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Frontiers in Physiology | www.frontiersin.org 1 March 2022 | Volume 13 | Article 813243
REVIEW
published: 17 March 2022
doi: 10.3389/fphys.2022.813243
Edited by:
Andrea Nicolò,
Foro Italico University of Rome, Italy
Reviewed by:
Annalisa Cogo,
Istituto Pio XII, Italy
Antonella LoMauro,
Politecnico di Milano, Italy
*Correspondence:
Eric Harbour
eric.harbour@plus.ac.at
Specialty section:
This article was submitted to
Exercise Physiology,
a section of the journal
Frontiers in Physiology
Received: 11 November 2021
Accepted: 28 January 2022
Published: 17 March 2022
Citation:
Harbour E, Stöggl T,
Schwameder H and
Finkenzeller T (2022) Breath Tools: A
Synthesis of Evidence-Based
Breathing Strategies to Enhance
Human Running.
Front. Physiol. 13:813243.
doi: 10.3389/fphys.2022.813243
Breath Tools: A Synthesis of
Evidence-Based Breathing Strategies
to Enhance Human Running
EricHarbour
1
*, ThomasStöggl
1,2, HermannSchwameder
1 and ThomasFinkenzeller
1
1 Department of Sport and Exercise Science, University of Salzburg, Salzburg, Austria, 2 Red Bull Athlete Performance Center,
Salzburg, Austria
Running is among the most popular sporting hobbies and often chosen specically
for intrinsic psychological benets. However, up to 40% of runners may experience
exercise-induced dyspnoea as a result of cascading physiological phenomena,
possibly causing negative psychological states or barriers to participation. Breathing
techniques such as slow, deep breathing have proven benets at rest, but it is unclear
if they can beused during exercise to address respiratory limitations or improve
performance. While direct experimental evidence is limited, diverse ndings from
exercise physiology and sports science combined with anecdotal knowledge from
Yoga, meditation, and breathwork suggest that many aspects of breathing could
beimproved via purposeful strategies. Hence, wesought to synthesize these disparate
sources to create a new theoretical framework called “Breath Tools” proposing
breathing strategies for use during running to improve tolerance, performance, and
lower barriers to long-term enjoyment.
Keywords: breathing pattern, coupling, running, techniques, strategies, respiration, ventilation
INTRODUCTION
Breathing is natural and automatic, sustaining life by the simple movement of air. Despite the
apparent simplicity of this process, the understanding of breathing has recently been advanced
extensively through investigations in medicine, sports science, and psychophysiology. e recent
SARS-COVID-19 global epidemic has reminded many of the signicance of breathing and
the consequences of respiratory distress.
Several recent studies have brought renewed attention to the anthropological roots of breathing
and its eect upon overall well-being. Yogic techniques have for millenia utilized breath awareness
and exercises to cultivate “prana” (meaning both “breath” and “life force” in Sanskrit), while
meditation, breathwork practices, and freediving also take advantage of breathing techniques
for calm, focus, and performance. Resonant frequency breathing performed in heart-rate
variability (HRV) biofeedback has signicant positive eects upon HRV itself, overall autonomic
nervous system regulation, and related emotional states such as anxiety and depression (Lehrer
et al., 2020). Performing these breathing techniques at rest has additive eects upon cognitive
function, decision-making, and concentration in sport (Jimenez Morgan and Molina Mora,
2017; De Couck et al., 2019). ese eects are extremely valuable in sports contexts where
both mental and physical performance aect positive psychological states such as perceived
Frontiers in Physiology | www.frontiersin.org 2 March 2022 | Volume 13 | Article 813243
FIGURE1 | Exercise breathing pattern changes during increasing exercise intensity. Note the nonlinear increase in breathing rate and unequal partitioning of EILV
and EELV as intensity increases. TLC, total lung capacity; LOV, lung operating volume; VC, vital capacity; RV, residual volume; EILV, end-inspiratory lung volume;
EELV, end-expiratory lung volume; and VT, tidal volume.
Harbour et al. Breath Tools: Breathing for Runners
ecacy and enjoyment (Ogles et al., 1995). Although slow
breathing is demonstrably ecacious at rest, the utility of slow
breathing during exercise is understudied.
Recent reviews have explored the various mechanisms that
may cause breathing to limit physical performance during
exercise (Amann, 2012; Dempsey et al., 2020), but little work
has attempted to address these mechanisms or improve breathing
directly during exercise. Although running is both one of the
most popular (Statista, 2018) and well-studied physical activities,
very few studies have directly investigated the use of breathing
techniques during running as done during Yoga, meditation,
and cycling (Vickery, 2008; Saoji etal., 2019). Running deserves
special attention not only for its immense global popularity
but also because runners are driven by a complex mix of
psychological and emotional motives (Ogles etal., 1995; Pereira
etal., 2021). Since breathing can heavily aect the psychological
perception of exercise (Laviolette and Laveneziana, 2014),
improving breathing during running may inuence tolerance
or psychological state during activity. Considering the popularity
of running and the diverse benets of breathing strategies in
other contexts, wesought to synthesize the available evidence
to demonstrate how breathing could beused to ease respiratory
distress and improve running performance and
psychological states.
is narrative synthesis has three main goals:
1. Provide an updated overview of exercise breathing pattern,
and identify respiratory limitations to running
2. Dene and describe breathing strategies that provide physical
and mental benets for runners
3. Discuss practical applications and recommendations for
future studies of breathing techniques during running.
RESPIRATION DURING EXERCISE
e onset of exercise stimulates rapid, characteristic changes
in ventilation (VE) over 20 times greater than that at rest
(hyperpnoea). e increase from an average 6 L/min up to
150 L/min occurs in response to various metabolic, homeostatic,
and peripheral stimuli (Figure 1). While not completely
understood, humans’ precise control of exercise hyperpnoea
is driven by multiple redundant control mechanisms, such as
biochemical feedback loops [especially by the partial pressure
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 3 March 2022 | Volume 13 | Article 813243
of carbon dioxide (pCO2) and blood pH], central command
(neural feed-forward), and peripheral aerent feedback from
the working limbs (Forster et al., 2012). During steady-state
exercise, the healthy respiratory system precisely tunes VE to
match metabolic rate and maintain equal O2 and CO2 balance
at every level of the system (Ferretti et al., 2017). Above the
respiratory compensation point (RCP; a.k.a., second ventilatory
threshold), VE increases nonlinearly beyond the increase in
CO2 consumption (VCO2). Ventilatory change points are trait-
and state-dependent, continuously adjusting to factors like
anaerobic energy utilization, blood buering, and metabolic
acidosis. Indeed, the respiratory system is remarkable in
responding “just right” to exercise in most scenarios, eciently
managing VE proportional to CO2 production (VCO2). Exercise
VE increases linearly (r2 = 0.99) with inspiratory drive (VT/TI;
measured as mean inspiratory ow), reecting increased neural
drive to the inspiratory musculature (Naranjo et al., 2005).
is is achieved via patterns of breathing rate (BR), depth,
and coordinated muscle activity that maximize O2 perfusion
and minimize the metabolic work of breathing (WOB; Dempsey
etal., 2020). Nevertheless, there is considerable individual and
situational variance in breathing pattern (BP) response to VE
demands (Naranjo et al., 2005; Gravier et al., 2013).
Exercise Breathing Pattern
During exercise, it is thought that individuals intuitively select
the BP that minimizes the metabolic cost of VE (Mead, 1960;
Benchetrit, 2000; Welch etal., 2019). is is termed the “principle
of minimal eort.” e popular denition of BP includes an
inhale, an exhale, and a pause (Tab l e 1 ). It is primarily
determined by four principal variables: inspiratory ow prole
(rate of airow during inhale), inspiratory duration (TI),
expiratory ow prole, and expiratory duration (TE; Tipton
etal., 2017). ese variables determine the typical BP descriptors
of BR (60*TB−1, where TB = TE + TI) and depth (tidal volume;
VT). Duty cycle (dc or breath ratio; measured as TI/TB) constrains
ow to determine BP timing, depth, and airway (nose vs.
mouth; Naranjo et al., 2005). ese components are regulated
by multiple overlapping control mechanisms, leading to a variety
of coordinated patterns to achieve respiratory homeostasis.
Unlike other physiological processes, BP can be consciously
altered, for example to befaster or slower. Although sometime
conscious, it is largely unconscious, with bidirectionality between
physiological and psychological mechanisms; this qualies BP
as a “psychophysiological” construct. While VE is ultimately
the product of BR and VT (Equation 1), these determinants
adjust dierently to various regulatory mechanisms, as do
related subcomponents of BP such as timing, coordination,
and coupling, discussed below (Tab l e 1).
VV
ET
BR
=*
Exercise BP is modulated by central and peripheral neural
mechanisms, chemoreex stimulation, attention, and emotions,
and biomechanical rhythms, among other factors. While VE
increase necessitates elevated breathing rate (BR, a.k.a. respiratory
frequency) and/or VT, their increases are independently regulated.
