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Stretching is the least important part of a warm-up!

Proposition for Debate - by Rachel Poon

Statement of the Topic
Introduction
Background Knowledge
Research Findings
Research Update - New Knowledge
Clinical Implications
Recommendations
Points of Consideration
Summary
Short Answer Review Questions
References

Statement of the Topic

Stretching is the least important part of a warm-up.

Introduction

Musculoskeletal injures such as muscle strains and tears are extremely common in sports injury. The overall result of muscle injury is not only influence on athlete performance but is also the source of pain. As muscle tightness is one of the predisposing factor for injuries, preventive measure such as stretching exercise have been wildly practiced from amateur players to elite athletes. It becomes an integral part of any sports activity.

In this essay, background knowledge of warm up and the theories of different stretching techniques will be discussed. Past researches on the effectiveness of stretching exercise and the most update findings will also be reviewed. Injury prevention is multi-factorial. It related to warm up, flexibility, strength and fatigue, level and type of activity. As flexibility plays a role in preventing injury, recommendation based on research findings on stretching routine will be given at the end of the passage.

Background Knowledge

Warm up

Warm-up and cool down exercises are highly recognized as essential parts of any sports activity. The aim of warm-up is designed to increase muscle-tendon suppleness, stimulate blood flow to peripheral, increase temperature of body, muscle tendon and connective tissue; and enhance free, coordinated movement. Examples are jogging, cycling, massage, stretching. Past researchers have investigated the effect of various modes of warm-up, such as jogging, cycling exercise, massage, heat, stretching, isometric contraction and proprioceptive neuromuscular facilitation(PNF).

Flexibility

Flexibility is defined as the range of motion of a joint or serious of joints that are influenced by muscles, tendons, ligaments, bones, and bony structures. It can be divided into static (end range of motion) and dynamic (compliance/ stiffness) flexibility. It is influenced by number of factors, such as level and type of activity, gender and age, temperature, and it is highly joint specific.

Stretching

Stretching is an important pre-exercise warm up. The aim of stretching is to increase muscle-tendon flexibility, prevent injury, prepare the athlete for exercise and competition, enhancing performance, improve range of motion and athletic function during rehabilitation phase follow injury, alleviate muscle soreness after prolonged activity, and enhance athlete’s well being. Some of the studies suggested stretching can influence on running economy. But further clarification is needed due to lack of compromised research findings. Common types of stretching techniques are: static, ballistic and PNF (contract relax, reciprocal relaxation).

Applied Physiology of Stretching

The four main mechanistic constraints during active or passive stretching exercises are: neurogenic constraints, myogenic constraints, joint constraints and skin. Neurogenic constraints refer to any active voluntary or reflex controlled mechanism, such as stretch reflex in which the golgi tendon organs (GTO) and muscle spindles involved in the length monitoring system. Myogenic constraints refer to any active or passive resistive property, such as viscoelasticity contributed by serial elastic components e.g. musculo-tendonous structure and aponeuosis. Joint constraints refer to any articular tissues for examples capsule and ligaments.

The action of static or ballistic stretching pulls the actin-myosin filaments beyond overlapping. It results in increase sacromere length, and overall increase the muscle length. By making use of the viscoelasticity of the muscle-tendon unit, "creep response" occurs under low load and long duration static stretch. As a result, temporary increase in muscle length can be achieved. It is also reported that stretching results in increase muscle compliance (reduce muscle stiffness), and decrease energy absorption to failure.

The theory behind of using PNF technique contract relax is the suppression of muscle spindles and GTO. In reciprocal relaxation the suppression of alpha and gamma motorneuron of antagonists occurs. Previous research showed contrast result in its effect on muscle relaxation during stretching. In both techniques the resistance to stretch is supposed to decrease. But in later studies, there were evidence of past- tetanic potentiation (increase H-reflex activity) and increase EMG during stretching exercise. Although the relevance of H-reflex to passive stretch is an uncertainty, the effective of PNF technique is still controversial.

Research Findings

Research findings supporting stretching is beneficial

In the study on comparing the effectiveness of static stretching and PNF on hamstring flexibility. No significant difference was found in both technique (21.3% and 25.7%). But it was found that both stretching routines was effectively increase hamstring isokinetic performance at selective speed (60°and 120° /sec eccentrically, 60°/sec concentrically).
The effects of two different stretching techniques: static stretching and proprioceptive neuromuscular facilitation (PNF) on gait economy was revealed in other study. The result showed that both procedures can improve gait economy at 60% VO2 max. In addition, static stretching also demonstrated improvement in gait effectiveness at 40% and 80% VO2 max.
It is shown that isometric exercise of TA, EDL and FDL of lower limb followed by stretching resulted in increase force to failure due to improved elasticity. Serial elastic component is subjected to stretching effect, as active muscle fiber contracted, connective tissue at musculo-tendous junction demonstrated some stress relaxation effect in isometric contraction.
In the study with 180 soccer players, a 10 minutes stretching in 20 minutes warm-up program could reduce injury rate by 25%.
The stretching, which followed isometric contraction then relaxation, is proved superior to 15 minutes of warm-up cycling or 6-15 minutes of massage in increasing the hip, knee and ankle range. In the same study, the combined effect of massage and cycling did not improve the range of motion. It was concluded that stretching is the best way to enhance flexibility.
Stretching is also recommended for preventing delay onset muscle soreness (DOMS). By comparing the effect of heat/cryotherapy with static stretching/proprioceptive neuromuscular facilitation, static stretching was proved superior to that of with PNF when combine with either heat or cryotherapy.
Early study has showed that heat and stretching increase muscule-tendon extensibility and joint flexibility.

