Rodrigo Luis Cavalcante Silva1; Elliott Hall2; Alex Souto Maior3
1 Graduate candidate of the Master’s Program in Rehabilitation Science at UNISUAM (Augusto Motta University Center), Brazil.
2 PhD
candidate, School of Sport and Exercise Sciences at Liverpool John Moores
University.
3 PhD,Professor
of the Master’s and Doctorate Program in Rehabilitation Science at
UNISUAM (Augusto Motta University Center), Brazil
Corresponding Author:
Alex SoutoMaior, PhD.
Augusto Motta University Center - UNISUAM Postgraduate Program in Rehabilitation Sciences Praça das Nações, 34 - Bonsucesso
ZIP Code 21041010 - Rio de Janeiro, RJ – Brasil
ABSTRACT
Running Title: Inspiratory muscle training and soccer players
Conflicts of interest: We have nothing to declare.
Background: Inspiratory muscle training (IMT) is an important method of attenuating both respiratory and peripheral effort perceptions, consequently improving neuromuscular performance and resulting in greater improvements in exercise capacity than with exercise training alone.
Objective: The aim of this study was to investigate the effects of IMT on exercise tolerance, repeated sprint ability (RSA) performance, maximal inspiratory pressure (MIP) and peak inspiratory flow (PIF) in a cohort of professional male soccer players.
Methods: Twenty-two healthy male professional soccer players (18.3 ± 1.4 years; 174.5
±
6.1 cm; 70.5 kg ± 4.6 kg; body fat 10.1 ± 4.2 %) from a club participating in the
Brazilian
first division soccer league
participated in this study. IMT consisted of 15 and
30 self-paced inspiratory breaths (each to 50% maximal static inspiratory pressure [P0]) in the 1-and 2-week intervention period, respectively. IMT was performed prior to soccer training (1 sets.d-1; 6 d.wk-1) with repeated sprint ability (RSA) assessed pre- and post the 2-week period of IMT.
Results: Statistical analyses identified a significant (p<0.001) decrease in sprint time post-IMT. Additionally, RSAbest, RSAmean, total sprint time and percentage of RSA performance decrement (RSA % dec) also showed significant decreases (p<0.0001) post- IMT.Additional measures including MIP and PIF werealso significantly elevated (p<0.0002)following the 2-week period of IMT.
Conclusion: In
conclusion, our results raise two important issues. Firstly, IMT demonstrated enhanced inspiratory
muscle strength in professional soccer players.
Secondly, this increase in inspiratory
muscle efficiency led to a decrease in sprint time
and
improved exercise tolerance. We recommend that a standard training protocol be
developed and tested in an experimental and control group with a large representative sample.
Key-words: Inspiratory muscle training; repeated sprint ability test; soccer players.
INTRODUCTION
Soccer matches are characterized by high-speed running while dribbling, passing, kicking or throwing the ball, with players required to make quick, precise movements, actions requiring multi-directional deceleration and acceleration, in addition to rapid changes of direction, all placing high demands on several physical components (Spencer et al., 2005; Maior et al., 2017). Execution of high-intensity, intermittent endurance and repeated-sprints actions incur high demands upon both aerobic and anaerobic metabolism, therefore professional soccer players must have the capacity to cope with these demands in order to maintain optimal performance (Spencer et al., 2005).
Increased ventilatory demands during exercise stimulate increased neural drive to the respiratory muscles, consequently promoting an increase in mechanical power developed by the inspiratory muscles (Butler et al., 2014). Thus, the development of new methods of training applied to performance could potentially improve neuromuscular responses and respiratory capacity, augmenting overall exercise tolerance. Inspiratory muscle training (IMT) is method of training which applies additional load to the diaphragm and accessory inspiratory muscles with the aim of enhancing their strength and endurance (Butler et al., 2014; Verges et al., 2007; Callegaro et al., 2011; Guy et al., 2014). Studies report IMT as a useful method to attenuate both respiratory and peripheral effort perceptions, consequently improving neuromuscular performance and resulting in greater improvements in exercise capacity than with exercise training alone (Archiza et al., 2018; Guy et al., 2014). Greater improvements are evident in less fit individuals and in those participating in sports of longer durations (Illi et al., 2012).
