Stretching and the pursuit of “flexibility” has long been a goal of many athletes, trainers, therapists, sports medicine practitioners, and society as a whole. The intentions of attaining this goal have been numerous and include preventing injury, improving athletic performance, retarding the affects of aging, and developing long ‘athletic-looking’ bodies. However as with all physical exercise activities, stretching and flexibility training has long fallen into the realm of ‘gym science,’ while the true science has failed to be recognized. This has lead to the creation of flexibility training programs, which have been largely ineffective, misguided, and often times dangerous.
Even in the rare situations where flexibility is actually attained using such training regimens, more often than not what the individual has actually managed to acquire is what I commonly refer to as “useless range,” or “useless flexibility.” In other words, they have managed to force their bodies to attain a range of motion in which they have absolutely no control. The ability for say a martial artist to simply do the splits does not necessarily mean that they will be able to kick an opponent in the head … it simply means that he or she is able to do the splits! That, in and of itself, has no real usefulness in sport, or in everyday life. Similarly for the weightlifting athlete, simply attaining enough flexibility to reach the bottom position of a proper squat does not automatically translate into the ability to generate strength from that position. A person’s ability to attain certain range of motion has no usefulness unless he/or she is able to control that range. In other words, the pursuit of flexibility in the absence of strengthening the newly acquired range does nothing more than produce “useless flexibility.” Only those who are able to maintain control of their bodies, even when in extreme ranges, are able to benefit from their new found ‘elasticity.’
This article intends to first dispel some of the myths that surround the topic of stretching and flexibility training, then briefly introduce a new adjunctive method of training used to create useful, functional flexibility (aka. Mobility) termed Functional Range Conditioning (FRC)™.
Dispelling the stretching myths…
Before discussing the concepts and benefits of proper flexibility and/or mobility training programs, it is important to first learn the “myths” which have long been propagated throughout the fitness world on the topic. Many of these fallacies have been entrenched into the minds of the so-called fitness or medical ‘experts,’ so dispelling such myths is not an easy task. In order to do so, we must forget about what the “gym science” has told us, relinquish “common sense,” and trust the actual science. Such science has been available for many years, however as it often does, science ruins perfectly wonderful theories, and thus is ignored by the masses. In situations when some of the more recent lines of research are actually taken into consideration, interpretations are commonly riddled with more fallacy than the original concepts.
Physiology of Stretching: What actually happens to our tissues when we stretch?
Historically, stretching was believed to increase the range of motion of a joint through decreases in something termed “viscoelasticity,” as well as by increases in the “compliance” of muscle. Viscoelasticity refers to the property of some materials that exhibit both “viscous” and “elastic” characteristics when undergoing deformation (a change in the shape or size of an object due to an applied force). Human muscle is such a material that possesses the ability to exhibit both behaviors. With a purely viscous substance, if a force is applied to it, the shape of the substance will change permanently. Thus when the force is removed, it will not return to its original shape. Further, the longer the force is applied to it, the greater the resultant change in shape (Molasses would be an example of a purely viscous substance). A purely elastic material on the other hand will exhibit change in length for a given force, and will return to its original length when the force is removed.
Compliance refers to how easily a substance’s shape will be altered under a load. A more compliant tissue will undergo length change under lesser force, whilst a stiffer tissue will require more force to create a comparable length change.
In theory, the fact that human muscle tissue acts as a vasoelastic material makes logical sense in the context of stretching. When one stretches for a period of time the viscous component of the muscle will lead to increased ranges of motion, however the elastic component will return the muscle to a normal resting length making at least a portion of the stretch short lived. If muscles were purely viscous, then the muscles length would remain in the stretched position permanently (i.e., ‘Gumby’). If muscles were purely elastic, then there would be no such thing as permanent improvements in flexibility.
However, as was previously stated, science ruins perfectly wonderful theories! What the science shows is that the immediate effect of stretching does appear to affect the viscoelastic behavior of muscles, but the duration of this effect has been shown to be short lived (Magnusson, Simonsen, Aagaard, & Kjaer, 1996; Magnusson, Aagaard, Larsson, & Kjaer, 2000). Studies looking at long term stretching (over a 3-4 week period) reveal improvements in flexibility and range, however no change in viscoelasticity. In other words, their flexibility improves but with no lasting change to the muscles structure (Magnusson, Simonsen, Aagaard, Soukka, & Kjaer, 1996; Halbertsma & Goeken, 1994).
