threshold level before exercise. Minus (—) values denote a rise in the threshold, plus ( + ) values a lowering of the threshold, -x-x- Subject showing maximum lowering of the threshold. Subject showing maxi mum rise of the threshold. Mean of all subjects. the rise in threshold is much more marked and extends over a longer time interval than the lowering of the threshold. The curve showing the mean response is of value mainly for showing the general biphasic character of the response rather than the
able variability in the time of occurrence of the depression phase the general effect of averaging their values would be to level off the curve. This biphasic response is some what similar to the effect of muscular exer cise on the fusion frequency of flicker.8
EFFECT OF EXERCISE ON DARK ADAPTATION In none of the tests was any correlation found between the physically trained and un trained subjects. DISCUSSION
The following factors may be concerned in the production of the changes in dark adap tation following exercise : 1. In muscular exercise, an irradiation of impulses from motor centers to other parts of the nervous system is generally assumed. This is thought to be responsible for the marked change in respiratory rate which oc curs immediately after exercise before any blood changes could have reached the respira tory center.9 This irradiation continues throughout exercise and may be responsible for the lowering of thresholds immediately following exercise. 2. The increased blood flow during exercise may improve the blood supply of the retina and brain, a factor which possibly would tend to lower thresholds. 3. The oxygen debt found in heavy exer cise is possibly the major factor in causing an elevation of thresholds. All investigators are agreed that reduced oxygen tensions, such as those caused by high altitude, cause an elevation of thresholds. 8 · 10 " 14 It would seem at first glance that the oxygen debt in muscular exercise acted in an exactly simi lar manner. However, the physiology of the two situations is different. In anoxia there is reduced oxygen saturation of arterial blood; whereas, in muscular exercise the blood becomes properly oxygen saturated as it passes through the lungs. Thus in mus cular exercise, the brain and eyes possibly do not receive a diminished oxygen supply. Nevertheless, the oxygen debt does express a need of oxygen by the organism and it is probably in some measure responsible for the elevated thresholds following muscular exercise. The maximum depression in the final rod threshold following exercise, as noted above, was 0.56 log units, or a change equal to the effect produced by an altitude of approximately 15,000 feet.
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4., Wald and associates18 have shown that the addition of 5-percent carbon dioxide to the air an individual at rest inspired elevated the final rod threshold from 0.2 to 0.5 log units (approximately a 1 ^ and threefold change, respectively). Conversely, washing out of carbon dioxide by breathng room air at rates 50 to 100 percent more rapidly than normal caused a lowering of the threshold of about 0.27 log units. Thus according to Wald et. ed., respiratory acidosis and alkalosis ex ert opposing effects upon the visual thresh old. Possibly the increased production of carbon dioxide and acidosis found in severe exercise may contribute to the elevated thresholds noted following exercise. It is interesting to note that most of these same factors have been used to explain the changes observed in the fusion frequency of flicker following exercise.8 The coexistence and temporal relation ships of these factors in exercise are re sponsible for its effects on dark adaptation. The depressing effect of heavy exercise is of importance in tasks performed at night and requiring good night vision—for ex ample, night flying. In general, the findings of Bodansky and Hendley 1 have been confirmed, although some differences are noted. In contrast to our observations, they were unable to demon strate a significant improvement in normal individuals shortly following exercise. Like wise, they found no correlation between the amount of exercise and the depression of sen sitivity obtained. In the experiments reported in this paper, normal individuals showed a statistically significant improvement in rod thresholds immediately following exercise followed by a depression of sensitivity simi lar to that obtained by Bodansky and Hend ley. Also in my experiments, there is corre lation between the severity of the exercise and the effects produced ; light exercise pro duces both a smaller improvement and de pression phase than does heavy exercise. Kekcheev's results have not been con firmed.
