The Role of L-Carnitine in Distance Athletes

Abstract

The purpose of this study was to perform a systematic review and summarize the current literature regarding L-carnitine and the potential role of sports especially in distance athletes. L-carnitine is a naturally occurring compound that plays an important role in mitochondrial β-oxidation. The main role of L-carnitine is to promote weight loss by increasing calorie expenditure. Also, L-carnitine plays an important role on recovery from strenuous exercise and may help to achieve quicker recovery and reduce muscle soreness. Finally, the results indicate that there is uncertainty in regards to how L-carnitine helps athletic performance. There are only three studies in the literature showing beneficial effects of L-carnitine on performance of athletes. On the contrary, three other studies have shown no effect of L-carnitine on performance.

Full text

International Journal of Sports Science 2018, 8(5): 158-163
DOI: 10.5923/j.sports.20180805.04
The Role of L-Carnitine in Distance Athletes
Gerasimos V. Grivas
School of Physical Education and Sport Science, University of Thessaly, Trikala, Greece
Abstract The purpose of this study was to perform a systematic review and summarize the current literature regarding
L-carnitine and the potential role of sports especially in distance athletes. L-carnitine is a naturally occurring compound that
plays an important role in mitochondrial β-oxidation. The main role of L-carnitine is to promote weight loss by increasing
calorie expenditure. Also, L-carnitine plays an important role on recovery from strenuous exercise and may help to achieve
quicker recovery and reduce muscle soreness. Finally, the results indicate that there is uncertainty in regards to how
L-carnitine helps athletic performance. There are only three studies in the literature showing beneficial effects of L-carnitine
on performance of athletes. On the contrary, three other studies have shown no effect of L-carnitine on performance.
Keywords L-carnitine, Distance athletes, Supplementation, Exercise, Performance
1. Introduction
Carnitine (L-3-hydroxytrimethylamminobutanoate) is an
endogenous compound that can be synthesized in the liver
and kidney from the essential amino acids lysine and
methionine or ingested through diet [8, 10, 27, 57].
L-carnitine plays a critical role in energy production and in
fat metabolism through its function as a transporter of
long-chain fatty acids into mitochondria for β-oxidation
[17]. In cells, it helps transport fatty acids into the
mitochondria, where they can be burned for energy.
Primary sources of dietary carnitine are red meat and dairy
products. L-carnitine is stored primary in skeletal muscle
(98%), but also in a much lower concentrations is found in
plasma [6, 15].
L-carnitine often receives patients with regular
hemodialysis, with metabolic disorders and in pregnancy
[33, 42]. However, L-carnitine plays a crucial role in
exercise and among athletes. A few studies demonstrated
the effects of L-carnitine in endurance athletes. Endurance
athletes use this supplementation to increase the oxidation
of fat during exercise and spare muscle glycogen [25]. One
of the main functions of performance enhancing drugs is to
increase the amount of red blood cells. It is often times
overlooked, be-cause of the obvious anabolic effects of
performance enhancing drugs. By increasing the oxygen
carrying capability of the blood, it helps give the body an
additional boost especially in stressful situations.
* Corresponding author:
grivasger@hotmail.com (Gerasimos V. Grivas)
Published online at http://journal.sapub.org/sports
Copyright © 2018 The Author(s). Published by Scientific & Academic Publishing
This work is licensed under the Creative Commons Attribution International
License (CC BY). http://creativecommons.org/licenses/by/4.0/
2. Different types of L-Carnitine
2.1. Acetyl-L-Carnitine
Acetyl-L-carnitine, or ALCAR, is L-carnitine to which an
acetyl group (-COCH3) has been added, is thought to be the
most bioavailable form of L-carnitine. Acetyl-L-Carnitine
is an amino acid the body uses to turn fat into energy. It
may also be used to treat neurological conditions such
as Alzheimer's disease. Also, is a popular endurance
supplement that plays a key role in energy production. There
are many benefits of this supplementation for endurance
athletes, but the most important are that improve exercise
performance, improve recovery after following exercise,
reduce muscle damage and soreness, increase ATP levels
and improve antioxidant status.
2.2. Propionyl-L-Carnitine
Also, is formed principally during amino acid catabolism
[44]. The main role of PLC is that helps the body to produce
energy. Furthermore, PLC is known to decrease lipid
peroxidation or the process wherein lipid membranes are
attacked by free radicals, causing cellular damage [3, 34].
Also helps increase the production of nitric oxide, which
promotes blood circulation and regulates blood pressure [2].
For endurance athletes, cellular damage could mean longer
recovery times and be more prone to muscular injuries in
training sessions. Also, is formed principally during amino
acid catabolism.
2.3. L-Carnitine L-Tartrate
L-carnitine L-tartate is the one of the most common
forms found in sports supplements, due to its rapid
absorption rate [13, 49, 45]. This supplement is found to
decrease muscle damage during recovery from resistance

