|MadSci Network: General Biology|
Any part of your body that is being exercised vigorously will expand. Have you ever ridden your bike in jeans over hilly terrain and found that when you got off your legs felt kind of strange and your jeans seemed tighter? It's the same premise: as you work your muscles, they use more oxygen - to get more oxygen your heart pumps your blood faster and your muscles become engorged. Once you cool down your blood gets redistributed to it's normal resting proportions. While running, the muscles in your feet are constantly at work absorbing shocks and maintaining balance thus becoming flushed with oxygenated blood and expanding
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