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Purpose: To compare the effect of a 20-minute nap opportunity (N20), a moderate dose of caffeine (CAF; 5 mg·kg-1), or a moderate dose of caffeine before N20 (CAF+N) as possible countermeasures to the decreased performance and the partial sleep deprivation-induced muscle damage. Methods: Nine male, highly trained judokas were randomly assigned to either baseline normal sleep night, placebo, N20, CAF, or CAF+N. Test sessions included the running-based anaerobic sprint test, from which the maximum (Pmax), mean (Pmean), and minimum (Pmin) powers were calculated. Biomarkers of muscle, hepatic, and cardiac damage and of enzymatic and nonenzymatic antioxidants were measured at rest and after the exercise. Results: N20 increased Pmax compared with placebo (P < .01, d = 0.75). CAF+N increased Pmax (P < .001, d = 1.5; d = 0.94), Pmin (P < .001, d = 2.79; d = 2.6), and Pmean (P < .001, d = 1.93; d = 1.79) compared with placebo and CAF, respectively. Postexercise creatine kinase increased whenever caffeine was added, that is, after CAF (P < .001, d = 1.19) and CAF+N (P < .001, d = 1.36). Postexercise uric acid increased whenever participants napped, that is, after N20 (P < .001, d = 2.19) and CAF+N (P < .001, d = 2.50) and decreased after CAF (P < .001, d = 2.96). Conclusion: Napping improved repeated-sprint performance and antioxidant defense after partial sleep deprivation. Contrarily, caffeine increased muscle damage without improving performance. For sleep-deprived athletes, caffeine before a short nap opportunity would be more beneficial for repeated sprint performance than each treatment alone.
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Caffeine Use or Napping to Enhance Repeated Sprint
Performance After Partial Sleep Deprivation: Why Not Both?
Mohamed Romdhani, Nizar Souissi, Imen Moussa-Chamari, Yassine Chaabouni, Kacem Mahdouani,
Zouheir Sahnoun, Tarak Driss, Karim Chamari, and Omar Hammouda
Purpose:To compare the effect of a 20-minute nap opportunity (N20), a moderate dose of caffeine (CAF; 5 mg·kg
1
), or a
moderate dose of caffeine before N20 (CAF+N) as possible countermeasures to the decreased performance and the
partial sleep deprivationinduced muscle damage. Methods:Nine male, highly trained judokas were randomly assigned to
either baseline normal sleep night, placebo, N20, CAF, or CAF+N. Test sessions included the running-based anaerobic sprint
test, from which the maximum (P
max
), mean (P
mean
), and minimum (P
min
) powers were calculated. Biomarkers of muscle,
hepatic, and cardiac damage and of enzymatic and nonenzymatic antioxidants were measured at rest and after the exercise.
Results:N20 increased P
max
compared with placebo (P<.01, d= 0.75). CAF+N increased P
max
(P<.001, d= 1.5; d= 0.94),
P
min
(P<.001, d= 2.79; d= 2.6), and P
mean
(P<.001, d= 1.93; d= 1.79) compared with placebo and CAF, respectively.
Postexercise creatine kinase increased whenever caffeine was added, that is, after CAF (P<.001, d= 1.19) and CAF+N
(P<.001, d= 1.36). Postexercise uric acid increased whenever participants napped, that is, after N20 (P<.001, d= 2.19) and
CAF+N (P<.001, d= 2.50) and decreased after CAF (P<.001, d= 2.96). Conclusion:Napping improved repeated-sprint
performance and antioxidant defense after partial sleep deprivation. Contrarily, caffeine increased muscle damage without
improving performance. For sleep-deprived athletes, caffeine before a short nap opportunity would be more benecial for
repeated sprint performance than each treatment alone.
Keywords:sleep restriction, daytime sleep, psychostimulant, RSA, inammation, antioxidant status
Several studies have reported that physical performances are
affected by partial sleep deprivation (PSD).
16
PSD reduces aerobic
intermittent,
1,2
time to exhaustion,
3,4
short-term all-out,
5
and
repeated sprint
6
performances. Several studies have found that
PSD caused by awakening at the end of the night had more
deleterious effects than PSD caused by a late bedtime on repeated
sprint performance during the postlunch dip (PLD).
1,3,6
Morning
performances were unaffected by PSD
1,5
, however, exercise per-
formed during or after the PLD would be affected by the PSD.
36
The interaction between the 2 process models of sleep regulation is
believed to be behind the previously mentioned outcomes.
7
Indeed,
sleep pressure increases exponentially with increased wakefulness
duration (homeostatic process S). Also, the PLD corresponds to the
secondary peak in sleepiness (circadian process C). Especially after
suboptimal nocturnal sleep, sleepiness increases and performance
decreases during the PLD.
8
Thus, PLD seems to be the perfect time
to nap, because sleep propensity is higher and sleep latency is
shorter.
9
Furthermore, PSD increases muscle, hepatic, and cardiac
damage and decreases antioxidant defense after a single bout of
exercise,
3,6,10
which would potentially affect recovery. Therefore,
upcoming training and competition would be potentially affected
by the incomplete recovery process.
10
Because PSD is very common
among athletes before major competitions,
11
the need to nd
strategies to reduce the negative effects of PSD on performance
and the increased cellular damage is paramount. Therefore, the
primary intent would be totake a nap or consume a psychostimulant.
It has been reported that even a short nap could be an efcient
countermeasure to sleep lossinduced sleepiness.
4,8,1216
Naps of no
longer than 20 minutes can restore cognitive impairment caused by
more than 16 hours of extended wakefulness.
17
From several studies,
20 minutes is regarded as the perfect duration of a nap, because it is
long enough to reduce sleepiness and short enough to prevent sleep
inertia.
4,8,13,1618
Sleep inertia is the groggy feeling that occurs at
awakening.
19
Its severitydepends on several factors such as the sleep
stage at awakening, the length of prior wakefulness, and the time of
day (for an extensive review, cf Hilditch et al
19
).
Napping has recently received increasing attention in sport
performance.
4,8,16,2023
Results range from improving various
physical performances
4,8,16,2022
to neutral effects.
23
It has been
suggested that the benecial effect of napping depends on athletes
need for sleep.
20
Napping would improve performance only for
athletes with suboptimal sleep. Likewise, napping reduces sleep
lossinduced pain sensitivity
18
and normalizes the effect of PSD on
cortisol,
24
norepinephrine,
18
and interleukin-6.
18,24
However, only
a few studies have examined the effect of napping on biochemical
response to exercise.
16,21
The latter investigations reported
Chamari and Hammouda participated equally in the study. Romdhani and Souissi are
with the High Inst of Sport and Physical Education, Ksar-Said, Manouba University,
Manouba, Tunisia; and Physical activity, Sport and health, UR18JS01, National
Observatory of Sports, Tunis, Tunisia. Moussa-Chamari is with the Physical Educa-
tion Dept, College of Education, Qatar University, Doha, Qatar. Chaabouni and
Mahdouani are with the Dept of Biochemistry, CHU Ibn Jazzar, Kairouan, Tunisia;
and the Laboratory of Analysis, Treatment and Valorization of Pollutants of the
Environment and Products (LATVEP), Faculty of Pharmacy, University of Monastir,
Monastir, Tunisia. Sahnoun is with the Laboratory of Pharmacology, Faculty of
Medicine, University of Sfax, Sfax, Tunisia. Driss is with the Research Center on
Sport and Movement (Centre de Recherches sur le Sport et le Mouvement, CeRSM),
UPL, UFR STAPS, Université Paris Nanterre, Nanterre, France. Chamari is with
Aspetar, Qatar Orthopaedic and Sports MedicineHospital, Doha, and ''OPS Research
Lab'', CNMSS, Tunis, Tunisia. Hammoudais with the High Inst of Sport and Physical
Education, University of Sfax, Sfax, Tunisia. Romdhani (romdhaniroma@gmail
.com) is corresponding author.
1
International Journal of Sports Physiology and Performance, (Ahead of Print)
https://doi.org/10.1123/ijspp.2019-0792
© 2021 Human Kinetics, Inc. ORIGINAL INVESTIGATION
conicting results regarding the effects of napping on sleep loss
induced inammation after exercise. Therefore, the effect of napping
on the biochemical response to exercise warrants further
investigation.
On the other hand, caffeine is the most widely consumed
psychostimulant in the world.
25
It offsets physical and cognitive
degradation with sleep loss.
25
However, data on the effects of
caffeine ingestion on short-term high-intensity performance are
controversial.
25
It has been reported that a moderate dose of
caffeine increased,
26
decreased,
27
or had no effects
28
on repeated
sprint exercise (cf McLellan et al
25
for an extensive review).
