Acute Effects of Different Types of Resistance Training on Cardiac Autonomic Modulation in COPD

Population

For this study, data from subjects of both sexes diagnosed with COPD were analyzed according to the Global Initiative for Chronic Obstructive Lung Disease,² clinically stable without exacerbations or changes in medications for at least 30 d and without participating in any type of physical activity and/or pulmonary rehabilitation in the previous 6 months.

The study did not include volunteers who presented any of the following characteristics: current smokers, the use of drugs that influence autonomic activity of the heart, people with alcoholism, people with known metabolic and/or endocrine disorders, home oxygen therapy, pathological conditions that impede the practice of physical training, unstable COPD, and participation in any other systematized exercise programs. Nonattendance in the training protocol for personal reasons, respiratory exacerbations during the training process, and time series of RR intervals that did not present >95% sinus beats were considered exclusion criteria for the study.

A total of 81 subjects without clinical and respiratory exacerbations with COPD were eligible for the study, and 48 subjects were included. The subjects were randomly allocated to the following 3 groups by drawing lots: conventional training (n = 16), elastic tube training (n = 18), and elastic band training (n = 14). Anonymity was preserved by allocating a number to each subject before the draw. Random assignment was achieved by an independent person who drew the sealed numbers before the start of the intervention. The participants were blinded to the study hypotheses. During the analyses, some volunteers were excluded due to errors in heart rate variability capture, so the final composition of the groups was as follows: conventional training (n = 13; degree II = 5, degree III = 6, degree IV = 2); elastic tube training (n = 10; degree II = 6, degree III = 4); and elastic band training (n = 11; degree II = 3, degree III = 6, degree IV = 2). The sample loss flowchart is presented in Figure 1.

• Download figure
• Open in new tab
• Download powerpoint

Fig. 1.

Flow chart. Subjects excluded from final analysis due to mistakes in heart rate variability capture.

The volunteers were informed of the objectives and procedures of this study and, after agreeing, signed an informed consent form. All the procedures used were approved by the research ethics committee of the Universidade Estadual Paulista under protocol number CAAE: 46065315.7.0000.5402 and complied with Resolution 196/96 of the National Health Council. The clinical trial was registered in the Brazilian Registry of Clinical Trials under protocol number RBR-6v9sjj.

Study Design

This was a prospective experimental study started in March 2015 and completed in July 2016. Data collection took place in the Center for Studies and Assistance in Physiotherapy and Rehabilitation of the Faculty of Science and Technology – FCT/UNESP, in the morning to avoid variation in circadian cycle. To reduce the anxiety of the volunteers during the protocols, only a small number of people circulated through the site. Before performing the protocol, the volunteers were instructed to eat a light meal and dress in appropriate and comfortable clothes for the physical effort. In addition, they were instructed not to ingest coffee, black tea, or chocolate. After being instructed on these guidelines, the volunteers gave their written consent and were submitted to the procedures described below.

The collection was performed to verify the autonomic cardiac modulation recovery against the acute performance of 3 different resistance training protocols. On reaching the collection site, the following variables were verified: age, weight, stature, systolic and diastolic blood pressure, oxygen saturation, subjective effort scale (Borg), and breathing frequency. Information on the volunteer was identified through the medical history with questions regarding any severe cardiovascular-, neuromuscular-, skeletal-, or lung-associated diseases, and any history of diseases and current clinical state (medications currently prescribed, and the presence of diabetes, arterial hypertension, and smoking risk factors). Anthropometry was performed to characterize the population and to investigate the presence of excess weight and obesity.¹⁸ Spirometry was performed to confirm the diagnosis of COPD and classify the severity of the air flow.¹⁹

A heart rate monitor (model RS800cx; Polar Electro Oy, Kempele, Finland) was then placed on the volunteers to record the pulse rate throughout the protocol, while they remained at rest in a sitting position for 20 min. The participants were instructed not to talk, make sudden movements, or sleep during this period. At the end of the rest period, the volunteers performed resistance training according to their previously randomized group: conventional, elastic bands, and elastic tubes. Immediately after the end of the training, the volunteers were again instructed to remain in a seated position for 60 min, which thus initiated the heart rate variability recovery period. The heart rate variability analysis protocol was established based on studies that analyzed post-exercise recovery.^20,21

Training Protocols

The exercise session lasted 60 min, and, at the beginning and end of the session, the vital signs were verified and overall stretches were performed, such as of the trunk musculature and the upper and lower limbs. For the 3 protocols, exercises were performed for shoulder flexion, elbow flexion, shoulder abduction, knee extension, and knee flexion, with 2 sets of 15 repetitions and a passive rest interval of 1–2 min between sets. For the resistance training, the load used for each subject was defined according to the maximum repetition test.

