Access to this full-text is provided by MDPI.
Content available from Nutrients
This content is subject to copyright.
Citation: Henselmans, M.; Bjørnsen,
T.; Hedderman, R.; Vårvik, F.T. The
Effect of Carbohydrate Intake on
Strength and Resistance Training
Performance: A Systematic Review.
Nutrients 2022,14, 856. https://
doi.org/10.3390/nu14040856
Academic Editor: Ajmol Ali
Received: 23 January 2022
Accepted: 16 February 2022
Published: 18 February 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
nutrients
Review
The Effect of Carbohydrate Intake on Strength and Resistance
Training Performance: A Systematic Review
Menno Henselmans 1, *, Thomas Bjørnsen 2, Richie Hedderman 1and Fredrik Tonstad Vårvik 1,2
1The International Scientific Research Foundation for Fitness and Nutrition, David Blesstraat 28HS,
1073 LC Amsterdam, The Netherlands; hurricanefitnessireland@gmail.com (R.H.);
ftvaarvik@gmail.com (F.T.V.)
2Department of Sport Science and Physical Education, Faculty of Health and Sport Sciences,
University of Agder, 4630 Kristiansand, Norway; thomas.bjornsen@uia.no
*Correspondence: Info@MennoHenselmans.com; Tel.: +31-61-809-5999
Abstract:
High carbohydrate intakes are commonly recommended for athletes of various sports,
including strength trainees, to optimize performance. However, the effect of carbohydrate intake on
strength training performance has not been systematically analyzed. A systematic literature search
was conducted for trials that manipulated carbohydrate intake, including supplements, and measured
strength, resistance training or power either acutely or after a diet and strength training program.
Studies were categorized as either (1) acute supplementation, (2) exercise-induced glycogen depletion
with subsequent carbohydrate manipulation, (3) short-term (2–7 days) carbohydrate manipulation
or (4) changes in performance after longer-term diet manipulation and strength training. Forty-
nine studies were included: 19 acute, six glycogen depletion, seven short-term and 17 long-term
studies. Participants were strength trainees or athletes (39 studies), recreationally active (six studies)
or untrained (four studies). Acutely, higher carbohydrate intake did not improve performance in
13 studies and enhanced performance in six studies, primarily in those with fasted control groups and
workouts with over 10 sets per muscle group. One study found that a carbohydrate meal improved
performance compared to water but not in comparison to a sensory-matched placebo breakfast. There
was no evidence of a dose-response effect. After glycogen depletion, carbohydrate supplementation
improved performance in three studies compared to placebo, in particular during bi-daily workouts,
but not in research with isocaloric controls. None of the seven short-term studies found beneficial
effects of carbohydrate manipulation. Longer-term changes in performance were not influenced by
carbohydrate intake in 15 studies; one study favored the higher- and one the lower-carbohydrate
condition. Carbohydrate intake per se is unlikely to strength training performance in a fed state
in workouts consisting of up to 10 sets per muscle group. Performance during higher volumes
may benefit from carbohydrates, but more studies with isocaloric control groups, sensory-matched
placebos and locally measured glycogen depletion are needed.
Keywords: resistance exercise; carbohydrate intake; muscle strength; performance
1. Introduction
Dietary carbohydrates can enhance performance in endurance sports, as they are
the preferred muscular energy substrate at moderate to high intensities [
1
]. There is
less research about carbohydrate requirements for strength training, such as Olympic
weightlifting, powerlifting and bodybuilding. Resistance training is metabolically distinct
from endurance training and leads to different training stimulus and adaptive responses,
so it may have different carbohydrate requirements [2].
Carbohydrates can be stored as glycogen in the liver (approximately 80–120 g) and
muscles (approximately 350–700 g) [
3
]. Muscle contractions during both low- and high-load
resistance training rely primarily on the anaerobic glycolysis pathway for energy, as there
Nutrients 2022,14, 856. https://doi.org/10.3390/nu14040856 https://www.mdpi.com/journal/nutrients
Nutrients 2022,14, 856 2 of 39
is insufficient oxygen to rely purely on the aerobic system and fatty acids to provide energy
sufficiently rapidly [
4
–
6
]. Hence, glycogen depletion could limit performance. Glycogen
is localized in three main subcellular compartments within the muscle cell; under the
sarcolemma, intermyofibrillar between the myofibrils and intramyofibrillar within the
myofibrils [
7
]. Glycogen depletion can occur locally in these subcellular glycogen depart-
ments after resistance training, even if whole-muscle glycogen levels are only partially
depleted [
8
]. Excessive glycogen depletion can contribute to muscle fatigue by lower-
ing ATP synthesis [
7
,
9
], and possibly also by lowering muscle excitation and impairing
calcium release from the sarcoplasmic reticulum [
10
,
11
]. Endurance exercise in a signif-
icantly glycogen-depleted state can also increase protein oxidation and reduce muscle
protein synthesis [
12
,
13
]; however, low pre-exercise glycogen availability has not been
found to significantly affect anabolic signaling or muscle protein synthesis after strength
training [
12
,
13
]. While low glycogen availability per se may not be detrimental for muscle
anabolism, it can impair strength performance and training volume [
14
,
15
]. In addition,
strength-trained individuals can achieve higher work outputs during exercise and have
a greater capacity for glycogen storage compared to untrained individuals [
16
,
17
]. Thus,
trained individuals may require higher carbohydrate intakes to optimize performance,
although training status does not seem to influence the relative level of glycogen depletion
after a given resistance training workout [18].
Previous reviews have recommended carbohydrate intakes of 8–10 g per kilogram
of bodyweight per day (g/kg/day) during ‘heavy anaerobic exercise’ [
16
]. Others recom-
mend 4–7 g/kg/day for strength athletes to optimize strength performance and hypertro-
phy
[19,20]
. These recommendations are not far from the common 6–12 g/kg/day recom-
mendation for endurance athletes [
1
]. The average daily intake of carbohydrates in body-
builders has been reported to range from 2.8 to 7.5 g/kg/day, compared to
4.2–8 g/kg/day
in strength-athletes [
20
,
21
]. However, none of these recommendations or practices stem
from a systematic literature review, only narrative reviews. Thus, this systematic re-
view examines whether carbohydrate intake influences acute and longer-term strength
training performance.
2. Methods
The present systematic review followed Preferred Reporting Items for Systematic
Reviews and Meta-Analyses (PRISMA) guidelines [
22
]. We did not pre-register the present
review, because the protocol did not fulfill the requirements for preregistration at Prospero,
which state that they do not accept reviews assessing sports performance as an outcome.
However, in retrospect, there are other options that we have used [23].
2.1. Search Strategy
A literature search was conducted in EBSCOhost within the MEDLINE and SPORT-
Discus databases, in addition to the SciELO database. Search terms included a combi-
nation of Medical Subject Headings (MeSH terms) and free-test words consisting of the
following keywords:
“(MH “Carbohydrates”) OR (“glycogen depletion” OR “high carbohydrate” OR “low
carbohydrate” OR keto* OR (maltodextrin N2 (supplement* OR intake) OR (glucose N2
(ingestion OR intake OR supplement) OR (carbohydrate* N6 (intake* OR supplement*
OR manipulat* OR consumption OR ingestion OR feeding OR restricti* OR diet OR drink
OR breakfast)) AND MH “Resistance Training” OR MH “Weight Lift*” OR (isokinetic
OR “strength training” OR “resistance training” OR “resistance exercise” OR powerlift*
OR weightlift* OR “power lift” OR CrossFit) AND (MH “Muscle Strength”) OR (strength
OR 1 RM OR performance OR failure OR power OR “total work” OR torque OR force
OR volume)”. The search strategy for each database can be found in the Supplementary
Material, gray literature (master theses, PhD dissertations and conference abstracts) were
searched for with the same keywords in Google Scholar. The last literature search included
publications up until the 1 January 2022 and was completed by RH and FTV.
Nutrients 2022,14, 856 3 of 39
2.2. Inclusion Criteria
Online published trials were included if they compared conditions with different
carbohydrate intakes, including supplements, and measured dynamic resistance training
performance as an outcome. Studies were categorized as either (1) acute carbohydrate
manipulation (up to 24 h) or supplementation prior to strength tests, (2) exercise-induced
glycogen depletion and carbohydrate manipulation prior to strength tests, (3) short-term
carbohydrate manipulation of at least a day and up to a week prior to strength tests or
(4) long-term changes in strength performance after more than a week of carbohydrate
manipulation and strength training. Strength performance was measured in the form
of maximal strength (1 repetition maximum (1 RM), isokinetic work or peak or average
torque), repetitions to failure (within a single set, number of sets to predetermined rep-
etition failure or total repetition volume when training to failure) or power (average or
peak). Isometric strength measurements were only included if participants also performed
dynamic strength measurements to ensure the assessed outcomes were practically relevant
to strength trainees. In addition, sprinting, agility, jumping, short-distance running or
Wingate performance were included as secondary outcomes if at least one of the primary
outcomes were measured. Participants had to be healthy (i.e., free of chronic diseases)
and below 60 years of age. Studies with concurrent training were included only if the
endurance training was performed in a separate session. Papers in all languages were
eligible. Congress abstracts were eligible for inclusion but presented in their own sections,
not among the main findings. Letters were not included.
2.3. Study Selection and Data Extraction
Title and abstracts were screened by HR and FTV, followed by review of the full texts.
Any disagreement between authors were discussed with all authors until a consensus
was reached. Each of the included studies’ citations and related review articles were
also screened for additional articles fulfilling the inclusion criteria. Data from each study
were extracted to a spreadsheet, including (a) citation, (b) study design, (c) participant
characteristics and sample size, (d) experimental details (including fed or fasted state and
carbohydrate intake in acute and glycogen depletion studies and daily macronutrient
intake in short- and long-term studies) and (e) results.
2.4. Quality Assessment
Study quality was assessed using the validated Tool for the Assessment of Study
Quality and Reporting in Exercise (TESTEX) scale [
24
]. TESTEX is a 15-point assessment
scale, consisting of 5 points for study quality and 10 for study reporting. Higher scores
reflect better study quality and reporting. However, points 6C (exercise attendance),
7 (intention to treat analysis), 10 (activity monitoring in control groups) and 11 (progressive
program) were excluded for the acute-, glycogen depletion- and short-term study categories,
as these items did not apply in an acute context where participants do not follow a long-
term diet and training intervention. Additionally, point 10 (activity of the control group)
was excluded for the assessment of the long-term studies, as we only included studies
with the same exercise intervention. For point 7 (intention to treat analysis), a point was
given if there were no dropouts and therefore no need for an intention-to-treat analysis. For
point 11 (consistent training intensity), a point was given if the participants were athletes
or strength trainees following their regular program. Thus, the maximum scores for the
acute and longer-term studies were 11 and 14, respectively. Furthermore, point 6C (exercise
attendance) was not considered applicable for the long-term studies of shorter duration in
which participants were not prescribed any training in between strength tests, so it was
marked as “n/a”. The assessment was performed independently by FTV and TB. If any
points were unclear, they were discussed until an agreement was reached. Based on the
sum of the scores, studies were classified as having either excellent quality (acute studies:
10–11 points, long-term studies: 12–14 points), good quality (acute: 8–9, long-term: 10–11),
fair quality (acute: 5–7, long-term: 7–9) or low quality (acute: <5, long-term: <7) [25].
Nutrients 2022,14, 856 4 of 39
3. Results
The literature search yielded a total of 504 papers after duplicate removal; 447 papers
were excluded based on their title and abstract. After examining the 57 remaining full
texts, 40 papers from the main search were included as well as four additional papers
from reference lists, four theses/dissertations and one from authors’ previous knowledge
on the topic (Figure 1), amounting to 19 acute, five exercise-induced glycogen depletion,
seven short-term and 17 long-term studies. Additionally, four published abstracts were
included (three acute and one short-term). Study quality in the acute, glycogen depleted
and short-term studies was rated good (8
±
1 points); longer-term study quality was
rated fair (
9±1 points
). See summary Tables 1and 2and individual study results in
Tables A1 and A2 (Appendix A).
Nutrients 2022, 14, x FOR PEER REVIEW 4 of 45
term: 10–11), fair quality (acute: 5–7, long-term: 7–9) or low quality (acute: < 5, long-term:
< 7) [25].
3. Results
The literature search yielded a total of 504 papers after duplicate removal; 447 papers
were excluded based on their title and abstract. After examining the 57 remaining full
texts, 40 papers fr om the m ain search were included as well as four additional pa pers from
reference lists, four theses/dissertations and one from authors’ previous knowledge on the
topic (Figure 1), amounting to 19 acute, five exercise-induced glycogen depletion, seven
short-term and 17 long-term studies. Additionally, four published abstracts were included
(three acute and one short-term). Study quality in the acute, glycogen depleted and short-
term studies was rated good (8 ± 1 points); longer-term study quality was rated fair (9 ± 1
points). See summary Tables 1 and 2 and individual study results in Tables A1 and A2
(Appendix A).
Figure 1. Flow chart of the study selection process.
Table 1. Summary of study quality assessment in acute-, glycogen depletion- and short-term studies.
Criterion n %
Study quality 1. Eligibility criteria specified 21 66
2. Randomization specified 5 16
3. Allocation concealment 30 94
4. Groups similar at baseline 32 100
5. Blinding of assessor (for at least one key outcome) 16 50
Study reporting 6a. Outcome measures assesses in 85% of participants 30 94
6b. Adverse events reported 1 3
8a. Between-group statistics reported—primary 32 100
Figure 1. Flow chart of the study selection process.
Table 1.
Summary of study quality assessment in acute-, glycogen depletion- and short-term studies.
Criterion n%
Study quality 1. Eligibility criteria specified 21 66
2. Randomization specified 5 16
3. Allocation concealment 30 94
4. Groups similar at baseline 32 100
5. Blinding of assessor (for at least one key outcome) 16 50
Study reporting 6a. Outcome measures assesses in 85% of participants 30 94
6b. Adverse events reported 1 3
8a. Between-group statistics reported—primary 32 100
8b. Between-group statistics reported—secondary 32 100
9. Points measures and measures of variability reported
31 97
12. Exercise volume and energy expenditure 29 91
1 = criteria met; 0 = criteria not met; n= number of studies meeting criteria: % = percentage of studies meeting
criteria. Thirty-one studies in total.
Nutrients 2022,14, 856 5 of 39
Table 2. Summary of study quality assessment in long-term studies.
Criterion n%
Study quality 1. Eligibility criteria specified 16 94
2. Randomization specified 0 0
3. Allocation concealment 12 71
4. Groups similar at baseline 15 88
5. Blinding of assessor (for at least one key outcome) 1 6
Study reporting 6a. Outcome measures assesses in 85% of participants 14 82
6b. Adverse events reported 7 41
6c. Exercise attendance reported 13 76
7. Intention-to-treat analysis 7 41
8a. Between-group statistics reported—primary 17 100
8b. Between-group statistics reported—secondary 17 100
9. Points measures and measures of variability reported
17 100
11. Relative exercise intensity remained constant 16 94
12. Exercise volume and energy expenditure 5 29
1 = criteria met; 0 = criteria not met; n= number of studies meeting criteria: % = percentage of studies meeting
criteria. Fourteen studies in total.
3.1. The Effect of Acute Carbohydrate Manipulation on Strength Training Performance
Nineteen publications met the inclusion criteria [
26
–
44
], summarized in Table 3and
Figure 2. Sixteen studies were crossover trials with an average of 11
±
4 participants
(median: 9) [
26
–
31
,
34
–
39
,
41
–
44
]; three studies were randomized controlled trials (RCTs)
with an average of 11
±
5 participants (median: 9) per group [
32
,
33
,
40
]. Participants
were young, with an average age of 23
±
2 years. Training status of the participants was
categorized as untrained [
32
], physically active [
42
], CrossFit trained [
38
,
44
], recreationally
trained [
27
,
40
,
43
] or strength-trained [
26
,
28
–
31
,
33
–
37
,
39
,
41
]. All participants were men
except for 6 of the 17 participants in Fairchild et al. [27] and all 13 in Raposo [37].
The participants were in fasted or unspecified conditions in 13 studies before car-
bohydrate manipulation and the performance tests [
27
,
29
–
33
,
36
–
39
,
41
,
42
,
44
]; six studies
were performed with both groups in a fed state (2.5–5 h) before performance was mea-
sured [
26
,
28
,
34
,
35
,
40
,
43
]. Only one of the studies was isocaloric [
36
]. Workout types
included traditional strength training [
26
,
29
–
35
,
37
,
39
–
43
], CrossFit [
38
,
44
], circuit train-
ing [
36
], and isokinetic exercise [
27
,
28
]. Fifteen studies measured performance as repetitions
to failure, sets to predetermined repetition failure, total training volume and/or total work
(kJ) during traditional strength exercises [
26
,
29
–
35
,
37
–
43
] or CrossFit [
36
,
44
], of which one
also included peak power [
30
] and two studies measured isokinetic performance (aver-
age and peak power, isokinetic peak or average torque, total and average work across
sets) [
27
,
28
]. Four studies also measured secondary outcomes, such as agility and sprint
time [
29
,
36
], jump distance and throwing performance [
29
] and work output measured as
caloric expenditure during maximal effort rowing [38].
3.1.1. Main Findings
In total, 11 of the 19 acute studies found no significant effect of carbohydrate in-
take on strength training performance [
26
,
31
–
35
,
37
,
38
,
41
,
43
,
44
]. Of the eight studies with
a significant between-group effect, six favored the higher-carbohydrate condition: five stud-
ies reported more repetitions to failure/training volume [
29
,
30
,
39
,
40
,
42
] (but not peak
power [
30
]) and one study reported greater isokinetic performance [
28
]. In these studies,
the higher-carbohydrate conditions also had a higher energy intake, because the control
conditions were either continuing their overnight fast [
39
], received a non-caloric placebo
after an overnight fast [
30
] or in an unspecified state [
42
], received 5.5 g amino acids as
placebo [
29
] or received a non-caloric placebo 3–5 h after a meal [
28
,
40
]. None of the
isocaloric comparisons found the higher carbohydrate condition had greater performance
than the lower carbohydrate condition [36,40,44].
Nutrients 2022,14, 856 6 of 39
Table 3. The acute effect of carbohydrate ingestion on strength training performance.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate (CHO) Intakes Fasted or Fed Results
Baty et al. [32]
RCT:
Healthy untrained men
(n= 32),
carbohydrate-protein group
vs. placebo group.
Training: 7 exercises (high pull, lat
pull-down, standing overhead press, knee
extension, leg curl, leg press and bench
press) with the two first sets as 8 RM, and
the third set with the same load as set 2 but
until voluntary failure.
