A Comparison Between the Mézières Method and Isostretching Postures for Frontal Stand Curvatures and Functionality in Elite Female Rhythmic Gymnasts with Low Back Pain: A Randomized Controlled Trial

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This study provides evidence that the Mézières and isostretching methods can reduce low back pain and improve spinal mobility in elite rhythmic gymnasts. These techniques may be applied by physiotherapists to support performance and injury prevention.

Abstract

Rhythmic and artistic gymnastics expose athletes to a high risk of musculoskeletal disorders such as low back pain (LBP), often caused by repetitive and intensive training demands. This study aimed to evaluate the effects of a 12-week postural treatment using the Mézières method, focused on posture correction and vertebral movement assessed with the Spinal Mouse system, in elite rhythmic gymnasts with LBP. A randomized controlled trial with two parallel groups was conducted, comparing the Mézières method to an equivalent isostretching intervention under similar conditions. Seventeen elite gymnasts with LBP participated, receiving two weekly sessions for 12 weeks. Frontal stand posture (upright, left, and right) was measured at baseline, post-treatment, and at 2, 6, and 12 weeks using the Spinal Mouse system. The experimental group (n = 8) received Mézières therapy; the control group (n = 9) received isostretching. Significant differences in pain reduction were found between the groups (p = 0.000). In the frontal upright position, lumbar and sacral segmental angles (p = 0.021) and regional inclination (p = 0.000) also showed significant group differences. Similarly, in the frontal left position, all vertebral variables except LSpTH12 also demonstrated significant differences between the groups, with p-values ranging from 0.001 to 0.017. Both treatments reduced pain and improved flexibility, but the Mézières group showed significantly greater improvements than the isostretching group.

1. Introduction

Low back pain (LBP) is one of the main alterations of the musculoskeletal system and one of the complaints with the highest incidence in rehabilitation centers [1]. The prevalence is so high that it is thought that approximately 70–80% of the population will suffer from this disease at some point in their lives [2], and in 40% of cases, the initial discomfort may become chronic [3]. In athletes, LBP, a musculoskeletal disorder, is associated with limitations in joint range, muscle spasms, a loss of muscle strength, and postural problems [4]. Competitive sports can lead to the development of LBP. The results of some studies have shown that low back pain affects more athletes than non-athletes and that low back pain increases with increasing frequency of training sessions [5].

In the case of rhythmic gymnastics as a discipline of sports, Fari et al. (2021) confirmed that it is an exhausting sport that requires considerable physical and mental effort to continuously adapt to the harmony between biomechanical and aesthetic efforts [6]. Gymnasts require coordination, joint mobility, postural adaptation, strength, speed, rhythm, agility, and dynamism. In rhythmic gymnastics, a refined quality of motor control, excellent capacity for expression, and elegance of technical gestures are very important [7,8]. Therefore, from an early age, high-performance training is required for the correct execution of sports gestures to achieve appropriate skills. The average amount of training in this sport discipline, according to Fari et al. (2021) [6], is 25–30 h per week. This is because of the high technical demands of this discipline [6,9]. Because of what they involve, rhythmic and artistic gymnastics are sports that put athletes at risk of musculoskeletal disorders such as LBP, postural disorders, and other important injuries mainly caused by the excessive use and repetition of the exercises, the same gestures, several times for each type of training [6,10,11,12,13,14]. LBP plays an important role in individual demographic and physical characteristics, effort, high training pace, reduced joint mobility, accelerated growth of the gymnast, excessive muscle flexibility, lack of muscle strength, years of experience, and practice of the sport [15,16].

The spinal alignment and functional symmetry of the trunk—particularly in the frontal plane—are critical for rhythmic gymnasts, where even minor asymmetries can compromise performance and increase the risk of chronic LBP. Interventions aiming to improve frontal spinal curvatures, trunk lateral mobility, and postural control are thus of special interest [17]. Two prominent postural approaches include the Mézières method and isostretching, both of which aim to restore postural balance, correct musculoskeletal dysfunctions, and reduce pain. The Mézières method is based on global postural re-education, focusing on muscular chain elongation, breathing control, and vertebral realignment through tailored static postures [18]. In contrast, isostretching combines isometric contractions with stretching exercises to enhance core stability, spinal alignment, and functional mobility, often using symmetrical movement sequences and controlled respiration [19].

