Morning Versus Afternoon Gymnastic Time and ...

Chronobiology International The Journal of Biological and Medical Rhythm Research

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Morning Versus Afternoon Gymnastic Time and Diurnal and Seasonal Changes in Psychophysiological Variables of School Children Georges Huguet, Yvan Touitou & Alain Reinberg To cite this article: Georges Huguet, Yvan Touitou & Alain Reinberg (1997) Morning Versus Afternoon Gymnastic Time and Diurnal and Seasonal Changes in Psychophysiological Variables of School Children, Chronobiology International, 14:4, 371-384, DOI: 10.3109/07420529709001458 To link to this article: http://dx.doi.org/10.3109/07420529709001458

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CHRONOBIOLOCY INTERNATIONAL, l4(4), 37 1-384 ( 1997)

MORNING VERSUS AFTERNOON GYMNASTIC TIME AND DIURNAL AND SEASONAL CHANGES IN PSYCHOPHYSIOLOGICAL VARIABLES OF SCHOOL CHILDREN Georges Huguet,"' Yvan Touitou,"* and Alain Reinberg' 'Laboratoire de Biochimie Mtdicale, Facultt de Mtdecine Pitit-Salpttriere, 91 Blvd. de I'HGpital, 75013 Paris, France 'Chronobiologie, Fondation A. de Rothschild, 29 rue Manin, 75940 Paris Cedex 19, France

ABSTRACT The aims of this study were to document time-related (morning versus afternoon) effects of physical activities (gymnastics) on a set of physiological and psychological variables in school children, including diurnal changes. For the study, 61 boys and 69 girls, 6 to 11 years of age, volunteered. They were considered healthy according to routine clinical criteria. They were synchronized with diurnal activity from around 07:OO to 21:OO and nocturnal reLt, time of year being taken into account. Tests were performed at school during 4 weeks of 4.5 days of school at fixed clock hours: 09:00, I I :OO, 14: 00, and 16:OO. Gym time was randomized with regard to week order and season. Four different classes (39 boys and 38 girls) were involved in psychophysiological tests, and two different classes (22 boys and 31 girls) collected saliva samples for morning free cortisol determination. Both t-test and threefactor analysis of variance (ANOVA) were used for statistical analyses. Better performances were obtained in June than in mid-winter with reference to letter cancellation and random number addition tests. As a group phenomenon, morning (09:OO to 1O:OO) versus afternoon (14:OO to 15:OO) gym was nor an influential condition with regard to sleep duration, oral temperature, self-rated fatigue and drowsiness, letter cancellation, addition tests, or salivary cortisol. However, gym-time-related differences were observed in classes of younger suhjects (e.g., 6-7 years) with regard to self-rated fatigue Submitted July 21, 1995; returned for revision October 17, 1995; accepted November 14.

1995. *To whom all correspondence should be sent.

371 0 1997 International Society for Chronobiology

372

HUGUET, TOUITOU, AND REINBERG and the letter cancellation test. Such variability among subgroups suggests that interindividual differences are likely to exist in younger children with regard to manipulation of environmental factors. In addition, gym itself (without gym time consideration) may be an influential factor with regard to diurnal patterns of some variables (e.g., the letter cancellation test). (Chronobiology International, 14(4), 371-384, 1997)

Key Words: Children-Diurnal and seasonal rhythms-Gymnastic time-Performance tests-Letter cancellation test-Salivary cortisol.

INTRODUCTION Circadian, as well as diurnal (restricted to the activity phase), changes have been documented in ratings of psychological tests of children (1-9), and circadian and diurnal changes have been documented in healthy adults regarding both physiological and psychological activities (10-14). However, the possible effect of the gymnastic time (e.g., morning versus afternoon hours) on diurnal changes of performance tests has not been explored in school children. Gymnastic and sport activities are scheduled in all education systems. In France, these types of non-exhausting physical activities represent a 30-to-45-minute time span daily during each of the 4.5 school days per week. The question is: Are they important to learning and therefore when to schedule them? The present study was designed to document time-related effects (e.g., morning vs. afternoon) of gymnastics at school in boys and girls between 6 to 11 years of age in a set of variables: observed wake-sleep cycle, oral temperature, self-rated fatigue, drowsiness, letter cancellation and addition tests, and salivary cortisol at the expected circadian peak time. These tests were selected according to several criteria. They are informative and easy to perform and thus are well accepted by children. They can be precisely quantified, and they did not require sustained effort or a great amount of time. Moreover, they can be programmed so as not to disturb the regular teaching at school.

