Flexibility is an important component

Transcription

1 Original Article Immediate Effect of Static and Proprioceptive Neuromuscular Facilitation Stretching on Hip Adductor Flexibility in Female Ballet Dancers Ercole C. Rubini, M.Sc., Andréa C. Souza, B.P.E., Mônica L. Mello, M.Sc., Reury F. P. Bacurau, Ph.D., Leonardo F. Cabral, B.P.E., and Paulo T. V. Farinatti, Ph.D. Proofs to: Abstract The aim of the present study was to investigate the immediate effects of static and proprioceptive neuromuscular facilitation (PNF) stretching on the flexibility of hip adductors in female ballet dancers. Forty-five subjects (age: 28.5 ± 8.0 years; minimum two years of ballet training) were randomly assigned to three groups: PNF (contract-release technique), Static, and Control. Subjects in the PNF and Static groups performed four sets of 30 second stretching with an interval of 30 seconds between sets. The control group stayed at rest for the same time spent by the PNF and Static groups during the stretching sessions. Maximal range of motion was measured before and immediately after the experimental and control protocols in all groups. The results indicated significant differences between pre- and post-stretching flexibility in both PNF and Static groups (p < ; effect size = 0.24 and 0.39, respectively), whereas no change was identified in the Control group (p = 0.265). However, no differences in post-exercise flexibility were found between PNF and Static groups (p = 0.235). It is concluded that static and PNF stretching methods provoked similar post-exercise acute effects on the maximal range of motion of hip adductors in highly flexible female ballet dancers. Flexibility is an important component of physical fitness that is usually included in general exercise prescription programs. 1 However, there is no consensus as to the best training method for inducing flexibility gains. The most common approaches are the static, dynamic, and proprioceptive neuromuscular facilitation (PNF) methods. 2 The effectiveness of these methods has been compared, but the available evidence is controversial. Many studies 3-8 have proposed that all of these stretching methods produce similar results. However, some researchers suggest Ercole C. Rubini, M.Sc., is at the Laboratory of Exercise Physiology, Estácio de Sá University, and Laboratory of Physical Activity and Health Promotion, University of the State of Rio de Janeiro, Rio de Janeiro, Brazil. Andréa C. Souza, B.P.E., is at the Laboratory of Exercise Physiology, Estácio de Sá University, Rio de Janeiro, Brazil. Mônica L. Mello, M.Sc., is the Rio de Janeiro Secretary of Education, Rio de Janeiro, Brazil. Reury F. P. Bacurau, Ph.D., is at the School of Arts, Sciences and Humanities, University of São Paulo, São Paulo, Brazil. Leonardo F. Cabral, B.P.E., is at the Laboratory of Exercise Physiology, Estácio de Sá University, Rio de Janeiro, Brazil. Paulo T. V. Farinatti, Ph.D., is at the Laboratory of Physical Activity and Health Promotion, University of the State of Rio de Janeiro, and the Sciences of Physical Activity Graduate Program, Salgado de Oliveira University, Niterói, Brazil. Correspondence: Ercole da Cruz Rubini, M.Sc., Rua André Rocha, 838, Taquara, Rio de Janeiro Brazil, ; ercolerubini@yahoo.com.br. that PNF is more efficient than the static or ballistic methods, 9-15 while others favor the static method over the other two. 16,17 Methodological differences within the studies, such as training status at baseline, number of sets and stimulus duration, or muscle group stretched, may help to explain such discrepancies. Some activities, such as dance and artistic gymnastics, clearly demand high flexibility levels and thus create a special concern for the development of this aspect of physical fitness. Female ballet dancers must be extremely flexible to meet the demands of the art form 18 ; hence, flexibility training is a major component of their physical conditioning, and stretching is optimized. Despite this fact, the stretching routines used in ballet training are frequently not supported by scientific evidence. 5,19-21 In the case of ballet dancers, data regarding flexibility responses to different stretching strategies are scarce Level of expertise is an essential issue in designing flexibility training programs. It might be assumed that highly trained subjects benefit less from stretching routines than less trained subjects, as they are probably near their maximum developmental potential. Therefore, in designing a training program for this specific population, it would be especially useful to know whether one stretching method produces better results than another. 177

