Story By: Jesse Moreton
This month’s installment comes from the remarks of Doug Richards, a U of T professor whose lecture was recently aired on TVO’s “Big Idea” program. I must also give credit to the studious patient who shared the link with me, although I will not name him for confidentiality.
So stretching. What is truth, what is fiction? For starters, let’s review the rules of the game. Richards explained that when any material (or tissue) is stretched, there is elastic deformation and plastic deformation. Elastic deformation occurs when a tissue is stretched and returns to its original shape or length. Once a yield point is reached, a tissue changes shape, occurs damage or breaks. This is plastic deformation. Ligaments, tendons and collagen with stretch 3-5% before they reach this yield point. At 7-10% stretch, they will break completely. Muscles have approximately twice the range before they reach their yield point and break. In other words, muscles will stretch better than ligaments and tendons.
Secondly, tissues in the body are semi-fluid. Semi-fluid materials do not change shape instantly like an elastic band. This quality is referred to as viscoelasticity. The water content slows the rate at which stretching occurs. Think of a hanging deer carcass that elongates over time. The physiological term for this is creep. As muscles are stretched for a long time they slowly get longer.
Richards paraphrased a study conducted by Stuart McGill, a biomechanics professor from U of W. (As a side-note, I worked in the same lab during my undergraduate education at Waterloo.) McGill found that slouching increased the range low back flexibility as the tissues slowly became longer. Maximum flexibility could be obtained after 45-60 minutes of slouching. However, after about 45-60 minutes of standing, the gains in range of motion were lost. The tissues slowly crept longer with slouching and crept shorter with standing. There was no overall gain in flexibility. According to Richards, McGill was hired as a consultant when Pearson International Airport was building a new terminal. The airport was having problems with passengers injuring their backs after getting off flights and picking up their luggage. McGill suggested having passengers walk for at least 5-10 minutes before picking up their luggage. This way their tissues would creep back (and away from the yield point) before bending over to pick up a heavy suitcase. If you’ve ever wondered why you have to walk to the opposite end of a terminal, now you know. It reduces your chance of plastically deforming (breaking or injuring) your tissues! It’s also good for you, unless you’re in a rush.
Another important consideration is to know what is being stretched. When we stretch, we’re not actually stretching joints. We’re stretching the structures that hold the joint together; ligaments, capsules and tendons. Muscles have multiple attachment points and overlap. Often we think we’re stretching a certain muscle but we’re actually stretching something else. Looser or longer tendons will be stretched before shorter or stiffer tendons. For example, to stretch the hamstrings athletes will sit with the legs extended in front. However, many athletes will simultaneously point the toes up and lean forward at the waist. This position will stretch the gastrocs (calf muscle), sciatic nerve and low back, but not the hamstrings!
I hope I’ve whet your appetite for more. Next month I’ll continue with Richard’s lecture, sprinkle in my own two cents and try to find some practical application.