HIIT Cardio recommendation please?

For my cardio I am used to doing something like 30 mins, 5mph, inline 4 on lifecycle treadmill.... sometimes I go random sometimes straight. The calorie couunter usually hits 400 - 450.

I want to switch to HIIT style. I think I will either switch to bike or track as it will be a pita to adjust up and down treadmill from sprint to jog.

What do you folks recommend for timing splits? I see some places saying 30 seconds sprint, 30 seconds jog repeat, some 1 min sprint 3 mins jog.... all over the place.

Thanks for any advice. I provided the first statements so that you know what kind of level I am already at.

It is my belief that HIIT is effective because during the hard phase (say the running phase) you are exceeding your sustainable aerobic threshold.
This has two implications. The first is that you are using non-aerobic energy pathways and the second is that you are enlisting fast twitch muscle fibres. These mean that you are working harder (and buring more cals) during this period of time than if you are at your sustainable aerobic limit. I know that I have exceeded my aerobic limit during the hard phase because I get lactic acid burn.

If you are running for 30 seconds at a pace that you could maintain for 1 minute, you should either run for 1 minute at that pace or run faster. You should aim to be pushing yourself to your limit during your hard phase - you cannot run any longer than you did, or any faster.

The split time is more complicated. Fit people recuperate after extreme exercise faster than unfit people (ie there pulse drops more quickly when the load is removed), so presumably they need shorter easy phases. Some programs have a 1 minute hard 2 minute easy phase for unfit people, changing to a 1 minute / 1 minute split as you get fitter. 30 seconds hard and 30 seconds easy sounds to short for recovery, you won't be cycling your pulse over a sufficiently wide range, but YMMV. Try all and see what your treadmill reckons is the maximum calorie expenditure (a pretty good guide to how hard you are working in total).

Lyle, where are you?

The high protein + carbs thing is very good after strength training.

After aerobics though, all you are doing is replenishing your glycogen. If you are doing the HIIT for weight loss, this is counter productive. With
HIIT (and intense exercise generally) you are burning calories faster than you can metabolise fat, and hence using up glycogen. This gives you a deficit that your body restocks next time you eat, in preference to storing fat. You give it a carb hit (and to a lesser extent a protein hit) and the glycogen is immediately replenished, and you lose this benefit. Its no more complicated than the old calories in vs calories out rule. Most people have supressed appetite after HIIT; use it (again, if your aim is weight loss).

Yes, that is your body getting rid of the excess nitrogen generated as a waste product when protein is metabolised for glycogen. I do not know how reliable a guide smelling Ammonia is to its concentration. Burning some protein is inevitable if you push yourself hard, which is why a lot of serious weightlifter types don't like cardio. I don't know the scientific truth of it, but if I smelled ammonia on my sweat and knew it was the smell of my muscles being broken down, it would certainly put me off ...

Thanks for the info... it's pretty hard to do on a treadmill, I find it pretty scary running quickly on them! I bought a stopwatch today and am going to switch to track. As I said, I hit around 300 cals readout in 20 mins so I'm pretty happy with that #.

Another 2 questions:

a) I see a fat loss recommendation to not eat for an hour or so after this type of excercise. My temptation however is to consume my usual post workout shake, with high protein and high simple carbs. What say you?

b) I associate an amonia scented sweat with muscle burn.... if I get this with HIIT am I pushing too hard?

Thanks again!

i guess it will depend on your goal.. if you're looking for general fitness, then do whatever you like.

if you have a race distance in mind then more specific training may be advised. most people would just advise you to up your weekly distance slowly and you'll get better.

if you're looking for calorie burn, i think you're misguided, but go ahead. try 30 seconds at a higher speed and a 1 minute recovery. do a few of these. if that seems easy, after a week or so, try for longer. keep adding until you find it too difficult, then back up a bit.