Outcome
: total weight lifted (kg) during the
last set per exercise and weight lifted scaled
per lean body mass multiplied by the
number of repetitions completed during the
last set per exercise.
CHO: 0.59 g/kg (44 g [6.2%]
and 1.5% protein).
Placebo: non-caloric.
Timing
: 355 mL 30 min prior to
exercise, 177 mL immediately
before and after the
fourth exercise.
Fasted
(12 h overnight).
No significant differences between
conditions in weight lifted the last set
or total training volume (total load
CHO-PRO: 534 ±80 kg vs. placebo:
556 ±82 kg; weight scaled per lean
body mass ×repetitions CHO-PRO:
93 ±17 vs. placebo: 92 ±21).
Dalton et al. [33]
RCT:
Strength-trained subjects
(n= 22), carbohydrates
(
n= 8
) vs. placebo (n= 8) vs.
control (n= 6) in
caloric deficit
Training: lower-body exercises (squat, leg
press and knee extension) and bench press at
60–80% of 10 RM, 5-sets per exercise.
Outcome: last set of knee extension and
bench press 80% of 1 RM to failure.
CHO: 1 g/kg
beverage supplement.
Placebo:
non-caloric supplement.
Control: no supplement.
Timing: 30 min before testing.
Overnight fasted.
No significant differences in
repetitions to failure between
conditions (knee extension CHO:
17 ±1, placebo: 17 ±2, control:
17 ±2; bench press CHO: 17 ±2,
placebo: 17 ±2, control: 16 ±3).
Fairchild et al. [
27
]
Counterbalanced crossover:
Strength-trained men
(n= 11) and women (n= 6),
carbohydrate vs. placebo.
Training
: one set of 3 RM knee extensions in
an isokinetic dynamometer, and again after
5, 15, 30, 45, 60, 75 and 90 min.
Outcome: peak and average
isokinetic torque.
CHO: 1.1 g/kg (75 g).
Placebo:
non-caloric supplement.
Timing: after the first baseline
3 RM.
Fasted
(>12 h overnight).
There was no interaction effect but
when adjusting for baseline values
a significant main effect between
conditions were observed where the
CHO condition resulted in a decline
(~2%-points) and maintenance in
average and peak torque,
respectively, compared to an increase
(~4–5%-points) in both for placebo.
Fayh et al. [34]
Crossover:
Strength-trained subjects
(n= 8), carbohydrate
vs. placebo.
Training: seven exercises (bench press, lat
pulldown, rear deltoid, barbell curl, hammer
curl, leg press and squat) with three sets
with an intensity of 70% 1 RM to failure.
Outcome: total training volume
(repetitions ×sets ×load).
CHO: 1 g/kg (84 g) of
maltodextrin
beverage supplement.
Placebo:
non-caloric supplement.
Timing
: 15 min before training.
Fed
(2 h pre).
No significant differences in total
training volume between conditions
(CHO: 12,944 ±2548 kg vs. placebo:
12,876 ±2025 kg).
Nutrients 2022,14, 856 7 of 39
Table 3. Cont.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate (CHO) Intakes Fasted or Fed Results
Haff et al. [28]
Crossover:
Strength-trained men
(n= 8), carbohydrate
vs. placebo.
Training: 16 sets of 10 repetitions with
isokinetic knee extension and flexion
Outcome
: total and average work (J) across all
sets, peak and average isokinetic torque (Nm)
across all sets.
CHO
: 1.0 g/kg prior to exercise
and 0.51 g/kg during exercise
(143 g in total).
Placebo: non-caloric.
Timing: before exercise and
after set 1, 6 and 11.
Fed
(3 h pre).
Significant greater total work (CHO:
24 ±2 J, placebo: 22 ±2 J), average
work (CHO: 1.5 ±0.1 J, placebo:
1.4 ±0.5 J), and average torque per
set (CHO: 105 ±8 Nm, placebo:
98 ±8 Nm) in knee extension in the
CHO condition. No differences were
observed between conditions in peak
torque in the knee extension or any
of the measurements for the
knee flexors.
Krings et al. [29]
Crossover:
Strength-trained men
(n= 7), carbohydrates,
amino acids and
electrolytes vs. amino acids
and electrolytes (placebo).
Training: explosive high-intensity training
and resistance training: hang clean at 50–70%
1 RM, front squat at 45–90% 1 RM, box jumps,
dumbbell bench press and barbell bent-over
row at 60–73% 1 RM, barbell reverse lunge at
55–70% 1 RM, single-arm shoulder press at
65–70% 1 RM, dumbbell biceps curl and
dumbbell overhead triceps extension at 60%
1 RM. Three to seven sets for all exercises.
Outcome
: last set to failure in dumbbell bench
press, barbell bent-over row, dumbbell biceps
curl and dumbbell overhead triceps extension.
Sprints, jump distance, overhead medicine
ball throws and agility tests.
CHOs: 15, 30 or 60 g/h
corresponding to a 3, 6 and 12%
solution. In addition to 5.5 g
amino acids (AA)
and electrolytes.
Placebo: 5.5 g AA
and electrolytes.
Timing: before exercise and
every 15 min during exercise,
total 5 dosages.
Fasted
(at least 10 h
overnight).
No significant differences in total
repetitions between CHOs and
placebo, but 15 g/h > 60 g/h. For the
bench press, all CHO groups
outperformed placebo without
dose-response. No significant
differences for the other three
exercises, two jumps or four run
times, except 60 g/h > placebo for
the 27-m sprint.
Kulik et al. [35]
Counterbalanced crossover:
Strength-trained men
(n= 8), carbohydrate
vs. placebo.
Training: sets of five repetitions at 85% 1 RM
until subjects could no longer squat to parallel,
failed to do a repetition every 8 s, or reached
voluntary failure, with 3-min rest between sets.
Outcome: repetitions and sets to failure, in
addition to volume load (load ×sets ×
repetitions) and total work (kJ).
CHO: 0.3 g/kg (28 g).
Placebo: non-caloric.
Timing: before and after every
other set of 5 repetitions.
Fed
(3 h pre).
No significant differences between
conditions in repetitions and sets to
failure or volume load and total load
(repetitions CHO: 20 ±15 vs.
placebo: 20 ±13, sets CHO: 4 ±3 vs.
placebo: 4 ±3, volume load CHO:
2929 ±2220 kg vs. placebo:
2773 ±1951 kg, work CHO:
30 ±22 kJ vs. placebo: 29 ±20 kJ).
Nutrients 2022,14, 856 8 of 39
Table 3. Cont.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate (CHO) Intakes Fasted or Fed Results
Lambert
et al. [26]
Crossover:
Strength-trained men
(n= 7), carbohydrate
vs. placebo.
Training: knee extensions at 80% of 10 RM,
first set was performed with 10 repetitions,
then subsequent sets were performed until
one failed to perform 7 repetitions in
a single set.
Outcome: repetitions and sets to failure.
CHO: 1 g/kg before exercise,
and 0.17 g/kg dosages during
exercise (97 or 125 g in total).
Placebo: non-caloric.
Timing: before exercise, an after
set 5, 10 and 15.
Relatively fed
(4-h pre).
No significant difference in repetitions
and sets to failure between the
conditions. However, there was
a tendency for more repetitions
(149 ±16 vs. 129 ±12, p= 0.067) and
sets (
17 ±2
vs. 14
±
2, p= 0.056) in the
CHO condition.
Laurenson and
Dubé[30]
Crossover:
Strength-trained men
(n= 10), carbohydrates
vs. placebo.
Training: Seven sets of squat and bench
press (60% 1 RM), first 6 with
a predetermined number of repetitions.
Outcome: last set was performed to
repetition failure where the total volume
(kg load ×repetitions) and peak power
output was measured.
CHO: 0.43 g/kg (36 g and 12 g
of protein).
Placebo: non-caloric.
Timing: two dosages, 12 and
26 min into exercise.
Fasted
(8–10 h).
Significantly more total bench press
volume in the CHO condition
(921 ±365 vs. 783 ±332). However,
no differences was observed in total
squat volume (CHO: 1009 ±433 vs.
909 ±472, p= 0.1) or peak power for
either bench press or squat.
Lynch [36]
Crossover:
Strength-trained men
(n= 15), carbohydrates vs.
high-protein (including
carbohydrates, protein
and fat).
Training: high-intensity resistance training
for 2 min (overhead push-press, dumbbell
push-press, squats and dumbbell push-ups)
for as many rounds as possible.
Outcome: performance tests 2 h after the
workout; agility T-test, push-up (repetitions
to failure), and 40-yard sprint.
CHO: A total of 0.84 g/kg (68 g).
High-protein: 40 g protein, 11 g
of carbohydrate and 6 g fat
(isocaloric to CHO).
Timing: within 5 min of
completing the first workout.
Not specified.
No significant difference between
conditions in agility T-test, push-ups to
failure or sprint. However, analyzing
all three performance variables
simultaneously yielded a significant
greater effect of the high-protein
condition compared to the
carbohydrate condition.
Maroufi
et al. [44]
Crossover:
Male CrossFit athletes
(n= 8),
carbohydrate-protein
supplement in two ratios
(2:2 or 3:1) vs. placebo.
Training: two 15–17 min CrossFit workouts.
Outcome: repetitions to failure.
CHO-protein (ratio 3:1): 67.5 g
CHO and 22.5 g protein.
CHO-protein (ratio 2:2): 45 g
CHO and 45 g protein.
Placebo: non-caloric.
Timing: 1 h and immediately
before testing.
Fasted
(overnight)
No significant difference between
conditions in repetitions to failure (3:1
ratio 341 ±56, 2:2 ratio 366 ±61,
placebo 346 ±65).
Naharudin
et al. [39]
Counterbalanced crossover:
Strength-trained men
(n= 16), breakfast vs.
a water-only breakfast.
Training
: Four sets to failure with squat and
bench press at 90% of 10 RM.
Outcome: repetitions to failure.
CHO: A total of 1.5 g/kg (116 g),
standardized breakfast meal,
~20% of estimated energy needs.
Control: water only.
Timing: 2 h before testing.
Fasted
(~10 h
overnight).
Significantly more repetitions to failure
in the CHO condition for squat
(68 ±14 vs. placebo: 58 ±11, effect
size [ES] = 0.98) and bench press
(40 ±5 vs. placebo: 38 ±5, ES = 1.06).
Nutrients 2022,14, 856 9 of 39
Table 3. Cont.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate (CHO) Intakes Fasted or Fed Results
Naharudin
et al. [41]
Counterbalanced crossover:
Strength-trained men
(n= 22), breakfast vs.
placebo-breakfast vs.
water-only.
Training: Four sets to failure with squat
and bench press at 90% of 10 RM.
Outcome: repetitions to failure.
CHO: A total of 1.5 g/kg
(117 g), standardized breakfast
meal, 496 kcal.
Placebo: semi-solid, 29 kcal
with low-energy flavored
squash and water.
Control: water only.
Timing: ~2 h before testing.
Fasted
(10–13 h
overnight).
Significantly more repetitions to
failure in the CHO and placebo
breakfast conditions in the squat
exercise (CHO: 44 ±10, placebo:
43 ±10, water-only: 38 ±10), but
not during bench press (CHO:
39 ±7, placebo: 38 ±7, water-only:
37 ±7). While there was no
significant difference in repetitions
completed in the CHO- vs. the
placebo condition.
Raposo et al. [37]
Counterbalanced crossover:
Strength-trained women
(n= 13), carbohydrates
vs. placebo.
Training: Five sets with 75% of 1 RM of
bench press and 85% of 1 RM for leg press.
Outcome: repetitions to failure and total
volume (sets ×repetitions ×load) for each
exercise and all exercises together.
CHO: A total of 1 g/kg (81 g).
Placebo: non-caloric.
Timing: A total of 1 h
before exercise.
Fasted
(overnight).
No significant differences between
conditions in repetitions to failure
and training volume (repetitions
bench press, CHO: 45 ±11 vs.
45 ±10; leg press, CHO: 112 ±59 vs.
98 ±38. Training volume bench
press, CHO: 1451 ±414 vs.
1430 ±387; leg press, CHO:
19,960 ±13,477 vs. 17,103 ±8927).
Rountree et al. [
38
]
Crossover:
Strength-trained men
(n= 8), carbohydrates
vs. placebo.
Training: Five rounds of wall throws with
a 9 kg medicine ball, box jumps, sumo
deadlift high pulls with 34 kg, push presses
with 34 kg for as many repetitions as
possible within 1 min, and rowing
ergometer at maximum effort for 1 min.
Outcome: repetitions to failure and caloric
expenditure during rowing.
CHO
: A total of 0.2 g/kg (16 g).
Placebo: non-caloric.
Timing: before exercise and
during the training session
(6 total dosages of 2.7 g each).
Fasted
(10–12 h
overnight).
No significant differences between
conditions in repetitions to failure
(total repetitions CHO: 279 vs.
placebo: 272) and caloric expenditure
during 1 min all out rowing
(kilocalories CHO: 42 vs.
placebo: 45).
Santos et al. [42]
Crossover:
Strength-trained men
(n= 8), carbohydrates vs.
placebo.
Training: one set of bench-press, 70% of
1 RM to failure.
Outcome: repetitions to failure.
CHO: A total of 0.27 g/kg
(20 g).
Placebo: non-caloric.
Timing: 1 h before training.
Not specified. Significantly more repetitions in the
CHO condition (13 ±2 vs. 11 ±2).
Nutrients 2022,14, 856 10 of 39
Table 3. Cont.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate (CHO) Intakes Fasted or Fed Results
Smith et al. [31]
Crossover:
Strength-trained men
(n= 13), carbohydrates vs.
carbohydrates + BCAA vs.
BCAA vs. placebo.
Training: barbell bench press, landmine
bent-over row, barbell incline press, and
landmine close-grip row. All exercises were
performed with 5 sets to failure at 65% of
1 RM.
Outcome: repetitions to failure.
CHO: A total of 0.44 g/kg
(36 g).
CHO + BCAA: A total of 36 g
and 7.5 g BCAA.
BCAA: A total of 7.5 g
Placebo: non-caloric.
Timing: the total dosage was
distributed to be ingested
before and after warm-up, and
after the last set of
each exercise.
Fasted
(10 h overnight).
No significant time ×treatment
interactions for any exercise for
repetition performance. However,
there was a treatment effect for
CHO + BCAA
compared to the other
treatments, but it was confounded by
an order effect. Additionally,
close-grip row repetitions to failure
were greater in the CHO-BCAA
condition compared to the
other conditions.
Welikonich [40]
RCT:
Recreational
strength-trained men
(n= 27), carbohydrates vs.
CHO-protein vs. placebo.
Training: multiple sets with leg press of
8–10 repetitions at 70% of 1 RM until fatigue
(unable to reach 8 repetitions)
Outcome: total number of repetitions in
addition to sets to failure, measured as total
training volume (load ×repetitions ×sets).
CHO: A total of 0.81 g/kg
(~60 g), 0 g PRO
CHO-PRO: A total of
0.65 g/kg (~50 g) CHO,
~14 g PRO
Placebo: non-caloric (15 kcal)
Timing: A total of 15 min
before training (~30 g) and
between every other set (in
total ~30 g).
Fed (standardized
liquid meal
5 h pre).
Significantly more repetitions in the
CHO and CHO-PRO condition
(CHO: 136 ±55/36, respectively) vs.
placebo (90 ±15). However, no
difference was observed between
groups in total volume of work
(CHO: 28,052 ±19,198 kg vs.
CHO-PRO: 24,836 ±9737 vs.
placebo: 15,934 ±3276 kg (p= 0.13).
Wilburn et al. [43]
Crossover:
Recreational
strength-trained men
(n= 10), carbohydrates
vs. placebo.
Training: Four sets of leg press at 70% of
1 RM to failure.
Outcome: repetitions to failure.
CHO: A total of 2 g/kg (180 g).
Placebo: non-caloric.
Timing
: 30 min before training.
Fed (3 h pre,
instructed not
to change
dietary habits).
No significant differences between
conditions (total repetitions CHO:
52 ±7, placebo: 54 ±8, p= 0.80).
Nutrients 2022,14, 856 11 of 39
Nutrients 2022, 14, x FOR PEER REVIEW 7 of 45
athletes after consuming a non-caloric placebo or after consuming 45 g carbohydrates and
protein or 67.5 g carbohydrates and 22.5 g protein.
Positive effects of higher carbohydrate intakes were more consistent in higher train-
ing volume workouts. In studies with performance tests consisting of more than 10 sets
per muscle group (11–17 sets), significant positive effects of higher carbohydrate intake
[28,40] or a trend thereof [26] were observed in three studies, whereas one study found no
significant effects [33]. Out of 14 studies [27,29,31,32,34–39,41–43] with lower-volume per-
formance tests (≤7 sets per muscle group), three studies [29,39,42] significantly favored
the carbohydrate conditions, and two favored the lower-carbohydrate conditions [27,36].
3.1.3. Results from Published Abstracts
Three published abstracts involving acute carbohydrate manipulation have been
published. Two of those observed no effect of carbohydrate intake on multiple sets of
squats to failure [45] or isokinetic work, power, fatigue and peak torque [46]. One study
found a carbohydrate supplement consumed in a semi-fasted state resulted in more rep-
etitions during the last set of leg presses, but there was no effect for total repetitions of
either the bench press or leg press [47].
Figure 2. Acute carbohydrate intake and effect on strength performance. ↑: “Greater performance for”.
Figure 2.
Acute carbohydrate intake and effect on strength performance.
↑
: “Greater performance for”.
Positive effects of carbohydrate intake were more prevalent when compared to fasts
of four or more hours, but the effect of fasting duration was not clear. In the six studies in
a relatively fed state with no more than five hours of fasting [
26
,
28
,
34
,
35
,
40
,
43
], three studies
found no significant effects of carbohydrate intake after 2–4 h fasts [
34
,
35
,
43
], one found
a non-significant trend for benefits in some of the outcome measurements after a four
hour fast [
26
] and two studies found a positive effect of supplementing carbohydrates
after a 3- or 5-h fast in some but not all of the tested outcomes [
28
,
40
]. In the 11 studies
comparing carbohydrate intake to an overnight fasted state [
27
,
29
–
33
,
37
–
39
,
41
,
44
], one
found a benefit of carbohydrates for both measured outcomes [
39
], two found a benefit
for some but not all of the performance measurements [
29
,
30
], seven found no significant
effects of carbohydrate intake [
31
–
33
,
37
,
38
,
41
,
44
] and one found a detrimental effect [
27
].