Peripheral muscle aerobic adaptations may affect repeated sprint ability (RSA) performance, which is a crucial fitness component for soccer players due to its involvement in many decisive activities during a soccer match, such as sprinting, accelerations, decelerations, and changes of direction (Archiza et al., 2018; Guy et al., 2014). A recent study showed that IMT aided the supply of oxygen and blood to limb muscles during sprint performance in professional female soccer players (Archiza et al., 2018). However, some studies suggest IMT may be beneficial for soccer players to improve their maximal inspiratory pressure but not the ability to tolerate high intensity exercise (Guy et al., 2014; Ozmen et al., 2017). Results from the existing scientific literature are contradictory, and there is apaucity of evidence relating to IMT and RSA for high performance in male soccer players. Thus, the aim of this study was to investigate the effects of IMT on exercise tolerance, repeated sprint ability (RSA), maximal inspiratory pressure (MIP) and peak inspiratory flow (PIF) in professional male soccer players. It was hypothesized that inspiratory muscle fatigue in the respiratory musculature, exercise tolerance, and sprint time would improve following IMT.
METHODS
Subjects and anthropometric measurements
The study included 22 healthymaleprofessional soccer players (18.3 ± 1.4 years; 174.5 ± 6.1 cm; 70.5 kg ± 4.6 kg; body fat 10.1 ± 4.2 %) from a club of the Brazilian first division soccer league participating in national competitions organized by the Brazilian Soccer Confederation (CBF). The players’ training frequency was 6.2 ± 0.7 days/week, with training programs consisting of jumps, contesting possession, sprints, resistance training, accelerations and decelerations. Exclusion criteria included: 1) smoking history during the previous 3 months, 2) presence of any cardiovascular or metabolic disease, 3) systemic hypertension (≥ 140/90 mmHg or use of antihypertensive medication), 4) use of anabolic steroids, drugs or medication with the potential to impact physical performance (self-reported), or 5) recent musculoskeletal injury, 6) symptoms of pain in any region of the body. The study was approved by the local institutional Ethics Committee for Human Experiments and was performed in accordance with ethical standards in sport and exercise science research (CAE:76189817.0.0000.5235). All data collection was carried out at the beginning of training sessions during preseason.
Body composition was assessed via bioelectrical impedance analysis using a device with built-in electrodesfor the hands and feet (InBody 720). Subjects wore their normal indoor clothing and were instructed to stand barefoot in an upright position with both feet on two separate electrodes on the surface of the machine, with arms abducted and hands gripping two electrodes fixed within the surface of two handles. All analyses were performed after an 8-hour fast. All biometric measures were undertaken in an acclimatized room (21o C). No clinical problems occurred during the study.
Repeated sprint ability test (RSA test)
The RSA test comprised 6 bouts of 2 × 20-m sprints which included one change of direction (180° turn) followed by 20 seconds of rest between efforts. All sprints were timed, with subjects starting 50 cm before the first photocell beam (Brower Timing System, Salt Lake City, 174 UT, USA; accuracy of 0.01 s). The photocell beam was fixed at a height of 1 m and for each sprint, subjects were instructed to sprint until they had crossed the 20 m line, before turning and sprinting backto cross the first photocell beam (Gharbi et al., 2014). Verbal encouragement was provided at all times and no subjects were excluded through injury during the experimental procedure. The following variables were derived from all RSA efforts: RSA best: best RSA performance time; RSA mean : mean RSA performance time; Total time sprint (TTS): the sum of all RSA sprint times; RSA % dec : the percentage of RSA performance decrement; The RSA dec (%) was calculated using the following formula:
Inspiratory muscle assessment and training
Respiratory muscle strength was tested through a single point of maximal pressure development at the mouth using portable handheld devices (POWER Breathe KH1 INSPIRATORY METER; Gaiam). Three trials were performed for each, with the best result recorded for analysis. Inspiratory muscle assessments were used to measure maximal inspiratory pressure (MIP) and peak inspiratory flow (PIF). The testing procedure for MIP assessment in the present study strictly followed the American Thoracic Society (ATS)/European Respiratory Society (ERS) guidelines for the testing of volitional respiratory muscle strength (American Thoracic Society/European Respiratory Society, 2002). In accordance with these guidelines, nose clips were used at all times, subjects were seated during each assessment and verbal encouragement was provided for subjects to perform maximal MIP and PIF efforts.
