effect of ramadan on the diurnal variation

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EFFECT OF RAMADAN ON THE DIURNAL VARIATION

IN SHORT-TERM HIGH POWER OUTPUT

Nizar Souissi,1,2,3 Hichem Souissi,1 Sonia Sahli,1 Zouhair Tabka,1

Mohamed Dogui,1 Jalila Ati,4 and Damien Davenne3

1

Department of Physiology, Sousse Faculty of Medicine, Tunisia2Research Unit, Evaluation, Sport, Health National Center of Medicine and Science inSport, Tunisia3Research Center on Sport Sciences (CRAPS EA 2131), University of Caen, France4Institut National de Nutrition et de Technologie Alimentaire, Tunisia

This study examined the effects of Ramadan fasting on anaerobic performances andtheir diurnal fluctuations. In a balanced and randomized study design, 12 subjectswere measured for maximal power (Pmax; force-velocity test), peak power (Ppeak),and mean power (Pmean) with the Wingate test at 07:00, 17:00, and 21:00 h on fourdifferent occasions: one week before Ramadan (BR), the second week of Ramadan(SWR), the fourth week of Ramadan (ER), and two weeks after Ramadan (AR).There was an interval of 28 h between any two successive tests. Oral temperaturewas measured before each test. Under each condition, the results showed a time-of-day effect on oral temperature. Analysis of variance revealed a significant (Ramadan time-of-day of test) interaction effect on Pmax. This variable improved significantlyfrom morning to evening before Ramadan (1.1+ 0.2 W . kg21), during the secondweek of Ramadan (0.6+ 0.2 W . kg21), and two weeks after the end of Ramadan(0.9+ 0.2 W . kg21). However, daily fluctuations disappeared during the fourthweek of Ramadan. For Ppeak and Pmean, there was no significant Ramadan test-time interaction. These variables improved significantly from morning to evening

before Ramadan ([1+ 0.3 W . kg21] for Ppeak and [1.7+ 1.6 W . kg21] for Pmean)

and in the second week of Ramadan ([0.9+ 0.6 W . kg21] for Ppeak and

[1.7+ 1.5 W . kg21] for Pmean). However, they were not affected by time-of-day inthe fourth week of Ramadan. Considering the effect of Ramadan on anaerobic per-formances, in comparison with before Ramadan, no significant difference wasobserved during Ramadan at 07:00 h. The variables were significantly lower in thesecond week of Ramadan and in the fourth week of Ramadan at 17:00 h and21:00 h. Pmean was not affected during the second week of Ramadan. In conclusion,the time-of-day effect on anaerobic power variables tends to disappear duringRamadan. In comparison with the period before Ramadan, anaerobic performances

Submitted January 2, 2007, Returned for revision February 22, 2007, Accepted June 28, 2007Address correspondence to Dr. Nizar Souissi, Institut Superieur de 1Education Physique de Sfax,

Route de 1aeroport, Sfax 3000, Tunisia. Tel.: 00216 96 818 633; E-mail: [email protected]

Chronobiology International, 24(5): 9911007, (2007)Copyright# Informa HealthcareISSN 0742-0528 print/1525-6073 onlineDOI: 10.1080/07420520701661914

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were unaffected in the morning but impaired in the evening during Ramadan. (Authorcorrespondence: [email protected])

Keywords Ramadan, Anaerobic power, Wingate test, Diurnal variation

INTRODUCTION

One of the most important rules of Islam is that any healthy adultMuslim must refrain from eating, drinking, smoking, and sexual relationsfrom sunrise to sunset during the month of Ramadan, the ninth month ofthe Muslim calendar. The rules of Ramadan allow for a partial fast withfood and water intake being permissible post-sunset and pre-dawn. The

common practice is to eat two meals: one large meal after sunset and amuch lighter one before dawn. Behavioral modifications are thus con-cerned with meal scheduling and shortening of time allowed for sleep.