Two studies did not specify whether the subjects were fed or fasted [36,42].
Positive findings of carbohydrate intake compared to fasting are not necessarily indica-
tive of a metabolic advantage of carbohydrate consumption. One study in resistance-trained
men [
41
] found that the ergogenic effect of the higher carbohydrate condition was a placebo
or at least non-metabolic effect: a carbohydrate-breakfast resulted in significantly more
squat (but not bench press) repetitions to failure compared to a water-only control group
but not compared to a flavor- and texture-matched placebo breakfast with only 29 kcal.
Two of the acute studies reported greater performance in the lower-carbohydrate
conditions: one favored a non-caloric placebo over carbohydrate intake for isokinetic
performance (when adjusting for baseline values) [
27
] and an isocaloric study favored
a high-protein beverage to a high-carbohydrate beverage for aggregate performance on
a battery of agility, push-ups and sprint tests, though not on any individually analyzed
test [36].
3.1.2. Carbohydrate Dosage and Training Volume
There was no dose-response effect of carbohydrate intake on performance. Significant
effects were observed with dosages as low as 0.27 g/kg [
42
], 0.81 [
40
] and
1.5 g/kg [28,39]
,
yet not found in five studies with 0.2–0.59 g/kg [
31
,
32
,
35
,
38
,
44
] or five studies at
0.89–1.5 g/kg [33,34,37,41,44]
or 2 g/kg [
43
]. Krings et al. [
29
] studied the effect of
15 g/h
,
Nutrients 2022,14, 856 12 of 39
30 g/h and 60 g/h of carbohydrates vs. placebo on strength training, running and jumping
performance. Supplementing with carbohydrates significantly improved performance
compared to placebo only in the bench press at all doses and for the 27-m sprint only at the
60 g/h dosage, without any dose-response effect. In fact, the 15 g/h group significantly
outperformed the 60 g/h group for the bench press and total repetitions across all resistance
training exercises. In absolute terms, the highest number of repetitions were achieved for
the bench press, bent-over row, and triceps extension in the 15 g/h carbohydrate group
and for the biceps curl in the 30 g/h carbohydrate group, none for the 60 g/h carbohydrate
group. The two other studies comparing multiple doses of carbohydrates also found no
effects of carbohydrate dosage on performance. Welikonich [
40
] had participants consume
a pre- and intra-workout drink with either 60 g carbohydrate or 50 g carbohydrate and 14 g
protein or placebo (21 kcal). The lower and higher carbohydrate drinks both improved leg
press repetition performance identically (135 total repetitions) compared to the placebo
drink. Maroufi et al. [
44
] found no significant difference in the total number of repetitions
that could be completed during two CrossFit workouts by CrossFit athletes after consum-
ing a non-caloric placebo or after consuming 45 g carbohydrates and protein or 67.5 g
carbohydrates and 22.5 g protein.
Positive effects of higher carbohydrate intakes were more consistent in higher training
volume workouts. In studies with performance tests consisting of more than 10 sets per
muscle group (11–17 sets), significant positive effects of higher carbohydrate intake
[28,40]
or a trend thereof [
26
] were observed in three studies, whereas one study found no sig-
nificant effects [33]. Out of 14 studies [27,29,31,32,34–39,41–43] with lower-volume perfor-
mance tests (
≤
7 sets per muscle group), three studies [
29
,
39
,
42
] significantly favored the
carbohydrate conditions, and two favored the lower-carbohydrate conditions [27,36].
3.1.3. Results from Published Abstracts
Three published abstracts involving acute carbohydrate manipulation have been
published. Two of those observed no effect of carbohydrate intake on multiple sets of squats
to failure [
45
] or isokinetic work, power, fatigue and peak torque [
46
]. One study found
a carbohydrate supplement consumed in a semi-fasted state resulted in more repetitions
during the last set of leg presses, but there was no effect for total repetitions of either the
bench press or leg press [47].
3.2. The Effect of Exercise-Induced Glycogen Depletion and Carbohydrate Manipulation on Acute
Strength Training Performance
Six studies were included that measured strength training performance after exercise-
induced glycogen depletion [
15
,
48
–
52
], summarized in Table 4and Figure 3. All were
crossover trials with an average sample size of 9
±
4, consisting of recreationally active [
15
],
high-intensity trained [
51
] or strength-trained individuals [
48
–
50
,
52
] with an average age of
24
±
2 years. Five studies contained only men [
48
–
52
]; one study consisted of five men and
one woman [
15
]. One study by Haff et al. measured glycogen depletion after nine sets of
squats and three sets of isokinetic leg extensions and again after three more sets of maximal
isokinetic leg extensions/flexions [
52
]. When training fasted, glycogen concentrations de-
creased by 19.2% after the squats, rising to 40.7% after the isokinetic exercise. When training
after consuming 1 g/kg carbohydrate pre-workout and every 10 min intra-workout, the
depletion levels were reduced to 15.2% and 26.5%, respectively. The five other studies
did not measure glycogen levels but instead designed their exercise-induced glycogen
depletion sessions to deplete glycogen stores by ~80% via bicycling based on previous
work [
15
,
48
,
50
,
51
] or high-volume (15 sets) strength training similar to the aforementioned
study by Haff et al. [
49
]. The low-carbohydrate conditions consisted of either continuing
their overnight fast [
50
], ~1.2 g/kg carbohydrates in the hours between their depletion
session and strength tests [
49
], normal/high carbohydrate intakes up until a three-hour
fast [
52
] or a daily carbohydrate intake of ~0.4–1.8 g/kg [
15
,
48
,
51
]. Carbohydrate intakes
in the high-carbohydrate conditions consisted of either 1.2 g/kg as a single [
50
] or repeated
Nutrients 2022,14, 856 13 of 39
dosage totaling ~2 g/kg [
49
,
52
], 7.7 g/kg/day [
48
], or they were not reported [
15
,
51
].
The strength workouts included traditional strength training
[48–50]
and isokinetic ex-
ercise
[15,51,52]
. Performance measures consisted of total training volume
[15,48,49]
or
total work (J) [
51
,
52
] in addition to power, force and velocity across sets [
50
] and peak and
average torque [15,51,52].
3.2.1. Main Findings
Three of the six studies favored the higher carbohydrate intake over the non-caloric
conditions [
15
,
49
,
50
]. Compared to a non-caloric placebo or unspecified condition, two stud-
ies observed significantly more repetitions to failure in the high-carbohydrate condi-
tions [
15
,
49
] and one study observed higher average power outputs [
50
]. The only calorie-
matched experiment by Mitchell et al. [
48
] found no significant between-group differ-
ences in total training volume during 15 sets of quadriceps strength training (five sets
each of squats, knee extensions and leg presses) at 15 RM repetitions failure. The glyco-
gen depletion workout consisted of bicycling followed by 48-h carbohydrate intakes of
0.38 g/kg/day (32 g/day) vs. 7.65 g/kg/day (643 g/day). A similar trial by Symons
and Jacobs [
51
] had trained men perform a glycogen depletion workout followed by 48 h
of a lower-carbohydrate diet (1.8 g/kg/day, 140 g) compared to an unspecified higher-
carbohydrate diet. Afterwards, they performed 50 maximal isokinetic leg extensions and
isometric strength tests. There were no significant between-group differences in isometric
strength, total work (J), neuromuscular fatigue or peak or average torque. In addition, no
group-differences were observed in total work (J), peak or average torque compared to the
non-caloric placebo condition in Haff et al. [52].
3.2.2. Carbohydrate Dosage and Training Volume
Training volume did not clearly mediate the effect of carbohydrate intake on strength
training performance. Positive effects were observed in workouts with 5–19 sets [
15
,
49
,
50
]
yet not in a trial with 15 sets [
48
] or during three sets of 10 repetitions [
52
] or during
50 maximal isokinetic knee extensions [
51
]. Similarly, no dose-response of carbohydrate
intake was evident, with a lack of an effect at 1.9 g/kg [
52
] and 7.7 g/kg/day [
48
] yet
significant effects at intakes of 1.2–2.0 g/kg [49,50].
Nutrients 2022, 14, x FOR PEER REVIEW 15 of 45
Figure 3. Exercise-induced glycogen depletion prior to carbohydrate intake and strength perfor-
mance tests. ↑: “Greater performance for”.
Figure 3.
Exercise-induced glycogen depletion prior to carbohydrate intake and strength performance
tests. ↑: “Greater performance for”.
Nutrients 2022,14, 856 14 of 39
Table 4. The effect of exercise-induced glycogen depletion and carbohydrate manipulation on acute strength performance.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate- (CHO) Intakes Fasted or Fed Results
Haff et al. [49]
Counterbalanced crossover:
Strength-trained men (n= 6),
carbohydrate vs. placebo.
Glycogen depleting workout:
Five sets of 10 repetitions in squats (65%
1 RM), speed squats (45% 1 RM) and
1-legged squat (10% 1 RM).
Training: A total of 4 h after the first
workout, session two was performed; as
many sets of 10 squats with 55% of 1 RM
as possible (to failure) with a 3-min
rest interval.
Outcome: completion of as many sets
with 10 repetitions as possible.
Both conditions received
a standardized high-carbohydrate
(~1.2 g/kg) lunch 2.5 h prior to
strength tests (~825 kcal).
CHO: 1.2 g/kg/h during the morning
session, 0.38 g/kg/h during the 4 h
recovery period between workouts,
while a non-specified dosage was
provided every second set (total
carbohydrate intake not specified).
Placebo: non-caloric.
Timing
: morning, recovery period and
during exercise.
Fed (2.5 h pre).
Significantly more repetitions
and sets to failure in the CHO
condition (total repetitions
CHO: 199 ±115 vs. placebo:
131 ±67, total sets CHO:
19 ±12 vs. placebo: 11 ±7).
There was no significant
difference in the total work
performed between conditions,
but a tendency for a difference
in favor of the CHO condition
(336 ±217 vs. placebo:
224 ±114, p= 0.066).
Haff et al. [52]
Crossover:
Strength-trained men (n= 8),
carbohydrate vs. placebo.
Training: Three sets of 10 repetitions of
knee extension and flexion in an isokinetic
dynamometer, pre and post depletion
workout: 3 sets of 10 repetitions of squats
(65% 1 RM), speed squats (45% 1 RM) and
1-legged squat (10% 1 RM).
Outcome: total and average work (J)
across sets, peak and average isokinetic
torque (Nm) before and after the
training bout.
CHO: A total of 1 g/kg pre and
0.3 g/kg 3 ×during the depletion
workout (163 g in total)
Placebo: non-caloric.
Timing: before exercise and
3 drinks during.
Fed
(3 h pre).
No significant differences in the
isokinetic measurements
between conditions.
(Glycogen levels were reduced
by ~41% in the placebo
condition and ~27% in the
carbohydrate condition.)
Leveritt and
Abernethy [15]
Crossover:
Recreationally active men
(n= 5) and women (n= 1);
first tested strength, then
performed a glycogen
depletion workout 5 days
later and 2 days of a low
carbohydrate diet (~100 g
per day) prior to strength
tests again.
Glycogen depletion workout:
cycling at 75% of VO2max for 1 h, 3 min
rest, followed by four 1 min bouts at 100%
of VO2max with 3-min rest intervals.
Outcome
: Three sets of isoinertial squat at
80% of 1 RM performed until failure with
3-min rest-intervals, in addition to
5 repetitions with isokinetic knee extension
torque at five different contraction speeds.
Lower carbohydrate: ~1884 kcal
1.21 g/kg (90 g carbohydrates).
Control diet:
Not reported.
Not specified.
Significantly more repetitions
at set 1 and 2 during squats in
the control diet group
compared to the low-
carbohydrate diet (set 1: CHO:
18 ±8, control: 12 ±5, set 2:
CHO: 14 ±6, control: 10 ±4.
No significant difference was
observed in set 3 (CHO: 10 ±7,
control: 11 ±4) or in torque
during knee extensions.
Nutrients 2022,14, 856 15 of 39
Table 4. Cont.
Study Design and Population Training Protocol and
Performance Outcomes Carbohydrate- (CHO) Intakes Fasted or Fed Results
Mitchell
et al. [48]
Counterbalanced crossover:
Strength-trained men (n= 11);
high-carbohydrate and
a low-carbohydrate condition
for 48 h after
glycogen depletion.
Glycogen depletion workout:
cycling at 70% of VO2max for 1 h,
followed by 1-min sprints at 115% of VO2
max with 1-min rest-intervals.
Outcome: after the 48 h diet period;
five sets at 15 RM of squats, leg presses
and knee extensions to failure.
Performance was quantified as total
volume lifted.
Lower carbohydrate: 3094 kcal
0.4 g/kg
CHO/protein/fat
32/226/230 g
Higher carbohydrate: 3206 kcal
7.7 g/kg
CHO/protein/fat
643/84/33 g
Not specified.
No significant differences in
total training volume between
groups (high-carbohydrate:
~15,800 kg, low-carbohydrate:
~15,500 kg).
Oliver et al. [50]
Crossover:
Strength-trained men (n= 16),
two carbohydrate conditions
with different molecular
weight and osmolarity
vs. placebo.
Glycogen depletion workout:
cycling for 60 min at 70% VO2max,
followed by six 1-min sprints at 120% of
maximal aerobic power.
Training: A total of 2 h after cessation of
the first workout, session two was
performed; squats at 75% of 1 RM, five sets
of 10 as explosive as possible.
Outcome: average power output, force
and velocity across all squat sets.
CHO
: 1.2 g/kg (106 g), high molecular
weight and low osmolarity (HMW),
and low molecular weight and high
osmolarity (LMW).
Placebo: non-caloric.
Timing: after the glycogen depletion
bout (2 h before strength training).
Fasted (overnight
12 h).
The carbohydrate conditions
achieved significantly greater
average power outputs and
movement velocities than
placebo, but the differences
between groups in total
training volume or average
force output were insignificant
or of ‘trivial’ magnitude.
Symons and
Jacobs [51]
Counterbalanced crossover:
Men (n= 8) with experience
with high-intensity training;
glycogen depleted the knee
extensors with cycling, then
subjects followed two diets
the next two days; low
carbohydrate diet or
a mixed diet.
Outcome: knee extension electrically
evoked isometric muscle force, voluntary
isometric strength and isokinetic total
work across all repetitions (J), peak and
average torque from 50 maximal unilateral
knee extensions, in addition to muscle
fatigue (average torque of the last three
contractions divided by the peak torque).
Lower carbohydrate: A total of
3000 kcal
140 g, 1.8 g/kg/day
(19%) carbohydrates.
Higher carbohydrate:
Not reported.
No significant differences
between groups in any of the
performance measurements.
Nutrients 2022,14, 856 16 of 39
3.3. The Effect of Short-Term Carbohydrate Manipulation on Acute Strength Training Performance
Seven studies that investigated the short-term effect of a higher-carbohydrate vs.
a lower-carbohydrate diet were included [
53
–
59
], summarized in Table 5and Figure 4.
These studies lasted for a duration of 48 h to 1 week (average 5 days). Four studies were
crossover trials with an average of 15
±
11 participants (median: 11) [
54
,
55
,
58
,
59
] and
three studies were RCTs with an average of 19
±
5 participants (median: 18) in each
study
[53,56,57]
. Participants were young, with an average age of 26
±
3. Three studies
included only men [
55
,
56
,
59
], two studies consisted of only women [
54
,
57
] and two studies
contained both sexes [
53
,
58
]. Training status was categorized as sedentary [
57
], recreation-
ally active [
54
], strength-trained [
55
,
58
] bodybuilders [
59
], CrossFit athletes [
53
] or hockey
athletes [
56
]. Daily carbohydrate intakes in the lower-carbohydrate conditions ranged from
31–346 g (average: 160 g) compared to 165–672 g (average: 390 g) in the higher-carbohydrate
conditions. Three of the short-term studies did not prescribe resistance training within the
study period [
54
,
55
,
58
]; in the other four studies, participants were instructed to continue
their regular resistance training [
59
] or physical activity [
57
], or sport-specific training [
56
],
or to complete a 1 week resistance training log and thus presumably continue their strength
training routine [
58
]. Exercise test protocols included dynamic resistance exercises for the
lower body [
54
,
55
,
57
,
59
] or the whole body [
56
,
58
] or CrossFit workouts [
53
]. Performance
measurements included isokinetic lower-body strength tests [
54
,
57
], maximal strength tests
(1 RM) [
56
,
58
], repetitions to failure, total training volume or work (J) [
55
,
58
,
59
], CrossFit
performance [
53
], jump height [
56
,
58
], lower- or upper-body power [
55
,
58
] and a Wingate
test [58].
3.3.1. Main Findings
None of the five randomized studies found significant effects of carbohydrate intake on
performance, including the only isocaloric study [
53
] and one of the two non-randomized
crossover trials [
59
]. A crossover trial by Sawyer et al. [
58
] favored the lower-carbohydrate
condition for some measures, but due to a lack of randomization or counterbalancing, it
was confounded by a possible order/familiarity effect.
Nutrients 2022, 14, x FOR PEER REVIEW 20 of 45
Figure 4. Short-term carbohydrate manipulation on strength performance. ↑: “Greater perfor-
mance for”.
Figure 4.
Short-term carbohydrate manipulation on strength performance.
↑
: “Greater performance for”.
Nutrients 2022,14, 856 17 of 39
Table 5. The effect of short-term (2–7 days) carbohydrate manipulation on acute strength performance.
Study Design and Population Training Protocol and Performance Outcomes Diet Results
Isocaloric studies
Dipla et al. [54]
Counterbalanced crossover:
Recreationally active women (n= 10);
control diet or a high-protein
lower-carbohydrate diet for
1 week each.
Outcome: handgrip strength and four sets of
16 maximal repetitions (120◦per seconds) with
isokinetic knee extensors and flexors contractions.
Isokinetic peak torque determined by three
maximal efforts, and muscle fatigue as the
percentage reduction in work produced in the
last set relative to the first set.
Lower carbohydrate: A total of
1305 kcal
CHO/protein/fat
99/131/43 g
Higher carbohydrate: A total of
1315 kcal
CHO/protein/fat
179/53/43 g
No significant differences in peak
torque or muscle fatigue
between groups.
Non-isocaloric, protein non-equated studies
Escobar et al. [59]
RCT:
Male (n= 7) and female (n= 11)
CrossFit athletes (n= 18);
high-carbohydrate (n= 9) or a control
group (n= 9). Subjects consumed their
regular diet for 5 days, then the
carbohydrate group increased
carbohydrate intake to 6–8 g/kg/day.
