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Original Research

The Acute Effects of Different Durations of Static Stretching on Dynamic Balance Performance

Costa, Pablo B1; Graves, Barbara S2; Whitehurst, Michael2; Jacobs, Patrick L2

Author Information
Journal of Strength and Conditioning Research: January 2009 - Volume 23 - Issue 1 - p 141-147
doi: 10.1519/JSC.0b013e31818eb052
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Abstract

Introduction

Stretching is possibly the most commonly practiced routine used by sports trainers and sports medicine professionals for injury prevention and sports performance enhancement (60). Experts have commonly recommended stretching as part of a preexercise warm-up (2,19,29). According to Schilling and Stone (49), stretching is believed to improve athletic performance and prevent sports injury. Thus, the practice of stretching seems to be a widely accepted means applied in the attempt to reduce injuries and improve performance (7,52). Although stretching is routinely practiced, research documenting the benefits is limited (37).

Stretching has not been shown to reduce delayed-onset muscle soreness (27,31,40) or reduce injury risk (47,48). In addition, several studies examining the effects of stretching on performance have reported adverse effects from stretching (8,10,12,14,17,18,37,65). However, studies using relatively moderate stretching protocols and/or more performance-based measures tend to report no significant effects of stretching on performance (1,33,35,36,39,58,62). For example, Ogura et al. (45) found a decrease in maximal voluntary contraction with 60 seconds, but not 30 seconds, of static stretching.

Previous studies investigating the effects of stretching on factors associated with performance have used stretching routines of a single muscle group (15-30 minutes) for durations considerably longer than those commonly applied in the field. Young and Behm (65) believe that the stretching protocols in many studies are not representative of typical warm-up methods used by athletes to prepare for exercise or competition. Furthermore, Fletcher and Jones (17) believe that longer stretching protocols (90 seconds to an hour) are unlikely to be used by athletes when preparing for competition.

Static stretching for periods of 45 seconds has been shown to decrease balance, increase reaction time, and increase movement time (8). By comparison, a shorter protocol with 3 repetitions of 15-second stretching did not have any positive or negative effect on reaction time or explosive force (1). Irrgang et al. (30) believe balance to be important for athletes because, if the ability to maintain balance is not successful, a fall may occur, and inefficient balance strategies may also result in poor athletic performance. Thus, decreased balance performance has also been associated with higher injury risk (43,56,57). This decrease could pose an even greater concern when taking into account that exertion decreases balance performance (26,32,46,53,55,59,61). In addition, only a few research studies have specifically focused on the effects of stretching in women (12-14,16,58). The only previously published study investigating the effects of stretching on balance was limited to male subjects (8). Furthermore, Cramer et al. (13) have recently stated that more evidence on the effects of stretching in women is needed.

The effects of different durations of static stretching on balance performance have not been examined. Thus, the purpose of this study was to examine and compare the acute effects of 2 different durations of static stretching on dynamic balance performance in young (college aged) recreationally active healthy women. On the basis of previously published research, it was hypothesized that longer duration stretching protocols, but not protocols of shorter duration, would adversely affect balance.

Methods

Experimental Approach to the Problem

A randomized, experimental, crossover design was employed. Testing took place on 3 occasions at least 48 hours apart in the Strength and Conditioning Laboratory at Florida Atlantic University. Balance tests were performed in 3 separate sessions, with 1 session serving as a control condition and 2 other sessions as interventions. The 2 stretching intervention sessions were the same except for different stretching durations (15 and 45 seconds). In all 3 testing days, subjects were tested with a Biodex Stability System (BSS) device before (pretest) and after (posttest) the control and intervention conditions. Subjects were asked to avoid strenuous activity or exercise, alcohol, and any medication before testing that could otherwise affect balance.

During the 2 intervention conditions, the subjects performed the pretests (balance) on the Biodex device, and then they performed a warm-up on a cycle ergometer (Lode, Corival-906900, Groningen, Netherlands) at 70 rpm with 70-W power output for 5 minutes adapted from Behm et al. (8). After the cycle warm-up, subjects participated in the treatment condition assigned for that session. In the 2 stretching interventions, the main lower-body muscle groups-quadriceps, hamstrings, and plantar flexor muscles-were passively stretched, based on a stretching protocol as described by Behm et al. (8). During the control session, the subjects rested in a chair for 26 minutes, the approximate time required to complete the 45-second stretching intervention. After the treatment assigned for that session, the subjects repeated the balance testing on the Biodex device.