Despite the large number of studies, the effects of caffeine on
the biochemical responses to exercise have shown contradictory
ndings. Caffeine may have anti-inammatory
29
or prooxidant
30,31
properties, and some studies have shown neutral effects of caffeine
on biomarkers of muscle injury.
32
Thus, the effect of caffeine
ingestion on repeated sprint performance and the associated bio-
chemical response to the exercise warrants more studies.
When multicomponent interventions were studied, the com-
bination of caffeine with a short nap resulted in better psychocog-
nitive performance than each intervention alone.
1315
Orally
ingested caffeine goes into action 30 minutes after ingestion
and has a long half-life (210 h).
33
Thus, caffeine should be
ingested shortly before a 20-minute nap to prevent it from dis-
turbing sleep and to maximize the gains obtained from nap.
13,14
To
the best of the authorsknowledge, the effects of a combination of
caffeine and a short nap were not tested for physical performance.
Therefore, the current study aimed to investigate the effect of a 20-
minute nap (N20), a moderate dose of caffeine (CAF; 5 mg·kg
1
),
and the combination of N20 with CAF (CAF+N) as possible
countermeasures to performance decrement during the PLD and
biochemical disruption after PSD.
Methods
Participants
First, 13 highly trained male judokas fullled the inclusion criteria
(nonhabitual nappers, nonsmokers, and caffeine naïve, ie, 80 mg
of caffeine·d
125
), volunteered to participate, and completed the
protocol. Only 9 participantsdata are included in the analysis
(18.78 [1.09] y, 170.83 [5.87] cm, 68.44 [6.19] kg, body mass
index = 23.42 [1.24] kg·m
2
). They were regularly engaged in
2 hours per day, 5 days per week of training (including high-
intensity intermittent training) and participated in competitions for
at least 5 years. Participants were recruited according to their
chronotype, explored via a morningness/eveningness questionnaire.
34
Only athletes with moderate and intermediate chronotypes (ie, those
who scored between 31 and 69 on the morningness/eveningness
questionnaire) were recruited. During the month preceding the experi-
ment, sleep diaries were collected (retiring and rising time, time in bed,
sleep latency, and waking frequency and duration). Only participants
who scored 5 on the Pittsburg Sleep Quality Index were recruited, to
avoid the involvement of participants with poor sleep.
35
The present
study was conducted according to the ethical guidelines of the
Declaration of Helsinki (64th World Medical Association General
Assembly, Fortaleza, Brazil, October 2013). The Manouba Univer-
sity Review Board approved the protocol (P-SC no. 009/15). All
participants were informed about the study design and potential risks
and signed an informed consent before the assessments began.
Participants were also informed about their right to withdraw
from the study at any time without any penalty.
Experimental Design
Before starting the main experimental protocol, participants under-
went 2 habituation sessions, in which they were familiarized with
the experimenters, laboratory, materials, napping room, tests, and
questionnaires (Figure 1).
Participants performed 5 test sessions 1 week apart in a
randomized and counterbalanced order. They were assigned to
either baseline normal sleep night, placebo (PLA), 20-minute nap
with PLA ingestion (N20), intake of 5 mg·kg
1
of caffeine without
napping (CAF), and intake of 5 mg·kg
1
of caffeine before N20
(CAF+N; Figure 1). During each session, participants came to the
laboratory at 2000 hours, ate a standardized dinner at 2030 hours,
and performed 90 minutes of free activity until 2200 hours, when
they were asked to go bed (ie, all lights and devices off). Except for
normal sleep night, when participants had a full sleep night (ie, time
in bed between 2200 hours and 0630 hours), all sessions were
undertaken after a PSD night (ie, time in bed between 2200 hours
and 0230 hours). They ate a standardized breakfast at 0700 hours.
After this, they were asked to not consume food, but water was
allowed ad libitum. They stayed awake until 1200 hours doing
passive activities (eg, watching television, playing cards or video
Figure 1 Simplied experimental protocol. All times are expressed in local time (GMT+1 h). CAF indicates 5 mg·kg
1
of caffeine; CAF+N,
5 mg·kg
1
of caffeine + 20-minute nap; N20, 20-minute nap with placebo; NSN, normal sleep night; PLA, partial sleep deprivation with placebo; RAST,
the running-based anaerobic sprint test.
(Ahead of Print)
2Romdhani et al
games, or reading). At 1200 hours, they ate a standardized isocaloric
lunch and reclined in a comfortable armchair. At 1400 hours,
participants in the nap condition entered the room that was condu-
cive to sleep (comfortably warm, fully dark, and quiet). At this time,
volunteers ingested 5 mg·kg
1
of pure powdered caffeine for CAF
+N or cellulose and starchbased PLA for N20.
13,14
The desired
amount of caffeine was measured with a specic Shimadzu (Shi-
madzu Corporation, Kyoto, Japan) electronic weighing machine
(±0.1 mg) and put into capsules to match PLA in weight, color, and
smell. After this, participants wore earplugs and eye masks and got
into bed, and they were allowed to 20-minute nap opportunity (from
1410 hours to 1430 hours). Participants in the no-nap condition
ingested caffeine or PLA at the same time (ie, 1400 hours). Constant
supervision was performed via an infrared camera connected, in real
time, to the experimenters computer. When the nap period elapsed,
participants were awakened by an alarm placed next to the bed. At
awakening, participants subjectively rated their sleep on a 100-mm
visual analog scale ranging from 0 (no sleep at all) to 100 (deep,
uninterrupted sleep). Four participantsdata were excluded from the
analysis because they were unable to fall asleep (scored 0 on the
visual analog scale). After the awakening, 30 minutes was allowed
for participants to overcome any sleep inertia.
8,16
Participants spent
the same period in the PLA and normal sleep night conditions
(ie, from 1400 hours to 1500 hours) watching a neutral documentary
while reclining in a comfortable armchair. Finally, the running-
based anaerobic sprint test (RAST) started at 1500 hours, followed
by a postexercise (ie, 5 min of passive recovery) blood sampling.
Participants completed the protocol during the postseason
period (April and May). At this time of year, daytime lasted
1306 hours (±21 min), because the sun rose at 0546 hours
(±12 min) and set at 1852 hours (±14 min). Participants simulta-
neously completed the nap in separate rooms, and they were
instructed to perform the same passive activities on sleep depriva-
tion nights. Laboratory conditions were set at temperature 25°C
(±1.8°C), humidity 35% (±3.2%), and luminosity (1) 2000 lux
during tests and (2) <5 lux during sleep.
Protocols
The Running-Based Anaerobic Sprint Test. The RAST was
developed by Draper and Whyte.
36
Its performance was correlated
to the Wingate test, and it can predict short-distance performance.
37
It is composed of 6 maximal all-out repeated sprints of 6to7
seconds interspersed with 10-second recovery periods, which is
similar to the effort during judo combat.
38
The RAST protocol
was followed according to the guidelines developed by the Uni-
versity of Wolverhampton, United Kingdom, and as described by
Romdhani et al.
6,16
Rating of Perceived Exertion. The CR-10 psychophysiological
scale allowed experimenters to assess the exertion experienced by
the athletes during the RAST.
39
Blood Sampling. Blood samples were collected and analyzed as
described by Romdhani et al.
6,16
All methods used in the sample
analysis are presented in Table 1.
Statistical Analyses. The statistical tests were processed in
GraphPad Prism 6 (GraphPad Software, San Diego, CA). All
values in the text, gures, and tables are reported as mean (SD).
The ShapiroWilks test revealed that data were normally distrib-
uted, and therefore parametric tests were used. For subjective sleep
quality, RAST performances, and [La], a 1-way analysis of vari-
ance (ANOVA) with repeated measures (5 conditions) was used.
For the remaining biochemical parameters, a 2-way ANOVA with
repeated measures was used (5 conditions ×2timingbefore and
after exercise). To assess the ANOVA practical signicance, partial
eta squared (η2
p) was calculated. When the ANOVA indicated a
signicant main effect or an interaction, the Bonferroni post hoc
test was used. In addition, the effect size (d) was calculated for
pairwise comparisons according to Cohen.
40
The magnitude of dwas
classied under the following thresholds: small (0.2 d0.5),
moderate (0.5 d0.8), and large (d0.8).
40
Further, mean differ-
ence (MD) and the 95% condence interval (95% CI) were provided
for pairwise comparison. The level of signicance was set at P<.05.
