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Contents lists available at ScienceDirect

Journal of Science and Medicine in Sport
journal homepage: www.elsevier.com/locate/jsams

Review

Inadequate sleep and muscle strength: Implications for resistancetraining
Olivia E. Knowles a , Eric J. Drinkwater b , Charles S. Urwin b , Séverine Lamon a ,Brad Aisbett a,∗abInstitute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia
Centre for Sport Research, School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australiaa r t i c l e

i n f oArticle history:
Received 14 November 2017
Received in revised form 14 January 2018
Accepted 23 January 2018
Available online xxx
Keywords:
Sleep restriction
Sleep deprivation
Resistance exercise
Performance
Skeletal muscle healtha b s t r a c t
Objectives: Inadequate sleep (e.g., an insufﬁcient duration of sleep per night) can reduce physical performance and has been linked to adverse metabolic health outcomes. Resistance exercise is an effectivemeans to maintain and improve physical capacity and metabolic health, however, the outcomes for populations who may perform resistance exercise during periods of inadequate sleep are unknown. The
primary aim of this systematic review was to evaluate the effect of sleep deprivation (i.e. no sleep) andsleep restriction (i.e. a reduced sleep duration) on resistance exercise performance. A secondary aim was
to explore the effects on hormonal indicators or markers of muscle protein metabolism.
Methods: A systematic search of ﬁve electronic databases was conducted with terms related to three combined concepts: inadequate sleep; resistance exercise; performance and physiological outcomes. Study
quality and biases were assessed using the Effective Public Health Practice Project quality assessment
tool.
Results: Seventeen studies met the inclusion criteria and were rated as ‘moderate’ or ‘weak’ for global
quality. Sleep deprivation had little effect on muscle strength during resistance exercise. In contrast,
consecutive nights of sleep restriction could reduce the force output of multi-joint, but not single-joint
movements. Results were conﬂicting regarding hormonal responses to resistance training.
Conclusion: Inadequate sleep impairs maximal muscle strength in compound movements when performed without speciﬁc interventions designed to increase motivation. Strategies to assist groups facing
inadequate sleep to effectively perform resistance training may include supplementing their motivation
by training in groups or ingesting caffeine; or training prior to prolonged periods of wakefulness.
© 2018 Published by Elsevier Ltd on behalf of Sports Medicine Australia.

1. Introduction
Sleep is essential for physiological and cognitive functioning.1,2
Inadequate sleep, that is, when an insufﬁcient duration or quality of sleep is obtained per night, is detrimental to health andwork productivity.2,3 As the world continues moving toward a 24h society, more people are getting less sleep.4 In recognition ofthis widespread issue, inadequate sleep has recently been declared
as a ‘public health problem’ by the US Centres for Disease Control and Prevention.1 It is estimated that inadequate sleep costs
up to US$680 billion of economic output across the US, UK, Japan,
Germany and Canada annually.1 Lifestyle factors such as work-∗ Corresponding author.
E-mail address: brad.aisbett@deakin.edu.au (B. Aisbett).

ing prolonged or irregular hours, social commitments and family
responsibilities can all contribute to inadequate sleep.1
Inadequate sleep may occur as a result of sleep deprivation, that
is, a sustained state of wakefulness with no sleep, or sleep restriction, that is, a chronically reduced sleep duration.5 Approximately
40% of adults experience inadequate sleep.1,3 Athletes, new parents
and older adults are particularly susceptible to sleep restriction or
sleep deprivation. These groups experience disturbances to their
sleep cycle (e.g. through training and competing at night, newborn feeding schedules or age-related sleep impairments) exposing
them to frequent inadequate sleep. Shiftworkers, who work outsideof a historically typical 7am to 6pm period6 and experience different feeding patterns and light-exposure schedules compared to
day-time workers, are also at risk of inadequate sleep.2 Shiftworkers may sleep for a short duration or at a time that is mismatchedwith physiological functions exhibiting a circadian rhythm, a process known as circadian misalignment,6 which can also result in

https://doi.org/10.1016/j.jsams.2018.01.012
1440-2440/© 2018 Published by Elsevier Ltd on behalf of Sports Medicine Australia.

