If you're already strength training and you do more sets of bicep exercises each week, your biceps tend to get thicker — and this link isn't just luck, it's a real pattern.

If you're someone who regularly lifts weights, doing more triceps exercises each week might help your triceps muscles get a little bigger—but only a little, and not as much as it helps your biceps.

If you're already strength training, doing more sets and reps doesn't always mean your arms and shoulders will grow much bigger—other things like rest, diet, and genetics also play a big role.

Two different weightlifting styles—one focused on heavy weights with long breaks, the other on lighter weights with short breaks—both grew arm muscles about the same amount when people lifted the same total amount over 8 weeks.

If you're already strength training and you suddenly do more than 50% extra workouts per week, your biceps and triceps might grow a bit more—but if you only increase a little or even cut back, you won't see a big difference in muscle size compared to those who ramped it up a lot.

If you're someone who lifts weights for fun and not professionally, your upper arm muscles grow about the same amount near the shoulder, middle, and elbow—no matter if you do more or the same number of sets and reps.