SUBJECTS, MATERIAL, AND METHODS Subjects For the study, 130 children, 61 boys and 69 girls, volunteered with parental consent and teachers’ help (Table 1). Some 77 were involved in the psychophysiological testing portion of the study, and 53 in its biochemical portion (salivary cortisol). Children were 6 to 11 years old, apparently healthy according to clinical criteria checked by both school and family doctors, with weight and height values falling within the 95% limits with reference to age and gender. Children were attending CP (Cours Prbparatoire: 6-7 years old) and CM1 (Cours Moyen, first year: 9-10 years old) and CM2 (Cours Moyen, second year: 10-11 years old). All the members of a given class in each grade group were included in the survey. An apparently rather good homogeneity existed in the distribution of children with respect to both age and grade. Six different classes took part. The number, age, and gender of subjects and type of documented activity are shown in Table

PSYCHOPHYSIOLOGICALVARIABLE CHANGES IN CHILDREN

373

Table 1. Test Subjects and Activities

No. Children (BMI) Total

Class

Tests

A, 6-7

0, F, D, L

15

0, F, D, L

Gym Class

Mean Age

Boys

(Years)

7 (21.59)

S(20.19)

6.37

January

June

Girls

Morning

Afternoon

years old 15

1 1 (18.53)

4(20.19)

6.49

June

January

years old C,9-10 0, F, D,L, A years old

22

lO(24.60)

12(24.13)

9.64

June

February

D, 10-11

0, F, D, L, A

25

10 (26.95)

15 (29.15)

Saliva cortisol

25

12 (26.95)

13 (24.52)

9.23

F, 10-11 Saliva cortisol years old

28

19 (26.75)

9 (29.15)

10.34

B, 6-7

10.63 February

June

years old E, 9-10

December

November

years old November December

A = random number addition test, BMI = body mass index (weight in kgheight in m2); D = selfrated drowsiness; F = self-rated fatigue; L = letter cancellation test; 0 = oral temperature.

1. All children were socially synchronized with diurnal activity from 07:30 (+30 minutes) to 21 :30 (E30 minutes) and nocturnal rest. They practiced sports at school (mainly gymnastics) but without specific training or competition. All families were upper middle class. All children participated in strenuous but non-exhausting physical activities at school (gymnastics, ball games, etc.). The activities lasted 30 to 40 minutes per schoolday, 4.5 days per week. Gym time was scheduled in the morning (from 09:OO to 1O:OO) during one semester and in the afternoon (from 14:OO to 15:OO) during the other one. In order to minimize seasonal, as well as day-of-week, effects (Is),each child was studied twice (e.g., mid-winter and early-summer) during a two-week span in randomized order (cf. Table 1). In addition, during the last of the two-week spans, the on-going gym time was maintained for the first week and reversed the second.

Test Scheduling and Data Gathering Children were trained and familiarized in advance to all the tests in order to minimize learning effects. Psychophysiological tests were performed at 09:00, 11:00, 14:00, and 16:OO. This schedule was selected in order not to disturb teaching and other regular school activities (e.g., lunch time from 12:OO to 13:OO). Test series were performed on Monday, Tuesday, Thursday, and Friday during each of the coupled two-week spans. Salivary samples for free cortisol determination were collected once a day, on morning awakening (about 07:30), during the two-week span, one before and the other after the alternation of the gym time (morning to afternoon or the reverse).

Type of Psychophysiological Tests Psychophysiological tests all were performed at 09:OO. 11:OO, 14:00, and 16:OO.

374

WGUET, TOUITOU, AND REINBERG Oral Temperature

Using a mercury clinical thermometer with 0.05”C precision, each child measured their oral temperature, which was read and recorded by one of the investigators. This variable was selected both to serve as a marker rhythm and to assess each subject’s synchronization (16). Self-Rated Fatigue and Drowsiness Two series of four visual analog scales (one for each variable) were displayed (horizontal rectangles 35 x 10 mm) on sheets, one per day per child. Each child was instructed to place a vertical pencil stroke on the pertinent horizontal rectangle (e.g., self-rated fatigue), imagining a meter on which the extreme right represented extreme plus (e.g., extreme fatigue) and the extreme left represented the extreme minus (e.g., extreme alertness). Scores were obtained by measuring the distance in millimeters from the left margin to the pencil stroke. Self-ratings were repeated at each of four designated clock times daily. Children were instructed to quantify their subjective feelings by answering simple but specific questions. For fatigue it was, “Now (time), how tired am I?” and “Now am I able to make a good effort?’ For drowsiness, the question was, “Now, am I sleepy?” Visual analog scales have been proven to be a most useful tool for quantifying these and other subjective variables both in adults (10,14,17) and in children (5,9,18), even to document diurnal changes at the age of 7 years. Letter Cancellation Test A large series of randomly organized letters is usually used for adult experiments, the task being to cancel one or several specified letters (6,19). As in a previous study (15) and based on the wishes of the consulted children, we used one page of Englishlanguage text rather than the random letter blocks used for adults. Although the text was meaningless to these French children, the format of the presentation was familiar to them. In addition, they agreed that “ W was an easy sign to be found, including younger subjects. Children were asked to cancel as many W’s as they could find during a 1minute span. The W density was 60 k 10 per printed page. The score was expressed as the number of W’s cancelledminute. Random Number Addition Test At each of the four test times, a sheet, differing from test to test, with 40 operations (2 figures from 0 to 9 to be added) was presented. For each addition, three “totals” were suggested. As fast as possible, the child had to tick the correct answer. The score was expressed as the number of correct results obtained during a 40-second span. Timerelated changes in random number addition tests have been previously reported (9. 20-22). Children of only two classes were asked to perform this test (Table 1).