1436
JOHN P. WENDLAND
It is suggested that as part of the stand ardization of dark-adaptation testing, in vestigators limit the physical activity of their subjects for one-half hour prior to testing. SUMMARY
Twenty-nine subjects were used, on whom 60 tests were performed, in studying the effect of light and heavy muscular exercise upon both the rate and final rod threshold of dark adaptation. Light exercise has essentially no effect upon the rate of dark adaptation and only a tendency to produce a slight biphasic re sponse in the rod threshold. For practical purposes it may be said to exert no effect on dark adaptation. Heavy exercise produces a tendency to elevation of the thresholds of the total darkadaptation curve and causes a marked bi
phasic response in final rod thresholds. The biphasic response consists in, first, a lower ing of the threshold of short duration, fol lowed by a rise in the threshold, often of considerable magnitude and of longer dura tion. In one subject, the depression of sensi tivity was equal to that produced in an in dividual at an altitude of 15,000 feet. In practical application, heavy exercise may be said to produce a definite decrease in ability to see at night. The factors responsible for these observa tions have been discussed and the impor tance of the changes in critical visual tasks performed at night pointed out. The Medical School (14). Acknowledgment: Sincere appreciation is ex pressed to Dr. Erling Hansen and Dr. Ernst Simon son for their interest and helpful suggestions in this study.
REFERENCES
1. Bodansky, Ο., and Hendley, C. D.: Effect of methemoglobinemia on the visual threshold at sea level, at high altitudes and after exercise. J. Clin. Investigation, 25 :717-722,1946. 2. Kekcheev, K. K.: Expediting adaptation to darkness. Nature, London, 151:617-618, 1943. 3. Mandelbaum, J.: Dark adaptation: Some physiologic and clinical considerations. Arch. Ophth., 26:203-239, 1941. 4. Palmer, C. E., and Blumberg, H.: The use of a dark adaptation technic (biophotometer) in the measurement of vitamin A deficiency in children. Pub. Health Rep., 52 :1403-1418, 1937. 5. Hecht, S., and Mandelbaum, J.: The relation between vitamin A and dark adaptation. J.A.M.A., 112:1910-1916, 1939. 6. Sheard, C.: Dark adaptation: some physical, physiological, clinical and aeromedical considera tions. J. Optic Soc. America, 34:464-S08,1944. 7. Fisher, R. A.: Statistical methods for research workers. Edinburgh, 1936. 8. Simonson, E., Enzer, Ν., and Benton, R. W.: The influence of muscular work and fatigue on the state of the central nervous system. J. Lab. & Clin. Med., 28:1555-1567, 1943. 9. Bainbridge, F. A.: The physiology of muscular exercise. New York, Longmans Green and Co., 1931. 10. Wilmer, W. H., and Berens, C.: Medical studies in aviation: V. Effect of altitude on ocular functions. J.A.M.A., 71:1394-1398,1918. 11. McFarland, R. Α., and Evans, J. N.: Alterations in dark adaptation under reduced oxygen tensions. Am. J. Physiol., 127 :37-50, 1939. 12. McDonald, R., and Adler, F. Η.: Effect of anoxemia on the dark adaptation of the normal and the vitamin A deficient subject. Arch. Ophth., 22:980-988, 1939. 13. Sheard, C.: Effects of anoxia, oxygen and increased intrapulmonary pressure on dark adapta tion. Proc. Staff Meet., Mayo Clin., 20:230-236,1945. 14. McFarland, R. Α., and Forbes, W. H.: The effects of variations in the concentration of oxygen and of glucose on dark adaptation. J. Gen. Physiol., 24:69-98, 1940. 15. Wald, G., Harper, P. V., Jr., Goodman, H. C, and Krieger, Τ. P.: Respiratory effects upon the visual threshold. J. Gen. Physiol., 25 :891-903, 1942.
J O H N P.
