RESEARCH ARTICLE
The effects of beetroot juice supplementation
on exercise economy, rating of perceived
exertion and running mechanics in elite
distance runners: A double-blinded,
randomized study
Carlos Balsalobre-Ferna´ndez1,2☯*, Blanca Romero-Moraleda2,3☯, Rocı´o Cupeiro2‡, Ana
Bele´n Peinado2‡, Javier Butragueño2‡, Pedro J. Benito2‡
1 Department of Physical Education, Sport and Human Movement, Universidad Auto´noma de Madrid,
Madrid, Spain, 2 Laboratory of Exercise Physiology Research Group, Department of Health and Human
Performance, School of Physical Activity and Sport Sciences-INEF, Universidad Politecnica de Madrid,
Madrid, Spain, 3 Faculty of Health, Camilo Jose´ Cela University, Madrid, Spain
☯ These authors contributed equally to this work.
‡ These authors also contributed equally to this work.
* carlos.balsalobre@icloud.com
Abstract
Purpose
Nitrate-rich beetroot juice supplementation has been extensively used to increase exercise
economy in different populations. However, its use in elite distance runners, and its potential
effects on biomechanical aspects of running have not been properly investigated. This study
aims to analyze the potential effects of 15 days of beetroot juice supplementation on physio-
logical, psychological and biomechanical variables in elite runners.
Methods
Twelve elite middle and long-distance runners (age = 26.3 ± 5.1yrs, VO2Max = 71.8±5.2
ml*kg-1*min-1) completed an incremental running test to exhaustion on a treadmill before
and after a 15-days supplementation period, in which half of the group (EG) consumed a
daily nitrate-rich beetroot juice and the other group (PG) consumed a placebo drink. Time to
exhaustion (TEx), running economy, vastus lateralis oxygen saturation (SmO2), leg stiffness
and rate of perceived exertion (RPE) were measured at 15, 17.1 and 20 km/h during the
incremental test.
Results
Likely to very likely improvements in EG were observed for the RPE (Standardized mean
difference (SMD) = -2.17, 90%CI = -3.23, -1.1), SmO2 (SMD = 0.72, 90%CI = 0.03, 1.41)
and TEx (SMD = 1.18, 90%CI = -0.14, 2.5) in comparison with PG. No other physiological
or biomechanical variable showed substantial improvements after the supplementation
period.
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OPEN ACCESS
Citation: Balsalobre-Ferna´ndez C, Romero-
Moraleda B, Cupeiro R, Peinado AB, Butragueño J,
Benito PJ (2018) The effects of beetroot juice
supplementation on exercise economy, rating of
perceived exertion and running mechanics in elite
distance runners: A double-blinded, randomized
study. PLoS ONE 13(7): e0200517. https://doi.org/
10.1371/journal.pone.0200517
Editor: Gordon Fisher, University of Alabama at
Birmingham, UNITED STATES
Received: March 15, 2018
Accepted: June 26, 2018
Published: July 11, 2018
Copyright: © 2018 Balsalobre-Ferna´ndez et al. This
is an open access article distributed under the
terms of the Creative Commons Attribution
License, which permits unrestricted use,
distribution, and reproduction in any medium,
provided the original author and source are
credited.
Data Availability Statement: Data are available
from figshare (https://doi.org/10.6084/m9.figshare.
5873190.v1).
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
Conclusions
Fifteen days of nitrate-rich beetroot juice supplementation produced substantial improve-
ments in the time to exhaustion in elite runners; however, it didn’t produce meaningful
improvements in running economy, VO2Max or mechanical parameters.
