“Marathon Mice” Spotlight a Rare Type of Muscle

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Here’s an interesting read by JR Minkel of Scientific American:

Researchers have prompted mice to grow whole muscles from a normally rare type of muscle fiber, yielding rodents capable of running harder and for longer stretches of time than their unaltered compeers. Such animals may help to determine the role of this poorly understood type of fiber and to identify drugs capable of counteracting muscle-wasting diseases such as muscular dystrophy in people.

Muscle fibers come in two general flavors–“slow-twitch” and “fast-twitch.” Slow-twitch fibers are redder (think beef or dark-meat chicken) and have more endurance than fast-twitch fibers (think pork or white meat), which contract faster but use energy less efficiently.

The muscles of the newly created mice are composed of an intermediatetype of fiber that is usually present in muscles only in small amounts.The researchers inserted a hyperactive form of a mouse gene called PGC-1Binto growing embryos and found that this uncommon fiber, called IIX,became abundant in the resulting mice, at the expense of fast-twitchfibers.

These IIX-rich animals had noticeably redder, slower-twitchmuscles and, as a result, were quite the little athletes, the groupreports in this month’s issue of the journal Cell Metabolism.They were able to run an average of 33 minutes before pooping out,compared with 26 minutes for their counterparts. “They did a lot betterthan their wild-type brethren,” says cardiologist Zoltan Arany ofHarvard Medical School, the study’s lead author. “It was veryimpressive.”

Researchers believe that PGC-1Bproduces a protein that helps activate other proteins, which, in turn,stimulate the genes that make IIX fibers. Members of the same group ina 2002 study discovered that a related gene, PGC-1A, turns fast-twitch fibers (called IIB) into the slow-twitch varieties (I and IIA).

Aranysays the findings could help shed light on the role of this type ofmuscle, which, until now, had been hard to pin down, because animalsnormally have relatively few IIX fibers. “These mice will be awonderful tool to study what IIX fibers are all about,” he says.Earlier research indicated, for example, that muscles spend time as IIXfibers when they transform from the fast-twitch IIB to slow-twitch IIA.

Manipulating the type of fibers present in human muscle couldalso help treat muscle-wasting diseases such as muscular dystrophy,Arany says, because experiments have shown that slow-twitch fibers maybe more resistant to wasting.

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Mike Young

Mike Young

Founder of ELITETRACK at Athletic Lab
Mike has a BS in Exercise Physiology from Ohio University, an MSS in Coaching Science from Ohio University & a PhD in Biomechanics from LSU. Additionally, he has been recognized as a Certified Strength & Conditioning Specialist (CSCS) from the National Strength & Conditioning Association, a Level 3 coach by USA Track & Field, a Level 2 coach by USA Weightlifting.
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