Sleep habits and strategies of ultramarathon

RESEARCH ARTICLE

Sleep habits and strategies of ultramarathon

runners

Tristan Martin 1 , Pierrick J. Arnal

2 , Martin D. Hoffman

3,4,5 , Guillaume Y. Millet

1*

1 Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada,

2 Rhythm, San Francisco, CA, United States of America, 3 Department of Physical Medicine &

Rehabilitation, Department of Veteran Affairs, Northern California Health Care System, Sacramento, CA,

United States of America, 4 University of California Davis Medical Center, Sacramento, CA, United States of

America, 5 Ultra Sports Science Foundation, Sacramento, CA, United States of America

  • gmillet@ucalgary.ca

Abstract

Among factors impacting performance during an ultramarathon, sleep is an underappreci-

ated factor that has received little attention. The aims of this study were to characterize

habitual sleep behaviors in ultramarathon runners and to examine strategies they use to

manage sleep before and during ultramarathons. Responses from 636 participants to a

questionnaire were considered. This population was found to sleep more on weekends and

holidays (7–8 h to 8–9 h) than during weekdays (6–7 h to 7–8 h; p < 0.001). Work was a mediator of napping habits since 19–25% reported napping on work days and 37–56% on

non-work days. There were 24.5% of the participants reporting sleep disorders, with more

women (38.9%) reporting sleep problems than men (22.0%; p < 0.005). Mean (±SD) sleepi- ness score on the Epworth Sleepiness Scale was 8.9 ± 4.3 with 37.6% of respondents scor- ing higher than 10, reflecting excessive daytime sleepiness. Most of the study participants

(73.9%) had a strategy to manage sleep preceding an ultramarathon, with 54.7% trying to

increase their opportunities for sleep. Only 21% of participants reported that they had a

strategy to manage sleep during ultramarathons, with micronaps being the most common

strategy specified. Sub-analyses from 221 responses indicated that sleep duration during

an ultramarathon was correlated with finish time for races lasting 36–60 h (r = 0.48; p < 0.01) or > 60 h (r = 0.44; p < 0.001). We conclude that sleep duration among ultramarathon run- ners was comparable to the general population and other athletic populations, yet they

reported a lower prevalence of sleep disorders. Daytime sleepiness was among the lowest

rates encountered in athletic populations, which may be related to the high percentage of

nappers in our population. Sleep extension, by increasing sleep time at night and daytime

napping, was the main sleep strategy to prepare for ultramarathons.

Introduction

Sleep quality and sleep wake cycle characteristics are underappreciated factors that can affect

sport performance [1–3]. Like other body functions, physiological and psychomotor functions

involved in exercise have a circadian rhythmicity, leading to a diurnal variation in sport

PLOS ONE | https://doi.org/10.1371/journal.pone.0194705 May 9, 2018 1 / 18

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OPEN ACCESS

Citation: Martin T, Arnal PJ, Hoffman MD, Millet

GY (2018) Sleep habits and strategies of

ultramarathon runners. PLoS ONE 13(5):

e0194705. https://doi.org/10.1371/journal.

pone.0194705

Editor: Øyvind Sandbakk, Norwegian University of Science and Technology, NORWAY

Received: August 25, 2017

Accepted: March 8, 2018

Published: May 9, 2018

Copyright: © 2018 Martin 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: All relevant data are

within the paper and its Supporting Information

files.

Funding: This material is the result of work

supported with resources and the use of facilities at

the VA Northern California Health Care System.

Rythm Company provided support in the form of

salary for author PJA, but did not play any role in

the study design, data collection and analysis,

decision to publish, or preparation of the

manuscript. The specific roles of this author are

articulated in the ‘author contributions’ section.

performance (for a review, see [2]). Sleep and sport/exercise have a strong relationship, mutu-

ally influencing each other, positively or negatively. Sleep deprivation is associated with higher

rating of perceived effort (RPE) values, potentially leading to reduced performance, particu-

larly in endurance event (e.g.[4,5]). It has also been suggested that sleep deprivation leads to a

higher rate of injury [6], reduces muscle glycogen stores [7] and alters recovery after muscle

damage induced by exercise [8]. Acute sleep deprivation and chronic sleep restriction also

induce alterations in glucose metabolism, with increases in insulin resistance and decreased

insulin sensitivity [9]. Both also impact different aspects of cognitive performance [10] such as

increased reaction time and lapses during attentional tasks [11,12] and psychomotor functions

