STUDY PROTOCOL
Effects of nutritional and hydration strategies
during ultramarathon events between
finishers and non-finishers: A systematic
review protocol
James W. NavaltaID1*, Victor D. Y. BeckID2, Taylor M. Diaz1, Vernice E. Ollano1
1 Department of Kinesiology and Nutrition Sciences, University of Nevada, Las Vegas, Las Vegas, NV,
United States of America, 2 Department of Physical Therapy, University of Nevada, Las Vegas, Las Vegas,
NV, United States of America
* james.navalta@unlv.edu
Abstract
Ultramarathon running is a sport that is growing in popularity. Competing in an ultramara-
thon event is physiologically taxing on the human body, and it should not be surprising that
not all individuals who enroll for an event ultimately finish. While many factors can contribute
to this phenomenon, it is likely that nutritional and hydration strategies play a large role
between finishing and not finishing an ultramarathon. No published paper has systematically
reviewed the effects of nutritional and hydration strategies during ultramarathon events
between finishers and non-finishers. This paper details our intended protocol with the follow-
ing steps that create the flow of the systematic review: 1) Determine the review question
and Participant, Intervention, Comparator, Outcome, Study Design (PICOS) criteria; 2) Cre-
ate inclusion and exclusion criteria; 3) Create and follow a search strategy; 4) Document
sources that are included and excluded according to the pre-determined eligibility criteria; 5)
Assess final sources for risk of bias; 6) Extract pertinent data from final full-text articles and
synthesize the information; and 7) Disseminate findings of the systematic review.
Introduction
Ultramarathon running is a sport that is growing in popularity. The oldest ultramarathon
event, the Comrades Marathon, began in 1921 covering 89.9 km (55.9 mi), and 17 of the 34
participants did not finish (50% DNF) [1]. Since that time, over 300,000 people have com-
pleted the race, which currently caps yearly enrollment at 20,000 participants [2]. Participation
in ultramarathon events has risen exponentially since the year 2000, with over a million run-
ners participating (1,042,156) [3]. The sport involves running or walking a distance greater
than a traditional marathon (42.2 km, or 26.2 mi). The most popular (over three-quarters of a
million entrants) ultramarathon distance is 50 km (31.1 mi) as it represents a distance just
above the traditional marathon [3]. Participation decreases as the distance gets longer (just
over 100,000 entrants for 100km [62.1 mi], and approximately 40,000 for 24 h events) [3].
Competing in an ultramarathon event is physiologically taxing on the human body. Ultra-
marathon running has been associated with an increase in cardiac troponin T (a measure of
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OPEN ACCESS
Citation: Navalta JW, Beck VDY, Diaz TM, Ollano
VE (2022) Effects of nutritional and hydration
strategies during ultramarathon events between
finishers and non-finishers: A systematic review
protocol. PLoS ONE 17(8): e0272668. https://doi.
org/10.1371/journal.pone.0272668
Editor: Samuel Penna Wanner, Universidade
Federal de Minas Gerais, BRAZIL
Received: April 8, 2022
Accepted: July 24, 2022
Published: August 19, 2022
Copyright: © 2022 Navalta 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: No datasets were
generated or analysed during the current study. All
relevant data from this study will be made available
upon study completion.
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
myocardial damage) [4], malondialdehyde and creatine kinase (lipid peroxidation) [5], and
oxidative stress [6]. Other reported effects include measures associated with cardiac fatigue
such as increased atrial volume [7]. Given these effects it should not be surprising that not all
individuals who enroll for an ultramarathon event ultimately finish. It is estimated that
between 20–50% of individuals who begin an ultramarathon do not finish [8]. While many fac-
tors such as gastrointestinal distress and discomfort can contribute to this phenomenon, it is
likely that nutritional and hydration strategies play a large role.
