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The Role of L-Carnitine in Distance Athletes


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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.
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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: (Gerasimos V. Grivas)
Published online at
Copyright © 2018 The Author(s). Published by Scientific & Academic Publishing
This work is licensed under the Creative Commons Attribution International
License (CC BY).
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, 1520
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
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 26
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
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
Daily L-carnitine dose
Treatment duration
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
Lower levels of CK and LDH
Giamberardino et al.
6 untrained male
3 g orally
Protective effect against pain and
Ho et al. 2010
9 male and 9 female
2 g orally
Reduce chemical damage and
muscle soreness
Spiering et al. 2007
8 untrained men
1-2 g orally
Reduce muscle soreness
Kraemer et al. 2003
10 resistance trained men
2 g orally
Quicker recovery
Volek et al. 2002
10 resistance trained men
2 g orally
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
Daily L-carnitine
Treatment duration
L-carnitine effects
Marconi et al. 1985
4 g orally
VO2max, lactate,
Increase in VO2max, no
change in RQ at fixed
Colombani et al.
4 g orally
Day of event
Marathon time
and postrace
No effects of L-carnitine
Arenas et al. 1994
2 g orally
Improvement VO2max
Gorostiaga et al.
2 g orally
RQ, VO2, heart
rate, lactate,
plasma glucose at
fixed workload
Decrease in RQ, no others
significant changes
Wachter et al. 2002
4 g orally
No effects of L-carnitine
Cooper et al. 1986
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
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 16 g,
the absolute bioavailability is 518%. 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
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
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... L-Carnitine is an essential chemical compound produced in a body through the essential amino acids, i.e., methionine and lysine. The manufacturing of L-Carnitine takes place in the kidney and liver with the help of amino acids [1]. L-Carnitine is obtained from external dietary sources as well. ...
... It is also highly used as a supplement for high tolerance power during exercise and the main source of energy production during the workout to make better performance. It is also used to decrease muscle soreness after a workout by simply increasing ATP levels and improving antioxidant status [1,5]. The structure of Acetyl L-Carnitine consists of ammonium ion and the acyl group, which is further specified as an acetyl group which results in the motion of acetyl-COA into mitochondria matrices for oxidation of fatty acids. ...
... And because of its high rate of absorption, it is readily undergoing the maintaining of damaged muscles during recovery after an intense workout [21,22], and many studies claim that it enhances strength during a heavy workout. Some studies also claim that three weekly supplement courses of L-tartrate will decrease muscle damage done by several intense workouts [1]. The structure of L-Carnitine L-Tartrate consists of tartrate ion, which is salt of tartaric acid and two ions of L-Carnitine are also present. ...
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L-carnitine, an amino acid derivative, is naturally synthesized in human bodies in very few amounts and can also be taken as a dietary supplement. This amino acid derivative is very popular among various medical drugs and in gym dietary nutrients. In addition, it plays an intense role in brain functioning, in the generation of energy, known to provide more oxygen for muscles and improve stamina, strength, and power. Besides its various applications, several myths are reported but do not have adequate scientific evidence to date. This review aims to investigate the effects of L-Carnitine as a drug and the myths related to it. This paper contains significant facts about L-Carnitine, i.e., its benefits, side effects, and myths. It will give a clear idea about L-Carnitine and its applications. This review paper discussed the characteristics of L-carnitine, which finds vast applications and benefits. This review paper has also discussed the most recent finding of L-Carnitine promoting atherosclerosis by way of trimethylamine N-oxide Meta organismal pathway along with its solution on trial bases. L-Carnitine has many applications in the clinic and personalized medicine; hence, it has an excellent scope for future works, which requires the trials of its applications on a large scale.
... Conversely, the increase in muscle carnitine content in young, healthy volunteers modulated changes in whole-body energy expenditure, quadriceps muscle fuel metabolism and gene expression, due to the increase in muscle fat oxidation owing to increased muscle long-chain FAs translocation via CPT1 [101][102][103]. Therefore, carnitine, that stimulates the transport of long-chain FAs across the inner membrane of the mitochondrion and short-chain FAs across several membranes, may lead to a detoxification process, eliminating those metabolites that could damage organelles [104,105]. Regarding the benefits of oral administration of L-carnitine, studies are contradictory, showing no gain [106,107] or less chemical damage and muscle soreness [108][109][110][111] or a better and faster recovery [112]. Since oxidation of the medium-chain FA octanoate is unchanged when exercise intensity shifts from 40% to 80% of VO 2max , medium-chain FAs should be able to bypass CPT1, as was the case for oleate, a CPT1-dependent long-chain FA [113]. ...