Recent work indicates that during exercise BR is more
“behavioral” and primarily driven by central command (activity
in motor and premotor areas of the brain) and muscle aerents
(Amann et al., 2010; Nicolo et al., 2016, 2017a, 2018). BR
and eort are closely correlated across many dierent exercise
intensities and experimental conditions (Nicolò et al., 2020b)
because perceived exertion is likely signaled by the magnitude
of central command outow (Marcora, 2009). At submaximal
intensities, BR is also aected by cognitive load, emotions,
environmental stress, and exercise rhythm (more on this below;
Homma and Masaoka, 2008; Grassmann et al., 2016; Tipton
et al., 2017). BR is acutely responsive, adjusting almost
immediately to abrupt changes in exercise intensity and stress,
such as anticipatory anxiety, pain, and cold exposure (Masaoka
and Homma, 2001; Tipton et al., 2017). At high relative
intensities above the RCP, continued increases in VE are
accomplished primarily via BR (tachypnoea; fast BR above
~80% peak BR); this point is termed the “tachypnoeic shi”
(Sheel and Romer, 2011). e correlation between BR and
perceived eort is particularly strong at these intensities as
BR adjusts independent of absolute workload, metabolism, or
muscular activation (Nicolò et al., 2018; Cochrane-Snyman
et al., 2019). is may be due to increased levels of central
command activity compared with low or moderate-intensity
exercise (Nicolò et al., 2020a). At maximal exertion, peak BR
varies substantially between individuals from 35 to 70breaths
per minute (bpm; Blackie et al., 1991; Naranjo et al., 2005).
While BR responds quickly to “fast” inputs, evidence suggests
that during exercise VT adjusts slowly to optimally match
alveolvar VE to VCO2 (Nicolò et al., 2017a, 2018). In their
“unbalanced interdependence” model, Nicolo and Sacchetti
(2019) propose that VT is secondarily regulated on the basis
of BR to maintain biochemical homeostasis. is dierential
control likely extends across most exercise intensities (Nicolo
etal., 2020). Studies report diverse responses of VT to increasing
exercise intensity; in untrained exercisers, VT tends to increase
until either the rst or second ventilatory threshold, aer which
it either plateaus or declines (Gravier et al., 2013). While this
plateau generally coincides with the tachypnoeic shi, some
elite athletes appear to increase VT beyond the RCP and up
to total exhaustion (Lucía et al., 1999). Generally, VT peaks
around 50%–60% (1.9–2.7 L) of vital capacity (VC; total amount
of air exhaled aer maximal inspiration; Blackie et al., 1991),
although in some untrained persons as low as 35% (Gravier
et al., 2013) and elite athletes as high as 70% VC (Lucía
et al., 1999).
e tachypnoeic shi typical of the RCP cannot entirely
explain VT plateau during normal exercise conditions, since
the plateau occurs before the RCP in some individuals (Gravier
et al., 2013), and not at all in others (Lucía et al., 1999).
Lung mechanoreceptor feedback may explain some of these
disparities. VT limits are likely governed by the principle of
minimal eort, as vagally-mediated aerent feedback from
pulmonary stretch receptors regulates lung operating volumes
[LOV; relative to end-inspiratory (EILV) and end-expiratory
volume (EELV)] to minimize the WOB (Breuer, 1868; Hering,
1868; Clark and von Euler, 1972; Sheel and Romer, 2011).
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 4 March 2022 | Volume 13 | Article 813243
ese mechanical limitations may interact with pCO2, which
is known to suppress pulmonary stretch receptor outow
(Schelegle and Green, 2001). Clark et al. (1980) observed this
phenomenon with progressive levels of hypercapnia during
incremental exercise increasing VT peak. Nevertheless, despite
higher relative VT peak, CO2 levels are similar or reduced in
elite athletes vs. untrained persons at equivalent absolute work
rates (Lucía etal., 1999). Hence, some of the mechanisms that
aect the VT plateau and tachypnoeic shi during exercise are
not yet entirely clear. Despite large inter-individual dierences
in relative VT peak, it is unclear if this is a xed characteristic
of BP; tness level and training appear to have no eect on
the VT plateau or the VE/VCO2 relationship (Salazar-Martinez
et al., 2016, 2018). It is believed that the attainment of VT
peak is the only circumstance at which VT substantially aects
BR (Sheel and Romer, 2011; Nicolò et al., 2018).
While the tachypnoeic shi is an adaptive, essential response
to maintain respiratory homeostasis at high relative exercise
intensities, it coincides with increased WOB, decreased ventilatory
eciency, and peripheral fatigue (Naranjo et al., 2005; Wa rd,
2007; Gravier et al., 2013). Although exercise below the RCP
triggers near-universal positive aect, there are homogenously
negative psychological changes above the RCP (Ekkekakis etal.,
2011). is may beexplained by the close correlation (r = 0.71)
between tachypnoea and dyspnoea during incremental exercise
(Tsukada etal., 2017). While the mechanisms causing dyspnoea
are complex and varied (Sheel et al., 2011), recent studies
suggest that the psychological “unpleasantness” dimension of
dypsnoea at its onset may contribute substantially to the near-
simultaneous presentation of tachypnoea (Izumizaki etal., 2011;
Tsukada et al., 2017).
Humans generally switch airway from the nose to mouth
as VE increases above 40 L/min (Saibene et al., 1978). Duty
cycle (dc; TI/TB) increases from resting values from about 40%
(slightly longer exhale than inhale) to 50% (equal inhale to
exhale) or greater at maximal intensity (Naranjo et al., 2005;
Ki and Williams, 2007; Salazar-Martinez etal., 2018). Shorter
TE vs. TI implies that mean expiratory ow rate must exceed
mean inspiratory ow rate (rate of airow during breath phase)
in order to maintain constant LOV.
Exercise-induced VE and drive increases trigger altered
ventilatory pump musculature activity and coordination. From
rest to 70% max workload, diaphragmatic pressure increases more
than twofold, accompanied by an increased velocity of shortening,
which contributes 70%–80% of the total inspiratory force (Wallden,
2017). As exercise intensity increases, active exhales (expiratory
muscle activation) lower the inspiratory WOB by reducing
end-expiratory lung volume, modulating lung compliance, and
storing elastic energy in the ventilatory pump musculature (Aliverti,
2016). e primary expiratory muscles are the internal obliques,
which may reach 50% maximum voluntary contraction at maximal
intensity (Ito etal., 2016). e intercostals, parasternals, scalenes,
and neck muscles contribute to ventilation at high intensities by
moderating EILV and airway caliber (e.g., dilation and
inammation). Altogether, the diaphragm and associated ventilatory
pump musculature are remarkably ecient [~3%–5% total O2
consumption (VO2)] and fatigue-resistant at submaximal intensities
(Welch et al., 2019; Sheel et al., 2020).
Locomotor-Respiratory Coupling
Humans are among a large proportion of animals that entrain
BR to movement. e synchronization of locomotion to breath
TABLE1 | List of breathing pattern components and common abbreviations.
Abbreviation Variable (units) Denition
BP Breathing pattern Differential trait and state-dependent control of breathing rhythm and mechanics
BR Breathing rate (bpm) Respiratory frequency; number of breaths taken per minute
Dc Duty cycle, breath ratio (%) Breath timing; relative percentage of inhale time to the complete breath cycle (TI/TB in %)
EELV End-expiratory lung volume Volume of the lungs at the end of an expiration
EID Exercise-induced dyspnoea Excessive perceived breathlessness during activity
EILV End-inspiratory lung volume Volume of the lungs at the end of an inspiration
FR Flow reversal Instant of breath switching; e.g., from inhale to exhale or exhale to inhale
LOV Lung operating volume (%) Mean diaphragm position at a given tidal volume (mean of EELV + EILV as % of TLC)
LRC Locomotor-respiratory coupling (steps:breath) Synchronization between ow reversal and movement; e.g., running footstrike
RV Reserve volume (l) Amount of air that remaining in airway and lungs after maximal expiration
TBBreath cycle time (s) Total breath time from inspiration to next inspiration (TI + TE)
TEExhale time (s) Exhale duration during one breath cycle
TIInhale time (s) Inhale duration during one breath cycle
TLC Total lung capacity (l) Total amount of air present in lungs after maximal inspiration
TLD Thoraco-lumbar depth (%) Ratio of thorax to abdominal expansion contributing to total tidal volume
VC Vital capacity (l) Total amount of air exhaled after maximal inspiration (TLC-RV)
VTTidal volume (l), depth Breathing depth; total amount of air inspired during one breath cycle
VDVentilatory dead space (l) Sum of airway volumes which do not contribute to gas exchange
VEMinute ventilation (L/min) Quantity of air breathed per minute
VO2Oxygen consumption (L/min) Oxygen consumption; difference between oxygen inspired and oxygen expired in a unit of time
WOB Work of breathing Metabolic energy demand of ventilation
- Thoraco-lumbar coordination (s) Breathing coordination; time lag between thoracic and abdominal ow reversal
- Ventilatory drive (l/s) Total output of ventilatory pump; mean inspiratory ow rate (VT/TI)
- Ventilatory efciency Ventilatory pump response to increasing demands, frequently measured as VE/VCO2 slope
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 5 March 2022 | Volume 13 | Article 813243
is termed “locomotor-respiratory coupling” (LRC), and involves
a dual-synchronization not only of frequency [e.g., BR = step
rate (SR)] but also event phase (e.g., footstrike synchronized
with breath onset; O’Halloran et al., 2012). While most
quadrupedal mammals utilize a 1:1 phase-locked locomotion-
to-breath ratio while running due to mechanical constraints
of the thorax, humans’ upright gait permits BR adjustment
independent of locomotion (Bramble and Carrier, 1983).
Although humans lack this mechnical constraint on breathing,
they have been observed performing LRC during several rhythmic
activities, such as walking, running, cycling, rowing, cross-
country skiing, and even nger-tapping (Bechbache and Dun,
1977; Persegol etal., 1991; Fabre etal., 2007; Bjorklund etal.,
2015; Mathias et al., 2020). Swimming is a prime example of
phase-locked breathing, as swimmers inhale during specic
phases of the stroke when the face is not underwater.