Salivary Cortisol Cortisol secretion, especially at its circadian peak time, is conventionally taken as an index of the organism’s reaction to environmentally challenging situations. In children, the circadian peak time occurs around the usual awakening time (e.g., 07:30) (23,24).

PSYCHOPHYSIOLOGICAL VARIABLE CHANGES IN CHILDREN

375

An excellent correlation between plasma total cortisol and salivary free cortisol from both venous and capillary blood was demonstrated (25). Is this the case with morning versus afternoon gym time? Just after awakening (07:30 k 30 minutes), but before breakfast, each child collected around 3 ml of saliva in a plastic tube that was brought to school and immediately transferred into the laboratory deep freezer until determinations. In order to avoid inter-assay variability, all determinations were performed in one series (2425). The assay sensitivity was 0.1 mg/dl.

Sleep Duration Lights-out (retiring) and lights-on (awakening) times were recorded individually with the help of parents on a daily basis.

Statistics Time series of each variable, by class, age. gender, and grade, were first visuali7.ed as chronograms that display the means as a function o f clock time 00 a weekly basis. Both t-test and three-factor analysis of variance (ANOVA) were used systematically for statistical tools to explore differences related to time of gym, in addition to time-related, gender-related, age-related, and other differences. including interactions among thcsc factors. Test times were given with reference to clock hour regardless of day 0 1 the week.

RESULTS Results are expressed according to time of day and season for each psychological and physiological variable, including salivary cortisol.

Time-of-Day Changes Subjective Sleep Duration Lights-on and lights-off occurred at about 07:30 and 2 1 :OO. respectively. Thc mcan duration of the reported sleep span, IOh f 30 niinutes (SEM), exhibited no statistically signiticant difference by age, gender, or time of gym.

Oral Temperature 'L\ were In classes B, C, and D, but not in class A (see Table I ) , diurnal chanb-: validated with regard to both morning and afternoon gym times. Mean values increased from 09:OO to 16:OO. A gender-related dift'crence was observed. with oral temperature being greater in boys than in girls, with p values ranging from p < 0.01 in childrcn of 6-7 years of age to p < 0.00001 in older ones (10-1 I years of age). A gym-time cl'fcct was not documented ( p > 0.05) for any of the four classes.

Self-Rated Fatigue Diurnal change in self-rated fatigue was not detected (p> 0.05) in classes A, C. or D and was rather small in amplitude (peak-to-trough difference) when validated in class

376

HUGUET, TOUITOU, AND REINBERG

B, with p < 0.04. No gender-related difference was found in classes B, C, or D, but large interindividual differences were observed in class A. A gym-time effect was not validated (p < 0.05) in classes A, C, or D, and was rather small in amplitude when validated (with p < 0.04) in class B. For this class, selfrated fatigue was greater with the morning than afternoon gym time. Self-Rated Drowsiness A diurnal change in drowsiness was not detected (p > 0.05) in any of the four classes, and a gender-related difference was only validated in class A. A gym-time effect on drowsiness was not documented (p > 0.05) in any of the four classes. A cross correlation was validated between self-rated fatigue and drowsiness, for boys as well as girls, in all classes. The correlation ranged from r = 0.72 with p < 0.001 in class B, to r = 0.27 with p < 0.05 in class D. Letter Cancellation Test Diurnal changes in the W cancellation test were validated (with p < 0.00001) in all four classes for boys and girls (Fig. 1). Poorest performance (smallest number of cancelled letters) occurred at 11:OO or 14:00, while best performance occurred at 1690 or 09:OO. No gender-related difference was observed, and no gym-time effect was validated in classes A, C, and D. In class B, children performed better (with p < 0.03) with afternoon compared to morning gym time. Cross correlation helped to document an agerelated effect with better performance in the older sub-groups (classes C and D; 9-11 years of age) as compared with the younger ones (classes A and B; 6-7 years of age with p < 0.02). Random Number Addition Test With regard to the age-related capability to perform additions, the test was restricted to older sub-groups C and D. A diurnal change was validated (with p < 0.0001), with best performances being at 11:OO and 14:OO and poorest at 09:OO and 16:OO (Fig. 2). Gym time had no effect on random number addition test performance. Salivary Cortisol at Presumable Peak Time A gender-related difference was observed for salivary cortisol at presumable peak time. In the age group of 9-10 year olds, the morning salivary cortisol was higher in boys than girls (with p < 0.005), while in the age group of 10-1 1 year olds the predominance was reversed (Fig. 3). No difference was validated between morning versus afternoon gym situations. Even the gender-related difference was not affected by gym time (Fig. 3).