It has been clearly established that many physiological variables andperformances display a circadian rhythm (Drust et al., 2005; Kline et al.,2007; Reilly et al., 1997). Indeed, the circadian fluctuations in responseto short-term exercise involving anaerobic metabolism have been welldescribed (Guette et al., 2005; Pearson & Onambele, 2005; Racinaiset al., 2004, 2005b; Souissi et al., 2004). It has been reported that avariety of factors, such as the type and intensity of exercise, morning-

nesseveningness chronotype, age, jet-lag, sleep deprivation, and time-of-day of training, can influence the diurnal variation in performance(Montelpare et al., 1992; Reilly et al., 1997; Souissi et al., 2002, 2003). Itis also known that environmental factors such as the timing of the rest-activity cycle (Apfelbaum et al., 1969) and meals (Nelson et al., 1975;Zigmond et al., 1974) may affect the circadian system. Moreover, it has

been previously shown that daytime fasting, modifications in sleep sche-dule, and psychological and social habits during Ramadan inducechanges in the rhythmic pattern of a number of hormonal (Bogdanet al., 2001) and nutrition-related biological variables (Iraki et al., 1997).However, there do not appear to be any published studies dealing withthe effects of Ramadan on the circadian rhythm of muscular performance.It is generally assumed that Ramadan fasting is associated with a reductionof total energy intake (Angel & Schwartz, 1975; Husain et al., 1987) anddecline in body mass (Bigard et al., 1998). Total short-term fasting is detri-mental to endurance (Aragon-Vergas, 1993) and anaerobic (McMurrayet al., 1991) performance. It is also known that a low energy dietreduces the isometric endurance of skeletal muscle, probably because ofa decrease in glycogen stores (Bergstrom et al., 1967).

Although it has been shown that Ramadan can result in a delayedbedtime and shortened sleep with partial sleep deprivation (Roky et al.,

2001), the effects of this altered sleep pattern on physical performance

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remain unknown. Indeed, there are very few investigations on the effectsof partial sleep deprivation on performance. However, it has been shownthat three nights of sleep restriction of at least 2 h does not seem to affectgross motor functions, including muscle strength and lung power orendurance running performance in both men (Reilly & Deykin, 1983)and women (Bambaeichi et al., 2005; Reilly & Hales, 1988). It has also

been reported that one night of total sleep deprivation did not have anynegative effects on muscular strength and power (Meney et al., 1998).However, there might be some masking effects on the circadian perform-ance rhythms. For example, it has recently been demonstrated that theeffects of sleep loss on muscular performances are dependent on thetime-of-day of the recordings (Souissi et al., 2003). It was reported that

one night of sleep deprivation impaired anaerobic performance of menin the evening at 18:00 h but not in the morning at 06:00 h.

Physiological changes during Ramadan are expected to result fromboth long-term dietary restriction and repeated partial sleep loss (Reilly &Waterhouse, 2007). Bigard et al. (1998) demonstrated a rapid decrease inmaximum isometric strength (MVC) of elbow flexor muscles and in muscu-lar endurance at both 35% and 70% MVC during Ramadan. Additionally,Sweileh et al. (1992) showed a decrease in maximal oxygen uptake(VO2max) during the first week of Ramadan with a return to the pre-Ramadan levels in the last week. The effects of Ramadan on diurnal vari-

ation in anaerobic performance during cycle ergometry do not appear tohave been assessed. Therefore, the aim of the present study was toconfirm that performance on the force-velocity (F-V) and 30 sec Wingatetests have time-of-day effects, and to examine the effects of Ramadanfasting on them. These two tests were used because they are used themost in the evaluation of anaerobic metabolism, and there are significantdifferences between them. In fact, Pmax calculated from the F-V test washigher than Ppeak measured during the Wingate test (Vandewalle et al.,1987a). In addition, during the F-V tests, the sprints were only about aquarter as long as the Wingate test. The energy would have been suppliedmainly from high-energy phosphate compounds, creatine phosphate (CP),and adenosine triphosphate (ATP). Because muscle stores of CP and ATPare extremely limited, the Wingate test induces a significant increase inanaerobic glycolysis (Bernard et al., 1998; Vandewalle et al., 1987b).