Results
Subjective Sleep Quality During the Nap
The 1-way ANOVA showed a signicant main effect of condition
on subjective sleep quality during the nap (F
2,7
= 41.1; P<.001;
η2
p=.83). There was no signicant difference between N20 (35.67
Table 1 Different Methods Used in Blood Analysis
Biochemical
variables Method
[La] Lactate oxidase peroxidase method (intraassay and interassay CVs were 0.9% and 1.9%, respectively)
GLC Glucose hexokinase method (intraassay and interassay CVs were 0.94% and 1.3%, respectively)
AST Kinetic method at 340 nm
CK Kinetic method at 340 nm
LDH NADH consumption method (intraassay and interassay CVs were 3.7% and 4.31%, respectively)
UA Colorimetric endpoint (intraassay and interassay CVs were 1.55% and 1.76%, respectively)
GPx Spectrophotometric method based on Paglia and Valentine method (1967; with kit from Randox Lab [Randox Laboratories
Ltd., Crumlin County Antrim, UK]; Ransel RS. 505). The intraassay and interassay CVs were 7.3% and 4.86%, respectively.
SOD SOD activity in erythrocytes was measured by the rate of inhibition of 2-(4-iodophenyl)-3-(4-nitrophenol)-5-phenyltetrazolium
chloride reduction. The kit used in this method was from Randox Lab (Ransod, RX MONZA). About 0.5 mL of whole blood was
centrifuged and then separated from the plasma. Erythrocytes were washed 4 times with 3 mL of 0.9% NaCl solution and centrifuged
after each wash. Then, 2.0 mL with cold redistilled water was added to the resulting erythrocytes, mixed, and left to stand at +4°C for
15 min. A 25-fold dilution of lysate was then added. The intraassay and interassay CVs were 5.96% and 4.64%, respectively.
Abbreviations: AST, aspartate aminotransferase; CK, creatine kinase; CV, coefcient of variation; GLC, plasma glucose; GPx, glutathione peroxidase; [La], plasma lactate;
LDH, lactate dehydrogenase; SOD, superoxide dismutase; UA, uric acid.
(Ahead of Print)
Caffeine and Napping for Short-Term Performance 3
[14.21]) and CAF+N (28.97 [9.24]) in the subjective sleep scores
(P= .667). However, sleep scores for N20 and CAF+N were
statistically higher than those for PLA and CAF (P<.001 for all).
RAST Performances
There was a signicant main effect on P
max
(F
2,7
= 35.5; P<.001;
η2
p=.91), P
mean
(F
2,7
=195.6; P<.001; η2
p=.97), and P
min
(F
2,7
=46.4; P<.001; η2
p=.93). P
max
increased after N20 (P<.01,
d=0.75, MD = 82.4 W; 95% condence interval [CI], 177.3 to
12.5 W) and CAF+N (P<.001, d=1.5, MD=101.1 W; 95% CI,
163.7 to 38.6 W) compared with PLA (Figure 2A). Furthermore,
P
max
increased after CAF+N compared with N20 (P<.001, d=0.89,
MD = 82.4 W; 95% CI, 259to24.8W)andCAF(P<.001,
d= 0.94, MD = 129.3 W; 95% CI, 302.2 to 42.4 W). P
min
increased after CAF+N compared with PLA (P<.001, d=2.79,
MD = 111.3 W; 95% CI, 185 to 37.6 W), N20 (P<.01,
d= 1.31, MD = 69.1 W; 95% CI, 123.9 to 5.6 W), and CAF
(P<.001, d=2.6, MD=125.8 W; 95% CI, 181 to 70.5 W).
P
mean
increased (Figure 2B) after CAF+N compared with PLA
(P<.001, d=1.93, MD=89.5 W; 95% CI, 165.1 to 13.9 W),
N20 (P<.001, d=1.2,MD=75.6 W; 95% CI, 132.5 to 17.1 W),
and CAF (P<.001, d=1.79, MD=95 W; 95% CI, 112 to
77.9 W) (Figure 2C). Rating of perceived exertion and Fatigue
index were unaffected by neither condition.
Plasma Lactate
There was a signicant main effect on plasma lactate ([La];
F
2,7
=32.03; P<.001; η2
p=.92). [La] increased after N20 (P= .008,
d=1.48, MD = 1.15 mmol·L
1
; 95% CI, 2.46 to 0.15 mmol·L
1
)
and CAF+N (P<.001, d= 2.53, MD =3.16 mmol·L
1
;
95% CI, 4.9 to 1.3 mmol·L
1
) compared with PLA (Figure 2D).
Biomarkers of Muscle and Hepatic Damage
and Glucose
ANOVA revealed a signicant interaction between exercise
and condition on aspartate aminotransferase (AST; F
4,32
=8.75;P<
.001; η2
p=.68), creatine kinase (CK; F
4,32
= 11.53; P= .009; η2
p=
.63), lactate dehydrogenase (LDH; F
4,32
= 9.73; P= .011; η2
p=.61),
and plasma glucose (GLC; F
4,32
= 13.77; P= .004; η2
p=.79). Postex-
ercise AST increased after all sessions (Figure 3A), with lower levels
after N20 compared with PSD (P<.001, d= 2.14, MD = 18.22 U·L
1
;
95% CI, 7.4 to 29.04 U·L
1
). Postexercise CK (Figure 3B)increased
only after CAF (P<.001, d= 1.19, MD =153.8 U·L
1
; 95% CI,
222.5 to 85.05 U·L
1
) and CAF+N (P<.001, d=1.36,
MD = 103.7 U·L
1
; 95% CI, 172.4 to 34.94 U·L
1
). Postexercise
LDH increased after CAF+N (P<.001, d= 1.72, MD = 126.4
UI·L
1
; 95% CI, 199.2 to 53.7 UI·L
1
) compared with rest
(Figure 3C). Postexercise GLC increased whenever caffeine was
added (Figure 3D), whether after CAF (P<.001, d=1.59,
MD = 1.39 mmol·L
1
; 95% CI, 2.2 to 0.5 mmol·L
1
)orafter
CAF+N (P<.001, d= 2.86, MD =2.3 mmol·L
1
; 95% CI, 3.1 to
1.5 mmol·L
1
).
Enzymatic and Nonenzymatic Antioxidants
There was a signicant interaction between exercise and condition
on superoxide dismutase (SOD; F
4,32
= 8.75; P<.001; η2
p=.68),
Figure 2 Individual maximum (P
max
; A), minimum (P
min
; B), and mean (P
mean
; C) powers and [La] concentrations (D) after different protocol
sessions. CAF indicates 5 mg·kg
1
of caffeine; CAF+N , 5 mg·kg
1
of caffeine + 20-minute nap; N20 , 20-minute nap with placebo ingestion;
NSN , baseline normal sleep night; PLA , partial sleep deprivation with placebo ingestion; [La], plasma lactate; PSD, partial sleep deprivation.
+,++,+++
Signicant difference in comparison with NSN session at P<.05, P<.01, and P<.001, respectively; **
,
***Signicant difference in comparison
with PSD session at P<.01 and P<.001, respectively;
##,###
Signicant difference in comparison with N20 values at P<.01 and P<.001, respectively;
ααα
Signicant difference in comparison with CAF values at P<.001. Bars represent the group means and SD.
(Ahead of Print)
4Romdhani et al
glutathione peroxidase (F
4,32
= 4.89; P<.01; η2
p=.45), and uric
acid (UA; F
4,32
= 11.53; P= .009; η2
p=.63). SOD increased after
N20 (P<.001, d= 1.68, MD = 310.9 unit per gram of hemoglobin
(U·g HB
1
); 95% CI, 563.2 to 58.6 U·g HB
1
) compared with
preexercise levels (Figure 4A). However, postexercise SOD
decreased after CAF session (P<.01, d= 0.77, MD = 294.9 U·g
HB
1
; 95% CI, 42.6 to 547.2 U·g HB
1
) compared with resting
values. Glutathione peroxidase (Figure 4B) increased after N20
compared with resting values (P<.01, d= 1.06, MD = 14.1 U·g
HB
1
; 95% CI, 26.8 to 1.4 U·g HB
1
) and compared with CAF
(P<.05, d= 0.65, MD = 13.7 U·g HB
1
; 95% CI, 0.2 to 27.3 U·g
HB
1
). Postexercise nonenzymatic antioxidant UA increased
whenever participants napped (Figure 4C), that is, after N20
(P<.01, d= 2.19, MD = 54.6 mmol·L
1
; 95% CI, 93.9 to 15.4
mmol·L
1
) and CAF+N (P<.001, d= 2.5, MD = 71.8 mmol·L
1
;
95% CI, 111.1 to 32.6 mmol·L
1
), and deceased after CAF
(P<.001, d= 2.96, MD = 72.8 mmol·L
1
; 95% CI, 33.6 to
112.1 mmol·L
1
).