Despite an apparent freedom from quadrupedal thorax
constraints on breathing, LRC in humans is likely aected by
various biomechanical phenomena specic to running. e
“visceral piston” (three-dimensional displacement of the
abdominal mass during locomotion) aects diaphragmatic
contraction via direct ligamentous connections (Daley et al.,
2013). Axial-appendicular dynamics have the potential to
positively or negatively aect VT depending on the phasic
relationship to inhale and exhale (Bramble, 1989). e eect
of footstrike timing and impact forces upon VT is termed
“step-driven ows,” and may aect VE up to 10%–12% (Daley
et al., 2013). is could be detrimental when the timing of
footstrike is out of phase (unsynchronized) with breath onset
(ow reversal; FR) but additive when in-phase (synchronized).
When the inhale is synchronized with peak visceral downward
velocity, it pulls on the diaphragm, increasing the velocity of
shortening. Daley et al. (2013) found that runners naturally
prefer LRC with phase synchronziation at additive (ow-
enhancing) phases, and that ventilatory transitions (change
from inspiration to expiration) were quicker in these conditions
of LRC. ey concluded that the visceral piston and rhythmic
arm movement substantially aect step-driven ows and LRC
has a physiologically signicant mechanical eect on breathing
dynamics. ese ndings suggest that LRC is a result of the
“minimal eort” hypothesis of breathing. If LRC reduces the
WOB, it may contribute to a delayed onset of ventilatory muscle
fatigue, especially at high exercise intensities, long exercise
durations, or in special populations predisposed to respiratory
distress (discussed below; Daley et al., 2013).
Locomotor-respiratory coupling is likely modulated by an
interaction of mechanical, neurological, and metabolic
interactions during running. Recent work indicates that LRC
in humans is probably neurophysiological in origin, as there
is a direct neurological link in humans between the respiratory
and locomotor central pattern generators in the spinal cord
(Le Gal et al., 2014; Del Negro et al., 2018). Group III and
IV aerent feedback from the working limbs appears to aect
LRC, since activities with higher-frequency limb movement
produce higher levels of entrainment (Bechbache and Dun,
1977; Caterini etal., 2016). However, close associations between
limb movement, BR, and pCO2 suggest that chemoreexive
feedback aects the strength of entrainment (Forster et al.,
2012). Cyclical, high-frequency activities such as running are
more likely to induce entrainment vs., for example, walking,
and LRC is most likely to occur at higher intensities near
VO2max (maximal oxygen uptake; Bechbache and Dun, 1977;
Bernasconi and Kohl, 1993). Notably, these studies reported
that increases in velocity of movement aected the strength
of LRC more than intensity increase via load or gradient.
ere appears to be an inuence of training history upon
entrainment, where task preference and experience are positively
associated with LRC onset and strength (Kohl et al., 1981;
Bramble and Carrier, 1983; Stickford et al., 2020). ese
relationships were independent of overall tness, so sport-
specic experience may coincide with LRC as a learned skill
(perhaps unconsciously). Finally, studies utilizing metronomes
to instruct movement appeared to quickly and strongly inuence
LRC (Bechbache and Dun, 1977; Bernasconi et al., 1995).
Entrainment is likely to occur spontaneously and consistently
in the presence of some or all of the above conditions.
Respiration as a Limiting Factor
e respiratory system in healthy individuals is considered to
begenerally well-adapted for the demands of exercise (Amann,
2012; Dempsey etal., 2020). Nevertheless, accumulating evidence
strongly suggests that the respiratory system is “underbuilt”
for the demands of intense exercise. At exercise around or
above 80%–85% VO2max, three primary mechanisms cause the
respiratory system to limit performance: exercise-induced arterial
oxyhemoglobin desaturation, excessive ventilatory muscle work,
and intrathoracic pressure eects on cardiac output (Amann,
2012). Specic scenarios (e.g., hypoxia and cold/dry climates)
expose respiratory system vulnerabilities at submaximal
intensities, and certain populations (e.g., elite athletes, females,
and elderly) are especially susceptible; these phenomena have
been recently detailed in extensive reviews (Dempsey et al.,
2020; Archiza etal., 2021). While the exact limiting mechanisms
dier (structural or functional), these situations and individuals
bring the respiratory system close to its physiological limits.
However, physiological limits do not fully explain the prevalence
of exercise-induced breathlessness (a.k.a dyspnoea; EID).
An estimated 20%–40% of otherwise healthy runners
experience EID even at low absolute exercise intensities
(Johansson et al., 2015; Smoliga et al., 2016; Ersson et al.,
2020). is could bebecause unt or deconditioned individuals
may approach high levels of exertion and experience limb
fatigue at low absolute workloads (Abu-Hasan et al., 2005). It
could also be related to mouth breathing, since mouth-only
breathing at submaximal intensities causes airway irritation,
and possibly subsequent exercise-induced laryngeal obstruction
(EILO; Mangla and Menon, 1981; Johansson etal., 2015). While
the majority of EID prevalence may beexplained by physiological
limitations and deconditioning, the other most likely cause is
dysfunctional breathing (Depiazzi and Everard, 2016). Distinct
from pathology, dysfunctional breathing (DB; suboptimal BP)
can cause otherwise healthy runners to experience premature
onset of fatigue and subsequent EID (Boulding et al., 2016).
Depiazzi and Everard (2016) submit that any BP deviating
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 6 March 2022 | Volume 13 | Article 813243
from slow, coordinated, diaphragmatic breathing has the potential
to be “dysfunctional.” Chronic stress (internal or external) or
negative emotional states could cause habitual DB during
exercise (Homma and Masaoka, 2008; Tipton et al., 2017).
Whether caused by physiological or psychological limits, fatigue
and EID could contribute to cessation of exercise, increased
rating of perceived exertion (RPE), or negative emotional states
(Figure 2; Bradley and Clion-Smith, 2009; Weinberger and
Abu-Hasan, 2009). Hence, here we aim to identify three
important shared phenomena that lead to respiration limiting
exercise performance, tolerance, and enjoyment: dynamic
hyperination, blood stealing, and hyperventilation.
FIGURE2 | The “respiratory limiting cycle” cascade of phenomena leading to respiration limiting exercise performance and enjoyment. Increasing exercise intensity
interacts with pre-existing individual constraints, causing an accumulation of respiratory phenomena that ultimately harm performance and cause dyspnoea. Dashed
arrows indicate mechanisms specic to high relative exercise intensities. Adapted with permission from BradCliff® and Bradley and Clifton-Smith (2009).
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 7 March 2022 | Volume 13 | Article 813243
Exercise BP may fail to provide the “just right” response
in the presence of ow limitation. During high intensity
exercise, large increases in ventilatory ow may cause narrowing
of the airway related to the Venturi eect and Bernoulli
principle, among other constraints. is is termed “exercise-
induced largyngeal obstruction,” and it is particularly common
in elite athletes who generate large VE at high intensities
(Smoliga et al., 2016). Up to 20% of elite athletes, females,
adolescents, and overweight individuals may experience this
during low-intensity activity (Smith et al., 2017; Dempsey
et al., 2020; Ersson et al., 2020). DB phenotypes including
upper-thoracic-dominant breathing and core muscle
hypertonicity (such as in low back pain compensation) are
also risk factors (Chaitow etal., 2014). Flow limitation could
lead to “breath stacking,” a negative consequence when
subsequent breaths have slightly larger inspiratory than
expiratory ow (Ward, 2007). Breath stacking causes EILV
and EELV to progressively increase, leading to dynamic
hyperination (Figure 3; Sheel et al., 2020). At these higher
LOV, the lungs are stier, less compliant, and require more
muscle work to expand (Sheel et al., 2020). Unfortunately,
dynamic hyperination places the diaphragm in a suboptimal
length for expanding the lungs and managing intrathoracic
pressures, further fatiguing the ventilatory musculature
(Aliverti, 2016).
Diaphragmatic breathing positively aects blood shiing
between the trunk and the extremities during exercise (Aliverti
etal., 2010). However, during heavy exercise above ~80% peak
work rate, increasing intra-thoracic pressure acts like a Valsalva
maneuver, decreasing stroke volume and cardiac output (Aliverti,
2016). Furthermore, at sustained high intensities the diaphragm
fatigues; it demands up to 14%–20% of cardiac output and
10%–16% of VO2 on top of concurrent accessory and expiratory
muscle fatigue (Welch et al., 2019). Ventilatory muscle fatigue
at high intensities triggers the metaboreex, which ensures
that the ventilatory pump maintains adequate perfusion by
shunting blood from the working muscles via sympathetically-
mediated vasocontriction. is competition for oxygen-rich
blood is termed “blood stealing”; a detailed review is available
elsewhere (Sheel et al., 2018). Although its negative
haemodynamic eects generally only occur above 85% VO2max,
its relationship to BP is unclear. Since the tachypnoeic shi
and dynamic ination associated with heavy exercise also elevate
the WOB, it is likely that they contribute to blood stealing
(Amann, 2012).
Exercise hyperpnoea is usually a “just right” respiratory
response to maintaining biochemical homeostasis with increasing
intensity (Dempsey et al., 2020). However, high BR may
bepsychologically disadvantageous, since the tachypnoeic shi
onset is closely associated with EID (Izumizaki et al., 2011;
Tsukada etal., 2017). Some runners may experience tachypnoea
and associated dyspnoea prematurely. Healthy adult females,
for instance, have hormonally-determined lung and airway
limitations that predispose them to higher average BR, lower
VT, and increased risk of EID (Itoh et al., 2007; Dempsey
et al., 2020). During running, VT is constrained more than
in other activities, and the tachypnoeic shi occurs relatively
earlier (Elliott and Grace, 2010; Marko, 2020). is limitation
is partially attributed to competing demands for postural and
ventilatory function upon the diaphragm as well as step-driven
ows (Chaitow et al., 2014; Stickford and Stickford, 2014).
