You probably already know this, but there are different levels of intensity when it comes to exercise. The intensity is something you choose. Depending on how hard you go or how easy you take it, you'll get different results. Taking it easy and slowing it down doesn't mean you're not working hard enough, it probably means you're working smart enough! There will be days when you need to push it more than usual, and it's important to know why. What happens inside your body during steady cardio training versus high intensity interval training is night and day. (You're already saying, "Yeah, no, don't put me down for cardio.")
Steady cardio training burns fat, builds endurance and targets Type I muscle fibers (slow fibers). Yes, running on the treadmill at a steady pace for 45 minutes will help your body burn fat. Taking a jog or dancing through a Zumba class, playing doubles tennis, hiking through the woods with the dog will gradually increase your endurance so you can make that run on the treadmill an hour or more without issue. It also helps the slow twitch muscle fibers get through other aerobic exercises with more endurance and power. You're like the energizer bunny!
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When you work within a steady cardio state, you're pulling the majority of your energy resources from the oxygen you're consuming. Oxygen mixed with the fat you store in your body activates the production of adenosine triphosphate, or ATP, which then helps the muscles to contract. You'll feel winded, but never so out of breath that you can't say your name. Your heart rate stays elevated at the same level for most of the workout, changing maybe 5 to 10 beats per minute in either direction at most. There are no real breaks during aerobic exercises.
HIIT workouts burn fat and calories, train Type II muscles to work in bursts and create an after-burn. There are breaks during HIIT workouts, but they don't feel like breaks! You're resting somewhere between 5 and 60 seconds. When you work out like this, you're switching back and forth between aerobic and anaerobic states. The latter happens when you reach the aerobic limit, meaning your body literally cannot take in oxygen fast enough or in quantities large enough to meet the demand of the work you're doing. Your super smart body switches to an anaerobic system that targets carbohydrates and calories instead. You're not using oxygen at this point, so your body won't be able to sustain this work level for very long. In fact, anaerobic training is performed in short bursts, like sprints.
The breaks you take will lower your heart rate to an aerobic level. Depending on the workout, you may hit your "anaerobic threshold" several times. Each time you hit that threshold and hang out in anaerobic land for 10 seconds to a full minute, you are setting up a very important recovery assistant called excess post-oxygen consumption, or EPOC. It refers to the amount of oxygen your body needs in order to recover and reinstate normal vitals. This is work. Work burns calories. This type of work can take hours. So, after a 30-minute HIIT workout, you're burning even more calories for hours and hours later as your body tries to reset itself.
Tip: After a HIIT workout, get some protein in your system right away to help repair the muscle fibers so your body can spend its energy on recovering all other processes. Click here for 10 protein-rich foods for your body.
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Bottom line: Steady cardio training should last longer than interval training. Your heart rate should remain at the same level during the entire workout and you won't take many breaks. It will burn fat with the help from oxygen and it will recruit your slow twitch muscle fibers. Steady cardio is excellent three to four times a week from walking to dancing to lifting weights. Interval training is a mix of aerobic and anaerobic states. You'll hit a threshold and switch states several times during your workout, boosting the EPOC effect for maximum calorie burn. You'll want to incorporate interval workouts one to two times per week, allowing enough time for full recovery (usually wait 24 hours before trying another HIIT workout). Strategically apply these to your weekly routine for maximum endurance and conditioning results.
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