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2

inadequate sleep.2 Inadequate sleep increases fatigue and reduces
the physical capacity for daily tasks.5 Sleeping less than 7 h pernight is also associated with an increased risk of cardiovasculardisease, type 2 diabetes and obesity by up to 48%.2
Physical capacity depends on several factors, including cardiovascular ﬁtness and muscle strength. Muscle strength is critical fordaily task capacity in new parents, older adults and shiftworkers,
as well as for performance in athletes. Sustained resistance training increases muscle strength and physical capacity7,8 and reduces
risk factors for type 2 diabetes, obesity and cardiovascular disease,9
which are over-represented in populations facing inadequate sleep.
Bi-weekly resistance training is recommended for all adults, forshort- and long-term health,10 but these guidelines do not consider the potential impact of inadequate sleep or daily ﬂuctuations
in strength and training capacity,11 nor how these factors interact
with changes in motivation and the optimal times of day12 or dayson which to train.
Resistance exercise has a chronic positive effect on skeletal
muscle mass,13 which underpins muscle strength. Skeletal muscle ﬁbres are made up of almost 90% of proteins.14 Skeletal muscle
mass is regulated by the ﬁne balance between the rate of protein synthesis and the rate of protein degradation occurring in
the muscle.14 When this balance is maintained, muscle mass ispreserved.14 Resistance exercise is a potent way to increase skeletal
muscle mass by triggering the molecular pathways that activate protein synthesis in the muscle.13 Resistance exercise places
mechanical load on the muscle, activating pathways that control
muscle protein synthesis13 in the cell. Resistance exercise also
stimulates the release of hormones that directly promote protein
synthesis (referred to as anabolic hormones), such as testosterone,
growth hormone and insulin-like growth factor 1 (IGF-1).15 At rest,
these hormones ﬂuctuate partially due to a circadian rhythm; thepeak of their secretion often occurring at the onset of or during
sleep.12 Their secretion in response to resistance exercise positively
inﬂuences muscle protein turnover,15,16 allowing for increases inmuscle mass and strength.
The prescription of resistance training may require particularcare for groups who are likely to train in conditions of inadequate
sleep or misalignment between their sleep time and endogenous circadian rhythm. Our group17 recently hypothesised that analtered sleep–wake cycle may be detrimental to skeletal muscle
health. Indeed, inadequate sleep increases the levels of hormonesthat directly promote protein degradation (referred to as catabolic
hormones), such as cortisol, and decreases the levels of anabolic
hormones in the blood.17 By disturbing baseline muscle protein
metabolism,17 inadequate sleep may blunt skeletal muscle adaptations to resistance exercise. Previous reviews18,19 have foundextended sleep deprivation can reduce muscle strength in athletes, yet have focused on providing recommendations to optimise
sleep. While improved sleep outcomes are critical for athletes, thetraining, work and lifestyle demands of these and other groups
could make sleep restriction unavoidable in some circumstances.
If resistance exercise is going to be a viable strategy to improveand maintain physical capacity and preserve metabolic health, prescription guidelines speciﬁc to groups facing inadequate sleep are
imperative. Therefore, the primary aim of this review is to evaluate the literature investigating the impact of inadequate sleep on
resistance exercise performance; a secondary aim is to explore theconsequences for regulators of muscle protein metabolism.
2. Methodology

ing Academic Search Complete, Medline Complete, Global Health
SPORTdiscus), Embase, Scopus, Web of Science and PubMed wasused to identify peer-reviewed, English-language studies of relevance, since inception. The key words for the search were as
follows: sleep deprivation; sleep loss; sleep restriction; circadian;
diurnal; time of day; shift work; night shift; insufﬁcient sleep;
inadequate sleep; sleep fragmentation; sleep interruptions; sleep
restoration; sleep extension and nocturnal searched together withresistance training; resistance exercise; strength training; weighttraining; physical training; physical conditioning; weight lifting;calisthenics; concentric; eccentric; isotonic and isometric searched
together with performance; physical performance; muscle; muscle
strength; muscle mass; hormone; cortisol; testosterone; protein synthesis; recovery; growth; IGF-1; insulin and metabolism. Search terms
were phrased and truncated as appropriate.
2.2. Eligibility criteria
The eligibility criteria required studies to investigate the effect ofinadequate sleep on resistance exercise (e.g. handgrip test) or training performance outcomes. Outcome measures of interest weremuscle strength and physiological response mechanisms underlying changes in muscle strength or size e.g. hormonal indicators ormarkers of protein metabolism. Title/s and abstracts were screened
for relevance to sleep and resistance exercise in adults and potentially relevant articles were accessed to assess the full text. Studies
were excluded if no nocturnal sleep loss occurred or if the sleep
deprivation or restriction period was not deﬁned. Animal studies and conference abstracts were also excluded. Screening, data
extraction and quality assessment were performed by two authors(OK, CU). Disagreement on any article or outcome was discussed
between authors and resolved by additional authors (ED, SL, BA)
where required.
2.3. Quality assessment
The Effective Public Health Practice Project (EPHPP) quality
assessment tool for quantitative studies21 was used to assess themethodological strength of each study. Standard scoring procedures were used to assign global scores based on the accumulationof strong, moderate or weak scores given across domains of selection bias, study design, confounders, blinding, data collection
method, and withdrawals and dropout21 (Table 2).
3. Results
3.1. Literature selection
The original search presented 1702 peer-reviewed, Englishlanguage articles, of which 997 were identiﬁed as duplicates(Fig. 1). Screening of titles/abstracts excluded 669 articles irrelevant to sleep loss and/or strength parameters. Twelve articles wereretrieved from reference lists of relevant articles. Thirty-one articles were excluded where the outcome measures were deemed
irrelevant, were conference abstracts or the full text could not
be retrieved. Studies investigating jetlag and Ramadan have beenpreviously reviewed22,23 and were therefore excluded. The ﬁnal
number of studies included in this review was 17. The study characteristics and key ﬁndings are presented in Table 1. The quality
assessment scores for each paper, based on the EPHPP tool, areshown in Table 2.

