Body builders’ mus­cles show sur­pris­ing ben­e­fits

The Weekend Australian - Travel - - Health - John von Rad­owitz

PUMP­ING iron could play a pre­vi­ously un­recog­nised role in pre­vent­ing obe­sity and di­a­betes, new re­search sug­gests. Sci­en­tists made the sur­prise dis­cov­ery that body builders’ ‘‘ type II’’ mus­cle helps to re­pro­gram the whole body’s me­tab­o­lism.

The find­ings sug­gest that re­sis­tance train­ing gym ses­sions may be part of the an­swer to keep­ing peo­ple trim and healthy.

It had been widely as­sumed that only aer­o­bic en­durance ex­er­cise, such as run­ning or swim­ming, had any sig­nif­i­cant in­flu­ence on the body’s en­ergy bal­ance.

This kind of ex­er­cise pro­duces ‘‘ type I’’ mus­cle con­tain­ing ‘‘ slow’’ fi­bres full of mi­to­chon­dria, the tiny pow­er­houses in cells that burn fuel to gen­er­ate en­ergy.

Type I mus­cle en­ables marathon run­ners to keep go­ing with­out get­ting tired.

In con­trast, type II mus­cle pro­duces the abil­ity to lift heavy loads or show a sprinter’s short burst of speed, but lit­tle stay­ing power.

Sci­en­tists in the US cre­ated a mouse dubbed ‘‘ My­oMouse’’ that could be made to bulk up with type II mus­cle sim­ply by switch­ing on a growth-reg­u­lat­ing gene called Akt1.

When the switch was turned off, and the mice were fed an eight-week sug­ary diet with a caloric com­po­si­tion sim­i­lar to hu­man ‘‘ fast food’’, they grew obese.

The an­i­mals also be­came in­sulin re­sis­tant, an early sign of di­a­betes, and de­vel­oped fatty de­posits in their liv­ers — a con­di­tion seen in hu­mans and known as fatty liver dis­ease.

Ac­ti­vat­ing the Akt1 gene im­me­di­ately led to the growth of type II mus­cle fi­bres.

But in­stead of pro­duc­ing strong and fat ‘‘ sumo’’ mice, as many of the re­searchers had ex­pected, the switch re­sulted in an­i­mals that lost weight.

Blood tests showed that the mice also be­came metabol­i­cally nor­mal, and they were cured of fatty liver dis­ease.

The ben­e­fi­cial changes oc­curred even when the mice con­tin­ued to eat a high calo­rie diet with­out tak­ing ex­tra ex­er­cise.

‘‘ This work shows that type II mus­cle doesn’t just al­low you to pick up heavy ob­jects, it is also im­por­tant in con­trol­ling whole body me­tab­o­lism,’’ says study leader Pro­fes­sor Ken­neth Walsh, from Bos­ton Univer­sity School of Medicine in Mas­sachusetts.

Fur­ther anal­y­sis re­vealed that the phys­i­ol­ogy and gene ac­tiv­ity of fat and liver cells in the mice had been altered.

The re­searchers sus­pect that sig­nalling mol­e­cules se­creted by mus­cles may be in­volved.

They are cur­rently in the process of iden­ti­fy­ing novel pro­teins in mus­cle that com­mu­ni­cate with other tis­sues.

The pro­teins, re­ferred to as ‘‘ myokines’’ from the Greek words ‘‘ mus­cle’’ and ‘‘ mo­tion’’, may pro­vide new tar­gets for obe­sity and mus­cle wast­ing drug treat­ments.

Re­port­ing their find­ings in the jour­nal Cell Me­tab­o­lism, the re­searchers con­cluded: ‘‘ Th­ese data... sug­gest that strength train­ing, in ad­di­tion to the widely pre­scribed ther­apy of en­durance train­ing, may be of par­tic­u­lar ben­e­fit to over­weight in­di­vid­u­als.’’

The re­sults may also pro­vide new in­sight into cer­tain as­pects of age­ing.

‘‘ Be­yond the age of 30, hu­mans lose ap­prox­i­mately six pounds (2.7 kg) mus­cle mass per decade,’’ says Pro­fes­sor Walsh.

‘‘ Sur­pris­ingly, age­ing in­di­vid­u­als pre­dom­i­nantly lose type II mus­cle. Thus a 50-year-old may be rel­a­tively good at play­ing ten­nis or jog­ging be­cause type I mus­cle is pre­served, but a mea­sure­ment of grip strength or core body strength could show ap­pre­cia­ble de­clines.’’ PA

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