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Original Research

Three Days of Static Stretching Within a Warm-Up Does Not Affect Repeated-Sprint Ability in Youth Soccer Players

Wong, Pui-Lam1; Lau, Patrick W C1; Mao, De Wei2; Wu, Yao Yu2; Behm, David G3; Wisløff, Ulrik4

Author Information
Journal of Strength and Conditioning Research: March 2011 - Volume 25 - Issue 3 - p 838-845
doi: 10.1519/JSC.0b013e3181cc2266
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Abstract

Introduction

Warm-up is a widely accepted practice preceding nearly every athletic event, and static stretching has been typically performed as a standard part of the warm-up routine (7). It has been shown that the effect of static stretching on subsequent performance is highly dependent on the type of performance being carried out (54). For example, tasks that are highly reliant on a single muscular contraction to generate force (3,5,6,12,13,19,36,37,42,56) are more consistently affected by acute bouts of static stretching. On the other hand, there is conflicting evidence regarding stretch-induced impairments on power and running activities. For example, a review of the recent literature shows 4 studies that report no effect of static stretching on jump performance (9,22,27,37), whereas 5 other studies report static stretch-induced impairments in vertical jump performance (8,24,25,39,49). Similarly, there are 5 recent studies reporting static stretch-induced decrements in sprint time (4,11,17,40,51) that contrast with 2 studies showing no effect of static stretching on sprint performance (23,48). Perhaps the response of multiarticular, bilateral, power-based activities (i.e., jumping and running) to a single bout of static stretching is more variable than uniarticular, unilateral strength (i.e., leg extensions) activities. However, many power-based sports such as soccer, North American football, hockey, and volleyball may practice and use static stretching for 3-5 consecutive days before a competition. The cumulative effect of daily repeated stretching could conceivably magnify stretch-induced power impairments.

In assessing soccer players' sprint performance, many previous studies measured players' single 30-m sprint performance with 2- to 3-minute recovery in between (10,52). However, during a 90-minute game, it is unlikely for a player to have 2- to 3-minute passive recovery, and it is more important for the player to repeatedly perform sprints with a short recovery time, or repeated-sprint ability (RSA) (46). Therefore, RSA is considered to more effectively simulate game performance as compared with a single bout of sprint (44,46). In this regard, the RSA test consisting of ≤10 sprint bouts with 20- to 30-second recovery times has been recommended (16). Contrary to a single sprint that mainly derives energy from anaerobic metabolism, the energy during RSA is derived from both anaerobic and aerobic metabolisms (44). Previous findings regarding the effect of static stretching on a single sprint (18,30,40) might not apply to RSA. However, to date, there is only 1 previous study examining the acute effect of static stretching on a biomechanically complex and metabolically more demanding activity such as RSA (4) and no published studies dedicated for soccer.

Furthermore, previous studies examining the effect of static stretching on single sprint performance among soccer players (30,40) did not address the real situation that considers the weekly periodization during a soccer season. In the study of Little and William (30), soccer players performed 3 different stretching protocols (i.e., static stretch, no stretch, and dynamics stretch) on 3 nonconsecutive days within 1 week, and 10- and 20-m sprint tests were performed after each of the stretching protocols. In another study of Sayers et al. (40), the soccer players were assigned to stretching or no-stretching groups, and a 30-m sprint test was conducted after the warm-up on 2 nonconsecutive days. However, during the competitive season, each team usually plays 1 official match per week, or sometimes 2 matches with 3-4 days apart. In the period of intense match fixture, an appropriate warm-up and cool-down protocol in the training session, before and after the match, is of great concern to the soccer coach and strength and conditioning specialist to reduce postexercise muscle soreness, remove accumulated muscle lactate, and promote better performance in the upcoming match. With the aforementioned controversy of static stretching on subsequent power performances, coaches apparently resist to incorporate it in the in-season daily warm-up routine. However, it is also conceivable that repeated daily stretching could result in a muscle that is more resistant to stretch-induced impairments, perhaps by developing a greater tolerance to stretch (31,32). Therefore, a study of warm-up protocol (with and without static stretching) used for 3 consecutive days before the test day and immediately before the RSA test would be of practical interest.

The purpose of this study was to examine the effects of performing 3 days of aerobic warm-up that included static stretching on RSA among youth soccer players. In addition to the warm-ups with or without static stretching, the 3 consecutive days of intermittent aerobic training mimicked the situation of intense match fixture. Specifically, the RSA test was performed after the warm-up routine (static stretching vs. no-stretching) on days 1 and 5 of the protocol. We hypothesized that as compared with aerobic warm-up alone (no-stretching), static stretching as part of the warm-up routine negatively influences the fastest sprint but not the RSA because of the longer duration of this type of exercise (7).