INTRODUCTION
Muscular exercise is one of the most im portant and most frequently encountered stress situations, and investigations of its effect on the dark-adaptation process is of considerable interest for various reasons. Muscular exercise, even of moderate inten sity, produces pronounced metabolic, circula tory, and respiratory changes and thus pre sents a useful method of studying the effect of these changes upon one of the most funda mental visual functions. Also, in situations where muscular exercise occurs in darkness, or prior to the entrance of an individual into darkness, the problem has obvious prac tical applications. In addition, any effect muscular exercise has on dark adaptation would be important in the standardization of dark-adaptation tests. In view of the large amount of research work performed during recent years on the effect of various factors influencing dark adaptation, one would expect a substantial number of publications dealing with the effects of muscular exercise. Actually, the literature is meager ; only two articles could be found dealing with this subject. Bodansky and Hendley 1 found that bi cycle ergometer exercise both in normal and methemoglobinemic individuals produced a rise in the rod thresholds after S to 10 min utes. However, the methemoglobinemic indi viduals showed an improvement in sensi tivity preceding the depression ; whereas, the normal individuals showed no improve ment at any time. There was no correlation between the amount of work done, which ranged from 20,000 to 35,000 foot pounds over a period of from 3 to 5 minutes, and the changes in threshold obtained. * From the Department of Physiological Hygiene and Division of Ophthalmology, University of Min nesota Medical School.
Kekcheev2 claimed that light muscular ex ercise reduced the duration of the darkadaptation process from 25 to 45 minutes to 5 to 6 minutes ; such a claim is surprising, as no other factor affecting dark adaptation has been noted to influence it to a compar able degree. His article is very brief, how ever, and does not give any details of his method. METHOD OF INVESTIGATION
A biophotometer was used but the tech nique of its use modified. The test area in this instrument normally consists of a quincunx of spots, the illumination of which may be varied by means of a rheostat ad justed by the examiner. Filters are present in the instrument which make the light in tensity of the two left-hand spots the high est, the central spot of medium intensity, and the two right-hand spots of least in tensity. The subject reports on any given threshold when he is able to distinguish the central and two left-hand spots of the quin cunx, but not the two on the right. Considerable justified criticism3"5 has been leveled at the results obtained with this in strument, as it has been used by various investigators. The major fault has been the lack of a fixation spot. This fault, however, is readily corrected by using the instrument according to the method first described by Sheard, 6 and this technique was followed in these experiments. All spots, except the upper-left and central spot, were covered with opaque adhesive tape. The subject fixes on the upper-left spot and reports on the ap pearance of the central spot as the brightness of both is increased. The change in wave length of the test light3 as the spots are dimmed is of no consequence in these studies since the same wave-length change is present both in the controls and in the tests follow ing exercise.
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1430
JOHN P. WENDLAND
The preadapting light incorporated in the biophotometer is of insufficient brightness to record the full extent of the visual adap tation curve. A brighter preadapting light, as mentioned below, was, therefore, used. The left eye was used in all determina-
which would increase the pulse rate by 25 to 30 beats per minute. SUBJECTS
The subjects were all college students be tween the ages of 17 and 29 years, with no
TABLE 1 SUMMARY OF METHODS OF TESTING THE EFFECT OF EXERCISE ON DARK ADAPTATION
Type of Exercise
Duration and Rate of Exercise
Procedure of Testing
Light Bicycle ergometer 35 min.; pulse increase Exercise started immediately of 25-30 beats per min. after preadaptation. Readings taken at 4, 8, ,12, 16, 20, 25, 30, and 35 min.
Rate of Dark Adap tation or Final Threshold
No. of Subjects; No. of Tests
Rate
9 subjects, 13 tests
Rate
8 subjects, 8 tests
Bicycle ergometer 10 min.; pulse increase Exercise started after full dark 25-30 beats per min. adaptation. Readings taken after exercise from 15 sec. to 13 to 15
Final threshold
5 subjects, 6 tests
Genuflexions
Final threshold
7 subjects, 7 tests
Rate
4 subjects, 4 tests
Genuflexions
2§—3 min.; pulse in Exercise started immediately crease of 25-30 beats after preadaptation. Readings taken at 4, 8, 12, 16, 20, 25, 30, per minute and 35 min.
