Ask Dr Adam: Why Do Some People Build Muscle More Easily?

Two people follow the same training plan and a similar nutrition programme, yet end up with very different muscle gains. It’s a common source of frustration, and it raises an obvious question: are some people simply fated to build more muscle than others?

Genetics usually gets the blame. But how much of the difference really comes down to DNA, and how much is still within your control? We asked Dr Adam to unpack what the evidence shows.

Why Do Muscle Gains Vary So Much?

At the risk of disappointing you, individual differences are real. But, as readers of my other Ask Dr Adam answers will know, it’s not as simple as you might think.

Across the scientific literature, it is extremely common to see big differences in how people respond, whatever the intervention. Those who change the most (typically the top 10 to 25% of participants) are often classed as high responders, while those who change the least (the bottom 25%) are seen as low responders. Scientists sometimes describe these patterns as phenotypes: observable traits in how a person responds.

When it comes to muscle gains, size is the most obvious result most people look for. More specifically, they mean muscle hypertrophy, the growth of muscle fibres. Unsurprisingly, research shows considerable variation in hypertrophy between people following similar resistance-training programmes. In one well-known study of 585 men and women, the change in biceps size after 12 weeks of the same arm-training programme ranged from a slight decrease of 2% to an increase of 59% (2). So why does the same programme give such different results?

Is It All In Your Genes?

To some extent, yes. At any given time, each of us has what could be called a “maximum phenotypic mass”. In other words, it is the amount of muscle your body is set up to support, based on your skeletal frame, development, genetics, hormones and the physical demands you habitually place on it.

Genetics influence both how much muscle we start with and how it is built. That includes muscle fibre size and type, limb proportions, and the architecture of our tendons and muscles. Genes also shape how we respond to training, through differences in satellite cells (more on those below), how sensitive muscle is to hormones such as testosterone, inflammation, tissue remodelling and the processes that build new muscle protein.

But there is no single “muscle-building gene”. Hypertrophy is a complex trait involving many genes, each contributing relatively little. Genetics help determine the size of the opportunity, the training stimulus you need and how quickly you adapt. They are not the sole governor of muscle gains.

Do Satellite Cells Hold The Key?

Think of each muscle as a bag. Training fills it, but existing muscle cells can only expand so far, so eventually growth hits a ceiling. To go beyond it, the bag itself needs to get bigger.

This is where satellite cells come in. They are stem cells that live in muscle. When muscle fibres are put under strain or damaged during training, satellite cells can become activated, multiply and add new nuclei to existing fibres, giving those fibres more capacity to grow. Human research has linked satellite-cell activity to subsequent muscle growth, which makes them a plausible part of the explanation for individual differences (1).

However, it would be an exaggeration to say that the number of satellite cells you have decides how much muscle you can gain. They are involved in a much broader process of muscle repair and remodelling, and their precise role in human muscle growth is still being studied. On their own, they don’t make you a high or low responder.

What About Hormones And Myostatin?

Myostatin is one of the body’s natural brakes on muscle growth. Experimentally blocking it can produce unusually high muscle mass, particularly in animal research, so it clearly matters biologically. But normal, everyday variation in myostatin doesn’t explain why one person gains more muscle than another.

The same caution applies to testosterone, growth hormone and IGF-1, a growth factor involved in tissue building. A big hormone spike straight after a workout does not reliably predict how much muscle that workout will build. What happens locally inside the muscle matters more than a brief rise in hormones circulating around the body. It is not just the signal that counts, but how the muscle responds to it.

Where Does Nutrition Fit In?

This is where the work of Emeritus Professor Joe Millward, a true legend in protein nutrition, is particularly useful. His Protein-Stat framework treats lean body mass as part of a regulated system. That system is shaped by body size, genetics, development, hormones, the demands you place on your body and dietary protein (3).

In practical terms, protein is not an unlimited muscle-building switch. It provides the amino acids muscle is built from and helps stimulate muscle protein synthesis, especially alongside resistance exercise. But it works within a system that regulates how much lean tissue your body can maintain or add.

Nutrition is therefore best understood as a gatekeeper rather than something that will single-handedly build bigger muscles. If you aren’t eating enough energy or protein, nutrition can substantially limit your progress. Once your intake is adequate, eating more brings progressively smaller benefits, and simply piling on extra protein is futile.

For most people doing resistance training, around 1.6g of protein per kilogram of body weight a day is a reasonable, evidence-based target. Individual needs vary, and a little more can help during dieting or when you’re unsure. It’s worth adding a caveat, though: some more recent estimates of protein requirements rely on a method that may well overstate what we truly need. Spreading your protein across several meals is also a sensible way to give your muscles repeated opportunities to build.

Don’t forget that getting enough energy overall is crucial too. Trying to build muscle while consistently under-eating makes it harder, because it compromises training quality, recovery and your body’s ability to lay down new tissue. That doesn’t mean you need a big calorie surplus: excess energy mainly adds fat rather than forcing extra muscle growth.

What If Your Progress Is Slow?

Don’t assume you have bad genetics. Start by checking whether your training is genuinely progressive and challenging your muscles enough to adapt and grow. Bear in mind, too, that the body adapts to changes in protein intake: eat far more than you need and it simply burns more of it.

It also helps to accept that people respond differently to different training approaches. Slow progress may reflect a poor match between the programme and the person, not an inability to build muscle.

The Bottom Line

Genetics are neither irrelevant nor the whole story. What you do with your nutrition and training determines how close you get to your own potential. So try not to compare yourself to others. Eat enough energy, get adequate (not excessive) protein, train progressively and recover properly. Then judge your muscle gains against your previous self, not against somebody else’s rate of growth.