Comparação do alongamento estático, balístico e contrair-relaxar nos músculos isquiotibiais

Objetivou-se, por meio deste estudo, comparar o efeito de tres tecnicas de alongamento muscular (balistico, estatico e contrai-relaxa) no ganho imediato de flexibilidade dos musculos isquiotibiais. Foram avaliados 23 sujeitos, de ambos os generos [media (DP) idade 21,17 (1,4)]. Todos os voluntarios realizaram o alongamento estatico, o balistico e o contrai-relaxa. Cada tecnica foi realizada em sessao unica com intervalo de sete dias entre as sessoes. Para avaliar os efeitos imediatos das diferentes tecnicas, realizaram-se, antes e apos a serie de alongamentos, os testes de flexibilidade Sentar e Alcancar e o Teste do Ângulo Popliteo. Em comparacao a linha de base, houve aumento significativo de flexibilidade para o teste do Ângulo Popliteo apos aplicacao do alongamento balistico (6,26%) e contrai-relaxa (6,5%), respectivamente (p<0,05). Ao contrair-relaxar as tres tecnicas em relacao ao escore de mudanca, encontrou-se diferenca consideravel no teste do Ângulo Popliteo para os alongamentos balistico e contrair-relaxar, porem, o Teste Sentar e Alcancar nao apresentou relevância. De acordo com esses dados, as tecnicas balisticas e -contrair-relaxar foram melhores que a tecnica de alongamento estatico, e ambas as tecnicas mostraram-se igualmente efetivas. As tecnicas de alongamento balistico e contrair-relaxar melhoraram a flexibilidade dos musculos isquiotibiais.


INTRODUCTION
There are several consequences resulting from the shortening of hamstring muscles among them postural deviations 1 , change of the lumbopelvic rhythm, low back pain 1,2 , predisposition to lesions 3 and development of patellar tendinopathy 2 .Considering this reality the performance of stretching exercises both in the practice of sports as in rehabilitation centers is frequent 3 .The practice of stretching exercises promotes some benefits such as improved athletic performance and functional gains in addition to the maintenance of health and fitness 4,5 .
The main stretching techniques are: static stretching, ballistic stretching and contract-relax stretching 6 .Static stretching is described as a method in which the soft tissues are stretched to the point of resistance or tolerance of the tissue held in this position 7 .The ballistic stretching is characterized by the use of vigorous and rhythmic movements of a body segment throughout this range of motion in order to lengthen a muscle or muscle group 8 while the contract-relax technique uses a brief isometric contraction of the agonist muscle which inhibits the muscle to be stretched and then performs the static stretching during the muscle relaxation 8,9 .
There are studies that suggest that the contractrelax and ballistic stretching technique proves more effective in gain of hamstring flexibility than static stretching technique.In contrast, studies show that static stretching may be the only one able to maintain a significant gain in amplitude of hamstring muscles over a prolonged period 4,6 .
The importance of studies related to the shortening of the hamstring muscles is due to the possibility of the occurrence of lesions caused by biomechanical changes that can lead to some disorders such as patello femoral dysfunction, pubic pain, back pain, patellar tendonitis and postural disorder 1 .The hamstring injuries accounting for 29% of all injuries in athletes and 12% to 31% of these athletes suffer reinjuries.In addition considering that in clinical practice it is usual to apply stretching protocols, the literature should present studies comparing the effects of stretching protocols, assessing the advantages and disadvantages of stretching techniques, including, static stretching, ballistic stretching and contract-relax stretching 10 .
Thus the objectives of this study were: to analyze the effectiveness of static, ballistic and contract-relax stretching techniques and compare the immediate effects of these techniques on the flexibility of hamstring muscles.

METHODOLOGY Subjects
Twenty-three university students from both genders, aged 18 to 25 years, were evaluated (Table 1).The volunteers were instructed not to practice stretching and/or muscle strengthening sessions of the lower limbs in the last three months prior to the study.Individuals who reported lesions in hamstring muscles in the last three months and those who made regular use of analgesic medication in the last two weeks were excluded from the sample.All volunteers signed a free and informed consent form.