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Since the lipid profile is altered by physical activity, the study of lipid metabolism is a remarkable element in understanding if and how physical activity affects the health of both professional athletes and sedentary subjects. Although not fully defined, it has become clear that resistance exercise uses fat as an energy source. The fatty acid oxidation rate is the result of the following processes: (a) triglycerides lipolysis, most abundant in fat adipocytes and intramuscular triacylglycerol (IMTG) stores, (b) fatty acid transport from blood plasma to muscle sarcoplasm, (c) availability and hydrolysis rate of intramuscular triglycerides, and (d) transport of fatty acids through the mitochondrial membrane. In this review, we report some studies concerning the relationship between exercise and the aforementioned processes also in light of hormonal controls and molecular regulations within fat and skeletal muscle cells.
... Различия сравниваемых групп по средней величине индекса АК/С0 оказались статистически незначимыми. При сравнении уровня связанного карнитина во всех трех группах статистически значимых различий выявлено не Выявленные различия в содержании свободного карнитина и соотношения АК/С0указывают на состоянии более эффективной клеточной энергетики именно у мальчиков -представителей аэробных нагрузок, так как высокое содержание свободного карнитина обеспечивает перенос большого количества жирных кислот через митохондриальную мембрану [10,11]. ...
Objective: to develop prognostic criteria for assessing the physical performance of children engaged in different sports, using the features of carnitine metabolism. Materials and methods: 94 young athletes and 37 students as a control group were included to the study. Indicators such as free and bound carnitine, maximum oxygen consumption (MOC) (as an indicator of physical performance), and the body composition were studied. Results: statistical analysis of the data indicated that the average amount of total carnitine in the group of children engaged in field hockey was lower (45.9±1.6 µmol/l) comparing with the group of representatives of cyclic sports (52.6±1.1 µmol/l) and with the group of control (46.3±1.0 µmol/l). The study of the level of MOC in the abovementioned groups revealed statistically significant differences. Thus, among the field hockey players the average level of absolute MOC was 2.2±0.1 lpm, swimmers – 3.8±0.2 lpm, in the control group – 2.7±0.1 lpm. The study showed significant positive correlation between the level of absolute MOC with total and free carnitine. The data obtained may indicate a greater aerobic performance in athletes with a higher content of free carnitine. Conclusions: thus, after studying the state of carnitine metabolism and maximum oxygen consumption, it becomes possible to predict the state of physical performance of children, which determines the measures to prevent health problems during intense physical activity.
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Background: Certain essential and conditionally essential nutrients (CENs) perform functions involved in aerobic exercise performance. However, increased intake of such nutrient combinations has not actually been shown to improve such performance. Methods: For 1 mo, aerobically fit, young adult women took either a combination of 3 mineral glycinate complexes (daily dose: 36 mg iron, 15 mg zinc, and 2 mg copper) + 2 CENs (daily dose: 2 g carnitine and 400 mg phosphatidylserine), or the same combination with generic mineral complexes, or placebo (n = 14/group). In Trial 1, before and after 1 mo, subjects were tested for 3 mile run time (primary outcome), followed by distance covered in 25 min on a stationary bike (secondary outcome), followed by a 90 s step test (secondary outcome). To test reproducibility of the run results, and to examine a lower dose of carnitine, a second trial was done. New subjects took either mineral glycinates + CENs (1 g carnitine) or placebo (n = 17/group); subjects were tested for pre- and post-treatment 3 mile run time (primary outcome). Results: In Trial 1, the mineral glycinates + CENs decreased 3 mile run time (25.6 ± 2.4 vs 26.5 ± 2.3 min, p < 0.05, paired t-test) increased stationary bike distance after 25 min (6.5 ± 0.6 vs 6.0 ± 0.8 miles, p < 0.05, paired t-test), and increased steps in the step test (43.8 ± 4.8 vs 40.3 ± 6.4 steps, p < 0.05, paired t-test). The placebo significantly affected only the biking distance, but it was less than for the glycinates-CENs treatment (0.2 ± 0.4. vs 0.5 ± 0.1 miles, p < 0.05, ANOVA + Tukey). The generic minerals + CENs only significantly affected the step test (44.1 ± 5.2 vs 41.0 ± 5.9 steps, p < 0.05, paired t-test) In Trial 2, 3 mile run time was decreased for the mineral glycinates + CENs (23.9 ± 3.1 vs 24.7 ± 2.5, p < 0.005, paired t-test), but not by the placebo. All changes for Test Formula II or III were high compared to placebo (1.9 to 4.9, Cohen's D), and high for Test Formula II vs I for running and biking (3.2 & 3.5, Cohen's D). Conclusion: In summary, a combination of certain mineral complexes plus two CENs improved aerobic exercise performance in fit young adult women.
