AUTHOR=Nicolò Andrea , Massaroni Carlo , Passfield Louis 

TITLE=Respiratory Frequency during Exercise: The Neglected Physiological Measure

JOURNAL=Frontiers in Physiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00922

DOI=10.3389/fphys.2017.00922

ISSN=1664-042X

ABSTRACT=<p>The use of wearable sensor technology for athlete training monitoring is growing exponentially, but some important measures and related wearable devices have received little attention so far. Respiratory frequency (<italic>f</italic><sub>R</sub>), for example, is emerging as a valuable measurement for training monitoring. Despite the availability of unobtrusive wearable devices measuring <italic>f</italic><sub>R</sub> with relatively good accuracy, <italic>f</italic><sub>R</sub> is not commonly monitored during training. Yet <italic>f</italic><sub>R</sub> is currently measured as a vital sign by multiparameter wearable devices in the military field, clinical settings, and occupational activities. When these devices have been used during exercise, <italic>f</italic><sub>R</sub> was used for limited applications like the estimation of the ventilatory threshold. However, more information can be gained from <italic>f</italic><sub>R</sub>. Unlike heart rate, <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub>, and blood lactate, <italic>f</italic><sub>R</sub> is strongly associated with perceived exertion during a variety of exercise paradigms, and under several experimental interventions affecting performance like muscle fatigue, glycogen depletion, heat exposure and hypoxia. This suggests that <italic>f</italic><sub>R</sub> is a strong marker of physical effort. Furthermore, unlike other physiological variables, <italic>f</italic><sub>R</sub> responds rapidly to variations in workload during high-intensity interval training (HIIT), with potential important implications for many sporting activities. This Perspective article aims to (i) present scientific evidence supporting the relevance of <italic>f</italic><sub>R</sub> for training monitoring; (ii) critically revise possible methodologies to measure <italic>f</italic><sub>R</sub> and the accuracy of currently available respiratory wearables; (iii) provide preliminary indication on how to analyze <italic>f</italic><sub>R</sub> data. This viewpoint is expected to advance the field of training monitoring and stimulate directions for future development of sports wearables.</p>