Despite the potential benefits of both interventions, most existing studies using these methods have focused on sagittal posture, flexibility, or performance-related outcomes such as vertical jump and trunk range of motion [17,18,19], leaving a gap in the understanding of how these techniques affect spinal symmetry and function in the frontal plane. This represents a crucial limitation, particularly for sports like rhythmic gymnastics where lateral trunk control and segmental vertebral alignment are fundamental.

This study aims to evaluate the effects of a 12-week intervention using the Mézières method compared with an equivalent isostretching protocol on frontal-plane spinal curvatures and pain perception in elite female rhythmic gymnasts with LBP. We hypothesize that the Mézières method will lead to greater improvements in postural symmetry and functional outcomes than isostretching.

2. Materials and Methods

2.1. Trial Design

This clinical trial was drafted and implemented in accordance with the CONSORT checklist guidelines [15]. A two-group parallel placebo randomized controlled trial (RCT) was conducted for three months between 20 February and 30 May 2022 to evaluate effectiveness through measurements planned after the intervention with the Mézières postural method, with two weekly sessions and a duration of 12 weeks. Assessments were performed at baseline and 2, 4, and 12 weeks after treatment.

Recruitment

A coach not otherwise involved in the study was recruited to facilitate the random assignment of participants. The participants were randomized into even groups (1:1) using an adaptive biased-coin design and received an anonymous participant ID.

The experimental group received the Mézières method intervention, while the control group received Isostretching postures as a placebo treatment. All treatments were performed by the same certified therapist with a minimum of five years of experience in postural treatments.

Before starting this trial, national Spanish elite athletes with low back pain were informed of the procedure and the objectives of this study and indicated their willingness to participate.

Informed consent was obtained prior to data collection from adults (>18 years of age) who participated in the study and from the legal guardians of participating minors under the age of consent. All the participants and guardians were provided with detailed information about the study’s purpose, procedures, and benefits and were given the opportunity to ask questions before providing written consent.

All the data collected, including images and videos, were anonymized. This study was registered at ClinicalTrials.gov (ID: NCT05149703) and had Ethics Committee approval from San Antonio Catholic University of Murcia, Spain, with protocol ID CE102105. The trial was implemented in accordance with the latest version of the Declaration of Helsinki.

2.2. Study Setting

This study took place in Santomera Sports Palace, Murcia, Spain.

2.3. Participants

A total of 35 elite female rhythmic gymnasts, aged between 10 and 30 years, were initially assessed for their eligibility to participate in the clinical trial. Of these, 20 athletes met the inclusion criteria, which required a minimum of three training sessions per week (each lasting at least 60 min), a total weekly training time of no less than seven hours, an NRS pain score between 3 and 8, and active participation in Spanish national rhythmic gymnastics competitions. The NRS pain score was selected to include participants experiencing at least a perceptible level of ongoing pain that might warrant intervention, while still allowing for a broader range of clinical presentations.

Participants must have had persistent low back pain diagnosed with an incidence of 3–12 weeks [20] in the lower portion of the spine [21], the area that extends from the last rib to the inferior gluteal folds [22]; must not have chronic disease or acute musculoskeletal injury; and must not have had disc disease or spondylolisthesis. Owing to the same level of competition, training time, frequency, and pain symptoms, the sample was expected to exhibit homogeneous characteristics.

These 20 eligible participants were randomly assigned to two equal groups: the Mézières group (n = 10) and the isostretching group (n = 10). Two participants from the Mézières group withdrew due to team changes, reducing the group to eight members. Additionally, one participant from the isostretching group dropped out after discontinuing the sport, leaving nine participants in that group. Consequently, the final sample size for analysis consisted of 17 athletes—8 in the Mézières group and 9 in the isostretching group. The flowchart provides the detailed distribution of the participants (Figure 1). Five main measurements were implemented in this trial, pre-treatment and 2 weeks, 6 weeks, and 12 weeks post-treatment. All measurements were conducted in the afternoon, specifically between 3:00 and 5:00 PM, prior to the athletes’ regular training sessions. This consistent timing was intended to avoid any acute effects of physical exertion on the measured variables.

