If you're a healthy man between 18 and 40 years old, your starting height, weight, and age won't really change how much muscle you build from working out. Basically, everyone in this age group tends to gain muscle at roughly the same rate when they follow the same training plan, no matter their body size.

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.

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.

Individual hypertrophic responses to resistance training are highly variable across muscle groups and are not consistently correlated between upper and lower body musculature.

Doing your workouts more often per week doesn’t seem to help you build more muscle, as long as the total amount of lifting stays the same.

Individual hypertrophic responsiveness to resistance training exhibits moderate inter-muscle correlation, but a substantial proportion of variability is attributable to non-exercise-specific biological factors.