When guys who lift weights contract their biceps at 70% of their max strength and their arm blood flow is restricted, their body seems to turn down the signal to the bigger, stronger muscle fibers more quickly than usual.

When guys who lift weights squeeze their biceps at 70% of their max strength, putting a tight band around their arm makes their muscles fire up their strongest muscle fibers faster than if they didn’t have the band.

When guys who lift weights squeeze their biceps at 70% of their max strength while wearing a tight band around their arm, their smaller, easier-to-activate muscle fibers don’t fire as much as they normally would.

When guys who lift weights squeeze their biceps at 70% of their max strength, putting a tight band around their arm makes their muscles fire more intensely than if they didn’t use the band.

When you squeeze your bicep gently but cut off some blood flow to it, your muscles seem to turn on their motor units more quickly and intensely than usual—like your muscles are working harder even though you're not lifting heavy.

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.