High-intensity interval training (HIIT) is all the rage these days. There is a lot of hype about HIIT cardio, mainly because it supposedly burns more calories in less time. In fact a 2018 global survey of fitness trends ranked HIIT No. 1 (when comparing emerging fitness trends), based on the responses of over 4,000 exercise professionals around the world.
Although Physical Activity Guidelines traditionally recommend about 30 minutes of vigorous activity five days a week to maximize fat loss, HIIT experts maintain that less exercise is equally as effective if the intensity level is high enough.
Is HIIT cardio too good to be true? Can you slash a 20-minute jogging session into a 3-minute session of jumping jacks to have the same results? Let's look at HIIT cardio in greater detail and see how it holds up to regular steady-state cardio while analyzing if it is better for fat loss than steady-state.
What is HIIT cardio?
HIIT is all about high intensity. This means for each cardio session, you do several short bursts of exercise interspersed with slower intervals. For example you sprint as fast as you can for two minutes and then slow down to a jog for the next two minutes, and then repeat this sequence.
There are several ways you can do HIIT cardio. You can do a running routine with sprint intervals, skipping routine or incorporate other compound movements. For example, you can do intervals of Burpees or Jumping Jacks with slow jogging between each. Most HIIT routines consist of movements that can be done from anywhere like Mountain Climbers, Squat Jumps, Burpees, etc.
How HIIT differs from steady-state cardio
The biggest distinction between steady-state cardio and HIIT is the intensity and duration. In HIIT cardio, you use 80-90% of your maximum heart rate for a shorter period. When you're doing HIIT cardio, you shouldn't be able to hold a conversation.
With steady-state cardio, you use only about 50-60% of your maximum heart rate for at least 45 minutes. You should be able to hold a regular conversation while exercising without feeling too breathless.
Another important distinction is that HIIT cardio is mainly an anaerobic activity. This means your body uses stored glucose in the muscles without relying too much on oxygen. Here your oxygen demand is greater than the oxygen supply, so your body has to release energy without oxygen. This also means that you will feel tired more quickly because anaerobic exercise releases a lot of lactic acids (a waste product of anaerobic energy release mechanism). Think about how breathless and tired you feel after a sprint as opposed to a long-distance run.
Steady-state or LISS (low-intensity steady state) cardio is aerobic. This means that it relies on oxygen to release energy. The energy release is moderate, steady over a long duration. Long-distance running, for example, is aerobic and counts as steady-state cardio.
The final most important distinction to make is the type of muscles each of them uses. HIIT cardio relies more on your fast-twitch muscles. These are the type of muscles used for short, intense bursts of exercise. LISS cardio relies on slow-twitch muscles, which are used for endurance exercises. Slow-twitch muscles are a lot leaner than fast-twitch muscles, which is why sprinters look a lot more muscular than long-distance runners. So, doing HIIT cardio will make you look a little more muscular than LISS cardio.
Which one is more effective at a fat loss?
Ultimately the big question for anyone on a weight loss journey is which method is more effective at fat loss. Many research studies have been conducted on this topic in the last decade.
In one study, a group of 43 women (18-22 years) were split into groups—one who did HIIT, another doing LISS for several weeks and a third control group who did no exercise. Body mass, body fat percentage and abdominal subcutaneous fat were all measured in the exercise groups. The results showed that the HIIT group achieved similar levels of fat loss to the LISS group, in half the amount of time. The average duration for the HIIT group was 36 minutes, while it was 68 minutes for the moderate cardio group.
In another 2012 study of 38 overweight men, impressive reductions in body fat were achieved through a HIIT program. They followed a 20-minute HIIT session for 12 weeks. The study also showed that aerobic capacity (max energy consumption) improved by 15% for the HIIT group.
Another 2011 study concluded that not only does HIIT cardio reduce body fat considerably in a short time, but it is also even more effective for diabetic individuals. Diabetic individuals showed greater reductions in subcutaneous fat. It is especially beneficial for diabetics because HIIT seems to significantly improve insulin resistance by as much as 36%.
So, the main takeaway is that HIIT cardio is just as effective as LISS, but is far less time-consuming. You can burn the same amount of fat in half the time. HIIT is even better if you have diabetes or insulin resistance, as it brings positive hormonal changes.
Additional health benefits of HIIT
As mentioned, HIIT vastly improves insulin resistance. It is a great prevention strategy for type 2 diabetes and heart disease.
Another benefit of HIIT? It raises your metabolic rate even after you're done working out because it elevates your resting heart rate. Numerous research studies corroborate this phenomenon that HIIT cardio increases calorie burning in the 24 hours after your workout. So, you burn more energy while you're resting in the hours after working out, more so than LISS cardio.
As mentioned earlier, HIIT cardio also gives you a more muscular physique than LISS. So, if this is your goal, then HIIT cardio kills two birds with one stone (by losing fat and building muscle at the same time).
The biggest problem with HIIT
The saying 'no pain no gain' rings very true for HIIT cardio. They are extremely physically intense. They are also harsh on your joints due to the high impact forces created in exercises like Burpees or Squat Jumps. So, if you're just starting your fitness journey or have weak joints, HIIT cardio may not be the best place to start.
So, should you do HIIT cardio? If you are already relatively fit and are a busy individual, HIIT cardio is perfect. It burns a lot of calories in a short amount of time, and even more so after the workout. However, if you have joint-related issues like arthritis or suffer from injuries, it's better to stick to LISS cardio.
Photo Credit: BartekSzewczyk/iStock
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