Table 1 Study characteristics of included articles

Sleep hygiene

Fullagar et al. [54]

Germany

Randomized crossover trial

No. of groups: two

Soccer

20, NR, 100% male

Sleep hygiene after friendly match with a kick-off time of 20:45 versus no sleep hygiene

Actigraphy and sleep diaries

REC: The Yo–Yo intermittent recovery test—level 2 and CMJ 12 h and 36 h post-match, submaximal interval-based running test 18 and 42 h post-match with a heart rate interval monitoring system; c-reactive protein, creatine kinase, and urea 10, 20, 34, and 44 h post-match

No differences in recovery of exercise performance or blood markers; sleep hygiene \(\uparrow\) total sleep time and number wake episodes compared with no sleep hygiene;

Van Ryswyk et al. [48]

Australia

Pre–post-trial

No. of groups: one

Australian football

25, 23.7 ± 2.0 y, 100% male

Sleep hygiene

Actigraphy, questionnaire (Pittsburgh Sleep Quality Index), and sleep diaries

CP: psychomotor vigilance task

No differences in CP or objective sleep parameters

Napping

Boukhris et al. [35]

Tunisia

Randomized crossover trial

No. of groups: three

Soccer, rugby, and handball

14, 20.3 ± 3.0 y, 100% male

40-min nap versus 90-min nap versus no nap

Nap: questionnaire (nap quality using a scale ranging from 0 to 10)

Night prior experiment: actigraphy

CP: DCT

PP: knee extensors maximal voluntary isometric contraction and 5-m SRT

40- and 90-min nap: \(\uparrow\) attention (DCT), KEMIVC, and 5mSRT; 40-min nap versus 90-min nap:↑ DCT, KEMIVC, and ↑ total distance in 5-m SRT (favoring 90-min nap)

Boukhris et al. [39]

Tunisia

Randomized crossover trial

No. of groups: two

Soccer, rugby, and handball

14, 20.3 ± 3.0 y, 100% male

40-min nap versus no nap

Nap: questionnaire (nap quality using a scale ranging from 0 to 10)

Night prior experiment: actigraphy

REC: CK, LDH, ASAT, ALAT, and CRP

PP: 5-m SRT

Nap \(\uparrow\) recovery and 5-m SRT performance (total and highest distance)

Daaloul et al. [49]

Tunisia

Randomized crossover trial

No. of groups: two

Karate

13, 23.0 ± 2.0 y, 100% male

30-min nap versus no nap, after a reference night and after a night with sleep restriction

Actigraphy and sleep diaries

CP: SRT, MRT, and LRT

PP: SJ, CMJ, and karate-specific test

After reference night: Nap \(\uparrow\) SRT, MRT, and LRT; no differences in physical performance

After a PSD night: \(\downarrow\) MRT, LRT, CMJ, and KST, no differences in SRT and SJ; Nap restored performance decreases in SRT, MRT, and LRT

Suppiah et al. [52]

Singapore

Studies 1 and 2: randomized crossover trial

No. of groups: two

Study 1: shooters

Study 2: track and field

Study 1: 12, 13.8 ± 1.0 y, 100% male

Study 2: 19, 14.8 ± 1.1 y, 100% male

30-min nap versus no nap

Nap: wireless dry electroencephalographic sensor

Night prior experiment: actigraphy

Study 1: PP: shooting assessment (20 competition shots) and HRV

Study 2: PP: 20-m sprint

Study 1: no differences in shooting performance or HRV after a nap

Study 2: \(\downarrow\) 20-m sprint performance

Petit et al. [36]

France

Counterbalanced and randomized crossover trial

No. of groups: two

From different sports

16, 22.2 ± 1.7 y, 100% female

20-min nap versus no nap in normal conditions and at 5-h advanced sleep schedules (simulated jet lag)

Polysomnography

PP: Wingate test and plasma lactate

No differences in physical performance and plasma lactate under normal conditions or simulated jet lag

Romdhani et al. [45]

Tunisia

Counterbalanced and randomized crossover trial

No. of groups: one

Judo

9, 18.5 ± 0.9 y, 100% male

20-min nap versus 90-min nap versus no nap after a night with sleep restriction

Nap subjective quality

CP: multiple-choice reaction time and simple reaction time (using a specialized software)

PP: RAST

N20 versus no nap: \(\uparrow\) in MCRT, \(\uparrow\) maximum power in RAST; no difference in SRT performance

N90 versus no nap: no differences in MCRT or SRT performance; \(\uparrow\) maximum, minimum, and mean power and fatigue index in RAST

Morita et al. [42]

