Stretching during warm-up
Physical exercise and training are major sources of injuries among warriors, so finding ways to reduce the risk of such injuries is important. One method often used with injury prevention in mind is pre-exercise stretching, but does it really work?
From the Field
Can stretching before exercise help prevent training-related injuries?
Stretching should be included as part of a warm-up prior to physical activity. A warm-up designed specifically for the type of activity that follows has been shown to be the most effective for performance enhancement. Stretching helps by improving flexibility and range of motion, and should be part of military fitness programs at all levels, but the value of stretching and warm-ups in general for reducing risk of injury is still in doubt.
Most professional trainers recommend stretching as part of a warm-up prior to exercise with the idea that it helps reduce the risk of training-related injury. However, researchers disagree on the effectiveness of stretching, as well as the type of stretching and the nature of the warm-up in general. In spite of this, it is possible to gather general guidelines that can be used to develop an individual warm-up that includes stretching.
And given the extent of training-related injuries in the military and the resulting loss of active-duty days, it seems important to pursue any activity that holds promise of reducing this problem. Pre-exercise warm-ups typically consist of some low-level cardiovascular activities along with stretching. More recently, warm-ups are being tailored to the type of exercise that will follow.
Myths and/or Claims
In general, athletes and trainers believe that stretching during the warm-up will improve performance and prevent injury that could result from the subsequent activity. However, it has been proposed that any warm-up that elevates the temperature of muscles, tendons, and ligaments will serve the purpose. In addition, it is important to keep in mind that improper stretching can actually cause injury.
Regardless of the debates on the value of stretching during a warm-up, there are four types of stretching that are recognized: static, dynamic, ballistic, and PNF (for “Proprioceptive Neuromuscular Facilitation). Static stretching involves slow, deliberate movements that apply force to lengthen the tissues. This type of stretching is generally regarded as being safe and effective to increase flexibility and range of motion (ROM), especially when practiced long-term. Despite the fact that most research on stretching has focused on this type, no optimal method of practice has yet been established.
The second method of stretching—and the most common form used by professionals during warm-up—is dynamic. It employs controlled movement through the range of motion for each target area, simultaneously lengthening and increasing the temperature of tissues. This suggests that it might be better than static stretching at increasing ROM, but studies so far have not confirmed this. One important advantage of dynamic stretching is that it can be tailored to the needs of a specific sport, which recent research indicates to be effective.
Ballistic stretching is in some ways similar to dynamic stretching, but the former adds bouncing or jerking motions, usually at the end of a range of movement. The goal is to further increase ROM, but it is easy to stretch muscles too far, resulting in injury, so ballistic stretching must be employed very carefully. In fact, if the goal of stretching during warm-up is to prevent injury, this type of stretching would seem to be potentially counterproductive.
The fourth and last type of stretching is PNF, which actually requires that one have a partner. It involves contraction of the muscle opposite the one that is being targeted for stretching, followed by static stretching of the target muscle. Studies indicate that this might be the most effective form of warm-up stretching to increase range of motion, but the risk of injury increases if either participant is careless. Proper form and technique are essential, so a trained partner is a good idea.
It is easy to overdo stretching, especially the ballistic and PNF types, so it should be practiced with caution. Those who are new to stretching, those who have extremely high or low flexibility in the back and hamstrings, and those with poor ankle flexibility need to begin with minimal stretching, increasing their range of motion in minute increments regularly and sticking with static and/or dynamic methods. And it is better to do a little stretching every day than a lot of stretching less often. Recovery from a stretching injury can be slow.
Summary for Military Relevance
Studies of injury rates in military training, especially among new recruits, continue to report high rates of injury—from 6% to 12% as of 2000, varying with unit, branch, age, previous level of activity, and other factors. Although there is no consensus as to the value of stretching for injury prevention, there is strong evidence that warm-ups—especially those tailored to a specific activity—do enhance performance. Since range-of-motion and flexibility are specific requirements for many types of military activities, stretching enters into the equation. Dynamic stretching is probably the best choice for most programs, although PNF may be feasible under some circumstances. Different warm-up programs should be designed for those at high risk of injury versus those at less risk, including different stretching protocols.
