Selected Topics in Athletic Training

The Role of Stretching in a Warm-Up

Deirdre McFate
California University of Pennsylvania

Abstract

This paper discusses the role of stretching in a warm-up protocol. Four types of stretching are defined and evaluated based on the acute and long-term effects they have on flexibility and performance measurements.

The Purpose of a Warm-Up

Stretching protocols are a key component of a pre-activity warm-up. Protocols associated with stretching have evolved over the years in order to be effective for a specific sport. However, there are numerous side effects of stretching which may limit performance in some athletes, and these effects may not be widely known. Certified athletic trainers need to be aware of these effects in order to provide the best possible care for their patients on and off the field.

An important aspect of pre-activity is the warm-up. Warm-ups can be either passive or active, with the main goal being to increase the muscle temperature without causing fatigue.¹ The commonly accepted theory is that increasing the temperature of a muscle will help enhance tissue flexibility.² Passive warm-ups occur when the internal body temperature is increased due to an outside force acting on the body such as a sauna or hot tub. Active warm-ups occur when the body itself is acting to increase internal temperature and can be of two kinds: general warm-up and specific warm-up.

General warm-ups consist of non-specific body movements such as jogging, cycling, or callisthenics.¹ On the other hand, specific warm-ups target the movements that are specific to the sport and use those activities to increase the internal body temperature while preparing for the activity.¹ Stretching is often included in a warm-up, whether it is static at the end of the warm-up, dynamic at the beginning, or is used throughout the warm-up.

In order to achieve optimal performance, a pre-activity protocol should systematically and progressively stimulate the musculature used during the activity³ The theoretical goal of an active warm-up is to optimize performance and reduce the incidence of injury through increased muscle temperature, muscle compliance, and efficiency of physiological responses.³ Pre-activity protocols typically include a combination of warm-up and stretching. The optimal time frame in which to stretch for an activity is sport-specific, as the varying types of stretching produce different physiological effects on the body. Stretching can be broken down into four basic categories: static, ballistic, dynamic, and proprioceptive neuromuscular facilitation (PNF). Each of these types of stretching can fit into a warm-up; however there are times in the warm-up when one type may be more beneficial than another.

Types of Stretching

Static stretching is often referred to as slow or passive stretching¹ and occurs when there is a slow and controlled movement to the end range of motion. The position is held for a length of time (typically 20-30 seconds), and the muscle is moved back to the natural position.¹ The stretch is then repeated several times to increase the end point in the muscle and connective tissue. This stretch is designed to lengthen the plastic (non-recoiling) connective tissue to achieve the greatest increase in permanent elongation.

Ballistic stretching is one form of active stretching, but the method used to perform this type of stretching may lead to an increased risk for injury.² This type of stretching utilizes the weight of a body part ( i.e., arm, leg, trunk) in order to move past the end range of motion and gain a greater muscle length.² Once the end range of motion is achieved, the body part is then “bounced” repetitively to push the muscle further past the end range of motion. Ballistic stretching may cause muscle injury, because the muscle is forcefully stretched. During ballistic stretching, the muscle is stretched at a fast rate and then rebounded back repetitively, resulting in greater tension and more absorbed energy within the muscle–tendon unit.²

Dynamic stretching is also a form of active stretching, but it is much more controlled than ballistic stretching. Dynamic stretching utilizes the principle of reciprocal inhibition in order to relax one muscle while its antagonist is contracted, pulling the muscle through the range of motion without forcefully pushing it past the end range of motion.² For example, the hamstring group actively contracts resulting in the inhibited quadriceps group causing the muscle group to be stretched. Motions such as arm circles and high knees fall into the dynamic stretching category. Dynamic stretching can easily be added into a warm-up routine and might be a useful protocol for increasing flexibility without decreasing athletic performance.²

Proprioceptive neuromuscular facilitation (PNF) stretching uses the principle of reciprocal interaction between agonist and antagonist muscles as well and it is a key component in PNF stretching. Reciprocal inhibition is the principle that the sensory signal that causes a contraction of agonist muscle also causes an inhibitory response in the antagonist of that muscle.² When the antagonist muscle is inhibited, it will be stretched in the opposite direction more easily.² There are several different methods of PNF stretching, including slow-reversal-hold, contract-relax, and hold-relax.² The muscle is passively moved to the end range of motion, and then the antagonist muscle isometrically contracts to inhibit the stretched muscle.1 After the isometric muscle contraction of the antagonist, the muscle is again stretched. The contractility of muscles provides the flexibility in the PNF technique, on the basis of the viscoelastic properties of muscle and neuromuscular facilitation.² The contracted muscle lengthens the noncontractile elements (perimysium, endomysium, tendon) and, consequently, causes a relaxation of the muscle–tendon unit and decreased passive tension in the muscle.² The contracted muscle also stimulates sensory receptors within the muscle: muscle spindles (negative stretch reflex) and Golgi tendon organs (GTOs) that help to relax, or inhibit, the tensed muscle; as a consequence, the muscle–tendon-unit becomes more relaxed after the contraction.²

Effects of Stretching on Flexibility

Stretching has effects on an acute and long-term level of flexibility, and both static and dynamic flexibility can be achieved. Static flexibility is defined as the available range of motion (ROM) to a joint or series of joints, while dynamic flexibility refers to the ease of movement within the obtainable ROM.⁴ Several studies have been conducted in order to determine the acute and long-term effects that various stretching protocols have on flexibility.

