Respiratory Frequency as a Marker of Physical Effort During High-Intensity Interval Training in Soccer Players

Abstract

Purpose: Variables currently used in soccer training monitoring fail to represent the physiological demand of the player during movements like accelerations, decelerations, and directional changes performed at high intensity. We tested the hypothesis that respiratory frequency (fR) is a marker of physical effort during soccer-related high-intensity exercise. Methods: A total of 12 male soccer players performed a preliminary intermittent incremental test and 2 shuttle-run high-intensity interval training (HIIT) protocols, in separate visits. The 2 HIIT protocols consisted of 12 repetitions over 9 minutes and differed in the work-to-recovery ratio (15:30 vs 30:15 s). Work rate was self-paced by participants to achieve the longest possible total distance in each HIIT protocol. Results: Work-phase average metabolic power was higher (P < .001) in the 15:30-second protocol (31.7 [3.0] W·kg−1) compared with the 30:15-second protocol (22.8 [2.0] W·kg−1). Unlike heart rate and oxygen uptake, fR showed a fast response to the work–recovery alternation during both HIIT protocols, resembling changes in metabolic power even at supramaximal intensities. Large correlations (P < .001) were observed between fR and rating of perceived exertion during both 15:30-second (r = .87) and 30:15-second protocols (r = .85). Conclusions: Our findings suggest that fR is a good marker of physical effort during shuttle-run HIIT in soccer players. These findings have implications for monitoring training in soccer and other team sports.

The Importance of Respiratory Rate Monitoring: From Healthcare to Sport and Exercise

“…Conversely, other physiological variables such as oxygen uptake, blood lactate, and heart rate may not be associated with perceived exertion and exercise tolerance in at least some of the aforementioned conditions [10,[12][13][14]16,21]. Furthermore, unlike other physiological variables, f R shows a rapid response at exercise onset and offset [12,14,15,231], with important implications for monitoring intermittent-based activities like soccer and other team sports [15]. As such, f R provides invaluable insight into physical effort, and its time course reflects exercise-induced fatigue in different populations [10,[12][13][14][15][16]18,21].…”

“…As recently reviewed by Nicolò et al [14], f R is one of the most important variables to be monitored during sport and exercise. It is closely associated with perceived exertion during exercise protocols with different durations, formats (e.g., continuous and intermittent) and modalities (e.g., cycling and running) [10,12,13,15,16,230], at least during high-intensity exercise [11]. Furthermore, it is associated with exercise tolerance under a variety of experimental conditions, including hyperthermia, cold, hypoxia, muscle damage, muscle fatigue, dietary-induced glycogen depletion, respiratory muscle fatigue, and prior exercise [14,20,21].…”

“…Furthermore, unlike other physiological variables, f R shows a rapid response at exercise onset and offset [12,14,15,231], with important implications for monitoring intermittent-based activities like soccer and other team sports [15]. As such, f R provides invaluable insight into physical effort, and its time course reflects exercise-induced fatigue in different populations [10,[12][13][14][15][16]18,21].…”

“…This is interesting considering that central command is also the primary regulator of perceived exertion [22,232,233], thus explaining the close association between these two variables [11][12][13][14]22]. In fact, f R has several advantages over perceived exertion monitoring as it is an objective physiological variable that can be monitored continuously and in real-time, and provides detailed information on how physical effort is distributed over a given training session or more [14,15]. When maximal effort is exerted, f R reaches peak values of about 50 breaths/min in the general population [234] and of about 60 breaths/min in athletes [12,13] ranging from 20-29 years old, but higher f R peak values can also be observed [15,235].…”

“…Furthermore, f R responds to a variety of stressors, including emotional stress, cognitive load, cold, and hyperthermia [6][7][8][9]. During exercise, f R is a good marker of physical effort and fatigue [10][11][12][13][14][15][16][17] and is associated with exercise tolerance in different populations [14,18]. Recent advances in the understanding of the control of ventilation corroborate the importance of monitoring f R and explain why f R but not tidal volume (V T ) (the other component of minute ventilation) responds to a variety of non-metabolic stressors [7,11,12,17,[19][20][21][22].…”