It should be kept in mind that stretching and warm-up are just part of an overall fitness program. Military physical training and fitness programs need to be modified in other ways, as well, to reduce injury rates. More information is available in HPRC’s Research Summary “Pre-Exercise Stretching and Warm-Up.”
* Bottom Line Up Front
- Physical-training injuries are the major cause of lost active-duty days.
- Military trainees with extremely high or low back and hamstring flexibility are more likely to experience physical-training injuries.
- Factors that increase risk of injury include age, smoking, biomechanical factors, previous history of injury, high volume of exercise and running mileage, and low levels of past physical activity and fitness.
- Pre-exercise warm-ups, including stretching, should be included in military physical training at all levels, with different programs for recruits at high risk of injury versus those at lower risk.
Most professionals and experts in the field of training and exercise believe the “warm-up” is an essential part of effective program design, and many would say that a warm-up not only prepares the body for the demands of the upcoming workout, but also has the potential to reduce the risk of injury in both the short and long term. The problem with this belief is that it is based largely on anecdotal accounts and personal experience, and there is great disparity in what constitutes a warm-up. In addition, while most agree on the purpose of the warm-up, the methods to accomplish the desired outcomes vary greatly.1-3 Thus, most research on the ability of a warm-up to prevent injury has focused on the type of warm-up (i.e., active or passive), whether or not stretching is included, and if so, what type of stretching is most effective. The stretching component of warm-up and its role in injury risk has received much attention in recent years. However, the conclusions are inconsistent and even contradictory, and it is clear that more research is required. Nevertheless, some guidelines can be drawn from the available literature and are presented here.
Historically the warm-up consists of low-level cardiovascular activities combined with some form of stretching; more recent recommendations include some type of sport-specific exercise.4,5 Those who advocate stretching disagree as to the type of stretching that may be optimal. The stretching is typically one or more of four basic types: static, dynamic, ballistic, or PNF (Proprioceptive Neuromuscular Facilitation). These are discussed in more detail below.
From a military perspective, the viability of pre-exercise warm-up as a means to prevent injury is especially important. A 1999 study6 revealed that injuries related to physical training were at that time the major cause of lost active-duty days in the Army—more, in fact, than all other outpatient conditions combined. More recent studies indicate no significant change in this situation.
There are numerous factors that underlie the high incidence of injury associated with physical training, including demographics (age, gender, race, etc.), anatomical features, past injuries, certain health behaviors (e.g., smoking), and physical fitness factors such as cardiorespiratory and muscular endurance and high or low flexibility. High training mileage and frequent marching and running have also been identified as increased-risk factors.6
Many believe that warming up prior to physical activity should always include stretching and this can help prevent injury. Injuries occur at a given muscle length, usually during the eccentric phase of contraction. When exerting eccentric force, such that the muscle must move beyond its “free range of motion,” the risk of injury may be heightened. If an individual is able to move through the full ranges of movement required by a given activity, without placing undue stress or load on the muscle, the risk of injury is lessened.3 Thus, stretching theoretically can help reduce such risk by increasing the range of motion (ROM).
Some have theorized that joint ROM would increase during a warm-up because the elevated core temperature would lower muscle, tendon, and ligament viscosity.3 As a result, warm-up could preclude stretching or, alternatively, could include dynamic stretching, which presumably can help increase core temperature.
Facts and Evidence
There are numerous challenges in examining the linkages between warm-up, stretching, and injury prevention, which one group identifies as “an obscure relationship.”7 Numerous authors have attempted to combine and parse the available data in their search for a definitive answer regarding the relative benefit of pre-exercise stretching, without much success. Nevertheless, there is much to be learned from the available information. What follows is a summary of the types of stretching and their effects on injuries and performance, as well as an examination of whether stretching should even be included in warm-ups.