Several systematic reviews have been conducted on various ultramarathon running topics
including psychology [9], limiting factors [10], long-term health problems [11], and patho-
physiology [12]. There has been a 50-year State of the Science offering [13], as well as a Posi-
tion Statement on Nutrition specific to training for a single-stage ultramarathon [14]. To our
knowledge, no published paper has reviewed the effects of nutritional and hydration strategies
during ultramarathon events between finishers and non-finishers. A “systematic review” was
selected as the methodology after reading published guidance on review types [15, 16]. The
primary aim of the proposed systematic review will be to find and describe the nutritional and
hydration strategies between single-stage ultramarathon finishers and non-finishers, and out-
comes reported in published literature. Based on the Preferred Reporting Items for Systematic
Reviews and Meta-Analyses (PRISMA) guidelines, the best practices for performing a system-
atic review include publishing the protocol independent of the review to ensure procedural
transparency [17]. As our systematic review of ultramarathon nutritional strategies will be, to
our knowledge, the first published on the topic, it is especially important to publish our proto-
col. This methods paper was written to achieve two objectives: 1) To adhere to the best prac-
tices stated in the PRISMA guidelines; and 2) To ensure procedural transparency.
Materials and methods
Developing the systematic review protocol began with members of the team performing scoping
searches in Google Scholar and PubMed. The scoping searches suggested that there were no
published systematic reviews of nutritional strategies between finishers and non-finishers of
ultramarathon events. The first author consulted peer-reviewed guidance [15, 16] about con-
ducting systematic reviews in health fields and has participated in the process previously [18].
The team deliberated and agreed upon the protocol presented in this article. The details of the
protocol are available via PROSPERO, an online international prospective register of systematic
reviews. The protocol was submitted on February 9, 2022 and registered on March 3, 2022
(PROSPERO ID: 42022308733). The protocol has the following steps that create the flow of the
systematic review: 1) Determine the review question and Participant, Intervention, Comparator,
Outcome, Study Design (PICOS) criteria; 2) Create inclusion and exclusion criteria; 3) Create
and follow a search strategy; 4) Document sources that are included and excluded according to
the pre-determined eligibility criteria; 5) Assess final sources for risk of bias; 6) Extract pertinent
data from final full-text articles and synthesize the information; and 7) Disseminate findings of
the systematic review. An optional part of systematic reviews that will be omitted is a meta-anal-
ysis. A meta-analysis will not be performed in this systematic review because the studies are
expected to include different ultramarathon distances, sample different populations, and mea-
sure different outcomes. Because of differences among these characteristics, the studies will not
be homogenous, which is necessary for a meta-analysis [19].
Step 1: Determine the review question and PICOS criteria
The first step is to determine the review question and PICOS criteria (Table 1). Because multi-
stage ultramarathon events stress the body from a nutritional and hydrational standpoint in a
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much different manner compared to single-stage events, we decided to focus on single-stage
events not lasting longer than 24 h. The event can be performed in any location (including
indoors on a treadmill). Studies with adults who enrolled in a single-stage ultramarathon
between the ages of 18–60 will be relevant. Controlled, uncontrolled, randomized, nonrando-
mized, and observational studies will be considered. Information about participants’ charac-
teristics, ultrarunning experience, and finisher or non-finisher status will be collected.
Step 2: Create inclusion and exclusion criteria
The second step is to create inclusion and exclusion criteria, or eligibility criteria. The review
question and PICOS criteria form the basis of this systematic review’s eligibility criteria, which
aim to be both explicit and succinct. These characteristics provide clarity to the review team
members, enabling the exclusion of irrelevant sources during the screening process. Expedi-
tious screening is important to the process because teams may be required to screen hundreds
to thousands of sources. In consultation of the review question and PICOS criteria, the eligibil-
ity criteria were created (Table 2). The inclusion criteria will allow for the inclusion of unpub-
lished master’s theses and doctoral dissertations. This decision was made to capture as much
data about nutritional and hydrational strategies during a single-stage ultramarathon event as
possible.
Step 3: Create and follow a search strategy
After determining eligibility criteria, the review team will proceed to the third step by creating
and following a search strategy (Table 3). Consistent with our PICOS and eligibility criteria,
we will search in four databases for all relevant studies, regardless of publication year. The
same search combination string will be used in each database (Table 3). The search combina-
tion was initially created by the full review team. An iterative process of revision ensued until
the search combination returned a manageable number of hits in each database (about 100–
1,000 hits).
Table 1. Review question and PICOS table.
Review
Question
Do finishers of single-stage ultramarathon events employ different nutritional and hydration
strategies than individuals who do not finish?
