Tingling Nipples. After a workout, a man's nipples sometimes tingle. And despite his feeling of accomplishment, he sometimes worries something is wrong. Why do his nipples tingle or itch? His breast tissue feels like it is on fire.
Hormones. First, hormone levels are responsible for different sensations in the nipples. In women, pregnancy can make nipples sore or tingle. Men have the same hormones as women, but in different concentrations.
In weight lifting, a person's hormone levels change. My previous research found that lifting increases both testosterone and growth hormone. In fact, exercise changes body composition by influencing hormone ratios.Testosterone, LiftingGrowth Hormone, Lifting

So:The tingling or burning sensation in a man's nipples may result from this hormone change.

Skin. There is another possibility that could cause nipple feelings. For endurance athletes, a common problem is nipple friction against the shirt. When running, a shirt rubs against the man's nipples.

And:For some runners, such as marathon runners, this can even lead to bleeding and soreness on the nipple.

Tip:Some runners use a lubricant, such as Vaseline, to reduce skin friction when running. This alleviates pain.

Discussion. The cause of tingling nipples may depend on your training. If you focus on heavy lifting, a hormone change may be behind the feelings. This means your body is responding to greater testosterone and growth hormone.
However, if you are trying to lose weight and are running, your shirt could be causing discomfort in the nipple region. Try using Vaseline or something to reduce this friction. This rubbing may be reduced after you lose weight.
Story. My nipples tingle often after lifting weights. I have investigated this interesting nipple-related topic. Some diseases, even serious ones, may provoke nipple sensations. But for a male weightlifter, there are more likely explanations.
Usually, when I do an exercise such as weighted dips or deadlifts, this will result in tingling nipples. The feeling is sometimes alarming. But once you are used to it, the feeling is pleasant.Dips

So:As a big and strong bodybuilder, you have lots of body parts that are not muscles. Your nipples are one of those parts.

However:It is unlikely that this nipple symptom reflects anything more serious than a temporary hormonal change.

Summary. Bodybuilding provokes many changes in a man's body. Even the man's nipples may feel different. They are responding to a hormonal shift caused by weight training. Other possibilities were also described.