If a person is able to increase flexibility over time in the absence of changes of the viscoelastic behavior of a muscle, then how does this improvement occur? It would appear that the bodies’ reaction to prolonged stretching is to increase stretch tolerance. In other words, with time, the body ‘allows’ more range to be achieved. As with any other decision the body makes, this ‘allowance’ is the work of the central nervous system (CNS – the brain and spinal cord). Stated simply, improvements in flexibility are the result of the nervous system allowing the tissues to stretch more, and not as a result of a change in the actual structure of the tissue. Thus stretching could be considered a method of training the nervous system rather than muscles.
A simple experiment can further illustrate this point. Stand next to a table that is approximately waist level. Now abduct the leg closest to the table onto it such that your hip is at ninety degrees. Are you able to do it? Most healthy, moderately fit individuals should be able. Now turn around so you’re opposite side is against the table and do the same thing. If you were able to hold each of your legs out at 90°>, then what is preventing you from being able to achieve a full split position (90+90=180°)? Barring some minimal influence of pelvic tilting, in a full split, each hip is achieving the exact same range of motion, and the muscles ‘restricting’ that particular motion (the adductors) are ‘stretching/lengthening’ the exact same amount as in our experiment. Why then can’t they do it at the same time? For those who need to brush up on their anatomy, I will tell you that there is no muscle in the human body that crosses between hip joints. Thus the only real ‘bridging’ tissue is your skin which is extremely flexible. The reason for this phenomenon comes down to an unwillingness of the central nervous system to allow this position to occur due to both fear of injury, as well as fear of being unable to recover from the position once you are in it. Thus, even though the position is well within the normal limits of the muscles length, because we are unable to control the weight of our body in the position, the nervous system does not allow it (Hence the need to develop strength and control in the outer ranges of motion – see below).
Does pre-exercise stretching help prevent injuries?
For many years now, sports-medicine professionals and trainers alike have promoted stretching as a way to decrease the risk of injury. To apply “common sense” to the matter, the more elasticity, or flexibility a tissue has, the harder it is for that tissue to ‘snap.’ Paraphrasing an old Chinese saying, “that which does not bend, breaks.” Although this theory makes sense to common standards, the science demonstrates that this theory does not apply to tissue injury.
Although muscles are sometimes injured when stretched beyond their capability, the majority of injuries occur within the normal range of motion of a tissue during eccentric activity (muscle lengthening under tension). The most important variable with respect to muscle injury is therefore not the length of the muscle, but the energy absorbed by the muscle. In other words, during physical activity, the tissues of the body are subjected to forces or “tissue insults.” When the amount of force, or insult, into the tissue exceeds the force absorbing capabilities of that tissue it causes injury. Stretching has been shown to temporarily decrease the tissues “threshold” for force absorption and therefore stretching before training or competition has not only been shown to not prevent injury, it may actually increase your chances! (Thacker, Gilchrist, Stroup, & Kimsey, 2004; Weldon & Hill, 2003; Herbert & Gabriel, 2002; Amako, Oda, Masuoka, Yokoi, & Campisi, 2003; Malliaropoulos, Papalexandris, Papalada, & Papacostas, 2004).
Does this mean that stretching should be abandoned?
Although it is a common occurrence in the health and fitness industry to ignore scientific literature that contradicts ones own philosophies and doctrines, it would seem to be just as common for people to use scientific research to make claims that far exceed the experimental results. With regards to stretching we see this with individuals who, in light of much of the research I have reviewed above, arrive at the conclusion that stretching should be avoided, as it serves no purpose. This is a highly exaggerated representation of the literature.
While it is true that “direct research” (studies looking specifically at a particular topic) surrounding the topic of the benefits of stretching is scarce, there have been studies that have looked to answer this question. For example there have been three studies that isolated the effect of stretching outside periods of exercise on injury risk. All suggest clinically relevant decrease in injury risk, which contrasts the recent meme in popular literature that stretching serves no purpose (Garrett, 1990; Safran, Seaber, & Garrett, 1989; Shellock & Prentice, 1985).