After baseline assessment (pre-training) all subjects were instructed to use the handheld pressure threshold breathing device (POWER breathe International Ltd, Warwickshire, United Kingdom) in the morning before soccer training (1 sets.d-1; 6 d.wk-1). The IMT protocol consisted of 15 and 30 self-paced inspiratory breaths (each to 50% maximal static inspiratory pressure [P0]) in the 1-and 2-week intervention periods, respectively. Post-training testing occurred 2 weeks after baseline and involved an identical testing battery.
Statistical Analysis
All data are presented as mean ± SD. Statistical analysis was initially performed using the Shapiro–Wilk normality test and the homocedasticity test (Bartlett criterion). Comparisons between RSA sets pre- and post-training were performed by two-way ANOVA with Bonferroni post-hoc tests. A Student’s t-test was used to assess differences within conditions (pre vs. post-IMT) for variables of the RSA test, MIP, and PIF. Additionally, the magnitude of effect sizes (ES; the difference between pretest and posttest scores divided by the pretest SD) was calculated from the scale proposed by Rhea (Rhea, 2004), for RSA best, RSA mean, RSA % dec, TTS, SPEED (m/s) and SPEED (km/h). The level of significance for all statistical comparisons was set at p<0.05 using GraphPad® (Prism 6.0, San Diego, CA, USA) software.
Results
Two-way ANOVA (Figure 1) demonstrated a significant decrease (p<0.001) in sprint times for all sets when comparing pre- to post- IMT. Likewise, Table 1 shows significant decreases in sprint times and the percentage decrement in RSA performance post-training. In addition, sprint speed increased significantly at post-training when compared to pre-training (P<0.0001). The ES statistics pre- and post-training presentlarge values for RSA best, RSA mean, TTS, and SPEED (m/s and km/h) with a moderate effect for RSA % dec (table 1).
Figure 1.Mean ± SD values from pre- and post-inspiratory muscle training during six sets of repeated sprints in professional soccer players. IMT= Inspiratory muscle training; *p<0.001 – pre vs. post-IMT.
Table 1: Performance and respiratory variables of professional soccer players pre- and post-IMT (n = 22).
Inspiratory muscle data from the pre- and post-training are presented in Figure 2. A significantly improved PIF was evident post-training (∆% = 19.1%; p=0.0002; Figure
2A) alongside significantly improved MIP (∆% = 15.4%; Figure 2B) after the 2-week period of IMT.
Figure 2. Mean ± SD values from pre- and after the 2-week period of IMT in professional soccer players. PIF= peak inspiratory flow; MIP= maximal inspiratory pressure; IMT= Inspiratory muscle training; *p<0.0002 – pre vs. post-IMT.
DISCUSSION
IMT has been investigated by multiple studies, with inspiratory muscles benefits demonstrated following periods training (Verges et al., 2007; Callegaro et al., 2011; Guy et al., 2014; Archiza et al., 2018). However, few studies have evaluated the effect of IMT on improvements in sprint time and exercise tolerance in professional male soccer players. The results of the present study show significantly increased inspiratory muscle strength (represented by MIP and PIF), exercise tolerance, and sprint speed (m/s and km/h) during post-intervention RSA testing. Furthermore, we observed a decrease in TTS, RSA best, RSA mean, and RSA % dec post-IMT. According to our results and previous studies (IMT = 6 week, 5 days per week and 30 inhalation repetitions), we suggest that IMT has the capacity to attenuate inspiratory muscle metaboreflex and blood lactate accumulation,and to improve oxygenation and blood supply to peripheral muscles during high-intensity exercise in this population (Archiza et al., 2018). In addition, IMT appears to contribute toward increases in inspiratory muscle strength, improvements in cumulative recovery during repeated sprint performance, and enhancements exercise tolerance (Butler et al., 2014; Verges et al., 2007; Callegaro et al., 2011; Guy et al., 2014). Furthermore, chronic IMT over 4-weeks (30 inspiratory efforts at 50% maximal static inspiratory pressure [P0] per set, 2 sets.d-1, 6 d.wk-1) before a 6-week interval training program, and an acute IM warm-up regimen (2 sets of 30 inspiratory efforts at 40% [P0]) before each workout, have the potential to augment exercise tolerance toan interval program by approximately 27% (Tong et al., 2010).
