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Stretching has long been an integral component of pre-performance activities for a multitude of athletic endeavors. Previous research has demonstrated that stretching may have detrimental effects on performance. Specific knowledge of the precise effects of stretching may influence the decision to appropriately apply stretching techniques in the sport and therapeutic settings.
The purpose of this pilot study was to examine the effects of static stretching, proprioceptive neuromuscular facilitation (contract-relax) stretching, and no stretching of the quadriceps muscle group on agility performance.
Twelve healthy, female, collegiate soccer players aged 18 – 25 performed one of the three stretching protocols (static, contract-relax, no stretch) and the agility test (T-test) on three non-consecutive days. Agility times were recorded and compared based on stretching technique and day that each test was performed.
No significant difference was found among the means of the different stretching techniques. The t-test agility performance times were as follows: control, =9.7 seconds; static stretch, =9.73 seconds; and contract-relax, =9.62 seconds.
The results of this study suggest that agility performance may be independent of stretching technique of the quadriceps performed in female collegiate soccer athletes. It is recommended that female soccer athletes about to engage in agility activity may perform either no stretch, static stretch, or contract-relax stretching according to individual preference.
Stretching is a common component of pre-performance activities for many athletic events. As such, the literature is rich with evidence supporting the effects of stretching on flexibility, with mounting evidence as to the effects of stretching on performance.1–5 However, limited research exists concerning the acute affects of different stretching techniques on athletic performance variables, specifically, agility.6
Several types of stretching techniques are currently incorporated by athletes for pre-event activities. Static stretching and proprioceptive neuromuscular facilitation (PNF) are common techniques used by therapists, athletic trainers, strength and conditioning professionals, and athletes to enhance flexibility.1,7–11 In most cases, these stretching activities are integrated as part of a warm-up session.
Some researchers studying the effects of stretching on performance have reported significant deficits in performance-related variables,9,10,12–17 while others found little or no difference.11,18 Church et al9 examined the effects of warm-up and flexibility treatments on vertical jump performance in females. Results demonstrated a decrease in vertical jump height for the PNF treatment group, leading researchers to speculate that performing PNF stretching techniques before a vertical jump test may be detrimental to performance. Wallmann et al10 investigated the effects of static stretching of the gastrocnemius on vertical jump performance in healthy adults. Researchers concluded that, since vertical jump height decreased by 5.6%, static stretching of the gastrocnemius had an immediate adverse effect on maximal jumping performance.
In contrast to the aforementioned findings, Unick et al11 examined the acute effects of stretching on vertical jump performance in female collegiate basketball players and concluded that vertical jump performance was not affected by stretching. They measured the effects of static and ballistic stretching, as well as power output at 15 and 30 minutes post-stretch. They reported no significant difference between power output and vertical jump values pre and post-stretch. Likewise, Behm et al13 reported that static stretching showed a 6.9% decrease in maximal voluntary contraction of the quadriceps while a control group experienced a 5.6% decrease in maximal voluntary control of the quadriceps from pre-test to post-test.
A major component of sport performance that has been poorly researched in the stretching literature is agility.19 The American College of Sports Medicine describes agility as the “…ability to rapidly change the position of the entire body in space with speed and accuracy20.” Agility can be thought of as a systemic integration of neuromuscular coordination, reaction time, speed, strength, balance. This complex nature of agility performance has lead many researchers to conduct studies that involve a breakdown of its component parts.
Cochrane et al21 additionally noted the complexity of factors that interact to produce agility performance and the difficulty in actually identifying and measuring those components. McMillian et al6 examined the effects of static versus dynamic warm-up protocols on agility performance, utilizing a common standardized agility test called the T-test. Results revealed a difference between the dynamic warm-up and both the static warm-up and no warm-up groups. Researchers concluded that a dynamic warm-up protocol may provide performance benefits that are superior to static or no warm-up protocols.
Given the paucity of literature regarding the effects of stretching on agility, the purpose of this pilot study was to examine the effects of three different stretching techniques (static, contract-relax stretching, and no stretch) on the quadriceps muscle group with regards to agility performance. The quadriceps muscle group was chosen primarily because females have been shown to be quadriceps dominant and it was thought that this dominance may be affected by stretching.27–29 The hypothesis to be tested is that agility performance would decrease in association with bouts of static stretching and PNF.
Twelve female Division I collegiate soccer players ages 18 – 25 ( mean = 19.17; SD = 0.94) participated in this study. The following criteria were used to select the subjects: a member of the women's soccer team, age 18–25, not currently pregnant, and no lower extremity orthopaedic injuries sustained within the last six months that would hinder the ability to give maximal effort during the T-test. Before initiating the study, the Biomedical Institutional Review Board of the University of Nevada, Las Vegas approved the study. Each subject gave both written and oral consent before engaging in the research protocol.
