The effects of Pilates vs. aerobic training on cardiorespiratory fitness, isokinetic muscular strength, body composition, and functional tasks outcomes for individuals who are overweight/obese: a clinical trial

Participants

Female and male adults ranging from 30 to 66 years of age who are overweight or obese were invited to participate in the study. The medical school where the study was performed included almost 5,500 staff members and 6,000 students, and the volunteers were drawn from this community. Inclusion criteria were: present BMI higher than 25 kg/m² and be classified as insufficiently active or sedentary according to International Physical Activity Questionnaire (IPAQ) (Craig et al., 2003). Exclusion criteria were present neurological, cognitive, orthopedic and respiratory disease. Subjects presenting cardiovascular or endocrine disease which were not controlled were also excluded. In addition, subjects who presented cardiovascular events during the exercise tests were also excluded. From July 2013 until December 2014, 115 volunteers performed a medical exam taking into account a medical history questionnaire and a medical physical exam. The follow-up for the first group of participants began in September 2013 and the last group ended in July 2015. Forty-six volunteers were excluded after the application of the inclusion and the exclusion criteria; the reasons for exclusion were: presence of cardiovascular disease (n = 45) and presence of arrhythmia (n = 1).

Of the 69 remaining participants, 25 were allocated to the control group, since the intervention protocols (Pilates or walking sessions) occurred during their working hours. The remaining 44 participants were randomly assigned by drawing their names written on pieces of paper from an opaque envelope and placing them in one of two experimental groups (Pilates or aerobic). During the entire intervention protocol, 9 volunteers dropped out of participation. One participant from the aerobic group withdrew due to knee pain. Eight participants from the control group did not attend the retest protocol; two of them reported back pain, two had undergone emergency surgeries (appendix and fracture), and four cited personal reasons. A flow diagram illustrating the study design and volunteer participation is presented in Fig. 1.

Comorbidities were detected during the medical exam, through self-reporting, with the following description: three participants with type 2 diabetes mellitus (Pilates group); 14 participants with hypertension (nine in the Pilates group, two in the aerobic group, and three in the control group); 18 participants with dyslipidemia (10 in the Pilates group, three in the aerobic group, and five in the control group), and 11 participants with hypothyroidism (7 in the Pilates group, two in the aerobic group, and two in the control group). All these presented comorbidities were under treatment and were controlled.

Subjects were informed of the study purpose and protocols, and all provided written informed consent before taking part in the study. The Human Research Ethics Committee of the University approved all experimental procedures (Approval number: 197.451) that complied with the principles outlined in the Declaration of Helsinki. This clinical trial was registered with the Brazilian Registry of Clinical Essays (ReBEC, Registro Brasileiro de Ensaios Clínicos—http://www.ensaiosclinicos.gov.br) and its registration code is RBR-7QNSH6. The authors confirm that all ongoing and related trials for this intervention were duly registered. It is noteworthy that the target sample size described in the clinical trial’s registration was 20 participants for each group. To ensure that 20 participants would conclude the study, more than 20 subjects were initially recruited, and after withdrawals, 17 participants from the control group, 21 from the aerobic group and 22 from the Pilates group participated through to the conclusion of the study.

The age of the participants who completed all phases of experimental protocol (n = 60) was 55.9 ± 6.6yrs (Pilates group), 42.4 ± 7.0yrs (aerobic group) and 45.5 ± 9.3yrs (control group). One-way ANOVA (analysis of variance) was used to verify differences in age and height before intervention. The one way ANOVA revealed that Pilates group was older than the other groups [F(2, 57) = 18.521, p < 0.01]. The height was not significantly different between Pilates (161 ± 6 cm), Aerobic (161 ± 8 cm) or Control groups (162 ± 7) [F(2, 57) = 0.25089, p = 0.78].

