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Study design
This is a randomized clinical trial (prospectively registered in ClinicalTrials.gov ID NCT05538520) that followed the recommendations of CONSORT [25]. The randomization process was performed by a blinded researcher who was not part of the study team. Random numbers were generated by online software (randomization.com), which distributed participants into two groups of equal size (1:1). The same researcher who performed the randomization process sealed the opaque envelopes containing the group that each participant would be allocated and handed it to the main researcher. Subsequently, blind participants individually received the envelope numbered according to their entry into the study and broke the seal to verify which would be their allocation group. In this study, because it is an intervention with exercise, it was not possible to blind the participants and the therapist responsible for the intervention.
Sample size
The sample calculation was performed using the Bioestat 5.3 program (Instituto Mamirauá, Amazonas, Brazil), taking into account the muscle strength values of the lower limbs available in a previous study [26]. In this case, the postintervention mean and standard deviation for muscle strength of the lower limb evaluated by the 10-RM test (kg) in the Leg Press between the group “dynamic stretching combined with resistance training” (337.1 ± 37.29) vs. the group “resistance training alone” (374.3 ± 32.07) was used, with test power at 80% and alpha value at 0.05, which generated the need for at least 16 participants in each group, already considering an additional 15%, to avoid a decrease in statistical power in case of sample loss.
Participants
The sample consisted of 32 female participants who were insufficiently active and apparently healthy; the participants were subdivided into two groups of equal size (Table 1). Recruitment was carried out in the city of Ibaiti, state of Paraná, Brazil, through poster advertisements posted in public places and advertisements on social media. The ethical norms established in the Declaration of Helsinki (1975, revised in 1983) were followed, and the study was approved by the Human Research Ethics Committee of the Universidade Estadual do Norte do Paraná, Brazil, before its beginning under the opinion number 5.548.126. All participants signed an informed consent form.
Inclusion criteria were as follows: a) being aged between 18 and 45 years old; (b) having a body mass index (BMI) between 18.5 and 24.9 kg/m2 (normoweight individuals); (c) not participating in physical exercise programs for at least six months; (d) being healthy, according to the Physical Activity Readiness Questionnaire (PAR-Q) [27]; (e) not reporting any known medical restrictions on physical exercise; (f) having no history of injury, trauma or illness in the last six months; (g) not having undergone previous surgery in the last six months; (h) not having cardiorespiratory and neurological musculoskeletal disorders; (i) not being under the action of drugs that cause muscle relaxation or that may inhibit muscle tonic action; (j) not using dietary supplements or anabolic steroids; (k) not being on a calorie-restricted diet; and (l) being insufficiently physically active according to the IPAC short version [28].
Exclusion criteria were: (a) starting the practice of any type of physical exercise during the study period; (b) refusal to participate in assessment or intervention procedures; (c) emergence of injuries or other intercurrence during the intervention period; (d) withdrawal from participating in the study.
Assessment procedures
Motor tests chosen as indicators of strength, vertical jump height, muscular endurance and flexibility were administered. These tests were administered at two times: (1) in the week before the interventions (preintervention assessment) and (2) in the week following the end of the interventions (postintervention assessment). Prior to the motor tests, all participants underwent a 10-minute warm-up on a cycle ergometer (60 rpm, 80 W). The same evaluator performed all motor tests, respecting a five-minute interval between each test, and the tests were performed in the same order of execution for all participants pre- and postintervention.
10-RM knee extensors
The muscle strength of the knee extensors was assessed using elastic bands (Thera Band GmbH, Hadamar, Germany) as previously described [29]. Three elastic bands (black, silver and gold) were used, which, depending on the number of layers and initial length, allowed fifteen different resistances, represented in kg, known from the percentage of displacement (Table 2) [29, 30]. The participants were positioned on the seat of a standardized chair and were tested on their dominant side. For the evaluation, the elastic band was attached immediately proximal to the lateral malleolus of the participants and on a backrest positioned behind the chair (~ 40 cm below the knee and ~ 160 cm behind this articulation). Participants were asked to perform the maximum number of repetitions with an elastic band of intermediate resistance (black). If they were able to perform 11 repetitions, an elastic band of greater resistance was selected for the next attempt. This procedure was repeated (maximum of 5 attempts with 5 min of rest between attempts) until the participant was able to perform 10 or fewer repetitions. The following prediction equation was then used: 1-RM = resistance in kg/(1.0278 – [0.0278 × reps]) [31]. Therefore, a 10-RM test was performed dynamically and with consecutive repetitions, but the values were subsequently adjusted to represent the 1-RM according to the procedure indicated in the validation study of this test [29]. This test demonstrated high validity against peak concentric exchange measured by an isokinetic dynamometer (r = 0.93) and test-retest reliability (ICC ≥ 0.98, CV [%] ≤ 3.44) [29].
Vertical jump
The countermovement jump test (sargent jump) was used to measure vertical jump height in cm. The objective of the test was to verify the highest height at the peak of the vertical jump, measuring two points marked on the wall by the participant himself, with the fingers of one of the hands dirty with chalk: (1) the initial measurement was obtained with the participant standing and erect, keeping the dominant arm extended parallel and above the head, marking the wall with chalk as high as possible, keeping the soles of the feet fully in contact with the floor; (2) the second measurement was obtained with the participant touching the wall with the fingers of the hand as high as possible during the peak of the vertical jump. Three attempts were allowed with intervals of two minutes between them, and the highest value in centimeters among the three attempts was recorded. This test demonstrated high validity (r = 0.99) and test-retest reliability (r = 0.99) [32].
