What it is: The sciatica nerve is the largest nerve in your body, running from under your uterus to your legs. When your growing baby presses on the nerve, some mommies-to-be experience a shooting pain in their lower back that radiates toward the back of their knee.
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How it affects exercise: If certain types of exercise make the problem worse, such as lifting weights or those moves where you're on your feet, find workouts that don't result in pain such as swimming, biking, or yoga. To get immediate relief, lie on your side opposite the pain to relieve pressure on the sciatica nerve, or if that doesn't work, try propping your feet up.