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Skeletal muscles have a fundamental role in locomotion and whole body metabolism, with muscle mass and quality being linked to improved health and even lifespan. Optimising nutrition in combination with exercise is considered an established, effective ergogenic practice for athletic performance. Importantly, exercise and nutritional approaches also remain arguably the most effective countermeasure for muscle dysfunction associated with ageing and numerous clinical conditions e.g. cancer cachexia, COPD and organ failure, via engendering favourable adaptations such as increased muscle mass and oxidative capacity. Therefore, it is important to consider the effects of established and novel effectors of muscle mass, function and metabolism in relation to nutrition and exercise. To address this gap, in this review we detail existing evidence surrounding the efficacy of a non-exhaustive list of macronutrient, micronutrient and "nutraceutical" compounds alone and in combination with exercise in relation to skeletal muscle mass, (protein and fuel) metabolism and exercise performance (i.e. strength and endurance capacity). It is long established that macronutrients have specific roles and impacts upon protein metabolism and exercise performance i.e. protein positively influences muscle muscle mass and protein metabolism, whilst carbohydrate and fat intakes can influence fuel metabolism and exercise performance. Regarding novel nutraceuticals, we show the following ones in particular may have effects in relation to: 1) muscle mass/protein metabolism: leucine, hydroxyl b-methylbutyrate, creatine, vitamin-D, ursolic acid and phosphatidic acid, and 2) exercise performance: (i.e. strength or endurance capacity); hydroxyl -methylbutyrate, carnitine, creatine, nitrates and b-alanine.
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This study provides a systematic review and meta-analysis of randomized controlled trials, which have examined the effect of the carnitine on adult weight loss. Relevant studies were identified by systematic search of PubMed, Embase, Cochrane Central Register of Controlled Trials and reference lists of relevant marker studies. Nine studies (total n = 911) of adequate methodological quality were included in the review. Trials with mean difference (MD) of 95% confidence interval (CI) were pooled using random effect model. Results from meta-analysis of eligible trials revealed that subjects who received carnitine lost significantly more weight (MD: -1.33 kg; 95% CI: -2.09 to -0.57) and showed a decrease in body mass index (MD: -0.47 kg m(-2) ; 95% CI: -0.88 to -0.05) compared with the control group. The results of meta-regression analysis of duration of consumption revealed that the magnitude of weight loss resulted by carnitine supplementation significantly decreased over time (p = 0.002). We conclude that receiving the carnitine resulted in weight loss. Using multiple-treatments meta-analysis of the drugs and non-pharmacotherapy options seem to be insightful areas for research. © 2016 World Obesity.
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This study was conducted to assess the effect of Two-week L-carnitine supplementation on known markers of oxidative stress and muscle damage following acute bouts of exercise in active healthy young men. Twenty-one active healthy men volunteered for this study. Participants were randomized in a double-blind placebo-controlled fashion into two groups: L-carnitine (C group; n=10) and placebo group (P group; n=11). They arrived at the laboratory after overnight fasting. A baseline blood sample was taken. Afterwards, subjects consumed either L-carnitine (2 capsules containing totally 2000 mg L-carnitine) or placebo (2 capsules containing totally 2000 mg lactose) daily for 14 days. On the day of the test, participants attended the athletics arena after overnight fasting. Then, participants were asked to run 14 km on the track at their highest ability. Blood samples were taken immediately, 2, and 24 hours after exercise. Plasma total antioxidant capacity (TAC), malondialdehyde (MDA) as thiobarbituric acid-reactive substance (TBARS) as a marker of lipid peroxidation, creatine kinase (CK) and lactate dehydrogenase (LDH) as markers of muscle damage were measured. TAC increased significantly 14 days after supplementation and 24h after exercise in C group compared with P group (P<0.05). Serum MDA-TBARS, CK, and LDH were significantly lower 24h after exercise in C group compared with P group (P<0.05). These results suggest that two-week daily oral supplementation of L-carnitine has alleviating effects on lipid peroxidation and muscle damage markers following an acute bout of exercise in active healthy young men.
