This work was supported by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology under Contract No. 2021$$-$$0.641.557 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; Contract No. 872574).

This study was granted ethical approval by the Ethics Committee of the University of Salzburg (reference number: GZ 13/2021), and the participants gave their informed consent.
1. Getting started with RunRhythm
<ol>
	<li>Have the participants fill out a prequestionnaire to include demographic information, as well as running, sports, and breathing experience.</li>
	<li>Download the application to a functioning smartphone running Android 8.0 or later. 
	&#8203;NOTE: Closed...

Enhancing Running Performance and Comfort Using RunRhythm

This methodology presents one of the first evidence-based, field-ready digital tools for instructing LRC to runners. Early results suggest that it is effective not only in quickly learning and adhering to LRC but can also be taught over time and retained. While LRC may emerge naturally with increased running experience, novices are less likely to perform it37. Coincidentally, they are especially likely to experience barriers to participation that include poor fitness and respiratory limitations<su...

Running is perhaps the most widely popular form of exercise in part due to its accessibility and range of physical and mental health benefits1,2. Nonetheless, many aspiring runners struggle to start or maintain running habits. This could be due to breathing difficulties, which affect an estimated 20-40% of runners3,4,5. Reducing exercise-induced breathlessness is theoretically possible with the use of specific breathing techniques, but the exact methods, risks, and benefits of doing so are unclear. While improving fitness and/or slow-paced breathing at rest may alleviate respiratory discomfort during exercise6,7, these solutions take weeks or months to realize benefits. Some research has speculated that the direct implementation of breathing techniques during exercise may be more effective at producing acute benefits8, although such investigations are limited. Digital tools that enable individualized instruction might be needed to perform such studies in an effective intervention format.
Locomotor-respiratory coupling (LRC) is a synchronization phenomenon in which breathing and movement are frequency- and/or phase-synchronized. In specific exercises such as running, LRC indicates a whole-integer ratio between breathing (BR) and step rate (SR), as well as phase locking of footstrike to breath onset (i.e., stepping exactly on inspiration). LRC can be expressed volitionally or automatically and may emerge as a learned behavior with exercise training9. Humans naturally synchronize gait with interfering auditory noises (including breathing) perhaps to reduce auditory stimulation, which suggests LRC has evolutionary phenomenology10. Some reports indicate that LRC benefits movement economy and performance, and reduces breathlessness11,12,13,14,15. Some studies reported negligible benefits16,17,18. Any physiological benefits could be related to &#34;step-driven flows&#34;: each footstrike creates downward momentum of the abdominal contents (the &#34;visceral piston&#34;), which when synchronized with the onset of inhale or exhale can be additive to ventilation.
Daley et al.19 measured ventilatory flow and impact forces during treadmill running and speculated that step-driven flows can contribute up to 10-12% to total ventilation. They also reported that it could speed up ventilatory transitions. Other neuromechanical mechanisms may interact with this phenomenon9. While the visceral piston is a result of precise phase coupling, frequency coupling may be independently valuable, especially to the novice runner. BR is closely related to effort across different exercise intensities20. As SR is generally stable and associated with running speed21, LRC may support self-awareness and enable easy pacing of BR and, thus, intensity throughout the run. Finally, LRC at uneven ratios (e.g., 5:1 steps per breath) could help to prevent exercise-related transient abdominal pain (&#34;side stitch&#34;). A majority of runners experience this temporary, but distracting and painful symptom each year22, often leading to their need to stop running. One theory of side stitch etiology is that repeated breathing on the same side footstrike may irritate the phrenic nerve. Thus, it might be avoided by LRC at uneven ratios, which leads to breathing on alternate legs.
Few reports have discussed how to support runners in performing LRC. At least two studies have exhibited biofeedback-style methods14,23 while many utilized simple verbal coaching24,25. While these methods have shown promise in stimulating LRC acutely, they are highly standardized and require specialized equipment. As such, they are likely not suitable for field applications, nor are they accessible to most runners. Regardless, sound guidance is a natural choice since humans intuitively synchronize movement to predictable auditory events (metronome or music)26. Applications should thus carefully consider sound tempo and structure in the context of motor learning. While simple, constant-tempo audio is predictable and efficacious for stimulating entrainment, it contradicts the naturally nonlinear behavior of step and respiratory rhythms in healthy runners27,28. Changing a runner&#39;s preferred SR might reduce running economy 29 or could modify injury risk factors30. Thus, sound instructions should be continuously adapted in real time to follow the runner&#39;s SR31.
We recently introduced a concept that integrates the above recommendations into a simple, user-friendly, custom smartphone application32. The first iteration allows for the selection of a single LRC ratio to be instructed throughout the run. The phone&#39;s stock SR algorithm is leveraged to provide real-time SR information to the application. Then, step-synchronized sounds are produced indicating when the runner should exhale and inhale: a high-pitched tone for steps during inhalation, and a low-pitched tone during expiration. Prescribed LRC ratios were derived from a control visit without breathing instruction. We found a large increase in LRC from 26.3 &#177; 10.7% to 69.9 &#177; 20.0% of the run with the application instruction during outdoor submaximal running. Limitations noted with the protocol and application include extensive familiarization required, limited sample size, and constant sound instruction. Hence, a new version of this application was developed to improve user experience and enable more broad testing and experimentation in field exercise. This application is titled RunRhythm since its intended purpose is to support runners in finding and maintaining a rhythm during running. It will be referred to hereafter as the app.
