CHANG­ING A REP­U­TA­TION

Runner's World (UK) - - Training -

Only ex­er­cise phys­i­ol­o­gists use the term OBLA. Coaches and run­ners say ‘lac­tate thresh­old pace’, ‘thresh­old pace’ or sim­ply ‘tempo runs’.

Break­ing through the con­fu­sion be­gins with un­der­stand­ing the role of lac­tate in mus­cle me­tab­o­lism. Lac­tate is a chem­i­cal with a bad rep­u­ta­tion, as­so­ci­ated with run­ning too long at anaer­o­bic paces. It has been blamed for ev­ery­thing from sore mus­cles to the dead-legs feel­ing you get at the end of fast-paced in­ter­vals. But none of this is true. Lac­tate is sim­ply a by-prod­uct of glu­cose me­tab­o­lism and is pro­duced any time you move a mus­cle. At low ex­er­cise lev­els, you use lac­tate nearly as quickly as it’s formed, and the amount that leaks from the mus­cles into the blood is mi­nus­cule. At higher lev­els – eg mod­er­ate-paced run­ning – you pro­duce it more quickly but also use it more quickly. More gets into the blood, but not much.

Around marathon pace, things change. By this point, the lac­tate level in the blood has edged up to about two mil­limoles per litre (mmol). That’s still low, but if you con­tinue to speed up, it rises more rapidly. By the time you’ve reached Daniels’ one-hour race pace, it’s dou­bled to four mmol, the clas­sic thresh­old level. Above that, it sky­rock­ets.

Mount­ing lac­tate lev­els sound like a bad thing, but research says they aren’t. Ge­orge Brooks, an ex­er­cise phys­i­ol­o­gist at the Univer­sity of Cal­i­for­nia, US, dis­cov­ered what is now known as the ‘lac­tate shut­tle’. He found that when lac­tate climbs, the body uses the blood to

ship some of it away from the hard-work­ing mus­cles where it is pro­duced to places where it can be used more ef­fec­tively. One of these is the heart, an­other is the brain. But it also goes to the liver, which can use other en­ergy sources such as fat to turn it back into glu­cose. Even some less-in­volved mus­cles, such as the arms, pull lac­tate out of the blood for fuel, in lieu of glu­cose.

This shut­tling makes it pos­si­ble for you to run faster, be­cause glu­cose is the body’s high-oc­tane fuel. We can gen­er­ate en­ergy much more rapidly with glu­cose than through lac­tate. So rather than be­ing a sign that our leg mus­cles are drown­ing in per­for­mance-im­ped­ing lac­tate, the rise of lac­tate means the body is mov­ing it to places where the power de­mands are lower, keep­ing the glu­cose for the run­ning mus­cles. ‘The or­gans that most need it get pri­or­ity and oth­ers rely on lac­tate,’ says Hal­li­will.

That said, ris­ing lac­tate and in­creas­ing fatigue go hand in hand, which means that even if lac­tate is no longer the evil we once thought it was, find­ing ways to train the body to use it more ef­fec­tively – in essence, post­pon­ing the point at which blood lac­tate starts to rise – will also post­pone the point of fatigue, with the hope of run­ning fur­ther, faster. This, in fact, is what thresh­old train­ing, in all of its con­fus­ing forms, is de­signed to do.

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