The Science of Stretching

10/27/2019

At the risk of treading on sacred ground, we will attempt to present an unbiased physiological assessment of what would be termed more so as static stretching.  Stretching is a bit of a ‘touchy’ subject given that many tend to adhere to the notion that stretching is generally ‘good’. And it is ‘good’ but the timing and type can make the difference.   

 

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. This makes a more dynamic warm-up prior to most sports preferable.  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. Dynamic warm-up or mobility including yoga series such as Sun Salutation.

 

Unfortunately, however, static stretching as part of a warm-up immediately prior to exercise has been shown detrimental to dynamometer-measured muscle strength and performance in running and jumping.  The loss of strength resulting from acute static stretching has been termed, “stretch-induced strength loss.”

 

In contrast to static stretching, dynamic stretching is not associated with strength or performance deficits, and actually has been shown to improve dynamometer-measured power as well as jumping and running performance.

 

The ‘stretch reflex’ is the mechanism by which the muscle initiates a contraction. Muscle can be divided into extrafusal and intrafusal fibers.  The extrafusal fibers contain contractile units called myofibrils and are what we generally refer to as muscle fibers. The intrafusal fibers are called muscle spindles and lie parallel to the extrafusal fibers.  

 

The intrafusal fibers are responsible for the stretch mechanism.  This stretch mechanism is what maintains the reflexive tone of the muscle.  The more reflexive tone the more responsive the muscle is to a given stimuli.  Less reflexive tone and less capacity for the muscle to fire and handle a load equaling what we think of as weakness.

 

Muscles are governed by an agonist/antagonist relationship and when a muscle is ‘weak’ or less reflexively capable of initiating the proper stretch response then the opposing muscle becomes ‘tight’ in an attempt to protect the weak muscle and the joint the muscle crosses.

 

Joints also rely upon tendons that connect muscle to bone as the primary means of protection for the joint.  Specifically, a sensory receptor called the golgi tendon organ regulates tension within the stretch response and mediates tension or ‘tightness’ for protection.

 

The brain and specifically the cerebellum dynamically regulates all proprioception or our perception of ourselves in space maintaining resistance to gravity and posture.  The cerebellum is generally known for Accuracy, Balance and Coordination preventing unwanted movement and mediating motor control via the stretch response in muscles. 

 

When we attempt to stretch through tightness and increase a joint’s range of motion, we are attempting to build stretch ‘tolerance’ in an attempt to override the brain’s protection largely mediated through the cerebellum and the golgi tendon.  The golgi tendon triggers the lengthening reaction which inhibits the muscles from contracting and causes them to relax. Other names for this reflex are the inverse myotatic reflex, autogenic inhibition, and the clasped-knife reflex. This basic function of the golgi tendon organ helps to protect the muscles, tendons, and ligaments from injury. 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 rendering the muscles less able to fire reflexively.

 

As the range of motion is increased the vast majority of studies indicate it is an increased tolerance to stretch and not muscle lengthening or extensibility.  And the gained ROM comes at the expense of motor control.  

 

An old athletic axiom is “We get injured in the ranges of motion we don’t train”.  This generally holds true and as one becomes hyper-mobile to some degree there is an increased risk of injury.  In instances of hyper-mobility, there is a gap between passive ROM or ROM attained through static stretching and active ROM or ROM with motor control.  

 

As mentioned earlier, dynamic stretching or mobility focused on moving the joints are excellent ways to prepare for any athletic endeavor.  These forms of warm-up require motor control and up-regulate the receptors that static stretching actually down-regulate.  

 

The question begs when is static stretching effective?  That’s a good question and probably open for debate. One theory for the euphoria some feel from stretching is related to the body’s need for nociceptive stimuli.  It’s a deeper topic to save for another blog, maybe the upcoming blog but it is an interesting theory. It’s also been theorized that the euphoria from massage is the same sort of nociceptive response that the body requires and can be traced to a lack of neural stimulation due to inefficiency of nociceptive receptors.

In short, incline your pre-activity stretching toward the dynamic and limit the static prolonged stretching.  As far as other times, it’s difficult to make a definitive statement for everyone but some will benefit from steering away from static stretching altogether and be advised