2 §-3 min.; pulse in- Exercise started after full dark crease of 25-30 beats adaptation. Readings taken after per min. exercise from 15 sec. to 13 to 15 min.
Heavy Standing running subject ran "all out" until exhaustion which in no case was more than 2J-3 min.
Exercise started immediately after preadaptation. Readings taken at 4, 8, 12, 16, 20, 25, 30, and 35 min.
Standing running subject ran "all out" Exercise started after full dark until exhaustion which adaptation. Readings taken after in no case was more exercise from 15 sec. to 13 to 25 than 2^-3 min. min.
tions; the test spot subtended an angle of one degree, 6 degrees temporal and superior to the fovea. The influence of light and heavy muscu-. lar exercise on both the rate and final rod threshold of adaptation was studied. The experimental arrangement and testing pro cedure are summarized in Table 1. In the light-exercise experiments, in order to make the work load physiologically comparable in various subjects of unequal muscular ca pabilities, exercise was performed at a rate
Final threshold
19 subjects, 20 tests
ocular defects. They were well trained on the apparatus in order to eliminate learning as a possible factor in the results obtained. In the experiments on the rate of dark adaptation, successive tests were made with no exercise in between to establish controls. In the experiments on the final rod thresh old, numerous readings were taken until the subject reached a level constant except for the slight unavoidable normal variability found in repeated readings. Exercise was then performed using the preëxercise read-
EFFECT OF EXERCISE ON DARK ADAPTATION
ings as controls. Only values exceeding the normal preëxercise variability are con sidered in this paper. Statistical analysis of the results was ac complished by means of the "t-test" (Fisher 7 ). The subjects performed no ex ercise, other than walking to the laboratory, for several hours prior to the tests and rested in a room, illuminated with 2 footcandles, for 15 minutes before the control tests were begun. TESTS
In the tests concerning the effect of ex ercise on the rate of adaptation the subject
1431
was begun after full dark adaptation. The same forms of exercise were used as in the experiments on the rate of dark adaptation. RESULTS
In tabulating the effects of exercise on the rate of adaptation, the readings taken during the course of adaptation are divided into 3 intervals. Interval I includes the readings at 4, 8, and 12 minutes ; Interval II, the readings at 16, 20, and 25 minutes ; and Interval III, the readings at 30 and 35 min utes. The results of light exercise are shown in Table 2. Columns 5 and 9 represent the effect
TABLE 2 EFFECT OF LIGHT EXERCISE ON THE RATE OF DARK ADAPTATION
Genufle ixions
Ergometer Exercise Subject
Interval I
Interval II
Interval III
T.D.A.
Interval I
Interval II
Interval III
T.D.A.
D.M. M.H.
+0.05
+0.04
+0.10
+0.06
B.S. B.S. B.S. E.T. E.T. L.W. P.W. P.W. T.G. M.O. C.P.
+0.07 -0.03 -0.01 -0.07 -0.07 +0.01 +0.05 +0.12 +0.07 +0.01 -0.05 -0.03
+0.04 +0.05 0 -0.08 0 +0.04 +0.12 +0.11 -0.01 +0.01 -0.05 +0.07
+0.06 +0.02 +0.08 +0.02 0 0 +0.12 +0.22 -0.10 -0.02 0 +0.04
+0.06 +0.02 +0.02 -0.05 -0.03 +0.02 +0.14 +0.14 -0.01 +0.01 -0.04 +0.02
-0.05 +0.01 +0.04
-0.04 +0.04 -0.07
-0.02 +0.02 -0.06
-0.04 +0.02 -0.02
-0.03
+0.09
+0.06
+0.04
0 -0.04 -0.05 -0.07
-0.01 -0.07 +0.07 +0.07
-0.06 0 +0.10 -0.02
-0.02 +0.01 +0.04 +0.01
Mean
+0.01
+0.03
+0.04
+0.03
-0.02
+0.01
+0.002
+0.005
K.J.
J.A.
