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Four-Week Dynamic Stretching Warm-up Intervention Elicits Longer-Term Performance Benefits

Herman, Sonja L1,2; Smith, Derek T2,3

Journal of Strength and Conditioning Research: July 2008 - Volume 22 - Issue 4 - p 1286-1297
doi: 10.1519/JSC.0b013e318173da50
Original Research

Herman, SL and Smith, DT. Four-week dynamic stretching warm-up intervention elicits longer term performance benefits. J Strength Cond Res 22: 1286-1297, 2008-The purpose of this study was to determine whether a dynamic-stretching warm-up (DWU) intervention performed daily over 4 weeks positively influenced power, speed, agility, endurance, flexibility, and strength performance measures in collegiate wrestlers when compared to a static-stretching warm-up (SWU) intervention. Twenty-four male National Collegiate Athletic Association Division I wrestlers were randomly assigned to complete either a 4-week treatment condition (DWU) (n = 11) or an active control condition (SWU) (n = 13) prior to their daily preseason practices. Anthropometric and performance measures were conducted before and after the 4-week experimental period (i.e., DWU or SWU). Measures included peak torque of the quadriceps and hamstrings, medicine ball underhand throw, 300-yd shuttle, pull-ups, push-ups, sit-ups, broad jump, 600-m run, sit-and-reach test, and trunk extension test. Wrestlers completing the 4-week DWU intervention had several performance improvements, including increases in quadriceps peak torque (11%), broad jump (4%), underhand medicine ball throw (4%), sit-ups (11%), and push-ups (3%). A decrease in the average time to completion of the 300-yd shuttle (-2%) and the 600-m run (-2.4%) was suggestive of enhanced muscular strength, endurance, agility, and anaerobic capacity in the DWU group. In contrast to the DWU intervention, there was no observed improvement in the SWU group for peak torque of the quadriceps, broad jump, 300-yd shuttle run, medicine ball underhand throw for distance, sit-ups, push-ups, or 600-m run, and decrements in some performance measures occurred. The findings suggest that incorporation of this specific 4-week DWU intervention into the daily preseason training regimen of wrestlers produced longer-term or sustained power, strength, muscular endurance, anaerobic capacity, and agility performance enhancements.

1Department of Sports Medicine, Rochelle Athletics Center, 2Division of Kinesiology and Health, College of Health Sciences, 3Department of Zoology and Physiology, College of Arts and Sciences, University of Wyoming, Laramie, Wyoming

Address correspondence to Dr. Derek T. Smith, smithdt@uwyo.edu.

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Introduction

Traditionally, static stretching has been utilized by coaches, athletic trainers, and other athletic personnel as a routine part of both practice and precompetition warm-ups (8,12,21,24,35,39). However, recent research shows acute static stretching regimens may negatively influence performance outcomes (15,16,24,25,39). Specifically, muscle strength and power production, knee flexion and extension 1 repetition maximum lifts, leg extension power, vertical jump, sprint speed, and mean speed of gymnasts' vault runs have all been reduced in terms of performance shortly after a static-stretching warm-up (SWU) (4,7-10,15,16,19,22,25,31,38).

Within many athletic settings, it is feasible to replace the typical SWU with a more active, dynamic, and sport-specific stretching warm-up aimed at optimizing performance. It is plausible that doing so may eliminate the deleterious effects on strength, speed, power, and agility associated with static stretching. A review by Bishop (6) and, more recently, the work of McMillan et al. (24) show dynamic warm-up (DWU) routines positively influence power, agility, and other performance measures. These conclusions, however, are contained to acute (i.e., immediate) enhancements in performance outcomes that were evident immediately or shortly after the DWU was performed. It remains to be determined whether these observed short-term and possibly transient performance benefits of a DWU can be maintained over a longer term. Thus, a logical, evidenced-based next step is to investigate whether longer-term performance enhancements may result when validated DWUs are incorporated consistently and repeatedly into daily training regimens.

