Static stretching is a misunderstood component of fitness, sports training and rehabilitation.  It is the goal of this post to explain 3 things:

·      What exactly happens when you static stretch

·      What are the limitations/negatives of static stretching

·      What are the positives/benefits of static stretching

Beyond that, it’s up to you to decide how (and if) you think that static stretching is something that you want to make a part of your fitness routine.

Some Anatomical Background Information:

The musculoskeletal system:

Muscles, bones, ligaments, tendons and connective tissue/fascia comprise what is called the musculoskeletal system of the body. The bones allow for upright posture and provide structural support for the body. The muscles allow the body to move (by contracting, and thus generating tension). Muscles are attached to the bone by tendons and when they contract, they create movement. The point where bones connect to one another is called a joint, and ligaments, joint capsules and connective tissue support this connection.

Muscle composition:

At the highest level, the (whole) muscle is composed of many strands of tissue called fascicles. (These are the strands of muscle that we see when we cut red meat or poultry.) Each fascicle is composed of fasciculi, which are bundles of many microscopic muscle fibers. The muscle fibers are in turn composed of tens of thousands of thread-like myofybrils, which can contract, relax, and elongate (lengthen). The myofybrils are (in turn) composed of up to millions of bands laid end-to-end called sarcomeres. Each sarcomere is made of overlapping thick and thin filaments called myofilaments. The thick and thin myofilaments are made up of contractile proteins, primarily actin and myosin.

The (basic) physiology of muscle contraction:

The way in which all these various levels of the muscle operate is as follows: Nerves connect the spinal column to the muscle. The place where the nerve and muscle meet is called the neuromuscular junction. When an electrical signal crosses the neuromuscular junction, it is transmitted deep inside the muscle fibers. Inside the muscle fibers, the signal stimulates the flow of calcium, which causes the thick and thin myofilaments to slide across one another. When this occurs, it causes the sarcomere length to shorten, which generates force (a.k.a contraction). When billions of sarcomeres in the muscle shorten all at once it results in a contraction of the ENTIRE muscle fiber.

Now, one important concept to understand is this: when a muscle fiber contracts, it contracts completely. There is no such thing as a partially contracted muscle fiber. Muscle fibers are unable to vary the intensity of their contraction relative to the load against which they are acting.  Rather, muscle contraction force varies in strength from strong to weak based on the NUMBER of fibers involved.  Basically, more muscle fibers are recruited, AS they are needed, to perform the job at hand. The more muscle fibers that are recruited by the central nervous system, the stronger the force generated by the muscular contraction.   This concept boils down to energy efficiency.  It takes energy to contract muscle fibers, and the body loves to conserve energy.  So, it recruits fibers on a one-by-one basis looking for the fewest needed to move the load.  This means that you use less muscle fibers to pick up a bottle of water than you do to lift a gallon of milk.

And finally:

The (basic) physiology of stretching:

The stretching of a muscle fiber begins with the sarcomere, the basic unit of contraction in the muscle fiber. As the sarcomere contracts, the area of overlap between the thick and thin myofilaments increases (discussed above). As it stretches, this area of overlap DECREASES, allowing the muscle fiber to elongate. Once the muscle fiber is at its maximum resting length (all the sarcomeres are fully stretched), additional stretching places force on the surrounding connective tissue. As the tension increases, the collagen fibers in the connective tissue align themselves along the same line of force as the tension. So as you continue to stretch, the muscle fiber is pulled out to its full length sarcomere by sarcomere, and then the connective tissue takes up the remaining slack. When this occurs, it may help to realign any disorganized fibers in the direction of the tension. This realignment may be what helps to rehabilitate scarred tissue back to health (during recovery from muscle injury/after surgery).

When a muscle is stretched, some of its fibers lengthen, but other fibers may remain at rest. The current length of the entire muscle depends upon the number of stretched fibers (similar to the way that the total strength of a contracting muscle depends on the number of recruited fibers contracting). One way to visualize this is to think of little groups of fibers throughout the muscle body stretching, while other groups of fibers are simply “going along for the ride". As such, the more fibers that are stretched in this process, the greater the length developed by the stretched muscle.

Relative to the process of stretching, it is also important to understand how the brain/neural components of the musculoskeletal system adapt to stretching. (FYI – this is the simplified version, so please just appreciate that there are other factors involved). When the muscle is stretched, so is the muscle spindle (a nerve control point located among groups of muscle fibers). The muscle spindle records the change in length of the muscle and how fast this change occurs.  It then sends signals to the spine, which then conveys this information to the brain.  Initially, this information triggers the stretch reflex, which attempts to resist the change in muscle length by causing the stretched muscle to contract. The more sudden the change in muscle length, the stronger the muscle contractions will be (why you don’t “bounce stretch.”) This basic function of the muscle spindle helps to maintain muscle tone and to protect the body from injury.  