Population
Ultramarathoners of any sex who enrolled in a single-stage ultramarathon event, between the
ages of 18–60 years old
Intervention
Single-stage ultramarathon event not longer than 24 h
• The ultramarathon must be performed continuously within 24 h and excludes multi-stage
events
Comparator
Completion of the single-stage ultramarathon event
Non completion of the single-stage ultramarathon event (considered as ‘did not finish’ or ‘DNF’)
Outcomes
Nutrition and hydration strategies employed during the event
• Macromolecules (carbohydrates, fats, proteins)
• Hydration (fluid type and pacing)
• Other supplements (vitamins and minerals)
Ultramarathon event characteristics: distance of race, start time, elevation profile, environmental
profile (temperature, humidity, windspeed)
Participants’ age, sex, body mass, height, years of ultrarunning experience, finisher or non-
finisher
Setting
Any physical environment (indoors, outdoors, urban, rural, built-up, or natural)
Study Design
Studies with interventions, as well as observational studies
• Controlled or uncontrolled
• Randomized or nonrandomized
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With the operational search combination established, each member volunteered for roles.
Two members formed Team A, and two members formed Team B. The two members of Team
A will search in Google Scholar and SPORTDiscus. The two members of Team B will search in
PubMed and Web of Science. This assignment of databases will divide the workload of the
search somewhat equally between the teams. The search, screening process, and inclusion pro-
cess represents the “search flow.” The search flow will channel an initially broad collection of
sources into increasingly smaller collections (Fig 1). The search flow is described in Step 4.
Table 2. Eligibility criteria.
Participants
Adults between the age of 18–60 years old, and any sex, gender, or nationality who has enrolled
in a single-stage ultramarathon not lasting longer than 24 h
Inclusion
Criteria
1. The source is a published article in a peer-reviewed journal or is an unpublished or findable
master’s thesis or doctoral dissertation
2. The source is written in English
3. The source reports the findings of an interventional or observational study
a. The intervention is any nutritional or hydrational supplement
b. At least one reported outcome is finishing or not finishing an ultramarathon event
The observation is nutritional, or hydration strategy utilized while performing an
ultramarathon event
Exclusion
Criteria
1. The source is not a published, peer-reviewed journal article or a findable and available
master’s thesis or doctoral dissertation
2. The source is written in any language other than English
3. The source reports the findings of an interventional study with an intervention or outcomes
irrelevant to this systematic review
a. The intervention is an ultramarathon without nutritional or hydration component
b. None of the reported outcomes are finishing or not finishing the ultramarathon event
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Table 3. Search strategy.
Investigators
Team A: TD and JN
Team B: VB and VO
Techniques
Search research databases for sources, including them in four stages:
1. Include sources by title
2. Include sources by abstract
3. Include sources by full text
4. Include sources from the reference lists of sources included by full text (journal articles, master’s
theses, and doctoral dissertations)
Databases
Google Scholar, PubMed, and SPORTDiscus, Web of Science
Included Types of Literature
Published, peer-reviewed journal articles; unpublished and published master’s theses and doctoral
dissertations
Publication Date Range
No limit
Intervention Search Terms
Outcome Search Terms
“Ultramarathon”
“24h ultramarathon”
“Ultra endurance”
“24h race”
“Finish”
“Completion”
“Complete”
“DNF”
“Dropout”
“Nutrition”
“Carbohydrate”
“Fats”
“Protein”
“Vitamins”
“Minerals”
“Hydration”
“Electrolytes”
“Water”
“Fluid”
“Supplements”
“Supplementation”
Search Combination
((ultramarathon) OR (“24h ultramarathon”) OR (“ultra endurance”) OR (“24h race”)) AND ((finish)
OR (completion) OR (complete) OR (DNF) OR (“drop out”)) AND ((nutrition) OR (carbohydrate)
OR (fats) OR (protein) OR (vitamins) OR (minerals) OR (hydration) OR (electrolytes) OR (water)
OR (fluid) OR (supplements) OR (supplementation))
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Step 4: Document sources that are included and excluded
according to the pre-determined eligibility criteria
The fourth step is the application of the systematic review process, the search flow (Fig 2). The
search flow is modeled on the 2020 PRISMA statement [17], containing four steps: 1) Identify
relevant sources by title, 2) Screen sources by abstract, 3) Assess and include sources by full
text, and 4) Include eligible sources from the references of full texts included in the third step.
During the search flow, it will be critical to document sources’ inclusion and exclusion clearly
[16, 19]. Clear documentation allows the systematic review to be transparent and reproducible.