Static stretching uses a “slow, deliberate” movement to lengthen soft tissue and is widely regarded as a safe and effective method to increase flexibility and ROM.8 It requires the individual to apply force to increase tissue length. Most of the research on warm-up stretching has been on this type, and it is clear that an acute bout of static stretching increases joint ROM, especially when practiced over the long term.2-14 However, the research studies have been highly variable, such that no optimal method or program has yet been established.
Dynamic stretching involves controlled movement through the available ROM to lengthen soft tissue. This is the most common form of stretching currently used in the warm-up phase by fitness professionals, and there is emerging research to provide support for its efficacy, although there is less research in this area and dynamic stretching is often confused with ballistic stretching (see below). Some studies have found that it is equally as effective as static stretching at gaining ROM.2,14 One proposed advantage, as mentioned above, is that it could increase joint core temperature and thereby improve ROM above what static stretching can achieve.3 Its main advantage, however, seems to be that it can be designed to focus on sport-specific movements, with recent research in support of this.15,16
Ballistic stretching is similar to dynamic stretching in that it involves movement and an application of force to the muscle-tendon unit, but there is a marked difference between the two: Ballistic stretching also involves bouncing or jerking motions to stretch target muscles, sometimes specifying that the bouncing motion be performed only at the end of the ROM and sometimes through the entire ROM.3,14,17,18 However, the use of momentum in ballistic stretching may take muscles past tissue extensibility limits, potentially increasing the risk of injury.19 In addition, it has been connected to muscle soreness and the potential to invoke the stretch reflex, both of which could negatively affect injury prevention and performance.2,14
PNF stretching most commonly involves a contraction of the opposing muscle, placing the target muscle on stretch, followed by a static contraction of the target muscle.12 However, there are a number of suggested protocols and use of this method requires potentially both more instruction and participation of a trained partner, increasing the risk of injury if either participant utilizes poor form or technique.19,20 On the other hand, PNF stretching is typically better at gaining ROM in comparison to other types of stretching.21 Moreover, one study showed that performing PNF twice per week, with only a single repetition, significantly increases ROM.12 Given the unique concerns regarding the safety and practicality of this technique, although much of the research has concluded that PNF stretching yields the greatest improvement in ROM, many authors also suggest further research.3,12-14,21,22
The majority consensus for now seems to be that stretching as part of a pre-activity warm-up does not contribute to overall injury reduction8,23-25, or at least that the jury is still out with a final verdict.8,26,27 It appears safe to say that stretching may reduce the likelihood of ligamentous and musculotendinous injuries if practiced regularly.26 In general, stretching—which targets soft-tissue compliance—may contribute to preventing injury in activities that require increased tendon viscosity and a compliant muscle-tendon unit, such as soccer or football.7 It is less promising for activities such as jogging or cycling, which consist of lower-intensity “stretch-shortening cycles” (SSCs) with active muscular contraction. Current practice has gradually shifted away from static to dynamic stretching in the warm-up28 because numerous studies have reported differential performance responses; the data are quite compelling in support of dynamic warm-up compared to static.29-35
The findings with regard to performance are equally equivocal. One literature review found that pre-exercise stretching decreases both force production and velocity of contraction, while regular stretching improves both; running economy improves with pre-exercise stretching, but long-term stretching has no effect; and pre-exercise stretching consistently resulted in diminished performance as measured by force, torque, or jumping.13 The same review did find agreement that regular stretching found improved performance as measured by isometric force production and contraction velocity, but that regular stretching appears to have little effect on running economy.
One important finding with regard to training regimens in general is that reducing the frequency, duration, and/or—in the case of running—distance, results in reduction in injuries.25 This issue of “overuse,” particularly in the military population, may have implications for evaluating the efficacy of any warm-up protocol or stretching routine. Some specific recommendations for warm-ups are listed in an Appendix at the end of this article.
The issue of fatigue during the warm-up is consistently raised in both the injury prevention and performance literature.3-5,36 As fatigue levels increase, tissue stiffness decreases, producing less efficient movement.37 This raises the question of whether attempting to train in a fatigued state, which might better simulate deployment and combat conditions, would enhance neural and other training adaptations.