Seasonal Changes Statistically significant differences between time series obtained during mid-winter (January-February) and early-summer (June) were observed for certain variables in experimental situations that can be compared with regard to age, gender, and gym time.


377

Letter Cancellation Test Diurnal Changes Class

Morning Gym.

Afternoon Gym.

26T

A

26T

20

20

14

14

8

8

E:

\

B

‘“T

‘“T

20

20

26

U

cr 2o

C

20

0

B

14

l4

P 2 D

8

26

26

20

20

14

14

8

8

09

11

14

16

09

11

14

16

Time of Day BOYS

rn

Girls

FIGURE 1. Diurnal changes in a letter cancellation test as a function of time of day with regard to gym time. Mean i SEM with four measures per day at 09:OO. 11:OO, 14:00, and 16:OO. Diurnal changes were validated (with p < 0.ooOOl) in all four classes for both boys and girls. No genderrelated difference was observed, and no gym-time effect was validated in classes A. C, and D.


378

Random Number Addition Test Afternoon Gym.

Morning Gym.

Class

23 21 C 19

19

17

17

15

15

\

g .Y

5

4

09

11

14

09

16

11

14

16

Time of Day Girls FIGURE 2. Diurnal changes in random number addition test as a function of time of day with regard to gym time. A diurnal change was validated (with p < 0.0001); a gym-time effect was not detected ( p > 0.05).

Sleep duration was not influenced by season. Self-rated fatigue and drowsiness were not influenced by time of year (with p > 0.05) in classes C and D involving older children. In younger children (classes A and B), however, self-rated faiigue and drowsiness were greater in winter than summer (with p < 0.002). For all classes (A, B, C, and D) and subgroups with regard to age and gender, a highly statistically significant seasonal difference was validated for the following variables. Oral temperature was higher in June than in mid-winter (with p < 0.000l).


379

Salivary Cortisol P am pied at 07:30H Morning Gym.

Afternoon Gym.

1

1

9 0.8

0.8

'f!

0.6

0.6

0.4

0.4

a \

9 to 10 Years

0

v

10 to 11

Years

1

1

9 0.9

0.9

-a

"

0.8

o.8 0.7

0.7

0.6

0.6

BOYS

m

Girls

FIGURE 3. Salivary cortisol at presumed peak time of its circadian rhythm in children. No difference in level was validated according to morning versus afternoon gym time.

LRtrer cancellarion scores were better in June than mid-winter (with p < 0.0001) (Fig. 4). For random number addifion, better scores occurred in June than mid-winter (with p < 0.00001) (figure not presented).

DISCUSSION Although suspected to exist, no experimental evidence showing seasonal changes in performance of school children was available. In the present study, our major aim was not to document annual changes. In fact, time of year was only taken into account essentially from a methodological point of view. We feel such changes are unlikely to be related to aging since subjects were randomized with regard to season (Table 1). Better performances in June than in winter were observed for letter cancellation and random addition tests in school children. It is presumably the result of multifactorial effects in

380


Letter Cancellation Test Seasonal Changes Class

-

Mid

Early - Summer

Winter

20

A

14

14

8

8

C

*i 26

26

d

B

\

20

20

8

14

14

8

8

26

26

20

20

14

14

g i

8 v9

C

u

a

$

D

8

8

26

26

20

20

14

14

8

8

09

11

14

16

09

11

14

16

Time of Day BOYS

m

Girls

FIGURE 4. Seasonal changes (midwinter, left, and early summer, right) in letter cancellation test performance as a function of time of day. Mean f SEM as for Fig. 1 . Letter cancellation was associated with better scores in early summer than midwinter ( p < 0.0001).