2.1. Search strategy
3.2. Sleep restriction
This review was conducted using the preferred reporting items
for systematic reviews and meta-analyses (PRISMA) statement.20 A
systematic search of the electronic databases EBSCOHost (search-

Seven studies investigated one night of sleep restriction24–30
and one study examined repeated nights (three or more) ofPlease cite this article in press as: Knowles OE, et al. Inadequate sleep and muscle strength: Implications for resistance training. J Sci
Med Sport (2018), https://doi.org/10.1016/j.jsams.2018.01.012

Sample size (n), PA
statusAge (mean ± SD),sex

Amount of sleep(protocola )Exercise protocol

Time of testing

Outcome measures

Key ﬁndingsb

Arnal et al.32

12, physically
active32.3 ± 3.9, M

5 nights of EXT or
HAB, followed by 1
night TSD

Strength test pre (D0) & post
(D1) TSD

1700 hIsometric knee
extension (time toexhaustion), knee
extension MVC

TSD compared to control
nightBlumert et al.36

Bougard et al.28

Bulbulian
et al.39

8, sedentary

9, national level
weight lifters

11, N/A

24, marine corps

30.0 ± 6.0, F

20.7 ± 1.2, M

21.5 ± 1.5, N/A

TSD/EX group:
22.1 ± 2.9, M

2.5 h sleep for 1
night (delayed
sleep onset)

1 night TSD

5 or 6 h sleep for 1
night (early
waking)

1 night TSD (withor without EX)

Strength test

RT session: snatch, clean &jerk, front squat; 6–7 sets,
1–2reps; 70–100% 1-RM
(additional submaximal sets
for front squat after 1-RM set)

Strength tests

Strength tests.
40 km march carrying 50% BW
performed during TSD for
TSD/EX group

0600 h &1800 h0900 h0600 h1600 hMVC & isokinetic
knee extension &ﬂexion peak torque

1RM, volume load
& training
intensity.
Blood samples (C,T)

MVC & isometricelbow ﬂexion
strength (meantorque)Isokinetic knee
extension & ﬂexion(peak torque &fatigue index)

TSD group:
21.7 ± 2.2, M

Chase et al.27

7, recreational
cyclists

24.0 ± 7.0, 6 M & 1F

3 h sleep for 1
night, (early
waking)Strength tests

60 min cycle sprint interval
session & leg press

0830 hIsokinetic knee
extension (peaktorque)↔ MVC or isokinetic peak
to torque↔ interaction between SR& time of day
TSD compared to control
night↔ 1RM, total volume load,
total training intensity↔ T, C, T/C ratio
5-h SR compared to 6-h SR↔ MVC or isometric mean
torque
TSD compared to control
night↓ knee extension peaktorque↔ fatigue index
TSD/EX compared to control
night↓ knee extension & ﬂexion
peak torque↔ fatigue index
SR compared to control night↔ peak torque

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Bambaeichi
et al.24↓ pre-exercise MVC (HAB,d = −1.38; EXT d = −0.33)↓ time to exhaustion (HAB,d = −1.31; EXT d = −0.52)
EXT compared to HAB↔ pre-exercise MVC↑ time to exhaustion(d = 0.51 at D0, d = 0.74 at
D1)
SR compared to control night

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Please cite this article in press as: Knowles OE, et al. Inadequate sleep and muscle strength: Implications for resistance training. J Sci
Med Sport (2018), https://doi.org/10.1016/j.jsams.2018.01.012

Table 1
Characteristics and key ﬁndings of studies related to inadequate sleep and resistance exercise.

