Strong evidence supports that higher levels of cardiorespiratory fitness (CRF) are associated with a lower risk of cardiovascular morbidity and mortality as well as all-cause mortality [1
]. In addition, CRF decreases the risk of developing some specific diseases [4
], such as chronic obstructive pulmonary disease (COPD) and lung or colorectal cancer [5
], most of which are associated with a large burden of disease [7
]. Furthermore, several studies have shown that higher levels of CRF may attenuate the negative association between CV risk factors and sedentary behaviours independent of physical activity [8
]. Thus, CRF emerges as an independent predictor for several chronic diseases [12
] and as a remarkable overall health status measure in different populations [12
To improve CRF, current evidence suggests that physical exercise must reach a minimum intensity [13
] of at least 45% oxygen uptake reserve in the general population and 70%–80% in athletes [15
]. Greater improvements in maximal oxygen uptake (VO2
max) are obtained with vigorous physical exercises when compared with moderate intensity exercises [3
]. Moreover, it has been suggested that some types of physical exercises that are not traditionally considered as cardiorespiratory exercises [16
], such as Pilates, could increase CRF.
Pilates has become popular in recent years as a holistic exercise [16
] focused on respiration, body control and accuracy of movements. Current evidence suggests positive effects of Pilates on respiratory muscle strength, balance, quality of life and overall physical performance [18
]. These benefits are observed not only in the healthy population but also in those with specific disorders, such as chronic low back pain [16
], multiple sclerosis [25
], breast cancer [26
] and Parkinson’s disease [27
]. The neuromuscular stimulation achieved during Pilates [28
] may be of sufficient intensity to improve CRF, providing benefits in VO2
max for individuals with different health conditions [29
]. Thus, it seems that Pilates exercises include a mind–body component [34
] that could have a beneficial impact in different populations.
However, evidence for the comparative benefits of Pilates vs. other physical exercises in terms of VO2
max remains inconclusive [22
], and there are no studies that have evaluated oxygen consumption during Pilates sessions. Therefore, it is difficult to assess whether Pilates exercises reach the minimum intensity needed to improve CRF. We conducted this systematic review and meta-analysis to determine the effectiveness of Pilates on CRF as measured through VO2
max. Moreover, we explored whether the effect of Pilates on CRF could be modified by the participant’s health condition or baseline VO2
2. Materials and Methods
2.1. Search Strategy and Study Selection
The present review and meta-analysis were reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [36
] and follow the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions [37
]. This study was registered through PROSPERO with registration number CRD42019124054.
We conducted a systematic literature search in the following databases: MEDLINE (via PubMed), Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE (via Scopus), Web of Science and the Physiotherapy Evidence Database (PEDro), from each database’s inception until September 2019 for studies aimed at determining the effectiveness of the Pilates method on CRF as measured through VO2
max. The search algorithm was conducted using PICO’s strategy (type of studies, participants, interventions, comparators and outcome assessment) and combined Medical Subject Headings, free-terms and matching synonyms of the following related words: (1) population: adults, “middle aged”, “young adult”; (2) intervention: Pilates, mind–body, “exercise movement techniques”; (3) outcome: “cardiorespiratory fitness”, “aerobic fitness”, “aerobic capacity”, “heart rate”; and (4) comparator: control conditions or another physical exercise. In addition, we searched the citations included in the identified publications deemed eligible for our study. The complete search strategy for MEDLINE is presented in Table 1
2.2. Eligibility Criteria
Two initial reviewers (RFR and CAB) independently examined the titles and abstracts of retrieved articles to identify suitable studies. Those studies in which the title and abstract were related to the aim of the present review were included for full text request. We included studies that (1) were conducted as randomised controlled trials (RCTs), non-randomised controlled trials (non-RCTs) or pre-post studies; (2) included a mean participant age ≥18 years; (3) involved participants in any health condition; and (4) were based on at least one exercise intervention described as “Pilates” (mat, machine or both). Studies were excluded if (1) outcome measurements were not reported as VO2 max values, or (2) they were not written in English, Spanish or Portuguese. A third reviewer (VMV) resolved cases of initial reviewer disagreement.
The present systematic review and meta-analysis were performed by collecting and analysing data from previous studies in which informed consent had been obtained by the respective original investigators. Therefore, this study was exempt from ethics approval.
2.3. Data Extraction and Quality Assessment
Two authors (RFR and CAB) independently extracted the following information from the included studies: First author’s name and year of publication; study design; characteristics of the participants included; mean age; sample size and percentage of female subjects; weekly frequency, period and modality of Pilates intervention; supervision of the intervention by a certified instructor; use of a detailed exercise protocol; the reported measurement of VO2 max; the device used to measure VO2 max; and main results. A third reviewer (VMV) resolved cases of author disagreement.
The risk of bias of RCTs was assessed using the Cochrane risk-of-bias tool for randomised trials (RoB 2.0) [38
], in which five domains were evaluated: Randomization process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result. Each domain was assessed for risk of bias. Studies were graded as (1) “low risk of bias” when a low risk of bias was determined for all domains; (2) “some concerns” if at least one domain was assessed as raising some concerns, but not to be at high risk of bias for any single domain; or (3) “high risk of bias” when high risk of bias was reached for at least one domain or the study judgement included some concerns in multiple domains [38
For pre-post studies and non-RCTs we used the Quality Assessment Tool for Quantitative Studies [39
], in which seven domains were evaluated: Selection bias, study design, confounders, blinding, data collection methods, withdrawals and dropouts. Each domain was considered strong, moderate or weak. Studies were classified as “low risk of bias” if they presented no weak ratings; “moderate risk of bias” when there was at least one weak rating; or “high risk of bias” if there were two or more weak ratings [39
Risk of bias was independently assessed by two reviewers (RFR and CAB). A third reviewer (VMV) was consulted in case of disagreement.