2.4. Outcomes

Athlete Observations and Physical Exploration Phase

Anthropometric data, including height and weight, were obtained, and information on sports career length, individual lifestyle, training sessions, training time, and lower back status was collected through questionnaires to identify differences between groups. The body temperature was also measured. The state of the skin, possible muscle contractures, bruises, edema, and swelling were observed and evaluated for possible treatment effects and study bias.

Pain intensity was measured using the Numeric Rating Scale (NRS), which consists of an adequate scale to measure the intensity of pain with a score of 0–10. The highest score is associated with the highest level of pain. It is a reliable and validated tool at clinical and experimental levels. In addition, it has shown sensitivity in assessing the effects of treatments [23,24].

An evaluator not otherwise involved in the study assessed the spinal curves of all participants in the three planes (frontal, sagittal, and transverse). Postural compensation and alignment were checked using a Spinal Mouse sensor instrument.

Spinal Mouse^® (Diag, Volketswil, Switzerland) [25,26,27] is a newly validated, reliable, non-invasive, computer-assisted wireless telemetry device for the assessment of spinal curvatures, mobility, and functionality.

This instrument is useful for the measurement of spinal movement and immediate numerical or graphic comparison in different planes (front/flexion/extension/inclination) due to its wireless monitor connection to a PC, offering a functional and postural evaluation report. The Spinal Mouse^® was manually guided along the spine. The exclusive software reproduces the measurements on-screen in real time. The data are collected and displayed on the screen so that they can be compared with standard values, allowing for an in-depth analysis highlighting hypo- and hyper-mobility.

Six plans were measured with the Spinal Mouse in this trial: frontal plan–frontal standing upright/frontal standing left/frontal standing right/frontal standing upright–frontal standing left/frontal standing upright–frontal standing right/frontal standing left–frontal standing right.

Supplementary File S1 gives a detailed illustrated protocol for the spinal vertebra measurements.

2.5. Intervention

The Mézières method and isostretching are both therapeutic approaches, with notable differences. The Mézières method is an assisted active treatment in which a therapist guides and corrects a patient’s posture by integrating deep breathing, isometric contractions, and proprioception. In contrast, isostretching is a fully active, self-directed treatment in which athletes independently perform postures following group instructions and a written protocol without direct therapist assistance. Isostretching postures closely resemble gymnastic training movements, making them suitable for a placebo group, with the protocol provided in a paper format for consistency.

2.5.1. Mézières Method Experimental Group

This intervention included three postures in the Mézières therapy. Specifically, the postures, performed at a frequency of two sessions per week for 12 weeks, consisted of supine gymnast, supine with upper extremities abducted at 120°, and gymnast in sitting/supine position with hips flexed at 90°. Postural positioning was performed for approximately 30 min. No more than one posture was maintained during each session. At the beginning of the study, a general physical examination with a maximum duration of 60 min was carried out to determine the state of the postural chains and to study the asymmetric imbalances of the posture and the curves of the back, seeking a global and individualized analysis of each athlete, since Mézières is a personalized therapy. The Mézières treatment prioritizes breathing exercises as an important part of rehabilitation, mobility of the spine, and stretching of the back muscles with special attention to the diaphragmatic, paravertebral, and latissimus dorsi muscles [13,28,29].

2.5.2. Isostretching Posture Control Treatment Group

There are 67 variants of isostretching in terms of bibliographic references, which are performed with a respiratory pattern where expiration predominates. In this trial, a total of six isostretching postures most similar to those in the Mézières method were followed. Three repetitions were performed in each of the isostretching positions. The positioning was fixed during inspiration. The time for which the position was maintained coincided with a deep and prolonged expiration of 6–10 s without losing control of the isostretching posture. This process was repeated at least three times. In total, each isostretching posture was maintained for approximately 10 min. Three different postures were implemented in each session lasting 30 min, held twice weekly. The order of the six postures, in threes in each session, did not matter [30,31].

