The goal of stretching is 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).  

We now know that to change the length of a muscle, we must hold a submaximal ‘stretch’ for 3-5 minutes – MINIMUM. This affects the deeper, thicker collagen fibers to make lasting change. This is myofascial stretching.

The criticism of passive stretching (bending forward and touching your toes and rising back up again) has been whether these changes persist or whether they are a temporary benefit that fades away.  

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. We now know this is not rue and is only a small piece of the puzzle.  We want to create optimal length, not maximal length, AND we MUST make sure we have a stable environment to prevent injury within this new available Range.

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 because of eccentric training.  This means that eccentric training creates new muscle units in series, like 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?  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.

References

O’Sullivan K, McAuliffe S & DeBurca N. The effects of eccentric training on lower limb flexibility: a systematic review. British Journal of Sports Medicine 2012; 46: 838-845.

Mahieu NN, McNair P, Cools A, et al. Effect of eccentric training on the plantar flexor muscle-tendon tissue properties. Med Sci Sports Exerc 2008; 40: 117–23.

Nelson RT & Bandy WD. Eccentric training and static stretching improve hamstring flexibility of high school males. J Athl Train

Aquino CF, Fonseca ST, Goncalves GGP et al. Stretching versus strength training in lengthened position in subjects with tight hamstring muscles: A randomized controlled trial. Manual Therapy, 2010, 15, 26-31.

Taylor DC, Dalton JD, Seaber AV, & Garret WE. Viscoelastic properties of muscle-tendon units: the biomechanical effects of stretching. American Journal of Sports Medicine 1990; 18:300-309.