The influence of two stretching techniques on standing hip range of motion.
Recent research has suggested that stretching may not enhance performance, depending on the actual sport and movement related activities. (4,8-10) Additionally, there has been some controversy over whether stretching does indeed reduce the occurrence of injury. (4,10-13) From the literature available to date, it appears that stretching during warm-up and in some specific sports (those that utilize a vertical jump) may actually be contraindicated for injury reduction and performance enhancement. (14) To date, there is not enough research evidence available to make global recommendations for all contexts in which stretching is utilized.
Commonly researched flexibility training programs are ballistic, static, and proprioceptive neuromuscular facilitation (PNF). Ballistic stretching involves repeated bouncing throughout a full range of motion of less than 15 seconds in duration. Static stretching is a slow controlled stretch that is held for at least 5 seconds and as long as 120 seconds. PNF stretch techniques, developed by Knott and Voss, are based on neuromuscular theories of inhibition and facilitation. (15) There is a growing body of research evidence that PNF techniques operate differently on a neuromuscular level than what was originally proposed by Knott and Voss. (11,12,16-18)
Flexibility training programs can also be classified as either active or passive. (19) Passive flexibility is defined as the maximum assisted ROM at a joint; active flexibility is defined as the maximum unassisted ROM at a joint. (19-21) Common types of passive flexibility training programs are static stretch and some PNF stretching techniques. Active flexibility techniques are Bartenieff Fundamentals (BF), Awareness Through Movement (ATM), and some PNF stretch techniques. (16,22-27)
Active flexibility is based on Sherrington's Law that a maximal concentric contraction of the agonist muscle will result in a maximal eccentric contraction of the antagonist muscle. (15) In order to improve active flexibility at a joint, the agonist muscle would have to be strengthened, or the antagonist muscle must exhibit decreased resistance. (19,20) In the literature, when stretching is characterized by the terms active and passive, it has been suggested that active flexibility has more uses because the effects can be more readily utilized by the participant. (3,19,20,28,29)
The Bartenieff Fundamentals (BF), developed by Irmgard Bartenieff, grew out of her career as a physical therapist working with polio patients and was first published in 1955. (30,31) The BF exercises are designed to increase ROM at the proximal joints through coordination of the supporting agonist and antagonist muscles. They consist primarily of unilateral muscle contractions of the prime movers resulting in joint actions of flexion, extension, abduction, adduction, and medial and lateral rotation.
Most studies that compare different types of stretching techniques have used intervention periods of 1 day or at most 1 week. Although an intervention period of 1 day may illuminate some of the immediate differences of the effects of the various stretching techniques, it provides little information on the long-term differences and effects of different stretching techniques, which is important in dance training. According to one group of researchers, an increase in integrated electromyography (IEMG) recorded motor unit activation during 3 to 5 weeks of a strength training program is due to neural adaptation, whereas an increase in IEMG after 5 weeks of training is due to an increase in the size of the muscle fiber itself. (32) A study of at least 3 weeks allows for neural adaptation to take place in a participant. Flexibility training programs are not primarily focused on maximally increasing a participant's muscular strength; however, in accordance with Sherrington's Law, there should be an increase in muscular strength of the agonist muscle in order for there to be an increase in the length of the antagonist muscle.
There is limited quantitative data documenting the effects of the BF exercises on joint ROM. (23,33) It is thought that they increase ROM at the proximal joints through Sherrington's Law and autogenic inhibition. The effects of PNF stretch techniques have been well documented. (2,4,6,18,34,35) A smaller number of studies have looked at the differences between active and passive stretch techniques. (19-21,27,36) Differences between passive range of motion (PROM) and active range of motion (AROM) while standing have been found in dancers. (37-39) The majority of these studies have measured these differences in standing with the gesture leg in the a la seconde position. There is some evidence that specific types of stretching and strength training interventions are effective in increasing standing PROM or AROM in dancers. (37-40)
The purpose of this study was to assess the effects of two supine stretching techniques commonly used by dancers on standing hip ROM.
