Comparação de diferentes intensidades de treinamento muscular inspiratório sobre o controle autonômico cardiovascular de ciclistas: estudo clínico controlado e randomizado
Abreu, Raphael Martins de
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Recently, inspiratory muscle training (IMT) has been widely used by professionals and amateurs’ athletes as a complementary exercise training method, with the aim of improving sports performance. However, there is still no consensus on the IMT prescription protocols in the literature, as well as the effects on cardiovascular autonomic control. It is known that the modulation of breathing has a strong influence on the cardiovascular system and that IMT can be an ally to improve cardiovascular homeostasis with possible effects on physical performance. Study 1 – Aims: To carry out a systematic review to determine if IMT promotes changes in cardiovascular autonomic responses in humans. Methods: The methodology followed the PRISMA statement for reporting systematic review analysis. MEDLINE, PEDro, SCOPUS and PubMed electronic databases were searched from the inception to March 2017. The quality assessment was performed using a PEDro scale. The articles were included if: (1) primary objective was related to the effects of IMT on the cardiovascular autonomic nervous system, and (2) randomized clinical trials and quasi-experimental studies. Exclusion criteria were reviews, short communications, letters, case studies, guidelines, theses, dissertations, qualitative studies, scientific conference abstracts, studies on animals, non-English language articles and articles addressing other breathing techniques. Outcomes evaluated were measures of cardiovascular autonomic control, represented by heart rate variability (HRV) and blood pressure variability (BPV) indexes. Results: The search identified 729 citations and a total of 6 studies were included. The results demonstrated that IMT performed at low intensities can chronically promote an increase in the parasympathetic modulation and/or reduction of sympathetic cardiac modulation in patients with diabetes, hypertension, chronic heart failure and gastroesophageal reflux, when assessed by HRV spectral analysis. However, there was no study which evaluated the effects of IMT on cardiovascular autonomic control assessed by BPV. Conclusion: IMT can promote benefits for cardiac autonomic control, however the heterogeneity of populations associated with different protocols, few studies reported in the literature and the lack of randomized controlled trials make the effects of IMT on cardiovascular autonomic control inconclusive. Study 2 – Aims: To evaluate the chronic effects of different IMT intensities on cardiovascular control in amateur cyclists. Methods: A longitudinal, randomized, controlled blind study was performed on 30 recreational male cyclists undergoing IMT for 11 wk. Participants were randomly allocated into sham-trained group (SHAM, n = 9), trained group at 60% of the maximal inspiratory pressure (MIP60, n = 10), and trained group at critical inspiratory pressure (CIP, n = 11). Electrocardiogram (ECG), finger arterial pressure, and respiratory movements were recorded before (PRE) and after (POST) training at rest in supine position (REST) and during active standing (STAND). From the beat-to-beat series of heart period (HP) and systolic arterial pressure (SAP), we computed time domain markers, frequency domain indexes in the low frequency (LF, 0.04–0.15 Hz) and high frequency (HF, 0.15– 0.4 Hz) bands, an entropy-based complexity index (CI), and baroreflex markers estimated from spontaneous HP-SAP sequences. Results: Compared with SHAM, the positive effect of MIP60 over the HP series led to the HF power increase during REST (PRE: 521.2 ± 447.5 ms2; POST: 1,161 ± 878.9 ms²) and the CI rise during STAND (PRE: 0.82 ± 0.18; POST: 0.97 ± 0.13). Conversely, the negative effect of CIP took the form of the decreased HP mean during STAND (PRE: 791 ± 71 ms; POST: 737 ± 95 ms). No effect of IMT was visible over SAP and baroreflex markers. Conclusion: These findings suggest that moderate-intensity IMT might be beneficial when the goal is to limit cardiac sympathetic hyperactivity at REST and/or in response to STAND. Study 3 – Aims: To evaluate the effect of IMT on cardiorespiratory coupling in amateur cyclists. Methods: Thirty male young healthy cyclists underwent a sham IMT-SHAM (n = 9), an IMT-MIP60 (n = 10) and IMT-CIP (n = 11). The ECG, non-invasive arterial pressure, and thoracic respiratory movement (RM) were PRE and POST at REST and during STAND. The beat-to-beat series of HP and SAP were analyzed with the RM signal via a traditional non-causal approach, such as squared coherence function, and via a causal model-based transfer entropy (TE) approach. Cardiorespiratory coupling was quantified via the HP-RM squared coherence at the respiratory rate (K2HP-RM), the unconditioned TE from RM to HP (TERM→HP) and the TE from RM to HP conditioned on SAP (TERM→HP|SAP). Results: In PRE condition we found that STAND led to a decrease of TERM→HP|SAP. After SHAM and CIP training this tendency was confirmed, while MIP60 inverted it by empowering cardiorespiratory coupling. This behavior was observed in presence of unvaried SAP mean and with usual responses of the baroreflex control and HP mean to STAND. TERM→HP and K2HP-RM were not able to detect the post-training increase of cardiorespiratory coupling strength during STAND, thus suggesting that conditioning out SAP is important for the assessment of cardiorespiratory interactions. Conclusion: Since the usual response of HP mean, SAP mean and baroreflex sensitivity to postural stressor were observed after MIP60 training, we conclude that the post-training increase of cardiorespiratory coupling during STAND in MIP60 group might be the genuine effect of some rearrangements at the level of central respiratory network and its interactions with sympathetic drive and vagal activity. General conclusions: According to this thesis, we conclude that the IMT, when performed at moderate intensity, is able to promote an increase in cardiac parasympathetic modulation at rest, as well as promoting a greater cardiorespiratory coupling to cope with the postural challenge, requiring lower cardiovascular autonomic to deal with orthostatic stress. This response may be beneficial for athletes, considering the constant exposure to physiological stresses to guarantee cardiovascular demand during sport.
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