2.4. Data Analysis
Primary data extracted from each study included mean VO2
max, standard deviation of pre-post intervention and sample size. Effect sizes (ES) and related 95% confidence intervals (CIs) were calculated for each study [40
]. The Dersimonian and Laird random effects method [41
] was used to compute pooled ES estimates and respective 95% CIs. We estimated the pooled ES for the effect of Pilates vs. the control group (CG). The heterogeneity of results across studies was evaluated using the I2
statistic, with I2
values of 0%–30% considered “not important” heterogeneity; >30%–50% representing moderate heterogeneity; >50%–80% representing substantial heterogeneity, and >80%–100% representing considerable heterogeneity. The corresponding p
-values and 95%CI for I2
were also considered [42
]. Finally, we conducted two additional analyses: (i) the pre-post ES of Pilates on the intervention group (Appendix A
), and (ii) the mean difference of Pilates vs. CG (Appendix B
For all the analyses, when studies reported data on two intervention groups of Pilates, the effects of both groups were pooled in order to calculate the average effect size. Finally, when studies reported more than one intervention, we only considered the Pilates intervention for conducting this meta-analysis.
A sensitivity analysis was conducted by removing each included study to assess the robustness of the summary estimates. Further, subgroup analysis based on participants’ health status and random-effects meta-regression by baseline VO2
max values were conducted to determine their potential effect on the pooled ES estimates. Finally, publication bias was evaluated through visual inspection of funnel plots and Egger’s regression asymmetry test for the assessment of small-study effects [43
]. Statistical analyses were performed using StataSE software, version 15 (StataCorp, College Station, TX, USA).
This systematic review and meta-analysis were performed to determine the effectiveness of Pilates interventions for improvement of CRF measured through VO2 max. Our findings highlight that Pilates is an alternative exercise to improve VO2 max values. Furthermore, our results were substantially modified by participants’ health conditions for Pilates vs. control group analyses but not for Pilates pre-post effect on intervention; otherwise, baseline VO2 max values could influence CRF improvement.
Although some studies [22
] have failed to show significant changes in CRF after Pilates intervention, no study has reported negative effects of Pilates on the CRF levels, and therefore the positive clinical implications should not be underestimated. Additionally, more significant benefits of Pilates on CRF were achieved when other activities, such as running, were included [33
] and this could be explained through a synergistic relationship between these training methods.
Evidence suggests that people with lower levels of CRF are more sensitive to improvement of this parameter [47
]. Accordingly, in our study estimates of pooled ES were higher in those studies in which participants had lower baseline CRF levels, such as people with health disorders. Conversely, our meta-regression analyses suggested that higher levels of VO2
max at baseline are related with higher ES of the Pilates intervention. These findings should cautiously be interpreted since they may indicate that the effect of Pilates in those studies with higher VO2
max levels at baseline were distortedly overestimated. Probably these biased estimates were a consequence of reporting results in absolute terms (change in VO2
max in ml) instead of in relative terms (percentage of increase in VO2
max), but could have clinical implications suggesting that Pilates exercise is an effective rehabilitation strategy for several disorders, including some cardiac pathologies. Moreover, Pilates exercise showed high compliance levels indicating that it may be better tolerated than the aerobic exercises typically employed in rehabilitation programs.
Three potential sources of improvement may explain the positive impact of Pilates intervention on CRF: Strengthening of the lumbopelvic region, increased flexibility of the ribcage and breathing exercises. First, the strengthening of lumbopelvic and core muscles induced by Pilates may produce a more efficient movement pattern in upper and lower limbs, as well as greater strength in expiratory muscles [19
]. Second, due to the flexibility improvement, a more efficient mobility pattern of the ribcage may be achieved [30
]. Finally, the breathing techniques adopted during Pilates training may increase lung capacity [29
] and functionality of intercostal muscles [17
]. On these bases, improved ventilation efficiency would be achieved, resulting in a higher flow of oxygenated blood into muscle tissues [35
], enhanced local circulation [19
] and muscle oxidative capacity [45
], and less energy waste. Therefore, Pilates could reach the minimum intensity required to improve CRF [13
] although no published study has verified this.
Our systematic review and meta-analysis present some limitations that must be stated. First, it was not possible to blind Pilates interventions and some of the included studies did not provide details about the randomisation sequence or allocation concealment. Second, considerable levels of heterogeneity were observed in the analyses, and we cannot omit this fact. Third, the heterogeneity of participants’ health conditions and the dose and intensity of the Pilates intervention could potentially affect our estimates. Fourth, significant publication bias was evidenced by Egger’s test and unpublished results could modify the findings of the present meta-analysis. Fifth, it should be highlighted the difficulty to comply with a full training program by very busy professionals, thus, this concern should not be neglected in the implementation of our results. Sixth, rarely it is possible to measure VO2 max directly in clinical settings, thus other more applicable procedures for indirect measurement of VO2 max should be used. Seventh, although subgroup analyses by participants’ health conditions modified the ES estimates, these results should be cautiously considered due to the lack of studies in each subgroup. Finally, due to the lack of long-term assessments, we could not determine whether the benefits to CRF measured through VO2 max are preserved over time. Therefore, our results should be cautiously considered.