3

Sample size (n), PA
statusAge (mean ± SD),sex

Amount of sleep(protocola )Exercise protocol

Time of testing

Outcome measures

Key ﬁndingsb

Cook et al.30

16, professional
rugby players

20.9 ± 0.9, M<6 h sleep (protocol
not reported)

RT session: squat, bench press,
bench row; 4 sets, repetitions
to failure; 85% 1-RM

1100 hTotal workload(volume x
intensity) & saliva
samples (C, T)

SR compared to control night

21.4 ± 5.3, 12 M &12 F

1 night TSD

Strength tests

0800 h &2000 hKnee extension &MVC

Goh et al.34

14, military service
members

20–30, M

1 night TSD

Strength tests

0800, 1300 h &every 3 h from1800–600 h

Handgrip strength& saliva samples(C)

HajSalem
et al.26

21, judo athletes

19.1 ± 1.2, M

4.5 h sleep for 1
night (early
waking)Strength tests pre- & post-judo
match

N/A

Handgrip strength

Meney et al.35

11, N/A

20–28, M

1 night TSD (day 1),
followed by 1 nightnormal sleep (day2)

Strength tests

Day 1: every
4 h from
0600–0200 h.
Day 2: every
4 h from
1000–2200 h

Handgrip, knee
extension & backextension strength

Reilly &Piercy31

Skien et al.37

8, trained

11, amateur rugby
league athletes

18–24, M

20.4 ± 2.5, M

3 h sleep eachnight, for 3 nights(delayed sleep
onset)

1 night TSD

Bicep curl, bench press, deadlift, leg press

Strength tests

Rugby match ∼7 h after
pre-match test and before TSD
period1700 hPre-match(8000 h),Post-match, 2 h& 16 hpost-match

1-RM

MVC & voluntary
activation of knee
extensors.

↔ handgrip strength↑ C at 1330 h only
SR compared to control night↔ handgrip strength
TSD compared to control
night↔ day 1 handgrip & knee
strength, ↓ back strength at
2am only↓ day 2 back strength
TSD compared to control
night↓ 1RM deadlift, leg press,
bench press↔ 1RM bicep curl
TSD compared to control
night↔ MVC (d = 0.13-0.33) &voluntary activation(d = 0.16-0.56)

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24, N/A

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Daviaux et al.33↓ total workload (d = 2.33)↑ baseline C (d = 0.41-0.80)↔ post-RT C↓ baseline (d = 0.67-1.09)
and post-RT T
SR (with caffeine) compared
to SR (placebo)↑ total workload (d = 1.47)↑ post-RT T↑ post-RT C
TSD compared to control
group↔ MVC strength↔ interaction between TSD& time of day
TSD compared to control
group

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4Please cite this article in press as: Knowles OE, et al. Inadequate sleep and muscle strength: Implications for resistance training. J Sci
Med Sport (2018), https://doi.org/10.1016/j.jsams.2018.01.012

Table 1 (Continued)

Sample size (n), PA
statusAge (mean ± SD),sex

Amount of sleep(protocola )Exercise protocol

Time of testing

Outcome measures

Key ﬁndingsb

Souissi et al.25

12, judo athletes

18.6 ± 2.4, M

3 h sleep for 1 night(delayed sleep
onset or early
waking)Strength tests pre- & post-judo
match

0900 h &1600 hHandgrip strength& elbow ﬂexor
MVC

Early waking SR compared
to control night

Takeuchiet al.38

11, N/A

12, strength
trained

22.0 ± 3.0, M

22.7 ± 2.2, M

2 nights of TSD

2 nights of TSD

Strength tests

1100 h:isokinetic tests

6 h hike between night 1 & 2 of
TSD

1400: MVC
tests

Strength tests

0000 hBench press & leg
extension strength(for 25 repetitions),
elbow ﬂexor & leg
extensor MVC

Handgrip strength,
isokinetic leg
ﬂexion & extension(peak torque)↓ knee extension torque at60◦ s−1

1 h of treadmill walking at 28%
VO2 max every 3 h for TSD/EX
group

Waterhouse
et al.29

10, N/A

23.3 ± 3.4, M

4 h sleep for 1 night(early waking)

Strength test (with or without
prior nap)

↔ bench press & leg
extension peak torque↔ MVC
TSD & TSD/EX compared tocontrol night

1400

Handgrip strength

TSD compared to TSD/EX↔ handgrip strength, knee
ﬂexion or extension torqueNap compared to no-nap↔ handgrip strengthM, male; F, female; n, number; PA, physical activity; N/A, not available; SD, standard deviation; TSD, total sleep deprivation; SR, sleep restriction; EXT, extended sleep; HAB, habitual sleep; TSD/EX, total sleep deprivation &exercise; MVC, maximal voluntary contraction; RT, resistance training; RTD, rate of torque development; h, hour; ms, milliseconds; min, minutes; km, kilometre .T, testosterone; C, cortisol; BW, body weight; VO2 max, maximal
oxygen uptake; ↔, no effect (p > 0.05); ↓, signiﬁcantly decreased (p < 0.05); ↑, signiﬁcantly increased (p < 0.05); d, Cohen’s d (representative of effect size, reported where available).
a
Sleep restriction studies only.
b
Key ﬁndings compared to a ‘control night’ indicate a within-groups study design whereas a ‘control group’ indicates a between-groups study design.