Japan

Non-RCT

No. of groups: two

Softball

16, IG = 22.1 ± 0.8 y, CG = 22.0 ± 0.9 y, 100% female

2-h nap versus no nap

Actigraphy, sleep diaries, and polysomnography

CP: three-ball cascade juggling

IG: \(\uparrow\) Three-ball cascade juggling performance

CG: = Three-ball cascade juggling performance

Hsouna et al. [40]

Non-reported

Counterbalanced crossover trial

No. of groups: two

Soccer

12, 23 ± 3 y, 100% male

40-min nap versus no nap after a simulated soccer match on previous night (kick-off at 21:00)

Nap: sleepiness (Stanford Sleepiness Scale) upon waking

Night prior experiment: actigraphy

PP: 5-m SRT

\(\uparrow\) total and best distance after nap; no differences in fatigue index

Nishida et al. [44]

Japan

Randomized crossover trial

No. of groups: three

Handball

11, 20.7 ± 1.2 y, 100% male

60-min nap versus 20-min nap versus no nap

Nap: subjective quality (visual analog scale, 0–10) and sleepiness before and after (Karolinska Sleepiness Scale)

Night prior experiment: wearable device (Fitbit charge 3)

Sleep quality: questionnaire (Pittsburgh Sleep Quality Index)

REC: HRV during nap

PP: Handball performance (20-m turnaround run, 10-m load run, and ball shooting)

No differences in handball performance or HRV; 60-min nap \(\uparrow\) shooting accuracy in individuals with poor sleep quality; HRV correlated negatively with 10-m load run in 60-min nap

Sleep extension

Roberts et al. [37]

Australia

Counterbalanced crossover trial

No. of groups: one

Cycling and triathlon

9, 30 ± 6 y, 100% male

Three consecutive days of sleep extension (30% more than a normal night) versus sleep restriction (30% less than a normal night) versus normal night

Actigraphy and sleep diaries

CP: psychomotor vigilance task

PP: ETT

Sleep extension compared with NN: \(\uparrow\) PVT and ETT performance; SR compared with NN: \(\downarrow\) PVT and ETT performance

Schwartz and Simon [43]

USA

Pre–post-trial

No. of groups: one

Tennis

12, 20.2 y (18–22),42% male

7 days of sleep extension (at least 9 h), including naps

Sleep diaries

PP: serving accuracy

\(\uparrow\) Serving accuracy and TST

Swinbourne et al. [50]

New Zealand

Pre–post-trial

No. of groups: one

Rugby

25, 25 ± 2.7 y, 100% male

Sleep extension (at least 10 h of sleep) via sleep scheduling advice, strategic napping, and sleep hygiene versus control

Actigraphy, questionnaire (Pittsburgh Sleep Quality Index), and sleep diaries

CP: the five-minute psychomotor vigilance test

\(\uparrow\) reaction time performance, \(\uparrow\) total sleep time, and \(\uparrow\) sleep efficiency compared to control

Mah et al. [41]

USA

Pre–post-trial

No. of groups: one

Basketball

11, 19.4 ± 1.4 y, 100% male

Sleep extension (at least 10 h in bed per night, with a regular sleep–wake schedule and napping encouraged)

Actigraphy and sleep diaries

CP: psychomotor vigilance task

PP: specific to basketball (timed 282 feet sprint, free throw, and three-point shooting accuracy)

\(\uparrow\) Psychomotor vigilance performance, timed 282 feet sprint, free throw, three-point shooting accuracy, and TST

Remove electronic devices

Jones et al. [34]

Australia

RCT

No. of groups: two

Study 1: water polo

Study 2: Triathlon

Study 1: 13, 17 ± 1 y, 46% male

Study 2: 12, 17 ± 1 y, 67% male

Remove electronic devices in the evening versus unrestricted electronic device use

Actigraphy and sleep quality diaries

Study 1: none

Study 2: CP: psychomotor vigilance test

Study 2: no differences in cognitive performance or sleep

Dunican et al. [32]

Australia

Non-RCT

No. of groups: two

Judo

18, 18 ± 2 y, 56% male

Electronic devices removed for a 48-h period versus unrestricted electronic device use

Actigraphy and sleep diaries

CP: The Cogstate research tool

PP: The single leg three hop test

No differences between groups in cognitive or athletic performance and sleep quality and quantity

Light interventions

Zhao et al. [38]

China

RCT

No. of groups: two

Basketball

20, 18.6 ± 3.6 y, 100% male

30-min red-light therapy every night versus no light intervention (placebo group) with the same device (device off)