Chronic supplementation of L-carnitine and carbohydrate has been reported to increase L-carnitine content in skeletal muscle and have positive influences on exercise variables and performance. This study investigated the acute intake of L-carnitine and carbohydrate on the exercise parameters of cycling. A total of 10 males (27.0 ± 4 years) completed two exercise sessions consisting of 40 min of cycling at 65% of VO2peak, followed by cycling to exhaustion at 85% of VO2peak. L-carnitine or a placebo was consumed 3 hours prior to exercise, and beverages consisting of 94 g of carbohydrate were consumed at both 2 hours, and 30 minutes prior to exercise. Repeated measures ANOVAs were used to compare respiratory exchange ratio (RER), blood lactate, and power output across experimental trials and time. A repeated measures t-test was used to analyze differences between conditions and time to exhaustion. RER was significantly lower (p=0.01) at baseline with L-carnitine ingestion (.83 ± .05) compared to the placebo ingestion (.86 ± .06). Blood lactate was significantly lower (p=0.02) after 10 minutes of cycling at 65% of VO2peak with ingestion of L-carnitine (35% change from baseline) compared to placebo ingestion (53% change from baseline). No differences were found for power output or time to exhaustion at 85% of VO2peak. Despite mentioned differences, acute intake of L-carnitine and carbohydrate does not appear to influence exercise parameters, likely due to a lack of sufficient change in the content of L-carnitine in skeletal muscle.
Increasing skeletal muscle carnitine availability alters muscle metabolism during steady-state exercise in healthy humans. We investigated whether elevating muscle carnitine, and thereby the acetyl-group buffering capacity, altered the metabolic and physiological adaptations to 24 weeks of high-intensity interval training (HIIT) at 100% maximal exercise capacity (Wattmax ). Twenty-one healthy male volunteers (age 23?2 years; BMI 24.2?1.1 kg/m(2) ) performed 2x3 minute bouts of cycling exercise at 100% Wattmax , separated by five minutes rest. Fourteen volunteers repeated this protocol following 24 weeks of HIIT and twice-daily consumption of 80g carbohydrate (CON) or 3g L-carnitine+carbohydrate (CARN). Before HIIT, muscle phosphocreatine (PCr) degradation (P<0.0001), glycogenolysis (P<0.0005), PDC activation (P<0.05), and acetylcarnitine (P<0.005) were 2.3, 2.1, 1.5 and 1.5-fold greater, respectively, in exercise bout two compared to bout one, whilst lactate accumulation tended (P<0.07) to be 1.5-fold greater. Following HIIT, muscle free carnitine was 30% greater in CARN vs CON at rest and remained 40% elevated prior to the start of bout two (P<0.05). Following bout two, free carnitine content, PCr degradation, glycogenolysis, lactate accumulation, and PDC activation were all similar between CON and CARN, albeit markedly lower than before HIIT. VO2max , Wattmax and work-output were similarly increased in CON and CARN, by 9, 15 and 23% (P<0.001). In summary, increased reliance on non-mitochondrial ATP resynthesis during a second bout of intense exercise is accompanied by increased carnitine acetylation. Augmenting muscle carnitine during 24 weeks of HIIT did not alter this, nor enhance muscle metabolic adaptations or performance gains beyond those with HIIT alone. This article is protected by copyright. All rights reserved.
Carnitine is needed for transfer of long-chain fatty acids across the inner mitochondrial membrane for subsequent β-oxidation. Carnitine can be synthesized by the body and is also obtained in the diet through consumption of meat and dairy products. Defects in carnitine transport such as those caused by defective activity of the OCTN2 transporter encoded by the SLC22A5 gene result in primary carnitine deficiency, and newborn screening programmes can identify patients at risk for this condition before irreversible damage. Initial biochemical diagnosis can be confirmed through molecular testing, although direct study of carnitine transport in fibroblasts is very useful to confirm or exclude primary carnitine deficiency in individuals with genetic variations of unknown clinical significance or who continue to have low levels of carnitine despite negative molecular analyses. Genetic defects in carnitine biosynthesis do not generally result in low plasma levels of carnitine. However, deletion of the trimethyllysine hydroxylase gene, a key gene in carnitine biosynthesis, has been associated with non-dysmorphic autism. Thus, new roles for carnitine are emerging that are unrelated to classic inborn errors of metabolism.