Two different studies^{5, 6} determined that static, ballistic, and dynamic stretching cause increases in flexibility measurements on an acute level. Static stretching created the greatest increase in flexibility, while ballistic and dynamic stretching produce minimal changes in flexibility. It was also found that dynamic stretching could cause decreases in flexibility if performed following a warm-up. These types of stretching clearly create changes in acute flexibility; however, chronic flexibility is also an important aspect to look at when evaluating stretching protocols.

Overall flexibility is considered an important aspect of fitness. Chronic increases in flexibility are synonymous with decreased tissue stiffness, and some researchers have stated that an increase in ROM does not necessarily indicate a decrease in passive stiffness, only an increased ”stretch tolerance. ”⁴ A number of studies^7,8 have examined the chronic effects of stretching on flexibility. These studies reached two separate conclusions; the first found no flexibility increases from either dynamic or static stretching, while the second found significant increases in flexibility from static stretching. These differences may be due to the methods used to conduct the research. The former study evaluated flexibility based on stretching included in a warm-up while the latter study used an extensive static stretching protocol. Because the results came from different interventions, they can both be accurate for that given situation. Obviously, stretching protocols have an effect on flexibility measurements in subjects. Performance is perhaps a more important aspect to examine. Athletes do not want their performance to be compromised due to the stretching protocol, which could have a profound effect.

Effects of Acute and Chronic Stretching on Performance

The type of activity must be taken into consideration when determining whether there is any effect on performance from stretching. For example, a protocol that may cause a decrease in the performance of a strength and power activity could present a positive influence on endurance activity or on athletes that are working for flexibility. Activities such as sprinting and weight lifting fall under the category of strength and power, and activities such as diving, dancing, and gymnastics fall into the category of athletes that are working for flexibility.²

As with flexibility, stretching has an effect on performance on an acute and long-term level. The acute effects have been studied in more depth, and the majority of research has drawn the same conclusion. The general consensus of numerous studies was that static stretching causes a decrease in strength and power performance and that dynamic stretching causes no negative side effects. ^5,9,10-14 These studies used different methods to evaluate the effect of stretching interventions on the performance of strength and power activities. Measurements such as sprint times, ^11,13,14 power exercises, ^5,10 and agility activities,^9,12 have determined the effects different stretching protocols have on acute performance measurements. In the studies, the researchers found that static stretching reduced the performance of power activities for at least 15 minutes post-stretch. The results of PNF stretching came to the same conclusion, although the performance decreases were not as large. Ballistic stretching was found to have a minimal effect on performance, and dynamic stretching showed the greatest increase in performance measurements. These results show the acute effects of stretching on performance as well as long-term performance. Although dynamic stretching leads to performance increases on an acute level, it may not contribute to long-term performance measurements. Static, ballistic, and PNF stretching protocols also need to be evaluated in order to determine the optimal protocols for long-term performance increases.

An extensive study of 24 collegiate wrestlers compared the effects of static and dynamic stretching on overall performance after four weeks of intervention.⁷ Significant increases in overall performance measurements in the dynamic stretching group were reported, with no change in the static stretching group.

In general, static stretching leads to the greatest long term increases in flexibility. Increases in flexibility can lead to increases in performance in some activities but decreasing performance in other areas. Female gymnasts require a dramatic ROM in many movements, while soccer players may benefit more from having “tighter” muscles.⁴ Each sport has different requirements of an athlete, and within that sport there are positions that require a variety of attributes. Goalkeepers in soccer display increased flexibility when compared to their team counterparts, and soccer players as a whole are tighter than the general non-soccer population.⁴ Swimmers have displayed an increase in flexibility in their ankles and shoulders, and baseball pitchers have an increase in external rotation of the shoulder. These differences in flexibility may be due to the stored energy potential in the elastic structures of a muscle.⁴ In other words, the tighter an athlete is, the more potential energy.  Because profiles of athletes appear to indicate specific flexibility patterns associated both between and within sports, evidence exists that flexibility must be related to sports performance.⁴ One surprising study measured the economy of walking and running in subjects with varying levels of flexibility. The study used ml O2/kg/m as the measurement for economy, and the researchers found that once speeds exceeded the normal walking pace of 4.8 km/h the subjects with the “tightest” flexibility measurements were the most economical.⁴ This study brought to light some surprising information. Although increased flexibility is important for performance in some sports that rely on extremes of motion for movement such as gymnastics and diving, decreased flexibility may actually increase economy of movement in sports that use only the mid portion of ROM.⁴

Summary

A key component in a pre-activity warm-up is a stretching protocol. Different stretching protocols, both acute and chronic, have a profound effect on the flexibility and performance of athletes. When developing a stretching program, the type of activity must be taken into consideration as each type of stretching produces different physiological effects. Athletic trainers should avoid statically stretching their athletes before activity and instead perform dynamic stretching. They also need to know how to improve long-term flexibility using static stretching post activity. In order to provide an optimal stretching protocol, the demands of the activity need to be evaluated and a program developed based on the protocol that has been determined to be optimal for that type of activity.

References