Two groups have genetically engineered different pathways that transform regular mice into the equivalent of Olympic-calibre endurance athletes.

The first group of researchers, from Howard Hughes Medical Institute in Chevy Chase, Maryland, enhanced the function of a single protein to make mice run twice as far as normal.

The protein, peroxisome proliferator-activated receptor (PPAR)-delta, is a master regulator of various genes. The researchers believed that increasing the activation of PPAR-delta would increase fat-burning, but they didn’t expect what happened to athletic ability.

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