The goals of the pre-exercise warm-up should be to promote an increase in core body temperature and blood flow, to increase muscle tendon suppleness, and to enhance free coordinated movements, which, in turn, help prepare the body for exercise (24,32,36). Performance tests, such as the vertical jump, the underhand medicine ball throw, and other jumping tests, collectively have been used to reflect achievement of these pre-exercise warm-up goals (24). A combination of these tests and other sport-specific tests assessing power, strength, and agility may be an effective means to evaluate whether longer-term performance benefits are achievable when a DWU intervention is incorporated into daily training regimens. Performance tests used to evaluate the effectiveness of any pre-exercise warm-up likely are sport-specific, and agreement upon which tests to include could be controversial. Employing a battery of performance tests may give a more comprehensive overview of outcomes related to the longer-term effectiveness of a DWU intervention. It is valuable for coaches, athletic trainers, and athletes alike to recognize the established acute improvements in strength, power, and agility associated with DWU (15,39). The value of this knowledge could be extended if the acute benefits of a DWU incorporated into daily training regimens transfer to longer-term, sustained performance benefits.

The current study sought to extend the acute performance enhancement following a DWU that McMillian et al. (24) demonstrated in a sample of military academy cadets. Accordingly, a goal of this study was to utilize a similar sample of participants with similar physical characteristics and demands (i.e., strength, power, agility, and endurance) to determine whether incorporation of a DWU intervention into preseason training elicits longer-term (i.e., sustained) performance enhancements. To this end, a sample of collegiate wrestlers participated in a DWU intervention study, which employed a randomized control trial design. The purpose of this study was to determine whether a 4-week DWU intervention positively influenced power, speed, agility, endurance, flexibility, and strength performance measures in collegiate wrestlers compared to an SWU.

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Methods

Experimental Approach to the Problem

An orientation to the study was coordinated for all potential participants. This orientation was divided into 3 sessions: a screening session to determine participant eligibility; an introduction to the study outlining the purpose, what participation would involve, and obtainment of informed consent; and a verbal description and visual presentation of the DWU, SWU, and functional performance tests. Participants were then asked to actively rehearse the DWU and SWU exercises specific to their assigned group. A battery of 11 performance tests also were rehearsed, and these performance tests were conducted prior to and following completion of the experimental period (i.e., intervention and control conditions). The experimental period was 4 weeks in duration and consisted of 2 randomly assigned weight class-matched groups completing either a DWU intervention or an active control condition (SWU) prior to their daily (i.e., 5 times a week) preseason practices. The DWU intervention and SWU active control condition components were replicated from the previously validated work of McMillian et al. (24) and are described in detail in Tables 2 and 3. The testing and intervention sequence of events, in order, were as follows: baseline anthropometric and performance measure testing; completion of the 4-week DWU intervention or the SWU active control condition prior to daily practice concurrently by the randomized weight class-matched groups; and repetition of anthropometric and performance measure testing at least 24 hours after completion of their most recent DWU or SWU, and practice, bout to avoid acute responses.

The study occurred during the collegiate wrestling preseason, so there were no organized competitions. In addition to the DWU and SWU components, preseason practices consisted of long distance runs and short to middle distance sprints on Monday and Friday. Tuesday, Wednesday, and Thursday consisted of mat work, which included technique instruction and drilling only. During these preseason practices, no live or full intensity matches between 2 wrestlers occurred, but technique and skill drilling between similar weight class partners, varying in intensity depending upon the drill, consistently occurred. The wrestlers also partook in resistance training 3 days a week under supervision of a university strength and conditioning coach. Importantly, the aforementioned preseason training (i.e., practices and conditioning) were designed to be identical for every wrestler regardless of his group assignment or weight class. The only feature of the preseason training that differed over the 4-week study between the groups was the type of warm-up performed (i.e., DWU or SWU) by the respective wrestler prior to engaging in his daily practice session.