International Journal of Sports Science 2018, 8(5): 158-163 159
exercises [23]. Several studies found that 3 weeks
supplementation with L-carnitine L-tartate reduces muscle
damage produced by an acute bout of high intensity
resistance exercise [28, 50].
3. L-Carnitine Deficiency
L-carnitine deficiency is caused by a deficiency in the
plasma membrane carnitine transporter with urinary
carnitine wasting causing systemic carnitine depletion.
Intracellular carnitine deficiency impairs the entry of
long-chain fatty acids into the mitochondrial matrix [16].
Systemic primary carnitine deficiency is characterized by
episodes of hypoketonic, hypoglykemia, hepatomegaly,
elevated transaminases, and hyperammonemia in infants;
skeletal myopathy, elevated creatine kinase (CK), and
cardiomyopathy in childhood; or fatigability in adulthood
[14]. The diagnosis is established by demonstration of low
plasma free carnitine concentration (<5 μM, normal 25-50
μM), reduced fibroblast carnitine transport (<10% of
controls), and molecular testing of the SLC22A5 gene on
newborn screening [31].
In a Japanese study [29], primary systemic carnitine
deficiency was estimated to occur in 1 per 40,000 births.
Wilcken et al. [2003] reports that in Australia the incidence
has been estimated to be between 1:37,000-1:100,000
newborns. The frequency of this condition in adults is not
known. However, in the United Kingdom, a previous report
identified 4 affected mothers in 62,004 infants screened, with
a frequency of 1:15,500. No studies have estimated the
incidence of primary carnitine deficiency in the United
States and in Europe, however is estimated to occur in
approximately 1 in 20,000-70,000 individuals based on
newborn screening data from various states including
Missouri, Texas, and California.
4. L-carnitine and Weight Loss
Three studies found dietary carnitine intake to be
important, and evidence suggests it may promote weight loss
by increasing calorie expenditure [24, 46, 47]. The study of
Stephens et al. [47] found that dietary carnitine intake to be
important supplementation with L-carnitine (of 2 x 1.36 g
per day for 12 weeks) helps to prevent gains in body weight
associated with increased energy intake. This maybe
attributable, at least in part to the increased muscle carnitine
concentrations (of up to 20%); increased energy expenditure
rates (of 6%); and/or enhanced expression of genes involved
in energy breakdown and storage [47].
A systematic review and meta-analysis of randomized
control trials testing the effects of L-carnitine on weight loss
[38]. In this meta-analysis were included nine studies and
the participants supplemented with L-carnitine for at least
one month. The results from meta-analysis suggested that
supplementing with L-carnitine led to a 1.33 kg greater
weight loss, on average, compared to a placebo. L-carnitine
supplementation led to significant weight loss in diabetic
and non-diabetic individuals, as well as obese and
nor-mal-weight people. Additionally, the meta-analysis
showed that the weight loss effects of L-carnitine are
strongest in the beginning but decrease over time. However,
the relevance of these findings is unclear because the
included studies varied widely in their design. In summary,
this me-ta-analysis of randomized controlled trials suggests
that supplementing with L-carnitine for more than a month
may promote modest weight loss.
5. L-carnitine and Recovery from
Strenuous Exercise
Found only two studies in distance runners that referred on
the effects of L-Carnitine in recovery after high intensity
training (Table 1). In a study by Colombani et al. [11],
demonstrated that an acute L-carnitine supplementation had
no ergogenic effect and did not improve the recovery in
endurance-trained athletes performing a long-distance run.
Moreover, the study of Stuessi et al. [48] examined the
effects of L-carnitine on recovery after exhaustive endurance
exercise. Twelve subjects received either 2 g L-carnitine.
Two hours after administration, the subjects performed a
constant-load exercise test cycling at their individual
anaerobic threshold to exhaustion. They found that 2 g of
L-carnitine taken 2 h before a first of two constant-load
exercise tests had no influence on the second tests performed
3 h after the first test. Also, one study used active healthy
men. More especially, in a study by Parandak et al. [37] 21
active healthy young men were given either 2 g L-carnitine
or a placebo daily for two weeks prior to an athletic test.
Compared to the control group, those who took L-carnitine
were found to have lower levels of certain markers that
indicate muscle damage.
Moreover, some studies used in untrained subjects and
examined the effects of L-carnitine in recovery after
intensive exercise (Table 1). Initially, in a study by
Giamberardino et al. [18] six untrained male followed a 7
weeks during which each subject: a) was given 3 g/d of
L-carnitine for 3 weeks and, after a week's interval, 3 g/d of
L-carnitine for 3 weeks; b) performed 2 step tests on the first
day of the 3rd and 7th week inverting the order of the
exercising limb. In a separate set of experiments carried out 8
months later, the possible effects of training on pain
parameters and creatine kinase levels were also investigated
in the same subjects. It is concluded that L-carnitine has a
protective effect against pain and damage from eccentric
effort. Two papers from the same lab [22, 45] were also used
in untrained male and female. L-carnitine supplementation
was given for 3 weeks (2 g/d). After 3 weeks of L-carnitine
supplementation loading, each participant then performed an
acute resistance exercise. They found that L-carnitine
supplementation can reduce chemical damage and muscle