MIP is a surrogate measurement for assessing respiratory capacity and inspiratory muscle strength (Butler et al., 2014). Previous studies in younger individuals observed an increase of 14% and 28% in MIP, suggesting neural adaptation, between 1 and 2 weeks post-IMT (Butler et al., 2014; Aznar-Lain et al., 2007). However, it appears that up to 11 weeks of IMTin elite rowers contributes to a 33.9% increase in MIP, but IMT > 11 weeks resulted in a 9.5% decrease in MIP (Klusiewicz et al., 2008). Recreational soccer players practicing IMT twice daily (morning and evening) for 30 self-paced inspiratory breaths across the 6-week intervention period showed a 13.4% increase in MIP post-intervention, associated with improved exercise tolerance and reduced blood lactate, but with no significant change in sprint time (Guy et al., 2014). A recent study observed increases of of 22.5% in MIP and improvements in RSA best performance time after 6 weeks of IMT in elite female soccer players (Archiza et al., 2018). Our results show a15.4% increase in MIP after 2 weeks of IMT, in combination with decreased total sprint times and increases in sprint speed (m/s and km/h). The combinations of these results suggest IMT may have the capacity to increase the strength of the inspiratory musculature and improve sprint performance in male and female professional soccer players, but not in recreational players. It is also noteworthy that the IMT performed for 2-6 weeks resulted in the most beneficial effects.
The potential mechanisms by which IMT contributes to skeletal muscle performance are multifactorial and complex, potentially resulting from altered muscle perfusion, substrate transfer, and immunological system adaptation. Thus, IMT elicits a hypertrophic response in the inspiratory muscles, which may contribute to increases in MIP, total lung capacity and spare the O2 and blood- flow requirements of ventilation and offset the metaboreflex, thereby increasing limb O2 delivery (Bailey et al., 2010; Downey et al., 2007). In addition, the reduction in expired minute ventilation during maximal-intensity exercise after IMT might also reduce the metabolic requirements of the inspiratory muscles, result in reduced VO2 slow-component amplitude and delay the recruitment of low-efficiency fibers (Bailey et al., 2010). Some studies highlight the importance of IMT to the immunological system through the concomitant increase of plasma interleukin-1β (IL-1 β) and reduction of plasma interleukin-6 (IL-6) responses to increased respiratory muscle exertion (Mills et al., 2013; Mills et al., 2014). These immunological responses may contribute to glucose uptake in the contracting myocytes, stimulating myogenesis, lipolysis and satellite cell proliferation (Carey et al., 2006; Wolsk et al., 2010; Kharraz et al., 2013). In addition, trunk rotation during changes of direction during the RSA test may contribute greater mechanical effort from parasternal intercostal muscle fibers compared to costal diaphragm fibers (Butler et al., 2014). However, the suggestion that IMT mightin fact limit exercise performance by the development of exercise-induced arterial hypoxemia and from fatiguing levels of respiratory muscle effort should be noted (Chilf et al., 2016).
STUDY LIMITATIONS
Limitations of our investigation include the participants’ age range and the fact we studied a cohort of well-trained athletes, both of which could influence both performance and inspiratory muscle strength capacity. Whilst our sample was homogenous, the sample size was not substantial enough to provide different inspiratory muscle conditioning programmers to separate sub-groups of professional soccer players, in order to quantify the effects of different protocols on the variables measured. Future investigations should assess tissue oxygenation using near-infrared spectroscopy, coupled with surface electromyography, to further explain the mechanisms underpinning alterations in inspiratory muscle strength following IMT.
CONCLUSION
In conclusion, the combinations of our results contribute to two key findings. Firstly, enhanced inspiratory muscle strength was observed in professional male soccer players after 2 weeks of IMT. Secondly, the increased efficiency of inspiratory musculature contributed to decreases in sprint time and improvements intolerance to intense exercise. However, there is a need for better understanding of the types and models (i.e., fixed vs. variable) of IMT loads used, as well as replicative data to confirm the outcomes of IMT.
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