Materials and Methods Participants
The participants in this study were 18 moderately active female undergraduate students who engaged in some form of physical activity at least 3 times per week for a minimum of 20 minutes during the 6 months prior to their involvement in the study. They had no current or chronic history of injury in their lower extremities.
All participants signed an informed consent document and completed a health history questionnaire prior to involvement, and the study was approved by a university Institutional Review Board. The participants were randomly assigned to one of three groups: active stretching (6), passive stretching (6), or control (6). They were instructed not to engage in any outside stretching exercises and not to change their activity level for the duration of the study. Non-dancers were used in order to control for both physical activity level and amount of time spent stretching outside of the research study.
A custom-made electrogoniometer (elgon) composed of two arms (each 20 cm in length) and a potentiometer (input impedance = 103 [ohm]) were used to record joint angles of the hip. The elgon was aligned with the subject's greater trochanter on the right limb. (17) Its signal was amplified by a Therapeutics Unlimited, Inc., Iowa City, IA., amplifier module (Model 544, input impedance = 107 [ohm], CMRR = 87 dB at 60 Hz). Velcro straps were used to secure the elgon to the subject's right thigh and waist. The elgon was used in this study to reduce the measurement reading error of the researcher and increase the reliability of the measurement over trials. A hand held goniometer was used to confirm the elgon measurements. The spine and pelvis were stabilized with Velcro straps to limit their influence on the results. A custom made stand measuring 46 inches in height by 36 inches in length was used for the standing hip ROM tests (Fig. 1).
ROM Tests and Trials
The participants executed two ROM tests in order to measure standing hip flexion and extension angles (Fig. 2). (23) Five trials each of standing hip flexion and extension were completed by each participant. Standing hip flexion was measured with the right knee bent at 90[degrees] to control for hamstring in volvement of the right hip (without internal or external rotation). Standing hip extension was measured with the right knee bent (without internal or external rotation) using a modified Thomas test. (41) All measurements were collected on the right limb of every participant. No warm-up was given prior to the ROM tests.
Pre-Test and Post-Tests
Two consecutive days of pre-testing were used to establish a stable baseline of joint ROM for each participant. All tests were conducted at the same time of day for each individual participant in order to control for temporal flexibility changes.
The two stretching groups received instruction in their specific stretch technique during the first day. Each group completed one session four times per week for 3 weeks (N = 12). The participants performed their stretching routines in the presence of the researcher to insure compliance, accuracy, and consistency of the intervention for the duration of the study. All sessions of both stretching techniques were completed in 8 minutes (4 minutes on each leg) to control for variation in total duration of the two techniques. All data collection and interventions were collected and administered by the same researcher.
Passive Stretch Technique
The passive stretch technique consisted of the participant lying supine with both legs flexed at the hips and knees. She was instructed to inhale and exhale slowly while the right hip was passively flexed as far as possible (without internal or external rotation) with the assistance of the researcher and held at end-point for 60 seconds. The right knee was bent at approximately 90[degrees] and the right ankle dorsi-flexed throughout the duration of the stretch. The leg that was not being stretched was flexed with the knee bent and foot flat on the testing table for support. This procedure was repeated four times consecutively on each leg (Fig. 3).
Active Stretch Technique
For the active stretching technique, the intervention consisted of the participant actively performing an alternating hip flexion exercise. (31) Initially, the participant assumed a supine position with both legs flexed at the hips and knees. She slowly inhaled and exhaled before flexing the hip to be stretched (without internal or external rotation), brought the knee toward the chest, held for 2 seconds, and then lowered the leg. The researcher verbally cued all the participants on when to inhale, exhale, and when to lift and lower the legs to insure that they all performed the technique consistently with respect to the duration of each component of the technique. The participant was instructed to keep the knee bent at 90[degrees] with the ankle dorsi-flexed throughout the duration of the stretch technique. The active stretch technique was performed for a total of 32 times, alternating legs (Fig. 3).
