DO THEY WORK? ARE THEY FOR YOU?

CAR­BO­HY­DRATE-FASTED WORK­OUTS

Triathlon Magazine Canada - - FEATURES - BY MATT FITZGER­ALD

IN AN­CIENT GREECE, Olympic run­ners some­times trained while car­ry­ing three­p­ound weights in their hands. The idea was to make run­ning a lit­tle harder dur­ing work­outs so that it felt eas­ier in races.

This sim­ple prin­ci­ple is still alive to­day. Some elite marathon­ers oc­ca­sion­ally do long runs while wear­ing weight vests. And toplevel ath­letes in a va­ri­ety of en­durance sports, rang­ing from cross-coun­try ski­ing to triathlon, do train­ing stints at high al­ti­tude for a sim­i­lar rea­son. Whereas car­ry­ing ex­tra weight chal­lenges and strength­ens the mus­cu­lar sys­tem, ex­er­cis­ing in oxy­gen-poor moun­tain air is harder on the car­dio­vas­cu­lar sys­tem, pro­vok­ing adap­ta­tions that make sea-level rac­ing eas­ier.

The lat­est way to make train­ing harder for the sake of mak­ing rac­ing eas­ier is carb-fasted work­outs. Since the 1960s, en­durance ath­letes have con­sumed carbs be­fore and dur­ing longer work­outs in or­der to gain a source of ex­tra en­ergy that en­hances per­for­mance. But a grow­ing num­ber of ath­letes are go­ing carbfree be­fore and dur­ing se­lect work­outs for an ex­tra chal­lenge that, they hope, will pay div­i­dends on race day. Do carb-fasted work­outs re­ally work? If so, how? the wall in a work­out or race, it was prob­a­bly be­cause the glyco­gen stores in your work­ing mus­cles fell too low.

But some­thing else hap­pens when your glyco­gen stores be­come de­pleted: Your mus­cles re­spond by mak­ing new mi­to­chon­dria, lit­tle “aer­o­bic fac­to­ries” that use oxy­gen to re­lease en­ergy from meta­bolic fu­els. And th­ese new mi­to­chon­dria en­able you to swim, bike and run faster and far­ther be­fore hit­ting the wall. So while con­sum­ing carbs be­fore and dur­ing ex­er­cise en­hances per­for­mance within work­outs, it in­hibits some of the fit­ness­boost­ing phys­i­o­log­i­cal adap­ta­tions that re­sult from train­ing.

This was shown in a 2013 study by sci­en­tists at the Swedish School of Sport and Health Sci­ences. Ten well-trained cy­clists com­pleted a 60-minute work­out. Be­fore the work­out, half of the cy­clists were fed low-carb meals and the other half ate nor­mally. Mea­sure­ments taken af­ter the work­out re­vealed that the gene gov­ern­ing mi­to­chon­drial bio­gen­e­sis had been up­reg­u­lated, whereas in the oth­ers it had not been.

In the­ory, then, do­ing carb-fasted work­outs with some reg­u­lar­ity should im­prove fit­ness and per­for­mance rel­a­tive to do­ing ev­ery work­out in a high-glyco­gen state. And a re­cent study by Martin Gibala and col­leagues at Mcmaster Univer­sity showed that in­deed it does. Eigh­teen healthy nonath­letes com­pleted a train­ing pro­gram con­sist­ing of two high-in­ten­sity in­ter­val work­outs per day, six days per week, for six weeks. Half of the sub­jects were fed plenty of carbs be­tween the two daily work­outs while carbs were with­held dur­ing this in­ter­val from the oth­ers. Over the six-week train­ing pe­riod, this se­cond group of sub­jects im­proved their per­for­mance in a fit­ness test by twice as much as the other sub­jects.

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