Sometimes the injury is to the leg, hip, or back and it prevents walking for a time.
Sometimes it is to the head, ears, or toes and changes balance and so that has to be relearned or recovered from.
With the elderly you also see a lot of people barely being strong enough to walk getting an ailment that puts them bed ridden for a few weeks or months and that is enough time for their muscles to atrophy enough that they slip below the line of being capable of walking any more.
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