Stretching Part 1: Are you really lengthening muscle?
By Henry Candelaria, BPHE, DC
Oakville Hospital - Work-Fit Total Therapy Centre
For years, stretching has been promoted as an integral part of any exercise program because of a reported decrease in risk of injury by improving range of motion (ROM), reduction in pain, reducing stiffness, and increasing overall athletic performance. Many different stretching techniques exist and therefore many different recommendations also exist, some based on scientific literature and others based on traditional strength and conditioning practices. However, new research has challenged these long-held concepts about common stretching programs and it is the hope of these series of articles to clarify some of those concepts and clear up the misconceptions through highlighting some of the new recommendations.
In this first segment, we will reveal what is actually happening during a stretch and how stretching appears to be increasing extensibility of muscle. In the second segment, we will talk about the role that stretching has to play, if any, in reducing the risk of injury and improving athletic performance. In the final segment of this three part series, we will summarize the current literature on the best stretching techniques to use, when to use them, and how frequent stretching is to be performed.
Let’s begin by talking about what happens during a stretch. There is a vast amount of evidence to support that stretching will improve ROM of a joint by allowing the muscles that cross that joint to be more extensible. If you think of a thick elastic band that undergoes repetitive stretching or a prolonged stretch, the elastic band will become less resistant to stretch over time due to the heating effect that occurs to the band with repetitive motion. The theory behind stretching is similar, except instead of elastic bands, we are dealing with living muscle tissue. There is a special property of living tissue that is referred to as viscoelasticity. What this means is that upon holding living tissue under tension for a prolonged period of time, the force required to hold that tissue at that length is reduced over time. This implies that a tissue can therefore withstand more tensile force at a specific length without undergoing damaging changes to the structure of that tissue. So, what this means is that a muscle tissue that is stretched is theoretically able to produce more force at a specific length without causing injury. This has obvious implications for performance. If an athlete is able to produce more force at a greater ROM without undergoing injury, then theoretically they are likely to have greater success than their counterpart who is limited in force production at extremes of ROM. This will be discussed further in the follow-up installments in this three part series.
However, this is not the whole picture. Recent evidence has suggested a neural based reason for the apparent increase in ROM that is seen with stretching. How does the nervous system influence ROM and what is the difference between objective and apparent increases in ROM? Well, all of us have experienced that uncomfortable sensation that is associated with stretching which feels like a numbing pull on muscles. It is not really painful but it is not comfortable either. That sensation is the key to improving apparent ROM. Before we continue, let me define what I mean by apparent and objective ROM. Apparent ROM implies that the joint appears to be traveling through a greater ROM because of nervous system factors, when in fact there is no change in length of the muscle if measured histologically. Objective ROM is when there are histological increases in ROM meaning that the muscle tissue itself has actually become longer. The majority of ROM increase that is experienced during stretching is achieved through apparent increases in ROM. That is that the increase in ROM that is seen with stretching is a function of an analgesic effect that occurs during the stretch. In other words, it hurts less to stretch!! We actually become numb, in a sense, to that uncomfortable sensation associated with stretching, and therefore over time and with repetition, we can take our joints to extremes of ROM.