GETTING serious about a sport can mean doing the previously unthinkable. Swimmers shave their bodies sleek. Cyclists take blood-boosters. And ultramarathoners have their battered toenails surgically removed — for good.

Toenail removal is not for the faint of heart, but it can be a big relief to people who compete in 50- or 100-mile races. Even the most hardened ultramarathoners, for whom 26.2 miles is a warm-up, can be distressed by bleeding under a nail or a loose nail that bangs repeatedly against the front of a shoe.

“From my experience, it’s the hard-cores” who choose to go without toenails, said Dr. Paul R. Langer, a Minneapolis podiatrist who has been on the medical team for a 250-kilometer 7-day race through the Gobi Desert. “Even within the ultra community, less than 10 percent or maybe even 5 percent are permanently removing their toenails.”

The average marathoner suffers from plenty of black-and-blue nails, but doesn’t sign up to have acid poured onto a nail bed for permanent removal.

Ultramarathoners, who number more than 17,000 nationwide, according to UltraRunning magazine — “appear crazy sometimes, but they are great strategists,” said Dr. Robert M. Conenello, a sports podiatrist who tended to contestants of a multiday race in the Sahara. “A lot of them look at their toenails as useless appendages, remnants of claws from evolutionary times long ago. I’ve heard them say, ‘Toenails are dead weight.’ ”

The most utilitarian of ultramarathoners remove the offending toenails and keep problem-free ones. Then they sport a checkerboard look in sandals.