METHODS

Subjects

Twelve healthy male physical education students (22.6+ 1.3 yrs,height 178.3+ 6.7 cm, and body mass 71.7 + 7.2 kg; mean+ SD) volun-

teered and give informed consent to participate in the study, which was

Effect of Ramadan on Short-Term High Power Output 993

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conducted in accordance with the ethical standards of the journal for theconduct of human biological rhythm research (Touitou et al., 2006). Thecriteria for participant inclusion for this study were that each subjectkept standard times for eating prior to the commencement of the study(breakfast at 07:00+ 1:00 h, lunch at 12:00+ 1:00 h, and dinner at20:00+ 1:00 h) and sleeping habits (sleeping between 23:00 and07:00+ 1:00 h). To ensure that participants were all of a moderatelymorning or intermediate type, they were further selected on the basisof their scores on Horne and Ostbergs questionnaire (1976). This last cri-terion produced a sample of participants sharing the same rising(06:30+ 00:30 h) and bed (23:00 + 00:30 h) times. Subjects were non-smokers who did not consume caffeine or alcoholic beverages. They

observed the Ramadan fast and abstained from liquids from approxi-mately 01:30 to 17:30 h for 30 days. At the time of the investigation, theRamadan month was from October 4th to November 3rd. The length ofeach fasting day was approximately 16 h.

Experimental Design

The experimental design was developed to have four testing periodsduring the study after a period of training for the tests: one week beforeRamadan (BR), the second week of Ramadan (SWR), the fourth week of

Ramadan (ER), and two weeks after Ramadan (AR). At each testingperiod, the subjects performed three test sessions (TS) at different timesof day07:00, 17:00, and 21:00 hover three days, with only one TS aday, providing a recovery period of at least 28 h between any two succes-sive TS. The TS were performed in a random order, and each commencedwith oral temperature and body mass measurements. Oral temperaturewas taken with a digital clinical thermometer (Omronw, Paris, France;accuracy+ 0.058C) inserted sublingually for at least 3 min. Digital scaleswere used to determine body mass (Terraillonw, Paris, France; precision:100 g). A force-velocity test and Wingate test were also completed in thesame order at each test occasion. The interval between completing theforce-velocity test and starting the Wingate test was 30 min.

Instructions concerning sleep, diet, and physical activity were given tothe subjects prior to experimentation:

. Before the month of Ramadan, participants were synchronized with anocturnal rest from 23:00+ 1 h to 07:00 h. During the month ofRamadan, the participants had to go to sleep before 01:30 h and towake at 07:00 h after a night of uninterrupted sleep. All participantskept the same hours of sleep during the four weeks of the experiment.Compliance to these rules was assessed using the Bastuji and Jouvet

(1985) calendar throughout the period. The average sleeping time of


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the participants was 01:50+ 00:15 h less during the four weeks offasting than during the week before Ramadan. During Ramadan, theparticipants refrained from eating or drinking during the daytime. Allmeals were eaten at a standard time within the participants usual sche-dules and Ramadan customs. There were also dietary restrictions prohi-

biting any food or drink that could enhance wakefulness, or agents suchas alcohol. The participants were required to record their food intakes ina diary over a span of three days for each week of physical testing. Therecords were analyzed by a nutritionist using a computerized nutritionsystem, the Food Processor, Nutrition and Fitness Software, ESHAResearch, Professional Nutrition Analysis Software and Databases(20022003).

. Throughout the experimental period, participants were requested tomaintain their habitual physical activity and avoid strenuous activityduring the 24 h before the test sessions. It was easy to control compliancewith these directions because the participants were students who hadexactly the same daily schedules in our institution.

Exercise Testing

Maximal power (Pmax), peak power (Ppeak), and mean power (Pmean) of

the legs were calculated according to the force-velocity (F-V) test protocol(Vandewalle et al., 1987b) and the Wingate test (Bar-Or, 1987). The testswere performed on a friction-loaded cycle ergometer (Monark 894E,Stockholm, Sweden) with an electronic rev-counter and recorder fittedonto the wheel.

