Efeito agudo de diferentes intensidades de exercício muscular inspiratório na variabilidade da frequência cardíaca no período de recuperação pós esforço em jovens saudáveis

Abstract

Introduction: It is known that acutely in inspiratory muscle exercise (IME) there are adjustments in the autonomic nervous system. However, there is inconsistency in the scientific literature regarding the autonomic response during the post-exertion recovery period when faced with different resistive loads used in EMI. Thus, it is essential to develop controlled and randomized studies that explore and compare the autonomic response at different IMT session intensities. Objective: Evaluate the cardiac autonomic response in healthy adults submitted to different EMI loads through heart rate variability (HRV) in post-exertion recovery. Methods: Men, sedentary, performed four sessions of EMI: Sham, IME 30%, IME 40% and IME 60% of maximum inspiratory pressure (PImax). The Sham session, IME 30% and IME 40% were performed with 8 sets of 2 minutes per 1 minute interval. The 60% IME session was performed with 4 sets of 2 minutes per 1 minute interval. In all sessions, the respiratory rate was maintained between 12 to 15 ipm. MIP was assessed by manovacuometry (MVD300). Pulse wave signals were recorded by digital infrared photoplethysmography (FinometerPro). All variables were measured simultaneously for 10 minutes at rest and during the recovery period (15, 30, 45 and 60 minutes). The signals in the form of pulse intervals (interval between beats -IEB) were extracted and the time series of normal intervals were transferred to the Kubios HRV Analysis software, version 3.1.0. In the time domain, the variables SDNN, RMSSD, NN50 and pNN50 were evaluated. In the frequency domain, the following variables were evaluated: LF and HF in absolute and normalized units, and the LF/HF ratio. Normality was tested using the Shapiro-Wilk test and for data that did not present a normal distribution, we chose to use the natural logarithm to use parametric tests. The ANOVA test for repeated measures was used to analyze the f values of the acute effect of the intervention on HRV, comparing exercise sessions (Sham vs IME 40% and IME 30% vs IME 60%) between the pre- and postexercise periods (baseline vs. recovery) followed by Bonferroni post-hoc when necessary. All tests were performed using SPSS version 20.0.0. It was considered as significant p<0.05. Results: Fifteen men (25±1 years, BMI 23.5±0.8 kg/m2) were evaluated. At both Sham and EMI 40%PImax intensities, we observed a decrease in HR and an increase in the IEB during the entire recovery period compared to baseline, similarly between intensities (HR time: p= 0.0001 and group: p=0.878; IEB time: p= 0.0001 and group: p=0.607). In addition, RMSSD and pNN50 had significantly higher values compared to baseline (time: p=0.013 and p=0.008, respectively), but similarly between protocols (group: p=0.458 and p=0.513, respectively). There were no changes or differences between protocols in the variables of the HRV frequency domain. In the comparison IME 30% vs. IME 60%, we observed a decrease in HR and an increase in IEB during the entire recovery period compared to baseline in a similar way between the intensities (HR time: p=0.0001 and group: p=0.162; IEB time: p=0, 0001 and group: p=0.196) In the RMSSD variables (time: p=0.02; group: p=0.07 ηp2= 0.216), NN50 (time: p=0.02; group: p=0.11 ηp2 = 0.171) and pNN50 (time: p=0.001; group: p=0.09 ηp2= 0.188) were statistically lower in recovery compared to baseline, but similar between sessions. Although there is no significance, in the frequency domain, the HF (ms²) showed a positive behavior in the effect size (Group: p= 0.09 and ηp2= 0.183). Conclusion: We can conclude that regardless of the resistive load used in each IMT session, there is an increase in the parasympathetic cardiac autonomic modulation indices in the post-session recovery period.