* Values are expressed in log units. Plus ( + ) denotes a lowering of threshold, minus (—) denotes a rise compared to the control. T.D.A. = total dark-adaptation curve.
was preadapted for a period of one minute to a light of 2,400 millilamberts subtending an angle of 41 degrees at the subject's eye. For light exercise two forms of exercise (bicycle ergometer and genuflexions) per formed as indicated in Table 1 were used. For heavy exercise but one form of exer cise (standing running all out) was used. In the tests concerning the effect of ex ercise on the final rod threshold, exercise
on the "total dark adaptation curve" (T.D.A.). The effect on the T.D.A. was arrived at by averaging the values of indi vidual readings taken during the entire course of dark adaptation as given in Table 1. A plus value denotes an increase in sensitivity (lowering of threshold), and a minus value a decrease in sensitivity (rise in threshold), compared to control values. It will be noted that most of the changes
1432
JOHN P. WENDLAND TABLE 3 EFFECT OF HEAVY EXERCISE ON THE RATE OF DARK ADAPTATION*
Subject
Heavy Exercise Inter val I
Inter val II
Inter T.D.A. val III
D.M. L.C. M.H. J.A.
+0.04 -0.07 0 -0.50
+0.01 +0.03 -0.08 -0.07
-0.10 +0.02 -0.16 -0.06
-0.02 -0.01 -0.02 -0.06
Mean
-0.01
-0.02
-0.06
-0.02
* Values are expressed in log units. Plus ( + ) de notes a lowering of the threshold, minus ( —) de notes a rise compared to the control. T.D.A. =total dark adaptation curve.
are of small magnitude and that they are both plus and minus. The statistical analysis of the results shows that light muscular ex ercise has no effect upon the rate of dark adaptation. The effects of heavy exercise on the rate of dark adaptation are represented in Table
3. It will be seen here that, under Intervals I and II, the values fall fairly equally on both the plus and minus sides. In Interval III, however, all the values are minus ex cept one and, in the column T.D.A., all values are minus. Statistical analysis shows that, although there is a tendency to a de crease in sensitivity in Interval III, which represents final rod thresholds, and in the T.D.A., none of the changes are of suffi cient magnitude to reach statistical signifi cance. Table 4 represents the results of the experiments with the effect of light exercise on the final rod threshold·—that is, on the threshold of the fully dark-adapted eye. It will be noted that there is a tendency to both a lowering and a raising of the threshold. The lowering of the threshold occurs imme diately after exercise and is of compara tively short duration as shown in Column 3 ; it is followed by a rise in the threshold of
TABLE 4 EFFECT OF LIGHT EXERCISE ON THE FINAL ROD THRESHOLD*
Subject
Lowering of Threshold
Time of Lowering Threshold
Duration of Lowered Threshold
Rise of Threshold
Time of Rise of Threshold
Duration of Rise of Threshold
ERGOMETER
s.c. s.c. W.P.
+0.16
CG.
+0.04
Mean
+0.04
B.S.
J.E.
0
+0.08 0
0
o-u 0 0-1 0
ο-έ 0
U
0 1 0 1
0 1
-0.08 -0.08 -0.04 -0.04 -0.12 0
3-5
5-15 6-8
31-41; 8-10 1-15 0
2 10 2 2* 15 0 11
-0.06
GENUFLEXIONS
W.P. D.M. B.S. O.G. CG.
0 0 0
+0.08 +0.08
L.H. W.N.
+0.04
Mean
+0.03
0
0 0 0
0-3*
2 f -2|; 3|-4i
0 0 0 3§
-0.04
0 1
0 0
0 0 0
i
-0.08
2 Ϊ
-0.02
9-11
0 0 0
2§-3;4-5;6-9 0 0
2 0 0 0 44 0 0 A
* Threshold changes are expressed in arbitrary log units and represent maximum changes. Plus ( + ) de notes a lowering of the threshold, minus (—) denotes a rise compared to values before exercise. Time inter vals are given in minutes and include the entire time any lowering or elevation of the threshold occurred.
