Simple exercises with no-tech equipment (call them paleo or playground exercises, depending on how much fun they are) have long found disciples at niche gyms and in movements such as CrossFit. But in the last year and a half, major health-club chains have begun making hefting sandbags and shaking 25-pound ropes the standard, ditching the fancy weight machines that have dominated gym floors for more than 30 years.

“I wouldn’t say obsolete, but there is a huge downtick in traditional strength-training equipment,” said David Harris, the national director of personal training for the Equinox chain. The company, based in New York, has thinned its ranks of chest press, leg press and leg extension machines to clear floor space so members can move freely. (Treadmills and other cardio machines aren’t going anywhere.)

Or as Monkey Bar Gym, which has its headquarters in Madison, Wis., states on a T-shirt: “Rage Against the Machines.”

In the race to make space for so-called functional fitness training — which encourages people to push, pull, squat and generally move their bodies as they might naturally — the first machines out the door are usually the ones that lock the body in place, working a single muscle.