Electromyographic analysis of trunk and pelvis muscles during Leg Circle on the mat and with springs on the Cadillac

ABSTRACT

This study aimed to investigate, through EMG, whether it is possible to change the requirement of the stabilizing muscles of the trunk and pelvis, performing the Leg Circle exercise on the mat and with different positions of springs on the Cadillac. Thirteen Pilates instructors practicing for at least six months and without pain performed 10 repetitions of the Leg Circle exercise in three situations: (1) Mat; (2) High springs (HS); (3) Medium springs (MS). EMG data were obtained from the abdominal internal oblique/transverse abdominal (IO/TVA), abdominal external oblique (EO), rectus abdominis (RA), and multifidus (MU) muscles, presented as a percentage of Maximum Voluntary Isometric Contraction (MVIC). Comparisons were carried out using repeated measures ANOVA (α=0.05). All muscles were influenced by the positioning of the spring. On the mat, the greatest activations occurred in the RA and EO muscles, while in the executions performed with springs, the most recruited muscles were IO/TVA (MS) and MU (HS). RA and OE muscles did not show differences between the HS and MS situations. The execution of the Leg Circle exercise on the mat and with springs generates changes in the recruitment of the evaluated muscles. We also observed that, when analyzing the exercise performed on the Cadillac between high and medium springs, there was a difference only for the IO/TVA and MU muscles.

Keywords:
Exercise and Movement Techniques; Rehabilitation; Electromyography

RESUMO

O objetivo do estudo é investigar, através da EMG, se é possível alterar a exigência dos músculos estabilizadores do tronco e da pelve, executando o exercício Leg Circle no solo e com diferentes posicionamentos das molas no Cadillac. Treze instrutoras praticantes de Pilates por no mínimo seis meses e sem dor realizaram 10 repetições do exercício Leg Circle em três situações: (1) Solo; (2) Molas altas (MA); (3) Molas médias (MM). Foram obtidos dados de EMG dos músculos oblíquo interno do abdômen/transverso do abdômen (OI/TS), oblíquo externo do abdômen (OE), reto abdominal (RA) e multífidos (MU) apresentados em percentual da CIVM. As comparações foram realizadas através da ANOVA de medidas repetidas (α=0,05). Todos os músculos sofreram influência do posicionamento da mola. No solo, as maiores ativações ocorreram nos músculos RA e OE, enquanto nas execuções realizadas com molas, os músculos mais recrutados foram OI/TS (MM) e MU (MA). Os músculos RA e OE não obtiveram diferenças entre as situações MA e MM. A execução do exercício Leg Circle no solo e com molas gera alterações no recrutamento dos músculos avaliados. Observa-se também que, ao analisar o exercício realizado no Cadillac entre molas altas e molas médias, houve diferença apenas para os músculos OI/TS e MU.

Descritores:
Técnicas de Exercício e de Movimento; Reabilitação; Eletromiografia

RESUMEN

El objetivo del estudio el investigar, através de la EMG, si es posible alterar la exigencia de los músculos estabilizadores del tronco y de la pelvis, ejecutando el ejercicio Leg Circle en el suelo y con diferentes posicionamientos de los muelles en el Cadillac. Trece instructores profesionales de Pilates durante al menos seis meses y sin dolor realizó 10 repeticiones del ejercicio Leg Circle en tres situaciones: (1) El suelo; (2) Muelles altos (MA); (3) Muelles medianos (MM). Se obtuvieron datos de EMG de los músculos oblicuos internos del abdomen / transverso del abdomen (OI / TS), oblicuo externo del abdomen (OE), recto abdominal (RA) y multífidos (MU) presentados en porcentaje de la CIVM. Las comparaciones se realizaron a través de la ANOVA de medidas repetidas (α=0,05). Todos los músculos sufrieron influencia del posicionamiento del muelle. En el suelo, las mayores activaciones ocurrieron en los músculos RA y OE, mientras que en las ejecuciones realizadas con muelles, los músculos más reclutados fueron OI / TS (MM) y MU (MA). Los músculos RA y OE no obtuvieron diferencias entre las situaciones MA y MM. La ejecución del ejercicio Leg Circle en el suelo y con muelles genera cambios en el reclutamiento de los músculos evaluados. Se observa también que, al analizar el ejercicio realizado en el Cadillac entre muelles altos y muelles medianos, hubo diferencia sólo para los músculos OI / TS y MU.

