I just can't imagine you lifting weights.我只是没法想象你剧中的样子.为什么后面用lifting?这是一种什么结构?

I just can't imagine you lifting weights.我只是没法想象你剧中的样子.为什么后面用lifting?
这是一种什么结构?

image doing 是想象正在做某事的意思
image to do 是想象要去做某事,但还没做.