Workout woes include damaged toenails, and Shape magazine's May issue talks about prevention and treatment. According to the magazine, "'Tennis toe'—the bruising and thickening of your big toenail—is the result of sports that involve quick stops and turns," and "'jogger's toe,' the loosening (or loss) of a nail, occurs due to repeated slamming."
Dermatologists tell the magazine to treat a bruised tip with a thick balm and to bandage it as well if the nail matrix is bruised. If the nail falls off, apply an antibacterial ointment and keep it covered.
Wearing shoes that fit well will prevent toenail damage.
Wearing flip-flops in gym showers will prevent athlete's foot. Get an over-the-counter cream to treat symptoms if you're infected.