Reproducibility is a hallmark of a systematic review that sets it apart from traditional literature
reviews [19].
Fig 1. The search flow funnels sources into smaller collections until the final articles are included.
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Eligibility criteria will be determined by four individuals (two independent teams of two—
Team A and Team B) who will work on selecting the studies. Individuals on the same team
will be blinded to the other’s decisions with screening completed independently. The alternate
team will resolve any disagreements.
To make the search flow reproducible, a specific tool in Google Sheets will be utilized [20].
The tool is a spreadsheet for Teams A and B to coordinate with each other and has four sepa-
rate sheets (one for each team member). During the first step of the search flow, members of
Team A and B will enter three types of values into the sheet: 1) the number of hits each data-
base returns, 2) the number of sources deemed relevant by title, and 3) the number of duplicate
sources identified across the databases (identical sources found in the other database). The
sheet will automatically sum these values. The sheet represents a precise record of members’
progression through the first step of the search flow. The sheet also helps members record
Steps 2–4.
Step 5: Assess final sources for risk of bias
The fifth step acknowledges that it is important for all systematic reviews to assess the included
sources’ risk of bias [16, 19]. Being transparent about the risk of bias allows readers to draw
conclusions concerning the quality and strength of evidence for interventions affecting the
outcome [16]. This systematic review will assess risk of bias at the study-level using tools spe-
cific to the study design. Randomized, parallel trials will be assessed by using the revised
Cochrane risk of bias tool for randomized trials (RoB 2) [21]. Non-randomized trials will be
assessed by using the risk of bias in non-randomized studies—of interventions (ROBINS-I)
tool [22]. The following characteristics will be assessed: deviations from the intended interven-
tion, missing outcome data, measurement of the outcome, selection of the reported result. Bias
will be evaluated by two independent teams of two individuals. The alternating team will
check the others work and settle any disagreements of individual judgements.
Fig 2. Search flow.
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Step 6: Extract pertinent data from final full-text articles and
synthesize the information
The sixth step is to extract pertinent data from the included full-text articles and write a narra-
tive synthesis. The following data will be extracted from study documents: participant charac-
teristics of age, body mass, height, years of ultrarunning experience, finisher or non-finisher.
Ultramarathon characteristics: distance of race, start time, elevation profile, environmental
profile (temperature, humidity, windspeed, start elevation). Nutritional supplementation dur-
ing the event: macromolecules (carbohydrates, fats, proteins), hydration (fluid type and pac-
ing), and other supplements (vitamins and minerals). We will contact investigators for
information that is not provided in the published document. We will report the average differ-
ences between finishers and non-finishers for macromolecules (carbohydrates, fats, proteins),
hydration (fluid type and pace of ingestion), and other supplements (vitamins and minerals).
Once all data are extracted, a narrative synthesis of the data will be written to report the main
findings and implications of the systematic review.
Step 7: Disseminate the findings of the systematic review
The final step is to disseminate the main findings and implications. The intention is to com-
plete the systematic review by August 2022 and submit the narrative synthesis for publication
in a peer-reviewed academic journal thereafter.
Final remarks
To our knowledge, the proposed systematic review will be the first to describe the effects of
nutrition and hydration between finishers and non-finishers of ultramarathon events as
described by the scientific literature. Because of this, the review will fill an important gap in the
literature. The protocol is presented here as a best practice [17] and to earn readers’ trust in the
review protocol. Additionally, the procedures described here can provide others a framework
to conduct their own systematic reviews if so desired.
Supporting information
S1 Checklist. PRISMA-P (Preferred Reporting Items for Systematic review and Meta-
Analysis Protocols) 2015 checklist: Recommended items to address in a systematic review
protocol.
(DOC)
Author Contributions
Conceptualization: James W. Navalta, Victor D. Y. Beck, Taylor M. Diaz, Vernice E. Ollano.
Writing – original draft: James W. Navalta, Victor D. Y. Beck, Taylor M. Diaz, Vernice E.
Ollano.
Writing – review & editing: James W. Navalta, Victor D. Y. Beck, Taylor M. Diaz, Vernice E.
Ollano.
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Effects of nutritional and hydration strategies during ultramarathon events between finishers and non-finishers: A systematic review protocol.
Navalta, James W,Beck, Victor D Y,Diaz, Taylor M,Ollano, Vernice E