Another factor could be surface inclination; Bernardi et al.
(2017) demonstrated that gradients above 20%–30% decrease
thoraco-lumbar coordination (r = 0.99) and subsequent ventilatory
eciency (r = −0.265). Subsequently, this harmed BP (lower
VT, increased BR), oxygen saturation, and performance. Since
these eects were independent of absolute altitude and fatigue,
they concluded that this was due to trunk inclination limiting
ribcage expansion.
If the tachypnoeic response is early, or inappropriately
dramatic, such as in hyperventilation DB, hypocapnia could
reduce peripheral muscle perfusion via the Bohr eect (Depiazzi
and Everard, 2016). is may accelerate blood stealing and
limb muscle fatigue. Additionally, lower pCO2 is associated
with earlier VT peak (Clark et al., 1980), which could lead to
accelerated increases in BR to increase VE. Hyperventilation
is accompanied by increased ow rates, which could lead to
airway narrowing and ow limitation (Dempsey et al., 2020).
FIGURE3 | Dynamic hyperination occurs when accumulated breath stacking progressively increases lung operating volume. When lung operating volume
approaches total lung capacity, lung stiffness, and suboptimal diaphragm position increase the work of breathing (WOB) and dyspnoea. TLC, total lung capacity;
LOV, lung operating volume; EILV, end-inspiratory lung volume; EELV, end-expiratory lung volume; and VT, tidal volume.
Harbour et al. Breath Tools: Breathing for Runners
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Hyperventilation, hyperination, and blood stealing might
together form a negative feedback loop if unchecked. If this
cycle is not addressed, it could lead to EID, impaired performance,
or negative emotional aect (Bradley and Clion-Smith, 2009;
Chaitow et al., 2014). If these phenomena could be avoided,
we theorize that individuals could benet from enhanced
performance, reduced perception of fatigue, or prevention of
negative psychological states (Figure 2).
A related, but intensity-independent aspect of respiratory
limitations almost unique to running is exercise-related transient
abdominal pain (ETAP), also known as “side stitch.” First
mentioned by Pliny the Elder, there is still no consensus on
the exact etiology of this unpleasant phenomenon (Morton
and Callister, 2015). Unfortunately, this unpleasant, painful
experience aects up to 70% of runners per year, which is at
best frustrating and at worst a reason for exercise cessation.
Some experts believe that phrenic nerve irritation related to
repeated right footstrike and exhalation synchronization might
bethe cause (Coates and Kowalchik, 2013). Specically, irritation
of the parietal peritoneum is the most likely cause of ETAP,
especially during running and in the right lower quadrant
(Morton and Callister, 2015). It could be that LRC at even
ratios (such as 2:1 strides per breath), leading to ipsilateral
footstrike on expiration, is actually a risk factor for developing
side stitch in runners.
Breathing Patterns Can BeModied and
Improved
While breathing usually provides the “just right” response to
the physiological demands of exercise, respiratory limitations
can lead to negative performance or psychological outcomes.
If BP can be “improved” to prevent or delay the onset of
dyspnoea, or to increase ventilatory eciency, then it can
benet not only exercise performance but also the psychological
eects of exercise. Although acute BP modication and longer-
term breathing “retraining” have well-established benets for
human health (Zaccaro et al., 2018; Lehrer et al., 2020), this
eld has only recently gained attention in exercise science. A
recent review addressed this disparity by exploring the utility
of breath retraining for respiratory-limited athletes (Allado
et al., 2021); they found that several targeted techniques (e.g.,
Olin EILOBI breathing) can improve symptoms of ow limitation.
Several studies have utilized principles of breath retraining at
rest (e.g., slow diaphragmatic breathing) to demonstrate increased
exercise performance (Jimenez Morgan and Molina Mora, 2017;
Bahensky et al., 2021), but it is unclear if these can
beimplemented during exercise, and what psychological benets
result. Whether modifying BP is possible without compromising
the “minimal eort” homeostasis of the respiratory system
requires discussion and more direct study. In fact, one study
examining the eects of internal attentional focus upon breathing
reported no overall benet for movement economy, despite
positive eects upon VE, respiratory quotient, and heart rate
(Schucker etal., 2014). Nonetheless, it is known that breathing
techniques improve positive emotion (Zaccaro et al., 2018),
and that positive emotions can increase running economy
(Brick et al., 2018), so some accommodation might unlock
such performance benets. In fact, doing so during running
might bethe most specic application to maximize adaptations.
Despite a lack of direct evidence, theoretical and experimental
ndings from elds, such as cycling, respiratory medicine, and
Yoga indicate various limiting mechanisms that can beaddressed
with breathing techniques. We hypothesize that breathing
strategies employed during running could improve performance,
attenuate EID, or enhance psychological states.
BREATH TOOLS
Renewed attention to breathing techniques has inspired
substantial scientic scrutiny and interest among practioners,
but to our knowledge, no one has yet attempted to summarize
breathing strategies for exercise in an evidence-based, organized
manner. us, the following section is a description of techniques
and “breath tools” with potential benets to the runner. Each
tool is described with an acknowledgement of some historical
and anecdotal perspectives as well as a synthesis of its benets
for running biomechanics, biochemistry, and psychophysiology.
e “advanced” tools are slightly dierent, as they increase
respiratory stress to catalyze positive adaptations via training.
We summarize these strategies in roughly ascending order of
benet, complexity, and risk.
Rate
Humans have long known the value of slower BR. While
religious ceremonies, Yoga, and meditation rituals have explored
the practice for thousands of years, recent work has conrmed
the value of slow breathing for biochemical and
psychophysiological benets at rest (Russo etal., 2017; Zaccaro
et al., 2018). Although evidence suggests that sustained high
BR during activity could lead to respiratory limitations (see
“Respiration as a Limiting Factor”), reduced BR has been
understudied as a standalone breathing strategy during running.
Slow BR may reduce the work of accessory respiratory muscles
and subsequent WOB during exercise (Chaitow et al., 2014;
Welch et al., 2019). Perhaps, the most simple advantage is
improved gas exchange. Since BR is inversely proportional to
VT at a given VE (Equation 1), slower breathing implicity induces
greater depth of breathing (Figure 4). Since there is a xed
anatomic dead space (VD; average 150 ml of airway segments
that do not participate in gas exchange), increases in VE via
VT (instead of BR) benecially manipulate relative VD (VD:VT
ratio). For example, in conditions of isoventilation (Equation
1), a BR increase from 20 to 40 bpm at 10 L/min VE causes an
increase of 30% VD relative to VT, and a reduction of 300 ml
in alveolar ventilation (Table 2). In contrast, increasing VE to
20 L/min by only increasing VT (to 1.0 L) has the eect of
halved relative VD (15%) and a 21% increase in alveolar ventilation.
Simplistically, increasing VE via VT (instead of BR) allows for
more oxygen-rich breaths and greater alveolar ventilation.
Several studies have demonstrated remarkable plasticity of
VT in healthy individuals at submaximal intensities (Vickery,
2008; Bahensky etal., 2019; Cleary, 2019; Bahensky etal., 2020).
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ese ndings may stand in contrast to the “minimal eort”
hypothesis. We suspect that since an already-small percentage
of VC is used for normal VT during exercise, an incrementally
larger VT does not undermine the lung volume/pressure
relationship, and the BR/VT relationship may bemore “exible”
than previously thought. is is likely not the case above the
RCP, where BR increases are driven substantially by central
command (Nicolò et al., 2018) and most exercisers reach VT
peak (Blackie et al., 1991). We suspect that this strategy is
most appropriate at low relative exercise intensities, and perhaps
not helpful or even harmful at high exercise intensities; future
studies should investigate this dierence.
Given the close association between BR and RPE (Nicolò
et al., 2018; Cochrane-Snyman etal., 2019), we speculate that
slower BR may decrease perceived feelings of eort at a given
exercise intensity. Hypothetically, slower BR may “trick” the
brain into feeling exercise to be easier. Hence, lower perceived
eort might be reected in improved performance or positive
psychological states (Noakes, 2012). Moreover, since BR reects
the physiological response to cognitive and environmental stress
at rest (Grassmann et al., 2016; Tipton et al., 2017), slowing
BR during exercise may improve mental performance and
calmness. As slow BR is known to positively impact autonomic
nervous system balance and vagal tone at rest (Lehrer et al.,
2020), it is possible that there is a similarly “optimal” BR
during running that enhances the pleasant feelings of exercise
(Homma and Masaoka, 2008). One study that manipulated
BR during cycling found lower RPE, suppressed sympathetic
and increased parasympathetic activity when breathing at very
low BR of 10 bpm vs. unconstrained BR (Matsumoto et al.,
2011). More studies are needed to evaluate such ndings
in running.
Another potential application of the “rate” strategy is to
regulate exercise intensity. As BR is closely correlated with
physical eort, wespeculate that constant BR may limit physical
output. Since mechanical limitations partially determine the
comfortable limit of VT, constant “paced” BR therefore has a
theoretical upper limit of VE. Paced BR therefore deterministically
FIGURE4 | Respiratory inductance plethysmography data from our lab showing normal breathing (dashed line) vs. “rate” breathing strategy (solid line). Note longer
breath duration (horizontal) and related larger tidal volume (vertical) for each breath cycle.
TABLE2 | Effect of breathing pattern on alveolar ventilation and dead space in three scenarios. Adapted from Braun (1990).
