People who grow their arms big don’t necessarily grow their legs big, and vice versa — muscle growth varies by person, not just by how heavy they lift.

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.

Even when you train one leg differently from the other, both legs tend to grow muscle in similar ways — which means your body’s natural biology, not the workout itself, is what really controls muscle growth.

For small muscle groups, unilateral and bilateral resistance training produce equivalent hypertrophic adaptations when volume and effort are matched.

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.

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.