Further, when looking at “indirect research” (research looking at various topics that can provide insight into an otherwise scarcely studied question) one can easily extrapolate a strong, evidence-based argument to promote the benefits of regular stretching practice. It would be far to ambitious to review all said studies here, however I will discuss a few research streams which pertains to the seemed intimate relationship between flexibility, strength, and nervous system function.
Aside from the obvious effects of improving flexibility and improving range of motion, research is also suggesting that stretching may also increase a muscle’s cross-sectional area (size) via a process termed “stretch induced hypertrophy” (Goldspink, Cox, Smith, Eaves, Osbaldeston & Lee, 1995; Always, 1994; Yang, Alnaqeeb, Simpson,& Goldspink, 1997). In fact, a recent study demonstrated that stretching regularly over a period of weeks improves results on tests of maximal voluntary contraction, jumping height and possible running speed (Shrier, 2004). These improvements may be attributed in part to muscular hypertrophy, however the author also offers an alternative hypothesis as well—a reduction in central neuromuscular inhibition. In other words, stretching may somehow teach the CNS to more fully activate the muscles involved in the task. Either way, this seems to indicate that stretching can positively influence acquisition of strength. The next question is, are the two mutually beneficial? The answer would seem to be yes as is suggested by a recent literature review looking at the effect of sole eccentric strength training on flexibility measures, which concluded that it indeed leads to improvement (O’Sullivan, McAuliffe, & Deburca, 2012). Further, as demonstrated by Simao (2011), it would seem that when strength and stretching tasks are assigned simultaneously, it results in a greater improvement in flexibility that occurs with individual application (Simão et. al, 2011). In other words, stretching may somehow teach the CNS to more fully activate the muscles involved in the task.
Common to both flexibility and strength is the involvement of the nervous system as a major underlying causative factor for improvement. In terms of strength, it is well know that its initial development is produced by neural signal adaptations as demonstrated, for example, by the common, rapid rise in strength measures displayed by newly trained, inexperienced weight lifters prior to any physical muscular alteration. For flexibility, as described above, recent research suggests it to be governed almost exclusively by the central nervous system activity.
This research points to a strong, mutually beneficial relationship between strength and flexibility, as well as a major (if not exclusive) influence of the nervous system as the underlying causative factor for improvement. It is thus surprising that the combination of strength and flexibility training techniques have so scarcely been explored as they are in the Functional Range Conditioning (FRC)™ system explained below.
- Improvements in flexibility are mostly the result of a change in the function of the central nervous system and not as a result of a change in the actual structure of muscle tissue.
- Research studies have not found that pre-exercise stretching prevents injury. In fact, it would theoretically increase the chance of injury by temporarily reducing the muscles ability to absorb force.
- Research suggests that stretching between bouts of exercise likely reduces the chances of injury during exercise.
- Several lines of research point to a mutually beneficial relationship between strength and flexibility development.
- More important than simple flexibility is end range control/strength. Improvements in flexibility in the absence of end range strength produces “useless flexibility” said ranges will be unattainable during functional movements.
Functional Range Conditioning (FRC)™
In light of the information presented above, Functional Range Conditioning (FRC)™ is a method of training that looks to coalesce research knowledge with clinical practice creating a system that is focused on the acquisition of mobility -- defined as the extent of controllable flexibility across articulations (flexibility + strength). In other words, the FRC™ system looks to not only improve passive flexibility, but also to develop control of newly acquired ranges of motion thus transforming them into active, strong, functional, useable ranges. This translates into various physical benefits including:
- Improved movement ability, quality, and efficiency
- Greater potential for force generation and athletic performance
- Improved joint health & safety
- Decreased tightness/muscle soreness
- Increased joint longevity
Still in its infancy, this new system of conditioning is gaining notoriety in the fitness community and is currently being used by professionals of various disciplines including strength and conditioning specialists, rehabilitation specialists, and manual therapists. Its principles have been successfully implemented with a variety of athletes from Major League Baseball players, Soccer and Hockey players, Jiu Jitsu/MMA competitors and professional dancers.
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- Magnusson SP, Aagaard P, Larsson B, Kjaer M. Passive energy absorption by human muscle-tendon unit is unaffected by increase in intramuscular temperature. J Appl Physiol 2000;88:1215-1220.
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- O’Sullivan, McAuliffe S, Deburca N. The effects of eccentric training on lower limb flexibility: a systematic review. Br J Sports Med 2012;46(12):838-845.
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