Force Velocity Test

The F-V test involved repetitive short maximal sprints (6 sec) againstincreasing braking forces that were set before the start of the exercise.Seat height was adjusted for each participant. This height was recordedand kept the same for each participant in each trial. The feet were heldin the pedals by means of toe-clips. The participant remained in a sittingposition during each F-V test and was vigorously encouraged to reachthe maximal pedaling rate as quickly as possible. The test began with a

braking force of 29.4 N. After 5 min recovery, braking force was increasedfrom 14.7 N to 19.6 N, depending upon each participants capability, andthe same exercise was repeated until participants were unable to reach apeak velocity higher than 100 rev . min21. The participants generally per-formed six or seven short all-out sprints. Peak velocity (V) was measuredduring each sprint for each braking force (F) and used to calculate the

force-velocity relationship for cycling exercises according to the least


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squares method. These force-velocity relationships were linear for peakvelocities ranging from 100 to 200220 rev . min21 (Vandewalle et al.,1987b). The relationship between force and velocity was expressed asfollows:

V V01 F=F0;

where V0 is the intercept with the velocity axis and F0 the intercept with theforce axis. An estimate of maximal velocity at zero braking force is pre-sented by V0. It was assumed that F0 was the braking force correspondingto zero velocity. Given the linear force-velocity relationship in cycling, theoptimal braking force and the optimal velocity (i.e., the braking force andthe pedal velocity corresponding to maximal power [Pmax]) were equal to0.5 F0)(Fopt) and 0.5 V0(Vopt). Therefore, Pmax is equal to:

Pmax 0:5V0 0:5F0 0:25V0F0:

The reproducibility of measurements was studied between performancesat 17:00 h and 21:00 h because no variations in performance hadoccurred. The test-retest mean coefficient of variation for Pmax was 2.5%and the retest correlation was 0.95.

Wingate Test

The Wingate test involved a 30 sec maximal sprint against constantresistance. For each participant, the load was determined according to

body mass using Bar-Ors (1987) optimization tables:

0:087kg kg1body mass:

Participants were given vigorous verbal encouragement during everytest. Seat height was adjusted to each participants satisfaction and toe-clips were used to prevent the participants feet from slipping off thepedals. Seat height was recorded and kept the same for each participantthroughout the trials. Peak power (Ppeak) was taken as the highest mechan-ical power elicited during the test. This index was taken as the highestaverage power during any 5 sec span. Mean power (Pmean) was theaverage power sustained throughout the 30 sec period. The powerdecrease (Wd) was the difference between the highest and lowest powerdivided by the highest. The test-retest mean coefficient of variation was2.6% for Ppeak and 2.3% for Pmean, and the retest correlation was 0.9 for

both.


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For both the F-V and Wingate tests, the characteristics of the cycle erg-ometer enabled P

max, P

peak, and P

meanto be calculated as follows:

for the F-V test: P (W) Foptkg 9:81 Vopt rev min1=60

6:12 m Foptkg Vopt rev min1

for the Wingate test: P (W) F kg 9:81 V rev min1=60

6:12 m Fkg V rev min1:

In both cases, 6.12 m was the distance covered by a point on the rim of theflywheel per pedal revolution.

Statistical Analyses

The data were analyzed using a two-way ANOVA, 4 (Ramadan) 3(time-of-day of tests), with repeated measures on both factors. Whenappropriate, significant differences among means were tested using theTukeys post hoc test. A correlation analysis between the temperatureand anaerobic performance parameters was also performed. A probabilitylevel of 0.05 was selected as the criterion for statistical significance. Statisti-

cal power was determined to be 0.80 for the sample size used at the 0.05 alevel. Effect sizes were calculated as partial eta-squared hp

2 to estimate themeaningfulness of significant findings. All statistical tests were processedusing STATISTICA Software (StatSoft, Paris, France). Within the textand tables, data are reported as the mean + SD (standard deviation) andis displayed as the mean+ SE (standard error) in figures.

RESULTS

Mean body mass, temperature, Pmax

, F0

, V0

, Ppeak

, Pmean

, and Wdvalues at the three times-of-day during BR, SWR, ER, and AR are pre-

sented in Table 1.

Body Mass and Energy Intake

The two-way ANOVA (Ramadan time of day) for body mass showedno significant effects for Ramadan or for time-of-day (p . 0.05). Compari-son of mean energy and macro-nutrient intakes by the participants duringthe day in the four different weeks showed no significant (p . 0.05) statisti-

cal differences (see Table 2).