2 178 Volume 15, Number 4, 2011 Journal of Dance Medicine & Science One matter that could help elucidate this question concerns the acute (or immediate ) flexibility responses to different stretching methods. It is a well-established fact that the chronic effects of flexibility training rely largely on successive acute responses to regular stretching sessions. 26 Hence, information about the immediate responses induced by different stretching techniques would be useful in defining which method would be most effective for increasing the flexibility of trained subjects such as ballet dancers. Unfortunately, this matter has been poorly investigated, and the available results are quite controversial Therefore, the aim of the present study was to investigate the acute effects of static and PNF stretching on the flexibility of the hip adductors in female ballet dancers. We hypothesized that PNF stretching would produce different acute effects on range of motion in this population compared to the static method. Methods Experimental Approach to the Problem This study compared the immediate effects of static and PNF stretching techniques on the flexibility of the hip adductors. Data were gathered on three nonconsecutive days, with 48 hours separating the sessions. At the first visit, subjects were tested for anthropometric characteristics (body mass, and height). A familiarization protocol was applied prior to the beginning of the study, consisting of: 1. assessment of hip adductor flexibility; 2. application of static and PNF techniques; and 3. re-measurement of hip flexibility. On the second visit, the hip flexibility was retested twice, with a 30-minute interval between tests in order to verify the within-day and dayto-day reproducibility of the obtained values. At the third visit, subjects were randomly assigned in equal numbers to one of three groups: Static, PNF, or Control. A between-group experimental design was adopted to avoid bias related to successive stretching sessions and evaluations. All groups performed the previously enumerated experimental procedures. There was no baseline difference between the three groups in the flexibility of hip adductors. No warm up was allowed before flexibility assessment or stretching protocols. It was requested that subjects minimize physical activities in the 48 hours prior to the experimental session, and they remained quiet in a controlled temperature room (23 C to 25 C) for 30 minutes before the stretching procedures began. Subjects Forty-five female ballet dancers volunteered for the study (age: 28.5 ± 8.0 years; height: ± 5.1 cm; weight: 56.5 ± 4.5 kg; minimum two years of ballet training). Exclusion criteria included bone, joint, or muscle problems that could limit stretching. Additionally, potential subjects exhibiting flexibility equal to or greater than 180 o of active extension were excluded because this elevated range of motion would limit the possibility of observing acute responses to stretching exercise. The experimental protocol had institutional ethical board approval, and all subjects signed an informed consent form prior to participation in the study. A Hip Flexibility Assessment To measure flexibility of the hip adductors, two flexometers (Code Research Institute, Brazil) were used (Fig. 1). The subjects lay in supine position on a rigid surface (7.0 cm x 26.6 cm x 15.7 cm) with hips flexed at 90 and legs elevated against a wall (Fig. 1A). The flexometers were positioned with the gauge immediately proximal to the tibial tuberosity. 27 When the lower limbs were completely vertical, the flexometers were adjusted to 0. During the test, the hips were maintained in slight external rotation. Movement was performed passively by the first evaluator, who pushed the subject s thighs toward the ground with her hands positioned immediately above the knees (Fig. 1B). The second and third evaluators were positioned at either side of the subject and registered the angles shown by the two flexometers. These values were added together to obtain the maximal range of motion. The test was terminated when the subject reported pain or the movement could not be continued further. The entire procedure did not take more than three seconds. As mentioned previously, the flexibility tests were repeated after a 48-hour interval to verify the testretest reliability. Excellent within Figure 1 Measurement of hip adductor flexibility using a flexometer: A, initial position; B, final position. B Author: Registered Trademark does not seem correct. Please confirm that the name Code Research Institute is trademarked