Figure 3 AST (A), CK (B), LDH (C), and GLC (D) before and after the exercise during different protocol sessions. AST indicates aspartate
amino transferase; CAF, 5 mg·kg
1
of caffeine; CAF+N, 5 mg·kg
1
of caffeine + 20-minute nap; CK, creatine kinase; LDH, lactate dehydrogenase; GLC,
plasma glucose; N20, 20-minute nap with placebo ingestion; NSN, baseline normal sleep night; PLA, partial sleep deprivation with placebo ingestion;
PSD, partial sleep deprivation;
,
••
,
•••
Signicant effect of exercise at P<.05, P<.01, and P<.001, respectively; *
,
**
,
***Signicant difference in
comparison with PSD at P<.05, P<.01, and P<.001, respectively;
#,##,###
Signicant difference in comparison with N20 at P<.05, P<.01, and P<.001,
respectively;
α,αα,ααα
Signicant difference in comparison with CAF at P<.05, P<.01, and P<.001, respectively. Data are presented as Mean (SD).
Figure 4 SOD (A), GPx (B), and UA (C) during different protocol sessions. CAF indicates 5 mg·kg
1
of caffeine; CAF+N, 5 mg·kg
1
of
caffeine + 20-minute nap; GPx, glutathione peroxidase; N20, 20-minute nap with placebo ingestion; NSN, baseline normal sleep night; PLA, partial sleep
deprivation with placebo ingestion; SOD, superoxide dismutase; UA, uric acid;
,
••
,
•••
Signicant effect of exercise at P<.05, P<.01, and
P<.001, respectively; *
,
**
,
***Signicant difference in comparison with PSD at P<.05, P<.01, and P<.001, respectively;
#,##,###
Signicant
difference in comparison with N20 at P<.05, P<.01, and P<.001, respectively;
α,αα,ααα
Signicant difference in comparison with CAF at P<.05,
P<.01, and P<.001, respectively.
(Ahead of Print)
Caffeine and Napping for Short-Term Performance 5
Discussion
The current investigation studied the effects of a 20-minute nap
(N20), the ingestion of 5 mg·kg
1
of caffeine (CAF), and their
combination (CAF+N) on repeated sprint performance (RAST)
and associated biochemical responses in PSD athletes. The main
ndings were that the combination of CAF+N resulted in the
highest RAST performances compared with PLA, CAF, and
N20. Interestingly, CAF increased muscle damage and decreased
antioxidant defense without improving performance. Analyzing
the effect of PSD compared with normal sleep is beyond the scope
of this study, and it is discussed elsewhere.
6
The short nap increased P
max
slightly but signicantly, con-
rming the ndings of earlier studies that reported improved all-out
8
and repeated
16,22
sprint and endurance
4,20
performance after a brief
nap. Also, the current results conrm literature ndings about the
limited effects of caffeine on short-term high-intensity exer-
cise.
25,27,28
Although the ergogenic effect of caffeine is higher in
caffeinenaïve participants,
25
the current results showed that
repeated sprint after CAF was no better than after PLA. Because
the effect of caffeine is dose dependent,
25
it could be possible that the
dosage of caffeine used was not high enough to improve repeated
sprint performance in sleep-deprived participants. To the best of the
authorsknowledge, the current study is the rst to compare the
effect of a short nap with a moderate dose of caffeine on physical
performance outcomes. N20 was more effective than CAF at least
for P
max
, which generally corresponds to the rst sprint of the
RAST. It is possible that napping is more efcient than caffeine at
offsetting the PLD sleep drive buildup and improving repeated
sprint performance of sleepy athletes. Indeed, it has been reported
that the wakefulness-promoting effects of caffeine do not replace the
restorative effects of sleep to the same extent.
41
The combination CAF+N was far more benecial for repeated
sprint than CAF or N20 conditions alone. Likewise, previous
literature has shown that the combination of caffeine with a short
nap was clearly superior to either caffeine alone or napping alone
in maintaining alertness
1315
and driving stimulator tasks
14,15
and
memory search tasks.
13
Carrier et al
42
reported that caffeine
ingestion before daytime sleep reduced the duration and the
intensity of slow wave sleep. In addition, caffeine before a PLD
nap blunted sleep inertia and promoted the benets of napping.
13
Mechanistically, caffeine acts as a nonselective, competitive
antagonist to adenosine receptors.
33
Adenosine is a sleep-pro-
moting substance that increases during wakefulness and modi-
es the neuronal activities in key brain areas that regulate sleep
homeostasis.
43
Caffeine exerts its alerting effects by binding to
adenosine receptors in the central nervous system and antago-
nizing adenosines effects. In addition, napping depresses the
homeostatic buildup of sleep drive (ie, decreases adenosine
concentration). It has been reported that sleep pressure dissipates
at a faster rate during sleep than its accumulation during wake-
fulness.
12
Therefore, it is possible that the double challenge to
adenosine system (ie, the combined effects of napping and
caffeine ingestion) dampened the sleep lossinduced homeo-
static component of sleep drive buildup (process S) more than
each intervention alone.
Plasma lactate showed a similar trend to RAST performance
(Figure 2D). Compared with PLA, postexercise [La] decreased
after CAF sessions, increased slightly after N20, and increased
notably after CAF+N. Thus, [La] increased relatively to exercise
load and was not inuenced by caffeine ingestion per se. However,
postexercise GLC levels increased after caffeine ingestion with or
without napping (Figure 3D). Indeed, it has been shown that
caffeine intake was associated with increased catecholamine levels,
which increase glycogenolysis and thus GLC.
31
In this regard, it
has been consistently reported that caffeine ingestion increases
energy availability and energy expenditure during exercise.
43
Nevertheless, despite the greater energy availability after caffeine
ingestion, repeated sprint performances were not any better than
those after PLA.
Postexercise CK increased whenever caffeine was added, with
or without napping, even when performance declined. Therefore,
the increased CK could be attributed to caffeine ingestion. Accord-
ingly, earlier studies have concluded that caffeine intake may
increase the risk of muscle damage in athletes.
31,44
In that regard,
Tauler et al
31
reported an increased inammatory response to
exercise through higher interleukin-6 and interleukin-10 after
the ingestion of 6 mg·kg
1
of caffeine. In addition, Bassini-Ca-
meron et al
44
reported that AST, LDH, and CK increased in
response to exercise after the ingestion of a similar dosage of
caffeine (ie, 5 mg·kg
1
) compared with PLA. However, in the
present study, the increase in LDH and AST was not caused by
caffeine ingestion. LDH increased concomitantly with the increase
in exercise performance. Also, AST did not increase further after
caffeine ingestion. However, CK increased only when caffeine was
added regardless of napping or exercise performance. With this in
mind, caffeine before repeated sprints should be ingested with
caution.
The present ndings showed a depressed antioxidative
capacity through lower SOD and UA after CAF. During and
after exercise, the generation of reactive oxygen species in-
creases dramatically due to the high metabolic rate and the
increased oxygen uptake. This break in the balance between
the generation and removal of reactive oxygen species creates a
situation known as oxidative stress. Without adequate antioxi-
dant defense, protein, lipid, and nucleic acid may be oxidized,
which causes degenerative diseases. SOD is the rst defensive
line against oxidative stress. Also, UA represents more than
50% of plasmatic antioxidant capacity.
45
Interestingly, napping
reversed the prooxidant effect of caffeine. In fact, enzymatic
(SOD) and nonenzymatic (UA) antioxidants increased after
napping with or without caffeine ingestion. This nding indi-
cates, for the rst time, that napping may produce a good defense
to exercise-induced oxidative damage, even with the consumption of
a prooxidant (ie, caffeine). Therefore, the positive effects of napping
not only improve exercise performance but also reduce the negative
effects of oxidative stress.
The current study was designed to mimic real-life situations in
which athletes and coaches do not perform objective sleep mea-
surement. After suboptimal nocturnal sleep or PSD, a moderate
dose of caffeine before a 20-minute nap in the PLD was benecial
for repeated sprint performance. However, participants in the
present study were caffeine naïve. Thus, the current ndings apply
only to habitually low caffeine consumers (<80 mg·d
1
). Further-
more, sleep quality during the nap was measured only subjectively,
which could limit the present ndings. Of note, caffeine ingested
shortly before a daytime nap did not lower sleep quality, at least
from a subjective perspective. We could not conrm whether
participantssleep during the nap was objectively unaffected by
caffeine ingestion, especially in caffeine-naïve participants. In
addition, we studied only the effects of a single dose of caffeine
and only 1 nap opportunity. It is possible that higher doses of
caffeine or longer naps result in better performance benets. Finally,
(Ahead of Print)
6Romdhani et al
in the present study, sleep deprivation was caused by early awaken-
ing (toward the end of the night). The effects of such a combination
on performance after PSD caused by late bedtime are unknown.
Therefore, further investigations are warranted.
Practical Applications
It is common for athletes to start a competition or training session
with sleep debt. The combination of caffeine ingestion and a short
afternoon nap could improve repeated sprint performance and
antioxidant mechanisms and reduce muscle damage. Nevertheless,
we advise athletes to be aware of the effects of caffeine ingestion
after PSD and before repeated sprint exercise, because it results in
increased muscle damage and would probably affect recovery
without improving performance.
