Load monitoring on Pilates training: a study protocol for a randomized clinical trial

A parallel randomized clinical trial is being conducted at the Center for Studies and Assistance in Physiotherapy and Rehabilitation of the Universidade Estadual Paulista (FCT/UNESP), Presidente Prudente, São Paulo, Brazil. The trial was registered at ClinicalTrials.gov (NCT03232866) and approved by the research ethics committee of FCT/UNESP (protocol 061942/2017). The study protocol follows the SPIRIT 2013 checklist (Standard Protocol Items: Recommendations for International Trials) [12] (Additional file 3) and TIDieR (Template for Intervention Description and Replication) [13], indicating that information about and the quality of the reports of the interventions are well described [14]. Prior to participation, the volunteers received oral and written instructions and signed a consent form agreeing to participate in the study. All personal data will remain confidential. Note that, although very unlikely, participants who suffer any kind of injury as a result of participation will receive a free medical evaluation and physiotherapy treatment.

Participants were divided into two groups: the Pilates group and the control group. Participants in the Pilates group underwent 12 weeks of Pilates exercises for three times a week, for a total of 36 sessions. Each session lasted for approximately 60 min. During this training period, participants were required to pass through the three levels of the Pilates method: basic, intermediate, and advanced. The control group were asked to maintain their current level of daily activities without taking any type of exercise training. A flowchart for the study and group composition are shown in Fig. 1.

A total of 54 healthy male volunteers were recruited from the local university (UNESP) through pamphlets, online media, personal invitations, telephone calls, and SMS messages. These procedures were recommended by Treweek et al. [15] as strategies to improve participant recruitment.

The inclusion criteria were: male; 18 to 35 years of age; healthy (self-report); not having practiced Pilates prior to the study; not a smoker or an alcoholic; not presenting with a metabolic, cardiac, or endocrine disorder; with no arrhythmia; not using drugs that influence the autonomic modulation of the heart; and without physical limitations such as musculoskeletal, inflammatory, or neurological diseases that would prevent them from doing Pilates.

Individuals who suffered from a musculoskeletal injury during training, those who attended less than 85% of training sessions, those who failed to progress between the three levels of the Pilates method, those who were unable to respond adequately to subjective scales, and those with errors in the captured RR intervals were excluded from the study. Participants were instructed to maintain their daily dietary routine, to abstain from taking anti-inflammatory medications and analgesics, and not to perform any other type of exercise during the intervention period. These requests were reinforced during the training period and monitored by self-report [16].

Prior to randomization, baseline data were collected from participants who meet the eligibility criteria and had signed the informed consent form. To maintain the blinding, randomization by group (Pilates group or control group) was performed by another researcher not involved in the recruitment using a computer-generated randomization schedule.

The exercises are shown in Additional file 1. The exercise sequences were divided in different ways to make the training more varied and to avoid dropouts (Additional file 2). The exercise schedule was produced by us based on an extensive bibliographical survey of Pilates exercises and their progression. We considered the degree of difficulty of each exercise as well as the dependence between volume and intensity.

Quantification of the internal training load was evaluated in each training session with the three monitoring tools: SPE [6], HR [18], and HRV [18]. For the monitoring to be considered successful, two of the three monitoring tools must yield significant results. In addition, the correlation between SPE and HR should be moderate to high so that they can be used in clinical practice as low cost and easily applicable tools.

The SPE consists of a scale proposed by Borg where the participants choose the descriptor and number that best represents their psychophysiological stress in the training session [6]. It is a scale from 6 to 20 points, where 6 means “no effort” and 20 means “maximum effort.” To avoid biased responses, the question was standardized as: “From 6 to 20 points, how do you rate your perception of effort now?” All responses were recorded in individual records. The participants had previously been made familiar with the scale [6].

Prior to the sessions, participants were told how to estimate their SPE. It was explained to them that during the exercises it was necessary to perceive how much effort they were using so that every 5 minutes during a session they could estimate the SPE according to their individual perception for how exhausting the exercises were.

In addition, 15 min after the end of each session, the participants estimated the SPE again [6]. This final SPE was multiplied by the duration of the session in minutes, and the product represents the internal load in arbitrary units. The intensity of the session was classified into three zones according to the Borg scale used by Moreira et al. [19].

Quantification of the internal load training using the HR was performed using the TRIMP method. This evaluates the volume and intensity of the session through specific scores in each training zone, as proposed by Edwards [18, 20].

In addition to these methods for monitoring the training load, HRV was analyzed. The weekly mean of rMSSD (rMSSDmean) expressed in milliseconds and the weekly intra-individual coefficient of variation of rMSSD (rMSSDcv) expressed as a percentage will be used [21, 22]. These indices will be transformed to logarithms to mitigate outliers and simplify the analysis.

The HRV will be calculated from the series of RR intervals captured by the cardiofrequency monitor using linear methods. It will be analyzed in the time and frequency domains. A Poincaré plot will be used. All HRV indices will be calculated by Kubios HRV software version 3.1.0.