[13]. Sleep deprivation and disruption of circadian rhythms also lead to elevated levels of

inflammatory markers such as interleukins (IL-6, IL 10) and tumor necrosis factor (TNF-α), and alter immune status [14,15]. The elevation of inflammatory markers, especially IL-6, has

been associated with increased pain ratings in response to sleep restriction [16]. In contrast,

good sleep, as well as sleep extension strategies, can enhance performance by preventing the

decrease in cognitive performance and reducing the RPE during exercise [11,17].

An ultramarathon is a category of long distance running longer that the traditional mara-

thon of 42.195 km, with races being of specific distances ranging from 50 km to 100 miles (161

km, e.g. Western States Endurance Run, Ultra-trail 1

du Mont Blanc 1

(UTMB 1

)) or even

longer (e.g., Tor des Geants 1

: 335 km), specific durations (24 h to 6 days) or in stages over

multiple days (e.g. Marathon des Sables). Ultramarathons, particularly those run on trails,

have become more and more popular [18]. Associated with this has been a growing interest in

research related to ultramarathon running [19]. Until now however, research has mostly

focused on factors that impact performance (like pain, gastro-intestinal distress or physiologi-

cal determinants) (e.g. [18]), health consequences of the elevated training load of ultramara-

thon runners [20], the medical issues and management of common injuries and illnesses

encountered in ultramarathons [21,22] and more specific issues such as exercise-associated

muscle cramping [23], exercise-associated hyponatremia [24] and fatigue/biomarkers changes

(e.g. [25,26]) during ultramarathons.

Ultramarathon participation requires high training loads and long duration training ses-

sions, leading to high recovery needs, particularly relative to sleep. Consistent sleep of 7–9 h

per night is recommended for healthy adults [27], but some authors suggest that athletes

should sleep between 9 and 10 h per night to allow sufficient recovery [28]. Moreover, some

ultramarathons are long enough that runners are required to maintain their effort for dura-

tions longer than their usual wakefulness period, with nocturnal activity and brief, or some-

times no, opportunities for sleep. Presumably, poor sleep habits and/or inadequate (or lack of)

appropriate sleep strategies before a race can potentially exacerbate fatigue, and increase risk

of injury, hallucinations and failure to finish.

To the best of our knowledge, only one study, conducted by Poussel et al. [29] on 303 fin-

ishers of the UTMB 1

, has focused on how ultramarathon runners manage sleep before and

sleepiness during an ultramarathon. The study used a questionnaire that was completed after

the 2013 UTMB 1

, a race in which the winning time is about 21 hours and runners are allowed

up to 46 hours to complete, so it involves one or two nights of sleep deprivation. Before the

race, 88% of runners reported that they adopted specific sleep management strategies such as

naps, increased sleep time during the previous nights, or training in sleep deprivation. Most

finishers (72%) reported that they did not sleep at all during the race, and not surprisingly,

these runners finished faster than those who slept. Race time was positively correlated with

drowsiness. Interestingly, runners who increased sleep time before the race as a pre-race strat-

egy also completed the race faster. This observation is in line with studies showing the effects

of prophylactic naps on vigilance (e.g [30]).

Sleep and ultramarathon

PLOS ONE | https://doi.org/10.1371/journal.pone.0194705 May 9, 2018 2 / 18

Competing interests: We have the following

interests: PJA is an employee of Rythm Company.

There are no patents, products in development or

marketed products to declare. This does not alter

our adherence to all the PLOS ONE policies on

sharing data and materials.

https://doi.org/10.1371/journal.pone.0194705

Thus, the first purpose of the present study was to further describe the habitual sleep char-

acteristics and strategies of ultramarathon runners relative to their intensity of training. We

included several components of their habitual lifestyle that might influence sleep behaviors

such as time of training, use of stimulants and napping, as well as the presence of sleep disor-

ders. The second purpose was to examine strategies used by runners to manage sleep before

and during ultramarathons. This descriptive analysis may be of practical importance for ultra-

marathon runners and coaches relative to preparation and performance and can also serve as

baseline information for future intervention studies on sleep and performance.