Handgrip
To determine handgrip strength, a digital hydraulic dynamometer (Saehan SH1001) was used. The participant had to be in a sitting position, with an erect spine and knees flexed at 90°. The dominant upper limb tested was positioned with the shoulder in adduction and neutral rotation, wrist in neutral position and elbow at a 90° angle. Participants were instructed to perform three repetitions of maximum contraction maintained for five seconds, with a 60-second interval between each repetition. The maximum voluntary contraction was determined by the highest value obtained in kg from the three attempts. This instrument demonstrated excellent validity (r ≥ 0.97) and test-retest reliability (r ≥ 0.98) [33].
1-min sit-ups
To evaluate abdominal muscle endurance, the 1-min sit-ups test was performed. In dorsal decubitus, the participant had to flex her knees, keeping the soles of her feet in contact with the ground, with her feet separated at a distance identical to the width of her hips. Her arms were crossed over her chest. The evaluator rested his hands on the participant’s feet to keep them in permanent contact with the ground. At the signal emitted by the evaluator, the participant raised the trunk until the anterior face of the forearms came into contact with the thighs, returning shortly afterwards to the initial position, with the contact of at least the anterior half of the scapulae on the ground. These movements had to be repeated over the course of one minute. The result was recorded as the number of correct repetitions performed in one minute. This test demonstrated high test-retest reliability (ICC = 0.91) [34].
Sorensen
To evaluate the muscular endurance of the trunk extensors, the Sorensen test was used. The participant had to be in ventral decubitus with the lower extremity of the body affixed to a stretcher, with the region of the anterior superior iliac crest demarcating the final point of support. Before starting the test, the participant was allowed to rest the upper extremity of the body, located outside the stretcher, on a chair. The test started when the participant raised her torso and remained without leaning on the chair, with her arms crossed in front of her chest, and kept her torso parallel to the ground for as long as possible. The test was interrupted when the participant could no longer sustain the position or was warned more than 2 times to align the trunk and maintain the neutral position. The test results were recorded within seconds. This test demonstrated moderate to high test-retest reliability in healthy adults (ICC ≥ 0.76 ≤ 0.97) [35].
Sit-and-reach
To assess the flexibility of the posterior region of the body, the sit-and-reach test with the Wells bench was used. The participant had to sit facing the bench, with bare feet, knees extended and the soles of the feet in contact with the bench. The participant extended her arms over the surface of the bench, with her hands positioned one over the other, coinciding with the tip of her middle fingers. Trunk forward flexion was requested, keeping the arms extended and the hand touching the measurement scale, trying to reach the greatest possible distance in a slow movement and without jerks. For the purpose of the final result of the test, the greatest distance in centimeters achieved in the series of three attempts was computed. This test demonstrated high test-retest reliability (r = 0.98) [36].
Pilates protocol
The intervention consisted of 24 sessions of Pilates exercises performed three times a week for 8 weeks. Each session lasted 50 min in the Traditional Pilates (TP) group and 40 min in the Non-Traditional Pilates (NTP) group. The sessions took place on Mondays, Wednesdays and Fridays in the afternoon. The equipment used to perform the exercises was as follows: Step Chair, Cadillac Trapezio, Reformer Universal and Ladder Barrel (ISP, Brazil).
The TP and NTP protocols were identical, except for the fact that TP performed stretching exercises at the beginning of the sessions and NTP did not (Table 3). TP performed a total of 20 exercises, while NTP performed 15 exercises. Participants were instructed to follow the principles of Pilates (center, control, concentration, fluidity, precision and breathing). The Pilates protocol containing the images of the exercises is available as a supplementary file.
The exercises were performed in a series of ten repetitions, with a one-minute rest interval between exercises. For load progression, the resistance of the springs in each piece of equipment was replaced (changing the position of the springs in the equipment or replacing the springs with others of greater resistance) every 15 days, as the evolution of the strength of the participants was observed. The number of sets, repetitions and rest intervals were always maintained.
To determine the level of effort and consequently the evolution of loads, verbal descriptions were used according to the OMNI scale [37]: extremely easy (OMNI 0–1), easy (OMNI 2–3), reasonably easy (OMNI 4–5), fairly difficult (OMNI 6–7), difficult (OMNI 8–9) and extremely difficult (OMNI 10). The effort level maintained during the sessions was between 8 and 9 (difficult). In all sessions, the participants were asked about possible adverse events resulting from the interventions. Any reported adverse events were noted on the individual form used to record the training.
Data analysis
Data normality was verified using the Shapiro‒Wilk test. To verify whether the groups presented differences at the beginning of the study, Student’s t test for independent samples was used. Intragroup alterations pre and postintervention were analyzed using Student’s t test for dependent samples for parametric data and the Wilcoxon test for nonparametric data. To verify differences between groups, analysis of covariance (ANCOVA) was performed, with postintervention data used as the dependent variable and preintervention data as the covariate. The homogeneity of variances was determined by Levene’s test. For nonparametric data, differences between groups at postintervention were calculated using the Mann‒Whitney U test.
Within-group and between-group effect sizes were calculated using Cohen’s d, which was considered trivial (0-0.19), small (0.20–0.49), medium (0.50–0.79) or large (≥ 0.80) [38]. Data were analyzed per protocol and by intention-to-treat analysis (ITT). As the results did not change, we present only the ITT data, including all randomized individuals (for missing postintervention data, preintervention data were imputed). To compare each adverse event reported between groups, the chi-square test was used. To determine the difference between groups in terms of the likelihood of developing any adverse events, odds ratio (OR) was calculated. For all tests, the significance level adopted was P < 0.05. Analyses were processed in SPSS 22.0 (Chicago, Illinois), except for effect size calculations (Cohen’s d), which were processed in GPower 3.1 (Franz Faul, Universität Kiel, Germany).
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