Thursday, April 10, 2008

Stretching the Warm-Up

The issue of the type of warm-up strategy and stretching has generated quite a bit of controversy. What is the best warm-up? How should players stretch before training? Does stretching prevent injury or affect performance? There are many questions and quick tour through the Internet reveals a variety of recommendations, several cautions and some misinformation. Part of the debate stems from the confusion in the scientific literature. After reviewing dozens of research articles, one finds a number of conflicting results and many confusing recommendations. But a close examination does reveal a few consistencies. There is enough solid information to make a few recommendations as to what components of a warm-up and what types of stretching are important what which ones are not.

The purpose of the warm-up and stretching is to prepare the athlete for the day's training session or match. The warm-up should accomplish three goals. The first is enhancing performance during the session or match. The second is reducing the risk of injury, particularly muscle strain. A third aim of a stretching program is improving flexibility and joint range of motion (ROM) over the long-term. The burning question is what types of activities will accomplish all three goals.

For the most part, there are three major type of stretching. Static stretching involves slowly stretching the target muscle and holding the position for 10-30sec. This can be done alone or with a partner. The second type of stretch is proprioceptive neuromuscular facilitation (PNF). PNF requires the target muscle be actively contracted immediately before the athlete performs a static stretch. Third, dynamic stretching is an activity where the speed and momentum of movement during activity brings about the stretch. Typically, movements that are “sport specific” are utilized to stretch the major muscle groups.

There are a few important concerns with scientific research into warm-up and stretching. The first is how “performance” is defined and whether or not the researcher’s definition matches performance on the field. Typically, performance is defined by a single sprint of 20-50m, vertical jump height or a shuttle run performed within a few minutes of the warm-up program. While sprinting, jumping and agility are integral parts of soccer performance, the measures used by researchers may not give a full picture of what might happen on the pitch over the course of a 90 minute session. Thus, it’s difficult to directly apply what is determined in the laboratory to the playing field. The second problem is that researchers often report “statistically significant” differences in performance variables. In some cases the differences may be very small, but from a statistical point of view, they are significant. The problem lies in the interpretation. Many will use these small variations to make dogmatic statements that one protocol is “bad” and other “good” when in realty, one approach may simply be “just a bit better”. Third, the goals of improving performance, reducing injuries and increasing flexibility seem to require different types of stretching exercises. One type of stretching may be preferable for maximizing immediate performance while another may be optimal for long-term improvements in flexibility

Warm-Up and Performance

Most researchers agree that for high-intensity activities such as soccer, a warm-up serves to improve performance and reduce the risk of injury by increasing body and muscle temperature. This is especially true for high-intensity activities such as soccer. The warm-up should include a period of low-intensity, dynamic activity designed to cause a light sweat but not to induce fatigue. The onset of sweating is a good indicator that the muscle temperature is raised to exercising levels. The duration and intensity of the warm-up will vary depend on the players’ individual fitness levels. As players become fitter, the intensity and duration of the warm-up can be increased.

Stretching and Performance

Research studies into the effects of stretching on performance show somewhat conflicting results. For static stretching done immediately before activity, the majority of studies show that it can diminish sprint performance, reduce vertical jump height and slightly reduce strength measures. This is compared to conditions where no stretching was performed. The effects though are not dramatic, for the most part small reductions. PNF also tends to reduce sprint and jump performance but the research results are somewhat conflicting so it is difficult to make firm conclusions. Dynamic stretching, on the other hand, seems to improve both parameters compared to either no stretching and static stretching. Again, the effects are not remarkable but there does seem to be improvements over other forms of stretching. One advantage of dynamic stretching seems to lie in the use of sport-specific activities. Including jump- and sprint-type movements during dynamic stretching seems to enhance performance in both activities. A word of caution here, the sprints and jumps measured in all of these studies were performed within minutes of completing the stretching routines. Therefore, it is very difficult to say with any confidence that one form of stretching or another will alter performance over the course of a match or training session.