2.6. Statistical Analysis

2.6.1. Power Analysis and Rationale for Sample Size

A previous estimate of the effect size was calculated using the G Power program (3.1.9.2), where for ≥75% power and a type I error rate of 0.05, assuming a common standard deviation of 0.5, a sample size of 18 gymnasts with an allocation ratio of 1:1 was required.

2.6.2. Statistics

Statistical analyses were performed using SPSS Statistics version 25 (IBM). Descriptive statistics were used to summarize the results.

The Shapiro–Wilk test was applied to evaluate the normality of each continuous variable. A p-value of <0.05 was considered indicative of a significant deviation from a normal distribution, in which case parametric tests were deemed inappropriate and non-parametric alternatives were selected (Mann–Whitney U test).

The means per group and the mean differences between the groups are described with standard deviations in 95% confidence intervals. Baseline comparisons between the groups were analyzed using an independent sample t-test. Primary outcomes, such as pain, status, and angles of movement, were analyzed at the four measurement time points in the short-term assessment. The differences between the intervention and control groups were assessed using covariates (factorial ANOVA). Interaction effects were estimated to determine whether the intervention was effective by executing a repeated-measures ANOVA comparing the groups.

3. Results

3.1. Participant Baseline Characteristics

Based on the test outcomes, variables such as height, weight, temperature, and NRS showed no significant deviation from a normal distribution (p > 0.05), justifying the use of parametric tests (t-tests or ANOVA) and reporting of arithmetic means. In contrast, age and training hours per week did not meet the normality assumption (p < 0.05), indicating the need for non-parametric tests (Mann–Whitney U) and the use of medians with interquartile ranges for descriptive statistics (

Table 1. Participant characteristics.

Groups		Mean	SD	Median	W Statistic	Test Used	t/U	p
Age	Isostretch			13.00	0.4895	Mann–Whitney U	15	0.032
	Mézières			13.50
Height	Isostretch	153.78	10.895		0.9657	Shapiro–Wilk	−1.051	0.7398
	Mézières	158.75	8.225
Weight	Isostretch	40.56	6.56		0.955	Shapiro–Wilk	−1.765	0.5404
	Mézières	47.06	8.612
Body Temperature	Isostretch	36.656	0.3432		0.9035	Shapiro-Wilk	0.803	0.0777
	Mézières	36.5	0.4536
Training hours per weak	Isostretch			15.00	0.7859	Mann–Whitney U	33.5	0.838
	Mézières			15.00
NRS	Isostretch	5.722	1.4814		0.9339	Shapiro-Wilk	1.187	0.254
	Mézières	4.938	1.2082

SD: standard deviation; t: Student’s t statistical test; U: Mann–Whitney nonparametric statistics; p: statistical significance; NRS: Numerical Rating Scale; W statistic: a value between 0 and 1 produced by the Shapiro–Wilk test that measures how closely the data follow a normal distribution.

).

The results of the Mann–Whitney U tests revealed a statistically significant difference in age between the isostretching and Mézières groups (U = 15.0, p = 0.0321), indicating that the age distribution between the two groups was not the same. In contrast, no significant difference was observed in training hours per week (U = 33.5, p = 0.8383), suggesting that both groups have a similar level of weekly training. These findings imply that while age may be a differentiating factor between the groups, their training commitments are comparable (Table 1).

No intergroup differences were observed for the regional and segmental vertebral parameters, excluding TH3-TH4 in the frontal standing left position; TH1-TH2, TH7-Th8, L3-L4, and THSp-TH12 in the frontal standing right position; TH11-TH12 and inclination in the frontal standing upright–left differences position; and TH1-TH2, TH7-TH8, and THSp-TH12 in the frontal standing left–right differences position (Expanded Table S2 at Supplementary File S2).

3.2. Multifactorial Analysis of NRS

A repeated-measures ANOVA with group as a between-subject factor, time as a within-subject factor, and time × group interaction showed a significant difference between the groups in terms of NRS outcome (F = 10.667; p =0. 00, η2 = 0.415) and time (F = 13.007; p = 0.000; η2 = 0.812). In addition, a multivariate ANCOVA with baseline data as the covariance showed a significant difference between the groups regarding NRS outcome (F = 4.215; p = 0.026; η2 = 0.605) (

Table 2. Regional vertebral characteristics for the frontal standing position.

