If the average person was asked to define "fitness", he/she might point to the ability to run a distance race (ie., "aerobic fitness") or the ability to lift a large amount of weight (ie., "muscular strength"). But, flexibility is a component of fitness too, even though it may not get as much attention or respect as its siblings.

This brings us to the concept of stretching. Almost all athletes -- from elite athletes down to the weekend warrior types -- stretch. Thus, it seems intuitive that stretching prevents injuries....why else would everybody be doing it, right?

Indeed, recent studies have shown that stretching can influence the viscosity of the tendon and make it significantly more compliant. Thus, many believe that increasing the flexibility of a muscle-tendon unit promotes better performances and decreases the number of injuries. Because of this belief, stretching exercises are regularly included in warm-up and cooling-down exercises. However, the sports medicine literature is divided on whether stretching prevents injury.

But, before we get into the science, let's review some basics:

TYPES OF STRETCHING

To be precise, stretching can be classified into 5 different types:

• Ballistic Stretching: This is defined as: rapid lengthening (stretching) of a muscle by the use of jerking or bouncing movements, for example, bouncing down to touch your toes. This type of stretching is not recommended. In fact, it mimics the type of sudden stress that produces muscle injuries in the first place. Jerking a muscle into a full stretch causes it to lengthen beyond a safe stretch and may injure the muscle...exactly the opposite of what you are trying to achieve with stretching.

• Static Stretching: This type of stretching is characterized by a slow and sustained (eg., for 15-60 secs) lengthening of a muscle by the athlete without help from a partner. This is one of the best types of stretching because it does not pose the risk of injury to muscle and connective tissue as ballistic stretching does.

• Passive Stretching: Passive stretching is identical to static stretching, except that a partner is used to gradually move the arm or leg. The advantage of using a partner is that a greater range-of-motion can be achieved compared to stretching without a partner.

• Isometric Stretching: Isometric stretching is simply static stretching with the aid of an immovable object.

• Proprioceptive Neuromuscular Facilitation (PNF) Stretching: PNF stretching sounds more complicated than it really is. Technically, PNF stretching involves passive muscle lengthening with the use of a partner after an antagonistic muscle is contracted. PNF stretching is considered to be an excellent technic however the risk of injury is slightly greater than the other methods since the range of the stretch can be greater.

STRETCHING TO IMPROVE FLEXIBILITY

One of the benefits of stretching is that it does improve flexibility, albeit, short-term. Stretching, combined with warming up, has been shown to increase the flexibility of the ankle, hip, and knee joints (Thacker SB, et al. 2004). However, an improvement in flexibility does not automatically mean fewer injuries or improved athletic performance. This is where there is confusion in the literature.

STRETCHING AND MUSCLE PERFORMANCE

As mentioned above, while stretching does increase the flexibility of specific joints, greater flexibility, in turn, does not always lead to improved performance. After static stretching, the muscle-tendon unit is weaker for 10-15 minutes (or longer, see below). This phenomenon has been called the "stretch lag" period, or, "tendon slack".

In fact, in some cases, stretching actually worsens (measurements of) muscle performance. Stretching has been shown to impair maximal voluntary contraction force (Behm DG, et al. 2001), muscular endurance (Kokkonen J, et al. 2001), and one-repetition maximum (Kokkonen J, et al. 1998) when it occurs just prior to the performance assessment.

A study of 40 females using a vertical jump test to assess muscle performance revealed that adding PNF stretching to a general warm-up routine worsened jumping ability (Church JB, et al. 2001).

Another study shows the effect of stretching on muscular strength over time (Fowles JR, et al. 2000). Subjects performed 13 stretches of the plantar flexors, holding each stretch for 135 seconds during a period of 33 minutes. Maximal voluntary isometric contraction (MVIC) was assessed 6 times during the ensuing 60 minutes. MVIC was depressed as follows:

Time / Percent Strength Decrease

• Time 0: -28%
• 5 min: -21%
• 15 min: -13%
• 30 min: -12%
• 45 min: -10%
• 60 min: -9%

The authors concluded that an intense prolonged stretch (of the plantar flexors) reduces maximum voluntary force for up to 1 hour after stretching.