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TABLE 1 Mean (+SD) Values for Body Mass, Temperature, Pmax, F0, V0, Ppeak, Pmean, and Wd at the Three Times of DayWeek of Ramadan (SWR), in the Fourth Week of Ramadan (ER), and after Ramadan (AR)

BM(kg)

Temperature(8C)

Pmax(W . kg21)

F0(kg)

V0(rev . min21)

Ppeak(W . kg21

BR07:00 h 71.3+ 7.3 36.0+ 0.4 11.7+ 1.5 15.4+ 1.3 215.2+ 10.7 10.4+ 0.917:00 h 71.1+ 7.3 36.7+ 0.3 12.8+ 1.6 16.6+ 1.5 213.3+ 11.0 11.2+ 1.021:00 h 71.5+ 7.1 36.9+ 0.3 12.3+ 1.3 16.1+ 1.4 215.1+ 8.8 11.2+ 0.5

SWR07:00 h 72.0+ 7.1 36.2+ 0.4 11.6+ 1.3 15.2+ 1.4 217.0+ 9.0 10.3+ 0.5

17:00 h 71.8+ 7.3 36.6+ 0.5 12.3+ 1.3 15.7+ 1.4 218.9+ 8.7 10.8+ 1.321:00 h 72.0+ 7.2 36.7+ 0.3 12.2+ 1.1 16.2+ 1.7 215.1+ 8.8 10.7+ 0.8

ER07:00 h 71.8+ 7.0 36.1+ 0.4 11.8+ 1.2 15.5+ 1.1 215.5+ 6.5 10.2+ 0.817:00 h 71.6+ 7.3 36.3+ 0.5 11.7+ 1.2 15.4+ 1.1 213.1+ 10.5 10.5+ 1.121:00 h 71.8+ 7.3 36.6+ 0.3 11.9+ 1.1 15.7+ 0.8 213.6+ 4. 8 10.4+ 0.8

AR07:00 h 71.6+ 7.4 36.0+ 0.7 11.5+ 1.1 15.2+ 1.8 216.1+ 7.5 10.2+ 0.817:00 h 71.7+ 7.3 36.6+ 0.2 12.5+ 1.1 16.4+ 1.7 215.2+ 12.8 10.6+ 1.021:00 h 71.7+ 6.8 36.6+ 0.2 12.4+ 0.9 15.9+ 1.2 218.0+ 10.9 10.7+ 0.7

Note: n 12 subjects.Significant difference in comparison with the morning; significant difference in comparison with before Ramadan at

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Temperature

The two-way ANOVA revealed a significant time-of-day effect(F(2,22) 55.02; p , 0.001). There was also a significant Ramadan effect(F(3,33) 9.3; p , 0.001) and a significant Ramadan time-of-day of testinteraction (F(6,66) 2.84; p , 0.05; see Figure 1). The post hoc testrevealed that oral temperature increased between morning and evening(p , 0.001) before Ramadan, in the second and fourth weeks ofRamadan, and two weeks after Ramadan. The increase was greater

before Ramadan (0.9+ 0.28C) than during SWR (0.6+ 0.38C) and ER

(0.6+ 0.28C) (p,

0.05). During Ramadan, in comparison with BR, oraltemperature was not affected in the morning. However, there was a signifi-cant decrease in oral temperature for ER at 17:00 and 21:00 h (p , 0.05).

TABLE 2 Mean (+ SD) Values for Daily Nutrient Consumption before Ramadan (BR), in the SecondWeek of Ramadan (SWR), in the Fourth Week of Ramadan (ER), and after Ramadan (AR)

BR SWR ER AR

Energy (kcal/d) 2899+ 403 2966+ 302 2834+ 291 2845+ 256Protein (g/d) 91.6+ 12.4 92.5+ 10.4 90.3+ 8.1 91.6+ 10.7Protein (%) 12.7+ 0.6 12.5+ 0.7 12.7+ 0.7 12.9+ 0.7Lipid (g/d) 101.6+ 18.4 103.7+ 13.5 98.5+ 11.2 100.3+ 11.8Lipid (%) 31.4+ 1.5 31.4+ 1.7 31.3+ 1.2 31.7+ 1.2Carbohydrate (g/d) 404.6+ 48.7 415.7+ 40.3 396.6+ 43.5 394.1+ 30.1Carbohydrate (%) 56.0+ 1.6 56.1+ 1.7 56.0+ 1.3 55.5+ 1.7

FIGURE 1 Mean values for oral temperature (n 12 subjects) at the three times of the day beforeRamadan (BR), in the second week of Ramadan (SWR), in the fourth week of Ramadan (ER), and

after Ramadan (AR).