Methods

Experimental Approach to the Problem

A within player, repeated-measure design was used to test the experimental hypotheses. All players participated in 2 study series (control series [CON]: aerobic warm-up; and static-stretching series [SS]: aerobic warm-up and static stretching), and each lasted for 5 days (Figure 1) in a counterbalanced order to limit any effects induced by the treatment orders. In each series, the RSA test was performed on days 1 and 5, separated by either 3 days of intermittent aerobic endurance training (CON) or the same aerobic training with static stretching (SS) from days 2 to 4 (Figure 1). In this regard, the same warm-up and cool-down protocol was used before and after all tests and exercises in the same series (Figure 1). There were 3 days of rest after the first series (random allocation of CON or SS), allowing the players to fully recover and return to a similar physical status at the beginning of the second series. To facilitate the incorporation of the results from the present study into most soccer teams, the warm-up periods used in the present study are short and with same duration (i.e., ∼15 minutes). Specifically, all players performed 13-minute slow jogging (∼8 km·h−1) with no static stretching exercises in CON. In the SS, the players performed 10-minute slow jogging (∼8 km·h−1) and a 3-minute static-stretching exercise program of the lower extremities (11). Repeated-sprint ability test was performed 2 minutes after the warm-up routine on days 1 and 5 of each series (30). All players had prior experience in RSA test and the static stretching exercises used in the present study. They performed the RSA test several times during the competitive season and static stretching exercises during daily training without supervision. The players were instructed not to participate in vigorous exercise 72 hours before the orientation session that was held 1 day before the first series. In addition, they were instructed not to participate in vigorous exercise throughout the study course. All tests and exercises were taken at the same time of the day under similar climatic conditions (temperature: 22-25°C; humidity: 30-40%) on natural grass, with the players wearing their own soccer shoes.

Figure 1
Figure 1:
The experimental design consisted of 2 series. The same warm-up/cool-down protocol was used before and after all tests and training in the same series. Ten players performed the control series (13-minute aerobic warm-up) in series 1, and the experimental series (10-minute aerobic warm-up and 3-minute static stretching) in series 2. The other 10 players performed the series in reversed order.

Subjects

Twenty youth soccer players participated in the study 1 week after the end of the season and when the regular soccer training had just ended. Their age, soccer experience, body mass, height, and body mass index were 16.8 ± 0.4 years, 6.6 ± 0.5 years, 68.2 ± 2.6 kg, 1.71 ± 0.01 m, and 23.3 ± 0.7 kg·m−2, respectively. These players compete at the highest match level for their age category. During the season, the players had soccer training thrice a week that each lasted for 2 hours and generally consisted of a 15-minute warm-up routine, 30-minute technical training, 30-minute tactical training, 40-minute simulated competition, and 5-minute cool-down. The study was conducted according to the Declaration of Helsinki, and the protocol was fully approved by the Clinical Research Ethics Committee. All players and their parents or guardians were properly informed of the experimental risks, nature of the study without being informed of its detailed aims, and both signed an informed consent document before the study.

Procedures

Repeated-Sprint Ability Test

The RSA test consisted of 9 30-m sprints (9 × 30 m) separated by a 25-second passive recovery period. The distance of 30 m was selected because it has been suggested as a standard distance in sprint test for soccer players (46). The time for the 25-second recovery was measured by a hand-held stopwatch. The sprint times were recorded by infrared light sensors (Brower Timing Systems, Salt Lake City, UT, USA, 0.01-second precision) located at 0 and 30 m with 1-m height. The players stood 0.5 m behind the sensor before they commence every sprint, and running started from the standing position. Each player was instructed and verbally encouraged to give a maximal effort during all RSA tests. The reliability of 9 sprint times was assessed by intraclass correlation coefficient (ICC), and the result shows that it was highly repeatable (ICC > 0.96; SEM < 0.04; and n = 20).