STRETCHING TO PREVENT INJURIES

Contradictory findings regarding the ability of stretching to prevent injuries have been reported in the literature. Stretching recommendations are clouded by misconceptions and conflicting research reports. Apparently, no scientifically based prescription for stretching exercises exists (Witvrouw E, et al. 2004).

One fundamental issue to consider is that, even though stretching improves flexibility, most injuries occur during an extremity's normal range of motion (ie., during eccentric contraction). Thus, it is illogical to conclude that improving flexibility will prevent most muscle injuries (Shrier I. 2000).

In 1999, Shrier reviewed the literature on stretching to prevent injuries. He found 12 papers with acceptable study design. Of those, 4 showed that stretching was beneficial, 3 showed that stretching was detrimental, and 5 showed no difference (Shrier I. 1999).

Australian researchers reviewed the literature in 2002 and found that stretching had no beneficial effect on delayed-onset muscle soreness (DOMS) and did not reduce the risk of injury (Herbert RD, et al. 2002).

A subsequent literature review, published in 2004 (Witvrouw E, et al. 2004), was much more revealing. These authors proposed a possible explanation for why there is disagreement on the issue of whether stretching prevents injury:

Witvrouw and colleagues believe that the type of sports activity in which an individual is participating needs to be considered. Sports that involve a lot of bouncing and jumping activities with a high intensity of stretch-shortening cycles (SSCs) (eg. basketball, football, soccer, tennis) require a muscle-tendon unit that is compliant enough to store and release the high amount of elastic energy that benefits performance in such sports. If the muscle-tendon unit is not compliant enough, the demands in energy absorption and release may rapidly exceed its capacity. This may lead to an increased risk for injury of this structure. Thus, when a sport demands stretch-shortening cycles (SSCs) of high intensity, such as jumping or abrupt changes in direction, stretching may be important for injury prevention.

In contrast, when the type of sports activity contains low-intensity, or limited SSCs (eg. cycling, jogging, swimming), there is no need for a very compliant muscle-tendon unit since most of the forces come from active muscle contraction to generate motion. Strong evidence exists that stretching has no beneficial effect on injury prevention in these sports.

In other words, whether or not stretching prevents injury depends on the type of activity being considered.

Witvrouw and colleagues believe that if this point of view is used when examining research concerning stretching to prevent injuries, the reasons for the contrasting findings in the literature are in many instances resolved.

USE OF STRETCHING TO HASTEN RECOVERY AFTER AN INJURY

While stretching to PREVENT an injury is not always helpful, the use of stretching to hasten recovery AFTER an injury has been shown to be beneficial:

• Hamstring Injuries: A Greek study randomized athletes with hamstring strains to light stretching (once per day) or a more vigorous program (4 times per day). The study was conducted from 1996-2001 and randomized 40 athletes into each of the 2 plans. All 80 athletes received RICE (rest, ice, compression, and elevation). The stretching involved static stretching for 30 seconds per stretch session.

The authors found that normal range-of-motion was achieved earlier in the 4 times per day group (5.6 days vs 7.3 days) and the time elapsed prior to achieving full athletic activity was also shorter in the 4 times per day group (13.3 days vs 15 days) compared to the once/daily group (Malliaropoulos N, et al. 2004.).

• Plantar Fasciitis: For plantar fasciitis, also known as "painful heel syndrome" or "proximal heel pain", stretching of the Achilles tendon has been shown to be beneficial in reducing pain, stiffness, and increasing range-of-motion (McNair PJ, et al. 1996; Porter D, et al. 2002). One study reported that a non-weight-bearing stretch of the plantar fascia was better than the classic standing Achilles tendon stretch (DiGiovanni BF, et al. 2003).

SUMMARY

Thus, while there still is some controversy regarding stretching to prevent injury, some conclusions can be offered:

• Stretching to PREVENT injury is most helpful in sports that involve sudden changes of direction, such as football, soccer, or tennis or sports that require lots of jumping such as basketball or volleyball. Stretching appears to be less helpful in sports that produce less shock to the muscles, such as cycling, jogging, or swimming.