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Force-Velocity Test

For Pmax, there was a significant time-of-day effect (F(2,22) 29.75;p , 0.001). There was also a significant Ramadan effect (F(3,33) 2.44;p , 0.05), and a significant Ramadan time-of-day of test interaction(F(6,66) 8.07; p , 0.01; see Figure 2). The effect size hp

2 was at 0.84,0.52, and 0.65 for time-of-day, Ramadan, and the interaction betweenthe two, respectively. Therefore, the partial eta-squared indicated thatthe variation in Pmax was directly attributable to time-of-day (84%), toRamadan (52%), and to the interaction between the two (65%). The posthoc test revealed that Pmax improved between morning and evening(p , 0.001) before Ramadan, during the second week of Ramadan, and

two weeks after the end of Ramadan. However, the diurnal variation dis-appeared during the fourth week of Ramadan. Pmax did not decrease inthe morning during Ramadan compared to BR. However, there was a sig-nificant decrease in Pmax in the second and fourth weeks of Ramadan at17:00 h and in the fourth week at 21:00 h. A significant positive correlationwas found between oral temperature and Pmax (r 0.67; p , 0.001).

There was a significant (F(2,12) 15.65; p , 0.001) time-of-day effectfor F0 but no significant effect for Ramadan. However, there was a signifi-cant Ramadan time-of-day of the test interaction (F(6,66) 3.78;

p , 0.01), as seen in Figure 3, with post hoc tests showing that F0 improvedsignificantly from morning to evening before Ramadan, in the secondweek of Ramadan, and two weeks after the end of Ramadan. Thesediurnal fluctuations disappeared during the fourth week of Ramadan. F0did not decrease during Ramadan at 07:00 h and 21:00 h. However,

FIGURE 2 Mean+ SE values for Pmax (n 12 subjects) at the three times of the day before Ramadan(BR), in the second week of Ramadan (SWR), in the fourth week of Ramadan (ER), and after Ramadan

(AR).


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there was a significant decrease in F0 in the second and fourth weeks ofRamadan at 17:00 h in comparison with BR. Additionally, V0 was unaf-fected by Ramadan, time-of-day of test, or by the interaction betweenthe two.

Wingate Test

There was a significant effect of time-of-day (F(2,22) 5.9; p , 0.01)and Ramadan (F(3,33) 4.7;p , 0.01) on Ppeak. However, there was no sig-nificant Ramadan time-of-day of the test interaction (p . 0.05; seeFigure 4). The effect size hp

2 was at 0.37, 0.49, and 0.11 for time of day,Ramadan, and the interaction between the two, respectively. Therefore,partial eta-squared indicated that the variance in Ppeak was associatedwith changes in time-of-day (37%) and in Ramadan (49%). However,there was a low impact (11%) of the interaction of time-of-day andRamadan. Ppeak improved significantly from morning to evening(p , 0.05) in BR and SWR. However, it was not affected by time-of-dayin ER and AR. In comparison with BR, no significant difference wasobserved in Ppeak during Ramadan at 07:00 h (p . 0.05), but Ppeak was sig-nificantly lower in SWR, ER, and AR at 17:00 and 21:00 h (p , 0.05). A sig-nificant positive correlation was found between oral temperature and Ppeak(r 0.64; p , 0.001).

There was also a significant time-of-day effect (F(2,22) 6.8; p , 0.01)and Ramadan effect (F(3,33) 5.3; p , 0.01) on Pmean. However, therewas no significant Ramadan time-of-day of the test interaction

(p . 0.05; see Figure 5). The effect size hp2 was at 0.41, 0.26, and 0.04

FIGURE 3 Mean+ SE values for F0 (n 12 subjects) at the three times of the day before Ramadan(BR), in the second week of Ramadan (SWR), in the fourth week of Ramadan (ER), and after Ramadan(AR).