			Frontal Standing Left				Frontal Standing Upright				Frontal Standing Right
	Vertebral Scanning		Mean	SD	t	p	Mean	SD	t	p	Mean	SD	t	p
Regional	Sac/Hip	Isostretch	1.22	9.667	−0.867	0.400	17.00	7.246	2.324	0.035	14.44	7.844	−0.557	0.586
		Mézières	5.25	9.438			9.63	5.605			17.25	12.658
	THSpTH12	Isostretch	−2.56	7.502	1.638	0.122	2.22	6.667	0.802	0.435	3.56	10.113	−2.348	0.033
		Mézières	−8.63	7.763			−23.75	97.341			17.13	13.643
	LSpTH12	Isostretch	−30.22	11.563	−0.613	0.549	−15.89	9.239	−0.819	0.425	15.33	11.203	0.636	0.535
		Mézières	−27.00	9.885			−12.50	7.597			10.50	19.523
	Inclination	Isostretch	−22.67	3.354	−1.763	0.098	3.33	1.732	1.227	0.239	29.22	8.599	−0.255	0.802
		Mézières	−18.75	5.651			2.25	1.909			30.25	7.924
	Length	Isostretch	410.89	46.145	−1.312	0.209	442.00	22.383	−0.867	0.400	429.89	37.605	−0.675	0.510
		Mézières	445.00	60.814			463.00	68.962			446.88	64.295

Sac/Hip: sacrum–hip; THSpTH12: thoracic spinal vertebrae and thoracic 12 region; LSpTH12: lumbar spine vertebrae and thoracic 12 region; SD: standard deviation; t: Student’s t statistical test; p: statistical significance.

).

3.3. Frontal Stand Upright Position Results

Referring to the frontal stand upright position, the L2-L3, L3-L4, L4-L5, and L5-S1 segmental variables and inclination regional variable showed a significant difference between the groups in terms of the angle in degrees (p < 0.05 in all cases). For time as a within-subject factor, the TH2-TH3, TH3-TH4, TH10-Th11, TH12-L1, L4-L5, and L5-S1 segmental variables and the Sac-Hip, LSp-TH12, and length regional variables presented a significant difference (p < 0.005 in all cases). Regarding the time*group interaction, the TH8-TH9 segmental vertebra and the Sac-Hip and LSp-TH12 regional vertebra showed a significant difference (p < 0.05 in all cases).

A multivariate ANCOVA with baseline measurements as the covariance showed a significant difference between the groups in terms of the TH2-TH3, L3-L4, L4-L5, L5-S1, Sac-Hip, LSp-TH12, inclination, and length variables (p < 0.005 in all cases) (Table 2).

3.4. Frontal Standing Left Position Results

Referring to the frontal standing left position, in the between-groups subject factor analysis of the repeated-measures ANOVA, a significant difference was shown in all vertebral variables (p < 0.05 in all cases) except for TH8-TH9, L1-L2, L3-S1, Sac-Hip, LSp-TH12, and inclination. In the time within-subject factor analysis, TH9-TH10, TH11-TH12, L4-L5, and all the regional vertebral variables showed a significant difference between the groups (p < 0.05). In the time*group interaction analysis, only the L4-L5 segmental vertebral variable showed a significant difference (F = 2.695 p = 0.039, η2 = 0.152). The multivariate ANCOVA showed a significant difference between the groups for the segmental vertebral variables (p < 0.05 in all cases), excluding TH1-TH2, TH3-TH4, TH5-TH7, TH8-TH9, TH10-TH11, and L4-S1, and all regional variables (Table 2).

3.5. Frontal Standing Right Position Results

For the frontal standing right position, the repeated-measures ANOVA was significant for the TH6-TH7 and TH11-TH12 segmental vertebral variables (p < 0.05) in the between-groups subject factor. The time within-subject factor analysis showed a significant difference in the TH1-TH3, Sac-Hip, THSp-TH12, and length variables (p < 0.05 in all cases). In the time*group interaction analysis, only the TH1-TH2, TH7-TH8, and THSp-TH12 vertebrae demonstrated a significant difference (p < 0.05). No significant differences between the groups were observed in the multivariate ANCOVA (

Table 3. Regional vertebral repeated-measures ANOVA.

