They recommend that you do not do exercise in the first week. Some slight exercise in the second week. More moderate exercise in the third week. By week 4 you should be able to do anything that you were capable of doing before you went on the program.
I followed this advice the first time I went on the program, and was able to train for a 20km race. I also ran the 20km while on the program, with no need to carb-up before the race or anything like that, and no need for energy bars during or after the race.
While you're on the program, you may be tempted to push yourself hard at the gym because you think it will speed weight loss. This can be deceptive.
All of the energy you use, both sitting on your ass and while pumping in the gym, is coming from the ketones in your system. Think of it as if the fat cells are like little taps, leaking ketones in to you. There's a finite amount in your system at any time. And you're usually exhaling or excreting them or urinating them as well.
Periods of intense exercise could deplete your the amount of ketones freely available in your system. And while they will be quickly replaced as your body sends out the signals to break into more fat cells, it does take *some* time, and if your system is depleted of ketones, you simply don't have any fuel. You could experience nausea, dizziness, extreme fatigue, fainting, shaking, sweating.
A gradual increase in the amount of exercise over the first few weeks trains the body to increase the rate of ketone production, so after a steady increase over 3 or 4 weeks, you should be able to do a regular session at the gym. Just don't push yourself beyond what you would have been capable of before starting LT.