Repeated-sprint ability was analyzed by 4 methods: (a) the fastest sprint time (FST) among the sprints, (b) average sprint time (AST) among sprints, (c) total sprint time (TST), and (d) percentage decrement score (%Decre) as reported by Glaister et al. (21). The TST is used because it has been recommended by a previous study of RSA (45). The %Decre is selected because it was recently reported as the most valid and reliable method of quantifying fatigue in the RSA test (21). To further examine the effect of static stretching on different phases within the RSA test, we divided the 9 sprints into 3 phases each consisting of 3 sprints. In this context, we analyzed the RSA as overall (all sprints), early phase (first to third sprints), middle phase (fourth to sixth sprints), and final phase (seventh to ninth sprints).

Warm-Up/Cool-Down Description

A 15-minute warm-up session (CON: 13-minute jog + 2-minute rest vs. SS: 10-minute jog + 3-minute static stretching + 2-minute rest) was implemented. In SS, 3-minute passive static-stretching exercises were included in the warm-up routine with a shorter aerobic warm-up to maintain the same total duration of the warm-up (i.e., 15-minute = 10-minute jog + 3-minute stretching + 2-minute rest). In this context, each player carried out unassisted static stretch exercises (slowly applied a stretch torque to a muscle, maintaining the muscle in a lengthened position) designed to stretch the lower body (11). The stretches were held at a point of mild discomfort for 20 seconds per muscle group (11). At the end of the stretch, the leg was returned to a neutral position, and the player stretched the other leg. The whole stretch cycle was performed twice (2 × 20 seconds with 1-minute rest in-between for each muscle group) (11), and the time was measured by a hand-held stopwatch. The investigator was present in all training sessions to provide detailed instructions and continually monitor the stretching activities and duration of each player.

Quadriceps stretching exercise: The player stood upright with 1 hand against a wall for balance. Then, the player flexed his or her dominant leg to a knee joint angle of 90°. The ipsilateral hand grasped the ankle of the flexed leg, and the foot was raised so that the heel of the dominant foot approached the buttocks (11).

Hamstring stretching exercise: The players performed hamstring stretch by standing erect with 1 foot planted on the floor and the toes pointing forward. The heel of the foot to be stretched was placed on the floor with the ankle dorsiflexed. The player then flexed forward at the hip, maintaining the spine in a neutral position while reaching the arms forward. The knee remained fully extended. The player continued to flex at the hip until a gentle point of discomfort was felt in the posterior thigh (11).

Intermittent Aerobic Endurance Training

Soccer includes high intensity and intermittent bouts of exercise. In the present study, the Yo-Yo Intermittent Endurance Run was used as intermittent aerobic endurance training because it is close to the activity pattern in soccer (33) and provides a standardized workout throughout the study course. In the Yo-Yo Intermittent Endurance Run (level 1), the players had to perform a series of 20-m shuttle runs at an incremental pace set by an audio metronome, and it was terminated when the player was unable to maintain the required speed (33). The distance covered in the first Yo-Yo Intermittent Endurance Run during the first series of each player was recorded, and each player was instructed to run the same individual distance in all intermittent aerobic endurance training afterward to maintain the same training intensity in both series. As recorded in the present study, the distance covered by all players was 3,157 ± 258 m.

Statistical Analyses

To address the hypothesis a 2-way repeated-measures analysis of variance (ANOVA) (2 × 3) with factors being (a) type of warm-up (SS included or no SS) and (b) RSA phase (early: first to third; middle: fourth to sixth; and final: seventh to ninth phase) was implemented. The analysis was used to examine the main effects and interactions that would allow a comparison of (a) RSA (FST, AST, TST, and %Decre) between CON and SS; and (b) comparison of the RSA (FST, AST, TST, and %Decre) between different phases (early, middle, and final). When significant differences were determined in the above analyses, pairwise comparisons were made using Bonferroni's adjustment to control the Type-1 error rate. Paired-sample t-test was used to compare the difference between RSA on days 1 and 5 within the same series. The significance level was defined as p ≤ 0.05. Effect size (Cohen's d) was calculated to determine the practical significance of static stretching on RSA (38). The magnitude of effect has been suggested by Rhea (38) as trivial (<0.35), small (0.35-0.80), moderate (0.80-1.50), and large (>1.5) for recreationally trained individuals. Values are mean ± SEM.

Results

Static stretching had trivial effects on overall RSA, whether it was implemented before or after 3 days of training (Table 1). Repeated-measure ANOVA showed no significant difference of the overall RSA (FST, AST, TST, and %Decre) between CON and SS, before (F = 0.01, p > 0.05) and after (F = 0.27, p > 0.05) 3 days of training. Comparison of RSA before and after 3 days of training showed no significant differences (p > 0.05) of AST and TST between CON and SS. But FST was significantly (p < 0.05) increased (CON: 4.42 vs. 4.31 seconds; SS: 4.42 vs. 4.34 seconds), and the %Decre was significantly (p < 0.05) smaller (CON: 6.12 vs. 8.16%; SS: 5.82 vs. 7.84%) after 3 days of training (Table 1).

