Stretching

Overview
Stretching is a form of physical exercise in which a specific skeletal muscle (or muscle group) is deliberately elongated to its fullest length (often by abduction from the torso) in order to improve the muscle's felt elasticity and reaffirm comfortable muscle tone. (Weerapong et al 189–206) The result is a feeling of increased muscle control, flexibility and range of motion. Stretching is also used therapeutically to to alleviate cramps. Stretching, in its most basic form, is a natural and instinctive activity; it is performed by both animals and humans. It can be accompanied by yawning. Stretching often occurs instinctively after waking from sleep, after long periods of inactivity, or after exiting confined spaces.

Many athletes stretch deliberately before or after exercise in order to increase performance and reduce injury. Whether this is helpful, has no effect, or even has detrimental effects is in dispute. While common, it may not be beneficial for all athletic activities.

Possible Benefits
In the literature described by Michael Yessis, there are many beneficial stretches that can improve Range of Motion (ROM) in athletes, especially runners. In his review, he cites benefits of stretching: To gain these benefits, Yessis describes different forms of stretching along with their individual benefits. He suggests that one stretching exercise may not be enough to prevent all types of injury. Therefore, multiple stretching exercises should be used to gain the full effects of stretching.
 * 1) may improve ROM
 * 2) reduce risk of injury
 * 3) prevent post-exercise muscle soreness
 * 4) slow delayed-onset muscle soreness (DOMS)

Research by Sharman et al. sought to find what techniques elongate muscles through "proprioceptive neuromuscular facilitation" (PNF) stretching. They used around seventy sources to compile their data. In this review, PNF stretching yielded the greatest change in range of motion (ROM), especially short-term benefits. Ballistic stretching was also beneficial in comparison; however, PNF techniques emphasize active flexibility and therefore get better results. Reasoning behind the biomechanical benefit of PNF stretching points to muscular reflex relaxation found in the musculotendinous unit being stretched. More common findings in literature suggest that PNF benefits are due to influence on the joint where the stretch is felt.

It has been suggested in some studies that overstretching or stretching to a point where pain is felt is inappropriate and detrimental. Effects on performance, both short and long-term, may include predisposition to injury and possible nerve damage (Yessis 8-18). Other findings in research conclude that active stretching routines will reduce muscle-tendon viscosity and increase muscle compliancy and elasticity. In sports activities where there are little or no short-stretching cycles, (bicycling, jogging, etc.) stretching routines may be detrimental to athletic performance and have no effect on reducing injuries (Witvrouw et al. 443-449).

In J.C. Andersen’s compilation of lower extremity stretching research, the effects of stretching before and after exercise were reviewed for evidence of muscle soreness. The seven articles referenced in his research came from sources such as MEDLINE and CINAHL. All data used came from studies that used static stretching programs and included average healthy participants between ages eighteen and forty. The results of Andersen’s research are somewhat limited, due to the nature of the literature he selected; however, his findings suggest that stretching has no beneficial effects on injury reduction. Two to five percent reductions in injury levels lead Anderson to believe stretching routines will not have impact on injury prevention or post-exercise soreness. Also, the concept that stretching decreases risk of injury in active muscles is negated by claims in the literature reviewed. Stretching as observed in the research found increased complaisance in relaxed muscle groups. This idea, in conjunction with stretch tolerance and stretch variability, does not encourage stretching to prevent injuries. The conclusion claims more research is needed to finalize evidence on the benefits of stretching (Andersen 218-220).

A study constructed by Nelson et al. set out to find the correlation between pre-exercise static stretching and its effects on muscle strength endurance. Two experiments were designed to find the initial links between pre-exercise stretching and muscle endurance.

Results of the study found both stretching experiments to reduce effectiveness of muscle strength endurance by up to thirty percent. They suggest that pre-exercise stretching induces a fatigue-like state in muscles which would clearly inhibit performance if the muscle is not at full potential.

Smaller amounts of research included state that stretching may cause ischemia in muscles, which reduces oxygen levels and the ability to remove metabolic waste. Higher levels of metabolic waste create a catalyst that contracts muscles. This may cause muscle injury in individual performance. Other theories included claim active static stretching increases inflow of Ca2+ from extra cellular spaces into the muscles being stretched. The increase of Ca2+ reduced the muscle twitch tension by up to sixty percent. Reasoning behind this claims that increased levels of Ca2+ in resting muscles predisposes individuals to fatigue quicker than individuals who did not stretch (Nelson, Kokkonen, and Arnall 338-343).

