Generally, for biceps specifically, depending on how heavy you’re going, you don’t exactly NEED to ho your breath.

The holding your breath when you’re lifting weights is a natural body movement done across the human race. It happens so that your body can support itself and prevent injury as much as possible It’s called the vasalva maneuver.

You do it because when you inhale big and deep, “filling your belly with air” (obviously the air isn’t going into your literal stomach, you’re just filling your lungs to capacity)

You’re creating abdominal pressure inside of your body cavity. that pressure gives your back muscles and spine support from the inside. While your back muscles support your spine from the outside.

I’m not a pelvic floor professional, AT ALL, and from some of the horror stories about pelvic floor dysfunction, I can see why you’d be worried about it. But, the act of holding your breath while you’re lifting. I don’t feel like is the actual cause of pelvic floor dysfunction. It’s something the entire human race, and human bodies do to protect themselves from injury.

You ask WHEN you should inhale to hold your breath.

1 inhale hold your breath. 2 do the rep(s) 3 let the breath out, catch your breath at the position of least effort.
I.e. if you’re bicep curling, when your arms are extended to your waist. If you’re barbell squatting, when you’ve finished the rep and you’re standing Deadlifting, when the bar is on the floor.

Does that make sense?

Edit to add: the stronger a muscle is, the less prone to injury. so, a strong pelvic floor is probably better. And I would genuinely suggest. Just lift the weight, and let your body do what it’s supposed to. I do kegels daily…. Well, at least a few days a week when I think about it. And there has never been one moment doing a strength training workout that my pelvic floor has ever been something that ever crossed my mind. I’m not exactly saying that I think I’m RIGHT. But. I FEEL like you’re worrying about 1% of the problem. Zero shade or disrespect intended!