The RR interval series was recorded before and after the 12 weeks of training. There were 1000 RR intervals in each data set. In addition, daily tracking of each session will be analyzed. Stretches of 256 consecutive RR intervals were recorded every 5 minutes. In both analyses, the most stable stretches were used to avoid any bias in the analysis and data interpretation [5]. The time series of RR intervals will undergo moderate digital filtering using Kubios, supplemented by manual filtering to eliminate premature ectopic beats and artifacts. Only series with more than 95% of sinus beats will be included in the final analysis [23].

The time domain (rMSSD and standard deviation of all RR intervals) [24], frequency (low and high) [23, 25, 26], and Poincaré plot (standard deviation of data from x = y and standard deviation of data from the line orthogonal to x = y that passes through the mean value of the data) [23, 27, 28] HRV indices will be used for the analyses before and after the 12 weeks of training. Only the time domain indices and the Poincaré plot will be used for daily tracking.

HR [23], respiratory rate measurements [29], and oxygen saturation [30] were captured. Blood pressure [31] was measured. A subjective pain assessment was obtained through a visual analog pain scale [32, 33]. Volunteers were asked to fill out a psychometric questionnaire [17] before and after the training period, as well as before all training sessions.

All these outcomes were collected in the initial evaluation and in the final evaluation after the 12 weeks of training, in addition to before and after each Pilates session. Table 1 lists outcome collection time points.

Baseline outcomes were collected prior to randomization. The final evaluation was conducted by trained evaluators blinded to group allocation. In addition, data were collected throughout the Pilates training period by independent evaluators. The study statistician will also be blinded. In this study, it was not possible to blind either the participants or the therapist who administered the Pilates sessions.

The sample calculation was carried out based on Barbosa et al. [34] with the rMSSD index. The clinically relevant difference was 19,02 ms and the standard deviation 23,94 ms. For a two-tailed hypothesis test, the significance level for the sample calculation was 5% and the power of the test was 80%. The sample size was calculated to be 25 per group. To account for withdrawals, the sample size was increased by 10% to give 27 volunteers per group.

Descriptive statistics will be used, and the results presented as means, errors, standard deviations, percentages, and absolute numbers. The normality of the data will be evaluated through a Shapiro–Wilk test. In the comparison of the population profile and the cardiorespiratory, autonomic, and psychometric measures in the initial and final evaluations, the paired t test will be used for normal data or the Wilcoxon test for non-normal data. In the comparison between the groups, the unpaired t test or Mann–Whitney test will be used depending on the normality of the data, with the significance level set at p < 0.05. Differences based on magnitudes (Δ = final value – initial value) will also be calculated [35, 36] to verify the differences between the initial and final time points.

To analyze weekly differences in training loads using the SPE, HR, and HRV indices (ln rMSSDweekly and ln rMSSDcv) over the 12-week study duration, magnitude-based inferences will be calculated [36].

For ln rMSSDweekly, the smallest worthwhile change was set at 3% [37]. For SPE, HR, and ln rMSSDcv, the smallest worthwhile change is defined as 0.2 × between-subject standard deviation. The quantitative chances to find differences in the variables to be tested will be assessed qualitatively as follows: <1% almost certainly not, 1–5% very unlikely, 5–25% unlikely, 25–75% possible, 75–95% likely, 95–99% very likely, and >99% certain. If the chances of having higher and lower results are both >5%, the true difference was assessed as nuclear [35]. The magnitude of the effect size will be qualitatively interpreted using the following thresholds: <0.2 trivial, 0.2–0.6 small, 0.6–1.2 moderate, 1.2–2.0 large, 2.0–4.0 very large, and >4.0 nearly perfect [35].

To determine the correlations (dose–response) between ln rMSSD, HR, and SPE, Pearson’s or Spearman’s correlation will be used according to the normality of the data. The threshold used to evaluate the correlations quantitatively will be based on Hopkins [35] using the following criteria: <0.1 trivial, 0.1–0.3 small, 0.3–0.5 moderate, 0.5–0.7 large, 0.7–0.9 very large, and >0.9 almost perfect.

The cutoff points for load increments with the HRV indices and SPE were obtained from the receiver operating characteristic curve. The sensitivity, specificity, positive predictive value, and negative predictive value for each level of the Pilates method will also be calculated. The area under the curve will be considered significant when values ≥0.65 are obtained [38]. In addition, a comparison will be made between the receiver operating characteristic curves of each HRV index to detect the most representative for determining the internal training load of the Pilates method.

The statistical analysis will be carried out with the Statistical Package for the Social Sciences, version 15.0 (SPSS Inc., Chicago, IL) and MedCalc Software bvba, version 14.10.2 (Oostende, Belgium). All data will be entered into the software twice. All participants included in the initial assessment will be considered under the intention-to-treat approach in which the worst outcome obtained by the study group will be selected to ensure the power of the data analysis.

The registration number is NCT03232866. The study start date was 1 September 2018. The primary completion date was May 2019. Patient recruitment is completed. The data were collected in June 2019. Altogether, 58 volunteers were assessed for eligibility, of whom four were excluded, so that 54 participants were randomized. All participants are attending ongoing study groups. The study completion date is December 2019.