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Subjects

A total of 24 male National Collegiate Athletic Association Division I collegiate wrestlers consented to participate. They were recruited solely from the varsity men's wrestling team at the University of Wyoming following agreement from the head wrestling coach and medical clearance from the team's general practitioner and orthopedic physician. Wrestlers were assigned randomly by using a random digit algorithm to either the treatment condition (i.e., DWU) or the active control condition (i.e., SWU) according to the following procedure. Only wrestling weight classes in which the team had at least 2 competitors were used for randomization. One wrestler from a weight class was randomly assigned to either the DWU or the SWU group. The other eligible wrestler from this weight class was then assigned to the opposing group. This procedure was repeated for all remaining wrestlers. When a weight class had more than 2 eligible wrestlers, the previous procedure was repeated for the remaining eligible wrestlers. In 4 weight classes, there was an uneven number (i.e., 3) of eligible wrestlers. After assignment of 2 wrestlers from the weight class, the third wrestler was randomly assigned to either the SWU or the DWU group. In total, 13 wrestlers were assigned to the SWU group, and 11 wrestlers were assigned to the DWU group. During the 4-week study, 3 wrestlers in the SWU group and 1 wrestler from the DWU group became injured, not as a result of their specific group assignment, quit, or were unable to continue participation. Based on these withdrawals, 10 wrestlers in each group completed the 4-week study, pretesting, and posttesting and were used in the final data analysis. Table 1 shows the age and physical characteristics of the 10 wrestlers in each group before and after the 4-week treatment period. The proposed study was approved by the Institutional Review Board for Projects Involving Human Subjects at the University of Wyoming.

Table 1

Table 1

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Procedures

Warm-up Protocols.

Participants performed specific exercises according to their designated warm-up group (i.e., DWU or SWU) 5 times a week for 4 consecutive weeks. The primary investigator led the DWU (Table 2) group, and an associate investigator led the SWU (Table 3) group. Both investigators were familiar and experienced with leading these types of warm-up routines. The DWU and SWU protocols were adopted directly from the work of McMillian et al. (24) and were followed precisely. One modification was made to both protocols; a neck stretch was added as participants needed to stretch their necks due to the nature of the sport of wrestling. Briefly, the DWU was divided into 2 components: calisthenics and movement drills. The included exercises targeted all major muscle groups, specifically the quadriceps, hamstrings, adductor and abductor muscles, gluteal muscles, latissimus dorsi, biceps, triceps, pectoralis muscles, deltoid muscles, and muscles of the trunk. Ten repetitions of each exercise were performed at a moderate pace. After completion of the calisthenic exercises, 5 movement drills were executed. These included high knees, lateral lunges, crossovers, skips, and a shuttle sprint. The SWU incorporated 8 stretches, with a 2-part stretch, focusing on the triceps, muscles of the trunk, hamstrings, quadriceps, gluteal muscles, abductors, and the triceps surea muscle group. Each static stretch was held for 30 seconds and performed only once. Both warm-up protocols lasted approximately 15 minutes. The SWU group performed their exercises in the wrestling room, while the DWU group performed their protocol within the same building but in the field house to avoid group contamination. Both groups completed their warm-up routines at the same time of day each day through the course of the intervention. On 4 occasions, the location of the warm-ups was changed, such that the primary investigator could observe the SWU group and leader to ensure that fidelity was maintained per the SWU protocol. Previously described wrestling practices occurred following the warm-up routines.

Table 2

Table 2

Table 3

Table 3

The lead investigator completed all data collection with the exception of scanning before and after dual-energy x-ray absorptiometry, which was conducted by a certified and trained exercise physiologist. Baseline data collection began 1 week prior to initiation of the 4-week experimental period. Posttesting began the day following completion of the 4-week experimental period. Performance measures were conducted at least 24 hours after the most recent warm-up (i.e., DWU or SWU) and practice to avoid any acute responses, as previously demonstrated by McMillan et al. (24) in a group of athletes who completed a dynamic-stretching warm-up.

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Description of Performance Measures.

Previous investigations have utilized the vertical jump test to evaluate power and agility (7-9). The 5-step jump, T-drill, and the medicine ball underhand throw for distance have also been used to measure leg power, agility, and total-body power, respectively (24). The current investigation incorporated a variety of performance tests selected based on their ability to assess the diverse physical demands of the sport of wrestling, tests that have been previously reported to be reliable and valid (3,24,27,33), and tests that have been previously used in studies evaluating the efficacy of dynamic stretching warm-up routines (24). The performance tests selected for this study assessed total-body explosive power; anaerobic fitness; muscle strength and endurance of the arms, shoulder girdle, and the abdominal muscles; lower-body power; acceleration; and agility (Table 4).

