If you're new to strength training, your bone size or density doesn't really predict how much muscle you'll gain in the first few months—people with all kinds of frames tend to gain muscle at similar rates.

If you're new to lifting weights, things like how much you eat, how much protein you get, how old you are, or your BMI don’t really help predict how much muscle you’ll gain in the first few months.

If you're new to lifting weights, having more muscle at the start doesn't really mean you'll gain more muscle from training — it's not a strong predictor of results, especially once you account for whether someone is male or female.

If healthy guys between 18 and 40 lift weights regularly for at least two weeks up to a year, they typically gain about 1.5 kilograms of muscle—no matter what kind of weight routine they follow.

If a young, healthy man lifts weights for 8 weeks, his muscles will likely get bigger—by about 6%, give or take a little.

If you're a guy between 18 and 40 and you start lifting weights, whether you're new to it or have been doing it for years, you probably won't gain much more muscle just because you're experienced—but the people who’ve trained the longest (4+ years) still tend to gain the most muscle, so experience doesn’t always make a clear difference.