Stretching and Injury Prevention

Surprisingly, there is quite a bit of debate as to whether stretching before training reduces the risk of injury, including muscle strains. Some studies show positive effects, others show no effects. The controversy surrounding stretching and injury is probably due to the different types of stretching routines, activities examined and injuries recorded. The studies that show positive effect of stretching examined, for the most part, high intensity activities such as sprinting, basketball and soccer. A recent study of English professional teams indicated that static stretches or PNF held for 15-30 seconds was associated with fewer hamstring injuries. Those studies that showed little or no effect looked at lower intensity, longer duration activities such as jogging, swimming and cycling. It is important to point out that no study shows that stretching increases injury risk. Based on this, most recommend stretching as a part of a warm-up as a slight balance of research indicates a preventative effect on muscle injury.

Stretching and Long-Term Flexibility

The third and final goal of a stretching program is increasing flexibility and joint ROM. Several studied show that improving both components can reduce the risk of muscle strain and tear as well an enhance performance. The most effective type of stretch to increase flexibility appears to be PNF flowed closely by static stretching. Again, the differences in improvement between these approaches are small though both techniques do seem to be more effective than dynamic stretching. Researchers have not examined if flexibility training best done as part of the warm-up, cool-down or as a separate session. Nevertheless, it is clear that PNF and static stretching can improve flexibility which, in turn, leads to long-term gains in performance and reductions in injury risk (see Injury Cutting-Edge Research: Joint ROM and Muscle).

Bottom Line

A warm-up is designed to prepare the player for practice and reduce the risk of injury. After sorting through the published researcher it appears that for high intensity activities such as soccer, a proper warm-up can contribute to these goals. As for stretching, there is not sufficient research information to enthusiastically endorse one approach over another. All three types of stretching are probably effective in reducing the risk of muscle strain and preparing the athlete for the day’s activity. Dynamic stretching may be a bit more advantageous in that the movements simulate the activities used in training or a match and the effects on performance seem to be somewhat greater. However, static stretching and PNF have the advantage of promoting the long-term benefits of improving flexibility. This in turn, lowers injury risk and enhances performance.

So, what should be done? A reasonable warm-up and stretching program should consist of the following:

  1. A period light jogging or other aerobic activity designed to elicit a light sweat. The goal here is to elevate body and muscle temperature.

  2. A period of sport-specific, dynamic stretching. This period may also include both static stretching and PNF for long-term improvement in flexibility.

  3. A period of dynamic activity incorporating movements similar to those needed for the day’s match training session.

It is certainly appropriate to modify the warm-up routine to meet the needs of individual players and teams. Since the differences between stretching routines in terms performance, injury risk and flexibility gains are relatively small, some variety can be introduced into the warm-up. Certainly the type of dynamic stretching can be changed to focus on different skills and techniques as well as incorporating various forms of ball work.

Further Reading

Dadebo B, White J, George KP (2004) A survey of flexibility training protocols and hamstring strains in professional football clubs in England. British Journal of sports Medicine, 38:388-394.

Little T, Williams AG (2006) Effects of differential stretching protocols during warm-ups on high speed motor capacities in professional soccer players. Journal of Strength and Conditioning Research, 20:203-2-7.

Rubini EC, Costa ALL, Gomes PSC (2007) The effects of stretching on strength performance. Sports Medicine, 37:213-224.

Sharman MJ, Cresswell AG, Riek S (2006) Proprioceptive neuromuscular facilitation stretching: Mechanisms and clinical implications. Sports Medicine, 36:929-939.

Shirer I (2004) Does stretching improve performance? A systematic and critical review of the literature. Clinical Journal of Sports Medicine, 14:267-273.

Thacker SB, Gilchrest J, Stroup DF, Kimsey CD (2004) the impact of stretching on sports injury risk: A systematic review of the literature. Medicine and Science in Sports and Medicine, 36:371-378.