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for time-of-day, Ramadan, and the interaction between the two, respect-ively. Therefore, partial eta-squared indicated that the variation in Pmeanwas directly attributable to time-of-day (41%) and to Ramadan (26%).

However, there was a low impact (4%) of the interaction of time-of-dayand Ramadan. Pmean improved significantly from morning to evening(p , 0.05) in BR, SWR, and AR; however, it was not affected by time-of-day in ER. In comparison to BR, no significant difference was observed

FIGURE 4 Mean+ SE values for Ppeak (n 12 subjects) at the three times of the day before Ramadan(BR), in the second week of Ramadan (SWR), in the fourth week of Ramadan (ER), and after Ramadan(AR).

FIGURE 5 Mean+ SE values for Pmean (n 12 subjects) at the three times of day before Ramadan(BR), in the second week of Ramadan (SWR), in the fourth week of Ramadan (ER), and after Ramadan

(AR).


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during Ramadan at 07:00 h (p . 0.05), but Pmean was significantly lower inER at 17:00 and 21:00 h (p , 0.05). However, P

meanwas not affected

during SWR. A significant positive correlation was found between oraltemperature and Pmean (r 0.66; p , 0.001).

Power decrease was unaffected by Ramadan, time-of-day of the test, orthe interaction between the two.

DISCUSSION

This study was designed to investigate the effect of Ramadan onanaerobic performance at different times of the day. The results showthat Ramadan modifies the diurnal pattern of anaerobic performance by

decreasing performance in the evening and afternoon but not in themorning.

In the present study, the Ppeak and Pmean were higher in the eveningthan in the morning before Ramadan. These results are consistent withprevious reports (Hill & Smith, 1991; Melhim, 1993; Souissi et al.,2004). However, not all (Down et al., 1985; Reilly & Down, 1992) previousstudies have used a similar research design. It has been suggested that thestrong level of motivation required from subjects to perform the multiple30 sec Wingate test might interfere with the results and therefore minimizethe time-of-day effect (Reilly & Down, 1992). Moreover, the time-of-day

effect on Pmax during the F-V test in this study also agrees with previousfindings (Bernard et al., 1998; Souissi et al., 2004). In the present study,F0 fluctuated during the day; however, V0 was did not vary. Theseresults agree with previous research (Bernard et al., 1998) and indicatethat the diurnal variation in Pmax may be dependent on the diurnal vari-ation in F0. It has been suggested that the higher value of Pmax, Ppeak,and Pmean in the evening may be linked to changes in body temperature(Bernard et al., 1998; Melhim, 1993). In support of this hypothesis, oraltemperature was found to be higher in the evening than in the afternoon,and a correlation between the oral temperature measured at rest beforethe test and the anaerobic cycling performance was also found. Althoughthe exact mechanisms of this relationship are not known, it has beensuggested that higher body temperature may enhance metabolic reactions,increase the extensibility of connective tissue, reduce muscle viscosity, andincrease conduction velocity of action potentials (Shephard, 1984).Indeed, Bergh & Ekblom (1979) demonstrated that maximal anaerobicpower drops by 5% for every 18C drop in muscle temperature inwarming and cooling experiments.

The time-of-day effect observed for oral temperature persistedthrough Ramadan; however, the differences between morning andevening were significantly lower (20.38C; p , 0.05) than before

Ramadan. It has previously been suggested that large changes in


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environmental temperature may affect physical performance (Racinaiset al., 2004, 2005a). However, as there was only a small change in environ-mental temperature conditions (288C to 268C; data from the NationalInstitute of Meteorology, Tunisia) during this experiment, it is probablethat other factors explain this change. It is most likely Ramadan directlyaffects the circadian rhythm of temperature, with a delay in the occurrenceof the acrophase and reduction in amplitude. In agreement with previousresearch (Roky et al., 2001), these results suggest that all the circadiansystems may also be affected by the exclusive evening meals and byrepeated partial sleep deprivation as previously shown.

