Amid the confusing torrent of advice about the best ways to build strength, I’ve taken comfort from a series of reassuringly simple studies from McMaster University over the past decade. Researcher Stuart Phillips and his colleagues have repeatedly demonstrated that if you do a series of lifts to failure—that is, until you can’t do another rep—then it doesn’t much matter how heavy the weight is or how many reps you do. As long as you’re maxing out, you’ll gain similar amounts of strength with light or heavy weights.
But there’s an interesting caveat to this advice, according to a new study from a team at East Tennessee State University led by Kevin Carroll, published in Sports: just because you can lift to failure doesn’t mean you always should.
Researchers have previously pointed out that it takes longer to recover from a strength training session when you go to failure than when you stop a few reps short, with negative neuromuscular effects lasting 24 to 48 hours. You also recovery more quickly even if you do the exact same number of reps but take a little extra rest halfway so that you don’t quite hit failure. On the surface, this is a trivially obvious point: of course it takes longer to recover if you work harder! The question, though, is whether there’s something particularly damaging or exhausting about going all the way to failure that outweighs the positive training effect you get from working harder.
That’s what Carroll’s new study investigates. He had 15 well-trained volunteers do 10 weeks of strength training three times a week (plus two days a week of sprint training, but that doesn’t end up being relevant here, other than to indicate that their overall training load was pretty high). They were divided into two groups: one trained to failure every workout, while the other trained to an assigned “relative intensity.” For example, if a subject was capable of doing three sets of 10 reps at 100 pounds for a given exercise, then if they were assigned a relative intensity of 80 percent they would lift three sets of 10 reps at 80 pounds instead.
The paper is freely available online if you want more details about the training program, but the key point is that they tried to keep two groups as even as possible. If the relative intensity group was assigned three sets of 10 reps for a given workout, then the train-to-failure group was assigned a weight with a goal of reaching failure on the third set after somewhere between 8 and 12 reps. If they did more or fewer reps than expected, the target weights were adjusted for the next session.
So, in summary, two groups doing almost the same training, except one group was hitting failure on the last set of each exercise in every workout. The initial results from this study were published last year, showing that the relative intensity group had greater improvements in maximum strength and vertical jump. The new paper adds a bunch of information based on muscle biopsies and ultrasound, showing a greater increase for the relative intensity group in overall muscle size, the size of individual muscle fibers, and the presence of several key molecular signals of muscle growth.
Before we conclude that failure is bad, there’s one other detail of the training program that’s worth mentioning. While the failure group was hammering away three times a week, the relative intensity group was doing two harder (though not to failure) workouts and one easier workout each week. For example, a max strength workout of three sets of five reps might start at 85 percent for the two hard workouts, but then drop to 70 percent for the easier one.
This seems like a whole different variable thrown into the mix, and it reminds me of a study from Marcas Bamman’s group at the University of Alabama at Birmingham a couple of years ago. In a big study of older adults, he found that doing two harder workouts and one easier workout each week produced better strength gains that just two hard workouts or just three hard workouts a week. He suggested that lingering inflammation in the muscles made the subjects unable to fully benefit from three hard workouts a week. Instead, doing a third easier workout added some fitness gains compared to just two weekly workouts, but still allowed the muscles to recover.
So to me, the message from the new study isn’t necessarily that lifting to failure is bad. It’s that lifting to failure all the time might be counterproductive (and especially so as you get older, Bamman’s results suggest). The point Phillips has been trying to make is that, for the vast majority of us, all the variables that make your head spin—sets, reps, one-rep max percentages, and so on—are utterly minor details compared to the main goal of simply doing the work, and sometimes pushing pretty hard. That’s still true, and I wouldn’t recommend trying to replicate the byzantine sequence of workouts in the new paper. But if “pretty hard” might mean stopping a rep or two short of failure without losing any of the benefits, that’s also nice to know.
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.