EFFECT OF EXERCISE ON DARK ADAPTATION somewhat longer duration (column 6 ) . However, the changes again are not statistic ally significant. The effect of heavy exercise on the final rod threshold is seen in Table 5. In the ma jority of subjects, the reaction is biphasic; that is, there is a temporary improvement
1433
ment immediately following exercise; whereas, all showed a reduction in sensi tivity beginning in 1 to 5^4 minutes follow ing exercise and lasting from 1 to 16 min utes. The improvement immediately follow ing exercise varied from none to 0.2 log units; the elevation of the threshold from
TABLE S E F F E C T OF HEAVY EXERCISE ON T H E FINAL ROD THRESHOLD*
Subject
L.C. E.B.
Lowering of Threshold
D.K. E.T, L.H.
+0.08 0 0 +0.04 +0.16 +0.20 +0.12 +0.12 +0.16 +0.04 +0.08 +0.04 0 +0.20 +0.04 +0.12 +0.12 0 +0.04 +0.08
Mean
+0.08
J.K. J.B.
M.O.
J.P.
H.S.
F.J.t
M.H. D.M. D.M. L.W. L.W.t J.P.W.Î H.W. P.W.
K.J.
Time of Lowering of Threshold Following Exercise
0-1 0 0
0-1
0-1 i; 2-Λ
Duration of Lowered Threshold
Time of Rise of Threshold Following Exercise
2-3; 7i-8i li-12 U-2J; 6 i - 7 i 2-3; 3i-4i; 7-12 7Wi li-6;10i-ll 2i-S;Si-7 lf-2i; 3 H 1-1i; 2J-8 3J-4; 7f-8i; 9^-10 l«-U;3-3i;4i-5i;7i-7i l i - 9 ; 12-13 2-2i;3f-ll 2-16 5 i - 7 ; 8 i - 9 i ; 11-12
14 3i
1
-0.24 -0.36 -0.32 -0.20 -0.08 -0.24 -0.20 -0.12 -0.28 -0.24 -0.16 -0.40 -0.44 -0.56 -0.24 -0.28 -0.28 -0.20 -0.12 -0.20
Si-5i; 6-14 Si-8 4-20 4-15
81 2i 16 11
2 3
-0.26
1 4
0 0
1
3*
o-i
i
ο-έ i-l
iA
o-i î
i-i\ n-n
o-i o-i
li 2
i *
1 4
0 0-1
0 1
0-1i; 2i-21 0-1Î 0
4,
o-i
o-i
0-1
Duration of Rise in Threshold
Rise of Threshold
1
U H
0
i
5H
2 Hi 1* 7 1 Si 4
i 51 21 U 7!
n U
Si
* Threshold changes are expressed in arbitrary log units and represent maximum changes. Plus ( + ) de notes a lowering of t h e threshold, minus ( —) denotes a rise compared t o values before exercise. Time inter vals are given in minutes and include the entire time any lowering or elevation of threshold occurred. t Artificial pupil used. î Pilocarpine fixation of the pupil.
in sensitivity of short duration, followed by a decrease in sensitivity often of con siderable magnitude and duration. Treated statistically the tendency shown in light ex ercise has here become highly significant. Superimposed upon the overall biphasic change are wavelike fluctuations of the threshold especially marked during the de pression phase. These fluctuations are evi dent in Columns 3 and 6, Table 5. There was no difference in the reactions between men and women. Sixteen out of 20 subjects showed some transitory improve-
0.08 to 0.56 log units. Thus, considerable individual variability was present. The maxi mum decrease in sensitivity of 0.56 log units represents almost a fourfold change in sensitivity. The mean lowering of the thresh old was 0.08 log units with a mean duration of 2/z minutes; the mean rise of threshold was 0.26 log units with a mean duration of 5J4 minutes. In two subjects, pilocarpine fixation of the pupil was used and in one, an artificial pupil. Control of pupillary size in this manner in no way influenced the response of the subject to the exercise.