Training: CrossFit workouts on day 6 and 7.
Outcome: number of repetitions performed in
a 12-min CrossFit workout on day 1, 5 and 9.
Lower carbohydrate: 1846 kcal
CHO/protein/fat
213/105/64 g
Higher carbohydrate: 2938 kcal
CHO/protein/fat
428/129/79 g
No significant differences between
groups in number of repetitions
during CrossFit training.
Hatfield et al. [55]
Counterbalanced crossover:
Strength-trained men (n= 8); diet with
50% or 80% of calories from
carbohydrates for 4 days.
Outcome: Four sets of 12 squat jumps at 30%
1 RM. Power output and total work (J)
was measured.
Lower carbohydrate: A total of
50% carbohydrates
Higher carbohydrate: A total of
80% carbohydrates
No significant differences between
groups in any of the
performance measurements.
Kreider et al. [56]
RCT:
Male athletes (n= 14); carbohydrate
supplement group (4 g/kg/day) or
a placebo group for 7 days.
Training: One to two intensive hockey training
sessions per day.
Outcome: vertical jump, 1 RM bench press and
leg press.
Lower carbohydrate: A total of
2398 kcal
346 g (58%) carbohydrates
Higher carbohydrate: A total of
3685 kcal
628 g (68%) carbohydrates
No significant differences between
groups in any of the
performance measurements.
Meirelles et al. [57]
RCT:
Sedentary women (n= 24); 500–800 kcal
deficit conventional diet (n= 12) or ad
libitum very low carbohydrate diet
(VLCD, n= 12) for 1 week.
Outcome: Three sets of 15 maximal effort knee
extensions in the concentric phase at a velocity of
60
◦
/s. Peak torque, average power, set total work
(J), and total work across all sets were measured.
Lower carbohydrate: A total of
<40 g carbohydrates per day
Higher carbohydrate:
CHO/protein/fat
48/22/30%
165 g carbohydrates
No significant differences between
groups in any of the
isokinetic measurements.
Nutrients 2022,14, 856 18 of 39
Table 5. Cont.
Study Design and Population Training Protocol and Performance Outcomes Diet Results
Moura et al. [59]
RCT:
Enhanced male bodybuilders (n= 11);
moderate energy deficit (n= 6) or severe
energy deficit (n= 5) with acute
strength tests in the fourth diet week
after two days of low-calorie
lower-carbohydrate intake and then
after 2 days of refeed with
higher-carbohydrate intake.
Training
: followed their usual resistance training
with five sessions per week.
Outcome: total repetitions to failure, 10 sets of
leg press at 70% 1 RM with 10 RM and 30 s
rest-intervals.
Lower carbohydrate:
Moderate energy deficit: 2968 kcal
CHO/protein/fat
227/295/98 g
Severe energy deficit: 2507 kcal
CHO/protein/fat
235/271/54
Higher carbohydrate:
Refeed after moderate energy deficit:
4039 kcal
CHO/protein/fat
687/151/76 g
Refeed after severe energy deficit:
3715 kcal
CHO/protein/fat
655/116/70 g
Combined moderate and energy
deficit groups:
Lower carbohydrate: A total of
2758 kcal
CHO/protein/fat
231/284/78 g
Higher carbohydrate refeed:
A total of 3892 kcal
CHO/protein/fat
672/135/73 g
No significant differences between
groups in number of repetitions.
Sawyer et al. [58]
Crossover:
Strength-trained men (n= 16) and
women (n= 15); habitual diet for 7 days,
and then a carbohydrate restricted diet
for 7 days.
Training: required to complete a 1-week
resistance trained log, so likely continued their
usual training.
Outcome: handgrip strength, bench press and
back squat 1 RM, bench press peak power,
followed by repetitions to failure, in addition to
countermovement vertical jump height and peak
power output from a 30 s Wingate.
Lower carbohydrate: A total of
2157 kcal
CHO/protein/fat
31/201/137 g
Higher carbohydrate: A total of
2537 kcal
CHO/protein/fat
265/145/100 g
Significantly greater handgrip
strength, squat 1 RM, and vertical
jump height in the carbohydrate
restricted condition compared to the
control condition, with no difference
in the other measurements.
Nutrients 2022,14, 856 19 of 39
3.3.2. Results from Published Abstracts
One published abstract involving short-term carbohydrate manipulation was in-
cluded [
60
]. In this study, 7 days of a carbohydrate loading diet did not increase resistance
training performance compared to a control condition.
3.4. The Effect of Longer-Term Carbohydrate Diets and Strength-Training on Changes in
Strength Performance
Seventeen studies that examined the long-term effects of different carbohydrate intakes
on resistance training performance met the inclusion criteria [
61
–
77
], summarized in Table 6
and Figure 5. Study durations ranged from three weeks to three months (average and
median: 8 weeks). Four studies were crossover trials with an average of
23 ±7 participants
(median: 11) [
61
,
64
,
70
,
75
]; 10 studies were RCTs [
62
,
65
–
68
,
71
,
73
,
74
,
76
,
77
] and three con-
trolled trials [
63
,
69
,
72
] with an average of 37
±
56 participants (median: 21) in each
study. Participants were young, with an average age of 29
±
8, and the majority were
men, but two studies consisted of only women [
66
,
73
] and six studies contained both
sexes [
61
–
63
,
69
,
72
,
75
]. Training status was categorized as untrained [
66
], active [
74
], mil-
itary trained [
71
,
72
], strength-trained [
63
–
65
,
73
,
77
], bodybuilders [
76
], powerlifters or
weightlifters [61,68], CrossFit athletes [62,69,75] or other athletes [67,70].
Daily carbohydrate intakes ranged from 15 to 347 g (average: 100 g, median: 44 g)
in the lower-carbohydrate groups, corresponding to 3–52% (average: 17%, median: 9%)
of total caloric intake, compared to 82 to 758 g (average: 330 g, median: 275 g) in the
higher carbohydrate groups, corresponding to 15–70 (average: 49%, median 47%) of total
caloric intake.
To improve dietary adherence, participants were either instructed to follow prescribed
diets [
61
,
71
,
76
], they were provided with a list of foods to eat [
67
] or menus [
75
], they had fre-
quent meetings with a dietitian [
63
,
66
,
72
], they had to deliver food records
[62,65,68–70,74]
,
they had frequent coaching and were given meal plans [
77
] or pre-cooked meals [
72
], or they
were supervised and provided with packed meals [
64
]. Six of the thirteen ketogenic diet
studies (<100 g/day carbohydrate) also monitored and confirmed ketosis with measuring
ketone levels [65,72,73,75–77].
1
Figure 5.
Long-term carbohydrate manipulation on strength adaptations.
↑
: “Greater performance for”.
Nutrients 2022,14, 856 20 of 39
Table 6. The effect of longer-term carbohydrate diets and strength training on changes in strength performance.
Study Design and Population Strength Training and
Performance Outcomes Diet Results
Isocaloric, isonitrogenous studies
Greene et al. [61]
Crossover:
Intermediate to elite male (n= 9) and female
(n= 5) powerlifters and Olympic weightlifters;
low-carbohydrate ketogenic diet or to continue
their usual ad libitum diet, in a random order
for 3 months (n= 12 completed).
Training: subjects were instructed to
maintain their normal training.
Outcome: 1 RM for one or all of the subjects’
competition lifts.
Lower carbohydrate: A total of
2072 kcal
CHO/protein/fat
41/119/159 g
Higher carbohydrate: A total of
2058 kcal
CHO/protein/fat
223/119/79 g
No significant difference
between groups in changes in
1 RM.
Gregory et al. [62]
RCT:
CrossFit athletes (n= 27) of both genders;
low-carbohydrate ketogenic diet (n= 12) group
or to maintain their normal dietary intake
(control, n= 15) for 6 weeks.
Training: Four CrossFit training sessions
per week.
Outcome: changes in countermovement
vertical jump height and standing long jump
length and time-performance during
a standardized CrossFit workout.
Lower carbohydrate: A total of
1581 kcal
CHO/protein/fat
44/92/115 g
Higher carbohydrate: A total of
1747 kcal
CHO/protein/fat
187/80/73 g
No significant differences
between groups in changes of
any of the
performance measurements.
Meirelles and
Gomes [63]
CT:
Overweight (≥25 BMI) but strength-trained
males and females (n= 21) self-selected to
follow a low-carbohydrate (n= 12) or
a conventional/habitual diet (n= 9) for
8 weeks.
Training: full-body resistance training was
performed three times per week, two sets of
11 exercises with 8–10 RM and 2-min
rest-intervals.
Outcome: 10 RM in the biceps pulldown,
triceps pushdown and leg press.
Lower carbohydrate: A total of
1566 kcal
CHO/protein/fat
83 g carbohydrates
1.5 g/kg/day protein
Higher carbohydrate: A total of
1459 kcal
CHO/protein/fat
171 g carbohydrates
1.6 g/kg/day of protein
No significant differences
between groups in changes in
any of the 10 RM tests.
Nutrients 2022,14, 856 21 of 39
Table 6. Cont.
Study Design and Population Strength Training and
Performance Outcomes Diet Results
Michalski et al. [
75
]
Female and male CrossFit athletes (n= 22); first
2 weeks of their usual diet, then
a low-carbohydrate ketogenic diet for 4 weeks.
Training: maintaining their usual training.
Outcome: as many repetitions as possible
within a 17 min CrossFit workout.
Lower carbohydrate: A total of
2807 kcal
CHO/protein/fat
33/125/238 g
Higher carbohydrate: A total of
2565 kcal
CHO/protein/fat
290/118/104 g
No significant differences
between groups in CrossFit
repetition performance.
Paoli et al. [76]
RCT:
Male bodybuilders (n= 19); low-carbohydrate
ketogenic diet (n= 9) or western diet (n= 10)
for 8 weeks.
Training: maintaining their usual strength
training (3–4 sessions per week).
Outcome: 1 RM squat and bench press.
Lower carbohydrate: A total of
3444 kcal
CHO/protein/fat
44/216/264 g
Higher carbohydrate: A total of
3530 kcal
CHO/protein/fat
488/223/79 g
No significant differences
between groups in
1 RM changes.
Van Zant et al. [64]
Crossover:
Strength-trained males (n= 6);
high-carbohydrate or a moderate-carbohydrate
diet for 3 weeks.
Training: maintaining their usual
strength training.
Outcome: knee- extension and flexion peak
torque and total work performed during
two sets of 30 isokinetic contractions, bench
press 1 RM and bench press repetitions to
failure at 80% 1 RM.
Lower carbohydrate:
CHO: A total of 4.2 g/kg/day
(~347 g)
Higher carbohydrate:
CHO: A total of 6.3 g/kg/day
(~520 g)
No significant differences
between groups in changes of
any of the
performance measurements.
Vidi´c et al. [77]
RCT:
Strength-trained males (n= 18);
low-carbohydrate ketogenic diet group (n= 9)
or a non-ketogenic diet group (n= 9) for
8 weeks.
Training: resistance training was performed
four times per week as a split-routine,
unspecified load, three sets and
6–12 repetitions per set.
Outcome: A total of 1 RM squat and
bench press.
Lower carbohydrate: A total of
2156 kcal
CHO/protein/fat
27/108/180 g
Higher carbohydrate: A total of
2191 kcal
CHO/protein/fat
82/110/158 g
No significant differences
between groups in
1 RM changes.
Nutrients 2022,14, 856 22 of 39
Table 6. Cont.
Study Design and Population Strength Training and
Performance Outcomes Diet Results
Wilson et al. [65]
RCT:
Strength-trained men (n= 25);
low-carbohydrate ketogenic diet group (n= 13)
or a western diet group (n= 12) for 10 weeks
(carbohydrates were then reintroduced in the
ketogenic group in the 11th week).
Training: resistance training was performed
three times per week as a split-routine,
65–95% of 1 RM, three to four sets per
exercise and 1–15 repetitions per set.
Outcome: bench press and back squat 1 RM,
and 10 s Wingate cycle sprint (peak power).
Lower carbohydrate: 2617 kcal
CHO/protein/fat
31/135/217 g
Higher carbohydrate: A total of
2545 kcal
CHO/protein/fat
317/131/84 g
No significant differences
between groups in changes of
any of the
performance measurements.
Isocaloric, non-isonitrogenous studies
De Oliveira
et al. [71]
RCT:
Male military police students (n= 16); protein
supplement (4 g/kg/day, n= 8) or
a carbohydrate supplement (225 g, n= 8) group
for 8 weeks.
Training: resistance training three ×per
week, 80% 1 RM for eight repetitions ×five
sets. Exercises were arm curls, preacher curls,
overhead triceps and lying down
triceps extension.
Outcome: maximal strength (1 RM) for all
exercises, and peak torque from five
repetitions of isokinetic elbow flexion
and extension.
Lower carbohydrate: A total of
3710 kcal
CHO/protein/fat
338/297/112 g
Higher carbohydrate: A total of
3767 kcal
CHO/protein/fat
581/130/100 g
No significant differences
between groups in changes of
1 RM or peak torque.
Kreider et al. [66]
RCT:
Obese women (n= 221); high-carbohydrate
(n= 92) or a high-protein, low-carbohydrate
diet (n= 129) for 10 weeks (diets consisted of
1200 kcal the first week, then 1600 kcals the
next 9 weeks).
Training: supervised whole-body circuit
resistance training three ×per week.
Outcome: bench press 1 RM and repetitions
to failure at 70% of 1 RM.
Lower carbohydrate: 1411 kcal
CHO/protein/fat
123/102/57 g
Higher carbohydrate: 1379 kcal
CHO/protein/fat
183/62/46 g
No significant differences
between groups in changes in
repetitions to failure or 1 RM.
Rhyu and Cho [67]
RCT:
Male taekwondo athletes (n= 20); ketogenic
diet group (n= 10) or a non-ketogenic diet
group (n= 10) for 3 weeks in a 25%
caloric deficit.
Training: resistance training and taekwondo
training were performed 6 days per week.
Outcome: grip strength, back strength and
repetitions of sit ups performed in 60 s, 100 m
sprint, Wingate peak and mean power and
fatigue index and standing broad
jump distance.
Lower carbohydrate: A total of
CHO/protein/fat
4/41/55%
22 g CHO per day
Higher carbohydrate: A total of
CHO/protein/fat
40/30/30%
No significant differences
between groups in changes in
any performance outcomes,
except for a significantly lower
(better) anaerobic fatigue index
during the Wingate test in the
ketogenic group.
Nutrients 2022,14, 856 23 of 39
Table 6. Cont.
Study Design and Population Strength Training and
Performance Outcomes Diet Results
Non-isocaloric, protein equated studies
Rozenek et al. [74]
RCT:
Active males (n= 46); high-carbohydrate diet
(n= 25) or a control group (n= 21) for 8 weeks.
Training: resistance training was performed
four times per week as a 2-split routine, eight
repetitions for four sets.
Outcome: 1 RM in bench press, leg press, lat
pull-down and in total.
Lower carbohydrate: A total of
2597 kcal
CHO/Protein/Fat
337/107/84 g
Higher carbohydrate: A total of
4339 kcal
CHO/Protein/Fat
758/109/87 g
No significant differences
between groups in changes of
maximal strength.
Non-isocaloric, non-isonitrogenous studies
Agee [68]
RCT:
Male powerlifters (n= 12); ad libitum
low-carbohydrate ketogenic diet (n= 4) or to
maintain their habitual diet, control group
(CON) (n= 8) for 6 weeks.
Training: resistance training was performed
four times per week as a 2-split routine,
4–12 repetitions forthree to five sets.
Outcome: 1 RM in bench press, squat
and deadlift.
Lower carbohydrate: A total of
1918 kcal
CHO/protein/fat:
107/136/106 g
Higher carbohydrate: A total of
2862 kcal
CHO/protein/fat:
268/166/121 g
No significant differences
between groups in changes of
maximal strength.
Kephart et al. [69]
CT:
Male (n= 9) and female (n= 3) CrossFit athletes
(n= 12); self-selected to either continue their
normal diet (n= 5) or follow a ketogenic diet
(n= 7) for 12 weeks.
Training: continued CrossFit workouts
(ketogenic diet group completed 27 workouts,
whereas the control completed 20 workouts).
Outcome: back squat and power clean 1 RM,
one set of push-up repetitions to failure and
400-m running time.
Lower carbohydrate: 1948 kcal
CHO/protein/fat:
15/89/170 g
Higher carbohydrate:
Not reported.
No significant differences
between groups in changes of
any of the
performance measurements.
LaFountain
et al. [72]
CT:
Healthy military men (n= 25) and women
(n= 4); self-selected to follow an ad libitum
ketogenic diet or to continue their normal
mixed diet for 12 weeks.
Training: supervised full-body resistance
training 2 ×per week. three to four sets,
4–12 repetitions at 60–95% 1 RM.
Outcome: countermovement vertical jump
power, 1 RM squat and bench press, 10 sprint
intervals and obstacle course performance.
Lower carbohydrate:
<50 g/day carbohydrates
Control diet:
>40% carbohydrates
No significant differences
between groups in changes of
any of the
performance measurements.
Nutrients 2022,14, 856 24 of 39
Table 6. Cont.
Study Design and Population Strength Training and
Performance Outcomes Diet Results
Paoli et al. [70]
Crossover:
Elite male gymnasts (n= 8); ad libitum
very-low-carbohydrate ketogenic diet for the
first 30 days, and then 30 days with a Western
diet 3 months later.
Training
: instructed to continue their normal
training schedule of approx. 30 h per week.
Outcome
: One set of pushups, pull ups, dips,
hanging straight and bodyweight leg raises
until failure, in addition to squat- and
countermovement jumps.
Lower carbohydrate: A total of
1973 kcal
CHO/Protein/Fat:
22/201/120 g
Higher carbohydrate: A total of
2276 kcal
CHO/protein/fat:
264/84/97 g
No significant differences
between groups in changes of
any of the performance tests.
Vargas-Molina
et al. [73]
RCT:
Strength-trained women (n= 21);
non-ketogenic diet (n= 11) or a ketogenic diet
(n= 10) for 8 weeks.
Training: supervised 2-split resistance
training four times per week (strength,
hypertrophy and muscle endurance phases:
3–25 repetitions ×3 sets).
Outcome: 1 RM squat and bench press, and
countermovement jump height.
Lower carbohydrate: A total of
1710 kcal
CHO/protein/fat:
39/115/122 g
Higher carbohydrate: A total of
1980 kcal
CHO/protein/fat:
282/97/51 g
Significantly greater increase in
changes of 1 RM for squat and
bench press in the non-ketogenic
diet group (10- and 3.3 kg
difference, respectively), with no
group differences in CMJ
performance.
