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.

When you do two different styles of weightlifting—one with heavy weights and fewer reps, and one with lighter weights and more reps—but match the total amount of work done, both can make your arm muscles grow just as much after 8 weeks.

If you're a young guy who already lifts weights, doing twice or three times as many sets per week won't noticeably grow your biceps more over six weeks — even if there's a small trend toward more growth.

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 do the same total amount of weightlifting work, lifting heavy weights with longer breaks and lifting lighter weights with shorter breaks both build muscle about the same, but lifting heavy gives you more strength.

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.