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(1) George Doyle / Stockbyte / Getty Images
(2-13) Brayden Knell / WebMD
(14)  Stockbyte / Getty Images 
(15) Brayden Knell / WebMD
(16) amana productions inc. / Getty Images

REFERENCES:

Jonathan Ross, personal trainer; owner, Aion Fitness, Bowie, Md.
Petra Kolber, spokeswoman, the IDEA Health and Fitness Association; contributing editor, Health magazine.
American College of Sports Medicine: “Physical Acitvity and Public Health Guidelines.”
Kathleen M. Zelman, MPH, RD, LD Director of Nutrition, WebMD.

Source