Conclusions
A short nap is benecial for partially sleep-deprived, caffeine-naïve
athletes. Not only are repeated sprint performances improved, but
also exercise-induced oxidative damage is reduced compared with
the same exercise performed without napping. Postexercise muscle
damage with or without napping was greater after caffeine ingestion,
and performance was not improved. Nevertheless, when caffeine
was consumed before a shortnap, repeated sprint performances were
better than after caffeine ingestion or a short nap alone.
Acknowledgments
The authors express sincere gratitude to the participants, Mr Firas Ben Slama,
and Dr Olfa Abene for their time and effort throughout the experiment.
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(Ahead of Print)
8Romdhani et al
... The present study was approved by the University of Manouba Institutional Review Board (P-SC N° 009/15) and was conducted according to the ethical guidelines of the Declaration of Helsinki (64 th World Medical Associa tion General Assembly, Fortaleza, Brazil, October 2013). a relatively small sample size, a short nap enhanced repeated sprint performance more than caffeine, and the combination of CAF+N20 enhanced repeated sprint performance more than napping alone or caffeine ingestion alone after PSD [3]. However, a recent study showed that such a combination was not any better than each treatment alone on reaction time in highly trained athletes [13]. ...
... Also, caffeine ingestion enhances forced respiratory volume in asthmatic and healthy subjects and during exercise [20]. One limitation to caffeine ingestion before exercise is the enhanced muscle damage [3,21,22], with or without performance enhancement [3]. During high-intensity exercise, the sarcolemma could be damaged due to metabolic and mechanical factors, resulting in muscle enzymes leaking into the circulation [23]. ...
... Also, caffeine ingestion enhances forced respiratory volume in asthmatic and healthy subjects and during exercise [20]. One limitation to caffeine ingestion before exercise is the enhanced muscle damage [3,21,22], with or without performance enhancement [3]. During high-intensity exercise, the sarcolemma could be damaged due to metabolic and mechanical factors, resulting in muscle enzymes leaking into the circulation [23]. ...
Article
Full-text available
To investigate the effect of 20 min nap opportunity (N20), 5 mg · kg-1 of caffeine (CAF) and their combination (CAF+N20) on the biochemical response (energetic biomarkers, biomarkers of muscle damage and enzymatic antioxidants) to the running-based anaerobic sprint test. Fourteen highly trained male athletes completed in a double-blind, counterbalanced and randomized order four test sessions: no nap with placebo (PLA), N20, CAF and CAF+N20. Compared to PLA, all treatments enhanced maximum and mean powers. Minimum power was higher [(mean difference) 58.6 (95% confidence interval = 1.31–116) Watts] after CAF and [102 (29.9–175) Watts] after CAF+N20 compared to N20. Also, plasma glucose was higher after CAF [0.81 (0.18–1.45) mmol·l-1] and CAF+N20 [1.03 (0.39–1.64) mmol·l-1] compared to N20. However, plasma lactate was higher [1.64 (0.23–3.03) mmol ·l-1] only after N20 compared to pre-exercise, suggesting a higher anaerobic glycolysis during N20 compared to PLA, CAF and CAF+N20. Caffeine ingestion increased post-exercise creatine kinase with [54.3 (16.7–91.1) IU·l-1] or without napping [58.9 (21.3–96.5) IU·l-1] compared to PLA. However, superoxide dismutase was higher after napping with [339 (123–554) U·gHB-1] or without caffeine [410 (195–625) U·gHB-1] compared to PLA. Probably because of the higher aerobic glycolysis contribution in energy synthesis, caffeine ingestion resulted in better repeated sprint performance during CAF and CAF+N20 sessions compared to N20 and PLA. Caffeine ingestion resulted in higher muscle damage, and the short nap enhanced antioxidant defence with or without caffeine ingestion.
... So far, 19 studies have investigated the effects of mid-day napping on anaerobic performance and strength of trained athletes or physically active individuals. [29][30][31][32][33][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Most of the studies reported significant improvements on sprinting ability, anaerobic performance and maximal strength after napping (1-11%, Table 1). In particular, 100% (10 out of 10 studies), 70% (7 out of 10 studies) and 67% (4 out of 6 studies) of the studies showed positive effects on sprinting ability, anaerobic performance and strength, respectively (Table 1). ...
... Yet to date, 17 studies have examined the effectiveness of daytime napping on athletes' perception of fatigue and/or recovery, alertness/sleepiness as well as the rate of perceived exertion (RPE). [29][30][31][32][33][34][35][36][40][41][42][43][45][46][47][48][49] Most of the existing studies provide evidence to support the opinion that following a mid-day nap athletes exhibit lower perception of fatigue, 33,42 lower tiredness, 41 better mood state, 33 lower stress 42 and anger or depression. 33,43 Accordingly, the existing studies agree that participants exhibit higher vigilance/alertness following napping, irrespective of the preceding nighttime sleep (ie, normal sleep or sleep deprivation). ...
... 56 Interestingly also, a recent study showed that following a night of partial sleep deprivation (total bed time: 4.5 h) a combination of 20-min nap and caffeine ingestion (5 mg.kg −1 ) prior napping was more beneficial compared to napping or caffeine alone in avoiding the nap-induced sleep inertia. 46 It should be noted, however, that from the existing studies investigating the effects of mid-day napping on athletic performance, only six of them have objectively recorded the nap duration (see limitations section). With this in mind, the exact amount of sleep obtained during mid-day naps in the existing protocols was not adequately quantified. ...
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Mid‐day napping has been recommended as a countermeasure against sleep debt and an effective method for recovery, regardless of nocturnal sleep duration. Herein, we summarize the available evidence regarding the influence of napping on exercise and cognitive performance as well as the effects of napping on athletes’ perceptual responses prior to or during exercise. The existing studies investigating the influence of napping on athletic performance have revealed equivocal results. Prevailing findings indicate that following a normal sleep night or after a night of sleep loss, a mid‐day nap may enhance or restore several exercise and cognitive performance aspects, while concomitantly provide benefits on athletes’ perceptual responses. Most, but not all, findings suggest that compared to short‐term naps (20‐30 min), long‐term ones (>35‐90 min) appear to provide superior benefits to the athletes. The underlying mechanisms behind athletic performance enhancement following a night of normal sleep or the restoration after a night of sleep loss are not clear yet. However, the absence of benefits or even the deterioration of performance following napping in some studies is likely the result of sleep inertia. The present review sheds light on the predisposing factors that influence the post‐nap outcome, such as nocturnal sleep time, mid‐day nap duration and the time elapsed between the end of napping and the subsequent testing, discusses practical solutions and stimulates further research on this area.
... Interestingly, some studies compared the effects of napping to the effects of caffeine (Horne and Reyner, 1996;De Valck et al., 2003;Schweitzer et al., 2006;Horne et al., 2008;Romdhani et al., 2021c). A short mid-afternoon nap was more efficient in reducing sleepiness than a moderate dose of caffeine taken in the early evening (Horne et al., 2008). ...
... A short mid-afternoon nap was more efficient in reducing sleepiness than a moderate dose of caffeine taken in the early evening (Horne et al., 2008). More interestingly, some studies combined napping and caffeine ingestion and found that the combination of caffeine with a short nap on a wide range of psycho-cognitive tasks (Horne and Reyner, 1996;Reyner and Horne, 1997;Hayashi et al., 2003), and repeated sprint performances (Romdhani et al., 2021c) was better than each of the interventions used separately. For instance, caffeine ingestion immediately prior to a 20 min nap produced better performances compared to caffeine alone or 20 min nap alone (Hayashi et al., 2003). ...
... Speaking of the effect of the caffeine and nap combination (CAF+N20), our findings indicate that the combination was not any better than each treatment alone on subjective and objective measurements, aligning with earlier reports (Bonnet and Arand, 1994;Horne and Reyner, 1996;Reyner and Horne, 1997;Hayashi et al., 2003;Schweitzer et al., 2006). However, other studies showed a greater performance after CAF+N20 compared to caffeine alone or napping alone (Bonnet and Arand, 1994;Horne and Reyner, 1996;Reyner and Horne, 1997;Hayashi et al., 2003;Schweitzer et al., 2006;Romdhani et al., 2021c). The participants' characteristics could explain these discrepancies. ...