Palabras clave:
Técnicas de Ejercicio y de Movimiento; Rehabilitación; Electromiografía

INTRODUCTION

The Pilates method became popular as a physical activity and as a rehabilitation tool, seeking to integrate the mind and body of practitioners^{1)- (3}. Maintaining the stability of the trunk and pelvis while performing the exercises is one of the main characteristics of this method^{1), (4}.

While classic training programs, such as strength training, use the increment of loads for training progression⁵, the Pilates method increases the challenges of instability, by variations in the execution of exercises or even in the loads of the springs as the practitioner evolves in training⁶. Nevertheless, the increase in progression within the method has been done subjectively⁷.

One of the exercises frequently used to challenge the stability of the hip/pelvis, in addition to promoting the functional and anatomical integrity of the hip joint, is the Leg Circle or Hip Circle. This exercise can be performed either on the mat, without any accessory, or on the Cadillac, where the individual is placed in supine position and the springs are placed on the head of the device and on the lower limbs, in the feet area^{6), (8}.

The fixation height, different deformation constants, or absence of springs, during the exercise, aim to help or hinder the maintenance of this stability. It has been shown in other exercises that different spring positions alter the muscular responses^{6), (7), (9}. However, as far as can be investigated, there is no information regarding the effects of different positioning of the springs on the stability of the Leg Circle exercise. Therefore, this study aims to investigate, by surface electromyography (EMG), whether it is possible to change the requirement of the stabilizing muscles of the trunk and pelvis, performing the Leg Circle exercise on the mat and with different positions of the springs on the Cadillac.

METHODOLOGY

Sample

The sample estimate was performed using G*Power 3.1.9.2, adopting the following criteria: 0.40 effect size; 5% probability of error; 80% statistical power; 0.5 correlation between measurements; assuming sphericity (E=1) for the family of repeated measures ANOVA statistical tests. The calculation defined the sample size in 10 subjects. Due to possible sample losses, 13 Pilates instructors were evaluated. The participants had an average age of 31.3 years (±5.3), height of 1.61cm (±0.05), and weight of 61.2kg (±6.1). Participants were selected intentionally, with the following eligibility criteria: being a Pilates instructor for at least six months; practicing at least once a week for at least six months; not having acute or chronic low back pain, pain in the lower limbs, or in the abdominal region.

Procedures

All collections were performed at the Exercise Research Laboratory of the Federal University of Rio Grande do Sul, scheduled according to the availability of the participants. Initially, the participants signed the Free and Informed Consent Form, which contained the objectives and procedures of the study. For each sample, an initial evaluation was performed, where data on weight, height, and age were obtained. This was followed by a warm-up, stretching, and familiarization with the proposed exercises. After this initial stage, the participant was prepared for data collection.

Initially, trichotomy and cleaning of the skin with alcohol on the evaluated muscles were performed. Disposable surface electrodes (Miotec DoubleTrace - 100; Ag/AgCl, 10mm diameter, self-adhesive, in bipolar configuration),were unilaterally fixedto the right of the Powerhouse muscles¹, namely: Rectus Abdominal (RA), Abdominal External Oblique (EO), Abdominal Internal Oblique/Transverse Abdominal (IO/TVA), and Multifidus (MU). After placing the electrodes, the tests of maximum voluntary isometric contraction (MVIC) of each muscle were performed. The MVICs of each of the muscles lasted 5 seconds with verbal encouragement, and two repetitions with an interval of two minutes were performed. The positioning of the electrodes and the conduction of the MVIC followed recommendations in the literature^{9)- (11}. The acquisition of electromyography data was obtained using the electromyograph of the brand BTS FREEEMG 1000 with a sampling rate of 1000Hz. The software used to acquire the electromyographic data was BTS Smart Capture.

