When we stretch, we aim to lengthen a muscle. According to the literature, this result is likely due to an improved tolerance to stretch (a neurological change) as well as a mechanical change in the tissue (the viscoelastic properties of the tissue). The criticism of stretching has been whether or not these changes persist or whether they are a temporary benefit that fades away. So is there something that can last longer, by changing the structure of the muscle?
Eccentric contraction is a muscular contraction in which the muscle lengthens while under load. Many people commonly call them “negatives” where the focus is not on the shortening of the muscle during exercise but rather the lengthening. An example would be a bicep curl when the weight is being lowered slowly and the bicep is getting longer while under load. For quite some time, eccentric exercises have been hailed as a great way to rehabilitate tendon injuries (although this is debatable). Eccentric exercise has also been found to help prevent muscular injuries by improving the tissue’s ability to contract while lengthening. The hamstring is a very good example of this. The muscle is thought to be strained during the lengthening phase of sprinting as the hamstring decelerates hip flexion and knee extension and the heel touches the ground. Strengthening the hamstring eccentrically can help to reduce the risk of injury as we have outlined in many previous blogs about the Nordic Hamstring exercise.
Historically, the common belief is that stretching is the only way to increase flexibility. Perhaps a newer concept is that eccentric exercise can improve flexibility. Athletes with “tight” hamstrings have a different ability to activate the muscle when it is lengthened. That is, when they are running they have a more difficult time generating tension in the muscle as it gets longer. Some newer literature has taught us about sarcomerogenesis as a result of eccentric training. This means that eccentric training creates new muscle units in series, similar to a train linking up and getting longer. What this does for the athlete is it allows them to be able to generate force in the muscle as it lengthens. When the joint is at a greater angle, they can generate more force. The authors of this research also found that eccentric training increases muscle length. So logically, many rehabilitation professionals are adopting this strategy as opposed to stretching. The reason for this is that stretching will just increase your range of motion and lengthen the muscle. Eccentric training will not just increase your range of motion and lengthen the muscle, but it will also strengthen the tissue so it can create more force at a greater angle. This doesn’t just benefit performance but also reduces injury. A systematic review published in 2012 found that among six research articles, they all showed support that eccentric loading increases range of motion or increased the fascicle length (or both). It did not matter what joint or what muscle group was studied, the findings were the same. The studies that were included found these benefits in the ankle, the hamstring and the quadriceps.
Does this mean we shouldn’t stretch? Not in my opinion. Yes, eccentric training may offer more benefits than static stretching, but that’s according to the current research that exists. What if this changes? Perhaps a prudent approach would be to do a little of both. Some eccentric training and some static stretching over time may assist in lengthening the muscle, increasing joint range of movement as well as being able to generate torque at longer muscle lengths. To me, that would be a very evidence-informed strategy; a combination of scientific evidence, my clinical experience (as I have seen benefits with both), and then considering what a patient feels is right for them.
By: Dr. Kevin McIntyre B.Kin, DC
Clinic Director – Burlington Sports Therapy
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