I work a M-F, 8-4, sedentary job.

I tend to do the same. Get up at sunrise, go for a walk, do some stretching, light body-weight stuff, etc. Daily I eat a very high fat breakfast, Bulletproof coffee and maybe some eggs which keeps me until the afternoon. I'll train when I get home (around 5:30) and then eat the bulk of my calories post-workout.

On days I fast, I'll usually go from 7 PM to 7 PM with an intense but shorter training session, or longer/slower lifting session.

Have you tried eliminating carbohydrate and protein during your fasts, which can still give you all the benefits even if you consume a lot of fat. This will supply you with more than enough energy to get through the day and train, especially once you get used to it? All depends on your goals and why you are fasting. For someone who is in shape, doesn't have fat to lose and just wants many of the benefits, you can somewhat "cheat the system" by abstaining from carbohydrate and protein for a prolonged period of time but still have adequate fueling from dietary fat.

I like the Leangains approach. I used to do fasted training after work, usually around 3-4 PM. In retrospect, I think this was too much fasting to do on a regular basis (3-4x/week). I now train earlier in the day (between 10-12) and break my fast after that.

If I went back to afternoon training, I think I would have a small pre-workout meal a few hours before training, protein+carbs. I think fasting all day 3-4 times a week is just too much stress.

Or you could try the fat fast approach. Guess you just have to see what works for you.

I do crossfit after work usually at 5:30pm. I eat lunch but usually nothing else until the workout so i am somewhat fasted.

I am usually mildly hungry on my way to CF since i eat a small breakfast and lunch. I guess i just try not to think about it until the workout starts, since for me intense exercise is an appetite killer and about 5 minutes into the workout all i want is water. My appetite is then at zero during the workout and for about an hour afterwards, but then i am ready to eat a grass fed steer.

The first few times i did this i found that my energy during the workout was somewhat uneven, but after a couple of weeks i adapted. Now, a funny thing happens, about 2/3 the way through the workout, i get a sudden burst of energy. Like i'll be gasping for breath at round 3 out of 5 but then at round 4 all of a sudden it is easy and i find another gear. My intuition is that my body is tapping into reserves here specifically because i am fasting, i am still carrying around about 10 pounds of unneeded fat so i think this is getting burned. I went down a notch on my belt after 5 weeks which is additional evidence.

http://www.marksdailyapple.com/gain-weight-build-muscle/#axzz20cJjxMEk

Good article above. Your body can take a whole hell of a lot in the way of working when it's tired or low on its typical fuel. If you're fat adapted, it can run for quite a while.

On a workout day I can do: -8 hour+ workday -Stronglift 5x5 reps which include 3 lifts (5sets of 5reps) (Squat, Bench, Bent over Row - Depending on the day) -6x 6:15 pace sprints for .15 miles -2 miles at 7:30 pace -5 sets of M-100 (Each set is 10 Thrust+Jump squats, 10x3 Mount climbers,10 Jump squats)

Pre-workout fuel: Next to no carbs at lunch (just some pulled pork) 7 hours before, 1 Kiwi, a small piece of honeydew.

When in doubt, push yourself (unless you have a musculoskeletal issue that will cause an injury.

Keep it up. Do it for your health! IF can be a great thing if done correctly. I'll do a week on and a week off.

Its fasted training, you are obviously going to be hungry & grumpy. You want a pep talk, here you go -Stop being a chode & Grow a pair. do it after work or don't do it at all.

Most people would do fasted training before breakfast. Dont skip any meals, especially not breakfast. Doing it before breakfast after a light supper means your body has been fasting overnight. Its much easier to stick to this.