Don't panic. Half a marathon is achievable just from general good fitness. Full marathon is the potential health destroyer.
Half or full, you need to get your body used to running or you'll get an injury. You'll probably get round ok, but you'll suffer after.
@Sharkstar started
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Half or full, you need to get your body used to running or you'll get an injury. You'll probably get round ok, but you'll suffer after.