The purpose of this report is to introduce a new digital tool and methodological approach that enables intuitive and field-ready LRC guidance for research studies involving experienced or aspiring runners. The app is a research-grade application in beta testing for Android devices. The core functionalities of the application are SR detection and LRC guidance. When running is detected, breathing sounds are created according to the selected settings in the user interface. The application calculates SR from the phone accelerometer using one of two algorithms: either the factory SR algorithm implemented by the device manufacturer or a custom SR algorithm created by the application manufacturer. Both algorithms produce a constant livestream of SR, which is then smoothed on a moving average according to an adaptive window. The window size is dynamic to balance reactivity and outlier smoothing. The result is a constantly updated value of live SR.
Since the app calculates SR from the device movement, the placement of the phone on the body is of utmost importance. Most stock SR algorithms are position-agnostic, and therefore, can be placed on any part of the body during running to produce accurate SR values. The custom algorithm implemented here also behaves as such. However, a firm placement closer to the center of mass may improve the stability of the SR detection, and as a result, the sound quality produced by the app. Pilot testing shows that placements with 1-dimensional oscillation (i.e., vertically up and down such as in a chest pocket or waist pack) may perform better than those with 2-dimensional movement (i.e., swinging such as in a thigh pocket or armband).
SR data are fed to an integrated sound engine (see the Table of Materials). Step sounds are played only if the system detects SR &#62; 0. When the SR is above a preset threshold (determined in backend settings [protocol section 3.6]; i.e., 120), the application understands that the user is running and triggers the start of breathing guidance sounds. Then, this live SR value is used to set the tempo of the step and breathing guidance sounds as long as a &#34;running&#34; SR value is maintained. When SR &#62; threshold, the sounds generated match the tempo of SR by default. The exception is when the backend setting &#34;sound tempo&#34; is altered (determined in backend settings [protocol section 3.5]). For example, with a selected upper limit of 180, even if the runner begins running at a higher SR of 185, the sound tempo will not exceed 180. When they lower their SR down to 175, the sounds will lower to 175, continuously adjusting within the preset limits. As described in protocol step 3.5, these sliders allow the user or researcher to set limits on the minimum and maximum sound tempo (bpm). The app allows different LRC ratios (steps:breath) to be selected before or changed during the run. The number of steps per breath phase can be changed from 2 to 9; i.e., a 2:3 ratio reflects 2 steps per inhale and 3 steps per exhale.
Different &#34;soundscapes&#34; were designed to provide a pleasant audio experience to more runners with diverse music tastes based on user feedback and early in-lab experiments33. They have different sounds mapped to the real-time step rate, the instructed breathing phases, and background ambient noise. Step sounds are simple beats that play at the tempo of each footstrike (i.e., right and left steps). Breath sounds integrate several sonic elements and play at a much slower tempo depending on the chosen LRC ratio. The soundscapes available are tribal: organic and instrumental with sharp breathing transitions and step sounds; calming: light and ocean-inspired with smooth transitions and step sounds; energizing: electronic and driving with sharp transitions and step sounds; minimal: simple and smooth with only breath sounds (no step sounds).
The voiceover feature adds simple voice cues corresponding to best-practice research findings regarding LRC familiarization. It provides a series of instructions at the start of the run and then every 5 min after that. First, it states the selected LRC ratio. Then, it states the intended breathing phase in sync with the sound cues for the first three breath cycles. Then it reminds the user, &#34;find your step rate, and step to the beat.&#34; For each run, a pre and post run questionnaire is integrated to add subjective feeling data to each run. The subjective vitality short scale34 asks a single item regarding the runner&#39;s feeling from 0 to 10. A 0-10 rating of the fatigue scale asks the user to rate their current state of fatigue. Finally, a 0-10 scale rates the degree of breathlessness currently experienced. All of these scales are asked before and after each run. Only after the run, the user is asked to rate their experience of the run&#39;s intensity (i.e., light, medium, high, intervals). Users can change the LRC ratio and temporality during the run using the on-screen interface or headphone controls. This may help users feel agency during the run and enables the exploration of personal suitability. In addition, the ratio may need to be quickly changed in response to running events (e.g., hills, fatigue). This protocol includes a description of how to run with the app and later recommendations for its use within research protocols of various types (i.e., indoor, outdoor, interventional, cross-sectional).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Android smartphone</td>
			<td>Samsung or Google</td>
			<td></td>
			<td>Minimum Android 8.0 required for application functionality</td>
		</tr>
		<tr>
			<td>FMOD engine&#160;</td>
			<td>Firelight Technologies Pty Ltd</td>
			<td></td>
			<td>Sound engine</td>
		</tr>
		<tr>
			<td>Hexoskin smart shirt&#160;</td>
			<td>Carr&#233; Technologies</td>
			<td></td>
			<td>Wearable sensor shirt</td>
		</tr>
		<tr>
			<td>RunRhythm application for Android&#160;</td>
			<td>adidas GmbH and abios GmbH</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

