Unless you have unlimited time and an unnatural enthusiasm for exercise, chances are you want to work out as little as possible to reap all the benefits. To get a sense of how much time and effort you have to put in to get the job done, a team of researchers put 34 fit dudes on one of three fitness routines for a study that was recently published in Medicine & Science in Sports & Exercise.
Although everyone performed the same seven exercises, like leg and chest presses, using weights heavy enough to exhaust their muscles after eight to 12 reps three times a week for eight weeks, the first group did just one set of each move while the second repeated the routine three times per session, and the third completed the entire workout five times during each gym visit.
The length of each workout varied: The single-set participants spent just 13 minutes working out, while members of the three-set group took 40 minutes to get through their exercises, and those who were prescribed five sets went at it for 70 minutes.
At the end of the eight-week period, researchers were surprised to see little variance in strength gains: Those who performed just one set of each exercise benefited just as much as those who did five times as much work. The only difference was muscle mass: Although everyone bulked up a bit, participants who did more than one set (i.e., three or five) of each move got bigger. In sum, the more reps subjects did, the larger their muscles got.
The takeaway: Unless your fitness goal is to, say, build out your booty—in which case, more sets are better—three 13-minute lifting sessions per week will probably do the trick if you’re setting out to get stronger.
That said, you’ll need to strain the muscles “to limp exhaustion,” meaning that by the end of each set, you should feel like you can’t possibly perform one more rep without taking a break, the study’s lead author, director of the Lehman College’s human performance program Brad Schoenfeld, told the The New York Times. And most people just don’t use heavy enough weights to push themselves that hard.
Although more research is needed to confirm the implications of these findings for women, “it looks like 13 minutes in the gym can lead to significant improvements” in strength, Schoenfeld said.
If this inspires you to halve your workout immediately, but you’re new to the whole heavy-lifting thing, ask a trainer about proper form since injuries will set you back regardless of how hard you work it.