Trainees experience more injuries if they score at the high or low extreme of back and hamstring flexibility, a finding which has been replicated in research with other military personnel27 and with collegiate athletes38. In addition, poor ankle flexibility compared to average ROM was associated with over twice the risk of injury; those with high flexibility experienced up to eight times the risk.39
There is some evidence that stretching, especially static, can lead to performance decrements.28,37 In addition, stretching can result in “stretch-induced strength loss,” thus becoming counterproductive for certain types of performance. It may be possible to minimize or eliminate stretch-induced strength losses with dynamic stretching, eccentric contractions, and at longer muscle lengths.5
A survey in 2000 reported that injury rates in military training remain high, at a rate of six to 12 per month for every 100 male recruits, although this rate varies by unit and branch.40 For example, the monthly injury rate reported for Naval Special Warfare training was 30 per 100 trainees. Risk factors for developing overuse injuries in military populations include age, smoking, biomechanical factors, previous history of injury, high volume of exercise and running mileage, and low levels of past physical activity and fitness. In addition, there is an inverse relationship between fitness level and the incidence of overuse injuries, with untrained soldiers getting injured at 4 times the rate of the more fit.41
Stratifying recruits based on injury risk, with differential training programs for those with a high potential for injury might help reduce overall injury rates.41 Recruits identified as being at higher risk might be required to participate in an 8-12 week “base conditioning phase” in which training would apply gradual and progressive overload, allowing time for greater physiologic, musculoskeletal, and neural adaptations. In the fitness world, this segment of training is termed “building up to game speed”; it seems that many recruits need to “build up to warrior speed.” Mainstreaming these recruits into the general training program would occur once they were able to meet minimum standards and had completed the “hardening” phase of conditioning to establish a more substantial fitness base upon which to build.
There is substantial support for including dynamic flexibility into the warm-up phase of training for all levels of military personnel. Current best practices include full-range, dynamic movement that reflects accepted specificity of training principles, where training methods have a direct connection to real-life performance. Based on the available information, we recommend the development of two dynamic warm-ups: one targeted those at high risk of injury, the other for those not deemed at risk.
Most research supports the concept that warm-up improves performance, but its impact on injury prevention is less conclusive, and the advantages of stretching are similarly inconclusive. Indications are that one of the most important features of a warm-up is that it should target body parts to be used in the upcoming activity, without producing undue fatigue, and that it be tailored to the fitness level of the individual. If stretching is included in a warm-up, dynamic stretching appears to be the most effective choice. While PNF stretching may provide greater benefits, it requires a trained assistant and carries a higher risk of injury if not practiced correctly.
The purpose or goal of the activity should determine the associated stretch/warm-up. The following list includes specific tips from reference articles that have attempted to provide guidelines based on the limited available research.
- Stretch as part of the warm-up at least 15-20 minutes prior to the activity.2
- During pre-exercise stretching, target muscle groups that have high risk of injury during this phase.5
- Conduct warm-up/stretch within 15 minutes prior to activity.3
- Tailor the movements to the activity and individual.3
- Consider long-term benefits of stretching and increased muscle length and ROM.3
- Stretch each muscle group three to five times with 15-20 second holds.2
- Perform at least four to five stretches for 60-seconds to pain tolerance to ensure decreased passive resistance.5
- Stretch for longer durations and lower force; at a minimum of three, 30-second stretches per muscle group at least once/week.3
- There may be no significant difference in ROM between holding stretches for 30 compared to 60 seconds.36
- Include dynamic movements pre-performance to minimize stretch-induced strength loss.5
- Intensity should approximate 40-60% VO2max, described as mild sweating without fatigue.3
- If a warm-up is of too low intensity, such as light calisthenics, it provides insufficient increases in muscle temperature and associated tissue changes.36
- High-intensity work results in fatigue and the potential performance decrements associated with anaerobic work.36
- For both intermediate and long-term efforts, the warm up needs to elevate oxygen consumption, yet build in sufficient recovery time prior to the target task to minimize fatigue and need for thermoregulation.36
- Intensity, duration, and recovery should be manipulated to achieve the desired results and should include activity-specific tasks.36
- Performing movements similar to the upcoming event may be more important in activities requiring extreme ranges of motion.5
- Incorporate warm-ups that target body parts to be used in the upcoming activity, without producing undue fatigue.4
- A warm-up protocol should include aerobic exercise, followed by stretching, and ending with an activity similar to the intended event.4
- Safran MR, Seaber AV, Garrett WE, Jr. Warm-Up and Muscular Injury Prevention: An Update. Sports Medicine. 1989;8(4):239-49.