381

which both external (e.g., learning span, good weather, forthcoming vacation, etc.) and also internal (e.g., seasonal rhythm in performance) factors are involved. This means that annual, in addition to diurnal and weekly, changes in performance should be investigated in school children (5,8,9,26). Both diurnal and seasonal changes in body temperature observed here are in agreement with those reported in young adults (27-29), but not in elderly persons, who present a peak time in winter (28). In one group of young children (6 to 7 years old, group B), the morning gym schedule was associated with a greater self-rated fatigue than the afternoon one. In children 9 to 11 years old, gym time at school (e.g., morning versus afternoon) does not seem to be a factor that influences diurnal changes in oral temperature, self-rated fatigue, drowsiness, sleep duration, or morning salivary cortisol level. In adult subjects, diurnal changes in salivary cortisol have been documented by Campbell et al. (30) with regard to physical activity phase shift. No change in mean level and morning peak height of cortisol was observed even when comparing strenuous versus non-strenuous physical activity. In adults, a5 stated by Klein and Wegman (31, pp. 2-3, 2-4): “Physical activity may influence mental performance through changes in the level of arousal: light to moderate physical work increases it, heavy work has the opposite effect.” It has been demonstrated that this effect depends on the time of day, as well as documented psychological variables (32). An exhausting physical load (30% of the maximum aerobic work capacity) improved scores on a visual-motor coordination test in the morning and afternoon but nor in the late evening and early night. However, the same exercise regimen impaired performance in a memory test at all hours of the day. In boys and girls of 9 to 11 years of age and, as a group phenomenon, it is likely that time of regular gymnastics is not a major influencing factor. The qualification regarding the group phenomenon relates to the fact that such a general statement does not take into account interindividual differences, which may help to better understand interclass differences reported here. As examples, self-rated drowsiness was associated with a gender-related difference in one class (A) but not in the other three; a gym-time effect was validated exclusively in class B for self-rated fatigue. This “class-effect” suggests tha1 we were dealing with non-homogenous subgroups of children in terms of reactivity to environmental factors. Presumably, they involve the influence of the teacher, the novelty of unusual tests performed at school, and other factors that may have masking effects on documented rhythm patterns (33). Therefore, our conclusion may be valid for a majority, but not for all individuals. Presumed interindividual differences in psychophysiological rhythms should be kept in mind for studies on children, a recommendation that has already been made for those on adults (34). In addition, “odd results” were observed in subgroups of younger subjects (classes A and B), a fact that suggests young children are more prone to react to environmental factors than older ones. The tempera1 patterns obtained in the present study in self-rated fatigue, drowsiness, and letter cancellation and addition tests differed at least to some extent from those obtained in adults (4) and even in children in other studies (3,6,8,35). For example, in the present study, the letter cancellation test exhibited a U-shape curve with poorer performance at 1l:OO and 14:OO. Curve pattern alterations have been documented in teenagers (14-16 years old) when they were exposed to an alteration in the schedule of their habitual activities at school (3). It may well be that physical activity, for example, related to gym (whatever its time) is able to alter the diurnal pattern of test performance. School girls 8-1 1 years of age conducting letter cancellation tests similar to those used here

382


exhibited the same temporal pattern in performance; a dome-shaped curve was detected, with best performance at I1:OO and 14:OO (8,35). Let us emphasize that the children in the last study were not participating in gym at school. It could well be that gym itself, rather than its timing within school hours, is a critical factor to be taken into account when documenting capabilities of children not only with regard to psychological tests but also to conventional evaluation of learning. Since physical activity (e.g., gym) is part of the natural behavior of children, the question now is to explore which types of quantified physical activities have to be recommended for the best benefit of children in terms of age, gender, learning, and, obviously, fun.

ACKNOWLEDGMENTS We thank G. Karmochkine, Director of the Elementary School of the Institut de Formation des Maitres de Pans; H. Chauvet, E. Gaudefroy, F. Belle, P. Roder, E. Masclet, D. Bonnerat, and J. Chanteux, schoolteachers; and the 130 children and their parents who contributed actively on aims, methods, and findings. We also thank Professors Franfois Testu, University of Tours, France, and Hubert Montagner, INSERM, for stimulating discussion of the data here presented. Special thanks are due to M. Mechkouri for his technical assistance in computer analysis of time series. The study was supported by grants in aid from Laurette Viza and Thirkse Tremel-Pontremoli donations for chronobiologic research at the Fondation A. de Rothshild, Paris, and the Conseil scientifique de I’universiti Pierre et Marie Curie.

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