1434
JOHN P. WENDLAND
Therefore, pupillary reactions cannot play a part in the results found. Figure 1 represents graphically the re sponse to heavy exercise. It will be seen that
0
I
2 3
actual average magnitude, for it was com puted by averaging the values of all the sub jects at given time intervals following the exercise. As the subjects showed consider-
4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 TIME IN MINUTES AFTER EXERCISE
Fig. 1 (Wendland). Effect of heavy exercise on the final rod threshold. "O" represents the threshold level before exercise. Minus (—) values denote a rise in the threshold, plus ( + ) values a lowering of the threshold, -x-x- Subject showing maximum lowering of the threshold. Subject showing maxi mum rise of the threshold. Mean of all subjects. the rise in threshold is much more marked and extends over a longer time interval than the lowering of the threshold. The curve showing the mean response is of value mainly for showing the general biphasic character of the response rather than the
able variability in the time of occurrence of the depression phase the general effect of averaging their values would be to level off the curve. This biphasic response is some what similar to the effect of muscular exer cise on the fusion frequency of flicker.8
EFFECT OF EXERCISE ON DARK ADAPTATION In none of the tests was any correlation found between the physically trained and un trained subjects. DISCUSSION
The following factors may be concerned in the production of the changes in dark adap tation following exercise : 1. In muscular exercise, an irradiation of impulses from motor centers to other parts of the nervous system is generally assumed. This is thought to be responsible for the marked change in respiratory rate which oc curs immediately after exercise before any blood changes could have reached the respira tory center.9 This irradiation continues throughout exercise and may be responsible for the lowering of thresholds immediately following exercise. 2. The increased blood flow during exercise may improve the blood supply of the retina and brain, a factor which possibly would tend to lower thresholds. 3. The oxygen debt found in heavy exer cise is possibly the major factor in causing an elevation of thresholds. All investigators are agreed that reduced oxygen tensions, such as those caused by high altitude, cause an elevation of thresholds. 8 · 10 " 14 It would seem at first glance that the oxygen debt in muscular exercise acted in an exactly simi lar manner. However, the physiology of the two situations is different. In anoxia there is reduced oxygen saturation of arterial blood; whereas, in muscular exercise the blood becomes properly oxygen saturated as it passes through the lungs. Thus in mus cular exercise, the brain and eyes possibly do not receive a diminished oxygen supply. Nevertheless, the oxygen debt does express a need of oxygen by the organism and it is probably in some measure responsible for the elevated thresholds following muscular exercise. The maximum depression in the final rod threshold following exercise, as noted above, was 0.56 log units, or a change equal to the effect produced by an altitude of approximately 15,000 feet.
1435
4., Wald and associates18 have shown that the addition of 5-percent carbon dioxide to the air an individual at rest inspired elevated the final rod threshold from 0.2 to 0.5 log units (approximately a 1 ^ and threefold change, respectively). Conversely, washing out of carbon dioxide by breathng room air at rates 50 to 100 percent more rapidly than normal caused a lowering of the threshold of about 0.27 log units. Thus according to Wald et. ed., respiratory acidosis and alkalosis ex ert opposing effects upon the visual thresh old. Possibly the increased production of carbon dioxide and acidosis found in severe exercise may contribute to the elevated thresholds noted following exercise. It is interesting to note that most of these same factors have been used to explain the changes observed in the fusion frequency of flicker following exercise.8 The coexistence and temporal relation ships of these factors in exercise are re sponsible for its effects on dark adaptation. The depressing effect of heavy exercise is of importance in tasks performed at night and requiring good night vision—for ex ample, night flying. In general, the findings of Bodansky and Hendley 1 have been confirmed, although some differences are noted. In contrast to our observations, they were unable to demon strate a significant improvement in normal individuals shortly following exercise. Like wise, they found no correlation between the amount of exercise and the depression of sen sitivity obtained. In the experiments reported in this paper, normal individuals showed a statistically significant improvement in rod thresholds immediately following exercise followed by a depression of sensitivity simi lar to that obtained by Bodansky and Hend ley. Also in my experiments, there is corre lation between the severity of the exercise and the effects produced ; light exercise pro duces both a smaller improvement and de pression phase than does heavy exercise. Kekcheev's results have not been con firmed.