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Purpose: To investigate the effects of placebo (PLA), 20 min nap opportunity (N20), 5mg·kg ⁻¹ of caffeine (CAF), and their combination (CAF+N20) on sleepiness, mood and reaction-time after partial sleep deprivation (PSD; 04h30 of time in bed; study 1 ) or after normal sleep night (NSN; 08h30 of time in bed; study 2 ). Methods: Twenty-three highly trained athletes ( study 1 ; 9 and study 2 ; 14) performed four test sessions (PLA, CAF, N20 and CAF+N20) in double-blind, counterbalanced and randomized order. Simple (SRT) and two-choice (2CRT) reaction time, subjective sleepiness (ESS) and mood state (POMS) were assessed twice, pre- and post-intervention. Results: SRT was lower (i.e., better performance) during CAF condition after PSD (pre: 336 ± 15 ms vs . post: 312 ± 9 ms; p < 0.001; d = 2.07; Δ% = 7.26) and NSN (pre: 350 ± 39 ms vs . post: 323 ± 32 ms; p < 0.001; d = 0.72; Δ% = 7.71) compared to pre-intervention. N20 decreased 2CRT after PSD (pre: 411 ± 13 ms vs . post: 366 ± 20 ms; p < 0.001; d = 2.89; Δ% = 10.81) and NSN (pre: 418 ± 29 ms vs . post: 375 ± 40 ms; p < 0.001; d = 1.23; Δ% = 10.23). Similarly, 2CRT was shorter during CAF+N20 sessions after PSD (pre: 406 ± 26 ms vs . post: 357 ± 17 ms; p < 0.001; d = 2.17; Δ% = 12.02) and after NSN (pre: 386 ± 33 ms vs . post: 352 ± 30 ms; p < 0.001; d = 1.09; Δ% = 8.68). After PSD, POMS score decreased after CAF ( p < 0.001; d = 2.38; Δ% = 66.97) and CAF+N20 ( p < 0.001; d = 1.68; Δ% = 46.68). However, after NSN, only N20 reduced POMS ( p < 0.001; d = 1.05; Δ% = 78.65) and ESS ( p < 0.01; d = 0.71; Δ% = 19.11). Conclusion: After PSD, all interventions reduced sleepiness and only CAF enhanced mood with or without napping. However, only N20 enhanced mood and reduced sleepiness after NSN. Caffeine ingestion enhanced SRT performance regardless of sleep deprivation. N20, with or without caffeine ingestion, enhanced 2CRT independently of sleep deprivation. This suggests a different mode of action of napping and caffeine on sleepiness, mood and reaction time.
... Recuperative naps could be a replacement for lost sleep, prophylactic naps are used ahead of an expected sleep loss, and appetitive naps are just for the joy of napping (21). Short recuperative and appetitive naps could be beneficial for physical and cognitive performance (22)(23)(24)(25)(26). Long recuperative daytime naps (27), but not long appetitive naps (28), could also be beneficial for physical and cognitive performances. ...
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Objective: Disrupted sleep and training behaviors in athletes have been reported during the COVID-19 pandemic. We aimed at investigating the combined effects of Ramadan observance and COVID-19 related lockdown in Muslim athletes. Methods: From an international sample of athletes (n = 3,911), 1,681 Muslim athletes (from 44 countries; 25.1 ± 8.7 years, 38% females, 41% elite, 51% team sport athletes) answered a retrospective, cross-sectional questionnaire relating to their behavioral habits pre- and during- COVID-19 lockdown, including: (i) Pittsburgh sleep quality index (PSQI); (ii) insomnia severity index (ISI); (iii) bespoke questions about training, napping, and eating behaviors, and (iv) questions related to training and sleep behaviors during-lockdown and Ramadan compared to lockdown outside of Ramadan. The survey was disseminated predominately through social media, opening 8 July and closing 30 September 2020. Results: The lockdown reduced sleep quality and increased insomnia severity (both p < 0.001). Compared to non-Muslim (n = 2,230), Muslim athletes reported higher PSQI and ISI scores during-lockdown (both p < 0.001), but not pre-lockdown (p > 0.05). Muslim athletes reported longer (p < 0.001; d = 0.29) and later (p < 0.001; d = 0.14) daytime naps, and an increase in late-night meals (p < 0.001; d = 0.49) during- compared to pre-lockdown, associated with lower sleep quality (all p < 0.001). Both sleep quality (χ2 = 222.6; p < 0.001) and training volume (χ2 = 342.4; p < 0.001) were lower during-lockdown and Ramadan compared to lockdown outside of Ramadan in the Muslims athletes. Conclusion: Muslim athletes reported lower sleep quality and higher insomnia severity during- compared to pre-lockdown, and this was exacerbated by Ramadan observance. Therefore, further attention to Muslim athletes is warranted when a circadian disrupter (e.g., lockdown) occurs during Ramadan.
... Recuperative naps could be a replacement for lost sleep, prophylactic naps are used ahead of an expected sleep loss, and appetitive naps are just for the joy of napping (21). Short recuperative and appetitive naps could be beneficial for physical and cognitive performance (22)(23)(24)(25)(26). Long recuperative daytime naps (27), but not long appetitive naps (28), could also be beneficial for physical and cognitive performances. ...
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Objective Disrupted sleep and training behaviors in athletes have been reported during the COVID-19 pandemic. We aimed at investigating the combined effects of Ramadan observance and COVID-19 related lockdown in Muslim athletes. Methods From an international sample of athletes ( n = 3,911), 1,681 Muslim athletes (from 44 countries; 25.1 ± 8.7 years, 38% females, 41% elite, 51% team sport athletes) answered a retrospective, cross-sectional questionnaire relating to their behavioral habits pre- and during- COVID-19 lockdown, including: ( i ) Pittsburgh sleep quality index (PSQI); ( ii ) insomnia severity index (ISI); ( iii ) bespoke questions about training, napping, and eating behaviors, and ( iv ) questions related to training and sleep behaviors during-lockdown and Ramadan compared to lockdown outside of Ramadan. The survey was disseminated predominately through social media, opening 8 July and closing 30 September 2020. Results The lockdown reduced sleep quality and increased insomnia severity (both p < 0.001). Compared to non-Muslim ( n = 2,230), Muslim athletes reported higher PSQI and ISI scores during-lockdown (both p < 0.001), but not pre-lockdown ( p > 0.05). Muslim athletes reported longer ( p < 0.001; d = 0.29) and later ( p < 0.001; d = 0.14) daytime naps, and an increase in late-night meals ( p < 0.001; d = 0.49) during- compared to pre-lockdown, associated with lower sleep quality (all p < 0.001). Both sleep quality (χ ² = 222.6; p < 0.001) and training volume (χ ² = 342.4; p < 0.001) were lower during-lockdown and Ramadan compared to lockdown outside of Ramadan in the Muslims athletes. Conclusion Muslim athletes reported lower sleep quality and higher insomnia severity during- compared to pre-lockdown, and this was exacerbated by Ramadan observance. Therefore, further attention to Muslim athletes is warranted when a circadian disrupter (e.g., lockdown) occurs during Ramadan.
... Taking long (> 90 min), or late (> 16:00) diurnal naps decreases the homeostatic drive for sleep [35] and increase insomnia symptoms during the subsequent night. Preferably, a moderate dose of caffeine immediately prior to starting a 30-min midday nap to maximize alertness and avoid sleep inertia at the awakening [48][49][50], would appear prudent to not interfere with the upcoming nocturnal sleep. , and H sleep efficiency (SE). ...
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Objective In a convenience sample of athletes, we conducted a survey of COVID-19-mediated lockdown (termed ‘lockdown’ from this point forward) effects on: (i) circadian rhythms; (ii) sleep; (iii) eating; and (iv) training behaviors. Methods In total, 3911 athletes [mean age: 25.1 (range 18–61) years, 1764 female (45%), 2427 team-sport (63%) and 1442 elite (37%) athletes] from 49 countries completed a multilingual cross-sectional survey including the Pittsburgh Sleep Quality Index and Insomnia Severity Index questionnaires, alongside bespoke questions about napping, training, and nutrition behaviors. Results Pittsburgh Sleep Quality Index (4.3 ± 2.4 to 5.8 ± 3.1) and Insomnia Severity Index (4.8 ± 4.7 to 7.2 ± 6.4) scores increased from pre- to during lockdown (p < 0.001). Pittsburgh Sleep Quality Index was predominantly influenced by sleep-onset latency (p < 0.001; + 29.8%), sleep efficiency (p < 0.001; − 21.1%), and total sleep time (p < 0.001; − 20.1%), whilst Insomnia Severity Index was affected by sleep-onset latency (p < 0.001; + 21.4%), bedtime (p < 0.001; + 9.4%), and eating after midnight (p < 0.001; + 9.1%). During lockdown, athletes reported fewer training sessions per week (− 29.1%; d = 0.99). Athletes went to bed (+ 75 min; 5.4%; d = 1.14) and woke up (+ 150 min; 34.5%; d = 1.71) later during lockdown with an increased total sleep time (+ 48 min; 10.6%; d = 0.83). Lockdown-mediated circadian disruption had more deleterious effects on the sleep quality of individual-sport athletes compared with team-sport athletes (p < 0.001; d = 0.41), elite compared with non-elite athletes (p = 0.028; d = 0.44) and older compared with younger (p = 0.008; d = 0.46) athletes. Conclusions These lockdown-induced behavioral changes reduced sleep quality and increased insomnia in athletes. Data-driven and evidence-based recommendations to counter these include, but are not limited to: (i) early outdoor training; (ii) regular meal scheduling (whilst avoiding meals prior to bedtime and caffeine in the evening) with appropriate composition; (iii) regular bedtimes and wake-up times; and (iv) avoidance of long and/or late naps.