Nutrients 2022,14, 856 25 of 39
Exercise protocols during the interventions included dynamic resistance training with
full-body workouts [
63
,
72
] or body part split workouts [
65
,
68
,
71
,
73
,
74
,
77
], maintenance
of non-specified/habitual resistance training [
64
], circuit training [
66
], CrossFit [
62
,
69
],
powerlifting and weightlifting [
61
], athletic sport-specific exercises in addition to strength
exercise [
67
] or high-level gymnastics training [
70
]. In the studies where participants
did traditional resistance training, the training consisted of 1–25 repetitions for 1–5 sets
with a moderate to high load (>50% 1 RM) 2–4 times per week
[61,63,65,67,68,71–74,77]
.
Six studies did not prescribe a training protocol but instructed the participants to con-
tinue their habitual resistance training program [
61
,
64
,
76
], CrossFit routine [
69
,
75
] or
gymnastic training schedule [
70
]. Performance measurements included isokinetic knee flex-
ion and extension strength tests in two studies [
64
,
71
], 1 RM strength tests in
twelve studies
[61,64–66,68,69,71–74,76,77]
10 RM performance in one trial [
63
], repeti-
tions to failure or total training volume in four studies [
64
,
66
,
69
,
70
], CrossFit performance
in two studies [
62
,
75
] and grip strength and various predominantly anaerobic athletic tests
in six studies [62,65,67,69,72,73].
Main Findings
In total, 15 out of 17 studies found no significant effects of carbohydrate intake on
strength training performance or strength development, including the eight studies with
isocaloric and isonitrogenous comparison groups [
61
–
65
,
75
–
77
]. The single study favoring
the higher-carbohydrate condition was Vargas-Molina et al. [
73
], who found significantly
greater 1 RM squat and bench press strength development but not countermovement jump
height after an 8-week higher-carbohydrate diet (282 g) compared to a low-carbohydrate
(39 g) ketogenic diet in strength-trained women. The high-carbohydrate diet group also
consumed more total calories (1980 kcal vs. 1710 kcal), resulting in fat loss in the ke-
togenic group but not the higher-carbohydrate group. The other 12 ketogenic studies
found no significant between-group performance differences; seven when groups were
isocaloric
[61–63,65,75–77]
, one when the ketogenic diet group was lower in calories [
68
],
and in four studies that did not report if energy intake significantly differed between
groups [
67
,
69
,
70
,
72
]. The single study favoring the low-carbohydrate ketogenic diet group
was by Rhyu and Cho [
67
], who found a lower Wingate “fatigue index” compared to
a non-ketogenic diet group; however, there were no significant between-group differences
in Wingate, maximal strength, 100 m-sprint or broad jump performance.
4. Discussion
The majority of 39 out of 49 studies, including all 16 isocaloric comparisons, found no
significant benefits of carbohydrate manipulation on strength training performance. Simi-
larly, three of the four published abstracts found no significant effects of carbohydrate intake
on strength training performance, whilst one found higher repetition performance in one
set for one exercise in the higher carbohydrate group but not for total repetition volume for
either measured exercise. Ten studies found that carbohydrate consumption might enhance
strength training performance in specific contexts, notably for otherwise fasted training,
workouts with volumes over 10 sets per muscle group and bi-daily workouts. Four studies
favored the lower carbohydrate condition, but these benefits may have been attributable to
study confounders, such as a higher protein intake, rather than carbohydrate restriction.
4.1. The Effect of Acute Carbohydrate Manipulation on Strength Training Performance
Out of the 19 included studies, 11 studies found no significant effects of carbohy-
drate intake on strength training performance [
26
,
31
–
35
,
37
,
38
,
41
,
43
,
44
], six studies found
significantly greater performance in the higher-carbohydrate conditions [
28
–
30
,
39
,
40
,
42
]
and two studies found significantly greater performance in the lower-carbohydrate condi-
tions [27,36].
Since there is no established mechanism by which carbohydrates would acutely im-
pair performance, the two studies finding negative effects of carbohydrates may be type
Nutrients 2022,14, 856 26 of 39
I errors. Fairchild et al. [
27
] found greater average and peak torque during seven sets of
3 RM isokinetic leg extensions after a non-caloric placebo than after consuming 1.1 g/kg
carbohydrate. Both were consumed after an overnight fast by strength-trained men and
women. However, the authors interpreted their findings primarily as a null effect rather
than an effect favoring lower-carbohydrate intakes. Lynch [
36
] compared a 0.81 g/kg
high-carbohydrate beverage to an isocaloric high-protein beverage in strength-trained men
during a double-blinded, randomized, controlled, crossover trial. The participants per-
formed a 15–18-min high-intensity resistance training workout followed by the drinks and
2 h rest before a test workout of agility T-tests, push-ups to failure and 40-m sprinting. The
high-protein drink resulted in greater performance on aggregate test performance, though
not on any individually analyzed test. Since amino acids are theoretically unlikely to aid
strength training performance via mechanisms not shared by carbohydrates (e.g., provid-
ing glucose via gluconeogenesis or insulin-mediated suppression of protein breakdown),
protein’s positive effect may have resulted from greater muscle protein synthesis and sub-
sequent recovery [
12
,
13
,
78
] in between the two workouts, rather than an acute ergogenic
effect per se. Thus, Lynch’s [
36
] findings may be interpreted as a null effect of carbohydrate
intake and a positive effect of protein intake, not a positive effect of carbohydrate restriction.
In the two other isocaloric comparisons with protein intake, protein intake had similar
effects on performance as carbohydrate [40,44].
The lack of acute effects of carbohydrate intake on acute strength training performance
in most studies can be understood based on its partial level of whole-muscle glycogen
depletion, particularly in the lower-volume studies. While high-intensity, anaerobic ex-
ercise may seem to rely greatly on carbohydrates, the total cumulative demand may not
easily exceed bodily stores during resistance training. Muscle contractions during both low-
and high-load resistance training rely primarily on the anaerobic glycolysis pathway for
energy, as there is insufficient oxygen to rely purely on the aerobic system and fatty acids
to provide energy sufficiently rapidly [
4
,
5
]. Glucose and glycogen are therefore primary
energy substrates to fuel anaerobic exercise such as resistance training [
79
,
80
]. Lambert and
Flynn [
6
] estimated the glycolytic system to provide 82% of the adenosine triphosphate
(ATP) demand of a set of biceps curls at 80% of 1 RM to muscular failure. However, the
total energy expenditure of strength training is generally lower than that of endurance-type
activities [
81
]. One reason for the lower energy expenditure is the involvement of eccentric
muscle contractions, which require relatively little energy expenditure compared to concen-
tric muscle contractions, because they involve biomechanical rather than chemical cleaving
of actin-myosin cross-bridges [
82
]. Second, strength training exercise is very intermittent
with often 1–3 min of rest after each set of exercise [
83
]. These rest periods allow the aerobic
system, which can be fueled by fatty acids rather than carbohydrates, to contribute a con-
siderable portion of the workout’s total energy expenditure: estimates range substantially
from 20 to 70% of resistance training energy expenditure [
84
,
85
]. Moreover, many sets
are short enough that the creatine phosphate system, relying on creatine and stored ATP,
can contribute approximately 16% of energy demands of a set of high-intensity resistance
training, with 31% contributions being possible with shorter-duration anaerobic efforts,
such as Wingate tests [
6
,
86
,
87
]. The variation in energy system contributions may partly
be explained by differences in pre-exercise glycogen stores. Low pre-exercise glycogen
stores have been found to reduce glycogen utilization for a given work output during en-
durance training [
88
], so the creatine phosphate and aerobic systems may contribute more
during low-carbohydrate diets. Churchley et al. [
89
] found that a resistance training session
induced 123 mmol/kg dry weight glycogen depletion under baseline circumstances, com-
pared to 91 mmol/kg dry weight after prior glycogen depletion with bicycling; however,
the difference was not statistically significant. Even assuming the lowest reported contribu-
tions of the aerobic and creatine phosphate systems, 20% and 16%, respectively, thereby
assuming a 64% glycolytic contribution, and assuming a hypothetical but realistic strength
training session energy expenditure of 500 kcal, this would require 80 g carbohydrate to
Nutrients 2022,14, 856 27 of 39
fuel. Assuming 500 g glycogen storage in a typical athlete [
3
], this would theoretically
amount to only 16% glycogen depletion.
Empirically, higher glycogen depletion levels have been reported. To the authors’
knowledge, the highest level of whole-muscle glycogen depletion after resistance training
in the literature is 41%, or 39% if we exclude isokinetic exercise [
4
,
5
,
8
,
18
,
52
,
79
,
89
–
94
]. For
example, Essén-Gustavsson and Tesch [
90
] found 28% quadriceps glycogen depletion in
bodybuilders after five sets each of front squats, back squats, leg presses and leg extensions
to failure at ~12 RM. Glycogen depletion only starts affecting neuromuscular functioning
when levels are reduced to approximately 250–300 mmol/kg dry weight [
10
], which
generally requires a depletion of over 40% from baseline, depending on the pre-exercise
levels. Thus, resistance training workouts generally likely do not deplete enough glycogen
to impair performance.
Overnight fasting should also not induce critically low glycogen levels: while liver
glycogen content decreases after overnight fasting [
95
], intramuscular glycogen stores are
not a substrate to maintain blood glucose concentrations and are therefore not depleted [
96
].
Given that the participants in the fasted acute studies were following their regular diet
and did not exercise the evening prior to morning strength tests, muscle glycogen levels
were likely not a limiting factor for strength training performance, at least in the lower-
volume studies.
However, high-volume workouts may induce critically low glycogen levels in a subset
of muscle fibers even when total muscle depletion levels are not critical. Hokken et al. [
8
]
recently found that a total quadriceps glycogen depletion level of 38% after 12 sets of
resistance training, excluding warm-up sets, was associated with approximately 50%
subcellular depletion specifically within type II muscle fibers. The lowest quartile of
intramyofibrillar, intermyofibrillar and subsarcolemmal glycogen stores decreased 72%,
60% and 62%, respectively. The depletion levels in the 25% most-depleted fibers were
in the range where contractile functioning may be impaired. A notable limitation of
Hokken et al. [
8
]’s study is that they estimated glycogen depletion from net utilization
and did not factor in intra-exercise glycogen resynthesis. Thus, they likely overestimated
the glycogen depletion. In comparison, Koopman et al. [
91
] found fiber-specific glycogen
depletion was limited to 40% in the IIa and 44% in the IIx fibers after 16 sets quadriceps
resistance training at 75% of 1 RM after an overnight fast in untrained individuals, although
a direct comparison between the two studies is limited by their use of different methods
to quantify glycogen depletion. Additionally, the participants in Hokken et al.’s [
8
] study
were weightlifters and powerlifters with a relatively low pre-exercise glycogen storage level
of 92 mmol/kg wet weight, despite being in a fed state. In comparison, Robergs et al. [
5
]
reported 120 mmol/kg and Haff et al. [
52
] reported 150 mmol/kg baseline glycogen stores
in strength trainees. It is possible Hokken et al.’s [
8
] weightlifters were unaccustomed to
high-volume ‘bodybuilding style’ workouts, so 12 sets of resistance training may not induce
critical glycogen depletion in trainees with more common levels of fed-state glycogen stores.
Nevertheless, critical depletion in type II muscle fibers after high-volume strength
training could explain the trend in the literature that acute ergogenic effects of carbohydrate
intakes are more prevalent, although not consistent, in workouts with more than 10 sets
per muscle groups. In the four studies with test workouts with more than 10 sets per
muscle group, there were two studies in favor of higher carbohydrate intakes [
28
,
40
],
in addition to a trend in a third study [
26
], one study reporting no effect [
33
] and no
studies favoring lower carbohydrate intakes. The study reporting no effect only measured
repetitions in the last set [
33
], in contrast to all sets in the studies reporting (a trend for)
benefits. Although we may expect the last set to be most affected by potential glycogen
substrate depletion during a workout, measuring repetition volume during all sets may
increase statistical power to detect potential benefits of higher carbohydrate intakes. In
the 14 studies with test workouts with 10 or fewer sets per muscle group, there were only
three studies in favor of higher carbohydrate intakes [
29
,
39
,
42
], nine studies reporting no
effect [
30
–
32
,
34
,
35
,
37
,
38
,
41
,
43
] and two studies favoring lower carbohydrate intakes [
27
,
36
].
Nutrients 2022,14, 856 28 of 39
However, none of the studies favoring higher carbohydrate intakes had isocaloric control
groups. Based on Mitchell et al. [
48
], in isocaloric conditions, carbohydrate intake may still
not affect resistance training performance in recreational strength trainees up to 15 sets per
muscle group even after a recent depletion workout.
The lack of isocaloric controls makes it impossible to determine whether the superior
performance in some studies can be attributed to carbohydrate intake per se. Based on
Naharudin et al. [
41
] there may also be a non-metabolic component to the ergogenic
effects of a pre-workout meal, regardless of carbohydrate intake. These researchers found
that a high-carbohydrate breakfast (1.5 g/kg) improved resistance training performance
compared to drinking only water after an overnight fast; however, a flavor- and texture-
matched placebo breakfast with only 29 kcal improved performance similarly. The sham
breakfast also reduced hunger similarly. Thus, the feeling of having consumed something
can be more important than carbohydrate intake per se. These results corroborate findings
from a similar perception of breakfast experiment prior to a 30 min endurance performance
trial [
97
]. However, another trial where the performance event was above 30 min and after
a glycogen depletion protocol found that while the sham breakfast significantly improved
performance over consuming just water, it did not raise performance to the level of a high
carbohydrate intake [
98
], presumably because carbohydrate was actually a performance
limiting substrate. While other strength training studies have attempted to match their
placebos to their carbohydrate supplements in the form of liquids (e.g., [
28
,
52
]), none
did so as rigorously as Naharudin et al. [
41
] with a semi-solid meal, double-blinding
and by telling the participants their meal ‘contained energy’. A follow-up study from
Naharudin et al. [99]
compared two isocaloric breakfast meals, a semi-solid one vs. a liquid
one. The semi-solid meal reduced hunger more and improved back squat repetition
performance more than the liquid meal, suggesting hunger suppression can have a positive
effect on resistance training performance. Since all studies finding benefits of higher
carbohydrate intakes also had a higher energy intake, none of these effects may have
necessarily been mediated by carbohydrate intake per se but rather by hunger suppression
resulting in higher training efforts.
Moreover, other studies have found that carbohydrate mouth rinsing—without any
actual carbohydrate consumption—can improve resistance training repetition performance
compared to placebo [
100
] and that any placebo mouth rinse, regardless of carbohydrate
content, can improve performance compared to water consumption [
101
]. A full review
of the carbohydrate mouth rinsing literature is beyond the scope of this paper, but these
findings cast doubt on the conventionally proposed metabolic role of pre-exercise feeding
or rather taste experience. A predominantly psychological ergogenic effect of pre-workout
feeding would also explain the complete lack of observed dose–response effect for carbohy-
drate intake in the literature, as well as by Krings et al. [
29
], since the sensation of having
consumed something may be more important than carbohydrate consumption.
In conclusion, carbohydrate intake per se, independent of energy intake, is mech-
anistically and statistically unlikely to acutely affect resistance training performance in
a fed state for workouts up to 10 sets per muscle group. Higher-volume workouts may
require higher carbohydrate intakes to optimize performance, but there is a clear need for
more isocaloric research with realistic placebos. However, given the uncertainty in the
literature, based on Lynch [
36
] and Krings et al. [
29
], strength trainees may be advised to
consume at least 15 g net carbohydrate and 0.3 g/kg protein within 3 hours pre-workout to
optimize performance. If the workout involves more than 10 sets per muscle group, higher
carbohydrate intakes might be warranted.
4.2. The Effect of Exercise-Induced Glycogen Depletion and Carbohydrate Manipulation on Acute
Strength Performance
Three out of six studies that included a glycogen depletion session prior to strength
tests found a positive effect of carbohydrate intake on performance [
15
,
48
–
52
]. Since the
cycling depletion workouts were designed based on previous work to deplete glycogen
Nutrients 2022,14, 856 29 of 39
stores by approximately 80% [
102
,
103
], it is likely that glycogen levels were below the
threshold of impairing neuromuscular functioning after the depletion workouts. So, it is
plausible the higher carbohydrate intakes helped bring glycogen stores back up to less
limiting levels before the strength training test workouts.
Higher carbohydrate intakes were mainly beneficial in studies with short recovery
times in between the depletion and the test workout. In the three studies with no more
than four hours of recovery in between the workouts [
49
,
50
,
52
], two favored the higher-
carbohydrate condition [
49
,
50
]. Only Haff et al. [
52
] found no benefit of carbohydrate
intake compared to fasting for the workout output of three sets of isokinetic leg exten-
sions, likely because they reported only 19% glycogen depletion after the prior depletion
workout consisting of three sets of isokinetic leg extension strength testing and nine sets
of squats. In the three studies with 48 h in between the two workouts [
15
,
48
,
51
], only
one favored the higher-carbohydrate condition [
15
]. Glycogen resynthesis post-workout
follows a biphasic recovery that is greatly enhanced by a high carbohydrate intake in
the first four hours
[80,104]
. Since the second workout consisted of 19 sets of squats in
the higher-carbohydrate condition in Haff et al. [
49
] and the participants in the lower-
carbohydrate condition in Oliver et al. [
50
] were fasted, 2 to 4 h was likely not enough
time to resynthesize glycogen back to levels that optimized performance during the second
workout in either study. In the studies with 48 h rest in between the depletion workout
and the test workout, only Leveritt and Abernethy [
15
] favored the higher-carbohydrate
condition and this study was confounded by only performing the depletion workout in
the lower-carbohydrate condition. Since the participants were only recreationally trained
men, it is possible that the depletion workout interfered with performance due to muscle
damage or otherwise incomplete recovery rather than glycogen depletion per se.
Two days may be enough time for complete glycogen resynthesis even on a low-
carbohydrate diet. While high carbohydrate intakes are needed to resynthesize glycogen
stores after exhaustive exercise as fast as possible [
80
], glycogen stores are partly autoregu-
lated, as glycogen content is inversely related to glycogen synthase I activity, thereby allow-
ing faster glycogen resynthesis after greater depletion, at least if substrate is available [
104
].