Procedures
The three stretching techniques were performed by all volunteers.Each stretching technique was performed in a single session with an interval of seven days between sessions in a randomization order.In assessing flexibility, the Sit and Reach Test (SRT) and the Popliteal Angle Test (PT) were used.Both tests, when using similar sample with the present study, showed in intraobserver analysis a ICC of 0.91 e 0.79 respectively, and in interobserver analysis a ICC of 0.71 and escore de cambio, se encontró diferencia considerable en el test del Ángulo Poplíteo para los alongamientos balístico y contrae-relaja, sin embargo el Test Sentar y Alcanzar no presentó relevancia.De acuerdo con esos datos, las técnicas balísticas y contrae-relaja fueron mejores que la técnica de alongamiento estático y, ambas técnicas, se mostraron igualmente efectivas.Las técnicas de alongamiento balístico y contrae-relaja mejoraron la flexibilidad de los músculos isquiocrurales.
Palabras clave | amplitud de movimiento articular; ejercicios de alongamiento muscular biomecánica.0.72 respectively 11 .Tests and stretching techniques were performed by the same evaluator with previous experience.Each test was applied before and after the completion of each technique.SRT which assesses the flexibility of the posterior muscular chain, was performed based on previous studies 12,13 .The subject was instructed to sit on the stretcher with knees extended and to perform a hip flexion with the elbow extended.The individual was asked to reach as far as possible without bending his knees.
To perform the PT styrofoam markers were placed in bony prominences of the greater trochanter, lateral epicondyle of the femur and lateral malleolus in the volunteer's dominant limb 14 .The contra lateral limb was stabilized in full extension and the dominant limb was stabilized at 90º of hip flexion with the knee relaxed.The goniometer was positioned with the fixed arm toward the greater trochanter of the femur and the movable arm toward the lateral malleolus.The volunteer was asked to extend his knee until the time he had the feeling of discomfort.Both tests were performed three times and the average of the three measurements was used for data analysis.
The order of application of each stretching technique each day was randomly selected (Figura 1).
• Static stretching: the hip of the volunteer was flexed passively by the examiner up to the maximum flexion point with the knee joint maintaining full extension.Five cycles of 30 seconds were performed with an interval of thirty seconds between cycles.• Contract-relax stretching: The hip of the volunteer was flexed passively by the examiner up to the maximum flexion point with the knee joint maintaining full extension.Five cycles of thirty seconds were performed, five seconds of isometric contraction and ten seconds of stretching with relaxed muscles.This process was performed twice so that the cycle of thirty seconds was completed.An interval of thirty seconds between cycles was also performed.• Ballistic stretching: flexion-extension movements of the hip with knee kept in full extension.The movements were performed by the examiner, with the fastest speed as possible, respecting the limit of each volunteer.Thirty cycles of thirty seconds were performed, with thirty seconds of interval between them.

Statistical analysis
Data analysis used the SAS software for analytical statistical calculations.The normality of data distribution was tested through the Shapiro-Wilk test.To compare data before and after stretching the 2-way repeated ANOVA (Analysis of variance) test was used followed by Tukey pos-hoc test.Futhermore, the data were reorganized according to the day.These data was reorganized to verify if the flexibility gain, regardless of the technique, was lasting.To compare data according to the day was used the 2-way repeated ANOVA followed by Tukey pos hoc test.The change scores between the three stretching techniques was performed by Friedman analysis of variance (ANOVA) test followed by Newman-Keus Student test, since the variances were not homogeneous.The significance level adopted for the data analysis was 5% (p<0.05).
There was no significant difference between initial values comparing the three techniques as well as between the final values both in the SRT (p=0.94,f=0.58; p=0.88, f=0.12 respectively) and in the PT (p=0.93,f=0.67; p=0.79, f=0.22 respectively) (Table 2).With regard to the difference in change score of each stretching technique, significance level was observed for the PT (p=0.01) when comparing ballistic and static techniques (p<0.05) and static and contract-relax techniques (p<0.05);however no significant difference was found when contract-relax and ballistic techniques were compared (p=0.09).There was no significant difference between final and initial values of each stretching technique applied to the SRT (p=0.66)(Table 3).The initial values of the SRT and PT in each day (D1, D2, D3), regardless of stretching technique, are shown in Table 4.There was no statistically significant difference for these values.