Flexibility
A study done by LaRoche and Connolly was designed to see whether stretching reduces frequency of sports-related injuries and increases individual performance. The study, conducted over a four-week period, involved male participants between the ages of eighteen and sixty who were not actively training. Participants were randomly assigned to three different stretching groups which included ballistic, static, and control groups. The study used a custom-built device to test the individual’s maximal hamstring resistance.

To see what stretching method worked best, participants first needed to experience Delayed Onset Muscle Soreness (DOMS). This was done by having individuals use a hamstring curl machine, doing three sets of fifteen repetitions with a one-minute break between sets. Stretching was done before and after exercise, only three days a week for a four-week period. Warm ups were a mandatory requirement before stretching. The results of the study found that both ballistic and static stretching yielded a large increase in individual range of motion (ROM). This is thought to be from an increase in stretch tolerance as opposed to actual muscle elongation. The study also found that ballistic stretching seemed to have the same effects as static stretching without any perceived negative effects. Although there was an increased range of motion due to stretching, there was no change in DOMS or muscle soreness (LaRoche and Connolly 1000-1007).

Uncertainty
For many, the idea of stretching means that injuries become less common and athletic performance is enhanced. Multifactorial claims in literature essentially discredit generally accepted ideas of stretching. In terms of genetic ability, some people are more flexible than others; this includes gender differences where women are generally more flexible than men. In this sense, some people are more predisposed to injuries than others. In addition to genetics, some studies found that stretching does not increase range of motion. Instead it increases individual stretch tolerance and may become detrimental to athletic performance. Still, other studies are nonspecific about what their research really found. Some measure capsular mobility as opposed to the joint-muscle compliance.

Overwhelming research concludes that pre-exercise stretching, especially for those who do not use short bursts of muscular activity, may result in a reduction in performance of up to five percent. At best, literature shows that weeks of regular stretching exercises, in conjunction with warm ups, may help athletes reduce injury by up to five percent. This small percent may help athletes who use short bursts of energy such as sprinters improve their fifty-yard running speed by fractions of a second. Other sports that use continuous movements, such as cycling, should not expect the same benefits. Regardless of research, athletes, especially runners, continue to stretch, attempting to reduce injuries and increase their performance. More detailed studies and research are needed to find all possible neurological effects of stretching (Shrier 22-26).

Research by Weerapong et al. was designed to find the effects of stretching on the body. In their research, they used ninety-nine peer-reviewed and scholarly sources to compile their data. Their sources came from three online databases which included PubMed, SPORT Discuss, and ProQuest 5000 International. The criteria for research looked for average healthy participants where no bias was placed on age, gender or physical abilities. All claims considered in the research were picked if they researched the long and short-term effects of stretching, while suggesting what effects stretching had on events such as injury occurrence, sport performance, and muscle soreness. Results of the study found that it is very common in literature to suggest stretching as a possible mechanism to prevent onset of injury and muscle soreness. This idea, however, while very common, does not specifically explain how stretching affects muscle properties on individual performance. Their findings suggest that common stretching methods, like static and ballistic stretches, decrease muscle performance and have inconclusive evidence to support the notion of injury reduction. Their research questions whether flexibility will reduce incidence of injury. A large number of their sources claim flexibility does not reduce incidence of injury; therefore, increasing range of motion is not needed. Their conclusion states that more research is needed to find the best stretching techniques that improve performance and reduce risk of injury (Weerapong, Hume, and Kolt 189-206).

A study done by Witvrouw et al. was done to find what relationship stretching has with injury prevention. Over forty sources of relevant literature were used in their review. Initially the documentation of stretching claimed to promote better physical performance and reduce risk of injury. The number of suggested ideas in recent literature makes the relationship between stretching and its effects ambiguous. Results of the research were two different findings, each of which has a different consideration based on individual activity:
 * They claim the reason behind conflicting data is due to the different levels of observed sports activity.
 * In activities where stretch-shortening cycles (SSC) are more prevalent, such as sprinting and jumping, the muscle-tendon units need to store and use more elastic energy
 * In activities which do not require as much SSC such as jogging, a more elastic muscle-tendon unit is not needed.

Physiology
Studies have shed light on what has turned out to be a fascinating and huge protein with skeletal muscle—aptly named, titin. A seminal study performed by Magid and Law, demonstrated convincingly that the origin of passive muscle tension (which occurs during stretching) is actually within the myofibrils themselves, not extracellular as had previously been supposed.

Summary
There are many recent studies and researched literature that have inconclusive evidence or contradict with other sources. More detailed evidence, especially pertaining to time, intensity, and repetition of stretches are needed. Stretching may be able to help athletic performance in some situations, but the most recent literature claims that pre-exercise stretching is detrimental to performance. Not all possible outlets of stretching have been explored; therefore, no specific claim can be made about the benefits of stretching.