Why is one eyelid swelling during extreme exercise.?

Bulging? If the eyelid/eye bulges with weightlifting, that could be an abnormality of the blood vessels called an orbital varix. Specifically, you will note the bulging happening when you are holding your breath and straining, such as with weight lifting. If this fits your symptoms, an exam, visual field and possible imaging to confirm the abnormality are in order.