Twelve weeks of daily L-carnitine and carbohydrate feeding in humans increases skeletal muscle total carnitine content, and prevents body mass accrual associated with carbohydrate feeding alone. Here we determined the influence of L-carnitine and carbohydrate feeding on energy metabolism, body fat mass andmuscle expression of fuel metabolism genes. Twelve males exercised at 50% maximal oxygen consumption for 30 min once before and once after 12 weeks of twice daily feeding of 80 g carbohydrate (Control, n=6) or 1.36 g L-carnitine+80 g carbohydrate (Carnitine, n=6). Maximal carnitine palmitolytransferase 1 (CPT1) activity remained similar in both groups over 12 weeks. However, whereas muscle total carnitine, long-chain acyl-CoA and whole-body energy expenditure did not change over 12 weeks in Control, they increased in Carnitine by 20%, 200% and 6%, respectively (P<0.05). Moreover, body mass and whole-body fat mass (dual-energy X-ray absorptiometry) increased over 12 weeks in Control by 1.9 and 1.8 kg, respectively (P<0.05), but did not change in Carnitine. Seventy-three of 187 genes relating to fuel metabolism were upregulated in Carnitine vs. Control after 12 weeks, with ‘insulin signalling’, ‘peroxisome proliferator-activated receptor signalling’ and ‘fatty acid metabolism’ as the three most enriched pathways in gene functional analysis. In conclusion, increasing muscle total carnitine in healthy humans can modulate muscle metabolism, energy expenditure and body composition over a prolonged period, which is entirely consistent with a carnitine-mediated increase in muscle long-chain acyl-group translocation via CPT1. Implications to health warrant further investigation, particularly in obese individuals who have a reduced reliance on muscle fat oxidation during low-intensity exercise.
L-Carnitine is a conditionally essential nutrient and plays an important role in mitochondrial β-oxidation. As a dietary supplement for athletes, L-carnitine has been investigated for its potential to enhance β-oxidation during exercise ultimately to improve performance. While some studies have shown a positive impact on VO(2 max) and other performance measures, other studies have found contradictory results. As such, investigations to a different mechanism by which L-carnitine supplementation could impact exercise and recovery were explored. Based on findings from cardiovascular research that L-carnitine enhances vascular endothelial function, an alternate hypothesis was developed. The hypothesis is centered on improving blood flow to muscle tissues and decreasing hypoxic stress and its resulting sequelae. Studies have shown a decrease in markers of purine catabolism and free radical generation and muscle soreness as a result of L-carnitine supplementation. Direct assessment of muscle tissue damage via magnetic resonance imaging also indicates the ability of L-carnitine to attenuate tissue damage related to hypoxic stress. L-Carnitine is regarded as a safe supplement for athletes and has been shown to positively impact the recovery process after exercise.
L-Carnitine, a naturally occurring compound, is indicated in the treatment of primary systemic carnitine deficiency. To assess the differences in pharmacokinetic parameters calculated from data corrected for baseline versus those from “uncorrected” data, compartmental fitting was carried out for baseline corrected and original plasma concentration data obtained following a single intravenous (iv) dose of 20 mg/kg. For free L-carnitine, mean volumes of distribution at steady state (Vdss) of the central compartment were similar using either approach (9.86 versus 11.2 L). However, Vdss (54.0 versus 29.0 L) and apparent elimination half-life (17.4 versus 5.0 h) were significantly different between the two data bases. Similar observations were noted for pharmacokinetic parameters based on plasma concentrations of total L-carnitine. Although the pharmacokinetic parameters obtained after baseline correction may represent the kinetics of a bolus dose, the pharmacokinetic parameters from uncorrected plasma data probably represent the clinical settings for patients. Baseline correction also probably has its greatest value in attempting to determine and/or define the biological half-life and Vdss for the “exogenously” administered dose and uncorrected data best describes the pharmacokinetics of composite endogenous and exogenous L-carnitine levels.