The Long Game
Forget stretching as you know it. There’s a better way to lengthen, strengthen, prime and protect your precious running muscles.
When you skip your 10 minutes of post-run stretching, you probably feel a twinge of guilt. If so, we have good news: a growing body of research suggests there’s actually a better way to improve and maintain flexibility, with huge benefits to your running.
The secret lies in eccentric training. That’s ‘eee-centric’, not ‘ex-centric’, and refers to the use of a specific type of muscular contraction.
“Recent evidence suggests that eccentric contractions can improve flexibility and range of motion, and may also confer benefits not observed with other types of stretching,” says Jamie Douglas, a strength and conditioning coach for High Performance Sport New Zealand, who’s working on a PhD in eccentric training and elite performance.
Recent research from San Jorge University, Spain, found twice-weekly eccentric training improved adaptation to load in runners’ Achilles tendons and calves, while a study published in The Journal of Strength and Conditioning Research found eccentric hamstring training increased flexibility, strength and the hamstring-to-quadriceps ratio – reducing subjects’ incidence of injury.
“An eccentric contraction, or active stretch, involves lengthening active muscle tissue against an external force,” says Douglas. It’s the opposite of a concentric contraction, when the muscle fibres are shortening. Picture someone doing a dumbbell curl: as the elbow bends, the biceps bulge as the contractile units (called sarcomeres) in the muscle fibres draw together – that’s concentric. As the arm straightens to lower the weight, the bulge disappears as the sarcomeres move further apart – that’s an eccentric contraction.
“Eccentric training combines strengthening and stretching,” says Dr Kieran O’Sullivan, a specialist musculoskeletal physiotherapist and author of a review on the effects of eccentric training on flexibility, published in the British Journal of Sports Medicine (BJSM).
One of the benefits O’Sullivan’s research highlights is a lengthening of muscle tissue. But traditional stretching lengthens muscles too, right? “While static stretching can change muscle length, the time it takes to achieve this is normally only possible in animal studies,” says O’Sullivan. “Stretching for several hours a day for several months – not what we humans typically do!”
So how come we feel more flexible after a good stretch? It’s partly due to a temporary reduction in the stretched muscle’s passive tension –
(its ‘resistance’ to stretching while in a resting state). But this perceived shift in flexibility is fleeting, and according to research, lost within an hour or so.
Then there’s what the scientists call ‘stretch tolerance’. “Static stretching improves what we call flexibility mostly by improving our tolerance for the feeling of being stretched,” says O’Sullivan. “In other words, passive stretching does not make our muscles longer, it makes us handle them being lengthened better.”
This lack of physical changes within muscle and connective tissue as a result of regular static stretching could explain the dearth of studies demonstrating an injuryrisk reduction or a performance boost as a result of stretching programmes. In fact, some studies showed that static stretching could have a temporary negative effect on performance, by reducing subsequent power output. Indeed, one 2016 review of studies found evidence of a 3.7 per cent reduction in physical performance following static stretching.
So what is eccentric training doing that static stretching isn’t?
BENDS WITH BENEFITS
“During an eccentric contraction, both muscle and tendon undergo large amounts of mechanical stress and damage,” says Douglas. “This triggers a series of chemical reactions that result in tissue remodelling. We see an increase in fascicle length [a fascicle is a bundle of muscle fibres], and thereby, muscle length.”
In contrast, static stretching doesn’t seem to notably alter the properties of the muscles. “Research has indicated static stretching doesn’t provide an adequate cell-signalling response to promote adaptations within the musculature,” says Tony Blazevich, a professor of biomechanics at Edith Cowan University in Australia and a leading researcher in the field. So static stretching doesn’t change the structure of the muscle.
One theory on how eccentric training increases fascicle length partly credits the addition of new sarcomeres, those contractile units within muscle fibres. These new sarcomeres make the muscle more pliable and increase its range.
There’s another benefit: eccentric contractions have been found to affect not just muscle length but also the lengthtension ‘curve’ (the relationship between how much force a muscle can exert and its length at the time it exerts that force). This shift has been flagged as important for injury prevention.
Paradoxically, while the passive stiffness of muscle decreases (in other words, the muscle becomes more pliable), tendon stiffness may actually increase as a result of eccentric training. If you were using passive range of motion (testing how far you can move a joint through its range without applying any force) as your measure of improvement, that might seem like a blow, since it would appear to have a negative effect on that
“STATIC STRETCHING DOES NOT SEEM TO NOTABLY ALTER THE PROPERTIES OF THE MUSCLES.”
range. But, says Douglas, this greater tendon stiffness has been shown to promote an increase in running economy via enhanced elastic energy return, which reduces muscle energy cost. It’s like catapulting something from a ‘tight’ elastic band, rather than from a ‘flabby’ one – the greater stiffness in the former results in significantly greater propulsion.
Blazevich does point out that eccentric contractions aren’t the only way to increase tendon stiffness. “The tendon doesn’t know what the muscle is doing, it only registers the force it’s experiencing – or possibly a change in its own length – and one of these two signals (force or stretch) triggers an increase in stiffness,” he says. “But because we can often produce more force eccentrically than when we contract a muscle isometrically or concentrically, the tendon ‘sees’ a greater force and is therefore stretched more. So eccentric training is particularly useful if you’re using it to produce more force than you could with other types of contraction.”
In his BJSM review, O’Sullivan found that eccentric training improved flexibility in the calves, quads and hamstrings (key running muscles) when it was assessed either by range of motion (how far can this muscle go?) or muscle fascicle length (how long is this muscle?).
A more recent study, published in Medicine & Science in Sports and Exercise, found a 2.5-fold increase in ankle dorsiflexion range from twice-weekly sessions of five to 12 maximal eccentric calf exercises, compared with passive stretching. “Improvements in strength and range of motion – along with a reduction in muscle stiffness and increased tendon stiffness – were also seen to a greater extent than has been found with static stretching in previous studies,” says Douglas.
Recent research has begun to identify other distinct and significant characteristics of these eccentric contractions – they can produce much higher forces than their concentric counterparts, and with low energy cost. This makes eccentric training an attractive option for athletic training and rehab; but increasingly, it’s also being used to improve mobility and strength in inactive populations, such as the elderly, and even astronauts. If we go back to the difference between a concentric contraction and an eccentric one, this makes sense – an