		Frontal Plan
		Trial Groups								Repeated-Measures ANOVA
		Isostretching				Mézières
		Pre		Post 3 Months		Pre Treatment		Post 3 Months		Groups		Time		Time*Groups
Pain Intensity		Mean	(SD)	Mean	(SD)	Mean	(SD)	Mean	(SD)	p	η2	p	η2	p	η2
NRS		5.722	1.4814	3.722	1.5434	4.938	1.2082	1.625	1.0607	0.005	0.416	0.000	0.813	0.108	0.445
Regional vertebral evaluation
Frontal standing upright	Sac/Hip	17.00	7.246	6.440	3.909	9.630	5.605	6.750	1.488	0.357	0.057	0.000	0.861	0.001	0.761
	THSpTH12	2.220	6.667	4.000	5.937	−23.750	97.341	1.630	1.408	0.428	0.042	0.161	0.398	0.442	0.251
	LSpTH12	−15.890	9.239	−6.110	6.274	−12.500	7.597	−5.380	2.669	0.879	0.002	0.021	0.591	0.037	0.546
	Inclination	3.330	1.732	2.890	2.421	2.250	1.909	2.750	2.121	0.000	0.828	0.122	0.431	0.413	0.263
	Length	442.000	22.383	438.780	26.076	463.000	68.962	500.000	70.593	0.082	0.189	0.017	0.179	0.213	0.101
Frontal standing left	Sac/Hip	1.220	9.667	−3.220	5.805	5.250	9.438	−0.380	3.739	0.227	0.096	0.009	0.643	0.432	0.255
	THSpTH12	−2.560	7.502	−6.440	8.890	−8.630	7.763	−14.880	7.140	0.008	0.387	0.017	0.178	0.987	0.006
	LSpTH12	−30.220	11.563	−26.890	8.253	−27.000	9.885	−23.250	8.860	0.952	0.000	0.060	0.502	0.299	0.315
	Inclination	−22.670	3.354	−27.330	4.690	−18.750	5.651	−22.630	7.891	0.544	0.025	0.006	0.207	0.069	0.133
	Length	410.89	46.145	425.670	31.325	445.000	60.814	495.880	71.742	0.034	0.267	0.001	0.264	0.442	0.060
Frontal standing right	Sac/Hip	14.44	7.844	8.890	4.314	17.250	12.658	8.750	5.946	0.830	0.003	0.028	0.163	0.300	0.077
	THSpTH12	3.560	10.113	26.330	12.410	17.130	13.643	28.130	9.463	0.071	0.201	0.000	0.440	0.010	0.196
	LSpTH12	15.330	11.203	19.78	7.067	10.500	19.523	14.880	5.866	0.379	0.052	0.548	0.049	0.682	0.037
	Inclination	29.220	8.599	29.440	7.073	30.250	7.924	27.880	7.882	0.750	0.007	0.959	0.010	0.615	0.043
	Length	429.890	37.605	435.330	40.872	446.880	64.295	491.880	63.831	0.106	0.165	0.001	0.253	0.317	0.074

Sac/Hip: sacrum–hip; THSpTH12: thoracic spinal vertebrae and thoracic 12 region; LSpTH12: lumbar spine vertebrae and thoracic 12 region; SD: standard deviation.

).

3.6. Frontal Standing Upright–Left Difference Position Results

In the frontal standing upright–left position, the between-groups subject factor repeated-measures ANOVA was significant for the TH7-TH9, TH9-TH11, L1-L2, Sac-Hip, and ThSp-TH12 variables (p < 0.05). In the time within-subject factor analysis, the TH9-TH10, TH11-L1, L4-S1, LSp-TH12, inclination, and length variables were statistically significant (p < 0.05 in all cases). For the time*group interaction analysis, the L5-S1 and inclination variables were statistically significant (p < 0.05). The multivariate ANCOVA showed a significant difference between the groups in the TH12-L1 and L5-S1 variables (p < 0.05) (Table 3).