Research findings supporting stretching is not beneficial

In the study in 1993, it suggested that a standard warm up, cool down and stretching exercise program did not prevent running injury for male recreational runners.
In some situation, stretching may do more harm that good. A good example is the imbalance in flexibility due to over stretching. A study showed that in female athletes who had more than 15% flexibility in right hip extensor, were found 2.6 times more likely to be injured. Subjects with left side more flexible was 1.5 times more likely to be injured.
Subjects with less gross flexibility were found more economical in walking and jogging with better oxygen consumption on treadmill.
No significant difference was found on hip range of motion, by comparing 15 minutes static stretching exercise with same period of cyclic exercise (both improved).

More related research is reported in the tables of summary in two reference journal articles. One of the characteristic of reviewed research is that most of the research only investigated the combined effect of different modes of warm up. Beneficial effect of stretching is shown using multiple intervention. Individual effect of particular technique is unavailable. So far no disadvantage of static stretch is reported.

Research Update - New Knowledge

In a randomized trial study of preexercise stretching for lower-limb injury prevention. 1538 male subjects were recruited in army setting. A 12-week active warm-up physical training was carried out with or without a 6 X 20 seconds stretching exercise. Result showed that there were 158 injuries in stretched group and 175 injuries in control group. It is concluded that stretching program did not significantly reduce the frequency of lower-limb injury. Fitness may be a more important factor in sport injury.
In similar setting study with military basic trainees . It studied the hamstring flexibility infleuence on injury rate. With 150 subjects in stretched group and 148 as control, a 13 weeks training program with or without 3 stretch sessions is carried out. Result indicated lower limb overuse injury rate of 16.7% in stretching group is significant lower that 29.1% in control group.
The other research studied the effect of stretching on delay onset muscle soreness and force loss following heavy eccentric exercise . Ten females (physiotherapy students) were recruited to perform 5 minutes of cycling warm up exercise at 60 rpm and a one leg hamstring (random selected) stretch of 4 X 20 seconds. Then the 10 X 10 isokinetic eccentric work is performed at 30°/sec with range 60°. The visual analogue scale is used to rate the soreness in first 96 hours. Result showed there was not significant different (stretch: 69mm, control: 71mm) stretching on preventing soreness and force loss.
A critical review is done on clinical and basis scientific literature of stretching prevent local muscle injury. 138 articles were searched in Medline and only 12 used control group. There were 4 articles suggested that stretching is beneficial. But, those studies included stretching in warm-up program with multiple intervention. 3 studies suggested that stretch is detrimental but the studies were not well controlled. 5 articles suggested stretching makes no difference but limitation of those 5 articles involved misclassification of subject/ control groups. From the basic science literature, there were five reasons suggested by the author why stretching before exercise would not prevent injury:
1. Increase in muscle compliance may cause tissues more readily to rupture due to decrease energy absorb to failure.
2. Stretching has no effect for activities which excessive muscle length is not an issue. For example, jogging.
3. Stretching has no effect on muscle compliance during eccentric activity, when most strains are likely to occur.
4. Stretching can produce damage at the cytosketal level.
5. Stretching mask the muscle pain due to increase pain tolerance after stretching.
In the study investigating the risk of ankle injury relate to ankle dorsiflexion range. 1093 male subjects (549 stretch, 544 control) is recruited in army. A 11 weeks training with or without a 2 x 20 seconds stretching on calf muscles is studied. Result of 23 injuries in stretch group and 45 injuries in controlled group demonstrated that poor flexibility of dorsiflexion pre-dispose higher ankle injury 2.5 times and 8 times higher compare with average and high flexibility group respectively.

In a literature review, Shrier (1999) summarized a number of articles on the effect of warm up exercises. It stated that there was no conclusion can be made that flexibility related to injury prevention.

Clinical Implications

According to the literature review, static stretching seems to be the most effective way as a preexercise warm up among static, ballistic and PNF. It is easier to learn when compare with PNF, and can be performed by self. Unlike PNF which physiotherapist need to be cooperate with. And it is also less susceptible to injury when compare with ballistic stretching. Ballistic stretch is believed to be more functional as sport activity involved dynamic movement. But, it is only recommend to higher level athletes. When prescribing static stretch exercise program, it is best to be corporate with other interventions to ensure its effectiveness.

During prescription of stretching exercise, the muscles need to be stretched should be sports specific. Apart from stretching large muscle groups for general flexibility, specific muscles stretch should be included when muscle length is a concern in the sports, or when prevention of recurrent injury is the targeted.

