HIIT vs LISS cardio
When HIIT hit the scene, it was a game changer, after decades of half hour, 45-minute LISS sessions, 10-15 minutes of sprints burned more calories and less muscle and had more of a metabolic increase.
HIIT or High Intensity Interval Training vs LISS or Low Intensity Steady State:
HIIT is doing a form of cardio at your 90% max effort followed by a period of recovery, repeated for several minutes. There are different methodologies, Tabata, which is 20 seconds of max effort followed by 10 seconds of rest for 4 minutes, or just 30 seconds on 30 seconds off, 1 minute on 1 minute off, for 10-15 minutes. Evidence suggests that the time periods aren’t that important, what is important is maxing out your Central Nervous System during effort periods while recovering as much as possible during rest periods. What seems to happen, is, because you max out the CNS, the body doesn’t try to slow down the metabolism and adapt as it does with LISS, it panics and revs up the metabolism to get through this stress. It also releases a hormone called cortisol in an effort to deal with the stress, cortisol is the hormone that causes things like a ‘runners high’ and is really addictive. Your body will eventually adapt though, so after 4-6 weeks, it’s time to change.
LISS is typical cardio, running, biking, elyptical, etc. If you stick to say a 30 minute run each day, your body gets better at it, meaning you will burn less calories, but it also will pair down and muscle to save calorie burn. This means, just using nice round numbers, if you burn 2000 calories a day at rest, then you start burning 300 a day running, your body will begin to pare down muscle, dropping your daily calorie burn from say 2000 to 1700 and it will get better at running, so now you only burn 200 calories a day with your run. So now, you have to run every day, to burn less calories than you were burning at rest before, 1900 vs 2000. These are made up numbers, but you get the idea.
HIIT seems to have less of a negative metabolism effect, but you shouldn’t do it for extended periods. Make strength training your focus and phase in occasional HIIT session for a few weeks when cutting.