Breathing pattern Minute ventilation
(VE, L/min)
Breathing rate (BR,
bpm) Tidal volume (VT, L) Dead space volume
(VD, ml)
Alveolar ventilation
rate (L/min) Relative VD (VD/VT, %)
Normal 10 20 0.50 150 7.0 30%
Slow, deep 10 10 1.0 150 8.5 15%
Fast, shallow 10 40 0.25 150 4.0 60%
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limits overexertion since VE cannot easily increase. For example,
given a typical VC of 4 L and assumed VT peak of 60% VC
(Naranjo etal., 2005), running with paced BR at 20 bpm would
limit comfortable VT to 2.4 L and VE to 48 L/m. If the runner
speeds up, increasing metabolic demands but not VE, there
might bea dissociation of the VCO2/VE relationship. Increased
pCO2 could trigger dyspnoea and air hunger (Sheel et al.,
2011); this is a strong cue to “slow down.” In this way, breathing
could beused to deliberately impose a limit on exercise intensity,
potentially aiding in sustainable pacing of exercise. is could
be especially helpful for unt beginner runners to prevent
overexertion. Considering the complex “minimal eort”
regulation of BP, paced BR during exercise could cause adverse
eects such as respiratory discomfort or EID; this requires
more study. Nonetheless, elite athletes express lower levels of
BP variability during exercise vs. healthy sedentary individuals
(Castro et al., 2017), suggesting that decreased BR variability
could beadvantageous. Experimental investigations could address
this topic by including subjective assessment of dyspnoea
intensity and discomfort on top of objective measurement of
physiological performance (Lewthwaite and Jensen, 2021).
Practical application of paced breathing during running
invites scientic exploration. In biofeedback studies, visual
feedback has been used to successfully x BR at specic rates
(Davis et al., 1999; Blum et al., 2019). Auditive feedback may
be especially appropriate for eld running, since over 60% of
runners listen to audio, on average, during their run (Nolan,
2016). We have demonstrated in our lab that runners can
easily follow continuous and periodic auditive BR instruction
during running (van Rheden etal., 2021). e specic parameters
for the “rate” strategy need further denition: there is likely
not an absolute “best” BR for all runners, but rather a relative
decrease that optimizes the benets outlined above. Nicolò
et al. (2017b) suggest monitoring BR as a percentage of an
individual’s peak BR (BR/BRPeak), and this could beused similarly
for the “Rate” strategy. A decrease of 10%–20% is perhaps
prudent as used in previous studies with breathing retraining
(Bahensky et al., 2021).
Deep
Given the interdependence of BR and VT, depth of breathing
is largely dependent upon the former. However, equivalent VT
can be achieved with more or less diaphragmatic engagement,
and at variable LOV. Pranayama Yoga, Zen, and Transcedental
meditation practices include conscious diaphragmatic breathing
exercises shown to beeective for improving exercise capacity,
stress reduction, and reducing symptoms of respiratory disease
(Hamasaki, 2020). us, breathing depth ought to beconsidered
distinctly modiable.
Although VT must adjust proportionally with BR to match
VE demands, it can perhaps be altered independently. Elite
athletes have demonstrated ventilatory compensation strategies
favoring VT increases relatively greater than non-elites, especially
in acute hypoxia (Lucía etal., 2001; Tipton etal., 2017). is
may be an adaptive mechanism to aid in the elevated VE
demands of high performance, as lung structure is remarkably
intractable even with training (Dempsey et al., 2020). Not
only is increasing VE via VT preferable and possible (section
“rate”), but this “depth” should come from the abdominal
ribcage (Figure 5).
Upper-thoracic dominant breathing is associated with
increased ow limitation, WOB, hyperventilation, and postural
instability (Nelson, 2012; Chaitow et al., 2014; Depiazzi and
Everard, 2016; Wallden, 2017). Conversely, diaphragmatic
breathing is correlated with various positive health benets,
including reduced resting heart rate, post-exercise oxidative
stress, increased postural control, and baroreex sensitivity
(Hazlett-Stevens and Craske, 2009; Martarelli etal., 2011; Nelson,
2012; Hamasaki, 2020). e eect of diaphragmatic breathing
during exercise on these parameters is unknown. We suspect
that this is due to methodological diculties in measuring
diaphragmatic contribution to breathing noninvasively.
Nonetheless, diaphragmatic deep breathing might help to
attenuate respiratory limitations in vulnerable individuals and
situations. We suspect that this could result in reduced risk
for EID and negative psychophysiological consequences.
Greater depth of breathing can beachieved through exercises
to improve diaphragmatic function, and thoraco-lumbar
coordination. Several publications have provided summaries
of such exercises, which include paced breathing, biofeedback,
and manual therapy (Hazlett-Stevens and Craske, 2009; Saoji
et al., 2019; Hamasaki, 2020). On the other hand, examples
of manipulating breathing depth during exercise are limited.
One simple method is implementing the “rate” strategy to
force VT to increase in response to slow BR (section “rate”).
However, this does not necessarily cue diaphragmatic breathing
as we have described. Some products such as the Buteyko
belt® (Buteyko Clinic International, Galway, Ireland) may bring
awareness to the diagphragm and abdominal ribcage via external
tactile stimulation, but it is unclear if these are suitable during
exercise. Sensors such as the Hexoskin garments (Carre
Technologies, Canada) are capable of measuring abdominal
ribcage expansion, but they experience signicant signal
contamination as a result of so tissue artifact when used
during running (Harbour et al., 2021). Visual and auditive
methods from the eld of biofeedback could be particularly
suitable for cueing this strategy during running.
Nose
e nose is the primary point of entry and exit of the airway
during healthy breathing at rest. It is functionally equipped
to humidify, warm, and lter inspired air (Walker et al., 2016).
It also increases nitric oxide production in the airway, and
has positive eects upon pulmonary perfusion (Sanchez Crespo
etal., 2010), head posture (Sabatucci etal., 2015), and cognitive
function (Zelano etal., 2016). Mouth breathing is more common
during exercise and for those with nasal breathing diculties
(Niinimaa, 1983). However, unlike nose breathing, habitual
mouth breathing is linked with DB and numerous pathologies,
including upper respiratory tract infections, rhinitis, and asthma
(Chaitow etal., 2014; Walker etal., 2016). Despite these concrete
advantages at rest, nasal breathing during exercise has seen
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mixed attention and enthusiam as a standalone breathing
strategy. Nose breathing is encouraged during Pranayama Yoga
exercises, and also popularized by authors/bloggers Brian
McKenzie (Sh//.®) and Patrick McKeown (Oxygen Advantage®)
as a psychophysiological state modulator. Humans usually switch
to mouth breathing at VE = 40 L/min, leading to the assumption
that mouth breathing is a requirement during exercise (Saibene
etal., 1978). Despite this assumption, studies have demonstrated
that humans have surprising exibility in airway choice during
exercise (Morton et al., 1995; Dallam and Kies, 2020).
omas et al. (2009) reported that subjects were able to
maintain nasal breathing up to 85% VO2max during exercise
when instructed with a familiarization but no other
accommodation. With an adaptation period, nasal breathing
during exercise may cause reduced BR, reduced hypocapnia,
and increased nitric oxide production (Dallam et al., 2018).
Nitric oxide production is itself benecial as a vasodilator and
bronchodilator (Sanchez Crespo et al., 2010; ornadtsson
et al., 2017), perhaps reducing the risk for ow limitation.
While nasal breathing utilizes a smaller airway, which is a
AB
CD
FIGURE5 | Schematic showing the difference between upper-thoracic dominant breathing (A,C) vs. “deep” diaphragmatic breathing (B,D). (A) Upper-thoracic
breathing elevates and expands the upper ribcage, visible in (C) respiratory inductance plethysmography measurements from our lab showing increased amplitude
in thoracic vs. abdominal bands. (B) Deep breathing attens the diaphragm against the inferior abdominal viscera, expanding the abdominal ribcage via pump- and
bucket-handle mechanisms. Adapted from Isometric angle of diaphragm and ribcage by Chest Heart & Stroke Scotland and Stuart Brett, The University of
Edinburgh 2018 CC BY-NC-SA; arrows added for emphasis.
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limitation at higher exercise intensities, it appears to increase
diaphragmatic function (Trevisan et al., 2015), which could
be a long-term advantage (see section “Deep”). Some studies
have reported favorable performance eects, such as decreased
respiratory exchange ratio, VO2, and increased running economy
and time to exhaustion (Morton et al., 1995; Recinto et al.,
2017). Weestimate that these eects might benecally decrease
RPE or dyspnoeic sensations, although direct study is required.
Conversely, nasal breathing during heavy exercise leads to
higher exercise HR and no dierence in power output or
anaerobic performance, perhaps as a result of greater inspiratory
muscle load (Recinto et al., 2017).
The filtration and humidification functions of the nose
may help at any exercise intensity to prevent EID and
pathogen or particulate inhalation (Mangla and Menon, 1981;
Aydın etal., 2014). The risk for Rhinitis and upper respiratory
tract infections is substantially reduced with nasal breathing
during exercise (Walker et al., 2016). Airway choice also
impacts head posture and glossopharyngeal mechanics (Okuro
et al., 2011; Sabatucci et al., 2015), suggesting that nasal
breathing could be a long-term strategy to prevent EILO.
Although there is limited evidence on the psychophysiological
correlates of nasal breathing during exercise, studies suggest
that nasal breathing at rest leads to improved cognitive
function, emotional appraisal, memory, and lower perception
of fear (Zelano et al., 2016). Hence, we suggest that nasal
breathing is beneficial for its positive effects on performance,
airway quality, and cognitive function during
low-intensity exercise.