Even fasted, the insulin release of elevated blood glucose levels during exercise, combined
with the ‘recycling’ of exercise-related lactate production via the Cori cycle, may allow
a glycogen resynthesis rate of approximately 1.9 mmol/kg/h the first 2 h after resistance
training [
92
] and likely faster after high-intensity endurance training [
105
]. A considerable
amount of glucose, up to the daily requirements during starvation, can also be obtained
from dietary fat intake or adipose tissue, via gluconeogenesis from the glycerol backbone of
triglycerides [
106
]. Third, glucose can be produced from glucogenic amino acids, although
this may only be desirable from a muscular anabolic point of view if the amino acids are
consumed in excess of requirements for muscle protein synthesis [107]. Phielix et al. [108]
measured the glycogen synthesis rates of sedentary and endurance-trained individuals
in an overnight fasted state (with saline infusion) at 2.0 mmol/kg/h and 3.7 mmol/kg/h,
respectively, using
13
C/
31
P magnetic resonance spectroscopy. Assuming a resting glycogen
storage level of 120 mmol/kg for strength trainees [
5
] and a depletion level of 80%, full
resynthesis in 48 h requires a glycogen synthesis rate of 2 mmol/kg/h, which may thus be
possible even in fasted conditions.
Just like in our other categories, none of the studies that favored the higher-carbohydrate
conditions were isocaloric. The only isocaloric study in this category by Mitchell et al. [
48
]
found no significant between-group differences in total training volume during 15 sets
of resistance training at 15 RM to failure after a glycogen depletion workout followed by
a carbohydrate intake of 32 g/day or 643 g/day for 48 h in strength-trained men. Lack of
isocaloric comparisons is particularly confounding in studies with prior glycogen deple-
tion workouts, because the extra carbohydrate/energy intake may not just aid glycogen
resynthesis but also neuromuscular recovery. Glycogen depletion workouts are by nature
exhaustive and generally a novel stimulus, so they have the potential to induce significant
muscle damage and neuromuscular fatigue that may take over 48 h to recover from [
109
].
Nutrients 2022,14, 856 30 of 39
Additionally, glycogen depletion after a novel workout may not reflect the depletion
level experienced by trainees habituated to the training stimulus and low-carbohydrate
diets [13,110], although other research finds no habituation effects [111,112].
In conclusion, in addition to the previous recommendations, higher carbohydrate
intakes are likely warranted for maximum performance when performing more than one
glycogen-depleting workout per day. If there are only a few hours in between workouts,
carbohydrate intakes up to 1.2 g/kg/h may be warranted to maximize glycogen resynthesis
and subsequent performance.
4.3. The Effect of Short-Term Carbohydrate Manipulation on Acute Strength Training Performance
None of the seven short-term experiments found any positive effects on acute strength
training performance following 2–7 days of a higher-carbohydrate intake compared to
a lower-carbohydrate intake, neither in an isocaloric comparison [
54
] nor non-isocaloric
comparisons [
53
,
55
,
56
,
58
,
59
,
63
]. For example, Moura et al. [
59
] observed that two days
of a high-carbohydrate refeed (672 g/day) did not increase repetitions across 10 sets of
leg presses in enhanced bodybuilders compared to 2 days of energy deficit with a lower
carbohydrate intake (231 g/day).
One study by Sawyer et al. [
58
] favored the low-carbohydrate condition, but it was
not randomized or counterbalanced. In this study, 31 strength trainees switched over
from a 41% carbohydrate intake to a 5% carbohydrate intake (31 g/day) for a week before
completing a battery of strength tests. After the low-carbohydrate diet, the participants
had lost bodyweight due to a 15% lower total energy intake, yet handgrip strength, squat
1 RM and vertical jump height improved significantly compared to earlier testing during
the higher-carbohydrate diet, although the squat strength improvement was only 0.9 kg.
Bench press 1 RM, power and repetitions to failure and Wingate power output did not
significantly change. Since the study design was not randomized, the improvements in
the lower-carbohydrate condition may have been due to a familiarization or training effect
rather than the diet, although the authors discounted this possibility based on the short
study duration in comparison to the minimum 2 years of previous training experience
of the participants. A familiarity effect would still imply that any ergogenic effects of
a 234 g higher carbohydrate intake was considerably smaller than the effect of a single
week of training in well-trained individuals (average 1 RM squat strength > 117 kg in
a sample with 48% women). Another possible confounder was that protein intake increased
significantly in the low-carbohydrate diet, although it still averaged 145 g/day during
the higher-carbohydrate diet and the higher-carbohydrate diet had a higher energy intake
(2537 vs. 2157 kcal).
The lack of any benefits of carbohydrate intake in the short-term studies can be under-
stood based on glycogen metabolism. The participants mostly performed habitual training
sessions with no more than 10 sets per muscle group, so it is likely that glycogen availability
was not a limiting factor for their workouts. The participants had at least 24 h in between
workouts in all the studies, which was likely sufficient for full glycogen replenishment.
Even for the glycogen depletion amount of the study with the highest reported depletion in
the literature after non-isokinetic resistance training, 39% or 46.6 mmol/kg [
52
], this would
require an average glycogen resynthesis rate over 24 h of 1.9 mmol/kg/h for full recovery.
This is on the lower end of the range of glycogen resynthesis rates (1.9–3.7 mmol/kg/h)
found in fasted individuals [
92
,
108
]. In conclusion, strength trainees are unlikely to be
limited by their carbohydrate intake to fuel habitual strength training workouts with no
more than 10 sets per muscle group.
4.4. The Effect of Longer-Term Carbohydrate Diets and Strength Training on Changes in
Strength Performance
A total of 16 out of 17 long-term studies found no significant benefits of carbohydrate
manipulation on strength-training performance and strength development, including
all isocaloric and isonitrogenous trials [
61
–
65
,
75
–
77
], all isocaloric non-isonitrogenous
Nutrients 2022,14, 856 31 of 39
trials [
66
,
67
,
71
], the only isonitrogenous but non-isocaloric trial [
74
] and four out of five
studies that equated neither protein nor energy intake between conditions [
68
–
70
,
72
,
73
].
One study favored the lower-carbohydrate condition [
67
] and one study favored the higher-
carbohydrate condition [73].
The only study favoring the higher-carbohydrate condition by Vargas-Molina et al. [
73
]
found greater increases in squat and bench press strength and fat-free mass (FFM) but not
countermovement jump height in the higher-carbohydrate condition. However, despite
the instruction to consume a similar energy intake, the lower-carbohydrate, ketogenic diet
resulted in significantly lower self-reported energy intake (1710 kcal vs. 1980 kcal) and
significantly more fat loss (1.1 kg loss vs. a non-significant 0.3 kg gain in the non-ketogenic
group). Since none of the other nine ketogenic diets (<100 g/day) found attenuated strength
development [
61
–
63
,
65
,
67
–
70
,
72
], the greater improvement in the higher-carbohydrate
condition may have been due to the energy surplus in that group, vs. the energy deficit
in the ketogenic group, rather than carbohydrate intake, although a recent meta-analysis
did not find significantly detrimental effects of a daily 567 kcal energy deficit on strength
development [113].
The only study favoring the lower-carbohydrate condition was by Rhyu and Cho [
67
],
which found reduced anaerobic fatigue during a Wingate test in the lower-carbohydrate
condition, but since none of the other performance tests favored the low-carbohydrate
condition, including Wingate mean and peak power, the relevance of this lone finding
is questionable.
Overall, the results indicate that carbohydrate intake does not have much, if any, effect
on long-term resistance training performance in isonitrogenous and isocaloric conditions.
The carbohydrate-independent pathways by which the body can synthesize glucose
may be sufficient in the context of sustainable training volumes and recovery times in
between workouts. If these pathways were inadequate to cover all glucose requirements
initially, they could become adequate over time, although this has yet to be observed in
strength trainees. Volek et al. [
114
] compared the glycogen depletion and recovery of
ultra-endurance athletes on a habitual 59% carbohydrate diet to those on a habitual 10%
carbohydrate diet after a three-hour run. Ninety minutes pre-workout and immediately
post-workout, the participants consumed an isocaloric (5 kcal/kg) and isonitrogenous
(14% protein) shake with either 5% carbohydrate for the low-carbohydrate dieters or 50%
carbohydrate for the high-carbohydrate dieters. Despite the large difference in habitual,
pre-exercise and post-exercise carbohydrate intakes, resting glycogen concentrations were
similar between groups, they decreased similarly during the workout (62–66%) and they re-
covered similarly over two hours back to 34–38% depletion. Other research finds habituated
exercise in carbohydrate-restricted conditions may decrease reliance on glycogen, although
all research so far is on endurance rather than strength training [
115
–
117
]. Furthermore,
Phinney et al. [
118
], found that during a ketogenic, protein-sparing modified fast with
endurance training, muscle glycogen levels stabilized at 69% of baseline after 6 weeks on
the diet, compared to 57% of baseline after the first week. Moreover, there was a decrease
the amount of glycogen depletion of their treadmill endurance test training from 16% at
baseline to 13% in week 1 and unmeasurable levels in week 6, while the time to exhaustion
increased by 55%.
Fifteen of the studies also estimated or measured fat-free-mass (FFM) or muscle thick-
ness. Given the relationship between muscle size and strength, a between-group difference
in muscle size could influence strength development [
119
], although the relation is also
affected by multiple other factors [
120
]. Most of these studies found no significant between-
group differences in these measures or body composition and thereby presumably muscle
mass, in line with the lack of differences in strength development. However, five studies
found a between-group difference favoring the higher-carbohydrate condition with either
a decrease (0.7–1.7 kg) in the lower-carbohydrate group [
61
,
72
,
73
] compared to an increase
in the higher-carbohydrate groups (0.5–0.8 kg) or a lower increase in FFM (1.4 kg vs.
3.4 kg and 0.6 kg vs. 2.2 kg) in the lower-carbohydrate condition [
74
,
76
], compared to
Nutrients 2022,14, 856 32 of 39
only one study favoring the lower-carbohydrate condition [
65
]. However, the aforemen-
tioned Vargas-Molina et al. [
73
] study finding greater increases in strength in the higher
carbohydrate condition was confounded by significantly lower energy intake in the lower-
carbohydrate condition, as was Rozenek et al.’s study [
74
] with 4339 kcal vs. 2597 kcal in the
higher- vs. lower-carbohydrate conditions, respectively.
LaFountain et al.’s
study [
72
] was
probably similarly confounded, as it had ad libitum diets without instructions regarding
energy intake, resulting in significant fat loss in the ketogenic diet group (
−
5.9 kg) but not
the control diet (
−
0.6 kg). Greene et al.’s study [
61
] was isocaloric based on self-reported
food logs and the authors noted that the loss of FFM in this study may have largely been
water and glycogen, combined with a previously reported overestimation of FFM loss
in carbohydrate-restricted athletes. Lack of significant loss of contractile muscle tissue
would explain why neither basal metabolic rate nor performance measures significantly
differed between groups. Similarly, in Paoli et al.’s [
76
] study, the participants did not
report significantly different energy intakes between groups; however, again only the keto-
genic diet group lost a significant amount of fat (
−
1.4 kg) and strength performance and
resting metabolic rate did not significantly differ between groups, so the greater FFM gain
may in the Western diet group may have been attributable largely to water and glycogen
losses in the ketogenic group. Glycogen levels have been shown to influence FFM mea-
surements [
121
]. Notably, Wilson et al. [
65
] demonstrated that one week of carbohydrate
reintroduction after a 10-week ketogenic diet increased FFM by 4.8%, while no change
was observed in the traditional high-carbohydrate group. Thus, the overall literature does
not support lower-carbohydrate diets impair muscular development when accounting
for energy intake and glycogen storage levels. However, from a practical standpoint it
seems more challenging to consume a target energy surplus in ketogenic diets, possibly
due to the appetite suppressive effect of ketogenic diets [
122
]. Muscular development is
significantly affected by energy balance [
113
]. Thus, strength development may eventually
be attenuated on a low-carbohydrate diet if less muscle size is gained in periods longer
than the three months of the included studies, as argued by others [
123
,
124
]. Nevertheless,
based on our systematic review of the available literature, carbohydrate intake does not
seem to have much, if any, effect on strength development up to three months duration.
4.5. Conclusions and Practical Applications
The majority of research, including every isocaloric comparison, did not find higher
carbohydrate intakes improve strength training performance, either acutely or over the
course of a strength training program, compared to lower carbohydrate intakes. There is
also evidence that the positive effects of higher carbohydrate intakes in comparison to noth-
ing or less filling controls can be non-metabolic, possibly mediated by hunger suppression
and subsequently greater exercise efforts. However, subgrouping the studies shows that
carbohydrate manipulation may be beneficial in certain contexts, namely otherwise fasted
training, workouts with more than 10 sets per muscle group and bi-daily workouts. These
contexts merit further study with sensory-matched placebos and isocaloric, isonitrogenous
control groups. Mechanistically, resistance training workouts up to 10 sets per muscle
group are unlikely to sufficiently deplete glycogen stores below the threshold of impairing
neuromuscular functioning. Glycogen resynthesis after such depletion may be complete
within 24 h even on low carbohydrate intakes via carbohydrate-independent pathways,
especially in trainees habituated to the training in low-carbohydrate conditions. However,
the existing literature on direct glycogen measurements is limited, so future research should
study how localized glycogen compartments are affected by training volume and how they
affect exercise performance. Since our findings are based on research on adults, future
research should also investigate if these findings can be extrapolated to individuals below
18 years of age or over 60 years of age.
Overall, our findings indicate conventional high-carbohydrate intake recommenda-
tions of 4–10 g/kg/day may be excessive for the performance of strength trainees, such as
bodybuilders, powerlifters and Olympic weightlifters. Based on the inconclusive evidence
Nutrients 2022,14, 856 33 of 39
and potential for benefits but not harm, strength trainees are advised to consume at least
15 g carbohydrates and 0.3 g/kg protein within 3 hours of their training sessions. If the
workout contains eleven or more sets per muscle group or there is another high-intensity
workout planned that day for the same musculature, higher carbohydrate intakes up to
1.2 g/kg/h may be warranted to maximize glycogen resynthesis in between workouts.
Future research is needed to validate these dosages.
Supplementary Materials:
The following are available online at https://www.mdpi.com/article/
10.3390/nu14040856/s1: Systematic Search Strategy.
Author Contributions:
M.H. formulated the research question, while M.H., T.B., R.H. and F.T.V.
contributed with the acquisition of data, analysis and interpretation, in addition to drafting and
revising the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding:
The Open Access fee was paid by The International Scientific Research Foundation for
Fitness and Nutrition. No other funding was received for this manuscript.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Conflicts of Interest:
Menno Henselmans, Thomas Bjørnsen, Richie Hedderman and Fredrik T.
Vårvik declare that they have no competing interests.
Appendix A
Table A1. Study quality assessment of the acute-, glycogen depletion- and short-term studies.
Study 1 2 3 4 5 6a 6b 8a 8b 9 12 Total
(Max 11)
Acute studies
Baty et al. [32] 1 1 1 1 1 1 0 1 1 1 1 10
Dalton et al. [33] 1 0 1 1 0 1 0 1 1 1 1 8
Fairchild et al. [27] 1 1 1 1 1 1 0 1 1 1 1 10
Fayh et al. [34] 1011010 1 111 8
Haff et al. [28] 0011110 1 111 8
Krings et al. [29] 1011110 1 111 9
Kulik et al. [35] 1011110 1 111 9
Lambert et al. [26] 0011110 1 111 8
Laurenson-Dubè[30]0011010 1 111 7
Lynch et al. [36] 1001110 1 111 8
Maroufi et al. [44] 1111000 1 111 8
Naharudin et al. [39]1011010 1 111 8
Naharudin et al. [41] 1 1 1 1 1 1 0 1 1 1 1 10
Raposo [37] 0 0 1 1 1 1 0 1 1 1 1 8
Rountree et al. [38] 1011110 1 111 9
Santos et al. [42] 1011010 1 111 8
Smith et al. [31] 1011110 1 111 9
Welikonich [40] 1001010 1 111 7
Wilburn et al. [43] 1011110 1 111 9
Glycogen-depletion studies
Haff et al. [49] 0011110 1 111 8
Haff et al. [52] 0011110 1 111 8
Leveritt-Abernethy [15]0011010 1 110 6
Mitchell et al. [48] 0011010 1 111 7
Oliver et al. [50] 1 1 1 1 1 1 0 1 1 1 1 10
Symons-Jacobs [51] 0011010 1 111 7
Nutrients 2022,14, 856 34 of 39
Table A1. Cont.
Study 1 2 3 4 5 6a 6b 8a 8b 9 12 Total
(Max 11)
Short-term studies
Dipla et al. [54] 1011010 1 111 8
Escobar et al. [53] 0011110 1 110 7
Hatfield et al. [55] 0011010 1 111 7
Kreider et al. [56] 1011010 1 100 6
Meirelles et al. [57] 1011001 1 111 8
Moura et al. [59] 1011010 1 111 8
Sawyer et al. [58] 1011010 1 111 8
1 = criteria met; 0 = criteria not met. Criteria 1; eligibility criteria specified, 2; randomization method specified,
3; allocation concealment, 4; groups similar at baseline, 5; blinding of assessor; 6a; outcome measures assessed
in 85% of subjects, 6b; adverse events reported, 8; between group statistical comparisons reported (a; primary
outcome, b; secondary outcome) 9; point measures and measures of variability of outcomes reported, 12; reported
exercise volume and energy expenditure.
Table A2. Study quality assessment of the longer-term studies.
