Quote (Kiston @ Aug 5 2010 05:46pm)
hey, i stumbled across a post that kind of scares me while just reading.
If you are eating carbs, high intensity cardio will, in my opinion, burn just as much fat as low intensity. Although high intensity cardio seems to inhibit fatty-acid mobilization and metabolism during actual exercise, it seems to cause a massive post-exercise fatty-acid mobilization. Basically, you burn carbs during high intensity cardio and burn more fat later on because of it. For about an hour after some high intensity cardio, your body is metabolizing fat to replenish intra-muscular triglycerides and other recuperate.
If you are in ketosis, you are not eating very many carbs. High intensity cardio *requires* glucose/glycogen because of the muscle fiber type used. This means that you should not do high intensity cardio while in ketosis --- your body will catabolize a lot of muscle in the process of obtaining glucose from amino acids and glycerol (cortisol and glucagon). This will not happen as much with low intensity cardio in ketosis, because you will be using mostly type 1 (oxidative) muscle fibers that can more easily burn fatty acids.
sounds like hiit is bad for keto? ive been doing 40min hiit ED
this is not exactly true and I'll tell you why.
While the muscles/liver are full of glycogen and the body is not in ketosis, the body will burn glycogen as fuel first for any aerobic activity. After the glycogen is totally depleted, the body shifts to peptide breakdown and fat breakdown. The body does not go into full ketosis after glycogen is depleted (contrary to popular belief). The reason for this is because the body still recalls that it is in a glycogen environment because of it's daily nutrition of carbs. When you strip the body of carbs for consumption and start feeding it mostly fats and protein, you make the body start the gradual process of switching over to ketosis. This can take UP TO 2 weeks...or as little as 2 days....depends on the person.
Anyway, back to the topic. So assuming you are NOT in ketosis...after glycogen is depleted it is indeed true that your body will not begin to burn fat until after the cardio. But here is the catch. If glycogen depletes during cardio (low or high intensity), and your body is NOT in ketosis...the first thing to be catabolized for energy is MUSCLE. That's right, the body begins to break down muscles for fuel in approximately 90% muscle and 10% fat. This progressively changes over the next 45-60 minutes and eventually fat and muscle are burned at approximately even amounts. The only way to stop this is to pump BCAA's before/during/after exercise in order to confuse the body into not breaking down essential peptides. Fat burning will still occur.
During ketosis however, the body is no longer burning glyocogen first. Glycogen is already depleted and has been for quite a long time. The body immediately uses lipids as energy, however the process is much slower and sustained longer than glycogen burning. Because of this, HIIT cardio is OPTIMAL because it gives the body a chance to recover between "sprints" (or any short burst of speed/intensity along the way). When you stick to a set pace the whole time, although less strain on the muscle fibers is present, it is less efficient at fat burning because of the reduced caloric load.
In essence, less HIIT is required for the same effect as long term low intensity cardio. You can do 20-30 mins of HIIT and stop which will generally keep muscle wasting at a VERY low percentage compared to 45-60 minutes of low intensity sustained cardio. It has been found that keto groups suffered less muscle wasting during HIIT in the 20-30 minute mark than control groups of others who relied on glycogen as fuel normally but were glycogen depleted prior to the cardio. In addition it was found that the keto group started suffering massive muscle loss after highly sustained cardio sessions (60+ minutes if I can remember).
So basically the key is:
for keto losses, keep to HIIT and keep it short...20-30 mins max at a time (i shoot for 30 mins post workout and 15 mins pre-workout)
for non-keto losses, keep to sustained cardio for 45-60 mins unless glyogen is pre-depleted, then stick to HIIT as well.