Doing light weightlifting with blood flow restriction four times a week for three weeks can make arm muscles grow a little in young, trained guys — about 4% to 8% bigger.

For guys who lift weights, doing arm curls with the arm stretched out doesn’t build more muscle than doing them with the arm bent, even when using light weights and blood flow restriction — at least over 3 weeks.

For young guys who lift weights, squeezing the biceps at the top or bottom of the move doesn’t make a difference in muscle growth when using light weights with blood flow restriction.

When young men who haven't trained before do arm exercises twice a week for about 2 months, their biceps and related muscles grow by about 6% on average.

When young men who don't work out start doing arm exercises twice a week for 10 weeks, their biceps get about 6% bigger.

Young guys who took a break from working out didn’t see much muscle growth in certain areas—like the middle of the outer thigh and upper arm—after nine weeks of doing the same strength exercises.