Okay ladies and Gents, the aim here is to lose maximum fat mass whilst at the same time holding on to as much muscle mass as possible. I'm not a fan of calorie restriction as I am a fan of calorie expenditure through exercising. Of course not all workouts are created equally. The type of exercise you need most now is a type that would speed your metabolism, preserve as much muscle as possible, whilst at the same time help you to lose some fat mass off your body. So it's maintain muscle, (not worried or concerned about building here yet), and lose fat. That in itself would speed your metabolism since muscle cells require much more energy to operate than fat cells, (which are just happy to tag along all day and night). I’m assuming you’re already involved in some weight training program here which goes a long way in preserving your muscles. You see if you use it, then you won’t lose it; simple really. Dropping calories drastically is dropping energy. HIIT requires every ounce of energy you can master. No point starting a workout feeling super strong at the outset only to fizzle right down with your head feeling like it weighs a ton as time passes by. The HIIT that I have in mind is based on timing more than the choice of exercises you decide to choose for yourself. I'll give you an example of timing first then I'll give you a variety of exercises you can do (if you like them that is). 1. Your total exercising time is 10 minutes and only ten minutes. 2. The more 10 minutes blocks you can do in a day/night the better 3. It goes without saying that this is a 7 day program/everyday and as I said above, preferably done few times a day (twice or thrice) especially on days off work/Uni etc. 4. The way I like to structure it seems so so easy yet it is very effective for what we want to achieve (super fast metabolism) 5. You warm up first by walking briskly for 5 minutes or so or riding a bike for 5. This would serve to raise your core temperature which is important before going all out at 100%. 6. You exercise all out (at 100% of your ability) for 10 seconds. 7. You go through an active recovery period of 50 seconds. That's 1 minute up already (taking away from our initial total of 10) 8. Continue with this "easy" pattern until the 10 minutes are up 9. Done! 10. Total time spent in a flat out mode is 100 seconds, or 1m, 40 sec. Yes, we can increase the intensity by adding few more seconds to the 10 and making it 15 or so. That comes later on as your body adapts to the first wave of 10 seconds and you become more comfortable with the whole idea. Now what exercise? Take your pick really. Sprint on grass for 10 then walk back for 50. Skip for 10 then walk for 50. Punch a bag for 10 then walk for 50. Burpees for 10, followed by 50 walking. Explosive squat position star jumps for 10 followed by 50 walking. Stationary bike all out for 10. Box jumps for 10 then 50 walking etc... The short amount of time spent in the high intensity zone won't be enough to catabolise your muscles. And no, you won't be using much fat if any whilst performing such a HIIT workout. But then, I never concern myself with what fat I'm using or losing whilst exercising; it's what happens when I stop that really matters. And what occurs after you stop is that your metabolism would have kicked up a gear. I'm not getting technical here so as to keep it simple and keep confusion out. Sounding sophisticated is not my aim now; positive results are what I care about and nothing less would satisfy me so… Okay, just to reiterate; HIIT would be the way to go for no more than 10 minutes. And no, you would not want to do it before weight training but after. You can also do it on your days off weight training, again for strictly 10 minutes. There is a reason why I don't like the "killer" workouts that take your lactic acid build up to great heights; they can actually (wait for it), decrease your fitness/aerobic level. So Lactate threshold workouts are not something that I would go along with. Yes you feel like you're about to die, (thinking that it's all for the best) where in fact it's for the worse. Hence, I advice a 10 minutes HIIT where you only go all out for about/between 20 to 30%, or 2-3 minutes out of those 10. So to have an edge on all those "secret" programs out there, do it the smart way and that does not mean running for miles on end or the "killing yourself with an acid bath" way, (been there done that). Too much lactate tolerance (high acidosis) training can cause aerobic performance to decline; hence I’d like to limit the high intensity component of HIIT to between 10 to 20 seconds max out efforts. Anaerobic training that only stimulates moderate accumulated lactate levels enhances anaerobic performance and maintains aerobic fitness. All the best. I thank you for your time. Fadi.