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Symons et al.40↓ Handgrip strength(3.1-8.4%) & MVC in theevening (15-24%)
Delayed onset SR compared
to control night↔ Handgrip strength &MVC
TSD compared to control
night

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Please cite this article in press as: Knowles OE, et al. Inadequate sleep and muscle strength: Implications for resistance training. J Sci
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Table 1 (Continued)

5

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Records identified through databasesearching(n = 1702)

Additional records identified
through other sources(n = 12)

Records after duplicates removed(n = 717)

Included

Eligibility

Screening

Idenﬁcaon

6

Records screened(n = 717)

Records excluded(n = 669)

Full-text articles assessed
for eligibility(n = 48)

Full-text articles excluded,with reasons(n = 31)Studies included inqualitative synthesis(n = 17)

Fig. 1. Flow diagram summarising study selection process. n = number.

Table 2
Quality assessment of studies using the Effective Public Health Practice Project (EPHPP) quality assessment tool for quantitative studies.
Study

Selection bias

Study design

Confounders

Blinding

Data Collection Method

Withdrawals and dropout

Global score

Arnal et al.32
Bambaeichi et al.24
Blumert et al.36
Bougard et al.28
Bulbulian et al.39
Chase et al.27
Cook et al.30
Daviaux et al.33
Goh et al.34
HajSalem et al.26
Meney et al.35
Reilly & Piercy31
Skien et al.37
Souissi et al.25
Symons et al.40
Takeuchi et al.38
Waterhouse et al.29

2
1
2
1
1
2
1
1
1
1
2
2
1
1
2
1
2

1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

1
1
1
1
1
1
1
2
3
3
3
1
1
1
1
1
2

3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3

1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1

1
1
1
3
1
1
1
1
1
1
2
1
1
1
1
1
1

Moderate
Moderate
Moderate
Weak
Moderate
Moderate
Moderate
Moderate
Weak
Weak
Weak
Moderate
Moderate
Moderate
Moderate
Moderate
Moderate

1 = strong; 2 = moderate; 3 = weak; Global scores were determined by the accumulation of domain scores for each paper. A ‘strong’ global score was given where studies had
no ‘weak’ domain ratings, a moderate global score was given where studies had one ‘weak’ domain rating and a weak global score was given where studies had two or more
‘weak’ domain ratings.

sleep restriction.31 Sleep opportunities varied from 2.5–6 h acrossstudies, with two implementing delayed bedtime24,31 and four
implementing advanced waking protocols.26–29 Souissi et al.25
compared both advanced waking and delayed bedtime protocols.
Time of testing varied from morning (0600 h) to late afternoon(1700 h). Most studies achieved ‘moderate’ EPHPP scores since
sleep restriction studies cannot blind participants. Two studies achieved ‘weak’ global scores for not providing information
regarding the control of confounders26 and for a high participant
non-completion rate28 in addition to a lack of blinding.
Reilly and Piercy31 exposed male participants to three nights ofsleep restriction (sleep opportunity between 0300–0600 h). Sleep
restriction signiﬁcantly and linearly decreased one repetition maximum (RM) strength for leg press and deadlift (at 1700 h) after

each successive night. Maximal bench press strength decreased
after the third night only. Total workload performed during a resistance training session decreased with one night of sleep restriction(∼6 h, time N/A).30 The resistance training (at 1100 h) included
four sets of repetitions to failure at 85% 1-RM for squat, benchpress and bent row exercises. However, one night of sleep restriction (at ∼0300–0600 h) demonstrated no effect on isometric andisokinetic knee extension and ﬂexion strength in females (at 0600
and 1800 h)24 or handgrip and elbow ﬂexor strength in males (at0900 and 1600 h).25 Advanced waking protocols (at ∼2300–0300)
demonstrated no effect on maximal handgrip strength,26 isokinetic
leg extension torque27 and isometric elbow ﬂexor strength28 whentested in the morning. A signiﬁcant decrease by 3–8% in handgrip strength and 15–24% in elbow ﬂexor MVC following advanced

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waking (at 2300–0200 h), was only found when strength tests
were conducted in the afternoon.25 Waterhouse et al.29 used anadvanced waking protocol (at ∼2300–0300 h) in conjunction withor without a day time nap; napping had no effect on handgrip
strength (at 1400 h). Elevated baseline cortisol and decreased baseline and post-exercise testosterone concentrations were attributed
to sleep restriction in one study.30 Collectively, these studies25,30,31
indicate that multiple nights of sleep restriction or an extended
wake time (e.g. more than twelve hours awake) following advanced
waking impair muscle strength and disturb the hormonal responseto resistance exercise.

