Comment by malfist

This exactly. FTP is functional threshold power, it's the maximum you can physically maintain in zone 4 heart rate for 40-60 minutes and it's physically exhausting. This is hard work, hardest work honestly. If you have gas left in the tank after you could had a higher FTP. I'll get out on the bike and do a zone 4 workout and keep a steady state of 180-200 watts through the first 20-30 minutes, by the end of the hour or hour and a half of my workout, even with breaks to break, reset heart rate, have some water, salt and glucose, I'm down to 120-150 watts at the end of the ride.

Basically, you can probably charge your macbook at peek power for an hour every other day, or every day for a short while if you're okay with burning out eventually.

Expect to need to eat 400-600 calories and a lot of water each time you do this.