After MVICs, reflective markers were fixed bilaterally in the following bone projections: Anterior Superior Iliac Spine, Greater Trochanter, Lateral Condyle of Femur, and Lateral Malleolus. The kinematic data were obtained by the BTS SMART-DX 700 system, composed of 10 infrared cameras with a sampling rate of 100Hz, and they were used for clipping and analysis of EMG signals. The participants were positioned on the Cadillac (Physio Pilates®) in supine position, centered, with their heads close to the tower where the springs are located. The participants performed the Leg Circle movement in three situations (Figure 1): (1) Leg Circle on the Mat; (2) Leg Circle with High Springs (HS); (3) Leg Circle with Medium Springs (MS). In HS, the hip starts with a 90° flexion, while in MS, the hip starts at 45°. The lower limbs are relaxed, maintaining the neutral position, characterized by a balance of torques between the springs and the weight of the segment. The experienced instructor recommended the neutral position of the pelvis. Ten repetitions of the gestures were performed at a speed of execution commonly performed by the participant in a lateral to medial direction. All executions were randomized.

Figure 1
Leg Circle exercise in different situations

A: leg circle solo; B: leg circle with high springs; C: leg circle with medium springs.

Data analysis

The analysis of the electromyographic data was performed using BTS Smart Analyzer , where the collected signals were submitted to a filtering procedure using a fourth order Butterworth bandpass filter, with frequency band between 20 and 400Hz. After the electromyographic signal filtering procedure, the repetitions were cut out, using the lower limb kinematics as reference. RMS (root mean square) values were calculated and normalized from the peak value of the RMS envelope obtained in the MVIC.

Statistical analysis was performed using SPSS 20.0. The comparisons of the electromyographic data for the Powerhouse muscles were performed using repeated measures ANOVA, considering the following situations: (1) Mat, (2) High Springs, and (3) Medium Springs. In case of statistical differences in the comparisons, the Bonferroni post hoc test was used. The significance level adopted was α<0.05.

RESULTS

Figure 2 shows the EMG activity data as a percentage of MVIC for each of the studied muscles and in the different positions. Based on the results of the repeated measures ANOVA, one can observe that the positioning or absence of the springs affects the EMG activation of the muscles: RA [F(2; 24)=41.383; p=<0.001; ƞ²=0.775]; EO [F(1.062; 12.743)=22.996; p=<0.001; ƞ²=0.657]; IO/TVA [F(1.246; 14.948)=13.184; p=0.002; ƞ²=0.524]; MU [F(1.271; 15.251)=8.223; p=0.008; ƞ²=0.407].

Figure 2
Mean and standard error of EMG activation as a percentage of MVIC during the leg circle on the mat, with high and medium spring

*Significant difference: p<0.05; RA: rectus abdominis; EO: abdominal external oblique; IO/TVA: abdominal internal oblique/transverse abdominal; MU: multifidus.

The RA and EO muscles presented the highest EMG activities performed on the mat compared to those performed with the springs in high (p=<0.001) and medium (p=<0.001) position. No difference was found comparing situations of high spring with medium spring for both muscles (p=1).

The IO/TVA muscle presented the highest EMG activities in the mat and medium spring, with no difference between these situations (p=0.072). There was a difference between mat and high spring (p=<0.001) and between the springs (p=0.02). The MU muscle obtained the highest EMG activities in the high spring situation, compared to the medium spring (p=0.01). No difference was found comparing the situations mat to high spring (p=0.075) or medium spring (p=1).

DISCUSSION

The proposed article aims to investigate, by surface electromyography, whether it is possible to change the requirement of the stabilizing muscles of the trunk and pelvis, performing the Leg Circle exercise on the mat and with different positions of the springs on the Cadillac. We found that the RA, EO, IO/TVA, and MU muscles were influenced by the change of position or absence of the springs in the execution of the Leg Circle exercise.