Study design

This study was a variation of the classic RCT for experimental groups. According to West et al. (2008), classical RCTs rely on the strong adherence of volunteers and, in some situations, very intense encouragement is necessary to guarantee the adherence, creating an unreal situation. In an alternative to this model, volunteers are allowed to choose the treatment they want to receive, rather than being randomly allocated in a group. This option is very interesting situations in which it is impractical or unrealistic to require adherence, and in which the adherence would only be possible through unrealistic encouragement. Considering that some participants could not participate in interventions due to their work activities, we decided to use a randomized encouragement design, since it would be unethical and unrealistic to request the volunteer to resign. Professionals who carried out the tests and measurements were blinded to the treatment conditions.

Since previous studies investigating aerobic training effects had found positive results with eight weeks of training (Ho et al., 2012; Many et al., 2013), participants in the aerobic and Pilates groups followed an experimental protocol for a period of eight weeks, with 60-minute sessions three times per week (totaling 24 sessions). Participants were asked not to initiate any other exercise activity apart from the one included in this study. When a participant missed three or fewer training sessions, the sessions were replaced at the end of the period, but if more than three sessions were missed, the participant was excluded from the study. Regarding adherence, only three participants needed to replace two exercise sessions at the end of the period, one from the Pilates group and two from the aerobic group. Therefore, by the end of the study, all participants for the aerobic and Pilates groups had completed 24 training sessions.

All participants from the three groups underwent tests performed over two consecutive days at the Exercise Physiology Laboratory of the Federal University of São Paulo (São Paulo, Brazil) both before and after the experimental protocol took place. The following assessments were conducted: food intake, cardiorespiratory maximal treadmill test, isokinetic strength testing, body composition and anthropometry, abdominal endurance test, trunk extensor endurance test, flexibility test and functional (stair and chair) tests.

As the control group did not follow an experimental protocol, for ethical reasons, control participants were offered the opportunity to participate in the Pilates or Aerobic program, according to the participant’s interest, after the conclusion of the study. Those who participated in the experimental protocol were offered the opportunity to participate in the other protocol that they did not take part in initially. Details of the study protocol can be found at http://dx.doi.org/10.17504/protocols.io.p5wdq7e.

Assessments

Interventions

Statistical analyses

Statistical analyses were performed using the Statistica software (Statsoft, Inc., version 6.0 for Windows, Tulsa, OK, USA). Data were expressed as mean ± standard deviation (SD). Variable distribution was tested by the Kolmogorov–Smirnov test, and variability by the Levene test. The sample size was planned to identify a difference between training groups of at least 2% of fat mass in a relatively homogeneous group of healthy adults. To this end, we used data from a pilot study. The target sample size was 20 participants in each group (alpha 0.05 and power 0.80). After data collection, a two-way ANOVA for time vs. group of fat mass (%) and the power observed (alpha = 0.05) yielded the interaction effect of 0.87; therefore, we conclude that the sample size was sufficient for subsequent analysis.

To verify the effects of the intervention programs, a two-way ANCOVA, conducted by using age as a covariate, was used to assess the groups (control vs. aerobic vs. Pilates) and the time (pre- vs. post-training) differences for the following measures: anthropometric and body composition; waist and hip circumferences; abdominal, trunk, chair, stair and flexibility tests; and isokinetic and cardiorespiratory measurements. Newman–Keuls post hoc test procedures were used to identify specific differences. In the absence of interactions, only main effects were analyzed. Where age presented no significant difference for the variable analyzed in ANCOVA test, a two-way ANOVA was used.

In order to compare the HR and RPE reached during the sessions between the two intervention groups we used an unpaired Student’s t test. Statistical significance was set at an α of 0.05 for all statistical procedures.

Calculation of effect size (d) was adopted in addition to the traditional statistical approaches. The measures of the effect size for changes in outcome were calculated by dividing the mean difference by the SD of the pre-training measurement. By calculating effect sizes, the magnitude of any change was judged according to the following criteria: d = 0.2 was considered a “small” effect size; d = 0.5 represented a “medium” effect size; and d = 0.8 was a “large” effect size (Cohen, 1988). Percent changes and 90% confidence intervals were also calculated.

