It’s always tempting to base your workout routine on the fake orgasm scene from When Harry Met Sally: you see someone with big muscles and think “I’ll have what she’s having.” Somehow, though, copying someone else’s training plan seldom produces the same results for you as it did for them. A new study from researchers at the Federal University of São Carlos in Brazil uses a very neat experimental design to put some numbers behind this observation, and offers some helpful insights on which details matter most (and least) for building strength.

The study, which was published in the Journal of Applied Physiology and led by Cleiton Libardi, put 20 volunteers (all men, unfortunately) through an eight-week training program involving single-leg presses and extensions. The catch: they did a different workout routine with each leg. With one leg, they did a plain-vanilla progressive training program involving four sets of each exercise with a two-minute rest, with the load chosen to reach failure between 9 and 12 repetitions. With the other leg, they did a variable routine that systematically switched up some of the parameters. Some workouts had a lighter load enabling 25 to 30 repetitions before failure; some involved six sets of each exercise rather than four; some involved eccentric contractions only; and some had four minutes of rest between sets rather than two.

My instinct was to assume that the variable routine would produce better results, since doing the same thing over and over should eventually run into diminishing returns. And when they took post-workout muscle biopsies, there was indeed some evidence that the leg doing the variable workout had slightly higher rates of muscle protein synthesis, which should in theory lead to greater muscle growth over time. But when they measured muscle size at the end of the eight-week training program, there was no difference between the two legs: they got bigger by roughly the same amount regardless of which training program they followed.

So the main result of the study is that following a complicated variable weight-training routine rather than a simple unvarying one doesn’t seem to make any significant difference to how much muscle you accrue. That’s useful to know, and perhaps de-stresses the weight room experience a bit since (as I’ve pointed out before) you probably don’t need to sweat the details.

But there’s a further analysis that the single-leg design enables: you can look at the variation in results from two legs in the same person following different training plans, and see how that compares to the variation between two legs in different people following the same training plan. That analysis is pretty eyebrow-raising: there’s 40 times more variability between people than there is between training plans. The people who gain lots of muscle do so regardless of the exact workout routine they follow; and it’s the same for the people who don’t.

On the surface, this seems a bit depressing. For someone like me, who looks like I was twisted together from a handful of pipe cleaners, it suggests that there’s no magic routine that will finally put some meat on my bones. Asking my bulked-up buddies what they do to put on muscle won’t help, because it’s their genes rather than their routines dictating the results.

But there’s a very important caveat that’s emphasized over and over in the study’s discussion section, almost to the point of comedy. After every conclusion they draw, they add “at least when resistance training protocols are performed with a high level of effort in resistance-training young men.” The subjects in the study had lots of experience lifting weights, and they were pushed very hard: both protocols involved lifting to failure in every workout. Notably, even though they’d been lifting already for an average of 2.5 years, every single subject was classified as a “responder,” defined as an increase in muscle size of greater than 2.8 percent, to both workout protocols. (One participant was marginally below that threshold after one of the routines.)

The big takeaway, then, isn’t that you can’t learn anything from the training of your betters. It’s that some lessons are more transferable than others. The number of sets, the amount of rest, how fast they’re lifting and lowering the bar, what supplements they took last night: probably not a big deal. (Though the slight differences in muscle protein synthesis in the new study suggest that small differences in muscle size might accrue over months or years.) What you should be noticing, instead, is that they’re working very hard—perhaps not all the way to failure, but pretty close. To max out your personal potential, whatever that happens to be, you’ll need to do the same.

My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available. For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.