3.3. Sleep deprivation
Six studies investigated the effect of one night of sleep deprivation on resistance exercise.32–37 Four studies32,33,36,37 wereconsidered of ‘moderate’ quality and two studies34,35 were unclear
in their control of confounders and did not blind participants,
resulting in ‘weak’ scores. Time of testing varied between studies,with tests conducted in the morning (∼0800 h),33 in the afternoon(∼1700 h)32 or at regular intervals (e.g. every 4 h) throughout theintervention.34,35
Blumert et al.36 found that sleep deprivation (24 h) had noeffect on 1-RM achieved or total workload during a resistancetraining session (at 0900 h). Similarly, sleep deprivation (24–40 h)
had no effect on maximal voluntary contraction (MVC) tests ofhandgrip,34 knee extension33 and back extension strength,35 tested
periodically. In contrast, Arnal et al.32 observed a signiﬁcant performance decrease for knee extension MVC (at 1700 h) following
sleep deprivation (34–37 h). One study37 investigated the effectof sleep deprivation (24 h) following an afternoon rugby matchwith no effect on leg extensor MVC or voluntary activation. Sleep
deprivation (24 h) demonstrated no effect on cortisol, testosteroneor the cortisol–testosterone ratio following a resistance training
session.36 However, salivary cortisol levels in sleep-deprived military personnel increased only at 1330 h in comparison to control
participants who slept overnight.34 The ﬁndings demonstrate thatmaximal muscle strength and cortisol-testosterone proﬁles are
typically maintained with a single night of sleep deprivation andresistance exercise.
Three studies38–40 investigated the effect of sleep deprivation on
muscle strength in conjunction with different exercise protocols
and all received ‘moderate’ EPHPP quality ratings. Sleep deprivation (64 h) elicited a signiﬁcant ≈19% decrease in knee extension
torque (at 0000 h) with no mediating effect of intermittent treadmill walking.38 Bulbulian et al.39 found a signiﬁcant decrease inpeak knee extension torque (at 1600 h) amongst sleep-deprived(30 h) US Marine Corps personnel, and an additional decrease inknee ﬂexion in those who also completed a 40-km march withexternal load. In contrast, Symons et al.40 found a 6-h hike during 60 h of sleep deprivation had no effect on upper body or lower
body isokinetic (at 1100 h) and MVC strength (at 1400 h), compared
to a control group who slept at night. Overall, these results are notconclusive regarding the effect of sleep deprivation with extended
exercise protocols on muscle strength.

4. Discussion
The following sections discuss the effect of sleep restriction andsleep deprivation on muscle strength and hormonal indicators ofmuscle protein metabolism, with the aim to provide context for
speciﬁc populations facing inadequate sleep and implications fortheir training.

7

4.1. Muscle strength in response to sleep restriction
Three consecutive nights of sleep restriction impaired maximal
force output where larger muscle groups were recruited.31 Compound, multi-joint exercises that recruit large muscle groups are
considered to be the most effective in increasing muscle strength.41
The ability to adapt to resistance exercise rather than execute
acute absolute strength is critical for preserving metabolic health; areduced force output induced by sleep restriction could, over time,diminish the positive impact of resistance training on metabolic
health. The ﬁndings are applicable to those facing frequent inadequate sleep, such as new parents or athletes in heavy training
and competition. No shiftwork studies identiﬁed in the original
search reported participants’ sleep opportunities or quantity andwere therefore excluded. The sleep–wake schedules and circadian rhythms of shiftworkers are likely to be different to otherpopulations, therefore the applicability of day-oriented ﬁndings
to shiftworkers, should be taken with caution. However, nightshiftworkers’ rate of torque development during knee ﬂexion has
been demonstrated to decrease by 13.9%, when tested after a
36-h work period, compared to day-shiftworkers.42 Therefore,
consecutive night shifts may also reduce force output in acute exercises recruiting large muscle groups, which could have adverse
implications for training load output. Total load output in a resistance training session (i.e. with a combination of sets, exercises
and repetitions) decreased with one night of sleep restriction inathletes.30 However, the workload performed in multi-joint exercises was restored with caffeine ingestion, compared to no caffeine
ingestion.30 Caffeine is a supplement used to increase physiological alertness and cognitive performance.6 However, the study by
Cook et al.30 maintained a constant exercise intensity, therefore
caffeine may also be valuable in offsetting rising perceived exertionand falling motivation caused by sleep restriction.30 Countering adiminished motivation to train from sleep-related fatigue, could beparticularly valuable for all groups facing inadequate sleep, as a low
motivation to train could be an equally large threat to preserving
muscle mass as a reduction in training workload itself.
To compound the effect of inadequate sleep, the time of day
that resistance exercise is performed may impact muscle strength,
due to circadian oscillations or the prolonged amount of prior waketime (e.g. due to advanced waking and/or a night shift). One study
reported a strength deﬁcit following a single night of sleep restriction, when athletes were woken early and tested in the evening.25
In fully rested people, the evening may present an optimal hormonal and metabolic environment in the muscle to maximise
resistance exercise adaptations.43 Therefore, the ﬁndings by Soussi
et al.25 may result from a shift in the circadian release of hormonesthat regulate muscle metabolism and suggest that morning training may be more effective for advanced waking groups. Baseline
cortisol is elevated and both baseline and post-resistance training
testosterone levels are lowered with a night of sleep restriction.30
Over multiple nights of sleep restriction alone, anabolic hormone
circulation is reduced by up to 15%,44 which may negatively impact
adaptations to resistance training. A longer prior wake time may
also reduce central drive.45 Therefore, cognitive impairments that
increase perceived exertion and decrease motivation for executing
maximal force may also be important to consider when prescribing training. Napping has been identiﬁed as an appropriate andfeasible approach to supplement an inadequate main sleep period
and restore cognitive alertness, in shiftworkers and older adults.46
A day time nap following sleep restriction had no effect on grip
strength.29 However, since only an acute isolated strength variable
was tested,29 napping may remain beneﬁcial prior to performing
resistance training with compound exercises that require greater
cognitive alertness. Collectively, the ﬁndings may be important forsleep-restricted groups who may perform resistance training more