The RA and EO muscles achieved their greatest EMG activities on the mat situation. This result may have occurred due to the greater demand for muscle contraction in the mat situation, in which there is no external support^{12), (13}, since, in the HS and MS situations, the movement becomes facilitated by the springs, regardless of anchorage height. This facilitation occurs mainly during the eccentric phase of the movement, where the springs assist in returning to the initial position. In the literature, the EMG behavior of Powerhouse muscles during different exercises on the mat is assessed 12,14-16. None of these studies evaluated the Leg Circle or Hip Circle exercise; however, they performed exercises with springs and elevated lower limbs. High recruitment was observed mainly in the RA¹² and EO^{14), (15} muscles, agreeing with the findings of this study, which also obtained high magnitudes for these muscles in the situations performed on the mat.

In both cases with springs, the low recruitment of electrical activity for RA and EO can be justified by the facilitation that they offer assisting in movement, making these more superficial muscles not to be recruited, unlike IO and MU muscles, which are deeper. While in the HS situation the demand for the posterior chain is greater, with the recruitment of MU and muscles that act on the hip⁷, in the MS situation, this requirement becomes lower, causing the recruitment of the MU muscle to decrease. Since RA and EO do not alter their EMG activity in the situation with external spring support, the IO muscle increases its recruitment to compensate for the alteration of the posterior chain, reinforcing its importance in stabilizing the lumbar-pelvic complex^{13), (17), (18}. In the literature, the comparison between high and low springs has already been verified⁹ in the hip extension and flexion exercise. The EO muscle showed greater EMG activity in the low springs situation, disagreeing with this study, which found no differences between the HS and MS situation for this muscle. In this study, this difference was found only for IO, which was not assessed in the mentioned study⁹. We speculate that the result may come from the stabilizing function of the lumbar-pelvic region performed by the deeper muscles of the abdomen, such as the internal oblique⁴, as well as from the spring position being medium in our study and not low as in the literature⁹.

Despite the expressive results and their applicability, this study has some limitations, such as: the muscles that act in the movement of the hip were not analyzed. This statement can answer questions that have been speculated based on literature studies. Thus, the relationship between Powerhouse and hip musculature can be investigated in future studies. We can also emphasize that the samples can influence the execution mode and result, because they present different levels of muscular strength and/or standardization of the springs used during the study. Despite not individualizing the resistance exerted by the springs, methodological care was taken to standardize the 45° (MS) and 90° (HS) angle of the pelvis and hips. In the HS situation, there is a difficulty of execution for some samples due to the resistance exerted by the springs, which can generate compensations.

Regarding the practical application of the study, Pilates instructors who aim to prescribe exercises with greater recruitment of the most superficial muscles, such as RA and EO, should take as a choice the exercises performed on the mat, while, when targeting deeper muscles, IO and MU, the choice should be medium and high spring exercises.

Within the Pilates method, there is a vast repertoire of exercises with countless possibilities. Some exercises are more effective than others for working on trunk stability and finding greater activation of the Powerhouse. To achieve the proposed objectives, it is necessary that the exercises are carried out effectively. With this study, the qualified professionals will be able, at the time of assembling their repertoire, to make the best choice in the prescription of the exercises, considering the degree of difficulty, position of the springs, form of execution, and activation of the Powerhouse.

CONCLUSION

The execution of the Leg Circle exercise on the mat and on the Cadillac generates changes in the recruitment of the stabilized muscles of the trunk and pelvis. In the mat situation, the RA and EO muscles are more activated than in spring situations. The IO/TVA muscle has greater activity on the mat and with a medium spring. In the MU muscle, the greatest activation occurred in the HS situation. Instructors who aim to prescribe exercises with greater recruitment of the more superficial muscles, such as RA and EO, should choose exercises performed on the mat, while, when targeting deeper muscles, IO and MU, the choice should be exercises with medium and high spring.

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• 5
  Study carried out at the Exercise Research Laboratory at Universidade Federal do Rio Grande do Sul (UFRGS).
• 6
  Funding source: nothing to declare
• 8
  Approved by the Ethics Committee of the Federal University of Rio Grande do Sul: CAAE No. 43223415.0.0000.5347

Publication Dates

• Publication in this collection
  11 Jan 2021
• Date of issue
  Jul-Sep 2020

History

• Received
  22 Apr 2019
• Accepted
  05 Feb 2020