Body composition effects

Traditionally, body mass reduction by decreasing fat mass is the main goal in obesity treatment, and several studies have investigated the effects of exercise for that purpose, although the importance of physical activity for weight loss assessed by body weight or BMI is controversial (Pedersen & Saltin, 2015). The aerobic exercise protocol employed in the present study promoted no difference in body composition. Cheema et al. (2015) also failed to find a significant loss of fat mass percentage after an aerobic program performed at moderate intensity for 12 weeks. Most likely, the amount of exercise (volume and/or intensity) necessary to produce weight loss needed to be greater than the one implemented in our study, and a restrictive diet would also be necessary for body mass loss.

Changes induced by the Pilates were greater than those promoted by aerobic training, as the Pilates group presented a significant increase in lean mass and decrease in fat mass. These results suggest that Pilates may be an interesting alternative to traditional aerobic training in order to improve body composition (Jago et al., 2006; Rogers & Gibson, 2009; Şavkin & Aslan, 2017). Conversely, due to the small effect size, the results should be viewed with caution. Moreover, there were no differences between groups after the intervention period. Previous studies also show effective results for Pilates in reducing fat mass and increasing fat free mass (Rogers & Gibson, 2009; Şavkin & Aslan, 2017). Therefore, despite the small effect size observed in our study after the Pilates, our results are in line with the literature. Conversely, these results are not a consensus. Segal, Hein & Basford (2004) showed no significant difference in body composition after Pilates. Methodological differences may be responsible for these conflicting results; different indirect methods—which tend to be inaccurate—used to assess body composition (Rogers & Gibson, 2009); a lack of information about the instructors’ certification (Segal, Hein & Basford, 2004; Rogers & Gibson, 2009); and significant differences in the protocol used (Pilates mats or apparatus, sessions per week and program duration); associated with a lack of diet control (Segal, Hein & Basford, 2004) hamper definitive conclusions on this topic. Considering that DXA, which has been previously demonstrated to be reliable (Choi et al., 2015) was used in our study to measure body composition, it can be concluded that Pilates may be considered an alternative exercise program for improving body composition.

Functional tasks tests

Both the aerobic and Pilates groups showed significant improvement on both tests, unlike the control group. However, the improvements on the chair and stair tests in the Pilates group were greater (i.e., had a higher effect size) than in the aerobic group. Moreover, only the Pilates group presented significantly better results in the chair test than the control group after the intervention. This improvement in functional tasks presented in both experimental groups is of fundamental importance for independent living and mobility (Miller & Wolfe, 2008).

Abdominal and trunk strength test and flexibility test

The abdominal and trunk strength tests performed in this study have been found to be reliable field tests (Sparling, Millard-Stafford & Snow, 1997; Demoulin et al., 2006). Moreover, sit and reach test has also been found to be reliable (Bozic et al., 2010). All three groups had higher values for the abdominal test after the 8-week intervention, suggesting that there was a learning effect on this test demonstrated by the improvement in the control group. Notwithstanding, both the intervention groups presented significantly higher results in the abdominal test after the intervention period than the control group. Demonstrating that both the aerobic and Pilates interventions were effective to improve abdominal strength. It is important to notice that the Pilates was more effective to improve abdominal muscle strength, demonstrated by the higher effect size value. In the same direction, trunk extensor muscle endurance showed a significant improvement only in the Pilates group, in the same way as flexibility. In general, these results were expected, since the Pilates method focuses on these muscles through posture and core exercises (Şavkin & Aslan, 2017). Although the effect size of this improvement was classified as large, after the intervention period there were no significant differences between groups. The individuals from each group were quite different and the SD of the measurements was very high; this may be the reason for the absence of significant difference between groups after the intervention, despite the improvement observed only in the Pilates group. We therefore conclude that for functional tasks (chair and stair tests), trunk and abdominal endurance tests, both training programs should be considered, but the Pilates can produce better results.