custom smartphone application to guide locomotor-respiratory coupling in the field using step-adaptive breathing sounds 

While running is amongst the most popular activities for competition and leisure, an estimated 20-40% of runners may suffer from respiratory limitations. Some of these runners may benefit from breathing techniques to improve performance or alleviate respiratory discomfort. One such technique is locomotor-respiratory coupling (LRC), a frequency and phase synchronization of breath to step. Studies have demonstrated that LRC may benefit ventilatory efficiency via "step-driven flows," and some experts have argued it could be used for pacing exercise or increasing positive emotional states. Nevertheless, it may be difficult to perform without coaching or guidance. Here we propose RunRhythm, a custom smartphone application to deliver step-synchronized sound guidance for LRC. This concept builds on previous evidence that sound guidance can be effective and integrates features to maximize adherence and individualization. Preliminary results show that this application is a promising and efficacious method suitable for research on LRC in field exercise. Recommendations for use and further development are discussed to further develop this concept for the benefit of a wider population.

Author Spotlight: Exploring Breathing Techniques and Digital Solutions for Enhancing Running Performance

Custom Smartphone Application to Guide Locomotor-Respiratory Coupling in the Field Using Step-Adaptive Breathing Sounds 

The app is the second iteration of this application designed for the purpose of supporting LRC and delivering an audio breathing guidance experience. Numerous pilot studies and one journal publication have been performed supporting its efficacy and confirming positive user experience. In a cross-sectional study investigating the acute effects of LRC instruction (mentioned in the Introduction), it was found that running with guidance greatly increased LRC in 17 novice runners32. For example, one pa...

Locomotor-respiratory coupling (LRC) is potentially advantageous for runners but may be difficult to perform. We introduce a custom solution implemented on a smartphone to individualize and guide runners toward LRC.

While running is amongst the most popular activities for competition and leisure, an estimated 20-40% of runners may suffer from respiratory limitations. ...

custom-smartphone-application-to-guide-locomotor-respiratory-coupling

Custom Smartphone Application to Guide Locomotor-Respiratory Coupling in the Field Using Step-Adaptive Breathing Sounds

Abstract