Table 4

Table 4

To assess total-body power, the medicine ball underhand throw for distance was utilized. McMillian et al. (24) and Stockbrugger and Haennel (33) identified this performance test as a valid and reliable way to assess explosive power for analogous total-body movement and general athletic ability. Participants were instructed on foot placement and the use of countermovements as long as the feet remained parallel on the ground. Two underhand tosses were performed, and the longer throw was recorded. Rest between trials was dependent on the time necessary for all 24 participants to complete 1 toss (i.e., approximately 3 minutes). The 300-yd shuttle run is a measure of agility and anaerobic fitness (3). This test is performed by completing 6 roundtrips of 25-yd sprints from the starting line to the 25-yd line marker. Foot and hand contact must be made on both the start and the finish lines. Participants' times were recorded to the nearest 10th of a second; they were given a 5-minute rest interval and asked to repeat the test. The shuttle run was performed twice, and the average of the 2 trials was determined. Typically, physical fitness tests are designed to evaluate endurance, flexibility, and strength of individuals in healthy populations (34). The Army Physical Fitness Test (APFT) is intended to be a measure of these physical fitness characteristics. Table 4 lists and describes the 5 components composing the APFT. Each exercise within the APFT targets a specific muscle group. Pull-ups are used to measure muscular strength and endurance of the arms and shoulder girdle (17). Muscle strength and endurance of the triceps, anterior deltoids, and pectoralis major are assessed through administration of push-ups, while bent-knee sit-ups are used to appraise abdominal muscle strength and endurance (27). The broad jump is a measure of lower-body power and acceleration. The 600-m run, the last piece of the APFT, is used to evaluate anaerobic fitness.

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Description of Flexibility Measures.

Flexibility can be assessed over numerous joints and by the use of different tests. This study focused on flexibility of the hamstrings muscle group and the trunk extensors muscle groups. The sit-and-reach test was used to measure hamstring flexibility and has been demonstrated to be reliable (3,27). The trunk extension test is a reliable measure of trunk extensor strength and flexibility (23,27).

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Description of Peak Torque and Anthropometric Measures.

Biodex testing was conducted over a 3-day period prior to and following the 4-week intervention period. It took place on days separate from performance measure testing. Biodex testing measured peak torque of the quadriceps and hamstrings muscle group. Participants were instructed to sit upright in the chair of the calibrated Biodex System 3 Pro dynamometer (Biodex Medical Systems, Inc., Shirley, NY). The lead investigator then secured the trunk harnesses, lap belt, and thigh belt to the side being tested in accordance with the Biodex user's guide. Three submaximal warm-up trials were performed prior to the 5 maximal voluntary concentric contractions at a velocity of 60°·s−1 in both flexion and extension. The test was repeated on the other leg with identical settings. Isokinetic dynamometers provide constant velocity with accommodating resistance throughout a joint's full range of motion (11). The use of isokinetic muscle contractions has become a popular, reliable, and valid test to evaluate dynamic muscle function in clinical and research settings (5,14,28,37). Drouin et al. (11) have stated that this form of objective measurement is the basis for measuring preseason dynamic muscle function.

Height, weight, and body mass index were obtained and recorded before and after the 4-week treatment period. Height was measured on a calibrated stadiometer to the nearest half centimeter, and weight was measured to the nearest half kilogram on a calibrated medical beam balance. Body mass index was calculated accordingly (i.e., body weight [kg]/height2 [m]2). Body fat percentage, lean body mass, and bone mineral density for each participant were determined by administration of a DEXA scan (Lunar Prodigy; General Electric).

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Statistical Analyses

Baseline (i.e., preintervention) participant descriptive variables, anthropometric variables, results of Biodex testing, and performance measures were analyzed between groups by multivariate analysis of variance. When indicated by a significant F value, post hoc testing using the Student-Newman-Keuls method was performed to identify significant group differences. For performance measures that were significantly different between groups at baseline (i.e., push-ups and 600-m run), percentage change (i.e., pretesting to posttesting) was calculated for each group, and this change was analyzed by comparing the 2 groups by 1-way analysis of variance. Change in participant anthropometric variables, descriptive variables, results of Biodex testing, and performance measures over the 4-week experimental period were analyzed by 2-way repeated-measures analysis of variance. Statistical analyses were carried out by using SigmaStat 3.11 for Windows (Systat Software, Inc., San Jose, CA). All data are expressed as mean ± SEM, and statistical significance was set a priori at p ≤ 0.05.