Study 1 2 3 4 5 6a 6b 6c 7 8a 8b 9 11 12 Total
(Max 14)
Agee [68] 1 0 1 1 0 0 1 0 0 1 1 1 1 1 9
Greene et al. [61] 1 0 1 1 0 1 0 1 0 1 1 1 1 * 0 9
Gregory et al. [62] 1 0 1 1 1 1 1 1 0 1 1 1 1 * 0 11
Kephart et al. [69] 1 0 0 1 0 1 0 1 0 1 1 1 1 * 0 8
Kreider et al. [66] 1 0 1 1 0 1 1 1 1 * 1 1 1 1 0 11
LaFountain et al. [72] 1 0 0 1 0 1 1 1 0 1 1 1 1 1 10
Meirelles-Gomes [63] 1 0 0 1 0 1 1 1 1 * 1 1 1 1 1 11
Michalski et al. [75] 1 0 0 1 0 0 1 1 0 1 1 1 1 * 0 8
De Oliveira et al. [71] 0 0 1 0 0 1 0 1 1 * 1 1 1 1 0 8
Paoli et al. [76] 1 0 1 1 0 1 1 1 1 * 1 1 1 1 * 0 11
Paoli et al. [70] 1 0 0 1 0 1 0 1 1 * 1 1 1 1 * 0 9
Rhyu and Cho [67] 1 0 1 1 0 1 0 0 1 * 1 1 1 1 * 0 9
Rozenek et al. [74] 1 0 1 1 0 1 0 1 0 1 1 1 1 1 10
Van Zant et al. [64] 1 0 1 0 0 1 0 1 1 * 1 1 1 1 * 0 9
Vargas-Molina et al. [73] 1 0 1 1 0 1 0 0 0 1 1 1 1 0 8
Vidi´c et al. [77] 1 0 1 1 0 1 0 1 0 1 1 1 0 0 8
Wilson et al. [65] 1 0 1 1 0 0 0 0 0 1 1 1 1 1 8
1 = criteria met; 0 = criteria not met. Criteria 1; eligibility criteria specified, 2; randomization method specified, 3;
allocation concealment, 4; groups similar at baseline, 5; blinding of assessor, 6a; outcome measures assessed in 85%
of subjects, 6b; adverse events reported, 6c; exercise attendance reported, 7; intention-to-treat analysis (*: 1 point
was given if there were no dropouts and therefore no need for an intention-to-treat analysis), 8; between group
statistical comparisons reported (a; primary outcome, b; secondary outcome), 9; point measures and measures
of variability of outcomes reported, 11; relative exercise intensity remained constant (*: 1 point was given if the
participants were athletes or strength trainees and followed their regular training program), 12; reported exercise
volume and energy expenditure.
References
1.
Burke, L.M.; Hawley, J.A.; Wong, S.H.S.; Jeukendrup, A.E. Carbohydrates for training and competition. J. Sports Sci.
2011
,29
(Suppl. 1), S17–S27. [CrossRef]
2.
Hughes, D.C.; Ellefsen, S.; Baar, K. Adaptations to Endurance and Strength Training. Cold Spring Harb. Perspect. Med.
2017
,
8, a029769. [CrossRef]
3.
Knuiman, P.; Hopman, M.T.E.; Mensink, M. Glycogen availability and skeletal muscle adaptations with endurance and resistance
exercise. Nutr. Metab. 2015,12, 59. [CrossRef]
4.
Tesch, P.A.; Ploutz-Snyder, L.L.; Yström, L.; Castro, M.J.; Dudley, G.A. Skeletal Muscle Glycogen Loss Evoked by Resistance
Exercise. J. Strength Cond. Res. 1998,12, 67–73. [CrossRef]
5.
Robergs, R.A.; Pearson, D.R.; Costill, D.L.; Fink, W.J.; Pascoe, D.D.; Benedict, M.A.; Lambert, C.P.; Zachweija, J.J. Muscle
glycogenolysis during differing intensities of weight-resistance exercise. J. Appl. Physiol. 1991,70, 1700–1706. [CrossRef]
6. Lambert, C.P.; Flynn, M.G. Fatigue during High-Intensity Intermittent Exercise. Sports Med. 2002,32, 511–522. [CrossRef]
7. Ørtenblad, N.; Westerblad, H.; Nielsen, J. Muscle glycogen stores and fatigue. J. Physiol. 2013,591, 4405–4413. [CrossRef]
Nutrients 2022,14, 856 35 of 39
8.
Hokken, R.; Laugesen, S.; Aagaard, P.; Suetta, C.; Frandsen, U.; Ørtenblad, N.; Nielsen, J. Subcellular localization- and fibre
type-dependent utilization of muscle glycogen during heavy resistance exercise in elite power and Olympic weightlifters. Acta
Physiol. 2020,231, e13561. [CrossRef]
9.
Duhamel, T.A.; Perco, J.G.; Green, H.J. Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic
reticulum responses in exercising males. Am. J. Physiol. Integr. Comp. Physiol. 2006,291, R1100–R1110. [CrossRef]
10.
Ørtenblad, N.; Nielsen, J.; Saltin, B.; Holmberg, H.-C. Role of glycogen availability in sarcoplasmic reticulum Ca2+kinetics in
human skeletal muscle. J. Physiol. 2011,589, 711–725. [CrossRef]
11.
Vigh-Larsen, J.F.; Ørtenblad, N.; Spriet, L.L.; Overgaard, K.; Mohr, M. Muscle Glycogen Metabolism and High-Intensity Exercise
Performance: A Narrative Review. Sports Med. 2021,51, 1855–1874. [CrossRef]
12.
Lemon, P.W.; Mullin, J.P. Effect of initial muscle glycogen levels on protein catabolism during exercise. J. Appl. Physiol.
1980
,48,
624–629. [CrossRef]
13.
Howarth, K.R.; Phillips, S.M.; MacDonald, M.J.; Richards, D.; Moreau, N.A.; Gibala, M.J. Effect of glycogen availability on human
skeletal muscle protein turnover during exercise and recovery. J. Appl. Physiol. 2010,109, 431–438. [CrossRef]
14.
Jacobs, I.; Kaiser, P.; Tesch, P. Muscle strength and fatigue after selective glycogen depletion in human skeletal muscle fibers. Eur.
J. Appl. Physiol. Occup. Physiol. 1981,46, 47–53. [CrossRef]
15.
Leveritt, M.; Abernethy, P.J. Effects of Carbohydrate Restriction on Strength Performance. J. Strength Cond. Res.
1999
,13, 52–57.
[CrossRef]
16.
Pendergast, D.R.; Meksawan, K.; Limprasertkul, A.; Fisher, N.M. Influence of exercise on nutritional requirements. Eur. J. Appl.
Physiol. 2011,111, 379–390. [CrossRef]
17.
Haff, G.G.; Lehmkuhl, M.J.; McCoy, L.B.; Stone, M.H. Carbohydrate supplementation and resistance training. J. Strength Cond.
Res. Natl. Strength Cond. Assoc. 2003,17, 187–196. [CrossRef]
18.
Bell, D.G.; Jacobs, I. Muscle fiber-specific glycogen utilization in strength-trained males and females. Med. Sci. Sports Exerc.
1989
,
21, 649–654. [CrossRef]
19.
Lambert, C.P.; Frank, L.L.; Evans, W.J. Macronutrient Considerations for the Sport of Bodybuilding. Sports Med.
2004
,34, 317–327.
[CrossRef]
20.
Slater, G.; Phillips, S.M. Nutrition guidelines for strength sports: Sprinting, weightlifting, throwing events, and bodybuilding.
J. Sports Sci. 2011,29 (Suppl. 1), S67–S77. [CrossRef]
21.
Burke, L.M.; Cox, G.R.; Cummings, N.K.; Desbrow, B. Guidelines for Daily Carbohydrate Intake. Sports Med.
2001
,31, 267–299.
[CrossRef]
22.
Page, M.J.; McKenzie, J.E.; Bossuyt, P.M.; Boutron, I.; Hoffmann, T.C.; Mulrow, C.D.; Shamseer, L.; Tetzlaff, J.M.; Akl, E.A.;
Brennan, S.E.; et al. The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ
2021
,372, n71.
[CrossRef]
23. Pieper, D.; Rombey, T. Where to prospectively register a systematic review. Syst. Rev. 2022,11, 8. [CrossRef]
24.
Smart, N.A.; Waldron, M.; Ismail, H.; Giallauria, F.; Vigorito, C.; Cornelissen, V.; Dieberg, G. Validation of a new tool for the
assessment of study quality and reporting in exercise training studies. Int. J. Evid.-Based Health 2015,13, 9–18. [CrossRef]
25.
Nunes, J.P.; Grgic, J.; Cunha, P.M.; Ribeiro, A.S.; Schoenfeld, B.J.; de Salles, B.F.; Cyrino, E.S. What influence does resistance
exercise order have on muscular strength gains and muscle hypertrophy? A systematic review and meta-analysis. Eur. J. Sport
Sci. 2020,21, 149–157. [CrossRef]
26.
Lambert, C.P.; Flynn, M.G.; Boone, J.B.; Michaud, T.J.; Rodriguez-Zayas, J. Effects of Carbohydrate Feeding on Multiple-bout
Resistance Exercise. J. Strength Cond. Res. 1991,5, 192–197. [CrossRef]
27.
Fairchild, T.J.; Dillon, P.; Curtis, C.; Dempsey, A.R. Glucose Ingestion Does Not Improve Maximal Isokinetic Force. J. Strength
Cond. Res. 2016,30, 194–199. [CrossRef] [PubMed]
28.
Haff, G.G.; Schroeder, C.A.; Koch, A.J.; Kuphal, K.E.; Comeau, M.J.; Potteiger, J.A. The effects of supplemental carbohydrate
ingestion on intermittent isokinetic leg exercise. J. Sports Med. Phys. Fit. 2001,41, 216–222.
29.
Krings, B.M.; Rountree, J.A.; McAllister, M.J.; Cummings, P.M.; Peterson, T.J.; Fountain, B.J.; Smith, J.W. Effects of acute
carbohydrate ingestion on anaerobic exercise performance. J. Int. Soc. Sports Nutr. 2016,13, 40. [CrossRef]
30.
Laurenson, D.M.; Dubé, D.J. Effects of carbohydrate and protein supplementation during resistance exercise on respiratory
exchange ratio, blood glucose, and performance. J. Clin. Transl. Endocrinol. 2015,2, 1–5. [CrossRef]
31.
Smith, J.W.; Krings, B.M.; Shepherd, B.D.; Waldman, H.S.; Basham, S.A.; McAllister, M.J. Effects of carbohydrate and branched-
chain amino acid beverage ingestion during acute upper body resistance exercise on performance and postexercise hormone
response. Appl. Physiol. Nutr. Metab. 2018,43, 504–509. [CrossRef] [PubMed]
32.
Baty, J.J.; Hwang, H.; Ding, Z.; Bernard, J.R.; Wang, B.; Kwon, B.; Ivy, J.L. The Effect of a Carbohydrate and Protein Supplement on
Resistance Exercise Performance, Hormonal Response, and Muscle Damage. J. Strength Cond. Res.
2007
,21, 321–329. [CrossRef]
33.
Dalton, R.A.; Rankin, J.W.; Sebolt, D.; Gwazdauskas, F. Acute Carbohydrate Consumption Does Not Influence Resistance Exercise
Performance during Energy Restriction. Int. J. Sport Nutr. 1999,9, 319–332. [CrossRef] [PubMed]
34.
Fayh, A.P.T.; Umpierre, D.; Sapata, K.B.; Neto, F.M.D.; De Oliveira, A.R.; Ii, I. Efeitos da ingestão prévia de carboidrato de alto
índice glicêmico sobre a resposta glicêmica e desempenho durante um treino de força. Rev. Bras. Med. Do Esporte
2007
,13,
416–420. [CrossRef]
Nutrients 2022,14, 856 36 of 39
35.
Kulik, J.R.; Touchberry, C.D.; Kawamori, N.; ABlumert, P.; Crum, A.J.; Haff, G.G. Supplemental Carbohydrate Ingestion Does Not
Improve Performance of High-Intensity Resistance Exercise. J. Strength Cond. Res. 2008,22, 1101–1107. [CrossRef] [PubMed]
36.
Lynch, S. The differential effects of a complex protein drink versus isocaloric carbohydrate drink on performance indices following
high-intensity resistance training: A two arm crossover design. J. Int. Soc. Sports Nutr. 2013,10, 31. [CrossRef]
37.
Raposo, K. The Effects of Pre-Exercise Carbohydrate Supplementation on Resistance Training Performance during an Acute Resistance
Training Session; University of South Florida: Tampa, FL, USA, 2011.
38.
Rountree, J.A.; Krings, B.M.; Peterson, T.J.; Thigpen, A.G.; McAllister, M.J.; Holmes, M.E.; Smith, J.W. Efficacy of Carbohydrate
Ingestion on CrossFit Exercise Performance. Sports 2017,5, 61. [CrossRef]
39.
Bin Naharudin, M.N.; Yusof, A.; Shaw, H.; Stockton, M.; Clayton, D.J.; James, L.J. Breakfast Omission Reduces Subsequent
Resistance Exercise Performance. J. Strength Cond. Res. 2019,33, 1766–1772. [CrossRef]
40.
Welikonich, M.J.; Nagle, E.F.; Goss, F.L.; Robertson, R.J.; Crawford, K. Effect Of Carbohydrate-Protein Supplementation On
Resistance Exercise Performance, Perceived Exertion, And Salivary Cortisol. Med. Sci. Sports Exerc.
2011
,43, 586–587. [CrossRef]
41.
Naharudin, M.N.; Adams, J.; Richardson, H.; Thomson, T.; Oxinou, C.; Marshall, C.; Clayton, D.J.; Mears, S.A.; Yusof, A.;
Hulston, C.J.; et al.
Viscous placebo and carbohydrate breakfasts similarly decrease appetite and increase resistance exercise
performance compared with a control breakfast in trained males. Br. J. Nutr. 2020,124, 232–240. [CrossRef]
42.
Dos Santos, M.P.P.; Spineli, H.; Silva, H.V.R.S.; Learsi, S.K.; De Araujo, G.G. Ingestion of a drink containing carbohydrate increases
the number of bench press repetitions. Rev. Nutr. 2019,32, e190056. [CrossRef]
43.
Wilburn, D.T.; Machek, S.B.; Cardaci, T.D.; Hwang, P.S.; Willoughby, D.S. Acute Maltodextrin Supplementation During Resistance
Exercise. J. Sports Sci. Med. 2020,19, 282–288. [PubMed]
44.
Maroufi, K.; Razavi, R.; Gaeini, A.A.; Nourshahi, M. The effects of acute consumption of carbohydrate-protein supplement in
varied ratios on CrossFit athletes’ performance in two CrossFit exercises: A randomized cross-over trial. J. Sports Med. Phys. Fit.
2021,61, 1362–1368. [CrossRef] [PubMed]
45.
Conley, M.; Stone, M.; Marsit, J.L.; O’Bryant, H.S.; Nieman, D.C.; Johnson, J.L.; ButTerworth, D.; Keith, R. Effects of Carbohydrate
Ingestion on Resistance exercise. J. Strength Cond. Res. 1995,9, 192–206.
46.
Vincent, K.R.; Clarkson, P.M.; Freedson, P.S.; DeCheke, M. 1092 effect of a pre-exercise liquid, high carbohydrate feeding on
resistance exercise performance. Med. Sci. Sports Exerc. 1993,25, S194. [CrossRef]
47.
Lepeley, A. The Effects Of Protein Versus Carbohydrate Consumption on Resistance Exercise Performance And Ratings of
Perceived Exertion In Women. Ph.D. Dissertation, TUI University, Cypress, CA, USA, 2012.
48.
Mitchell, J.B.; DiLauro, P.C.; Pizza, F.X.; Cavender, D.L. The effect of preexercise carbohydrate status on resistance exercise
performance. Int. J. Sport Nutr. 1997,7, 185–196. [CrossRef]
49.
Haff, G.G.; Stone, M.H.; Warren, B.J.; Keith, R.; Johnson, R.L.; Nieman, D.C.; Williams, F.; Kirksey, K.B. The Effect of Carbohydrate
Supplementation on Multiple Sessions and Bouts of Resistance Exercise. J. Strength Cond. Res. 1999,13, 111–117. [CrossRef]
50.
Oliver, J.M.; Almada, A.L.; Van Eck, L.E.; Shah, M.; Mitchell, J.B.; Jones, M.T.; Jagim, A.R.; Rowlands, D.S. Ingestion of high
molecular weight carbohydrate enhances subsequent repeated maximal power: A randomized controlled trial. PLoS ONE
2016
,
11, e0163009. [CrossRef]
51.
Symons, J.D.; Jacobs, I. High-intensity exercise performance is not impaired by low intramuscular glycogen. Med. Sci. Sports
Exerc. 1989,21, 550–557. [CrossRef]
52.
Haff, G.G.; Koch, A.J.; Potteiger, J.A.; Kuphal, K.E.; Magee, L.M.; Green, S.B.; Jakicic, J.J. Carbohydrate supplementation attenuates
muscle glycogen loss during acute bouts of resistance exercise. Int. J. Sport Nutr. Exerc. Metab. 2000,10, 326–339. [CrossRef]
53.
Escobar, K.A.; Morales, J.; Vandusseldorp, T.A. The Effect of a Moderately Low and High Carbohydrate Intake on Crossfit
Performance. Int. J. Exerc. Sci. 2016,9, 460–470. [PubMed]
54.
Dipla, K.; Makri, M.; Zafeiridis, A.; Soulas, D.; Tsalouhidou, S.; Mougios, V.; Kellis, S. An isoenergetic high-protein, moderate-fat
diet does not compromise strength and fatigue during resistance exercise in women. Br. J. Nutr.
2008
,100, 283–286. [CrossRef]
[PubMed]
55.
Hatfield, D.L.; Kraemer, W.J.; Volek, J.S.; Rubin, M.R.; Grebien, B.; Gomez, A.L.; French, D.N.; Scheett, T.P.; Ratamess, N.A.;
Sharman, M.J.; et al. The Effects of Carbohydrate Loading on Repetitive Jump Squat Power Performance. J. Strength Cond. Res.
2006,20, 167–171. [CrossRef] [PubMed]
56.
Kreider, R.B.; Hill, D.; Horton, G.; Downes, M.; Smith, S.; Anders, B. Effects of Carbohydrate Supplementation during Intense
training on Dietary Patterns, Psychological Status, and Performance. Int. J. Sport Nutr. 1995,5, 125–135. [CrossRef]
57.
Meirelles, C.; Candido, T.; Gomes, P.S. Effects of short-term very low-carbohydrate or conventional diet on strength performance.
J. Sports Med. Phys. Fit. 2010,50, 189–195.
58.
Sawyer, J.C.; Wood, R.J.; Davidson, P.W.; Collins, S.M.; Matthews, T.D.; Gregory, S.M.; Paolone, V.J. Effects of a Short-Term
Carbohydrate-Restricted Diet on Strength and Power Performance. J. Strength Cond. Res. 2013,27, 2255–2262. [CrossRef]
59.
Moura, R.F.; De Moraes, W.M.A.M.; De Castro, B.M.; Nogueira, A.L.P.; Trindade, T.B.; Schoenfeld, B.J.; Prestes, J. Carbohydrate
refeed does not modify GVT-performance following energy restriction in bodybuilders. Clin. Nutr. ESPEN
2021
,43, 308–316.
[CrossRef]
60.
Mirdha, P.; Nalgirkar, V.; Patil, A.; Potaliya, P.; Gupta, V.K. Effect of Carbohydrate Loading on Resistance Exercise and Muscle
Mass: A Prospective Study. Mymensingh Med. J. MMJ 2021,30, 826–829.