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8effectively with caffeine ingestion or following a nap; or prior to
prolonged waking periods.
4.2. Muscle strength and hormonal responses to sleep deprivation
Blumert et al.36 conducted a resistance training session after
a night of sleep deprivation. The session consisted of Olympicstyle lifts performed by experienced, national calibre weightlifters,
tested in groups. No change was found in training capacity or testosterone and cortisol response, suggesting that inadequate sleep
does not disrupt the performance or hormonal response to resistance exercise. The ﬁndings conﬂict those of Cook et al.30 (seeSection 4.1) but given similar timing of sampling with respect tothe training session and time of day, it is difﬁcult to explain theapparent differences. Blumert et al.36 suggest that being appropriately motivated may negate the effect of acute sleep deprivationon performance. Social facilitation induced by group training islikely to increase motivation47 and may be an ideal approach formaintaining strength during training. Given the complexity of thelifts and the training experience of the participants, it is difﬁcult
to generalise the ﬁndings of Blumert et al.36 to non-athlete populations, experiencing inadequate sleep and performing moderate
forms of resistance training. However, training in groups is likely
to be beneﬁcial for less experienced trainers,47 such as younger
athletes, new parents, older adults and shiftworkers. The remaining studies also suggest that a night of sleep deprivation may beinsufﬁcient to elicit a deﬁcit in MVC strength33–35,37 or change incortisol proﬁle.34 However, following one night of sleep deprivation and then a recovery sleep, back strength decreased comparedto two nights of normal sleep. The ﬁndings may be applicableto groups who train after a recovery sleep, such as new parents
or shiftworkers who work 24-h shifts (e.g. military services orsome ﬁre departments48 ). Perhaps more importantly, the ﬁndings
highlight the need for all groups to employ training motivation
strategies, even after a recovery sleep. Muscle strength and hormonal responses may be maintained following one night of sleep
deprivation; however, this may be dependent on the type of resistance exercise, training status and training environment.
Studies implementing sleep deprivation alongside continuous
exercise protocols reported mixed results for muscle strength.38–40
One study found that more strength variables decreased with exercise than with sleep deprivation alone,39 suggesting that exhaustive
exercise may exaggerate the negative relationship between sleep
deprivation and resistance exercise. This knowledge is critical for
exercise professionals to ensure that exhaustive training is notplanned around periods when their recreational clients or professional athletes may be sleep deprived. While this type of extended
sleep deprivation with intense physical work may be applicable tomilitary personnel and some physically demanding occupations, it
is less translatable to other groups facing inadequate sleep who may
not perform physically demanding tasks outside of their resistancetraining.