3 Author: Figure 2 has been typeset based on your manuscript - PLEASE PROOFREAD carefully. Author: Definition of PNF changed to follow abstract. NO STRETCHING The subjects remained supine and quiet for 210 s and day-to-day reliability was shown by intraclass correlation coefficients (within-day range = to 0.914, day-to-day range = to 0.924; p < 0.01). Stretching Protocol (Fig. 2) Stretching stimulus was applied by means of the static method and PNF, always in the same position adopted for the flexibility testing. Hip range of motion was assessed 10 seconds before and after the stretching protocols. The following are brief descriptions of each stretching method and control session: 1. Static: The hip adductors were passively stretched for 30 seconds in 4 sets separated by 30 second intervals. 2. PNF technique: The hip adductors were passively stretched for 10 seconds, then a 10-second active muscle contraction against resistance imposed by the evaluator at the inner thigh region was performed, and finally the hip muscles were extended by the evaluator for another 10 seconds. Four sets were performed, also Familiarization with the Static and PNF Protocols and randomization into experimental and control groups. STATIC STRETCHING 30 s at the maximal range of motion 4 sets with 30-s intervals Journal of Dance Medicine & Science Volume 15, Number 4, 2011 PNF STRETCHING 10 s at the maximal range of motion, 10 s active contraction against the stretch, 10 s at the maximal range of motion 4 sets with 30-s intervals Figure 2 Experimental protocols (Control, Static, and PNF Groups). PNF = proprioceptive neuromuscular facilitation. separated by 30-second intervals. 3. Control session: Subjects did not perform the stretching exercise after the first and before the second flexibility assessments. However, between the first and second tests they remained lying quietly for 210 seconds. Statistical Analyses The assumption of data normality was proven by univariate analysis. Therefore, the effects of static and PNF stretching methods on hip flexibility were compared by a 3 x 2 ANOVA for repeated measures, followed by Tukey post-hoc test whenever necessary. All calculations were made by means of the software SPSSTM 16.0 (Chicago, Illinois, USA), and p 0.05 was adopted as significance level. Results Table 1 presents the mean values for pre- and post-stretching conditions in all experimental groups. Withingroup significant differences (pre x post) were observed only in Static and PNF groups (p < ; effect 179 size = 0.24 and 0.39, respectively). No significant differences between Static and PNF groups were found in either pre- or post-stretching conditions (p = and p = 0.320, respectively). Discussion The present study investigated the acute effect of static and PNF stretching on hip adductor range of motion in female ballet dancers. The results suggested that static and PNF techniques were equally effective for increasing flexibility immediately following the stretching protocols. Thus, the hypothesis that different effects would be induced by these methods was not verified. Before stretching, the subjects exhibited flexibility values ranging from 138 to 180. In order to classify the dancers flexibility, their values were compared to the reference values for unilateral hip adductor flexibility. 28 Of the 45 participants, 16 had flexibility classified as moderately high, and the other 29 were highly flexible. The mean range of motion was 78.7 ± 5.7, which was also considered to be high flexibility (above 76 ). 28 Increase in flexibility depends on such structural and neural factors as viscoelastic relaxation, reflex activity, and muscle compliance Additionally, Magnusson and colleagues, 32 Halbertsma and Goeken, 35 and Halbertsma and associates 35 have suggested that the acute effect of stretching can change pain perception and consequently increase tolerance for exercise performed at extreme ranges of motion. Since dancers habitually show high flexibility levels, tolerance for movements performed at extreme ranges of motion may be an important aspect of their training. A few studies have proposed that PNF would be more effective than the static method of stretching for Table 1 Range of motion (degrees) Hip Adductor Flexibility in Control, Static, and PNF Groups for the Pre- and Post-stretching Conditions Control (n = 15) Static (n = 15) PNF (n = 15) Pre Post Pre Post Pre Post 159.9±11.5 ( ) 160.2±11.8 ( ) 153.3±11.3 ( ) 156.0±11.1* ( ) ±11.4 ( ) ±11.3* ( ) Values expressed as means ± standard deviations (minimum-maximum). *Significant difference compared to pre-stretching (p 0.05).