Nutrients 2022,14, 856 37 of 39
61.
Greene, D.A.; Varley, B.J.; Hartwig, T.; Chapman, P.; Rigney, M. A Low-Carbohydrate Ketogenic Diet Reduces Body Mass Without
Compromising Performance in Powerlifting and Olympic Weightlifting Athletes. J. Strength Cond. Res.
2018
,32, 3373–3382.
[CrossRef]
62.
Gregory, R.M.; Hamdan, H.; Torisky, D.M.; Akers, J.D. A Low-Carbohydrate Ketogenic Diet Combined with 6-Weeks of Crossfit
Training Improves Body Composition and Performance. Master ’s Thesis, James Madison University, Harrisonburg, VA, USA,
2016.
63.
Meirelles, C.M.; Gomes, P.S.C. Effects of Short-Term Carbohydrate Restrictive and Conventional Hypoenergetic Diets and
Resistance Training on Strength Gains and Muscle Thickness. J. Sports Sci. Med. 2016,15, 578–584.
64.
Van Zant, R.S.; Conway, J.M.; Seale, J.L. A moderate carbohydrate and fat diet does not impair strength performance in moderately
trained males. J. Sports Med. Phys. Fit. 2002,42, 31–37.
65. Wilson, J.M.; Lowery, R.P.; Roberts, M.D.; Sharp, M.H.; Joy, J.M.; Shields, K.A.; Partl, J.; Volek, J.S.; D’Agostino, D. The Effects of
Ketogenic Dieting on Body Composition, Strength, Power, and Hormonal Profiles in Resistance Training Males. J. Strength Cond.
Res. 2021,34, 3463–3474. [CrossRef] [PubMed]
66.
Kreider, R.B.; Rasmussen, C.; Kerksick, C.M.; Wilborn, C.; Taylor, L.; Campbell, B.; Magrans-Courtney, T.; Fogt, D.; Ferreira, M.;
Li, R.; et al.
A Carbohydrate-Restricted Diet during Resistance Training Promotes More Favorable Changes in Body Composition
and Markers of Health in Obese Women with and without Insulin Resistance. Physician Sportsmed. 2011,39, 27–40. [CrossRef]
67.
Rhyu, H.-S.; Cho, S.-Y. The effect of weight loss by ketogenic diet on the body composition, performance-related physical fitness
factors and cytokines of Taekwondo athletes. J. Exerc. Rehabil. 2014,10, 326–331. [CrossRef] [PubMed]
68.
Agee, J.L. Effects of a Low-Carbohydrate Ketogenic Diet on Power Lifting Performance and Body Composition. Master’s Thesis,
James Madison University, Harrisonburg, VA, USA, 2015.
69.
Kephart, W.C.; Pledge, C.D.; Roberson, P.A.; Mumford, P.W.; Romero, M.A.; Mobley, C.B.; Martin, J.S.; Young, K.C.; Lowery, R.P.;
Wilson, J.M.; et al. The three month effects of a ketogenic diet on body composition, blood parameters, and performance metrics
in crossfit trainees: A pilot study. Sports 2018,6, 1. [CrossRef]
70.
Paoli, A.; Grimaldi, K.; D’Agostino, D.; Cenci, L.; Moro, T.; Bianco, A.; Palma, A. Ketogenic diet does not affect strength
performance in elite artistic gymnasts. J. Int. Soc. Sports Nutr. 2012,9, 34. [CrossRef] [PubMed]
71.
De Oliveira, P.V.; Baptista, L.; Moreira, F.; Junior, A.H.L. Correlação entre a suplementação de proteína e carboidrato e variáveis
antropométricas e de força em indivíduos submetidos a um programa de treinamento com pesos. Rev. Bras. Med. Do Esporte
2006
,
12, 51–55. [CrossRef]
72.
LaFountain, R.A.; Miller, V.J.; Barnhart, E.C.; Hyde, P.N.; Crabtree, C.D.; McSwiney, F.; Beeler, M.K.; Buga, A.; Sapper, T.N.;
A Short, J.; et al.
Extended Ketogenic Diet and Physical Training Intervention in Military Personnel. Mil. Med.
2019
,184,
e538–e547. [CrossRef]
73.
Vargas-Molina, S.; Petro, J.L.; Romance, R.; Kreider, R.B.; Schoenfeld, B.J.; Bonilla, D.A.; Benítez-Porres, J. Effects of a ketogenic
diet on body composition and strength in trained women. J. Int. Soc. Sports Nutr. 2020,17, 19. [CrossRef]
74.
Rozenek, R.; Ward, P.; Long, S.; Garhammer, J. Effects of high-calorie supplements on body composition and muscular strength
following resistance training. J. Sports Med. Phys. Fit. 2002,42, 340–347.
75.
Durkalec-Michalski, K.; Nowaczyk, P.M.; Główka, N.; Ziobrowska, A.; Podgórski, T. Is a Four-Week Ketogenic Diet an Effective
Nutritional Strategy in CrossFit-Trained Female and Male Athletes? Nutrients 2021,13, 864. [CrossRef]
76.
Paoli, A.; Cenci, L.; Pompei, P.; Sahin, N.; Bianco, A.; Neri, M.; Caprio, M.; Moro, T. Effects of Two Months of Very Low
Carbohydrate Ketogenic Diet on Body Composition, Muscle Strength, Muscle Area, and Blood Parameters in Competitive
Natural Body Builders. Nutrients 2021,13, 374. [CrossRef] [PubMed]
77.
Vidi´c, V.; Ili´c, V.; Toski´c, L.; Jankovi´c, N.; Ugarkovi´c, D. Effects of calorie restricted low carbohydrate high fat ketogenic vs.
non-ketogenic diet on strength, body-composition, hormonal and lipid profile in trained middle-aged men. Clin. Nutr.
2021
,40,
1495–1502. [CrossRef] [PubMed]
78.
Børsheim, E.; Cree, M.G.; Tipton, K.D.; Elliott, T.A.; Aarsland, A.; Wolfe, R.R. Effect of carbohydrate intake on net muscle protein
synthesis during recovery from resistance exercise. J. Appl. Physiol. 2004,96, 674–678. [CrossRef] [PubMed]
79.
MacDougall, J.D.; Ray, S.; Sale, D.G.; McCartney, N.; Lee, P.; Garner, S. Muscle Substrate Utilization and Lactate Production
During Weightlifting. Can. J. Appl. Physiol. 1999,24, 209–215. [CrossRef] [PubMed]
80.
Murray, B.; Rosenbloom, C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr. Rev.
2018
,76, 243–259.
[CrossRef]
81.
Brewer, C.B.; Booher, B.M.; Lawton, N. Comparison of Acute Energy Expenditure and Rating of Perceived Exertion in Equivalent
Bouts of Circuit Training and Treadmill Running. J. Strength Cond. Res. 2021,35, 680–687. [CrossRef]
82.
Herzog, W. Why are muscles strong, and why do they require little energy in eccentric action? J. Sport Health Sci.
2018
,7, 255–264.
[CrossRef]
83.
Grgic, J.; Schoenfeld, B.J.; Skrepnik, M.; Davies, T.B.; Mikulic, P. Effects of Rest Interval Duration in Resistance Training on
Measures of Muscular Strength: A Systematic Review. Sports Med. 2017,48, 137–151. [CrossRef]
84.
Vianna, J.M.; Lima, J.P.; Saavedra, F.J.; Reis, V.M. Aerobic and Anaerobic Energy During Resistance Exercise at 80% 1RM. J. Hum.
Kinet. 2011,29A, 69–74. [CrossRef]
Nutrients 2022,14, 856 38 of 39
85.
Brunelli, D.T.; Finardi, E.A.R.; Bonfante, I.L.P.; Gáspari, A.F.; Sardeli, A.V.; Souza, T.M.F.; Chacon-Mikahil, M.P.T.; Cavaglieri, C.
Acute low- compared to high-load resistance training to failure results in greater energy expenditure during exercise in healthy
young men. PLoS ONE 2019,14, e0224801. [CrossRef] [PubMed]
86.
Baker, J.S.; McCormick, M.C.; Robergs, R.A. Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise.
J. Nutr. Metab. 2010,2010, 905612. [CrossRef]
87. Beneke, R.; Pollmann, C.H.; Bleif, I.; Leithäuser, R.; Hütler, M. How anaerobic is the Wingate Anaerobic Test for humans? Eur. J.
Appl. Physiol. 2002,87, 388–392. [CrossRef] [PubMed]
88.
Sherman, W.M.; Costill, D.L.; Fink, W.J.; Miller, J.M. Effect of Exercise-Diet Manipulation on Muscle Glycogen and Its Subsequent
Utilization During Performance. Int. J. Sports Med. 1981,2, 114–118. [CrossRef] [PubMed]
89.
Churchley, E.G.; Coffey, V.G.; Pedersen, D.J.; Shield, A.; Carey, K.A.; Cameron-Smith, D.; Hawley, J.A. Influence of preexercise
muscle glycogen content on transcriptional activity of metabolic and myogenic genes in well-trained humans. J. Appl. Physiol.
2007,102, 1604–1611. [CrossRef]
90.
Tesch, P.A. Glycogen and triglyceride utilization in relation to muscle metabolic characteristics in men performing heavy-resistance
exercise. Eur. J. Appl. Physiol. Occup. Physiol. 1990,61, 5–10. [CrossRef]
91.
Koopman, R.; Manders, R.J.F.; Jonkers, R.A.M.; Hul, G.B.J.; Kuipers, H.; van Loon, L.J.C. Intramyocellular lipid and glycogen
content are reduced following resistance exercise in untrained healthy males. Eur. J. Appl. Physiol. 2005,96, 525–534. [CrossRef]
92.
Pascoe, D.D.; Costill, D.L.; Fink, W.J.; ARobergs, R.; Zachwieja, J.J. Glycogen resynthesis in skeletal muscle following resistive
exercise. Med. Sci. Sports Exerc. 1993,25, 349–354. [CrossRef]
93.
Roy, B.D.; Tarnopolsky, M.A. Influence of differing macronutrient intakes on muscle glycogen resynthesis after resistance exercise.
J. Appl. Physiol. 1998,84, 890–896. [CrossRef]
94. Tesch, P.A.; Colliander, E.B.; Kaiser, P. Muscle metabolism during intense, heavy-resistance exercise. Eur. J. Appl. Physiol. Occup.
Physiol. 1986,55, 362–366. [CrossRef]
95.
Taylor, R.; Magnusson, I.; Rothman, D.L.; Cline, G.W.; Caumo, A.; Cobelli, C.; Shulman, G.I. Direct assessment of liver glycogen
storage by 13C nuclear magnetic resonance spectroscopy and regulation of glucose homeostasis after a mixed meal in normal
subjects. J. Clin. Investig. 1996,97, 126–132. [CrossRef] [PubMed]
96.
Ejensen, J.; Rustad, P.I.; Kolnes, A.J.; Lai, Y.-C. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin
Sensitivity by Exercise. Front. Physiol. 2011,2, 112. [CrossRef]
97.
Mears, S.A.; Dickinson, K.; Bergin-Taylor, K.; Dee, R.; Kay, J.; James, L.J. Perception of Breakfast Ingestion Enhances High-Intensity
Cycling Performance. Int. J. Sports Physiol. Perform. 2018,13, 504–509. [CrossRef] [PubMed]
98.
Waterworth, S.P.; Spencer, C.C.; Porter, A.L.; Morton, J.P. Perception of Carbohydrate Availability Augments High-Intensity
Intermittent Exercise Capacity Under Sleep-Low, Train-Low Conditions. Int. J. Sport Nutr. Exerc. Metab.
2020
,30, 105–111.
[CrossRef]
99.
Naharudin, M.N.; Yusof, A.; Clayton, D.J.; James, L.J. Starving Your Performance? Reduced Preexercise Hunger Increases
Resistance Exercise Performance. Int. J. Sports Physiol. Perform. 2021,1, 1–7. [CrossRef]
100.
Decimoni, L.S.; Curty, V.M.; Almeida, L.; Koch, A.J.; Willardson, J.M.; Machado, M. Carbohydrate mouth rinsing improves
resistance training session performance. Int. J. Sports Sci. Coach. 2018,13, 804–809. [CrossRef]
101.
Green, M.S.; Kimmel, C.S.; Martin, T.D.; Mouser, J.G.; Brune, M.P. Effect of Carbohydrate Mouth Rinse on Resistance Exercise
Performance. J. Strength Cond. Res. 2020; publish ahead of print. [CrossRef]
102.
Costill, D.L.; Pearson, D.R.; Fink, W.J. Impaired muscle glycogen storage after muscle biopsy. J. Appl. Physiol.
1988
,64, 2245–2248.
[CrossRef]
103.
Gollnick, P.D.; Piehl, K.; Saltin, B. Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity
and at varying pedalling rates. J. Physiol. 1974,241, 45–57. [CrossRef]
104. Ivy, J.L. Muscle Glycogen Synthesis Before and After Exercise. Sports Med. 1991,11, 6–19. [CrossRef]
105.
Pascoe, D.D.; Gladden, L.B. Muscle Glycogen Resynthesis after Short Term, High Intensity Exercise and Resistance Exercise.
Sports Med. 1996,21, 98–118. [CrossRef]
106.
Bortz, W.M.; Paul, P.; Haff, A.C.; Holmes, W.L. Glycerol turnover and oxidation in man. J. Clin. Investig.
1972
,51, 1537–1546.
[CrossRef] [PubMed]
107. Ruderman, N.B. Muscle Amino Acid Metabolism and Gluconeogenesis. Annu. Rev. Med. 1975,26, 245–258. [CrossRef]
108.
Phielix, E.; Begovatz, P.; Gancheva, S.; Bierwagen, A.; Kornips, E.; Schaart, G.; Hesselink, M.K.C.; Schrauwen, P.; Roden, M.
Athletes feature greater rates of muscle glucose transport and glycogen synthesis during lipid infusion. JCI Insight
2019
,4, e127928.
[CrossRef]
109.
Thomas, K.; Brownstein, C.G.; Dent, J.; Parker, P.; Goodall, S.; Howatson, G. Neuromuscular Fatigue and Recovery after Heavy
Resistance, Jump, and Sprint Training. Med. Sci. Sports Exerc. 2018,50, 2526–2535. [CrossRef] [PubMed]
110.
Creer, A.; Gallagher, P.; Slivka, D.; Jemiolo, B.; Fink, W.; Trappe, S. Influence of muscle glycogen availability on ERK1/2 and Akt
signaling after resistance exercise in human skeletal muscle. J. Appl. Physiol. 2005,99, 950–956. [CrossRef] [PubMed]
111.
Knuiman, P.; Hopman, M.T.E.; Wouters, J.A.; Mensink, M. Select Skeletal Muscle mRNAs Related to Exercise Adaptation Are
Minimally Affected by Different Pre-exercise Meals that Differ in Macronutrient Profile. Front. Physiol. 2018,9, 28. [CrossRef]
112.
Camera, D.M.; West, D.W.D.; Burd, N.A.; Phillips, S.M.; Garnham, A.P.; Hawley, J.A.; Coffey, V.G. Low muscle glycogen
concentration does not suppress the anabolic response to resistance exercise. J. Appl. Physiol. 2012,113, 206–214. [CrossRef]
Nutrients 2022,14, 856 39 of 39
113.
Murphy, C.; Koehler, K. Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and
meta-regression. Scand. J. Med. Sci. Sports 2021,32, 125–137. [CrossRef]
114.
Volek, J.S.; Freidenreich, D.J.; Saenz, C.; Kunces, L.J.; Creighton, B.C.; Bartley, J.M.; Davitt, P.M.; Munoz, C.X.; Anderson, J.M.;
Maresh, C.M.; et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism
2016
,65, 100–110. [CrossRef]
115.
Phinney, S.D.; Bistrian, B.; Evans, W.; Gervino, E.; Blackburn, G.L. The human metabolic response to chronic ketosis without
caloric restriction: Preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism
1983
,32,
769–776. [CrossRef]
116.
Helge, J.W.; Watt, P.W.; Richter, E.A.; Rennie, M.J.; Kiens, B. Fat utilization during exercise: Adaptation to a fat-rich diet increases
utilization of plasma fatty acids and very low density lipoprotein-triacylglycerol in humans. J. Physiol.
2001
,537, 1009–1020.
[CrossRef] [PubMed]
117.
Zderic, T.W.; Davidson, C.J.; Schenk, S.; Byerley, L.O.; Coyle, E.F. High-fat diet elevates resting intramuscular triglyceride
concentration and whole body lipolysis during exercise. Am. J. Physiol. Metab. 2004,286, E217–E225. [CrossRef] [PubMed]
118.
Phinney, S.D.; Horton, E.S.; Sims, E.A.H.; Hanson, J.S.; Danforth, E.; Lagrange, B.M. Capacity for Moderate Exercise in Obese
Subjects after Adaptation to a Hypocaloric, Ketogenic Diet. J. Clin. Investig. 1980,66, 1152–1161. [CrossRef]
119.
Taber, C.B.; Vigotsky, A.; Nuckols, G.; Haun, C.T. Exercise-Induced Myofibrillar Hypertrophy is a Contributory Cause of Gains in
Muscle Strength. Sports Med. 2019,49, 993–997. [CrossRef] [PubMed]
120. Folland, J.P.; Williams, A.G. The Adaptations to Strength Training. Sports Med. 2007,37, 145–168. [CrossRef] [PubMed]
121.
Toomey, C.M.; McCormack, W.G.; Jakeman, P. The effect of hydration status on the measurement of lean tissue mass by
dual-energy X-ray absorptiometry. Eur. J. Appl. Physiol. 2017,117, 567–574. [CrossRef]
122.
Deemer, S.E.; Plaisance, E.P.; Martins, C. Impact of ketosis on appetite regulation—A review. Nutr. Res.
2020
,77, 1–11. [CrossRef]
123.
Tzur, A.; Roberts, B.M. The Ketogenic Diet for Bodybuilders and Physique Athletes. Strength Cond. J.
2020
,42, 108–115. [CrossRef]
124.
Valenzuela, P.L.; Castillo-García, A.; Lucia, A.; Naclerio, F. Effects of Combining a Ketogenic Diet with Resistance Training
on Body Composition, Strength, and Mechanical Power in Trained Individuals: A Narrative Review. Nutrients
2021
,13, 3083.
[CrossRef]
Content uploaded by Fredrik Tonstad Vårvik
Author content
All content in this area was uploaded by Fredrik Tonstad Vårvik on Feb 21, 2022
Content may be subject to copyright.