Implementing nasal breathing during exercise requires
awareness and accommodation. Anecdotal evidence suggests
that 10–12 weeks are required for meaningful changes in
nasal breathing comfort and relief of airway restriction to
occur, while intervention studies have examined learning
periods of up to 6 months (Dallam et al., 2018). Conversely,
several reports indicate that nasally-restricted breathing causes
nasal airway resistance to drop in days and even minutes
as a result of nitric oxide production and shifting nasal
mucosa (Shturman-Ellstein etal., 1978; McCaffrey and Kern,
1979; Mertz et al., 1984). Rather, nasal breathing is self-
manifesting: performing it encourages subsequent ease. In
fact, nasal airway resistance falls during exercise, regardless
of the airway used (Olson and Strohl, 1987). This is why
the “nose” strategy is indeed an accessible choice for most
runners; barriers to uptake are most likely related to
habituation alone. Nasal breathing requires some adaptation,
but the ideal protocols and individual differences need more
investigation. An understudied aspect is whether diaphragm
fatigue is improved or harmed with nose breathing, given
its active resistance as a smaller airway. Finally, werecommend
exercising caution when performing studies on nasal breathing
in an exercise physiology setting specifically related to
spiroergometry masks and their adverse effects on BP (Gilbert
etal., 1972; Laveneziana etal., 2019). Future studies should
explore nasal breathing in natural running settings with
minimally invasive equipment, and also the details of nasal
breathing accommodation.
Active Exhale
e benets of long, slow exhales have been long promoted
in Yoga and meditation elds to enhance health and well-being
(Saoji et al., 2019). Some running coaches and experts have
also touted this strategy, suggesting it enhances breathing depth
and aerobic endurance (Jackson, 2002; Coates and Kowalchik,
2013). Although there are few studies directly examining
manipulation of the exhale phase during exercise, combined
evidence from other domains supports several advantages of
“active” exhales.
Longer exhales may exploit respiratory sinus arrythmia to
improve HRV and subjective well-being at rest (Matsumoto
etal., 2008; Van Diest etal., 2014). While inspiration enhances
sympathetic and suppresses parasympathetic activation, during
expiration, the opposite occurs, triggering vagal aerents (Seals
et al., 1993; Hayano etal., 1994). is phenomenon has been
observed during incremental exercise (Blain etal., 2005). Indeed,
breathing may bethe main mechanism responsible for short-
term HR uctuations, especially at higher intensities (Bernardi
et al., 1990; Prigent et al., 2021). Matsumoto et al. (2011)
tested this eect during exercise: longer exhales (33 vs. 50%
dc) caused improved HRV, ventilatory eciency (VE/VCO2
19.1 ± 2.9 vs. 22.1 ± 4.4), and VO2 during incremental cycling.
ese profound results have yet to bereplicated in the literature.
A separate but related approach to exhale manipulation is
conscious recruitment of the expiratory musculature. Although
expiration becomes active by default during exercise, additional
contraction of the abdominals may confer additional benets.
In other words, stronger, forced exhales in combination with
a lower duty cycle make the “active exhale.” Active exhales
cause a fuller upward excursion of the diaphragm, which
generates passive elastic forces, lowers diaphragmatic work, and
assists in postural stabilization (Wuthrich et al., 2014; Wallden,
2017). Greater abdominal recruitment might help to partition
the WOB and delay the onset of ventilatory muscle fatigue
at high intensities, but this aspect is apparently unstudied.
While active exhales are automatic in most situations, the
respiratory limitations outlined above can cause this pattern
to become dysregulated. Hence, in the presence of these
limitations, it is possible that purposeful active exhales could
assist in maintaining optimal LOV (Figure 6). Lower duty
cycle limits inspiratory ow, and allows more time for expiratory
ow; this may reduce expiratory ow limitation. In addition,
the assymetric ow prole accompanying long exhales implies
that peak negative inspiratory pressure exceeds negative expiratory
pressure. is could have net positive eects on intrathoracic
pressure as a limiter to cardiac output during high-intensity
exercise (Amann, 2012). No studies have explored this aspect
yet in the literature.
e mountaineering community has long-touted a version
of active exhales (“rescue breath” or “pressure breath”) for
managing respiratory distress at altitude (Expeditions, 2014).
Ian Jackson’s Breathplay technique highlights this strategy,
claiming a number of benets that were examined by Woj t a
et al. (1987) aer a 3-day training period. e study found
a delayed onset of fatigue, lower HR (1.9%), and longer time
to exhaustion (7.2%) during an incremental cycling test to
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exhaustion. In addition, they reported a substantial delay in
the onset of peak CO2 (40%), presentation of RQ = 1 (60 s
later), and anaerobic threshold (120 s). Replication studies are
needed to conrm these distinct results. Positive expiratory
pressure may contribute to these ergogenic eects; Rupp etal.
(2019) reported that forced exhales benet peripheral and
central circulation and oxygenation, especially in hypoxia, that
is probably caused by increased alveolar pressure and resultant
hyperperfusion. When used intermittently, this may allow
marginal increases in pCO2, which enhance the Bohr Eect.
is may be especially relevant for individuals and situations
predisposed to hypocapnia, such as intense exercise and
hyperventilation DB.
A valuable addition to the active exhale is phonation. For
example, the yogic technique Bhramari Pranayama (humming
during the exhale) may be eective in cueing active exhales
since it not only adds additional airway resistance on the
out-breath, but it profoundly increases free nitric oxide (up
to 15-fold at rest; Weitzberg and Lundberg, 2002; Pramanik
etal., 2009). is may enable nasal breathing at higher intensities,
or ease ow limitation. is unconventional aspect has the
additional benet of amusement for the runner (or those around
them). Future work should clarify whether this technique can
reduce respiratory limitations or if it might adversely irritate
laryngeal structures, especially whether there is an ideal frequency
to perform it.
Performing active exhales during running probably requires
attention, instruction, and habituation. Visual modes of
biofeedback may be especially effective if displaying real-
time LOV. A valuable cue may be to “squeeze all the air
out” (Jackson, 2002) or fully “empty” the lungs before the
inhale (Johnston et al., 2018). Other techniques such as
pursed lips breathing could be combined to exploit the
ergogenic effects of positive expiratory pressure, which is
particularly relevant when exercising at high intensity or
altitude (Rupp etal., 2019). A major limitation to studying
or performing the active exhale is its deviation from the
“minimal effort” BP; duty cycle is remarkably constant in
most healthy exercisers (Naranjo et al., 2005), and it may
require substantial cognitive focus to maintain this technique
for long periods of time.
Sync
Locomotor-respiratory coupling, once penned “rhythmic
breathing” by medical doctor Irwin Hance in 1919, has been
the object of much scientic investigation for at least 50 years,
and has wide cultural inuence (Hey etal., 1966; Coates and
Kowalchik, 2013). While bipedalism gives humans exibility
to perform it or not during locomotion, LRC has been observed
at many ratios during running (commonly reported 4:1, 6:1,
8:1, 5:1, and 3:1 steps per breath; Bramble and Lieberman,
2004; Stickford and Stickford, 2014).
FIGURE6 | Respiratory inductance plethysmography (RIP) data from our lab showing normal breathing (dashed line) vs. “active exhale” breathing strategy (solid
line). Note that raw RIP data depict inductance, where signal increases (upward slope) correspond to the exhale phase. Observe the identical breath cycle time, but
shorter relative inhale and longer exhale (smaller breath ratio) as well as lower average lung operating volume throughout the breath cycle (higher signal units
indicating decreased sensor stretch).
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A
B
FIGURE7 | Respiratory inductance plethysmography data from our lab showing locomotor-respiratory coupling (LRC). (A) Phase synchrogram and LRC ratio
plotted during 8 min of running at an instructed LRC ratio 3:4 (steps per inhale:steps per exhale). Note the quantity of steps synchronized with inspiration vs.
expiration. All relative phase shifted 90° for visibility. (B) Subsection of 10 s of raw RIP and hip-mounted accelerometer data while running at 3:4 LRC. Dotted lines
added to emphasize step & ow reversal synchronization.
e passive assistance of step-driven ows may assist VE
increases without elevating the WOB (Daley etal., 2013; Stickford
and Stickford, 2014). Several studies report that LRC decreases
VO2, increases running economy, and reduces dyspnoea (Garlando
et al., 1985; Bernasconi et al., 1995; Takano and Deguchi, 1997;
Homann etal., 2012). Some have speculated that active exhales
may further enhance the exhale phase in combination with LRC,
as concentric contraction of the abdominal and pelvic oor
musculature may optimize visceral compressive forces when
synchronized with step-driven ows (Daley etal., 2013; Wallden,
2017). e “free” work granted by step-driven ows may realize
some of the benets of other strategies, since greater VT enables
slower BR and reduced ow velocity at a given VE. If this eases
ow limitation or EID, then it can also lead to associated positive
psychological outcomes.
As noted in section “respiration as a limiting factor,” LRC
at even ratios (e.g., 4:1 or 6:1) could bea risk factor for side
stitch. However, it might also be used to prevent it. Some
experts recommend exhalation on alternate steps specically
to avoid side stitch (Jackson, 2002; Coates and Kowalchik,
2013). Using an odd-numbered LRC ratio (e.g., 5:1 or 7:1;
Figure 7) causes exhales to occur on opposite footstrikes,
potentially limiting parietal peritoneum irritation. is might
avoid such unpleasant pain and discomfort during running.
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Locomotor-respiratory coupling may be energetically
advantageous not only for its synergistic respiratory advantages,
but also as a mediator of BR and running pace. As described
in the “rate” strategy, given the close correlation between BR
and RPE, and also the known stability SR during running
(Van Oeveren et al., 2019), LRC may be an eective way to
stabilize running pace. LRC ratios of 4:1 and 5:1 for a runner
with a preferred SR around 180 (right and le, steps per
minute) would thus correlate to BR of 45 and 36, respectively.