4 180 Volume 15, Number 4, 2011 Journal of Dance Medicine & Science improving flexibility. For example, Sharman and coworkers 2 have suggested that PNF performed at extreme ranges of motion would induce higher flexibility gains than other training methods. However, many other studies indicate that both static and PNF stretching methods can induce an acute increase in flexibility and improve pain tolerance. 5,8-11,27,37 Moore and Hutton 15 hypothesized that static and PNF stretching would induce similar flexibility gains, but also that pain perception would be higher when performing the PNF technique. Several factors may help to explain these differences, such as the flexibility level of the observed populations (from college students to elite athletes 9-11 ), the inclusion of subjects of both sexes, 10,11 and predominantly low sample sizes. 9 In two studies, the static stretching was performed with just one set of 10 second duration, 9-10 which is less than the usually recommended stimulus. 1 In another study, 11 no description of the stretching procedures was provided. The present findings do not concur with the thinking 2,9-11 that there would be differences in the ability of the static and PNF methods to increase maximal range of motion, at least not immediately after stretching. We were able to find two other studies that produced results similar to ours. 5,27 One of them evaluated female 5 and the other male college students. 27 Like the present study, the protocols were matched for stretching duration in the two methods 4 sets of stretching for 30 seconds, with a 30-second interval between sets. Some studies have demonstrated that stretch routines are deleterious to subsequent tasks requiring high strength or power levels. 21 While Nelson and coworkers 38 observed that strength was reduced after stretching, no matter how familiar subjects were with stretching exercises, other studies reported a positive chronic effect of stretching on performance in resistive exercises. 26,39 Such discrepancy warrants additional investigation to elucidate the possible acute and chronic concurrent effects of high intensity and volume stretching on the performance of choreographed movements, especially in sequences that depend largely on muscle strength and power. Conclusion The two stretching techniques studied here were equally effective for immediately increasing flexibility of the hip adductors in female ballet dancers. These results warrant further study of the effects induced by different methods of stretching on the long-term increase in the range of motion in highly trained subjects. The present findings suggest that the type of flexibility training used may not be an issue of primary concern; that choice may depend more on such factors as compatibility with a given element of the ballet training (e.g., strength, power, or motor learning), as well as the comfort and safety of the performed exercises. Editors Note As the Journal has been expanded in length since plans for this special issue guest edited by Dr. Peterson were finalized, space was available here to move this article into this issue rather than in its scheduled publication in the next issue. Serendipitously, it shares with the special issue articles an involvement with the dancer s hip, albeit from a very different perspective. References 1. American College of Sports Medicine: position stand on the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med Sci Sports Exerc. 1998;30(6): Sharman MJ, Cresswell AGV, Riek S. Proprioceptive neuromuscular stretching. Sports Med. 2006;36(11): Funk DC, Swank AM, Mikla BM, et al. Impact of prior exercise on hamstring flexibility: a comparison of proprioceptive neuromuscular facilitation and static stretching. J Strength Cond Res. 2003;17(3): Hardy L, Jones D. Dynamic flexibility and proprioceptive neuromuscular facilitation. Res Q Exerc Sport. 1986;57(2): Rubini EC, Gomes PSC. Efeito agudo dos alongamentos estático e FNP e sua duração. Braz J Exerc Physiol. 2004;3(1): Williford HN. A comparison of proprioceptive neuromuscular facilitation and static stretching techniques. Amer Corr Ther J. 1985;39(2): Winters MV, Blake CG, Trost JS, et al. Passive versus active stretching of hip flexor muscles in subjects with limited hip extension. Phys Ther. 2004;84(9): Sullivan MK, Dejulia JJ, Worrel TW. Effect of pelvic position and stretching method on hamstring muscle flexibility. Med Sci Sports Exerc. 1992;24(12): Etnyre BR, Abraham LD. Gains in range of ankle dorsiflexion using three popular stretching techniques. Am J Physical Med. 1986;65(4): Etnyre B, Lee E. Chronic and acute flexibility of men and women using three different stretching techniques. Res Q Exerc Sport. 1988;59(3): Osternig LR, Robertson RN, Troxel RK, Hansel P. Differential responses to proprioceptive neuromuscular facilitation (FNP) stretch techniques. Med Sci Sports Exerc. 1990;22(1): Sady SP, Wortman M, Blanke D. Flexibility training: ballistic, static or proprioceptive neuromuscular facilitation? Arch Phys Med Rehabil. 1982;63: Tanigawa MC. Comparison of the hold-relax procedure and passive mobilization on increasing muscle length. Phys Ther. 1972;52(7): Wallin D, Ekblom B, Grahn R, Nordenborg T. Improvement of muscle flexibility: a comparison between two techniques. Am J Sports Med. 1985;13(4): Moore MA, Hutton RS. Electromyographic investigation of muscle stretching techniques. Med Sci Sports Exerc. 1980;12(5): Bandy WD, Iron JM, Briggler M. The effect of static stretch and dynamic range of motion training on the flexibility of the hamstring muscles. J Orthop Sports Phys Ther.

