I Have A Nine Year Old Describing Muscle "wiggling" (tremulous

i have a nine year old describing muscle "wiggling" (tremulous weakness) and pain in the hamstrings for two days. no known particular strain, but she was playing and riding bikes and kneeling playing games the day before she reported it. walking and running fine, though she says it bugs her. sounds like a muscle strain to me, but i was wondering what, if anything, i should be watching for/alarmed about.