A one-way ANOVA was used to analyze the participants' descriptive characteristics of age, height, and weight. A repeated-measures ANOVA (group x day) was used to analyze the data gathered on the pre- and post-standing hip ROM tests and the maximum hip flexion angles during the intervention. Tukey's post hoc tests were used to determine which group was significantly different from the other for any results that had significant main effects. The level of significance in all analyses was determined by a two-tailed test with a probability of p < 0.05. The Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL) was used to complete all of the analyses.
The primary objective of this study was to determine if the two supine stretching techniques produced an increase in standing hip ROM as compared to the control group.
Participants' Descriptive Characteristics
The participants' descriptive data by groups are presented in Table 1. In general, the control group was taller and heavier than the other groups. The active stretch group was both older and shorter than either the passive stretch group or the control group. However, none of these differences was statistically significant except for the height of the control group [F(2,16) = 8.47, p < 0.05].
Pre-Hip and Post-Hip ROM Tests
The means and standard deviations of the pre- and post-standing hip ROM tests are presented in Tables 2 and 3. Two hip ROM tests were conducted during each of the testing sessions: standing hip flexion and standing hip extension. As expected there were no significant differences in the standing hip extension tests for any of the three groups between the pre- and post-sessions. There were significant differences between the group means on the standing hip flexion test [F(4,86) = 7.03, p < 0.01] for both intervention groups between the pre- and post-test days. On average, the control group had greater absolute values on the pretest days for all hip ROM tests than both intervention groups.
Both stretch groups' means increased from day 1 and day 2 of the pre-testing to the final post-test day. The control group's mean for the standing hip flexion test decreased across the 3 days of testing.
In summary, the passive stretch group had a greater increase in hip flexion angle during the standing hip flexion test than the active stretch group. Both of the intervention groups had statistically significant increases in standing hip flexion angles as compared to the control group.
In general, the findings of this study are consistent with those of previous studies on the ability of stretching to increasing hip flexion, in that there was a minimum increase in hip ROM of 10[degrees] for both the active and passive stretch groups. (23,22,33-35,42,43) In contrast to the values reported on the differences between active and passive stretch techniques, (2,16,19,20,22,28,36) the passive stretch group exhibited a greater increase in standing hip flexion compared to the active stretch group.
Although the results of the standing hip extension test were not significant, there was a change of 1[degrees] to 8[degrees] for all groups. This increase may be due to the 15 hip extension tests administered over the course of the study.
Because the pre-test and post-test measures were used to determine the intervention effects a control group was necessary in order to determine if the changes in hip ROM were due to the ROM tests or to the stretching techniques. The control group means for the standing hip flexion and standing hip extension tests were not significantly different from the pre- to post-test means, suggesting that the ROM tests did not influence the participants' standing hip ROM during the duration of the study.
Most previous studies investigating the effects of different stretching techniques used a single pre- and post-test design. Many of these studies have brief treatment durations of 1 week. (3,17-19) In this study, both the active and passive stretch groups had an increase in mean hip flexion angles of 8[degrees] to 12[degrees] from the first to the second pre-test days.
The control group mean was larger than both intervention group means on pre-test day one for both standing hip ROM tests. All three groups of participants exhibited normal standing hip ROM on pre-test day 1. A standing hip ROM value of 90[degrees] for flexion and 10[degrees] for extension falls in the normal range. (44) There were no parameters set for participant inclusion dependent on existent hip ROM. From pre-test day 1 to pretest day 2, all three group means for the hip ROM tests regressed toward each other. Most studies in the literature use ROM gain scores as the method for statistically evaluating their data. However, gain scores may not be the most appropriate method of evaluating differences among hip flexion stretching techniques. This is particularly true when there seems to be a wide range of values within a study sample population.
