How heavy you lift doesn't determine how strong you become, according to a surprising new study published in the Journal of Applied Physiology. Wait, what?
Researchers took 49 young men with previous experience weight training and had them do a weight-lifting program for 12 weeks. Half of the men lifted weights light enough that they could do sets of 20 to 25 reps before failing (which the study considered "light weights"). The other half lifted weights so heavy they could only do 8 to 12 reps before failing ("heavy weights"). At the end of 12 weeks, the researchers concluded, "Our data show that in resistance-trained individuals load, when exercises are performed to volitional failure, does not dictate hypertrophy or, for the most part, strength gains."
Translation? Basically they found that all the men, regardless of how heavy they were lifting, increased their strength and decreased their body fat in similar amounts. The dudes lifting 15-pound weights got just as strong as the guys lifting 50. So does this mean the light weights vs. heavy lifting debate is settled?
Not necessarily, says Dan Roberts, a celebrity strength and conditioning coach, trainer, and author of Methodology X. "New research never 'proves' anything," he says. "All this study really says is that there needs to be more research done before we can draw real conclusions." (And, he says, it does make a difference that they only studied male subjects.)
Before you ditch your heavy weights for Barbie-pink 3-pounders, he adds that the results aren't as surprising as they may first seem. "The general consensus has always been that volume (how often you lift and how many reps you do) is the most important factor in seeing results from lifting weights," he explains. "No one thinks you need to lift incredibly heavy weights to get stronger."
Rather than focusing on lifting heavy, he says it's more important to focus on lifting enough. For example, back squatting as heavy a weight as you can handle for one rep isn't going to make you much stronger. Lightening your load a bit to something you can do for 8 to 12 reps will help you a lot more. Add in two more sets a couple of times a week and you'll start getting seriously stronger. In the end, you're decreasing the load and increasing volume so you can train your muscles to do more—it's all a trade-off between weight and volume.
How you're lifting the weights is also more important than how heavy they are, says Lawrence Betz , NSCA-CSCS, director of the Brooklyn Athletic Club. Make sure you're not trying to lift so heavy that you have bad form. And include appropriate rest periods—otherwise you're just headed for added injury instead of added muscle. "Everything matters: Sets, reps, tempo, rest, and exercise selection will all determine what kind of results you get from your weight lifting," Betz says.
But what about those workout instructions that tell you never to lift heavier than 2- or 3-pound weights? If you enjoy doing them, that's fine Roberts says, but know that there's no research showing those work any better either—and they're extremely time-consuming. Better yet, he says instead of getting locked into one program, try lots of different things to see what works for you.
"You shouldn't be too strict with your training," he says. "Mix things up—variety will help you get better results and it's more fun."