Subjects

Twenty-eight healthy, recreationally active women between the ages of 18 and 35 voluntarily participated in the experiment (Table 1). “Recreationally active” was defined as having participated in a minimum of 1 exercise session per week for the preceding 2 months and to have not participated in structured exercise training during that period. Individuals with previous history of lower-body injury, any impairments of the spinal column, or dysfunction of the vestibular system that could otherwise affect testing procedures or outcomes were excluded from the study. A health history questionnaire was used to determine the health and injury status of the subjects. The participants were asked to maintain their current exercise and daily lifestyle activities during the course of the study. Each participant was verbally informed of the protocol and asked to read and sign a consent form. The study was approved by the Florida Atlantic University Institutional Review Board before any subject recruitment or data collection.

T1-23
Table 1:
Physical characteristics of women subjects.

Static Stretching

The subjects performed a stretching protocol based on a previous study by Behm et al. (8) investigating the effects stretching had on balance, reaction time, and movement velocity. The present study expanded on that work by examining the effects of the stretching protocol used in the Behm study (45 seconds) in comparison with the effects of a protocol the authors considered to more closely reflect those regularly used in field settings (15 seconds). The stretching movements included passive unilateral knee flexion, supine hip flexion, ankle dorsiflexion with an extended knee, and ankle dorsiflexion with a semiflexed knee. During all stretches, the targeted limb was moved slowly until a mild discomfort was acknowledged by the subject, who was instructed to relax while the stretched position was maintained for 45 or 15 seconds, depending on which stretching intervention was performed for that particular day. Each stretch was repeated 3 times, with a 15-second rest between each stretch repetition, and repeated on the opposite limb. The same researcher controlled the range of motion and resistance for all participants.

Balance Testing

Dynamic balance was measured using a BSS (Biodex Medical Systems Inc., 1999, Shirley, NY). This Biodex device consists of a movable circular platform measuring 55 cm in diameter. The BSS has been proven to provide reliable measures of dynamic balance (4,5,11,28,50). The platform can tilt 20° from horizontal in all directions (360° range of motion), anterior-posterior and medial-lateral, simultaneously. According to Testerman and Vander Griend (54), this dynamic condition is similar to actual functional activities resulting in instability. The BSS device is interfaced with dedicated software (Biodex, Version 1.08, Biodex, Inc.) allowing the BSS to measure the degree of tilt in each axis, providing an average sway score. Eight springs located underneath the outer edge of the platform provide the resistance to movement. Resistance levels range from 8 (most stable) to 1 (least stable). One of the outcome measures for the Biodex device is the overall stability index (OSI). The OSI is an index of the average tilt in degrees from the center of the platform. Testerman and Vander Griend (54) believe OSI to be the best indicator of the overall stability of an individual to balance the platform. The higher the OSI numeric value, the greater the variability from horizontal positioning-that is, the greater the instability in balancing the platform. Conversely, lower scores indicate greater stability.

Stability testing was performed without footwear. Subjects were instructed to establish a foot position and comfortable stance width that allowed them to maintain the platform as stabilized (leveled horizontally) as possible. Foot position was recorded and marked with tape using coordinates on the platform's grid to ensure the same stance and, therefore, consistency on future tests. Foot placement was extremely important for testing the BSS because the position of the foot in reference to the center of the platform can change the way balance is maintained and, consequently, alter stability scores (50).

Subjects were instructed to maintain the platform in as level a position as possible for the duration of the test. Subjects were required to maintain an upright posture while keeping arms to their sides and looking straight ahead at a wall approximately 0.5 m away. Subjects were allowed 3 practice trials before each test trial. Each testing trial lasted 20 seconds. The resistance level used was set at number 3 on a scale ranging from 1 (least stable) to 8 (most stable).

Statistical Analyses

A 2 × 2 (intervention × time) repeated-measures analysis of variance (ANOVA) was used to analyze the results of the balance testing. A significance level of p ≤ 0.05 was considered statistically significant for this analysis. When justified, paired t-tests were performed between pre- and posttests to confirm significant changes within each condition. Bonferroni-type adjustment was employed to establish a significance level of p < 0.0167 for these tests. All statistical analyses were performed using the Statistical Package for Social Sciences for Microsoft Windows (version 15.0, 2006; SPSS, Inc., Chicago, Ill).