DISCUSSION
This study aimed to compare the immediate flexibility gain of the hamstring muscles after applying the static, ballistic and contract-relax stretching techniques.The results of PT suggest that the ballistic and contract-relax stretching were able to increase the immediate flexibility of the hamstring muscles.These data corroborate the findings of other studies on the implementation of stretching protocols to increase the flexibility of the hamstring muscles 15,16 .
There are several techniques to assess changes in muscle flexibility based on the joint and movements to be evaluated.Thus functional tests used to assess the flexibility of hamstring muscles may include knee extension movements and flexion of the trunk on the hip joint 12 .PT measures the flexibility of hamstring muscles 17 and shows good reliability when performed in healthy subjects 18 .SRT also shows good reliability to assess the flexibility of hamstring muscles 19,20 , but also measures the flexibility of the lower body segment 19 .PT may have been more sensitive to changes in flexibility of hamstring muscles after application of three stretching techniques.
The immediate flexibility gain can be explained by the viscoelastic properties of the muscle.This property is a response of the muscle-tendon unit to stretching with fixed length, which generates a decrease in stress over time.This reduced length of the muscle-tendon unit is known as stress relaxation and allows a deformed of the muscle-tendon unit more easily in the next repetition, thus providing greater flexibility 16 .Another explanation found is based on the increased tolerance of the muscletendon unit to elongation, although this mechanism is still unknown 21 .
Further, contract-relax stretching can also be explained by neurophysiological factors based on the findings of reciprocal inhibition and subsequent induction.Reciprocal inhibition describes the phenomenon that while a muscle group is activated, its antagonist is inhibited, thereby facilitating the elongation of this muscle-tendon unit 22 .Concerning to gains of flexibility that was observed after application of ballistic stretching, the literature reports that movements produced to perform the ballistic stretching can lead to a warming up of the body musculature.The increase of muscle temperature during strain can produce a decrease in viscosity of tissues and rectify the undulations of collagen 23 .The results of change score of PT suggest that ballistic stretching and contract-relax are both equally effective and better than static stretching.Even though no significant difference between ballistic and contract-relax stretching techniques in the immediate flexibility gain of these muscles was found.
There are studies showing effects similar to those of this study in relation to the flexibility of the hamstring muscles and found lack of significant improvement in flexibility after the implementation of the ballistic and contract-relax techniques when compared to static stretching 24,25 .However others studies have found no significant difference between the static and contract-relax stretching or between static and ballistic techniques in the flexibility gain of hamstring muscles 15,26 .
The difference between results observed in this study to those reported in literature are due to the performance of stretching protocols that used the onset of pain sensation as reference, whereas in the present study, maximum tolerance to stretching without pain was used 21 .Moreover these differences may also have occurred due to the various protocols used in the studies, variations in positions to perform the muscle stretching techniques, the choice of the lower limb to be used and also the evaluation methodology.This suggest new researches that include a larger number of subjects, different genders and ages are important.
Moreover there was no significant difference in the initial values of the SRT and PT for each collection day regardless of the stretching technique applied.This demonstrates that the performance of any of the three stretching techniques applied in five series of 30 seconds and only once a week is not enough to gain lasting flexibility.
In this study no interference of the accumulation of stretching exercises in initial assessments that took place in the second and third days was observed since no significant statistical difference was observed in the initial values of each day for both tests regardless of the stretching technique applied.
In terms of limitations of the study the number of subjects is small and so the extrapolation of data for different populations and muscle groups should be made with caution.Further randomized controlled trials should be performed in order to establish specific benefits of static ballistic and contract-relax stretching.

CONCLUSION
The results of this preliminary study suggests that ballistic and contract-relax techniques may improve the immediate flexibility gain of the hamstring muscles.The ballistic stretching and contract-relax stretching are both equally effective and better than static stretching which had no any effect on flexibility gain.

Figure 1 .
Figure 1.(A) Popliteo Angle Test; (B) Sit and Reach Test A B

Table 1 .
Subjects characteristic SD: standard deviation; BMI: body mass index

Table 2 .
Popliteal angle test and Sit and reach test before and after the application of stretching techniques: static, ballistic and contract-relax SS: Static Stretching; BS: Ballistic Stretching; CRS: Contract-Relax Stretching; SD: standard deviation.* significant difference before and after application of the technique of ballistic stretching.** significant difference before and after application of technical contract-relax stretching.

Table 3 .
Change score of the Sit and Reach Test and of the Popliteal Angle Test for the three stretching techniques applied p<0,05 in relation to static stretching and ballistic stretching; ** p<0,05 in relation to static stretching and contract-relax stretching; Values presented in median (minimum-maximum) *

Table 4 .
The initial values of the Sit and Reach Test and of the Popliteal Angle Test in three days regardless of the stretching technique applied SD: standard deviation