Questionnaire (Pittsburgh Sleep Quality Index) and serum melatonin

PP: Cooper 12-minute run

Red-light therapy group: \(\uparrow\) distance in Cooper 12-min run performances, \(\uparrow\) serum melatonin, and \(\uparrow\) sleep quality

Placebo group: no differences in Cooper 12-min run test performance, serum melatonin, or sleep

Rosa et al. [51]

Brazil

Pre–post-trial

No. of groups: one

Swimming

22, 24.8 ± 3.4 y, 50% male

Bright-light therapy (with portable glasses) and sleep hygiene

Actigraphy and sleep diaries

CP: psychomotor vigilance test

\(\uparrow\) reaction time performance, delayed sleep/wake cycles, and \(\downarrow\) total sleep time

Mindfulness

Jones et al. [33]

USA

Non-RCT

No. of groups: two

Rowing

27, 18–23 y, 100% female

Mindfulness-based stress reduction versus no intervention

Actigraphy and questionnaire (Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale)

PP: rowing performance (6000 m ergometer test)

\(\uparrow\) in rowing performance and subjective sleep quality, and \(\downarrow\) in sleepiness, compared with control group

Cold water immersion

Chauvineau et al. [55]

France

Counterbalanced and randomized crossover trial

No. of groups: three

Running

12, 28 ± 5.8 y, 100% male

Whole CWI versus partial CWI versus control (sitting for 10 min)

Actigraphy, questionnaire (the Spiegel Sleep Inventory), polysomnography, and core body temperature

REC: Hooper Index and creatine kinase pre- and post-simulated trial, post-CWI, 24 h and 48 h; the Total of Recovery Scale post-CWI, 24 h and 48 h; CMJ and KEMIVC pre- and post-simulated trial, 24 h and 48 h; Nocturnal HRV in simulated trial day

No differences in fatigue or muscle damage, core temperature, TST, SE, WASO, and latency; CWI \(\downarrow\) arousals; whole CWI \(\downarrow\) parasympathetic modulation

Combination of two or more strategies

Duffield et al. [56]

Australia

Randomized crossover trial

No. of groups: two

Tennis

8, 20.9 ± 3.6 y, 100% male

Sleep hygiene, CWI, and full-body compression versus control (passive stretching)

Actigraphy

REC: fatigue, vigor (the Brunel Mood Scale), muscle and joint soreness (1–10 Likert scale)

\(\downarrow\) muscle and joint soreness, no differences in vigor; large effect sizes though non-significant results for \(\downarrow\) fatigue, and \(\uparrow\) TST; no differences in SE or SL

Lever et al. [53]

Australia

Randomized crossover trial

No. of groups: two

Tennis

17, 15.7 ± 1.1 y, 58% male

Sleep hygiene and mindfulness versus no intervention

Actigraphy and sleep diaries

PP: match performance (games won or lost)

No differences in match performance; \(\uparrow\) TST, no change in SE, SL, WASO, WE, and WED

Romdhani et al. [47]

Tunisia

Counterbalanced and randomized crossover trial

No. of groups: four

Judo

23, 19.78 ± 1.41 y

Study 1: 9, 100% male

Study 2: 14, 100% male

Study 1: after a night with sleep restriction, no nap with placebo (NNP) versus no nap with caffeine (NNC) versus 20-min nap with placebo (NP) versus 20-min nap with caffeine (NC)

Study 2: after a normal night, NNP versus NNC versus NP versus NC

Nap subjective quality (100-mm analog scale) and sleepiness before and after (Epworth sleepiness scale)

CP: simple and two-choice reaction time (using a specialized software)

Study 1: \(\uparrow\) SRT performance in NNC; \(\uparrow\) TCRT performance in NP and NC; \(\downarrow\) sleepiness in NNC, NP, and NC

Study 2: \(\uparrow\) SRT performance in NNC; \(\uparrow\) TCRT performance in NP and NC; \(\downarrow\) sleepiness in NP

Romdhani et al. [46]

Tunisia

Counterbalanced and randomized crossover trial

No. of groups: five

Judo

9, 18.78 ± 1.09 y, 100% male

Normal sleep night without nap (NSN) versus NNP versus NNC versus 20-min NP versus 20-min NC, after a night with sleep restriction

Nap subjective quality (100-mm analog scale)

PP: RAST and plasma lactate

20-min NC \(\uparrow\) RAST performance, compared with NNP, NNC, and 20-min NP; \(\downarrow\) RAST performance in NNP and NNC, compared with NSN; NC and NP restored RAST performance compared with NSN; 20-min NP \(\uparrow\) Pmax compared with NNP; lactate \(\uparrow\) with 20-min NC and NP, compared with NNP