Results

The purpose of this study was to examine and compare the acute effects of 2 different durations of static stretching on dynamic balance performance. Repeated-measures ANOVA did not detect significant main effects for either intervention (p = 0.456) or for time (p = 0.540). However, there was a significant intervention × time interaction (p < 0.05). The paired t-test analyses indicated that the control condition and the 45-second stretching protocol did not significantly alter balance scores. Conversely, the 15-second stretching protocol significantly improved balance scores by 18.0% (p = 0.004). Table 2 summarizes the results of the pre- and posttests for the control, 15-second duration, and 45-second duration protocols. Figures 1, 2, and 3 display the pre- and post scores for the control, 15-second, and 45-second condition, respectively. Figure 4 displays the change scores for all conditions.

T2-23
Table 2:
Results of overall stability index testing for the 3 study conditions.
F1-23
Figure 1:
Results of overall stability index testing (mean ± SEM) for the control condition, p = 0.952.
F2-23
Figure 2:
Results of overall stability index testing (mean ± SEM) for the 15-second condition. *Indicates statistically significant pre- to posttest difference, p = 0.004.
F3-23
Figure 3:
Results of overall stability index testing (mean ± SEM) for the 45-second condition, p = 0.498.
F4-23
Figure 4:
Change scores for the control, 15-second, and 45-second conditions, p = 0.049.

Discussion

The purpose of this study was to examine the effects of different durations of static stretching on dynamic balance. Several studies have reported decrements in performance after a session of static stretching (8,12,14,37,65). However, only one research study has examined the acute effects of stretching on balance (8). Our study was the first to investigate the effects of different durations of stretching and the first to examine the effects within a population of women. The results of the current study demonstrate that a relatively moderate stretching protocol may actually improve dynamic balance. Moreover, the control and 45-second stretching protocol did not significantly change from pre- to posttest, suggesting that longer-duration stretching protocols may not adversely affect balance.

The findings of the present study are not consistent with those of Behm et al. (8), who found a decrease in balance performance a 45-second-duration stretching protocol. This difference in outcomes could be due to different testing devices or to different biomechanical responses due to gender. Behm and associates assessed balance using a self-constructed device, whereas the present study used a commercial apparatus commonly applied in research settings. Additionally, Knudson et al. (33) have stated that a reverse placebo effect may exist, by which individuals would expect to perform better after stretching.

Mechanical and neural factors influence the responses to stretching (23). Accordingly, changes in joint range of motion after static stretching have been reported to be caused by changes in musculotendinous stiffness (15,21,22,38) or in pain tolerance (24,25,41,42). Consequently, a less stiff musculotendinous unit may increase the time for forces and signals to be transmitted between the central nervous system and skeletal system (18). Therefore, Young and Elliott (64) have stated that a high level of musculotendinous stiffness may ensure a fast transmission of muscular force to the bones. Behm et al. (8) have suggested that a more compliant musculotendinous unit has more slack on the connective tissue, hence affecting muscle activation, which could alter reaction and movement time, consequently affecting balance and stability, or the proprioception of a limb.

Although measurement of musculotendinous stiffness was beyond the scope of this study, a moderate stretching protocol (15 seconds) may cause changes in muscle-tendon unit stiffness that are not detrimental in nature given the positive outcomes with such stretching protocol. Additionally, repeated and prolonged passive stretching has been shown to decrease reflex activity resulting from reduced sensitivity of the muscle spindles to repeated stretch (3), which may partly explain the effects of stretching on balance. Again, a moderate stretching protocol may avoid possibly unfavorable reflex activity decrements. Moreover, static stretching has been shown to improve joint position sense, which investigators believe could be an increased proprioceptive feedback (20). This improvement in proprioception could be a mechanism that might, consequently, improve balance.