3.7. Frontal Stand Upright–Right Difference Position Results

The frontal stand upright–right difference position demonstrated significant differences in the between-group subject factor analysis in the repeated-measures ANOVA for the TH8-TH10, TH11-TH12, THSp-Th12, and length variables (p < 0.05 in all cases). The time within-subject factor analysis was statistically significant for the TH7-TH8, TH11-TH12, and THSp-TH12 variables (p < 0.05). The time*group interaction analysis was significant for the TH1-TH2 and L3-L4 variables (p < 0.05). No significant differences between the groups were observed in the multivariate ANCOVA (Table 3).

3.8. Frontal Stand Left–Right Difference Position

For the frontal stand left–right difference position, the TH1-TH2, TH3-TH4, TH6-TH8, TH11-TH12, THSp-TH12, and length variables were statistically significant in the between-groups subject factor repeated-measures ANOVA (p < 0.05). The TH1-TH3, TH11-TH12, and THSp-TH12 variables were significant in the time within-subject factor analysis (p < 0.05 in all cases). Only the TH1-TH2 segmental variable showed a significant difference between the groups in the multivariate ANCOVA (F = 4.200, p = 0.030, η2 = 0.512).

Table 3 presents a summary of the results from the regional vertebral analysis, including the baseline and three-month follow-up means and standard deviations (SDs).

Table S4 in Supplementary File S3 provides detailed results for the segmental and regional vertebral variables measured using the Spinal Mouse instrument.

4. Discussion

The hypothesis of this study proposed that the Mézières method would lead to greater improvements in postural symmetry and functional outcomes than isostretching in elite rhythmic gymnasts with low back pain. This expectation was supported by the results. The Mézières group demonstrated greater improvements in frontal spinal curvatures, particularly in the upright and left standing positions, indicating enhanced postural symmetry. Furthermore, the significant differences observed in left and right inclination positions, combined with a notable reduction in pain perception, suggest a functional gain linked to improved lateral trunk mobility. These outcomes highlight the therapeutic potential of postural re-education techniques that focus on muscular chain elongation and vertebral alignment in managing both structural imbalances and clinical symptoms in this population.

The Mézières method and isostretching postures were implemented and compared in the same time period in this trial because even though they are individualized treatments, they are also based on the same therapeutic principles [22,31]: (a) verifying and correcting compensations and aligning the spine through the application of previous tension with the placement of the pelvis and (b) providing fixation of the different elements and an increase in muscle tension through stretching and isometric contraction, accompanied by deep and prolonged expiration, descent of the shoulders (isometric fixation), and lengthening of the spine [30]. The most similar postures among the intervention methods were selected for this study. In addition, the deep breath respiration technique was applied in both study groups.

Improvements were most consistent in the frontal upright and left standing positions, where segmental and regional vertebral parameters revealed notable group differences favoring the Mézières group. These changes reflect enhanced vertebral symmetry and lateral trunk control, likely contributing to the observed reduction in discomfort. Moreover, the longitudinal design revealed progressive improvements over time, confirming the sustained benefit of the intervention period. Overall, these findings support the efficacy of the Mézières method not only in alleviating symptoms but also in promoting structural and functional adaptations in the frontal plane.

These findings support the hypothesis that the Mézières method promotes greater improvements not only in spinal alignment but also in functional parameters such as lateral trunk mobility. The measured asymmetries and segmental misalignments—particularly under frontal inclination—are critical indicators of functional limitations in athletes with low back pain. Their reduction in the Mézières group suggests enhanced neuromuscular coordination and postural control. Furthermore, previous studies have noted that correcting asymmetrical spinal loading can directly contribute to reduced nociceptive input and improved movement efficiency [22,30]. Thus, the observed improvements in left–right trunk inclination positions may reflect a functional gain closely tied to pain modulation. This emphasizes the dual role of postural interventions in restoring biomechanical symmetry and alleviating clinical symptoms.

Our results are aligned with those of previous research. Guastala et al. (2016) [22] demonstrated that both global postural re-education and isostretching were effective in improving flexibility and pain in participants with musculoskeletal dysfunctions. Mann et al. (2009) [31] reported improvements in low back pain and flexibility following ten isostretching sessions in a sample of university students, suggesting the clinical applicability of this method. Similarly, Prado et al. (2021) [30] reported that Mézières therapy improved vertebral symmetry and mobility in elite rhythmic gymnasts with LBP, offering structural improvements in postural control.