Introduction
Performance at the highest level of competition in endurance events depends on several physi-
ological, psychological and biomechanical parameters [1–5]. Even marginal gains in some var-
iables might represent a competitive edge to win the race or break records; for instance,
wearing energy-recovering shoes have shown to increase running economy by about 4%,
which might have helped in the recent first sub-2h attempt on the marathon [6]. Maximal oxy-
gen consumption is one of the most relevant physiological variables in distance running per-
formance [7,8]; however, in elite athletes other variables seem to influence competitive success
to a greater extent [4,9]. Among them, running economy (i.e., the oxygen consumption at a
certain pace) has been proposed as one of the most important variables in distance running
performance. Theoretically, better running economy means either being able to run at the
same pace with a lower exertion or, for the same energy consumption, being able to run faster
[9,10]. Therefore, researchers and trainers are focused now on finding strategies to increase
economy in different kinds of endurance athletes such as runners, cyclists or swimmers. In
this sense, different studies have shown that heavy-loaded resistance training produces a
meaningful increase in running economy of athletes at different levels, including elite partici-
pants [11,12]. Besides training interventions, different nutritional strategies have also been
used to increase distance running performance, from high-carbohydrate to ketogenic diets
[13–15]. However, during the last decade one particular supplement has been investigated as a
potential beneficial aid for endurance events: beetroot juice [16,17]. Beetroot juice is a high
source of nitrate (NO3
-) that has been proposed to increase NO (nitric oxide) availability, a
potent signaling molecule that can increase vasodilatation, mitochondrial respiration or glu-
cose uptake, among other factors related to exercise performance [17]. Several studies have
shown that beetroot juice supplementation for about a week does have an ergogenic effect in
moderate trained runners, mainly via an increase in running economy [16,18,19]. However,
there is a lack of studies analyzing its potential benefits in elite subjects, who might need a
higher dose or exposure than recreational athletes to obtain the desired increases in perfor-
mance. A recent study [20] observed that 8 days of beetroot supplementation didn’t increase
performance variables in elite 1500m runners; however, whether larger interventions might
have benefits in elite populations is unknown. Moreover, to the best of our knowledge, no
studies have analyzed the potential effects of beetroot supplementation in mechanical aspects
of running such as leg stiffness, a variable that has been linked to running economy in different
studies [21–23]. For this, the purpose of this study is to analyze the physiological, psychological
and biomechanical effects of beetroot juice supplementation in elite distance runners.
Materials & methods
Participants
Twelve elite middle and long-distance runners, including European medalists and Olympians
were recruited from the High Performance Center of Madrid, Spain to join this investigation.
Inclusion criteria were as follows: male competitors in national and international events, with
Beetroot juice supplementation and exercise economy, rating of perceived exertion and running mechanics
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personal bests in the urban 10k below 32 min, and below 3min50s. in the 1500m. See details in
Table 1. Prior to commencement, all participants provided written informed consent. Participants
were instructed to not consume beetroot of any form 2 months before the start of the intervention
and to maintain their normal diet throughout the testing period, to follow the same diet for 24
hours prior to each trial, to avoid food and drink in the hour before each trial, and to refrain from
strenuous exercise for 24 hours before each trial. None of the participants followed a plant-based
(vegetarian or vegan) diet, and they never consumed nitrate-rich beetroot juice in the past. The
study protocol complied with the Declaration of Helsinki for Human Experimentation and was
approved by the Institutional Review Board of the Universidad Camilo Jose´ Cela.
Procedures
Beetroot juice supplementation protocol. Participants were randomly assigned to either
a placebo (PG) or an experimental (EG) group in a double-blinded manner so neither the ath-
letes nor the main researchers could possibly identify who were consuming a nitrate-rich beet-
root juice supplementation. See Fig 1.
Participants in EG consumed a high-nitrate beetroot juice (6.5-mmol NO3-/70-mL, Beet It
Sport; James White Drinks, Ipswich, United Kingdom) for 15 consecutive days with their
breakfast meal, while participants in PG consumed a nitrate-free placebo from the same manu-
facturer (0.065-mmol NO3-/70-mL Beet It Sport; James White Drinks, Ipswich, United King-
dom) for the same amount of time. Placebo drinks had the exact same packaging, color, smell
and taste as its nitrate-rich counterpart, so neither the athletes or the researchers could know
who were consuming what. Participants were instructed to not use mouth rinse during the
supplementation period.