The results of this study are relevant to the training and well-being of dancers for two reasons. They lend evidence-based support for the use of supine stretching in dance training. Additionally, the results suggest that depending on an individual dancer's flexibility goals or requirements, they could utilize either active or passive stretching techniques to improve their standing hip flexion.
In summary, based on the results of this study, it seems that the duration of the stretching program is one of the contributing factors to the amount of improvement that is attained in hip ROM testing. Although the passive stretch group had greater increases in standing hip ROM at the end of the study, the technique used requires assistance. Though not as effective as the passive stretch technique, the active technique did significantly increase the standing hip ROM. Active stretching techniques may be particularly useful due to the greater control the individual has over the entirety of the stretch and consequently the avoidance of over stretching.
Hip flexion in an upright posture is a body movement that is commonly found in many athletic activities, such as dance and gymnastics. Dance technique utilizes standing hip flexion at the barre, in the center, and across the floor, as well as in performance. The results of this study suggest that both the active and passive stretch techniques (performed in a supine position) influenced the standing hip ROM. Furthermore, the results indicate that supine hip flexion stretching programs can influence standing hip flexion, which is a more complex motor skill to execute. As this study had a small number of participants (N = 18), more studies with larger sample size and a transfer test of standing hip ROM would be needed to examine whether stretching programs actually do transfer to useable hip ROM while dancing, thus lending practical evidence for what has been theorized in the literature.
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Elin E. Lobel, Ph.D., G.C.F.P., C.M.A.
Elin E. Lobel, Ph.D., G.C.F.P., C.M.A., Department of Kinesiology, Towson University, Towson, Maryland.
Correspondence: Elin E. Lobel, Ph.D., G.C.F.P., C.M.A., Department of Kinesiology, Towson University, 8000 York Road, Towson, Maryland 21252-0001; firstname.lastname@example.org.
Caption: Figure 1: Custom made stand used for standing hip ROM.
Caption: Figure 2: Pre-test and post-test measures of hip ROM.
Caption: Figure 3: Active and passive stretch conditions.
Table 1 Physical Characteristics of the Three Groups of Participants (N = 18) Group N Age (years) Height (cm) Weight (kg) M SD M SD M SD Active 6 27.0 (9.7) 161.8 (5.9) 57.1 (4.7) Passive 6 22.3 (2.3) 163.9 (5.9) 62.5 (15.6) Control 6 26.3 (5.3) 175.3 (6.4) * 71.6 (15.3) M = Mean; SD = Standard Deviation; * p < 0.05. Table 2 Pre-Standing and Post-Standing Hip Flexion for Active, Passive, and Control Groups Group Range of Motion ([degrees]) Pre 1 Pre 2 M SD M SD Active 86.9 (33.6) 94.9 (16.2) Passive 85.9 (25.9) 97.5 (16.3) Control 93.1 (24.5) 89.5 (22.9) Group Range of Motion Difference ([degrees]) Post M SD (Post-Pre1) Active 97.1 (23.1) * 10.2 Passive 118.4 (12.3) * 32.5 Control 88.9 (22.5) -4.2 M = Mean; SD = Standard Deviation; * p < 0.01. Table 3 Pre-Standing and Post-Standing Hip Extension for Active, Passive, and Control Groups Group Range of Motion ([degrees]) Pre 1 Pre 2 M SD M SD Active -6.3 (18.3) -13.2 (8.9) Passive -8.4 (13.2) -17.4 (9.9) Control -10.3 (13.3) -14.2 (10.9) Group Range of Motion Difference ([degrees]) Post M SD (Post-Pre1) Active -14.4 (8.8) 8.1 Passive -16.4 (18.3) 8.1 Control -11.3 (14.4) 1.0 M = Mean; SD = Standard Deviation.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Author:||Lobel, Elin E.|
|Publication:||Journal of Dance Medicine & Science|
|Date:||Jan 1, 2016|
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