While both methods have proven effective in other contexts, this study focused specifically on their differential effects on the frontal plane posture of high-level rhythmic gymnasts, which represents a novel contribution. Unlike prior studies centered on the sagittal plane or general flexibility, our findings address the influence of these interventions on lateral trunk control, vertebral asymmetries, and postural imbalances during frontal standing, a critical component for injury prevention and performance in this population.

Notably, statistically significant differences favoring the Mézières group were consistently found in the upright and left frontal standing positions. These positions are particularly important in rhythmic gymnastics due to frequent lateral displacements, and the observed improvements suggest that Mézières therapy may enhance neuromuscular control in those movements. Interestingly, the greater improvement observed on the left side may be explained by the gymnasts’ dominant use of their right sides, highlighting the value of addressing postural imbalances through individualized therapy.

Although Cools et al. (2007) [32] explored upper limb dominance in gymnasts and noted strength differences between dominant and non-dominant arms, their findings on unilateral adaptation may partially help interpret the lateralized effects found in our sample. However, given that their focus was on scapular and shoulder control, the extrapolation of these results should be approached with caution.

The decision to evaluate posture in rhythmic gymnasts experiencing LBP stemmed from the unique physical demands and biomechanical stresses associated with this sport. Rhythmic gymnastics requires an exceptional combination of flexibility, strength, and repetitive hyperextension movements of the spine, which predisposes athletes to postural deviations and musculoskeletal injuries, particularly in the lumbar region [6,10,14]. Postural assessment is critical in this population because altered alignment or compensatory mechanisms can contribute to LBP development and persistence.

By analyzing posture, it is possible to identify specific postural imbalances such as hyperlordosis, pelvic tilts, or scapular misalignments, which may exacerbate spinal loading and strain. Understanding these postural deviations enables a targeted approach for injury prevention and management, including tailored training modifications, rehabilitation protocols, and corrective exercises.

Moreover, rhythmic gymnasts are a unique athletic group in which aesthetics and extreme ranges of motion are prioritized, often at the expense of spinal health. This makes them particularly vulnerable to overuse injuries such as LBP, highlighting the need for specific postural evaluation. By addressing posture-related factors, we aimed to provide actionable insights into both the prevention and treatment of LBP, ultimately enhancing athletic performance and longevity in sports.

Limitations

The sample size was small because of the high professional level and participant inclusion criteria. All participants were ranked in the top four elite national positions in 2022 Spanish competition. The lack of scientific evidence for Mézières and isostretching treatments makes any discussion of the findings and results difficult. This additional physiotherapy has gained ground without much scientific evidence of its effectiveness. Spinal Mouse instruments are expensive and are not a common therapeutic evaluation tool found in every physiotherapy center. It is not easy to demonstrate the efficacy of a postural treatment because a long duration is the principal characteristic of this treatment. Finally, only one sex was analyzed, female elite athletes with low back pain, which hinders the adaptation of the results for all athletes of the same discipline.

Study strengths

The elite athletes were blinded to the study groups. The range of movement, segmental and regional stabilization variables, three different positions (frontal standing upright/left/right), and three position differences (frontal standing upright–left/upright–right/left–right) were scanned and specifically analyzed for each vertebra (C7-S1).

This evaluation provides validity and expands the findings regarding the influence of Mézières and isostretching treatments in athletes with low back pain. The facility of this replicability study must be mentioned because of its evaluation and treatment explication with illustrative postures.

5. Conclusions

The results of this study support the initial hypothesis, demonstrating that the Mézières method leads to superior improvements in frontal spinal curvatures and functional postural symmetry in elite female rhythmic gymnasts with low back pain when compared to isostretching. These adaptations, observed particularly in the upright and lateral standing positions, reflect enhanced trunk control and structural alignment, likely contributing to the significant reduction in discomfort reported by the athletes. These findings underscore the value of individualized postural treatments in managing musculoskeletal imbalances in high-performance athletes. Future research should explore long-term effects and the integration of these approaches into multidisciplinary rehabilitation and training protocols.