Physiological parameters
Incremental running test. The maximal graded test was performed with a computerized
treadmill (H/P/COSMOS 3PW 4.0, H/P/Cosmos Sports & Medical, Nussdorf-Traunstein,
Germany) to determine each subject’s maximal VO2, and to measure running economy at dif-
ferent speeds. Expired gases were measured breath-by-breath with the Jaeger Oxycon Pro gas
analyser (Erich Jaeger, Viasys Healthcare, Germany). Heart response was continuously moni-
tored with a 12-lead ECG. Participants started with 3 minutes warm-up at 10 km/h. Then the
protocol continued with 3 steady state steps of 3 min each, at 15, 17.1 and 20 km/h. Subse-
quently the speed was increased to 0.2 km/h every 12 seconds until exhaustion. A slope of 1%
was set throughout the test [24]. All the tests fulfilled at least 2 of the following criteria [2]: A
respiratory exchange ratio (RER) >1.10, a plateau in VO2 (corresponding to a variation of,
100 mlmin-1) despite an increase in exercise intensity and a peak HR>220-age. This test was
conducted at baseline and repeated 24-h after the 15th day of supplementation, so there were
at least 24h after the last beetroot juice ingestion.
O2 saturation measurement.
Throughout all the graded tests O2 saturation (SmO2, in %)
was registered using near-infrared spectroscopy by placing a wearable device on the belly of
the vastus laterallis (Moxy Monitor, Minnesota, USA). In this study, a wearable device was
used to measure the muscle oxygenation in the vastus lateralis of dominant leg (along the
Table 1. Characteristics of the participants. Personal bests are expressed as range.
Age (yrs.)
Height (cm)
Weight (kg)
VO2Max (mlkg-1min-1)
PB in urban 10 km (min:s)
PB in outdoor 1500m (min:s)
Experimental group
27.3±7.8
1.79±0.07
69.2±8.6
69.1±5.3
29:22–31:00
3:32–3:45
Control group
24.2±2.9
1.78±0.04
65.2±2.6
72.3±6.8
28:28–30:54
3:43–3:45
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vertical axis of the thigh, approximately 10–12 cm above the knee joint [25]. The device was
wrapped by an elastic tight without occluding the blood flow. Black bandages covered the
device to eliminate background light [26].
Biomechanical parameters
To measure leg stiffness the validated Runmatic app v2.8 installed on an iPhone 6 with iOS
10.3.3 was used following the procedures described elsewhere [27]. The Runmatic app was
used to record leg stiffness during the first minute of each steady state on the incremental test
(i.e., at 15, 17.1 and 20 km/h), and mean scores were registered.
Psychological parameters
At the completion of each steady state step of the incremental running test (i.e., during the last
10 seconds of the 3-min run at 15, 17.1 and 20 km/h) participants were asked to rate their RPE
Fig 1. CONSORT flowchart.
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in a 1–10 scale. Before starting the incremental test, participants were given instruction to
point to a number on a sheet held by a researcher corresponding to their RPE at each step dur-
ing the trial. Participants were told that 1 means no exertion at all, and 10 means maximal
exertion.
Statistical analyses
Data is presented as mean with standard deviations. The non-parametric Mann-Whitney’s U
statistical test was used to compare the pre-post differences between the experimental and pla-
cebo groups. Also, the standardized mean differences (SMD) with the corresponding 90% con-
fidence interval (CI) were calculated using a magnitude-based inference approach [28]. The
criteria for interpreting the magnitude of the SMD were: trivial (<0.2), small (0.2–0.6), moder-
ate (0.6–1.0) and large (>1.0). Probabilities were also determined to establish whether true dif-
ferences were lower, similar or higher than the smallest worthwhile change (0.2 x between–
participant SD). Quantitative chances of better or worse effects were assessed qualitatively as
follows: <1%, almost certainly not; 1–5%, very unlikely; 5–25%, unlikely; 25–75%, possible;
75–95%, likely; 95–99%, very likely; and >99%, almost certain. If the changes of better or
worse were both >5%, the true difference was assessed as unclear. Statistical analyses were per-
formed using a custom spreadsheet [28] and SPSS 24 for Mac. The level of asymptotic signifi-
cance was set as p< 0.05.
