[MichaelRenor]

I'd like to add my own data points for low-carb/ketosis and exercise. In the beginning it was very hard and I felt extremely lethargic (typically 3 to 4 days after switching to < 30g carbs a day). My exercise at the time was 2 miles on the treadmill and 20 minutes of full body weight lifting (squats, etc).

The worse I ever felt was during that time (3-4 days in). After that I would slowly improve and within a few weeks could almost reach my normal max, though never exceeded them. The bonus part was that I was melting off pounds of fat.

This was just my experience. I found that salty drinks (such as chicken stock) helped a lot when first beginning low carb to prevent the lethargic feeling ~3 days in.