The Long Game

For­get stretch­ing as you know it. There’s a bet­ter way to lengthen, strengthen, prime and pro­tect your pre­cious run­ning mus­cles.

Runner's World South Africa - - CONTENTS - BY SAM MUR­PHY

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.”

FLEX AP­PEAL

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

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