While scientists at a recent conference believe that some people build muscle more easily than others, the differences are more subtle than they previously thought.Flamingo Images/Getty Images
Perhaps you wonder if big muscles are one of those things that only happens to other people.
You’ve tried every machine at the gym. You’ve hoisted heavy weights and sweated through bodyweight routines. You bought kettlebells. Meanwhile, you have friends who seemingly begin to inflate at the mere mention of strength training. What gives?
That’s the riddle that scientists from around the world gathered to contemplate at a three-day conference last fall organized by Juha Ahtiainen, a muscle researcher at the University of Jyväskylä in Finland. “Response heterogeneity,” which describes how different people respond to the same training stimulus, is a hot topic in exercise science these days.
Dr. Ahtiainen and his colleagues shared the key takeaways from their discussions in a recent issue of the Journal of Applied Physiology. Here are the highlights.
There’s less variability than you think
Strength training does work. After eight to 12 weeks of systematic training, you can reliably expect to gain between 1.3 and 1.8 kilograms of muscle on average, according to one recent meta-analysis.
But if you assign 100 people to follow an identical program, some will gain twice that amount while others won’t gain anything. That’s what studies consistently find.
More recently, scientists have realized muscle gain or loss fluctuates between people without any training involved, which could be a result of measurement error, normal biological fluctuation, or changes in environment or lifestyle. The question becomes: Is there more variability after strength training than in a non-training control group? Surprisingly, studies have reached conflicting conclusions.
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Overall, the scientists at Dr. Ahtiainen’s conference do believe that some people build muscle more easily than others — but the differences are more subtle than they previously believed.
As for the more serious worry that some people are “non-responders” who don’t get any benefit at all from strength training, there is hope.
In a 2024 study from Brazilian researchers, lengthening workouts from one set to four sets per exercise turned 80 per cent of apparent non-responders into responders. Another study found that when you consider multiple outcome measures — not just muscle size but also strength, physical function and muscle fibre properties — every subject improved in at least one outcome.
The basics apply to everyone
There are some group differences. Older adults, for example, tend to gain less muscle for a given workout stimulus.
On the other hand, women gain proportionally the same amount of muscle as men, relative to their smaller-on-average body sizes. This remains true even after menopause, despite changes in circulating hormones.
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More surprisingly, people with mostly slow-twitch muscle fibres — think skinny long-distance runners — gain just as much muscle, proportionally, as those with mostly powerful fast-twitch fibres. The details of their workouts will differ, with slow-twitchers typically doing more reps with lighter weights to reach a comparable level of fatigue. But the results are the same.
To really maximize your results, you can tweak what exercises you do, how much weight you lift relative to your max, how many sets to do and so on, as described in the American College of Sports Medicine’s newly updated position stand on resistance training.
But the main takeaway remains simple: Lift some weights, do it consistently and don’t sweat the details. Others may progress faster than you — but if you stick with it, strength training will work for you, too.
Alex Hutchinson is the author of The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.