ing the real-world importance of the relationship between thesevariables.50 The quality of the studies in the current review were
mostly evaluated as ‘moderate’ with four studies assigned a ‘weak’
global score. It is important to note that participant blinding cannot
be controlled for in sleep deprivation or restriction studies, therefore none of the studies were able to achieve ‘strong’ global scores.
Studies that received a ‘weak’ global score also typically scoredpoorly in the domains of selection bias, study design or confounding
variables. Implementing a rigorous design is important to ensurethat appropriate conclusions are made for individuals experiencing
inadequate sleep. Finally, the ﬁndings from this review are limited
by a lack of shiftworker studies and by a small sample of athlete
studies that have mostly implemented severe sleep restriction (3 h)or sleep deprivation (>60 h) periods. Therefore, the reader should
consider these limitations regarding the practical application of theﬁndings.
4.4. Future directions
Only four of the reviewed studies included female participants,
and only one of these analysed sex differences. The circadian regulation of hormones in women is largely dependent on menstrual
cycle phase.51 Disrupted circadian rhythms, which may occur withinadequate sleep, are associated with menstrual disturbances.51
Precisely how circadian rhythms, menstrual disturbances, inadequate sleep and skeletal muscle metabolism interact is unknown
and warrants the inclusion of women in future studies.
No studies in the current review investigated the direct effectof resistance exercise on skeletal muscle adaptation with inadequate sleep. Nevertheless, authors have hypothesised mechanisms
whereby inadequate sleep may dampen anabolic hormones andsignalling molecules, consequently down-regulating skeletal muscle protein turnover and growth.17,18 Recent rodent studies support
these hypotheses. Sleep deprivation induced a decline in testosterone, IGF-1 and skeletal muscle mass in male Wistar rats.52,53
Sleep deprivation also elevated the levels of ubiquitinated proteins,which are markers of protein degradation, in rodents.52,53 While
research in humans is warranted, animal models may provide novel
insights into our understanding of the musculoskeletal health problems that may be associated with inadequate sleep.2 Interestingly,
rodents who were subjected to an eight-week resistance training
protocol prior to sleep deprivation suffered fewer adverse consequences compared to untrained rats.52,53 Resistance training may
therefore have a protective effect against the increase in catabolism
induced by sleep deprivation.54 The ﬁndings compel future investigations into the value of resistance training for preserving thehealth of sleep-deprived populations. Speciﬁcally, further researchshould examine resistance training and skeletal muscle health withmoderate sleep restriction (5–6 h) that more accurately reﬂects theexperience of populations battling inadequate sleep.
5. Conclusions

4.3. Limitations
The time spent in sleep is important to quantify accurately.
Only three studies27,28,32 in the current review used actigraphy
or polysomnography to assess sleep duration prior to or during
the intervention. While sleep diaries correlate well with sleep timing and duration, they are not as valid as actigraphy monitors inassessing sleep to wake transitions, nor polysomnography, which
remains the gold standard.49 Several studies were also limitedby their statistical analysis, whereby only statistical signiﬁcancewas reported, with no acknowledgement of effect sizes or statistical power. The magnitude of effect that inadequate sleep has on
resistance exercise and muscle health is essential to determin-

The current review suggests that sleep deprivation or sleep
restriction can impair acute maximal muscle strength in compound movements, when motivation is not facilitated. However,the ﬁndings regarding the testosterone-cortisol response to resistance training remain mixed, with further research required to
afﬁrm changes associated with inadequate sleep. Importantly, thisreview is limited by only one study of consecutive nights of sleep
restriction existing and only two studies implementing a resistancetraining session. Regular and structured resistance training sessions, rather than singular testing bouts, are important for skeletal
muscle adaptation. Therefore, the interaction between inadequate
sleep and resistance training should be the focus of future work.

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The limited research makes it difﬁcult to provide evidencebased resistance training recommendations for groups experiencing inadequate sleep. However, based on the reviewed evidence,
tentative suggestions can be made. Populations who experience sleep deprivation or sleep restriction may want to perform
resistance training in groups to maintain motivation and sustain a manageable lifting intensity that will provide an adequate
mechanical stimulus to the muscle. Additionally, to reduce themultiple adverse effects of sleep-related fatigue (e.g., elevated perceived exertion, reduced concentration and alertness), these groups
should endeavour to train with prior ingestion of caffeine or before
waking time extends considerably. Napping or caffeine ingestion
prior to training may improve cognitive function and preserve
lifting performance in compound movements requiring increased
alertness. While the evening presents an optimal hormonal milieu
for resistance training in non-sleep fatigued people,43 the morning may be an appropriate time for sleep-restricted groups to train
if wake time is short and motivation is high; this is dependent
on training and working schedules and requires further research.
Finally, future studies should prioritise quantifying the interaction of inadequate sleep and resistance training on markers ofskeletal muscle metabolism. These investigations will underpin thedevelopment of appropriate guidelines for resistance training withinadequate sleep.
Acknowledgement
SL is supported by a Discovery Early Career ResearchAward (DECRA) from the Australian Research Council (ARC)(DE150100538).
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