1436
JOHN P. WENDLAND
It is suggested that as part of the stand ardization of dark-adaptation testing, in vestigators limit the physical activity of their subjects for one-half hour prior to testing. SUMMARY
Twenty-nine subjects were used, on whom 60 tests were performed, in studying the effect of light and heavy muscular exercise upon both the rate and final rod threshold of dark adaptation. Light exercise has essentially no effect upon the rate of dark adaptation and only a tendency to produce a slight biphasic re sponse in the rod threshold. For practical purposes it may be said to exert no effect on dark adaptation. Heavy exercise produces a tendency to elevation of the thresholds of the total darkadaptation curve and causes a marked bi
phasic response in final rod thresholds. The biphasic response consists in, first, a lower ing of the threshold of short duration, fol lowed by a rise in the threshold, often of considerable magnitude and of longer dura tion. In one subject, the depression of sensi tivity was equal to that produced in an in dividual at an altitude of 15,000 feet. In practical application, heavy exercise may be said to produce a definite decrease in ability to see at night. The factors responsible for these observa tions have been discussed and the impor tance of the changes in critical visual tasks performed at night pointed out. The Medical School (14). Acknowledgment: Sincere appreciation is ex pressed to Dr. Erling Hansen and Dr. Ernst Simon son for their interest and helpful suggestions in this study.
REFERENCES
1. Bodansky, Ο., and Hendley, C. D.: Effect of methemoglobinemia on the visual threshold at sea level, at high altitudes and after exercise. J. Clin. Investigation, 25 :717-722,1946. 2. Kekcheev, K. K.: Expediting adaptation to darkness. Nature, London, 151:617-618, 1943. 3. Mandelbaum, J.: Dark adaptation: Some physiologic and clinical considerations. Arch. Ophth., 26:203-239, 1941. 4. Palmer, C. E., and Blumberg, H.: The use of a dark adaptation technic (biophotometer) in the measurement of vitamin A deficiency in children. Pub. Health Rep., 52 :1403-1418, 1937. 5. Hecht, S., and Mandelbaum, J.: The relation between vitamin A and dark adaptation. J.A.M.A., 112:1910-1916, 1939. 6. Sheard, C.: Dark adaptation: some physical, physiological, clinical and aeromedical considera tions. J. Optic Soc. America, 34:464-S08,1944. 7. Fisher, R. A.: Statistical methods for research workers. Edinburgh, 1936. 8. Simonson, E., Enzer, Ν., and Benton, R. W.: The influence of muscular work and fatigue on the state of the central nervous system. J. Lab. & Clin. Med., 28:1555-1567, 1943. 9. Bainbridge, F. A.: The physiology of muscular exercise. New York, Longmans Green and Co., 1931. 10. Wilmer, W. H., and Berens, C.: Medical studies in aviation: V. Effect of altitude on ocular functions. J.A.M.A., 71:1394-1398,1918. 11. McFarland, R. Α., and Evans, J. N.: Alterations in dark adaptation under reduced oxygen tensions. Am. J. Physiol., 127 :37-50, 1939. 12. McDonald, R., and Adler, F. Η.: Effect of anoxemia on the dark adaptation of the normal and the vitamin A deficient subject. Arch. Ophth., 22:980-988, 1939. 13. Sheard, C.: Effects of anoxia, oxygen and increased intrapulmonary pressure on dark adapta tion. Proc. Staff Meet., Mayo Clin., 20:230-236,1945. 14. McFarland, R. Α., and Forbes, W. H.: The effects of variations in the concentration of oxygen and of glucose on dark adaptation. J. Gen. Physiol., 24:69-98, 1940. 15. Wald, G., Harper, P. V., Jr., Goodman, H. C, and Krieger, Τ. P.: Respiratory effects upon the visual threshold. J. Gen. Physiol., 25 :891-903, 1942.