Brandenburg (10) believes that studies with longer stretching protocols yield larger decrements in performance, whereas shorter protocols elicit smaller reductions in performance. Brandenburg suggests that these studies seem to point toward an association between performance and stretch duration (10). This association of performance and stretch duration has been clearly demonstrated by Ogura et al. (45), who has reported decreases in maximal voluntary contractions with 60, but not 30, seconds of static stretching. In our study, the 15-second stretching protocol significantly improved balance scores. On the other hand, these results were not similar to the findings by Brandenburg (10) or Kokkonen et al. (37), who observed strength performance decrements with a 15-second stretch protocol. In addition, Fletcher and Jones (17) found improved sprint performance (as evidenced by decreased sprint times) with 1 set of 20-second stretching.

Knudson and Noffal (34) report meaningful decreases in maximal handgrip only after 20-40 seconds of stretching. In another study, 3 repetitions of 15-second stretching did not significantly alter vertical jump kinematics (33). Also, 2 repetitions of 15 seconds did not significantly affect tennis serve performance (35). In addition, a stretching protocol with 3 repetitions of 15 seconds did not have a positive or negative effect on reaction time or explosive force (1). Even longer-duration stretching protocols of 30 seconds for 3 repetitions did not significantly alter vertical jump performance in trained women (58) or kicking range of motion or foot speed in trained men (63). Similarly, Koch et al. (36) found no significant differences in broad jump performance in trained and untrained men and women with a 10-second stretching of various muscle groups. Furthermore, Young and Elliott (64) found that 3 repetitions of 15-second stretching decreased drop jump but not concentric jump performance.

A trend seems to exist whereby static stretching of moderate duration produces either no significant change or a positive effect, particularly with performance-based measures. Little and Williams (39), who found no detrimental effects from 30 seconds of stretching on performance measures, suggest that if static stretching is to be used, minimizing stretches to short durations may minimize decrements to performance. Similarly, Ogura et al. (2007) state that previous studies reporting performance decreases from stretching have used protocols that are not representative of practical stretching regimens (45). Moreover, static stretching has been shown to improve joint position sense, which investigators believe could be caused by increased proprioceptive feedback (20). This improvement in proprioception could be a mechanism that might, consequently, improve balance.

Although range of motion was not measured in our study, women have generally been shown to have greater flexibility than men (6,9,51). Thus, the women might have been less affected by the stretching protocol than a population of men would be. Similarly, women did not demonstrate decreases in peak torque or mean power output even with 4 repetitions of 30 seconds of stretching (16). The current study did not assess trained athletes, which may limit the generalizations to this specific population. Similarly, because the present study used only women subjects, the effects of different durations of static stretching on balance should be examined in men and also in older adults and children. Also, future stretching and balance research should focus on the chronic effects of a consistent static stretching exercise program. Furthermore, other performance-related measures should be scientifically reassessed using the relatively shorter stretch durations used in the current study. In addition, Young and Elliott (64) believe the effects of stretching may be diluted by a positive influence of a jogging warm-up. By contrast, physical exertion has been shown to decrease balance performance (46,53,55), and, therefore, future studies investigating the effects of stretching on balance should consider avoiding active warm-ups.

The results of this study have revealed that a stretching protocol with 45-second hold durations does not adversely affect balance. In addition, the current study reveals that a moderate, 15-second stretching protocol induced significant improvements in dynamic balance performance by increasing postural stability. Therefore, a moderate stretching protocol with 15-second durations of stretching on each muscle group seems to be sufficient to improve dynamic balance performance.

Practical Applications

One factor to be considered with stretching programs is the time allocated for this component of training. According to the American College of Sports Medicine (2), a stretching routine should last 15-30 minutes. Potential benefits related to stretching need to be objectively considered relative to the time necessary for this type of training. Because of a lack of positive effects, McMillian et al. (44) concluded that stretching may be unnecessary for athletes and teams under certain time constraints. Knowing whether the time spent on a stretching program would be better used in a more specific training regimen is important. When aiming to improve individual aspects of an athlete or a team, consideration must be taken regarding the cost-benefit relationship between a stretching protocol and the possible benefits.

Strength and conditioning professionals and sport coaches who may be concerned with possible balance performance decreases from static stretching may not have to avoid this form of preexercise activity when dealing with a young, recreationally active population of women. More importantly, moderate, shorter-duration stretching protocols seem to improve dynamic balance performance in young women.

Acknowledgments

We would like to thank all of the subjects who participated in this study. The results of the current study do not constitute endorsement of any of the products by the authors or the NSCA.

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Keywords:

Biodex; flexibility; stability; warm-up; women

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