The T-test (Figure 1) is a common test used to measure 4-directional agility, and evaluates the ability of the subject to rapidly change direction while maintaining balance without loss of speed.19 The subject starts with both feet behind a line and sprints 10 yards forward, then shuffles 5 yards to the left, followed by 10 yards to the right, then 5 yards to the left, and finally, 10 yards backward to the original starting point. Pauole et al19 demonstrated that the T-test is a reliable and valid measure of leg speed, leg power, and agility.
Four cones were placed on the floor using the standard parameters for the T-test as described by Pauole et al.19 Additionally, two timing photo-cells (Lafayette Instrument Co., Lafayette, IN) were placed 6 ft apart at the start/finish position to record the time it took each subject to complete the T-test. One plinth was used for the PNF stretching station and one stool was used for the stretching subject to hold on to for balance during the static stretching station. One stopwatch was utilized to measure the duration of stretch at each station, and one stop-watch was used to time the 5-minute self-selected jog warm-up.
A repeated-measures design was used to determine the effectiveness of different stretching techniques on agility performance in female college soccer players over a one week period. The dependent variable was the time it took each athlete to complete the T-test. The independent variable consisted of three stretching techniques: contract-relax, static stretching, and a control group.
A pre-study information session was conducted in which subjects were instructed on the testing protocol as well as the proper method for each technique. A demonstration of the T-test was given and all subjects were asked to perform the T-test one time to allow for familiarity with the test. Subjects were also instructed not to participate in excessive physical activity prior to the testing sessions, but to continue with their normal workout routines.
Data was collected on three non-consecutive days over the course of one week. Using a balanced Latin square22 to reduce test order bias, subjects were randomly assigned into one of three different test orders as follows:
Prior to engaging in the stretching protocols, each subject completed a 5-minute warm-up jog at a self-selected speed. The purpose of this jog was to provide a general warm-up to minimize the risk of straining the quadriceps muscles during a maximal agility effort. Subjects then completed the assigned stretch protocol for that day. Immediately after completing the protocol, subjects performed the T-test one time. The three stretching protocols were as follows:
A one-way repeated measures analysis of variance (ANOVA) was used to analyze the differences among the three different stretching protocols. Statistical significance was set at p= 0.05 and all analyses were carried out using the Statistical Package for the Social Sciences version 13.0 (SPSS, Inc, Chicago, IL).
A repeated measures ANOVA revealed no statistically significant difference among the means, F(2,22) = 0.759, p=0.480, power = 0.162 for the control (no stretch), static stretching, and contract-relax stretching techniques in T-test agility performance times. The mean T-test performance times and standard deviations for control, static stretching, and contract-relax stretching as well as 95% confidence intervals are displayed in Table 1.
The purpose of this pilot study was to examine the differences among three different stretching techniques on agility performance in female collegiate soccer athletes. The results of this study revealed no differences among the three treatment groups on agility performance times.
An accurate comparison of this study to other studies is difficult secondary to a lack of published literature about the topic. However, results of this study are consistent with a similar study conducted by Faigenbaum et al5, in which researchers examined the acute effects of pre-event static stretching, dynamic exercise, and static stretching and dynamic exercise combined on vertical jump, medicine ball toss, 10-yard sprint, and pro-agility shuttle run in teenage athletes. Prior to testing, participants performed 5 minutes of walking/jogging followed by one of the warm-up protocols. Results revealed that performance on the vertical jump, medicine ball toss, and 10-yard sprint were significantly improved after dynamic exercise, and dynamic exercise and static stretching combined, as compared to static stretching alone. No significant difference was noted in the agility performance after the three different warm-up protocols. These results led researchers to believe that pre-event dynamic exercise or static stretching followed by dynamic exercise may be more beneficial than pre-event static stretching alone in teenage athletes participating in power activities.
Little and Williams18 examined the effects of different stretching protocols during warm-ups on high-speed motor capacities in 18 professional soccer players. Their design was similar, in that they examined the effects of no stretching and static stretching on agility performance. However, their design differed as they incorporated a dynamic stretch, rather than a PNF stretching technique. In addition, the agility task was performed on a zigzag course, versus the T-test used in the current study. These authors concluded that there was no difference between the control and static stretching groups. This result is consistent with the results revealed in the present study; however, the authors did report that the dynamic stretch protocol produced significantly faster agility performance than did both the control and static stretch groups.
Although a paucity of literature exists regarding the effects of stretching on agility performance, other components of agility have been researched, namely, speed and strength. The evidence on the effect of stretching on sprint performance provides conflicting results with questionable research quality making definitive conclusions difficult.24 However, work by other researchers4,17 supports the hypothesis that static stretching has a detrimental effect on sprint performance.