Isokinetic strength test

Isokinetic dynamometry is a method commonly used to assess muscle performance, both in research and in clinical practice (Granata, Abel & Damiano, 2000; Fleury et al., 2011; Andrade et al., 2013). As has been previously demonstrated, isokinetic dynamometry is a reliable and sensitive instrument to evaluate therapeutic intervention outcomes, including in young or elderly people (Capranica et al., 1998; Eitzen, Hakestad & Risberg, 2012; Andrade et al., 2013).

Isokinetic muscular strength, mainly in the Pilates group, was expected to show a significant improvement, but there were no changes in isokinetic PT for either muscular group assessed (knee flexor and extensor muscles) at 60°/s and 240°/s. Since Pilates exercises are not isokinetic exercises, the mode of contraction and the angular speed are different, and this lack of specificity of the evaluation (isokinetic dynamometer) may contribute to unexpected results. Another possible explanation for the absence of difference in isokinetic strength results after the intervention in the Pilates group may be related to the lower power of isokinetic analysis. For flexor and extensor PT values, the observed power ranged from 0.06 to 0.43. Lower power means that there is a high probability of concluding there is no effect when one actually exists. In other words, the number of subjects in this study might be not sufficient to ensure (to a particular degree of certainty) that the interventions produced no effects on muscular isokinetic strength.

Cardiorespiratory maximal treadmill test

In the present study, the Pilates group showed a significant increase in $\dot{V}$O₂max after the intervention, which did not occur in the aerobic group, although the Pilates intervention was less intense than the walking intervention (internal training load 192 ± 69 vs. 252  ± 106). The lack of $\dot{V}$O₂max improvement after aerobic training was in accordance with previous data (Shinkai et al., 1994; Fiorilli et al., 2017). Shinkai et al. (1994) studied the effects on $\dot{V}$O₂max of a 12-week aerobic program plus voluntary food restriction for mildly obese middle-age women. The authors observed no change in absolute $\dot{V}$O₂max/peak values (L/min), and a significant increase only in relative $\dot{V}$O₂max/peak values (mL/kg/min) after the program, which could be attributed to the significant body mass loss observed, instead of a real $\dot{V}$O₂max improvement. Fiorilli et al. (2017) also studied the effects on $\dot{V}$O₂max of an aerobic or resistance program. Interestingly, their results showed higher $\dot{V}$O₂max values for the resistance-training group than for the aerobic training group.

With regards to $\dot{V}$O₂max, this variable can be derived from the Fick equation: $\dot{V}{O}_{2}max=COmaxx\left(Ca-C\bar{v}\right)O_{2}max$. Therefore, $\dot{V}$O₂max depends on the maximal CO (cardiac output) and the maximal $\left(Ca-CO{\bar{v}}_2\right)O_{2}max$) (difference between oxygen concentration taken from arterial and mixed venous blood). In most situations, $\left(Ca-C{\bar{v}}_2\right)O_{2}max$) does not vary much between individuals, so the $\dot{V}{O}_2$ is usually limited by the maximal CO (Bassett & Howley, 2000); however, in some special situations, such as detraining, very sedentary people or muscular dystrophy, it may be limited by a low maximal (Ca-C ${\bar{v}}_2$) O₂, resulting from a low muscular mass capacity.