The present study showed that the performances of the Wingate andF-V tests were unaffected in the morning. However, it was also demon-

strated that Ramadan fasting was associated with reduced anaerobicpower compared with the control period, both in the afternoon andevening. Muscle power is mainly determined by its structure, myosin com-position, and metabolic factors related to phosphagen stores and velocityof ATP hydrolysis (Bigard et al., 1998). As there is no change in the levelof exercise performed by participants during the whole experiment, it isnot clear why Ramadan would affect anaerobic performances only in theafternoon and evening. An effect of diet cannot be excluded, but ourresults show that daily energy intake and macronutrients intake did notchange in our experiment. These observations agree with some (Elati

et al., 1994), but not all (Angel & Schwartz, 1975; Husain et al., 1987), pre-vious studies that show a decrease in total energy intake. A hypo-energydiet may affect muscular performance, probably by progressive glycogendepletion (McMurray et al., 1991; Takeuchi et al., 1985). However, ithas been demonstrated that a short period of energy restriction, even ifit induced a decrease in muscle and liver glycogen stores, did not altermuscle strength and anaerobic power (Bigard et al., 1993; Symons &

Jacobs, 1989).Partial sleep deprivation can be expected to occur in Ramadan.

However, several studies have also reported that brief, supramaximal,exercise performance can be maintained under sleep deprivation(Mougin et al., 1996; Symons et al., 1988a, 1988b, Takeuchi et al.,1985). In contrast, we demonstrated that one nights sleep deprivationimpaired anaerobic performance during both Wingate and force-velocitytests at 18:00 h, but not in at 06:00 h (Souissi et al., 2003). The presentresults demonstrate anaerobic performances are affected only in theevening and afternoon but not in the morning during Ramadan, whichmay be explained by the same phenomenon. Taken collectively, theseresults suggest that Ramadan might act directly on the circadian rhythmof anaerobic performance by affecting both the acrophase and amplitudeof the proposed circadian rhythm of Ppeak, Pmean, and Pmax. Unfortunately

this experimental design only employed three testing times of the day,


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which is not be enough to verify this hypothesis. Another possible expla-nation for the decrease in performance at 17:00 and 21:00 h is thatRamadan increases fatigue at these times of day. During a normal day,fatigue has been shown to be higher in the afternoon than morning(Nicolas et al., 2005), and this time-of-day effect could have been enhancedduring Ramadan, leading to a reduced capacity to maintain effort at thehighest level.

It is possible that the decrease in power during Ramadan may occurbecause participants are less motivated and less aroused. Sleep deprivationprimarily affects the higher cognitive centers of the central nervous system(Bonnet, 1980), and motivation is a key factor in the validity of tests ofanaerobic power and capacity. The classic observation of Ikai & Steinhaus

(1961) showed how maximum voluntary muscular contraction is closelydependent on the level of arousal in the individual being tested. Theimpact of diurnal variation in arousal upon muscular performance isalso well documented (Shephard, 1984). Sleep deprivation bothdampens and distorts the normal circadian cycle of arousal, with a decreaseof alpha wave activity on the electroencephalogram (Akerstedt, 1979;Kollar et al., 1966; Shephard, 1984). The lack of an effect of Ramadanon Ppeak, Pmean, and Pmax in the morning may be due to the fact that motiv-ation and arousal are less affected by partial sleep loss in the morning thefollowing day. However, the mechanism whereby Ramadan only decreases

anaerobic performance in the afternoon and evening is not clear. Furtherstudies are needed to address the mechanism underlying the effect ofRamadan on anaerobic performance.

In conclusion, the time-of-day effect in anaerobic power variables tendsto disappear during Ramadan. Ramadan fasting impaired anaerobic per-formance in the afternoon and evening; however, the morning perform-ance on the Wingate and F-V tests were unchanged during Ramadan.Some involvement of circadian rhythm impairment is suspected.

ACKNOWLEDGMENTS

The authors wish to express their sincere gratitude to DouglasMcCarthy (Open Globe) for his help with the English reading of the manu-script and to all the participants for their maximal effort and cooperation.

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