Why don't muscle cell changes explain why some people build muscle faster than others?

What we’ve found so far points to other factors possibly playing a bigger role, even though we haven’t looked at them directly in this set of studies. The classic measurements used to track muscle growth — such as fiber thickness or satellite cell activity — didn’t consistently match up with how much muscle people actually gained. That means if you’re trying to understand why someone responds better to training, looking only at their muscle cells might miss the bigger picture.

This doesn’t mean muscle cell changes aren’t important — they’re still part of the process. But they don’t seem to be the main reason for differences in how quickly people build muscle. Other things, like how the body signals growth, how well nutrients are used, or how the nervous system activates muscles, could be contributing. We haven’t reviewed those factors here, so we can’t say how much they matter.

The evidence we’ve reviewed so far doesn’t give us a clear answer about what does drive those differences — only that muscle cell changes alone don’t explain them.

If you’re training and wondering why your progress doesn’t match someone else’s, it’s not necessarily because your muscles aren’t changing enough. The reasons might be deeper — and still hidden from view.