Now, if the force and suddenness of the stretch exceed the muscle’s ability to safely contract for protection (a.k.a. exceed it’s strength), another neural component, the golgi tendon organ (GTO), goes into action and takes power over the muscle spindle.  Basically - when muscles contract (possibly due to the stretch reflex), they produce tension at the point where the muscle is connected to the tendon. This is where the golgi tendon organ is located. The golgi tendon organ then records the change in tension, and the rate of change of the tension, and sends signals to the spine to convey this information. When this tension exceeds a certain threshold, it triggers the lengthening reaction, which inhibits the muscle’s contraction and instead cause it to relax and lengthen. The lengthening reaction is possible only because the signaling of golgi tendon organ to the spinal cord is powerful enough to overcome the signaling of the muscle spindles telling the muscle to contract.  Think of the two systems as a “double fail-safe” that ultimately helps decrease your injury risk.

Why we stretch slowly, and for a prolonged period of time:

One of the reasons for holding a stretch for a prolonged period of time is that as you hold the muscle in a stretched position, the muscle spindle habituates (becomes accustomed to the new length) and reduces its signaling. Gradually, you can train your stretch receptors to allow greater lengthening of the muscles.  This, in turn, also increases your “flexibility” as the muscle spindle now allows your muscle to stretch farther prior to contracting.

Another reason for holding a stretch for a prolonged period of time is to allow the lengthening reaction (caused by the golgi tendon organ) to occur, thus helping the stretched muscles to relax. Obviously, it is easier to stretch, or lengthen, a muscle when it is not trying to contract.

Fun fact:

Some sources suggest that with extensive training, the stretch reflex of certain muscles can be voluntarily controlled so that there is little or no reflex contraction in response to a sudden stretch. (This is a “wow” statement in case you were wondering…) While this type of control provides the opportunity for the greatest gains in flexibility, it also provides the greatest risk of injury if used improperly. It is worth noting that high level/professional athletes and dancers at the top of their sport (or art) are believed to actually possess this level of muscular control (so don’t feel bad if you tried to drop into a full split and things went badly…).

What the current research is saying about static stretching:

The "bad":

There have been countless studies done on stretching and its effect on general sport performance.  The majority of the current research suggests that static stretching PRIOR to activity can induce temporary weakness in the muscle, decrease the ability of the muscle receptor to engage the “stretch reflex” and can increase injury risk.  Literature notes that there is a loss of contractile power/strength for up to 30 minutes after static stretching and as such, the muscle cannot contract maximally if needed. This is not new information - most of the research draws from studies performed as early as the 90’s and 00’s. As a PT, I would agree with this stance and recommend a more dynamic warm-up prior to most sports.  If you must static stretch prior to activity (because your sport requires it/it is part of your personal routine), consider then progressing to a gentle, dynamic warm-up prior to the actual activity.

The "good":

There are positive benefits of static stretching on overall health, mobility and flexibility. As we discussed above, stretching does cause the muscle and tendon to lengthen, and these changes can be somewhat permanent and definitely beneficial to sport and wellness. I’m going to argue (and I have some research to support me) that static stretching AFTER activity has immense value – especially if you’re trying to get more flexible, treat injury and improve your overall mobility.  Along those lines, if you’re an aerialist, acrobat, gymnast, dancer or yogi – it is essential for skill acquisition and improved technique.

When you stretch after activity, the muscles are tired and well vascularized (think lots of healthy, nutritious blood-flow).  The fatigue allows you to take advantage of the lengthening reaction (discussed above) and the sarcomeres are less able to contract (so they “can’t fight” as strongly against the stretch).  Several articles also suggest that stretching (gently) after activity can decrease post-workout soreness. Finally, a good workout will cause some micro-trauma to the muscles and the subsequent adaption (what makes us stronger) may occur with increased fiber length when your stretch afterwards.  This means that as you gain strength, stretching after a workout can allow you to prevent the associated loss of flexibility that occurs with muscle fiber growth (more to come on that during a later blog).

In summary:

Static stretching is something that can be dangerous and beneficial, and as such, be sure that you are aware of technique and the reasoning behind it.  Follow the advice of your physical therapist, doctor and coach - and yes, be “flexible” about it.  

References:

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