For the maximum repetitions test, the subject was required to perform 15 maximum repetitions; the number of repetitions used for the initial test. Therefore, the test was valid when performed with a load (tubes, bands, or machines) that allowed the execution of 15 maximum repetitions. The test was considered invalid if the subject did not complete the range of motion and/or compensations. Both the test and the training were tolerated to execute up to 2 maximum repetitions. The participants performed up to 3 trials with a 2-min interval between attempts, and verbal stimulation was given to the subjects throughout the trials.

For the conventional resistance training, bodybuilding equipment (Ipiranga, São Paulo, Brazil) was used, being a simple pulley for the upper limbs and a flexor and extensor chair for the lower limbs. Resistance training with elastic tubes was performed by using Lemgruber latex elastic tubes, of different diameters and thicknesses, in addition to metal rings, bundles (plastic cable) for fixing the elastic tubes to the rings, and a specific chair with hooks for fixing the tubes and handles for the upper limbs. For the resistance training with elastic bands, a variety of Theraband elastic bands (Theraband®, Akron, Ohio) were used (yellow [1.3-kg resistance with 100% elongation percentage], red [1.8 kg], green [2.3 kg], blue [3.2 kg], and black [4.4 kg]). Determination of the length of the elastic tubes and elastic bands was performed according to the distance from the upper or lower limb of each subject to the hook (fixed point) on the chair. Thus, the length differed from one subject to another according to the recommendations proposed by Ramos et al.⁸

Three senior physical therapists who specialized in pulmonary rehabilitation and/or musculoskeletal rehabilitation (FFL, BSAS and APCFF) and one physical therapist (FZ) were responsible for the assessment and management of the exercise sessions in the three intervention groups. The physical therapists provided close supervision during the sessions for all training protocols. The researcher who performed the data analyses was blinded to group allocation throughout the study.

Analysis of Heart Rate Variability

Heart rate variability analysis was performed from the series of RR intervals captured by using the Polar Electro Oy and linear methods, analyzed in the time and frequency domains.¹³ For this analysis, the time series of RR intervals was initially subjected to digital filtering by using Polar Pro Trainer software, complemented by manual filtering for elimination of premature ectopic beats and artifacts. Only series with >95% sinus beats were included in the study.²² Visual analysis of the time series was performed to verify the absence of ectopic artifacts or beats that could interfere with the heart rate variability analysis.

For the analysis of heart rate variability in the time domain, the root-mean square of differences between adjacent normal RR intervals in a time interval (rMSSD) and standard deviation of all normal RR intervals (SDNN)¹³ were used which reflect respectively vagal modulation and global variability. In the frequency domain, spectral components of low frequency (LF) (global variability) and high frequency (HF) (vagal modulation), in ms,² and normalized units (nu), and the relationship between them (LF/HF) were used.¹³ The frequency bands used for each component were LF = 0.04–0.15 Hz and HF = 0.15–0.40 Hz. The spectral analysis was calculated by using fast Fourier transform.¹³ All heart rate variability indices were processed by using Kubios HRV software (Biosignal Analysis and Medical Imaging Group, Kuopio, Finland), version 2.0.²³

The series of RR intervals were analyzed at the following moments: M1 (5 min at rest), M2 (5 min initial recovery), M3 (5th-10th min of recovery), M4 (15th-20th min of recovery), M5 (25th-30th min of recovery), M6 (40th-45th min of recovery), and M7 (55th-60th min of recovery), which contained 256 consecutive RR intervals in these intervals.¹²

Statistical Analysis

For analysis of the data of the population profile, the descriptive statistical method was used, and the results are presented as mean ± SD, median, minimum and maximum numbers, and CI. The normality of the data was evaluated by using the Shapiro-Wilks test. For comparison of the characteristics of the sample, one-way analysis of variance (ANOVA) was used with the Tukey honest significant difference test (age, weight, and body mass index) and the Kruskal-Wallis test with Dunn test (height).

The comparisons of heart rate variability indices among the protocols (conventional vs elastic tube vs elastic band) and moments (rest vs recovery times) were performed by using the technique of ANOVA for models of repeated measurements in the 2-factor scheme (mixed ANOVA). Repeated measurement data were checked for breach of sphericity by using the Mauchly test, and the Greenhouse-Geisser correction was used when sphericity was violated.

For analysis of the moments (rest vs recovery times), the Bonferroni test was used for parametric or the Dunnett test for non-parametric distribution and the analysis of the different moments between the groups was carried out by using one-way ANOVA or the Kruskal-Wallis test. Statistical significance was set at 5% for all analyzes.

The sample was calculated based on the study by Santos et al,²⁴ in which an index of instantaneous recording of beat-to-beat variability (SD1) (reflecting vagal modulation) was selected. The difference to be detected was 7.97 ms and the SD was 6.45 ms. The significance level for the sample calculation was 5%, with a test power of 80% and a 2-tailed hypothesis test. The value obtained from the sample calculation was 10 subjects per group.