I used to love lifting.

Do it then. The depression will make it hell at first, but force yourself to even just do 5 minutes. Reconnecting with things you used to enjoy but (I'm assuming) fell out with due to the depression will help immensely.

Do you have a therapist or psychiatrist? Nailing down potential root causes could help as well, once you have the energy and motivation to get to work on it. You got this!