No idea about weight lifting, but I cycle about 300km strenuously every week in a fasted (18ish hours) state. Doesn’t feel quite as good as cycling in a fed state, but it’s not a big difference either.
Not very helpful….but I found that longer runs were difficult when I ran completely fasted (calorie deficit and running after 12-14 hrs of fasting). Got the weight off though…. now I’m trying to maintain and have increased calories the night before my morning runs and it is easier! Have put 3lbs back on but I figured that was an ok trade off
Medium training is doable. When training hard, IF goes straight out the window and rapid weight gain ensues.
So I pick exercises very selectively these days, carefully avoiding things like squats and deadlifts. Hopefully I can get to a metabolic level one day, where I can do them again.
Long bike rides are no problem fasted if you are riding in Z2 or Z3. If you are doing more intense work - intervals, lots of climbing you might need to fuel (I would). Phil Maffetone is good to read on Z2 training and fuelling