Most of today’s top trainers will tell you that lifting light weights to slim down isn’t a grand plan, despite fears of “bulking up” from heavy lifting. But a new study says that, on the flip side, adults who are intimidated by heavy weights shouldn’t despair: Lifting little weights can still produce big results in muscle mass. This is particularly good news for older adults who risk injury or joint pain from lifting heavy weights, but need the exercise to maintain muscle mass. For the rest of us? Trainers aren’t so sure this is grounds to give yourself a break at the gym.
The study, led by Stuart Phillips at McMaster University in Ontario, examined a group of 21-year-old men who were all weight-lifting novices. Three times a week, the men did knee extensions on a weight machine; on one leg, they lifted 80% of the maximum weight they could lift to fatigue, for 8 to 10 reps. On the other leg, they lifted 30% max to fatigue, at around 25 reps. Comparing MRIs of the men’s quadriceps before and after ten weeks of training, they found that there wasn’t much difference in muscle change between the heavy and light lifters.
Phillips thinks this is great news for “mere mortals”—non-athletes who want to build or maintain muscle mass for health reasons, but may be put off by the prospect of lifting heavy weights. But even he admits that not everyone agrees:
As word has begun to get out, Phillips says he’s “been deluged with emails from trainers” who challenge the results. “They’re very resistant to these types of findings. It challenges dogma.”
They’re probably also resistant to the study because it was small, limited to men, and limited to a very young age group (incidentally, not the age group that’s most at risk for injury when lifting heavy weights), but the findings do challenge what most trainers tell us, most of the time: That we need to lift heavy weights to see results.
Despite Stuart’s findings, trainers aren’t likely to change their tune anytime soon, so long as clients’ goals remain the same. As long as the majority of Americans are looking to lose weight and build muscle in a small amount of time, heavy weights are still the most efficient answer. But what the best trainers and researchers should tell you is that what you do is dependent on your goals and personal history—unfortunately, there’s no weight that fits all.