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Results

At baseline and following the 4-week intervention, the 2 groups (i.e., DWU and SWU) were similar in age and anthropometric characteristics (Table 1). There were no baseline (i.e., preintervention) differences between groups for 9 of the 11 performance assessments; the exceptions were the push-up test, in which baseline muscular endurance was lower (63 ± 13 versus 72 ± 4, respectively; p < 0.05), and time to completion for the 600-m run was longer (135.6 ± 4.6 seconds versus 126.9 ± 2.8 seconds, respectively; p < 0.05) in the SWU group than in the DWU group. Neither warm-up intervention influenced peak torque of the hamstrings, flexibility of the hamstrings or trunk, nor muscular endurance required to perform the pull-up test.

Overall the 4-week DWU intervention positively modulated the remaining 7 performance assessments. Specifically, peak torque of the quadriceps increased 11.0%; broad jump increased 4.0%; medicine ball underhand throw for distance increased 4.0%; sit-ups increased 11.0%; push-ups increased 3.0%; the average time to completion of the 300-yd shuttle run decreased 2.0%; and the completion time of the 600-m run decreased 2.4% (Figures 1-6). There were no observed improvements in the SWU group for peak torque of the quadriceps, broad jump, medicine ball underhand throw, sit-ups, or 300-yd shuttle run (Figures 1-5). Figure 6 shows that the 600-m run and push-up performance were diminished in the SWU group after 4 weeks of typical SWU. Thus, performance improvements made by the DWU group for the 300-yd shuttle run (Figure 5) and the push-up test (Figure 6) were accentuated in light of the decrements observed in the SWU group. While the DWU elicited other positive performance improvements, these gains were not statistically greater than those of the SWU group at the end of the 4-week intervention period.

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

Figure 5

Figure 5

Figure 6

Figure 6

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Discussion

The purpose of this study was to determine whether a 4-week DWU incorporated into the daily training regimen of collegiate wrestlers positively influenced measures of power, speed, agility, muscular endurance, flexibility, and strength. The primary findings of the current study are as follows. First, the 4-week DWU intervention elicited improvements in the majority of performance measures that assessed power, speed, agility, endurance, flexibility, and strength. Second, the observed performance improvements in the DWU group were entirely absent in the active control group performing an SWU. The SWU employed in this study was customary of the warm-up used previously by this collegiate team and is likely comparable to that employed in many other sports at varying competitive levels. Third, performance for the push-up and 600-m run tests decreased in the SWU group, and these decreases further supported previous reports of performance decrements associated with SWU routines (19,26). To the authors' knowledge, this is the first study to extend previous reports of acute performance enhancement following a DWU to longer-term and sustained performance gains. Performance gains following a DWU have been previously demonstrated immediately following completion of the actual DWU routine (6,24). In the current study, performance benefits from a DWU intervention in collegiate wrestlers occurred and persisted over a 4-week period and were evident at posttesting, which occurred at least 24 hours following completion of their last DWU.

Identical or similar performance measures to those employed in this study have been used previously to evaluate power, speed, agility, endurance, flexibility, and strength performance (15,19,24), and acute improvements in performance have been reported immediately following completion of a DWU (15,21,24,39). Within the context of the current study design, it is not possible to tease out the dose-response or temporal sequence leading to the observed performance gains in the DWU group; that is, it is possible that the performance gains that were observed may have been greater had they been measured immediately following the DWU routine. However, the significant improvements that occurred and appear to be sustained as a result of the 4-week DWU intervention have important training and competition implications. The findings suggest that incorporation of a 4-week DWU into the daily training regimen of wrestlers results in longer-term or sustained performance enhancements.

