Clearing up the confusion
In Part 1 we defined the terms associated with the word Stretching.
Most of the confusion about stretching comes from the fact that “stretching” means different things to different people. Most research has investigated only static stretching and only now are we learning about the effects of the other types of stretching. Stretching also is used interchangeably with “warm-up” so that increases confusion as well. We now know that warming-up can include stretching of different types, but must include other movement activities as well to be most effective. This is a topic for another blog post.
While static stretching is definitely effective at producing a short-term increase in the range of motion at a particular joint as measured in a static position, it is not clear that this additional range of motion will carry over to dynamic movement.
Also, the amount of increase in static flexibility appears to be largely related to the person's tolerance to the discomfort of a stretching position, not major changes in the material properties of the muscle/tendon. Another caveat to this is that passive stretching (using an external force - often a person) can cause a large amount of tension on the muscle (extension). Vigorous, forceful stretching can weaken and injure muscles by stretching ligaments or creating unsafe loads.
Ruth Solomon, Professor emeritus at the University of California, Santa Cruz, states that if you don't stretch and strengthen together, you'll have a weak muscle. The strength must balance the stretch if you want to control your movements. "If the muscles are really stretched out, the ligaments may not be able to protect the joints," she said. "So you get unstable joints, particularly knees, and you may get hyperextension and ligament tears." Resource
A growing number of studies have documented decreased muscular performance after stretching. Dr. Stuart McGill has stated that "static stretching deadens the muscle from a neural perspective - diminishing the stretch reflex and reducing peak strength and power." Resource
This is certainly not advantageous immediately prior to an activity like running. The cause appears to be a decrease in the speed of nerve impulse causing a reduced ability to activate the muscle. This, in turn, decreases the force of muscular contraction.
Another area of confusion lies in the definition of muscle tone.
Tone is the resting tension of a muscle brought about by the constant flow of nerve stimuli. Muscle length is usually a physical representation of muscle tone. Abnormal tone can create resistance to the ability of the muscle to elongate. Muscles can be hypertonic or tight and hypotonic or weak. Both tight and weak muscles are usually the result of poor postural and movement habits.
Noted therapist Gray Cook states, the individual with a flexibility problem will actually tighten and contract the muscle that they are trying to stretch. The reason the muscle is tight in the first place, is probably because it is being used improperly. This muscle may be activated twice as frequently as it should because of a lack of muscle strength or coordination in another area of the body. This muscle is actually tight because it's protecting itself; it's been overused and it's generally fatigued. Part of its protection involves shortening its length to reduce its workload (contractile length) and guard against unforeseen stretching. Pushing the stretch can actually, in some cases, make the muscle you're stretching contract even harder. Resource
This is due to Sherrington’s Law of reciprocal inhibition, i.e. a tight muscle will inhibit its antagonist (e.g. tight quadriceps and hip flexors will inhibit the hamstrings).
See Part 3 here.