Originally Posted by hamster

First of all, a healthy diaphragm is extremely hard to tear. Nearly all cases are caused by blunt force trauma such as being hit by a car.

However, if it is torn and it has not been fully healed, you're at the increased risk. Anything that increases intra-abdominal pressure can reopen the tear. This includes weight lifting, strenuous cycling, jumping (from as low as 2 feet), and even coughing.

I would suggest to give up weight lifting, to avoid intervals or any kind of strenuous aerobic exercise, and generally take it easy twice as long as your longest interval between tears.

Disclaimer: I am not a doctor.