A blond woman in a hot pink spandex tank hoists a sledgehammer over her shoulders, then slams it down with a dull thud onto the big tire in front of her. Beside her, another woman swings her sledgehammer even higher, grimacing and groaning with the effort. Their faces are bright red and dripping with sweat. It’s 9:45 a.m. and 85 degrees, and the sun is glinting off the asphalt of the strip-mall parking lot where the women are laboring."Swing it higher, above your shoulder!” a woman bellows at them, even as they gasp each time they raise their hammers, each time they let them fall.

As one woman pauses to wipe the sweat from her eyes, she spots me studying her. I’ve been trying not to stare, but it’s a strange spectacle, this John Henry workout of theirs, hammering away in front of a women’s fitness center, just a few doors down from a smoke shop and a hair salon. It looks exhausting, and more than a little dangerous. (What if a sledgehammer slips and flies from one woman’s hands, braining her companion?) It also looks fruitless. Why not join a roofing crew for a few hours instead? Surely, there’s a tunnel somewhere that needs digging, or at least some hot tar that needs pouring.

But paying to simulate backbreaking labor under the watchful eye of a demanding authority figure seems to be a common desire these days. When I type “sledgehammer” into Google later that day, the first suggestion is “sledgehammer workout,” a search term that pours forth half a dozen enthusiastic re-enactments of life on a steel-driving chain gang.

Fitness culture couldn’t have changed more significantly since the late ’60s. Back then, residents of my small Southern hometown would spot my father, an early jogger, and yell out of their car windows, “Keep running, hippie!” These days there aren’t that many joggers in my Los Angeles neighborhood, but every other block there’s another fitness center offering boot-camp classes or Brazilian jiujitsu, with people inside punching, kicking and yelling at one another like drill sergeants. Jim Fixx’s freewheeling running disciples have been replaced by packs of would-be Navy SEALs, sprinting up sandy hillsides with backpacks full of rocks strapped to their shoulders.