Table 1
Table 1:
Comparison of overall RSA between the 2 warm-up series (n = 20).*

Before undergoing the 3 days of training, static stretching had a trivial effect on early, middle, and final phases of RSA, except for the %Decre in the middle phase and %Decre in the final phase where static stretching had small effects (Table 2). Repeated-measures ANOVA showed no significant difference between CON and SS in early (F = 0.01, p > 0.05), middle (F = 1.94, p > 0.05), and final (F = 1.05, p > 0.05) phases of RSA (Table 2). Moreover, middle-phase RSA of CON was significantly slower compared with its early phase (p ≤ 0.05, Table 2). Final-phase RSA of CON and SS were significantly slower than their respective early phases (p ≤ 0.05, Table 2).

Table 2
Table 2:
Comparison of split RSA between the 2 warm-up series (n = 20).*

After 3 days of training, static stretching had trivial effect on early, middle, and final phases of RSA, except for the %Decre in the final phase where static stretching had small effects (Table 2). Repeated-measures ANOVA showed no significant difference between CON and SS in early (F = 0.60, p > 0.05), middle (F = 0.92, p > 0.05), and final (F = 2.01, p > 0.05) phases of RSA (Table 2). Moreover, early phase RSA of SS was significantly slower (p ≤ 0.05) as compared with the values before 3 days of training (Table 2).

Discussion

This study aimed to examine the effects of incorporating static stretching in aerobic warm-up and performed for 3 consecutive days (before and after each training) and before the RSA test. There was no significant difference, and only trivial effects in overall RSA between CON and SS were observed before and after 3 days of training (Table 1). These results did not support our first hypothesis that static stretching negatively influences the fastest sprint. However, the results supported our second hypothesis that static stretching does not affect overall RSA. The present study showed that incorporating static stretching in the daily warm-up routine for 3 consecutive days and before RSA test would not negatively affect the fastest sprint and overall RSA. This agreed with a previous study that found acute static stretching did not negatively affect the 10- and 20-m sprint performance in soccer players (30).

The above results could be explained by 3 factors: The duration of static stretching, the effect of aerobic warm-up, and the study design that RSA test was performed 2 minutes after warm-up. The duration of static stretching employed in the present study (2 × 20 seconds with 1-minute rest in between for each muscle group) was short and did not inhibit subsequent performances (1,30,42,55). This is supported by recent studies that reported that a greater duration of static stretching resulted in greater deficits (26,53), suggesting a dosage effect. It has been reported that single static stretching <30 seconds does not negatively affect reaction time (1), muscular strength/force (1,55), countermovement vertical jump, 10- and 20-m sprints, and agility in soccer players (30,42). In contrast, single static stretching exercises of a muscle group for ≥30 seconds negatively affects maximal strength (42) and jumping performance (53). The decrease of musculotendinous unit stiffness (or increased compliance) could be the result of long-duration static stretching (50) or continuous motion (such as jogging as used as aerobic warm-up in the present study) (34). The less stiff or more compliant musculotendinous unit has a decreased ability to store elastic energy in its eccentric phase (29) and subsequently less efficient force transfer from the muscle to the tendon (28) which adversely affects the sprint performance (18). Conversely, other studies found no changes in stiffness of musculotendinous unit following 60- to 90-second static stretching (31,34). However, the prolonged static stretching for a single muscle group (that is unlikely to be used by athletes in preparation for competition) leads to acute neural inhibition and a decrease in the neural drive to muscles, resulting in a reduction in power and force output (2,37).

The design of the present study with RSA tested 2-minutes after warm-up might have reduced the acute effect of static stretching on RSA. This factor has been postulated in an upper-body study (47) and confirmed in a lower-body study (14). In the study of Torres et al. (47), participants performed upper-body muscular strength and power tests 5 minutes after the static stretching (2 × 15 seconds) on upper-body muscle groups. It was found that no significant difference in the test parameters between static stretching and no-stretching was observed, possibly because of the 5-minute duration between static stretching and the test, which allows acute static stretch-induced responses to dissipate. In another study of DePino et al. (14), participants performed static stretching (4 × 30 seconds with 15-second rest) on the hamstrings, and it was found that the effect of static stretching lasted only 3 minutes after cessation of the stretch. Six minutes after cessation of the stretch, the hamstring flexibility returned to the prestretch level. Therefore, we suggest providing a sufficient recovery period between static stretching and performance (>3 minutes) to reduce the possible stretch-induced detrimental effects (14).