• Do not stretch extensively (if at all) within 15-60 minutes prior to a competitive event.

• If you do stretch prior to a competitive event, work that muscle group for a few minutes to help the muscle(s) recover to their normal length and power capacity. For example, if you have just stretched your hamstrings and the front of your thighs to get ready for a race, do some light jogging for several minutes before the race begins.

• Avoid ballistic stretching: It is more likely to cause injury than other technics.

• Stretching injured muscles does appear to hasten recovery.

FOR MORE INFORMATION

The web site www.TheStretchingHandbook.com has useful resources on stretching, including an extensive library of articles and a free newsletter.

A very succinct, yet thorough, review of the sports medicine literature on stretching was published in the Sept./Oct. 2002 issue of ACSM's Health and Fitness Journal (see Bracko MR, below). Although this publication is intended for sports medicine professionals, the article is written in an easy-to-understand style.

For a "how-to" book filled with diagrams, get the classic Stretching by Bob Anderson. Even though this book was originally published in 1980, it demonstrates every kind of stretch and stretching routine you can imagine.

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REFERENCES

Behm DG, Button DC, Butt JC. Factors affecting force loss with prolonged stretching. Can J Appl Physiol 2001;26:261-272. Abstract

Bracko MR. Can stretching prior to exercise and sports improve performance and prevent injury? ACSM's Health and Fitness Journal 2002;6:17-22. (no abstract)

Church JB, Wiggins MS, Moode FM, et al. Effect of warm-up and flexibility treatments on vertical jump performance. J Strength Cond Res 2001;15:332-336. Abstract

DiGiovanni BF, Nawoczenski DA, Lintal ME, et al. Tissue-specific plantar fascia-stretching exercise enhances outcomes in patients with chronic heel pain. A prospective, randomized study. J Bone Joint Surg Am 2003;85-A:1270-1277. Abstract

Fowles JR, Sale DG, MacDougall JD. Reduced strength after passive stretch of the human plantar flexors. J Appl Physiol 2000;89:1179-1188. Abstract

Herbert RD, Gabriel M. Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. BMJ 2002;325:468. Abstract

Kokkonen J, Nelson AG, Andrew C. Acute muscle stretching inhibits maximal strength performance. Res Quart Exerc Sport 1998;69:411-415. Abstract

Kokkonen J, Nelson AG, Arnall DA. Acute stretching inhibits strength endurance performance. Med Sci Sports Exerc 2001;33:11A. (no abstract)

Malliaropoulos N, Papalexandris S, Papalada A, et al. The role of stretching in rehabilitation of hamstring injuries: 80 athletes follow-up. Med Sci Sports Exerc 2004;36:756-759. Abstract

McNair PJ, Stanley SN. Effect of passive stretching and jogging on the series elastic muscle stiffness and range of motion of the ankle joint. Br J Sports Med 1996;30:313-317. Abstract

Porter D, Barrill E, Oneacre K, et al. The effects of duration and frequency of Achilles tendon stretching on dorsiflexion and outcome in painful heel syndrome: a randomized, blinded, control study. Foot Ankle Int 2002;23:619-624. Abstract

Shrier I. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. Clin J Sports Med 1999;9:221-227. Abstract

Shrier I. Stretching before exercise: an evidence based approach. Br J Sports Med 2000;34:324-325. Abstract

Thacker SB, Gilchrist J, Stroup DF, et al. The impact of stretching on sports injury risk: a systematic review of the literature. Med Sci Sports Exerc 2004;36:371-378. Abstract

Witvrouw E, Mahieu N, Danneels L, et al. Stretching and injury prevention: an obscure relationship. Sports Med 2004;34:443-449. Abstract

ABOUT THE AUTHOR

Stan Reents, PharmD, is a former healthcare professional. He holds Personal Trainer and Lifestyle Counselor certifications from the American Council on Exercise and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics).  He can be reached at: Editor@athleteinme.com.