- Smith CA. The warm-up procedure: To stretch or not to stretch. A brief review. Journal of Orthopaedic and Sports Physical Therapy. 1994;19(1):12-7.
- Woods K, Bishop P, Jones E. Warm-up and stretching in the prevention of muscular injury. Sports Medicine. 2007;37(12):1089-99.
- Fradkin AJ, Zazryn TR, Smoliga JM. Effects of Warming-up on Physical Performance: A Systematic Review With Meta-analysis. Journal of Strength & Conditioning Research. 2007;24(1):140-8.
- McHugh MP, Cosgrave CH. To stretch or not to stretch: the role of stretching in injury prevention and performance. Scandinavian J Med Sci Sports. 2010;20:169-81.
- Jones BH, Knapik JJ. Physical Training and Exercise-Related Injuries: Surveillance, Research and Injury Prevention in Military Populations. Sports Medicine. 1999;27(2):111-25.
- Witvrouw E, Mahieu N, Danneels L, McNair P. Stretching and Injury Prevention: An Obscure Relationship. Sports Medicine. 2004;34(7):443-9.
- Weldon SM, Hill RH. The efficacy of stretching for prevention of exercise-related injury: a systematic review of the literature. Manual Therapy. 2003;8(3):141-50.
- Hart L. Effect of Stretching on Sport Injury Risk: a Review. Clinical Journal of Sport Medicine. 2005;15(2):113.
- Rancour J, Holmes CF, Cipriani DJ. The Effects of Intermittent Stretching Following a 4-Week Static Stretching Protocol: A Randomized Trial. Journal of Strength & Conditioning Research. 2009;23(8):2217-22.
- Rubini EC, Costa ALL, Gomes PSC. The Effects of Stretching on Strength Performance. Sports Medicine. 2007;37(3):213-24.
- Sharman MJ, Cresswell AG, Riek S. Proprioceptive Neuromuscular Facilitation Stretching: Mechanisms and Clinical Implications. Sports Medicine. 2006;36(11):929-39.
- Shrier I. Does stretching improve performance? A systematic and critical review of the literature. Sports Medicine. 2004;4(5):267-73.
- Wilkinson A. Stretching the truth. A review of the literature on muscle stretching. Australian Physiotherapy. 1992;38(4):283-7.
- Clark A, Twist P. The Dynamic Warm-Up. IDEA Fitness Journal. 2007;February:28-31.
- Beedle BB, Leydig SN, Carnucci JM. No difference in pre- and post-exercise stretching on flexibility. Journal of Strength & Conditioning Research. 2007;21(3):780-3.
- Alter MJ. Science of Stretching. Champaign, IL: Human Kinetics; 1988.
- Nieman D. Exercise testing and prescription. 6th ed. New York: McGraw Hill; 2007.
- Hedrick A. Dynamic Flexibility Training. Strength and Conditioning Journal. 2000;22(5):33-8.
- Ninos J. PNF-Self Stretching Techniques. Strength & Conditioning Journal. 2001;23(4):28-9.
- Fasen JM, O'Connor AM, Schwartz SL, Watson JO, et al. A Randomized Controlled Trial of Hamstring Stretching: Comparison of Four Techniques. Journal of Strength & Conditioning Research. 2009;23(2):660-7.