This is the first study investigating the effect of incorporating static stretching before and after daily training routine (for 3 consecutive days) and immediately before the test on subsequent RSA. It appears that incorporating static stretching in the daily training routine would diminish its acute detrimental effect on performance. This routine is supported by the study of Chaouachi et al. (11), where static stretching (same as the present study) and sprint training were performed twice a week for 6 weeks, and it was found that these participants were more resistant to stretch-induced sprint deficits over 5, 10, and 30 m, as compared with participants who did not perform static stretching training (e.g., sprint training alone). Furthermore, it has been shown that chronic static-stretching training changes the stretch tolerance (31) but not the musculotendinous properties (32). Therefore, individuals who perform static stretching regularly might have greater tolerance for the acute static stretching performed before performance and thus have minimal possible disruptive changes in musculotendinous properties (11).

This study showed that static stretching has trivial effects on early, middle, and final phases of RSA before and after 3 days of training (Table 2). Performances that rely primarily on a single muscular contraction to generate force and power are more affected by acute bouts of static stretching (54). In addition, Beckett et al. (4) showed that performing static stretching (1 × 20 seconds) on 6 lower-body muscle groups before the RSA test highly affects the performance in the 0- to 5-m phase but has less effects on the subsequent distances. Sprinting requires a rapid transition from eccentric to concentric muscle action, and the amount of elastic energy that can be stored in the musculotendinous unit is a function of stiffness (41). Consequently, static stretching decreased the musculotendinous unit's stiffness (15,35), and decreased activation of the stretched muscles' motor unit (35) that might affect the eccentric phase of stretch-shortening cycle in early phase of sprint (4,18). Furthermore, RSA seems to be predominantly affected by the metabolic factor instead of the mechanical factor because it has been reported that during a 10 × 6-second sprint separated with 30-second rest, the ATP-PCr concentration decreased to 57% of the resting value after the first sprint and progressively declined to 16% after the 10th sprint (20). In addition, as compared with a single sprint, the greater muscle and blood lactate concentrations after RSA test indicates that ATP-PCr resynthesis is not complete within short-recovery periods (44). Thus, during RSA, it appears that the influence of energy metabolism outweighs the mechanical property that is affected by acute static stretching (15,35). However, whether the energy expenditure during single sprint and RSA is altered after acute static stretching is unclear, and future research is warranted to examine the energy consumption and metabolism during repeated-sprint with and without prior static stretching. Additionally, future studies are suggested to include muscle biopsy to look at the cytoskeleton to understand the underlying effect of stretching on the musculature.

Practical Applications

Contrary to most of the published literature that acute static stretching adversely affects single sprint (18,35,40) and RSA performances (4), performing static stretching after aerobic warm-up for 3 consecutive days and before repeated-sprint test did not negatively affect RSA in the present study. In addition, previous studies have shown that individuals who perform static stretching regularly might have greater tolerance for the acute static stretching performed before performance and thus have minimal possible disruptive changes in musculotendinous properties (11). Presently, as controversial evidence was observed regarding the effect of static stretching on RSA, it is premature to recommend that static stretching could be included in the in-season daily warm-up routine. However, because static stretching is the practice of some players preceding training and competition, based on the results of the present study and published literature, it can be conservatively suggested to perform static stretching with a short duration for each muscle group (2 × 20 seconds with 1-minute rest in between as used in the present study, or <30 seconds as reported by previous studies [1,55]) to avoid changing the mechanical property of the musculotendinous unit and thus affecting subsequent performance. Moreover, the intensity of static stretching should be less than maximal tension (53), and it should provide an adequate recovery period between static stretching and performance (>3 minutes) (14). To further reduce any possible negative effects of static stretching on subsequent performances, dynamic stretching can be performed after static stretching to decrease overall musculotendinous compliance and enhance muscle activation (30,43). Finally, it is important to note that soccer involves other athletic abilities (e.g., jumping) that may be more likely to be affected by acute static stretching (54).

Acknowledgments

There is no competing interest declared. The results of the present study do not constitute endorsement of the product by the authors or the NSCA.

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Keywords:

football; recovery; multiple-sprint; interval; intermittent

© 2011 National Strength and Conditioning Association