It is probable that the $\dot{V}$O₂max/peak improved in the Pilates group as a consequence of a higher maximal CO resulting from the higher maximal HR reached at the end of the cardiopulmonary test. Moreover, as indicated above, in detraining or very sedentary people, the $\dot{V}$O₂max may be limited by a low maximal (Ca-CO ${\bar{v}}_2$) O₂. Considering that the Pilates group exercises are focused on muscular conditioning, it is possible that the increase in the $\dot{V}$O₂max/peak resulted from the observed muscular mass improvement after the program, too. However, it was not possible to state that the aerobic capacity of the muscular mass has increased. The aerobic group failed to show an improvement in the $\dot{V}$O₂max/peak after the training period. During the walking session, the HR mean was 123 ± 11 bpm (HR corresponding to the VT), which represents about 78% of the maximal HR for this group, which is in accordance with aerobic program recommendations (training intensity greater than 60% of the HRmax, with 3–5 sessions/week for 30 min/session). Although moderate aerobic exercise has been extensively suggested for obese people (Pedersen & Saltin, 2015; Burgess et al., 2017; Mabire et al., 2017), our data were in line with other previous literature data (Cheema et al., 2015) which demonstrated that moderate walking performed for 3 months (4 times a week) was not effective to improve aerobic fitness in overweight and obese adults. It is possible that an even greater effort intensity or training period is necessary to produce an increase of maximal CO and/or maximal (Ca-CO ${\bar{v}}_2$) O₂ resulting in greater $\dot{V}$O₂max/peak. Other studies that used high-intensity interval training showed significant improvement in the $\dot{V}$O₂max/peak (Cheema et al., 2015; Ruffino et al., 2017), so exercise intensity may be crucial to improve the $\dot{V}$O₂max/peak.

Although there was no significant difference between groups after the intervention period, the improvement in $\dot{V}$O₂max/peak in the Pilates group was classified as medium, and considering the strong association between an increase in the $\dot{V}$O₂max/peak and reduced all-cause and cardiovascular disease mortality (Lee et al., 2011; Barlow et al., 2012), this is a meaningful benefit of Pilates.

VT is another aerobic index that has great practical application. Besides VT, prolonged exercise leads to progressive metabolic acidosis and exhaustion. VT depends on peripheral circulatory factors, specifically on the oxidative capacity of the contracting muscles (Weltman, 1995). In this study, the $\dot{V}$O₂ in the VT increased significantly only in the Pilates group (d = 0.6). Muscle conditioning is one of the objectives of the Pilates. Possibly better muscle conditioning, characterized by improved peripheral capillarization and muscle oxidative capacity, were responsible for the $\dot{V}$O₂ improvement measured at the VT. In order to better understand the $\dot{V}$O₂max/peak, VT, and RCP improvement in the Pilates group, future studies should evaluate muscular oxidative capacity. In addition, further studies, aiming to investigate the Pilates and walking training effects on more general health parameters, such as the risk of morbidity and mortality, or on muscular oxidative capacity should be developed.

Strengths and limitations of this study

The external validity of the study was guaranteed through an extensive process of volunteer recruitment (social networks and within the medical school) and through the randomization process that divided the volunteers between the two intervention groups. One should, however, consider the cost of a Pilates practice program in a studio. This aspect should be taken into consideration in the appointment of a physical health program for individuals who are overweight/obese.

A possible bias of this study is the inclusion of both men and women. However, an attenuating factor is that both intervention groups contained the same number of men.

Another possible bias is the lack of randomization between control and experimental groups. Twenty-five volunteers asked to participate in the control group, because the intervention protocol (Pilates or walking sessions) was during their working hours. If a random order were used, very intense encouragement would be necessary to guarantee adherence, creating an unreal situation. In order to avoid this bias, these volunteers were allocated to the control group. Choosing for non-randomization between the control and experimental groups could have created a bias as a result of the lack of homogeneity of the baseline data, which, fortunately, did not occur; there was no significant difference in baseline data for muscular performance (strength, endurance, and flexibility), body composition, or functional tasks outcomes.

The same intervention period of 8 weeks was performed for both Aerobic and Pilates groups. It was chosen as it was important that the two groups were submitted to the same training volume. Considering that the aerobic training is usually performed for 12 weeks in previous studies, perhaps other outcomes can be found with longer intervention periods.