Dierent LRC ratios could thus be utilized as a “gears” system
corresponding to dierent perceptual and physiological levels
of eort.
Since a primary mechanism of LRC during running appears
to be neurological, purposeful performance of LRC may have
additive psychological benets. e immersive
psychophysiological experience of ow is suggested to occur
with the presence of three conditions: an activity with clear
goals and progress, immediate feedback, and balance between
perceived challenges and competence (Snyder et al., 2020).
Entrainment, such as that of breath to step during LRC, is
likely to enhance ow experience in runners (Bood et al.,
2013; Nijs et al., 2020). Indeed, LRC during running satises
the primary conditions for inducing a trance state: physical
exertion, rhythm, and concentration (Damm etal., 2020). Such
rhythmicity is comforting, sedating, and hypnotic, and rhythmic
stability may lower stress on the nervous system by reducing
cognitive fatigue (Ross et al., 2013). Future studies should
explore LRC and ow phenomenology especially as it pertains
to runners.
e practical application of LRC is not trivial. It is possible
that the additional concentration required to execute LRC
during running negates any physiological benet. Nevertheless,
past studies that found no benet for LRC examined it in
untrained individuals or during unfamiliar tasks (Yonge, 1983;
Maclennan et al., 1994). Perhaps some learning and
accommodation is required to realize ergogenic advantages.
Although many elite runners perform it unconsciously
(Bonsignore et al., 1998; McDermott et al., 2003), limited
evidence is available regarding learning this as a deliberate
breathing strategy, especially in sub-elite runners. A notable
exception instructed LRC via haptic feedback (vibration) timed
with footstrikes on either the exhale or inhale (Valsted et al.,
2017). ey found comparable success when the feedback was
periodic (1 min of instruction followed by 2 min or no instruction)
or self-selected vs. continuous. Nonetheless, some runners found
LRC dicult or the instruction annoying. Attention is needed
in this eld to develop intelligent systems for LRC instruction
and feedback, with auditive modes being understudied. Runners
should probably synchronize breath to step, instead of step to
breath, since deviating from individually preferred SR might
beenergetically disadvantageous or increase injury risk (Adams
et al., 2018; De Ruiter et al., 2019). Smart feedback systems
should consider adapting breath instruction to the current SR
to avoid such eects and to maximize entrainment (Bood etal.,
2013; Van Dyck et al., 2015). Practically, runners should use
an odd ratio (such as 5:1 or 7:1) to capture the benets of
longer exhales and side stitch prevention.
Advanced Breath Tools
ese breathing strategies are labeled “advanced” because they
require either special equipment or are especially dicult to
perform. ey also carry some risk, which should beconsidered
in context vs. the potential benets and population of interest.
Nevertheless, they are included here because they have
demonstrated ergogenic benets and are suitable for application
during running.
Strength
Respiratory muscle training (RMT) has been extensively studied
as an alternative strategy to improve breathing during exercise.
e use of resistive breathing devices such as the Training
Mask® and POWERbreathe® stress the respiratory system,
resulting in positive changes in ventilatory eciency, muscle
recruitment patterns, oxygen delivery, and reduced WOB and
dyspnoea (Karsten etal., 2018; Shei, 2018; Lorca-Santiago etal.,
2020). Readers are directed to these three recent reviews for
a detailed explanation of these mechanisms. While the majority
of studies leverage these methods at rest, several studies have
examined the eects of concurrent resistive breathing during
exercise (Hellyer et al., 2015; Porcari et al., 2016; Barbieri
etal., 2020). Experts in this eld have suggested that concurrent
RMT is underexplored and may, in fact, bethe most eective
means of transferring the benets of RMT to sport performance
(Karsten et al., 2019). Unfortunately, high-quality studies
examining these scenarios are lacking.
e Olin EILOBI techniques were developed by J. Tod Olin
and colleagues as a variant of inspiratory resistance breathing
specically to address EILO (Johnston etal., 2018). ey were
conceived to be used specically during exercise when EILO
occurs to maximize specicity. Although primarily developed
for clinical applications, the self-resisted nature of this technique
may qualify as RMT and besuitable for other settings. Johnston
et al. (2018) report alleviation of EILO symptoms in 66% of
their participants, and we suspect that this could be valuable
for other runners to prevent ow limitation. While this technique
is complex to learn, some components (emptying, abdominal
ribcage focus) may behelpful for improving breathing mechanics.
We found exactly one study that specically tested RMT
methods during running. Granados etal. (2016) reported that
wearing the Training Mask® (Training Mask LLC; Cadillac,
MI, United States) during running at 60% VO2max induced
hypoxaemia without substantial increases in RPE or anxiety.
ey concluded that incorporation of RMT methods part-time
in a training routine is a convenient, time-ecient approach
to benet from RMT. Nevertheless, more studies are needed
to explore long-term use of such methods. If the muscle
recruitment pattern triggered by resisted breathing is not deep
& diaphragmatic, it may not accumulate adequate stimulus to
induce diaphragmatic hypertrophy, or it may habituate DB
(Karsten et al., 2018, 2019). While many respiratory-limited
individuals could benet substantially from RMT’s subsequent
reduction in EID (Bernardi et al., 2015), females appear less
receptive to its benets (Schaer et al., 2019). Finally, while it
could be dangerous to induce additional respiratory distress
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 16 March 2022 | Volume 13 | Article 813243
FIGURE8 | Respiratory inductance plethysmography data from our lab showing normal breathing with one approximate 10 s end-expiratory breath hold. Note the
very long double exhale and brief diaphragm twitch.
during running, the potential ergogenic and psychological
benets suggest that careful protocol development is a key to
making this a viable breathing “strategy” among runners.
Hold
Breath holding (BH, also known as hypoventilation, CO2
tolerance, or air hunger training) garnered recent popularity
due to large performance benets reported in swimming and
techniques popularized by freediving (Holfelder and Becker,
2019). e various eects of hypoxia and hypercapnia have
been rigorously studied (Millet etal., 2016; Girard etal., 2020),
and BH is an accessible method for runners to replicate such
benets. In short, BH is a strong metabolic stressor similar
to hypoxic training that causes accelerated muscle deoxygenation,
hypercapnia, and increased muscle activity during exercise
(Kume etal., 2016; Toubekis etal., 2017). BH protocols lasting
3–5 weeks reported performance gains of 3%–4% related to
two acute mechanisms: increased stroke volume (up to 30%)
and haemoglobin concentration (up to 10%; Woorons et al.,
2016; Lapointe et al., 2020; Woorons et al., 2020). ese
ergogenic benets are likely due to increased le ventricular
stroke volume (Woorons et al., 2021b) and post-BH spleen
contraction (Inoue et al., 2013). Only one study was found
that examined the acute eects of BH during running (Woorons
et al., 2021a). ey reported dramatic central and peripheral
deoxygenation when performing maximal end-expiratory BH
at 60%–100% of maximal aerobic velocity, which could provide
adequate stimulus for the aforementioned training eects if
performed systematically.
Characteristics of elite free-divers suggest that long-term
adaptations to BH include reduced CO2 chemosensitivity and
increased lung volume (Bain etal., 2018; Elia etal., 2019). Repeated
hypercapnia (Bloch-Salisbury etal., 1996) and endurance training
(Katayama et al., 1999) cause long-term adaptations to lower
chemosensitivity (measured as the ventilatory response to a given
absolute workload). Moreover, reduced chemosensitivity during
exercise is a characteristic of trained athletes vs. healthy sedentary
individuals (McConnell and Semple, 1996). While increased pCO2
is responsible for the sensation of “air hunger” (Banzett et al.,
1990), it also allows for enhanced O2 transport via the Bohr
Eect. Decreased CO2 sensitivity, therefore, may allow for enhanced
ventilatory eciency and reduced BR. No studies could be found
directly investigating this mechanism in exercise.
Performing BH during running is best in a safe, supervised
environment with prior familiarization with BH techniques at
rest. e cited studies suggest a work:rest ratio of 1:1.5 or 1:2
(e.g., 10 s hold followed by 20 s running) for 10–12 repetitions.
Notably, participant instructions oen include counting cycles
per breath to “pace” BH duration; this is could facilitate use
of the “hold” tool in the eld. Most protocols recommend
end-expiratory BH since it accelerates hypoxaemia and
hypercapnia; this is done by performing a long exhale, and
then another, down to residual volume (Figure8). End-inspiratory
BH and very slow BR trigger similar levels of hypercapnia,
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 17 March 2022 | Volume 13 | Article 813243
but not of hypoxaemia required to maximize training eects
(Yamamoto etal., 1988; Holfelder and Becker, 2019). Adverse
eects include hypercapnia-induced headaches, lung injury,
syncope, and neurological harm if performed too oen or
aggressively (Matsuo etal., 2014). “Hold” is likely to beintensely
dicult and psychologically unpleasant since it induces large
feelings of air hunger. is may increase the risk for anxiety
and emotional distress in many individuals (von Leupoldt etal.,
2008). Conversely, if it can betolerated long enough to realize
its dramatic performance benets, it may cause benecial
reductions in EID, especially at high intensities. Important
work is being done to assist the execution and safety of BH
with wearable devices (Vinetti et al., 2020), but this has not
extended to BH during running.
PRACTICAL APPLICATIONS
Breathing is Quantiable
e control and expression of breathing pattern is tractibly
understood and every step can be reliably and specically
measured (Del Negro etal., 2018). We suggest measuring and
reporting dyspnoea intensity and discomfort in exercise studies
since these data points assist substantially in identifying
respiratory limitations (Lewthwaite and Jensen, 2021). If a
runner has access to qualied exercise physiology personnel,
cardiopulmonary exercise testing procedures can be especially
useful; we recommend measuring ventilatory thresholds,
tachypnoeic shi onset, VO2max, and approximate representations
of ventilatory eciency (including, but not limited to: running
economy, VE/VCO2 slope, and VT/BR quotient). Voluntary
spirometry measures such as forced expiratory volume and
maximum voluntary ventilation may provide additional insights.