The evidence regarding the effects of stretching on force, torque, and jump performance also appears to provide inconclusive results.9–11,13,25 Whereas Wallmann et al10 and Church et al9 reported significant decreases in vertical jump height after bouts of static stretching and PNF stretching, respectively, Unick et al11 reported no difference in vertical jump scores as a result of static or ballistic stretching. The Unick et al11 study included 16 actively trained women who performed a series of vertical jumps at 4 minutes, 15 minutes, and 30 minutes after stretching the ham-strings, quadriceps, and gastrocnemius/soleus muscle complex. The protocol required the stretch to be held for a period of 15 seconds. This short time period may not have been long enough to induce a tissue extensibility change within the muscle. Research has shown that at least 30 seconds is needed to be effective in bringing about a change in flexibility.2,26 In addition, the vertical jumps were performed after 4 minutes of walking; which may have allowed the muscle to return to its pre-stretched length, thereby, affecting the results.
Power et al25 found that no difference existed in vertical jump scores after a static stretching routine. However, decreases in isometric maximal voluntary contraction and an increase of inactivation of the quadriceps were found to be statistically significant. Maximal voluntary contraction force of the quadriceps muscle showed a 9.5% decrease over the course of the 120 minute measurement period, while a 5.4% increase of inactivation of the quadriceps muscle was revealed, suggesting that static stretching may adversely affect these variables. Behm et al13 reported similar results in regard to maximal voluntary contraction of the quadriceps muscle. In their study, the static stretching group showed a 6.9% decrease in maximal voluntary contraction of the quadriceps muscles while the control group experienced a 5.6% decrease in maximal voluntary contraction of the quadriceps muscle from pre-test to post-test.
Although these previous studies revealed decreases in both speed and strength, which are components of agility, the studies do not appear to be consistent with the present results, which showed no differences in agility T-test performance scores. This may be because much of the current literature involves examining the effects of stretching on performance utilizing the hamstrings and triceps surae musculature.
In the present study, the authors chose to isolate the quadriceps muscle group, primarily because females have been shown to be quadriceps dominant and it was thought that this dominance27–29 may be affected by stretching. Additionally, there is very little, if any, literature investigating the effects of stretching on performance of only the quadriceps muscles. However, the results of this study reveal that the quadriceps muscle group may only play a small role in the variance of agility performance. Consequently, agility performance does not appear to be immediately affected by stretching only the quadriceps muscle group.
Strengthening other muscle groups may have varied the results. But it would be difficult to determine effects of stretching several muscle groups at once as this stretching may allow the muscles to return to their pre-stretched length prior to athletic performance due to the length of time between stretches.
Other limitations in this study include varying of testing times, activity level of the subjects prior to our testing time, and a small testing sample. There were some variations regarding data collection times due to time constraints on the part of the soccer team. For example, on Monday and Wednesday, data were collected at 2:00 p.m., while on Friday, data collection occurred at 9:00 a.m. Concerning activity level, the subjects were in a pre-season conditioning program, so we could not control the activity level of each subject prior to data collection, although we did ask the participants to maintain their current level of physical activity during the testing week. This variance in activity level may have affected the effort given by each subject while performing the T-test. The number of subjects participating in this study was small; a larger sample size would be more desirable and may have increased the power of the study. As such, the power was very low for the study. Consequently, the chance of making a type 2 error was high. However, as this was a feasibility study, we believe that the results from this study offer evidence for investigating the effects of stretching using the quadriceps and other muscle groups on agility performance using a more rigorous design.
This study holds relevance to the field of sport research in that current literature has demonstrated both the positive and adverse effects of stretching on flexibility, running, jumping, muscle strength, and power output; however, despite the availability of such literature, little research exists that investigates the acute effects of stretching on agility performance. Agility is a major component of many popular sports. Scientific knowledge regarding the effects of stretching on agility may be beneficial in the development of a training regimen designed to enhance athletic performance.
In conclusion, the results of the present study suggest that static stretching, contract-relax stretching, and no stretching of the quadriceps muscle group have no immediate adverse effect on agility performance in female collegiate soccer players. Further controlled-randomized trials are needed to fully examine and understand the complex nature of this topic. Also, a follow-up study with a larger sample size is needed. In addition, future research should also examine other muscle groups, motivational factors involved in stretching and performance, and athlete preferences and beliefs towards the effects of stretching and performance. It is recommended that female soccer athletes about to engage in agility activity may perform either no stretch, static stretch, or contract-relax stretching according to individual preference with no adverse effects on performance.