- Shrier I. Stretching before exercise: an evidence based approach. British Journal of Sports Medicine. 2000;34(5):324-5.
- Herbert RD, Gabriel M. Effects Of Stretching Before And After Exercising On Muscle Soreness And Risk Of Injury: Systematic Review. BMJ: British Medical Journal. 2002;325(7362):468-72.Jamtvedt G, Herbert RD, Flottorp S, Odgaard-Jensen J, et al. A pragmatic randomised trial of stretching before and after physical activity to prevent injury and soreness. British Journal of Sports Medicine. 2010;44(14):1002-9.
- Yeung EW, Yeung SS. A systematic review of interventions to prevent lower limb soft tissue running injuries. British Journal of Sports Medicine. 2001;35(6):383-9.
- Small K, McNaughton L. A systematic review into the efficacy of static stretching as part of a warm-up for the prevention of exercise related injury. Research in Sports Medicine. 2008;16:213-31.
- Thacker SB, Gilchrist J, Stroup DF, Kimsey CDJ. The Impact of Stretching on Sports Injury Risk: A Systematic Review of the Literature. Medicine and Science in Sports and Exercise. 2004;36(3):371-8.
- Fletcher IM, Monte-Colombo MM. An investigation into the possible physiological mechanisms associated with changes in performance related to acute responses to different preactivity stretch modalities. Applied Physiology, Nutrition & Metabolism. 2010;35(1):27-34.
- Faigenbaum AD, Bellucci M, Bernieri A, Bakker B, et al. Acute effects of different warm-up protocols on fitness performance in children. J. Strength Cond. Res. 2005;19(2):376-81.
- Fletcher IM, Anness R. The acute effects of combined static and dynamic stretch protocols on fifty-meter sprint performance in track-and-field athlete. Journal of Strength & Conditioning Research. 2007;21(3):784-7.
- Fletcher IM, Jones B. The effect of different warm-up stretch protocols on 20 meter sprint performance in trained rugby union players. Journal of Strength & Conditioning Research. 2004;18(4):885-8.
- Holt BW, Lambourne K. The impact of different warm-up protocols on vertical jump performance in male collegiate athletes. J. Strength Cond. Res. 2008;22(1):226-9.
- Little T, Williams AG. Effects of differential stretching protocols during warm-ups on high-speed motor capacities in professional soccer players. J. Strength Cond. Res. 2006;20(1):203-7.
- Manoel ME, Harris-Love MO, Danoff JV, Miller TA. Acute Effects of Static, Dynamic, and Proprioceptive Neuromuscular Facilitation Stretching on Muscle Power in Women. Journal of Strength & Conditioning Research. 2008;22(5):1528-34.
- Pearce AJ, Kidgell DJ, Zois J, Carlson JS. Effects of secondary warm up following stretching. Eur. J. Appl. Physiol. 2009;105(2):175-83.
- Bishop D. Warm Up II: Performance Changes Following Active Warm Up and How to Structure the Warm Up. Sports Medicine. 2003;33(7):483-98.
- Wilson JM, Flanagan EP. The Role of Elastic Energy in Activities with High Force and Power Requirements: A Brief Review. Journal of Strength & Conditioning Research. 2008;22(5):1705-15.
- Howell DW. Musculoskeletal profile and incidence of musculoskeletal injuries in lightweight women rowers. The American Journal of Sports Medicine. 1984;12(4):278-81.
- Pope R, Herbert R, Kirwan J. Effect of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in Army recruits Australian Journal of Physiotherapy. 1998;44(3):165-72.
- Kaufman KR, Brodine S, Shaffer R. Military training-related injuries: Surveillance, research, and prevention. American Journal of Preventive Medicine. 2000;18(3, Supplement 1):54-63.
- Rosendal L, Langberg H, Skov-Jensen A, Kjaer M. Incidence of injury and phyiscal performance adaptations during military training. Clinical Journal of Sport Medicine. 2003;13:157-63.