160 Gerasimos V. Grivas: The Role of L-Carnitine in Distance Athletes
soreness after physical exercise.
On the contrary, there are some studies that referred in
resistance trained subjects (Table 1). Two studies from the
same lab [28, 50] investigated the effects of L-carnitine
supplementation on recovery after resistance exercise. The
subject was 10 resistance trained men consumed L-carnitine
supplement (2 g L-carnitine/day) for 3 weeks before
obtaining blood samples on six consecutive days. Blood was
also sampled before and after a squat protocol (5 sets, 15–20
repetitions). The results demonstrate that L-carnitine
supplementation is effective in assisting recovery from
high-repetition squat exercise.
6. Effects of L-carnitine on Athletic
Performance and Recommended
Dosage
Some athletes take L-carnitine to improve performance.
However, three studies find no consistent evidence that
carnitine supplements can improve exercise or physical
performance in healthy subjects at doses ranging from 2–6
grams/day administered for 1 to 28 days [4, 5, 7]. (Table 2)
There is a debate about the effects of L-carnitine on
athletic performance in distance runners. Some studies found
that this supplementation improve athletic performance.
More specifically, Gorostiaga et al. [19] suggested that 2 g of
L-carnitine during 28 days increased lipid use in muscle and
decreased respiratory quotient during submaximal exercise.
Also, in the study of Arenas et al. [1] sixteen well-trained
male athletes received 2 g orally of L-carnitine for 28 days
and after the endurance athletes started a 4 weeks endurance
training program. They found improvement in VO2max after
L-carnitine administration. (Table 2)
On the other hand, some studies have seen not improve of
performance in distance runners. The study of Marconi et al.
[32] found 6% increase of VO2max in endurance runners.
They suggested that this improvement is probably affected
by variables, other than L-carnitine loading, of a
physiological (e.g. initial muscle glycogen stores) and/or
psychological nature. Also, Colombani et al. [11] examined
the effects of L-carnitine supplementation on physical
performance. Seven male subjects were given supplements
of 2 g L-carnitine 2 h before the start of a marathon run and
again after 20 km of the run. They found that acute
administration of L-carnitine did not improve the physical
performance of the endurance athletes during the run and did
not alter their recovery. In the study of Greig et al. [20]
examined the effects of 2 g oral supplementation of with
L-carnitine for 2 and 4 weeks. The results of treatment with
L-carnitine demonstrated no significant changes in VO2max
or in maximum heart rate. Furthermore, in the study of
Wachter et al. [51] 8 male adults were treated with 2x2 g of
L-carnitine per day for 3 months. Exercise tests were
performed using a bicycle ergometer for 10 min at 20%, 40%,
and 60% of the individual maximal workload, respectively,
until exhaustion. They found that supplementation of
L-carnitine is not associated with a significant increase.
Moreover Cooper et al. [12] used loading of the athletes
with L-carnitine for 10 days before running a marathon. The
time of marathon run reduced by 3.2%, after loading of
L-carnitine, but this improvement was small and not
significant.
Moreover, some studies used in untrained subjects and
examined the effects of L-carnitine on athletic performance.
DiSilvestro et al. [53] suggested that 2 g orally of L-carnitine
for 4 weeks improve aerobic exercise performance in fit
young adult women. In the study of Shannon et al. [54] 21
untrained male received 3 g orally of L-carnitine for 24
weeks. They found improvements in VO2max. Also, in the
study of Burrus et al. [55] suggested that 3 g orally of
L-carnitine 3 h prior to exercise did not improve time to
exhaustion at 85% of VO2max. In the review of Stephens
et al [56], suggested that feeding of 2-5 g/d L-carnitine for 1
week to 3 months prior to bout of exercise had no effect on
exercise performance.
Table 1. Studies that examine the effects of L-carnitine in recovery after strenuous exercise
Study
Population
Daily L-carnitine dose
Treatment duration
(weeks)
L-carnitine effects
Colombani et al. 1996
7 male athletes
4 g orally
Day of event
Did not improve the recovery
Stuessi et al. 2005
12 male athletes
2 g orally
Day of event
Did not improve the recovery
Paradank et al. 2014
21 male active
2 g orally
2
Lower levels of CK and LDH
Giamberardino et al.
1996
6 untrained male
3 g orally
3
Protective effect against pain and
damage
Ho et al. 2010
9 male and 9 female
untrained
2 g orally
3
Reduce chemical damage and
muscle soreness
Spiering et al. 2007
8 untrained men
1-2 g orally
3
Reduce muscle soreness
Kraemer et al. 2003
10 resistance trained men
2 g orally
3
Quicker recovery
Volek et al. 2002
10 resistance trained men
2 g orally
3
Effective in assisting recovery
CK: creatine kinase, LDH: lactate dehydrogenase