Results
Participants in EG showed unclear improvements in heart rate (SMD = 0.03, 90%CI = -0.36,
0.42) and running economy expressed in VO2 (SMD = 0.36, 90%CI = -0.5, 1.21) in compari-
son with PG. Also, changes in the VO2Max did not substantially differ in EG in comparison
with PG after the supplementation period (SMD = 0.04, 90%CI = -0.87, 0.95). However, likely
to very likely improvements in EG vs. PG were observed for the RPE (SMD = -2.17, 90%CI =
-3.23, -1.1), SmO2 (SMD = 0.72, 90%CI = 0.03, 1.41) (in the three steady stages) and time to
exhaustion (SMD = 1.18, 90%CI = -0.14, 2.5). Finally, no substantial improvements in leg stiff-
ness (SMD = -0.14, 90%CI = -0.44, 0.17) were observed during any of the steady stages of the
incremental test as revealed by the low to trivial SMD and the range of the 90%CI. See Fig 2,
Table 2 and Table 3 for more details.
Discussion
The results of our study showed low to trivial improvements in different physiological mea-
sures such as running economy at different paces after 15-days of nitrate-rich beetroot juice
supplementation in elite distance runners. These results are in line with other experiments
conducted with elite distance athletes, in which submaximal exercise economy was not altered
after the supplementation period either [20,29]. The supplementation period in our study was
about twice larger than other experiments with elite runners; however, more days of ingestion
of nitrate-rich beetroot juice supplementation doesn’t seem to boost the adaptations in sub-
maximal exercise economy that this supplement has extensively showed to produce in less
trained populations [17,18].
A novel contribution from our study was the analysis of the potential benefits of beetroot
juice ingestion on different biomechanical variables that has been linked to running perfor-
mance in the literature, such as leg stiffness [23,30]. For example, leg stiffness has showed to be
negatively associated with running economy, since, in theory, a stiffer lower limb would store
a higher amount of elastic energy that would assist in the force production during running
and, therefore, it would reduce the cost of the exercise [9,23]. Results in our study showed
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trivial effects of beetroot juice supplementation in leg stiffness, similar to submaximal running
economy.
Contrary to the results discussed above, likely to very likely large improvements were
observed both in the rate of perceived exertion and the time to exhaustion in the experimental
group in comparison with the placebo group after the supplementation period, where athletes
who consumed nitrate-rich beetroot juice endured more time before voluntary stopping the
incremental test on the treadmill. One potential explanation for this observation is the moder-
ate increase in the SmO2 of the vastus lateralis of the athletes from the experimental group in
comparison with the control group after the supplementation period. Participants who con-
sumed nitrate-rich beetroot supplementation had larger percent of oxygen saturation in their
muscles than their counterparts during exercise. That could have limited the accumulation of
fatigue-related metabolites and reduce the depletion of PCr, which, in the end, could increase
the time to exhaustion. NIRS is used for providing information about performance and oxygen
muscle function and to evaluate response before, during and after exercise. In our study, the
initial-during-end-exercise SmO2 was greater in experimental group. That finding is related
Fig 2. Forest plot with standardized mean differences (SMD) and 90% confidence interval (CI) for the rate of perceived exertion
(RPE) and oxygen saturation (SmO2) at different running paces. Lower scores (i.e., to the left in the X-axis) means lower scores in the
experimental group.
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with recovery capacity and improvements in performance status delaying the fatigue [31].
Then, greater availability of O2 could have impacted RPE and, finally it could have led to the
observed increase in the time to exhaustion in the experimental group. For example, several
studies have observed that increased oxygen availability via hyperoxia enhances exercise per-
formance [32]. Nevertheless, further investigations are needed to better understand the mecha-
nisms by which beetroot juice supplementation could reduce RPE and increase time to
exhaustion in an incremental test on a treadmill in elite distance runners.
