It’s one of the most popular assumptions in all of gymdom: To get big muscles, you need to lift big weights. Fitness culture is rife with terms like “Max out” and “Go hard or go home” (although, thankfully, “No pain, no gain” seems to have been retired).
But despite the conventional wisdom in strength and conditioning circles, heaving massive loads isn’t the only way to build muscle. In fact, it may not be necessary at all, as science is beginning to prove. So if you fear heavy weights, or have injuries that prevent you from using them, lighter training can still lead to the gains you seek.
Just what constitutes “heavy” lifting is open to debate, but exercise science generally defines it as weights that are 80% or more of the heaviest load you can manage for one rep. (This amount will usually allow you five reps or fewer.) Training that heavy recruits a large number of muscle fibers, particularly the fast-twitch ones that have the most potential for growth and power production. If you’re a competitive lifter or power athlete, such as a football player, you must build your workouts around low-rep barbell training to see the best results, but if you’re merely looking to put on muscle and improve your physique, you may do better to limit it.
The main downside to heavy lifting is the injury risk. “Training like a powerlifter gets you strong but can also beat you up,” says Jason Ferruggia, a strength coach and author in Los Angeles. Heavy weights can wear down joints over time and lead to chronic conditions like tendinitis. But perhaps more compelling is the evidence that lighter lifting is just as effective as heavy training. So why risk crushing your joints if you don’t have to?
“A muscle needs to be stressed under load for an adequate amount of time to stimulate a growth response,” says Ferruggia. “Science has pointed to a duration of 40 to 70 seconds as being the most effective. This is why bodybuilders do eight to 12 reps for upper-body exercises and 10 to 20 for lower-body,” which induces greater fatigue in the muscle and causes it to build back up with a better work capacity. “So if you’re doing a routine like five sets of five, you’re not going to grow maximally.”
In a meta-analysis published in the European Journal of Sports Sciences last year, researchers looked at 17 different studies comparing low-load training (60% or less of max) with higher-load protocols (65% or more). They found no major differences in subjects’ muscle and strength gains, and even noted that these findings run contrary to current exercise guidelines that specify a need for loads of 65% or greater to achieve gains. Ferruggia agrees: “Textbooks might tell you it’s impossible to gain on high-rep training, but if you add 10 pounds to what you can lift for 20 reps, you’ll be bigger—just without the joint stress that comes from chasing PRs.”