Identification of potential mechanisms explaining the observed performance gains following longer-term and habitual use of a DWU as part of a daily training regimen are numerous and beyond the scope of this study. Several plausible explanations have been reported from studies that investigated improvement in performance factors acutely following a DWU. In a review by Bishop (6), it was suggested that active warm-ups correlate to the actual movement of active muscle groups and may offer the following mechanistic benefits: an increase in muscle and core temperature, a decrease in stiffness of muscles and joints, an increase in nerve impulse transmission rate, an alteration in the force-velocity relationship, and an increase in glycogenolysis, glycolysis, and high-energy phosphate degradation. Active, dynamic stretching increases core temperature more so than any other form of stretching. This temperature increase enhances nerve receptor sensitivity and nerve impulse speed, which collectively lead to more rapid and forceful muscle contractions (15). It is possible that the chronic use of the DWU produced such neuromuscular and energetic adaptations that were at least temporarily sustained and may have contributed to the findings, but this possibility is speculative, as direct measurement of these physiological mechanisms was not performed. Additionally, increased muscle twitch force and rate of force development from contractile element conditioning may have theoretically occurred and persisted as a result of the 4-week DWU. Increased postcontraction neural (i.e., sensory) activity could allow for a more rapid and forceful response to subsequent muscle lengthening. These neural explanations have been validated in well-controlled laboratory environments and postulated as viable explanations for acute performance enhancement following DWU routines performed immediately prior to assessments of power and agility (13,24,30). Whether these neural mechanisms are adaptive and sustainable to longer-term (i.e., chronic) DWU training is unclear and, in the context of a longer-term DWU intervention, largely unreported. The findings, however, appear to be supportive of at least a mild sustainment and trainability of some of these aforementioned physiological mechanisms as a result of a dynamic-stretching warm-up. The available acute mechanistic evidence would suggest that the DWU intervention may have enhanced the rate of neural, circulatory, energetic, and temperature responses when challenged by the performance tests. However, it is important to note that the postintervention performance tests were done at least 24 hours following the last DWU session, with no formal warm-up prior to measurement. Thus, the improvement in the performance measures may have relied heavily upon the most rapid and immediately available physiological mechanisms, likely enhanced and trained neuromuscular facilitation, speed of impulse conduction, and receptor sensitivity.

Explanation of the findings may also include prevention or minimization of deleterious physiological adaptations associated with static and passive stretching that tend to acutely inhibit strength, endurance, and power. Increased compliance of the musculotendinous unit (MTU), acute neural inhibition, and decreased neural drive to muscles following an SWU have been consistently found to reduce power output (2,16,18,20,29). Dynamic, specific, and active warm-ups may prevent or minimize decreases in maximal voluntary contraction associated with static and passive stretching (4,19,24). Furthermore, DWUs may, in part, minimize or prevent the prolonged (i.e., up to 1 hour) reduction in force generation capacity that has been associated with SWUs (16). Whether incorporation of DWUs as part of daily training regimens minimizes or prevents any reduction in force generation capacity or whether DWU interventions actually serve to improve capacity is presently unknown; however, the results are supportive of these notions and warrant further investigation.

In addition to the performance enhancement that occurred in the DWU group for the majority of power, speed, agility, endurance, and strength performance measures assessed, it is important to highlight performance decrements that occurred in the SWU group. Following the customary SWU employed in this study, performance for the push-up test decreased 3.7% (i.e., approximately 8 push-ups in 2 minutes). Additionally, performance for the 600-m run decreased by 2.5%, adding approximately 3.5 seconds to the time to completion after the 4-week SWU intervention. As reported by Fletcher and Jones (15), static and passive stretching is known to cause slower sprint times. Although their report employed a sprint of significantly less distance (i.e., 20 m) than the 600-m run employed in this study, the current finding supports the noted negative impact that SWUs may have on speed performance measures.

McMillian et al. (24) recently reported that the U.S. Army Physical Fitness School developed a DWU for individuals and military units. This group conducted a study in which modest power and agility performance enhancements were reported acutely following a DWU (24). This work is consistent with the review by Bishop (6), which indicated short-term performance gains are likely following an active warm-up of moderate intensity. The participants in the study by McMillian et al. were a group of military cadets who were participating in club sports (i.e., rugby, lacrosse, or strength and conditioning). While it is interesting to note some similar physical demands between the athletic military cadets in their study and the wrestlers in this study, the current findings further extend the short-term findings of McMillian et al. to include longer-term and sustained performance enhancements derived from a DWU protocol incorporated into daily training regimens 5 days a week.

