Stretching has long been used in the world of athletics and rehabilitation to promote flexibility, improve motion and ease discomfort associated with muscles. The act of stretching was traditionally thought to bring a host of outcomes, and stretching has had a global, general use for many different activities.
Forexample, the studies used varied types of stretches, varied volume of stretching, and different muscle groups. But even with these inconsistencies, there is such a thing as too much of a good thing. Studies show that too much dynamic stretching can actually impair performance.7 Groups that did two-to-three bouts of dynamic stretching vs. one-to-two bouts had decreased performance, likely because of induced fatigue.
While stretching still has many benefits and is a multifaceted technique, various types of stretching are now being used to achieve more precise outcomes. Essentially, the desired outcome may vary depending on the type of stretching chosen.
The Advent of Dynamic Stretching
Historically, stretching has been used to obtain gains in flexibility of musculoskeletal structures to reduce the risk of injury, enhance muscle performance and reduce soreness associated with tight muscles.1 While stretching is still used for these purposes, different types of stretching can be used depending on the desired outcomes. The outcome of the stretching, or more specifically, the activity the stretching is intended for, has changed with the advent of dynamic stretching.
Dynamic stretching certainly altered traditional stretching practices and parameters as they relate to the activity or sport at hand. Before dynamic stretching was commonly practiced, a traditional light aerobic warm-up was used, followed by a period of static stretching in preparation for activity or sport.
The conventional wisdom and research at the time recommended a static, sustained stretch of at least 30 seconds to facilitate increased flexibility of the muscles being stretched. The thought was that this technique would allow for improved muscle length and performance, and thus reduce the risk of injury.1,2
Dynamic stretching altered the parameters of stretching by allowing for the movement of the entire upper- or lower-body segments. This movement is conducted in a range of motion that's comfortable in a controlled, repetitive fashion. Unlike static stretching, there's no appreciable sustained hold at the end of the motion.3Static and dynamic stretching are indeed different in how they are conducted, and are also different in the benefits they seem to present. One of the big differences according to general consensus is that dynamic stretching should be used prior to the start of sporting activity, and static stretching should be used to achieve improved muscle length and flexibility.
It is thought that dynamic stretching may be the safer type of stretching before activity.3-8 Is this an accurate simplification, or is it a rule of thumb with exceptions?
Static Stretching: Still a Role
It's widely accepted that static stretching, when used in a pain-free ROM with proper technique and duration, can improve flexibility.1-4,8 Moreover, the effects of this type of stretching have been shown to last for nearly 24 hours, though the greatest gains in muscle length are reported immediately after stretching for about 15 minutes.2
These benefits seem to occur without a warm-up performed prior to stretching. If the goal is improving flexibility of a muscle group, it's reassuring to note that a warm-up may not be necessary to facilitate gains.
The practical implication of this is that patients may be more likely to work stretching into their daily routines if they don't have to perform a time-consuming warm-up prior to their prescribed stretches. As such, home compliance of issued stretches may improve if warm-ups aren't necessary prior to stretching to achieve the desired increase in flexibility.
While it's been established that static stretching can improve muscle flexibility, does it improve flexibility more than dynamic stretching? Theories have been proposed that the controlled, swinging motions to end-range typical of dynamic stretching have a lengthening effect on muscles. It's speculated that the movement of the antagonist muscle causes the opposite muscle group to lengthen via reciprocal inhibition.3
Despite such proposed theories, a majority of the research tends to show that static stretching has a greater effect on flexibility in comparison to dynamic stretching.3-5 While gains in flexibility are seen with dynamic stretching, some studies have found that static stretching is two-to-three times more effective at improving flexibility.
So although dynamic stretching has been shown to improve flexibility, bigger gains appear to be made with static stretching.3-5 This bears implications when working with different patient populations. If you're working with patients with pathological muscle tightness from a previous injury who present with reduced flexibility, static stretching may be the most viable type of stretching.
Dynamic stretching may prove to be enough for healthy patients without reduced flexibility to prepare them for sport or activity. However, if a patient has reduced flexibility from previous injury or pathology, dynamic stretching may not be enough to improve flexibility. This patient may need a combination of static and dynamic stretching before he can safely transition to participation in sport activities.
For patients who have pathological tightness, only performing dynamic stretching may actually be detrimental to their sports performance, and increase the likelihood of injury if they don't have the anatomical ROM required of the sport.
Why does static stretching get a bad rap when done prior to athletic performance? Cumulative literature suggests that performing static stretching prior to athletic activity may impair performance.3-8 Research reports indicate the potential for reduced muscle power, speed and force production after performing static stretching.
This could consequently affect sports or activities that require explosive, ballistic-type movements. Some proposed mechanisms for this are hypermobility/hyperflexibility sacrificing stability, alteration of muscle length/strength relationships, inhibition of the myotonic stretch reflex, relaxation of sensory-motor recruitment, reduced motor-unit firing, and altered kinesthetic response. There is even evidence that dynamic stretching may improve athletic performance.6-8
Sport-specific performance dimensions such as power, peak torque production, agility, sprinting performance, and vertical jump height have all been suggested to improve in comparison to subjects who use static stretching or do not stretch at all.6-8
Making the Choice
While it may seem conclusive that dynamic stretching should be used across the board prior to athletic activity, it's unfortunately not so clear-cut. Dynamic stretching is likely to carry the greatest benefit for patients and athletes who are healthy and haven't had a previous musculotendinous injury.
Even across healthy, athletic populations, however, dynamic stretching has not shown universal benefit. Some studies show a discrepancy with the dynamic warm-up rule of thumb by demonstrating no short-term benefit with strength, sprint performance and vertical jump height.6-7 This may be because apples were compared to oranges, and not all studies used the same dynamic warm-up strategies.
With this in mind, a patient's level of conditioning should be paramount when prescribing dynamic stretching. The volume of this type of warm-up should vary depending on the patient's level of fitness. An involved bout of dynamic stretching may benefit a fit individual, and conversely may be a detriment to a less-conditioned individual.
Varied studies are finding muscle-length changes that are dependent on blood flow, and vice versa.9 Perhaps part of the gains noted with stretching are due to a vascular response in addition to the musculotendinous response. Other studies are demonstrating improvements in sports performance with dynamic stretching that are being attributed to VO2 max and increased oxygen consumption.6 Perhaps the differences between static and dynamic stretching with performance are in part due to different amounts of relative oxygen consumption.
Another potential variable that's received little research attention are muscle-fiber types and motor units with stretching. If static stretching is believed to lengthen mainly slow-twitch motor units, would dynamic stretching be more appropriate for muscle groups consisting mostly of fast motor units?
While it may seem to be a good rule of thumb that dynamic stretching should be used prior to sports activity and static stretching should be used to improve flexibility, there are exceptions to the rule. Further research will likely provide even more exceptions to the rule. The practitioner must always be mindful of the intended population, history of injury, the outcomes desired from stretching, and what other physiological variables are going to affect such outcomes. The decision on what type of stretching is best for a patient indeed requires the skilled care and thought of the clinician.
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Ben Wiggin is practice manager of Back Bay Rehabilitation in Tamworth, N.H. He specializes in orthopedic and sports medicine-related injuries. He can be reached at firstname.lastname@example.org