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Background Sleep loss may influence subsequent physical performance. Quantifying the impact of sleep loss on physical performance is critical for individuals involved in athletic pursuits. Design Systematic review and meta-analysis. Search and Inclusion Studies were identified via the Web of Science, Scopus, and PsycINFO online databases. Investigations measuring exercise performance under ‘control’ (i.e., normal sleep, > 6 h in any 24 h period) and ‘intervention’ (i.e., sleep loss, ≤ 6 h sleep in any 24 h period) conditions were included. Performance tasks were classified into different exercise categories (anaerobic power, speed/power endurance, high-intensity interval exercise (HIIE), strength, endurance, strength-endurance, and skill). Multi-level random-effects meta-analyses and meta-regression analyses were conducted, including subgroup analyses to explore the influence of sleep-loss protocol (e.g., deprivation, restriction, early [delayed sleep onset] and late restriction [earlier than normal waking]), time of day the exercise task was performed (AM vs. PM) and body limb strength (upper vs. lower body). Results Overall, 227 outcome measures (anaerobic power: n = 58; speed/power endurance: n = 32; HIIE: n = 27; strength: n = 66; endurance: n = 22; strength-endurance: n = 9; skill: n = 13) derived from 69 publications were included. Results indicated a negative impact of sleep loss on the percentage change (%Δ) in exercise performance (n = 959 [89%] male; mean %Δ = − 7.56%, 95% CI − 11.9 to − 3.13, p = 0.001, I² = 98.1%). Effects were significant for all exercise categories. Subgroup analyses indicated that the pattern of sleep loss (i.e., deprivation, early and late restriction) preceding exercise is an important factor, with consistent negative effects only observed with deprivation and late-restriction protocols. A significant positive relationship was observed between time awake prior to the exercise task and %Δ in performance for both deprivation and late-restriction protocols (~ 0.4% decrease for every hour awake prior to exercise). The negative effects of sleep loss on different exercise tasks performed in the PM were consistent, while tasks performed in the AM were largely unaffected. Conclusions Sleep loss appears to have a negative impact on exercise performance. If sleep loss is anticipated and unavoidable, individuals should avoid situations that lead to experiencing deprivation or late restriction, and prioritise morning exercise in an effort to maintain performance.
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Purpose: To investigate the effects of napping after partial sleep deprivation (PSD) on reaction time, mood, and biochemical response to repeated-sprint exercise in athletes. Methods: Nine male judokas performed 4 test sessions in a counterbalanced and randomized order. Participants accomplished 1 control session after a normal sleep night (NSN) and 3 after PSD with (1) no nap, (2) ∼20-min nap (N20), and (3) ∼90-min nap (N90) opportunities. Test sessions included the running-based anaerobic sprint test, reaction time, Hooper index, and Epworth Sleepiness Scale. Muscle-damage biomarkers and antioxidant status were evaluated before and after exercise. Results: PSD decreased maximum (P < .001, d = 1.12), mean (P < .001, d = 1.33), and minimum (P < .001, d = 1.15) powers compared with NSN. However, N20 and N90 enhanced maximum power compared with PSD (P < .05, d = 0.54; P < .001, d = 1.06, respectively). Minimum power and mean power increased only after N90 (P < .001, d = 1.63; P < .001, d = 1.16, respectively). Epworth Sleepiness Scale increased after PSD (P < .001, d = 0.86) and decreased after N20 (P < .001, d = 1.36) and N90 (P < .001, d = 2.07). N20 reduced multiple-choice reaction time (P < .001, d = 0.61). Despite performance decrement, PSD increased postexercise aspartate aminotransferase (P < .001, d = 4.16) and decreased glutathione peroxidase (P < .001, d = 4.02) compared with NSN. However, the highest performances after N90 were accompanied with lesser aspartate aminotransferase (P < .001, d = 1.74) and higher glutathione peroxidase (P < .001, d = 0.86) compared with PSD. Conclusions: Napping could be preventive against performance degradation caused by sleep loss. A short nap opportunity could be more beneficial when the subsequent effort is brief and requires frequent decision making. However, a longer nap opportunity could be preventive against muscle and oxidative damage, even for higher performances.
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Purpose. To compare the effect of different durations of nap opportunity during the daytime on repeated high-intensity short-duration performance and rating of perceived exertion (RPE). Methods. Seventeen physically active men (age: 21.3±3.4 y, height: 176.7±5.9 cm, body mass: 71.8±10.2 kg) performed a 5 m shuttle run test (to determine best distance (BD), total distance (TD) and fatigue index (FI)) under four conditions: a 25 min nap opportunity (N25), a 35 min nap opportunity (N35), a 45 min nap opportunity (N45) and control (no-nap) (N0). The sleep quality of each nap opportunity was evaluated using a scale ranging from 0 “no sleep” to 10 “uninterrupted, deep sleep throughout”. The four conditions were performed in a random order. RPE was recorded after each repetition of the test and the mean score was calculated. Results. BD increased after N25 (+6%) and N45 (+9%) compared to N0 (p<0.05) and was significantly higher after N45 compared to N35 (p<0.05). Compared to N0, the three nap opportunity durations enhanced TD (p<0.05) with greater enhancement after N45 compared to N25 (+8% vs. +3%) and N35 (+8% vs. +3%). For FI, no-significant differences were observed between the three nap opportunity durations and N0. The mean RPE score was significantly higher after N25 (+20%) and N0 (+19%) compared to N45 (p<0.05). All participants were able to fall asleep during each nap condition with a sleep quality score of 6.9±1.0, 7.0±0.7 and 7.1±0.8 for N25, N35 and N45. Conclusion. A nap opportunity during the daytime was beneficial for physical performance and perceived exertion with the N45 being the most effective for improving performance and reducing fatigue during the 5 m shuttle run test. The implication of the present study is that athletes might benefit from a nap opportunity of 25, 35 or 45 min before practice or before a competition.
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To compare the effects of two types of partial sleep deprivation (PSD) at the beginning (PSDBN) and the end (PSDEN) of the night on mood, cognitive performances, biomarkers of muscle damage, haematological status and antioxidant responses before and after repeated-sprint exercise in the post-lunch dip. Fourteen male athletes performed the Running-based Anaerobic Sprint Test following: (i) baseline normal sleep night, (ii) PSDBN, or (iii) PSDEN in a randomized and counter-balanced order. During each condition, participants performed simple and choice reaction time tests, the Profile of Mood States, subjective sleepiness, and the Running-based Anaerobic Sprint Test. Plasma biomarkers of muscle damage, total blood count, and antioxidant activities were measured at rest and after the repeated sprint in the three conditions. PSDEN decreased Pmax (p=0.008; d=1.12), Pmean (p=0.002; d=1.33) and Pmin (p=0.006; d=1.15), whilst PSDBN decreased Pmean (p=0.04; d=0.68) and Pmin (p=0.028; d=0.58), in comparison with baseline. PSDEN exerted stronger effects on Pmax (p=0.013; d=0.74) and Pmean (p=0.048; d=0.54) than PSDBN. Moreover, PSDEN increased subjective sleepiness (p<0.001; d=1.93), while PSDBN impaired choice reaction time (p<0.001, d=1.89). Both PSD types decreased resting glutathione peroxidase (p<0.001; d=5.43, d=3.86), and increased aspartate amino-transferase levels (p<0.001; d=1.36, d=1.37) respectively for PSDEN and PSDBN. PSDEN decreased repeated-sprint performances more than PSDBN in the post-lunch dip. This could be explained by the lowered mood and resting antioxidant status and the increased inflammatory profile after PSDEN. Repeated-sprint exercise resulted in greater inflammation after PSDEN, despite the decreased physical performance. The drop of resting antioxidant defence and haemoglobin concentration after PSDEN could explain the increased sleep drive at the post-lunch dip.