International Journal of Sports Science 2018, 8(5): 158-163 161
Table 2. Studies that examine the effects of L-carnitine on performance
Study
Population
Daily L-carnitine
dose
Treatment duration
(weeks)
Endpoints
L-carnitine effects
Marconi et al. 1985
6 competitive
walkers
4 g orally
2
VO2max, lactate,
RQ
Increase in VO2max, no
change in RQ at fixed
workload
Colombani et al.
1996
7 male athletes
4 g orally
Day of event
Marathon time
and postrace
lactate
No effects of L-carnitine
Arenas et al. 1994
16 male athletes
2 g orally
4
VO2max
Improvement VO2max
Gorostiaga et al.
1989
9 male and 1 female
2 g orally
4
RQ, VO2, heart
rate, lactate,
plasma glucose at
fixed workload
Decrease in RQ, no others
significant changes
Wachter et al. 2002
8 trained male
4 g orally
12
VO2max
No effects of L-carnitine
Cooper et al. 1986
10 male marathon
runners
4 g orally
10 days
Marathon time
Reduce by 3.2%
VO2max = maximal oxygen consumption during exercise; RQ = respiratory quotient (VCO2/O2).
7. Bioavailability of L-carnitine in
Athletes
The bioavailability of L-carnitine from food can vary
depending on dietary composition. Bioavailability of
L-carnitine from oral supplements ranges from 14-18% of
the total dose, 15.1 ± 5.3% for the tablet and 14.8 ± 5.1%
for the chewable tablet [15, 39]. After oral doses of 1–6 g,
the absolute bioavailability is 5–18%. Less is known
re-garding the metabolism of the acetylated form of
L-carnitine, acetyl-L-carnitine; however, bioavailability of
acetyl-L-carnitine is thought to be higher than L-carnitine. In
the studies of Sahajwalla et al. [41] and Segre et al. [43]
reported an absolute bioavailability of 18% after a single oral
dose of 100 mg/kg as L-carnitine solution. Also, Harper,
Elwin and Cederblad [21] reported a value of 16% (1.98g as
a single oral dose of 6 x 330mg tablets with 200mL of water).
Finally, Rizza et al. [40] reported absolute bioavailability
values of 16 ± 3% and 14 ± 2% for oral doses of 20 mg/kg
(approx. 2 g) and 100 mg/kg (approx. 6 g), respectively.
8. Conclusions
L-carnitine is unique in its essential role in energy
metabolism, transporting fatty acids across the mitochondrial
membrane for subsequent breakdown and energy generation
[23].
The main limitation of the present systematic review is the
small number of included studies that used distance athletes.
Although, the vast majority of the studies recruited untrained
or resistance trained athletes.
The main role of L-carnitine is to help populations with
certain conditions achieve a higher level of exercise
performance, particularly those with various dimensions of
cardiovascular disease. These results indicate that there is
uncertainty in regards to how L-carnitine helps athletic
performance. Found six studies that examined the effects of
L-carnitine on athletic performance. From these six studies,
three studies in the literature showing beneficial effects of
L-carnitine on performance of athletes [1, 19, 32]. On the
contrary, three of studies have shown no effect of L-carnitine
on performance [11, 12, 51].
However, it is clear that L-carnitine plays an important
role on recovery from strenuous exercise [22, 45]. The
majority of studies suggested a dose of 2-4 g/d of
L-carnitine.
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