Methods

Procedure

Ultramarathon runners were invited to complete a questionnaire through electronic mailings,

postings on various ultramarathon-related web sites and forums, and advertisements in maga-

zines related to ultramarathon running in France, Italy and the US. Conditions for participating

were a minimum age of 18 yrs and having completed an ultramarathon at some time in the

past. All participants completed a secure anonymous web-based questionnaire (Google Survey)

that included demographic questions, in addition to questions related to sleep, medical history

and training history. The questionnaire was offered in French, Italian and English. All proce-

dures were approved by the University of Calgary Conjoint Health Research Ethics Board.

The questionnaire inquired about independent variables, corresponding to subject charac-

teristics such as age, weight, height, history of training and competition in ultramarathons. It

also examined various behaviors that might influence sleep (time of day when training was

performed), sleep habits (sleep duration during weekdays, weekends and holidays), use of

naps, and history of sleep disorders (difficulty falling or remaining asleep, use of sleep medica-

tion and medical assistance with sleep problems). The questionnaire also included the Epworth

Sleepiness Scale (ESS) [31,32]. The ESS is a self-administered questionnaire used to investigate

excessive daytime sleepiness that has a high level of internal consistency as measured by Cron-

bach’s alpha (0.88). Scores on the ESS can range from 0 to 24, and a score above 10 is regarded

as an indicator of excessive sleepiness. Additionally, ESS scores of 0–5 indicate low normal

daytime sleepiness, 6–10 indicate high normal daytime sleepiness, 11–12 indicate mild exces-

sive daytime sleepiness, 13–15 indicate moderate excessive daytime sleepiness, and 16–24 indi-

cate severe excessive daytime sleepiness.

Participants were also asked if and how they have been attentive to their sleep in the days

and nights preceding an ultramarathon and if and how they manage sleep during ultramara-

thons. When they indicated they had a strategy, they were invited to describe the type of strat-

egy used. In case of a mismatch in the provided answers (e.g. if the runner answered “yes” to

the question “did you sleep during the race?” then wrote “I did not sleep”), the written

response was considered to be correct. For those with a sleep strategy during an “overnight

ultramarathon” and a “longer than 2 night ultramarathon”, we requested the participant’s

sleep duration (in minutes) and the race finish time (in hours). If respondents provided infor-

mation for several race experiences, we considered each of them. If an answer did not contain

both sleep duration and race finish time, the response was not considered for analysis. We also

considered the number of sleep episodes, the location of the sleep episodes (aid station, build-

ing, etc. vs outside, i.e. on the trail) and the time of day for the sleep episodes.

Statistical analysis

Descriptive statistics are presented. The data are reported as mean and SD since they passed

normality testing, performed using the Skewness-Kurtosis test. Missing data are noted where

Sleep and ultramarathon

PLOS ONE | https://doi.org/10.1371/journal.pone.0194705 May 9, 2018 3 / 18

https://doi.org/10.1371/journal.pone.0194705

pertinent. Normality allowed us to use Generalized Estimating Equations (GEE) to compare

sleep durations during weekdays, weekends and holidays [generalized linear model and gener-

alized estimating equations (GENLIN) procedure], due to the correlated nature of observa-

tions from the same participant. Other associations between variables were assessed using a

Chi-square test, with phi (ϕ) value to report the effect size. Correlations between sleep duration during a race and race finish time were determined using Pearson correlation analyses. Statisti-

cal analysis was performed with SPSS (24.0) and statistical significance was set at p < 0.05.

Results

Population

Out of the 636 participants, 393 responded in French, 118 in Italian and 125 in English. They

consisted of 541 (85.1%) men and 95 (14.9%) women. Mean (± SD) height and weight were 177.8 ± 8.5 cm and 72.3 ± 8.4 kg for men and 165.2 ± 24.6 cm and 57.2 ± 8.1 kg for women, respectively. Other subject characteristics are shown in Table 1.

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