5 Journal of Dance Medicine & Science Volume 15, Number 4, ;27(4): Davis DS, Ashby PE, McCale KL, et al. The effectiveness of 3 stretching techniques on hamstring flexibility using consistent stretching parameters. J Strength Cond Res. 2005;19(1): Gupta A, Fernihough B, Bailey G, et al. An evaluation of differences in hip external rotation strength and range of motion between female dancers and non-dancers. Br J Sports Med. 2004;38(6): Shrier I, Gossal K. Myths and truths of stretching. Phys Sportsmed. 2000;28(8): Shrier I. Why and whom to stretch? Phys Sports Med. 2002;33: Rubini EC, Costa ALL, Gomes PSC. The effects of stretching on strength performance. Sports Med. 2007;37(3): Koutedakis Y, Jamurtas A. The dancer as a performing athlete: physiological considerations. Sports Med. 2004;34(10): Koutedakis Y, Sharp NC. Thighmuscles strength training, dance exercise, dynamometry and anthropometry in professional ballerinas. J Strength Cond Res. 2004;18(4): Koutedakis Y, Hukam H, Metsios G, et al. The effects of three months of aerobic and strength training on selected performance and fitnessrelated parameters in modern dance students. J Strength Cond Res. 2007;21(3): Koutedakis Y, Myszkewycz L, Soulas D, et al. The effects of rest and subsequent training on selected physiological parameters in professional female classical dancers. Int J Sports Med. 1999;20: Kokkonen J, Nelson AG, Eldredge C, Winchester JB. Chronic static stretching improves exercise performance. Med Sci Sports Exerc. 2007;39(10): Gomes PSC, Rubini EC. Estabilidade e consistência interna da medida de amplitude do movimento de abdução do quadril. Braz J Exerc Physiol. 2004;3(1): Leighton JR. Manual of instruction for Leighton flexometer. Spokane, WA: Leighton Flexometer, Inc., Avela J, Kyrolainen H, Komi PV. Altered reflex sensitivity after repeated and prolonged passive muscle stretching. J Appl Physiol. 1999;86(4): Avela J, Finni T, Liikavainio T, et al. Neural and mechanical responses of the tríceps surae muscle group after 1h of repeated fast passive stretches. J Appl Physiol. 2004;96: Duchateau J, Guissard N. Neural aspects of muscle stretching. Exerc Sport Sci Rev. 2006;34(4): Magnusson PS, Simonsen EB, Aagaard P, et al. Mechanical and physiological responses to stretching with and without preisometric contraction in human skeletal muscle. Arch Phys Med Rehabil. 1996;77: Rubini EC, Gomes PSC. A titina e suas implicações na elasticidade muscular- breve revisão. Braz J Exerc Physiol. 2004;3(1): Magnusson SP, Aagaard P, Simonsen EB, Boisen-Møller F. Passive tensile stress and energy of the human hamstring muscles in vivo. Scand J Med Sci Sports. 2000;10(6): Halbertsma JPK, Göeken LNH. Stretching exercises: effect on passive extensibility and stiffness in short hamstrings of healthy subjects. Arch Phys Med Rehabil. 1994;75: Halbertsma JPK, Bolhuis AIV, Göeken LNH. Sport stretching: effect on passive muscle stiffness of short hamstrings. Arch Phys Med Rehabil. 1996;75: Beedle B, Leydig S, Carnucci J. No difference in pre- and post-exercise stretching on flexibility. J Strength Cond Res. 2007;21(3): Nelson AG, Kokkonen J, Eldredge C. Strength inhibition following an acute stretch is not limited to novice stretchers. Res Q Exerc Sport. 2005;76(4): LaRoche DP, Lussier MV, Roy SJ. Chronic stretching and voluntary muscle force. J Strength Cond Res. 2008;22(2):