Summarizing, results in our study are in line with other investigations that observed no sig-
nificant increases in running economy after a supplementation period with nitrate-rich beet-
root juice in elite athletes [20,29]; however, the large increase in the time to exhaustion, the
reduction in RPE and the increase in the oxygen saturation of the vastus lateralis during exer-
cise, observed after 15 consecutive days of nitrate-rich beetroot supplementation provide
novel information about the effects of this nutritional aid. Further investigations are required
Table 2. Mean values and standard deviations for the experimental and placebo groups before (Pre) and after (Post) the supplementation period.
Experimental group
Placebo group
Pre
Post
Pre
Post
Biomechanical parameters
Leg stiffness (kN/m)
15 km/h
7.9 ± 0.9
8.6 ± 1.4
8.4 ± 1.2
8.5 ± 1.4
17.1 km/h
8.5 ± 1.2
8.7 ± 1.2
7.9 ± 1.1
8.3 ± 1.3
20 km/h
8.9 ± 0.8
9.2 ± 1.3
7.5 ± 1.0
8.1 ± 0.8
Physiological parameters
RE (mlkgmin-1)
15 km/h
50.8 ± 3.5
52.6 ± 2.8
52.3 ± 3.3
53.7 ± 3.8
17.1 km/h
58.3 ± 2.7
60.4 ± 2.3
60.1 ± 3.8
62.1 ± 3.3
20 km/h
67.3 ± 4.4
69.5 ± 2.9
70.5 ± 5.1
71.4 ± 4.8
RER
15 km/h
0.87 ± 0.02
0.83 ± 0.02
0.91 ± 0.02
0.87 ± 0.01
17.1 km/h
0.93 ± 0.02
0.90 ± 0.03
0.96 ± 0.02
0.94 ± 0.02
20 km/h
1.03 ± 0.01
0.97 ± 0.04
1.07 ± 0.03
1.03 ± 0.03
HR (bpm)
15 km/h
147.2 ± 13.7
146.9 ± 11.2
157.3 ± 10.0
151.4 ± 12.4
17.1 km/h
160.6 ± 12.2
157.3 ± 9.2
168.1 ± 8.1
165.9 ± 7.1
20 km/h
164.2 ± 19.1
168.4 ± 11.4
164.6 ± 21.1
177.1 ± 4.6
SmO2 (%)
15 km/h
41.7 ± 7.1
47.7 ± 3.9
46.6 ± 15.5
43.7 ± 5.9
17.1 km/h
34.4 ± 3.5
41.0 ± 2.0
38.2 ± 16.4
37.8 ± 5.2
20 km/h
24.4 ± 2.8
31.0 ± 6.9
26.8 ± 12.1
27.7 ± 4.8
TEx (s)
1173.0 ± 87.1
1269.0 ± 53.6
1251.0 ± 52.6
1230 ± 73.5
VO2Max (mlkgmin-1)
69.1 ± 5.3
70.1 ± 7.0
72.3 ± 6.8
74.9 ± 6.1
Psychological parameters
RPE
15 km/h
2.4 ± 0.5
2.3 ± 0.5
2.4 ± 0.5
3.5 ± 0.8
17.1 km/h
3.8 ± 0.8
4.0 ± 0.8
4.4 ± 0.5
5.6 ± 0.8
20 km/h
6.0 ± 0.7
6.0 ± 1.0
7.2 ± 0.4
7.7 ± 1.0
Abbreviations: RE = running economy; VO2Max = maximal oxygen consumption; RER = respiratory exchange ratio; TEx = time to exhaustion; HR = heart rate;
SmO2 = saturation of muscle O2; RPE = rate of perceived exertion
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to confirm the findings of the present study, as well as to better understand the mechanisms
behind these potential benefits for elite distance runners.