Several limitations and assumptions are inherent within the current study. First and foremost, there is an assumption within the randomized 2-group intervention study design that confounders were similar in both groups and that other aspects of their training regimens were similar between both groups over the duration of the 4-week study period. To accommodate this assumption, several controls were enforced. The groups were matched by weight within the eligible sample of wrestlers as well as possible. Fortunately, after dropout occurred, the groups were equally represented by wrestlers matched by weight class; for example, 1 wrestler in the 133-lb class was represented in each group, and 2 wrestlers in the 125-lb class were represented in each group. The primary investigator was present and supervised the fidelity of the SWU and DWU interventions and wrestling practices, including mat work, weight training, and conditioning. To the investigator's knowledge, the wrestling practice activities were identical for every wrestler, such that the weight training prescribed for and completed by 1 133-lb wrestler matched that prescribed for and completed by another 133-lb wrestler in the opposing group, although absolute strength may have differed. Duration and frequency of training regimens were similar for all participants. The activity and training that may have occurred outside of the formal wrestling practices and intervention were held in check by requiring the participants not to participate in physical activities outside of practice for the duration of the study and by interviewing the participants on a weekly basis to ensure that they were compliant. Second, it is possible that day-to-day testing variation may have occurred for the battery of performance measures and influenced the results. The performance measures were not repeated on a second day at baseline or following the intervention, which is a limitation, but all of the participants were highly skilled athletes and were familiar with all of the performance measures performed, with the exception of the isokinetic muscle strength test. Third, it is conceivable that unknown or unreported injury or fatigue in the participants may have influenced their performance. The performance measures were performed 24 hours after their last exercise bout and without formal SWU or DWU, so it is believed that fatigue was minimized and that if it were present, it should have been equivalent between the groups. With the exception of the participants who discontinued participation, the authors are not aware of any performance-limiting injuries. Lastly, the battery of performance measures employed in this study was chosen because it is believed they are specific to and representative of the power, speed, agility, endurance, and strength demands of the sport of wrestling. Moreover, most of the performance tests have been previously employed and were familiar to the wrestlers. However, it is recognized that more sensitive, robust, and specific measures of power, speed, agility, endurance, and strength could have been selected. Based on these limitations, caution is urged in generalizing the findings to other sports, activities, athlete populations, interventions, and training regimens in which the DWU is not identical to that of McMillian et al (24).

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Practical Applications

Individuals participating in sport have always been encouraged to warm up before engaging in vigorous activity. Arnheim and Prentice suggested that a warm-up should last 10 to 15 minutes and the activity to be performed should begin no later than 15 minutes after termination of the warm-up (1). The warm-up should start with 2 to 3 minutes of activity that incorporate large muscle groups, such as jogging or biking, to allow the participant to break a sweat, which signifies an elevation in core temperature and metabolic rate. Sport-specific stretching exercises should be introduced into a warm-up immediately following the 2 to 3 minutes of light activity. Individuals may then progress to sport-specific skills related to the activity at hand. For example, members of a wrestling team should start their warm-up with a light jog and progressively move into somersaults, cartwheels, jumping jacks while jogging, high-knee exercises, and so forth. Once their core temperature has increased, which is evident through sweating, they should begin drilling, which includes slowly to moderately paced technique activities. At this point, the athletes should be physiologically ready to wrestle a live match. Ideally, static stretching should occur upon completion of practice in an effort to restore range of motion and maintain flexibility, without compromising performance (8).

An important and practical aspect of the current study was that the DWU intervention was incorporated relatively seamlessly into the normal daily wrestling practice and training regimen. Within this context, the findings may be of particular interest in that benefits were observed for several performance measures following 4 weeks of a dynamic warm-up as part of a typical practice routine. No additional time or equipment was required for this minor modification to the daily wrestling practice and training routine. It is likely that similar practice routine changes to incorporate DWUs for other sports and activities could be made without significantly disrupting the typical workout routine. However, whether incorporation of a DWU into the training regimens of sports other than that covered in this study will elicit similar performance benefits remains to be studied.

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Acknowledgments

The authors would like to thank the University of Wyoming wrestling coaches for being open-minded to and agreeing to the incorporation of a dynamic warm-up into their typical wrestling routines. We would also like to thank the wrestlers for consenting to participation and for their compliance to the intervention.

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Keywords:

static warm-up; muscular endurance; agility; anaerobic fitness; wrestlers

© 2008 National Strength and Conditioning Association