Editing Calorie restriction (section)

===Activity levels===
Calorie restriction preserves muscle tissue in nonhuman primates<ref name="McKiernan2012">{{Cite journal |display-authors=6 |vauthors=McKiernan SH, Colman RJ, Aiken E, Evans TD, Beasley TM, Aiken JM, Weindruch R, Anderson RM |date=March 2012 |title=Cellular adaptation contributes to calorie restriction-induced preservation of skeletal muscle in aged rhesus monkeys |journal=Experimental Gerontology |volume=47 |issue=3 |pages=229–236 |doi=10.1016/j.exger.2011.12.009 |pmc=3321729 |pmid=22226624}}</ref><ref name="ColmanSarco2008">{{Cite journal |vauthors=Colman RJ, Beasley TM, Allison DB, Weindruch R |date=June 2008 |title=Attenuation of sarcopenia by dietary restriction in rhesus monkeys |journal=The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences |volume=63 |issue=6 |pages=556–559 |doi=10.1093/gerona/63.6.556 |pmc=2812805 |pmid=18559628}}</ref> and rodents.<ref name="DirksNaylor">{{Cite journal |vauthors=Dirks Naylor AJ, Leeuwenburgh C |date=January 2008 |title=Sarcopenia: the role of apoptosis and modulation by caloric restriction |journal=Exercise and Sport Sciences Reviews |volume=36 |issue=1 |pages=19–24 |doi=10.1097/jes.0b013e31815ddd9d |pmid=18156949}}</ref> Muscle tissue grows when stimulated, so it has been suggested that the calorie-restricted test animals exercised more than their companions on higher calories, perhaps because animals enter a foraging state during calorie restriction. However, studies show that overall activity levels are no higher in calorie restriction than [[ad libitum]] animals in youth.<ref name="Faulks2006">{{Cite journal |vauthors=Faulks SC, Turner N, Else PL, Hulbert AJ |date=August 2006 |title=Calorie restriction in mice: effects on body composition, daily activity, metabolic rate, mitochondrial reactive oxygen species production, and membrane fatty acid composition |journal=The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences |volume=61 |issue=8 |pages=781–794 |doi=10.1093/gerona/61.8.781 |pmid=16912094 |doi-access=free}}</ref>