For a detailed description of these laboratory-based procedures,
the reader is directed to recent reviews (Janssens etal., 2013;
Barnes and Kilding, 2015; Laveneziana etal., 2019; Segizbaeva
and Aleksandrova, 2019; Ionescu et al., 2020).
Recent developments in wearable sensors have expanded the
capabilities of respiratory system monitoring outside of the lab.
Non-contact methods such as respiratory inductance
plethysmography and capacitive sensors can provide estimations
of BR, thoraco-lumbar coordination, and the ratio of thoracic-
to-abdominal ribcage breathing (thoraco-lumbar depth) and VT
in the eld (Bernardi et al., 2017; Leutheuser et al., 2017;
Massaroni et al., 2019). Combined FR and step detection in
garments such as the Hexoskin® (Carre Technologies, Canada)
could enable LRC estimation in the eld (Harbour etal., 2021),
although such applications are scarce. When viewed in combination
with performance measures, monitoring BP may therefore reveal
deep individual constraints and context-specic insights that
could be modied or improved with these proposed breath
tools. Alternatively, these BP measurement methods and protocols
could also be used to scientically evaluate the eectiveness of
these strategies during breath retraining interventions.
Using Breath Tools
Although the value and quantity of resources related to breath
retraining at rest is substantial, less is known regarding implementing
breathing strategies during running. While we have provided
some specic recommendations for each strategy, some general
recommendations can bemade. Simple awareness of BP encourages
slow BR and greater depth during running (Schucker etal., 2014;
Schucker and Parrington, 2019). Breathing exercises at rest can
develop awareness of thoraco-lumbar coordination that carries
over into exercise performance (Hagman etal., 2011; Kiesel et al.,
2020). Runners can easily access such exercises in many Yoga
and meditation practices (Ma et al., 2017; Saoji et al., 2019).
A unified theory of breathing strategy prescription would
carefully choose the techniques above specific to the needs
of the runner and scenario (Tab l e 3 ). Wepropose the “Sync”
TABLE3 | Overview of breath tools strategies description and application.
Breath tool Description Primary mechanisms Advantages Disadvantages Applications
Rate ↓ and/or paced BR ↓ relative VD; ANS regulation ↑ perfusion; ↓ dyspnoea;
and pacing assistance
↑ VT at less-compliant lung
volumes, initial air hunger
Novice runners; low-intensity
exercise
Deep ↑ VT via diaphragmatic
engagement
↓ BR; ↑ abdominal ribcage
contribution to VE
↓ WOB, LOV; ↑ postural
control
Difcult to cue Biofeedback; thoracic-
dominant breathers
Nose Constant or intermittent
nasal breathing
↑ NO; ↑ air humidication,
warming, and ltration
↓ airway constriction; ↑
diaphragmatic activation
Difcult at high intensities;
time required for habituation
Low intensity exercise;
extreme climates
Active exhale Longer, forceful exhale
phase with/without
phonation
↓ expiratory ow velocity: ↑
abdominal engagement,
expiratory pressure, and NO
↓ ow limitation, LOV; ↑
perfusion; and ANS
regulation
↓ relative TI; difcult to cue Constant for calming effects;
intermittent during high
intensity or at altitude
Sync Step & breath
synchronization at whole-
integer ratios
Step-driven ows; rhythmic
entrainment
↓ WOB; pacing assistance;
hypnotic
Difcult to learn; even ratios
↑ side stitch
Odd ratios for ↓ side stitch; ↑
breath awareness
Strength Respiratory muscle
resistance training
↑ ventilatory muscle
activation, metabolic stress
↓ WOB, dyspnoea; ↑
diaphragmatic activation
Special equipment needed;
unclear protocols
Low intensity exercise;
training for competition
Hold Intermittent brief end-
expiratory breath holds
↑ biochemical stress, spleen
contraction
↓ chemosensitivity;
cardiovascular performance
Risk of syncope, intense air
hunger unpleasant
Pre-competition; elite sport
Mechanisms, advantages, and disadvantages are based on a mixture of theoretical and empirical evidence as described in the main text. Applications are based on preliminary
subjective ndings of the authors, and do not constitute absolute recommendations. ANS, autonomic nervous system; BR, breathing rate; LOV, lung operating volume; NO, nitric
oxide; TI, inhale time; WOB, work of breathing; VT, tidal volume; and VD, dead space.
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 18 March 2022 | Volume 13 | Article 813243
tool as a near-universal practical recommendation, since it
can be leveraged to manipulate BR, depth, and timing.
However, there is limited knowledge available on how to
learn this skill. Simply counting steps per breath is likely
only suitable for skilled runners with experience in rhythm
(e.g., musicians or dancers). Coates and Kowalchik (2013)
describe a multi-step learning process that may besuitable
for coaches and athletes in field running. This could
becombined with the “gears” system suggested by McKenzie
(2020) to adjust BP to running intensity, or the postural
and verbal cues of Jackson (2002) to maintain active exhales
and proper abdominal engagement. Preliminary data from
our lab suggest that even novice runners can perform this
skill within one session given step-synchronous audio
guidance, although with variable cognitive load.
e eld of Human-Computer Interaction shows immense
promise in learning breathing strategies during running, with
demonstrators such as Strive (Valsted et al., 2017) and
Counterpace® (Constantini et al., 2018) exploiting step-
synchronized feedback modes. Core principles such as multi-
sensory experience, user-centered design, and embodied
interaction can guide the design of future systems to teach
runners how to breathe during running (Wiehr et al., 2017;
Mencarini et al., 2019; van Rheden et al., 2020). We propose
auditive and haptic-based feedback systems that are eld-ready
with real-time learning possibilities regarding the runner’s
current BP and adherence to the desired strategy.
Evidence suggests that breathing strategies such as LRC
might be more eective at relative intensities lesser or greater
than self-selected speeds (Stickford and Stickford, 2014).
Variations away from preferred gait speed tend to increase
the energy cost of transport (Hunter and Smith, 2007); thus,
at metabolically “suboptimal” speeds, breathing strategies have
a greater theoretical benet. At lower intensities, wehypothesize
that most runners could benet from slower, deeper, nose
breathing, which reduces the risk for respiratory limitations.
ese benets may beespecially helpful in extreme environments
(hypoxic, dry, and cold) when the risk for EID is higher (Weiler
et al., 2016). At higher intensities, strategies such as the active
exhale and sync might bemore helpful, as they might improve
gas exchange, optimize trunk kinematics, lower the WOB, and
maintain sustaintable BR. Wespeculate that the greatest benets
would be realized in respiratory-limited runners; this requires
more study.
LIMITATIONS
Although breathing during running is measurable, modiable,
and improvable, several limitations must be addressed before
further study and application. Our review includes a mix of
experimental and theoretical evidence which requires more
direct investigation. Notably, there is a strong hypothesis that
BP manipulation is likely to be ineective or even harmful
when initially employed. If indeed healthy human ventilatory
response is “just right,” and lung structure is not plastic (Dempsey
et al., 2020), then perhaps changing BP will not result in
improved respiratory performance. Ventilatory eciency and
overall BP are considered the result of complexity in a well-
adjusted system (Benchetrit, 2000); any pertubations could
benot only cognitively demanding, but also energetically costly.
On the other hand, studies have shown that positive BP changes
can be habituated over time periods spanning 2–6 months
(Vickery, 2008; Dallam et al., 2018; Bahensky et al., 2019,
2021). It is unknown when exactly BP changes occur and
under what conditions. Some studies have questioned the benet
of internal focus during running, suggesting it leads to technique
breakdown and performance disruption (Beilock et al., 2002;
Hill et al., 2020). us, there may bea switching point when
the mental eort to change BP decreases, perhaps unlocking
resultant benets. Nevertheless, changing BP requires a
suppression of natural reexes and ingrained habits. More work
is needed to clarify if, how, and when BP changes and which
conditions facilitate this.
CONCLUSION
We have synthesized the evidence to demonstrate how
purposeful breathing strategies might improve running via
specic biochemical, biomechanical, and, ultimately,
psychophysiological mechanisms. Breathing strategies have the
potential to signicantly improve ventilatory eciency and
exercise performance but estimates of eect size are scarce
and variable. It is likely that breathing strategies do not acutely
improve exercise performance but have the potential to increase
it 1%–5% over a longer learning period. Respiratory-limited
individuals have the most to gain by using these techniques.
We theorize that the greatest benets are psychological;
increased exercise tolerance or positive psychological states
might increase runners’ exercise habits and long-term training
adherence. Intervention studies are needed to study these
likely transformative benets in vivo, especially over longer
durations and with populations predisposed to
respiratory limitations.
AUTHOR CONTRIBUTIONS
EH and TF: conceptualization. EH: writing—original dra
preparation and visualization. EH, TF, and TS: writing—review
and editing. TF and HS: supervision and funding acquisition.
HS: project administration. All authors contributed to the article
and approved the submitted version.
FUNDING
is work was partly funded by the Austrian Federal Ministry
for Transport, Innovation and Technology, the Austrian Federal
Ministry for Digital and Economic Aairs, and the federal
state of Salzburg under the research program COMET—
Competence Centers for Excellent Technologies—in the project
Digital Motion in Sports, Fitness and Well-being (DiMo).
Harbour et al. Breath Tools: Breathing for Runners
Frontiers in Physiology | www.frontiersin.org 19 March 2022 | Volume 13 | Article 813243
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