Stretching Before Exercising Weakens Muscles

That may be adequate for running, but it won't do for regimens with extreme range of motion, such as martial arts. We stretch for half an hour prior to a workout punctuated with short one-minute warm-ups every five minutes or so, and it definitely reduces injuries (which, as the GP has it, is the intent... not for "strength"... in fact, I've never heard — anywhere — that the act of stretching increases strength for the immediately succeeding session of exercise. I've been teaching martial arts for over twenty years.)

I can also tell you that if your body isn't prepared to reach an extended position, and it has to go there, either because you forced it to or someone else did, you had better have stretched first and be warmed up.

As for this line in TFS: "The old presumption that holding a stretch for 20 to 30 seconds -- known as static stretching -- primes muscles for a workout is dead wrong. It actually weakens them", the science of this has been known for many years. What happens is that the working elements of the muscle fibers are laid against each other in pairs with an intervening layer between; the more overlap, the more power can be generated because the overlapping surface area of the layer between is where the work gets done. When fibers are stretched, there is less overlap, hence the muscle can generate less power, but the muscle is longer.

Think of your forearm extended, and look at your bicep... see how it is long? Lots of fiber layers have slid against each other and now have considerably less overlap. Now move your arm to the 90 degree position at the elbow, and look at your bicep; it's bunched up, even if it isn't tense: many fiber layers are now slid to an overlapping position.

The number of fibers involved is the factor that determines the total amount of strength in your motion; high recruitment of fibers results in a strong motion, low recruitment results in a weak motion. We train to develop the ability to generate high recruitment on demand. But no matter the recruitment, if you start from a highly non-overlapped position, eg a stretched one, you'll generate less power with the stretched muscle.

This is the basis for moves like arm locks; if the arm is extended, not only is the leverage at the joint reduced, making it more difficult to close the arm against the lock, but the muscle is extended by the lock so that fiber overlap is minimal, which reduces the amount of force that can be generated by the muscle — it is literally a "double-whammy", and accounts for why a fully executed lock is so hard to exit using direct force (correct exits involve rotation of the arm or the lock itself in order to effect closure of the joint, and a good lock prevents such rotation.)

For any motion, you typically will have two muscle groups involved; the agonist, which is the muscle doing the work, and an antagonist, which is the muscle that would be responsible to reverse the motion. In the case of bending at the elbow, to close the arm, the bicep is the agonist and the triceps is the antagonist. If you are trying to open your arm, that is, extend your forearm, then the roles are reversed: The triceps is the agonist and the bicep is the antagonist. One of the key elements of controlling the force your body can generate is learning to really relax the antagonist, and again, stretching helps by teaching you what a really relaxed and extended muscle feels like; it is difficult to minimize fiber recruitment if you don't know what it feels like and the muscle isn't accustomed to that condition.

Anyway, my recommendation is that athletes ignore this report entirely; stretching significantly increases your range of motion, particularly in your ankles, legs, groin, waist, wrists, fingers, back, neck and shoulders, and to the degree that your sport requires (or risks) large range of motion and easy movement, you should include gentle and comprehensive stretching regularly interspersed by minor warming of the muscles as part of your regimen any time you start cold, or become cold (where "cold" means not warmed up in the muscular sense.) This will help reduce injuries, increase general flexibility, and it helps relax the antagonist muscles to reduce wasted energy. To the extent that it reduces power, the trade off is well worth it, in my estimation. Injuries, in a word, suck.

Stretching Before Exercising Weakens Muscles