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Purpose: The purpose of the research was to investigate the sport-specific performance effect of a brief afternoon nap on high-level Asian adolescent student-athletes that were habitually short sleepers. Methods: In the studies, participants were randomly assigned to a nap or non-nap (reading) condition. In the first study, 12 male shooters (13.8 ± 1.0 yrs) performed a shooting assessment (20 competition shots) with heart rate variability monitored during the assessment. In the second study, 19 male track & field athletes (14.8 ± 1.1 yrs) performed a 20m sprint performance assessment. Subjective measures of sleepiness and alertness were obtained in both studies. Results: The brief nap had no effect on any measure of shooting performance (p > 0.05) and autonomic function (p > 0.05) in shooters. However, fastest 20m sprint times increased significantly (p < 0.05) from 3.385 ± 0.128 sec to 3.411 ± 0.143 sec, with mean 2m times trending towards significance (p < 0.1) amongst the track & field athletes. No significant differences were observed in any other measures. Conclusions: The results of the research indicate varying effects of naps between sport-specific performance measures. Napping had no effect on shooting performance while a negative effect existed in 20-m sprint performance, potentially due to sleep inertia. Considering these findings, some caution is warranted when advocating naps for adolescent athletes.
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This study aimed to investigate the effects of time-of-day, 24 and 36 hours of total sleep deprivation (TSD), and recovery sleep (RS) on repeated-agility performances. Twenty-two physical education students (11 male and 11 female students) completed 5 repeated modified agility T-test (RMAT) sessions (i.e., 2 after normal sleep night [NSN] [at 07:00 and 17:00 hours], 2 after TSD [at 07:00 hours, i.e., 24-hour TSD and at 17:00 hours, i.e., 36-hour TSD], and 1 after RS at 17:00 hours). The RMAT index decreased from the morning to the afternoon after NSN ( p < 0.05, d = 1.05; p < 0.01, d = 0.73) and after TSD ( p < 0.001, d = 0.92; d = 1.08), respectively, for total time (TT) and peak time (PT). This finding indicates a diurnal variation in repeated agility, which persisted after TSD. However, the diurnal increase in PT was less marked in the female group after NSN (2.98 vs. 6.24%). Moreover, TT and PT increased, respectively, after 24-hour TSD ( p < 0.001; d = 0.84, d = 0.87) and 36-hour TSD ( p < 0.001, d = 1.12; p < 0.01, d = 0.65). Female participants' PT was less affected by 24-hour TSD (1.76 vs. 6.81%) compared with male participants' PT. After 36-hour TSD, the amount of decrease was not different between groups, which increased the diurnal amplitude of PT only for male participants. Total sleep deprivation suppressed the diurnal increase of PT and increased the diurnal amplitude of oral temperature only in women. Nevertheless, RS normalized the sleep-loss–induced performance disruption. Conclusively, sleep loss and RS differently affect repeated-agility performance of men and women during the day. Sleep extension postdeprivation could have potent restorative effect on repeated-agility performances, and female participants could extract greater benefits.
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The effectiveness of a nap as a recovery strategy for endurance exercise is unknown and therefore the present study investigated the effect of napping on endurance exercise performance. Eleven trained male runners completed this randomized crossover study. On two occasions runners completed treadmill running for 30 min at 75% V̇O2max in the morning, returning that evening to run for 20 min at 60% V̇O2max, and then to exhaustion at 90% V̇O2max. On one trial, runners had an afternoon nap approximately 90-min before the evening exercise (NAP) whilst on the other runners did not (CON). All runners napped (20 ± 10 min), but time to exhaustion (TTE) was not improved in all runners (NAP 596 ± 148 s vs. CON 589 ± 216 s, P=0.83). Runners that improved TTE after the nap slept less at night than those that did not improve TTE (nighttime sleep 6.4 ± 0.7 h vs. 7.5 ± 0.4 h, P<0.01). Furthermore, nightime sleep predicted change in TTE, indicating that runners sleeping least at night improved TTE the most after the nap compared to CON (r2 = -0.76, P=0.001). In runners that improved TTE, ratings of perceived exertion (RPE) were lower during the TTE on NAP than CON compared to runners that did not improve (-0.4 ± 0.6 vs. 0 ± 0, P=0.05). Reduced exercising sense of effort (RPE) may account for the improved TTE after the nap. In conclusion, a short afternoon nap improves endurance performance in runners that obtain less than 7 h nighttime sleep.
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The present study aimed to investigate the effects of 20-min (N20) and 90-min (N90) nap opportunities after partial-sleep-deprivation (PSD) on the hematological and biochemical responses to repeated-sprint exercise. Nine male judokas randomly performed, in a counterbalanced order, the running-based anaerobic sprint test (RAST) in three occasions (i.e., after no-nap, N20 or N90) following PSD. During each session, total blood count, plasma ions and biomarkers of muscle damage were collected before and after the RAST. Both nap opportunities enhanced repeated-sprint performance, and N90 resulted in higher enhancement. N90 resulted in higher post-exercise Monocytes (MO) (p<0.001; d=1.51), Lymphocytes (LY) (p<0.001; d=0.61), Hemoglobin (HB) (p<0.001; d=1.09), Hematocrit (HT) (p<0.001; d=0.9), Sodium (p<0.001; d=1.01) and Potassium (p<0.001; d=9.54) in comparison with no-nap. However, N20 increased MO, LY, platelet and mean corpuscular hemoglobin and decreased mean corpuscular volume. Strong correlations were found between mean and minimal power and LY (p<0.001, r=0.53; r=0.55), HB (p<0.001, r=0.58; r=0.56) and HT (p<0.001, r=0.58; r=0.61), respectively. There was no significant effect of napping on muscle damage. Therefore, napping improved repeated-sprint performances and associated hematological and biochemical responses after PSD.
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Purpose The effects of sleep deprivation on physical performance are well documented, but data on the consequence of sleep deprivation on recovery from exercise are limited. The aim was to compare cyclists’ recovery from a single bout of high-intensity interval training (HIIT) after which they were given either a normal night of sleep (CON, 7.56 ± 0.63 h) or half of their usual time in bed (DEP, 3.83 ± 0.33 h). Methods In this randomized cross-over intervention study, 16 trained male cyclists (age 32 ± 7 years), relative peak power output (PPO 4.6 ± 0.7 W kg−1) performed a HIIT session at ±18:00 followed by either the CON or DEP sleep condition. Recovery from the HIIT session was assessed the following day by comparing pre-HIIT variables to those measured 12 and 24 h after the session. Following a 2-week washout, cyclists repeated the trial, but under the alternate sleep condition. Results PPO was reduced more 24 h after the HIIT session in the DEP (ΔPPO −0.22 ± 0.22 W kg−1; range −0.75 to 0.1 W kg−1) compared to the CON condition (ΔPPO −0.05 ± 0.09 W kg−1, range −0.19 to 0.17 W kg−1, p = 0.008, d = −2.16). Cyclists were sleepier (12 h: p = 0.002, d = 1.90; 24 h: p = 0.001, d = 1.41) and felt less motivated to train (12 h, p = 0.012, d = −0.89) during the 24 h recovery phase when the HIIT session was followed by the DEP condition. The exercise-induced 24 h reduction in systolic blood pressure observed in the CON condition was absent in the DEP condition (p = 0.039, d = 0.75). Conclusions One night of partial sleep deprivation impairs recovery from a single HIIT session in cyclists. Further research is needed to understand the mechanisms behind this observation.
Article
Purpose: It has been suggested that napping is the best recovery strategy for athletes. However, researches on the impacts of napping on athletic performances are scarce. The aim of this study was to determine the effects of a 30-minute nap following a partial sleep deprivation, or a normal night condition, on alertness, fatigue, and cognitive and physical outcomes. Methods: Thirteen national-level male karate athletes were randomized to experience nap and no-nap conditions, after either a reference or a partial sleep deprivation night. The nap lasted 30 minutes at 13:00. The post-nap testing session started at 14:00 by quantifying subjective alertness and fatigue. Cognitive and physical performances were respectively measured before and after the Karate Specific Test (KST) by Simple Reaction Time (SRT) test, Lower Reaction Test (LRT), Mental Rotation Test (MRT), Squat Jump (SJ) and Counter Movement Jump (CMJ) tests. Results: After a reference night, the nap improved alertness and cognitive outcomes (SRT, LRT, and MRT). No effects on subjective fatigue and physical performances were found. After a partial-sleep deprivation, the nap restored subjective alertness and the decrement in performances caused by sleep loss in most of the tests (MRT, LRT, and KST), but no effects were observed in subjective fatigue and CMJ. After the fatigue induced by KST, there was an ergogenic effect of the nap on the physical performances (CMJ, and SJ), and a partial psychogenic effect on the cognitive performances (LRT). Conclusion: A 30-minute nap enhances cognitive outcomes. It is also an effective strategy to overcome the cognitive and physical deteriorations in performances caused either by sleep loss or by fatigue induced by exhaustive trainings in the afternoon.