Practical application and conclusions
Fifteen consecutive days of nitrate-rich beetroot juice supplementation didn’t increase running
economy, locomotion mechanics or muscular power in elite distance runners. However, time to
exhaustion in an incremental test on a treadmill, as well as rate of perceived exertion at different
running paces were meaningfully higher and lower in the experimental group in comparison with
the placebo group, respectively. These results might be explained in part by a higher muscle oxy-
gen saturation observed in the vastus lateralis of the runners from the experimental group in com-
parison with the control group. Anyhow, one of the most performance-related variables in
distance running (i.e., time to exhaustion) showed large improvements after 15-days of nitrate-
rich beetroot juice supplementation. These results could have potential practical application for
elite distance runners seeking nutritional strategies to improve their running performance.
Supporting information
S1 File. CONSORT 2010 checklist of information to include in a randomized controlled
trial.
(DOC)
S2 File. Study protocol as approved by the ethics committee.
(PDF)
Author Contributions
Conceptualization: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda.
Data curation: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda.
Formal analysis: Carlos Balsalobre-Ferna´ndez.
Table 3. Pre-post differences on the studied variables in the placebo vs experimental conditions.
SMD (90%CI)
Chances of being beneficial/trivial/harmful
Qualitative inference
% of change (experimental vs placebo)
P
Biomechanical parameters
Leg stiffness
-0.14 (-0.44, 0.17)
4/61/36
Possibly
2.25 vs 4.64
0.310
Physiological parameters
RE
0.36 (-0.5, 1.21)
63/24/13
Unclear
7.07 vs 4.5
0.589
VO2Max
0.04 (-0.87, 0.95)
37/31/32
Unclear
4.41 vs. 3.66
1.000
Av_RER
-0.2 (-1.15, 0.74)
50/27/22
Unclear
-4.7 vs. -3.6
1.000
TEx (s)
1.18 (-0.14, 2.5)
90/6/4
Likely
8.18 vs 1.6
0.310
Av_HR
0.03 (-0.36, 0.42)
22/64/15
Unclear
-0.26 vs. 1.14
0.792
SmO2
0.72 (0.03, 1.41)
91/7/2
Likely
17.8 vs. -2.64
0.167
Psychological parameters
RPE
-2.17 (-3.23, -1.1)
100/0/0
Very likely
-9.0 vs 20.4
0.016
Standardized mean differences (SMD) with 90% Confidence Intervals (CI) express the magnitude of the difference on the pre-post changes between the experimental
and placebo groups. Positive values reflect higher increments on the placebo group after the supplementation period, while negative scores reflect lower increments on
the experimental group after the supplementation period. P is the asymptotic significance of the Mann-Whiteny’s U test.
Abbreviations: RE = running economy; VO2Max = maximal oxygen consumption; Av_RER = average respiratory exchange ratio (whole test); TEx = time to exhaustion;
Av_HR = average heart rate (whole test); SmO2 = saturation of muscle O2; RPE = rate of perceived exertion
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Investigation: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda, Rocı´o Cupeiro, Ana
Bele´n Peinado, Javier Butragueño, Pedro J. Benito.
Methodology: Carlos Balsalobre-Ferna´ndez, Rocı´o Cupeiro, Ana Bele´n Peinado, Javier
Butragueño.
Supervision: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda, Rocı´o Cupeiro, Ana
Bele´n Peinado, Javier Butragueño, Pedro J. Benito.
Writing – original draft: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda.
Writing – review & editing: Carlos Balsalobre-Ferna´ndez, Blanca Romero-Moraleda, Rocı´o
Cupeiro, Ana Bele´n Peinado, Javier Butragueño, Pedro J. Benito.
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The effects of beetroot juice supplementation on exercise economy, rating of perceived exertion and running mechanics in elite distance runners: A double-blinded, randomized study.
Balsalobre-Fernández, Carlos,Romero-Moraleda, Blanca,Cupeiro, Rocío,Peinado, Ana Belén,Butragueño, Javier,Benito, Pedro J