As the suggested stretch holding period was quite variable among literatures, therapists should take few factors into consideration, such as viscoelasticity of muscles at different temperature (warm or cold weather), with or without other form of warm-up such as jogging and cycling, or players level of sports activity. In clinical situation, general guideline according to the review can be followed.

Balance in flexibility is also be considered in clinical situation. As a greater difference in flexibility in either one aspect of the body may lead to injury, stretching exercise including both agonist and anta-gonist should be prescribed to both limbs.

Recommendations

Stretching technique

Static stretching is more recommended than PNF among the techniques. But it is only showed beneficial when multiple intervention is implemented. A study by demonstrated that isometric contraction would produce same relaxation effect as passive stretching. As lengthening of connective tissue occur in both routines. The author also suggested that combination of contraction and stretching is even more effective to promote relaxation. As research findings related to PNF is uncertain, the use of PNF in injury prevention is still controversial.

Holding Period

Most of the literature suggested stretch holding period range from 10 to 30 seconds. Some stated that 30 second or less is recommended. During the stretch one should felt the stretch, but with no pain and within comfortable zone. As pre-disposing injury such as microscopic muscle tears due to over-stretching may contribute to the subsequent muscle injury. Moreover, 12-18 seconds is recommended by since stress relaxation occurs in that period. Other suggested that 15 seconds stretch is as effective as 45 seconds and 2 minutes stretch on hip abduction range.

Repetition

The first 4 repetition is shown to be most effective . A repetition of 2 to 4 times is also recommended by another author. Other opinions such as 5 to 6 times in improving hip, knee and ankle flexibility are said to be effective.

PNF

Specifically for PNF technique contract- relax, literature suggested that one should contract and hold 6-8 seconds, then relax and stretch for other 6-8 seconds. This maneuver should be repeated 3-6 times.

Points of Consideration

Stretching should be done 15-20 minutes before exercise, and 5-10 minutes after exercise.
Holding period can be vary due to difference in viscoelasticity of different muscle at different temperature, difference in muscle architecture, and arrangement of connective tissue.
Stretching exercise should be carried out throughout the season as well as off-season. Only long-term stretching program can improve overall flexibility.
Balance in flexibility should be considered. Stretching should be done on both agonist and anti-gonist on both limbs.
Care should be taken when implement stretching program with athletes whom processed hyperlaxity. There are 3 clinical tests which is recommended to assess athletes' hyperlaxity.
As elasticity of slow-twist fiber is greater than fast-twist fiber, therefore the fast-twist fiber is more susceptible to injury. Athletes participate in high intensity sports such as splinting may require stretching more than an endurance runner.

Summary

In this essay, the background knowledge of warm up and techniques of stretching are reviewed. We also looked at some of the past research findings on effectiveness of stretching exercise, as well as the most update findings. There is a trend of evidence that stretching actually shows no difference on injury rate.

Little research was found related to disadvantages of static stretching, but only stretching included in warm up program is shown beneficial. In clinical setting, the dosage of stretching exercise is a concern. Static stretching is more recommended and should following the guideline described above. Stretching is still an important part of any sport activity from recreational to elite level.

Short Answer Review Questions

What are the four main mechanistic constraints during stretching exercise? Give definitions to each constraints.
Describe the theories behind the two PNF stretching techniques:
- Contract-relax
- Reciprocal relaxation
According to the article of , what are the 3 clinical tests recommended to assess athletes’ hyperlaxity?
Give 5 reasons why stretching may not be beneficial in some cases.
Where are the locations of all serial elastic components?
Summarize the general guideline on stretching exercise prescription, including static stretching and PNF techniques.

References

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Ekstrand J and Gillquist J (1982): The frequency of muscle tightness and injury in soccer players. American Journal of Sports Medicine 10:75-78.
Ekstrand J, Gillquist J and Lilzedahl S (1983): Prevention of soccer injuries: supervised by doctor and physiotherapist. American Journal of Sports Medicine 11:116-120.
Gleim G and McHugh M (1997): Flexibility and its effects on sports injury and performance. Sports Medicine 24:289-299.
Gleim G, Stachenfeld N and Nicholas J (1990): The influence of flexibility on the economy of walking and jogging. Journal of Orthopedic Reserve 8:814-823.
Godges J, MacRae H, Longdon C, Tinberg C and MacRae P (1989): The effects of two stretching procedures on hip range of motion and gait economy. Journal of Orthopedic and Sports Physical Therapy 10:350-357.
Hartig D and Henderson J (1999): Increasing hamstring flexibility decreases lower extremity overuse injuries in military basic trainees. The American Journal of Sports Medicine 27:173-176.
Hubley C, Kozey J and Stanish W (1984): The effects of static stretching exercises and stationary cycling on range of motion at the hip joint. Journal of Orthopedic and Sports Physical Therapy 6:104-109.
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Pope R, Herbert R, Kirwan J and Graham B (2000): A randomized trial of preexercise stretching for prevention of lower-limb injury. Medicine and Science in Sports and Exercise 32: 271-277.
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Exercise Physiology Educational Resources 2000