High-intensity interval training, also known as HIIT, is all the rage with trainers and fitness fans. HIIT is great for your metabolism, but not so helpful for weight control.
Obviously the military elite, like the prospective SEAL in the photo above, are capable of doing lots of pullups, but I personally really have to strain to do one pullup. Just the effort leaves my muscles quivering, my heart pounding, and my arms so exhausted that I have trouble rewarding myself with ice cream when I leave the gym.
OK, I'm kidding about the ice cream, mostly. The fact is, high-intensity exercise takes on different guises for different people of different fitness levels. For a young, fit person, all-out exercise on a stationary bike for 30 seconds followed by a 4-minute rest period might qualify as HIIT. For someone who weighs 500 pounds, putting on their shoes might be equally strenuous. For just about anyone who works out under the guidance of a fitness trainer, HIIT is currently the exercise regimen of choice, and not without good reason.
HIIT sessions take as little as 25-30 minutes from warm up to cool down. Quick bursts of extreme physical exertion, lasting from 10 seconds to 4 minutes, are followed by much longer rest periods, up to 4 minutes each.
There's no doubt that HIIT can lower blood glucose levels, even in diabetics brave enough to attempt it. There's no doubt that HIIT builds up muscle. What HIIT can't do for you is to give you six-packs abs or, for some of us, even reduce our keg.
What Qualifies as HIIT?
Most Cross-Fit routines qualify as HIIT. So does the Seven-Minute Workout. It's easy to organize a HIIT workout on a treadmill, a stationary bike, or even ellipticals.
HIIT is about relative intensity, not absolute intensity. An older person might achieve maximum heart rate while walking up a flight of stairs. A younger person might need to use a stationary bike set for maximum resistance. Walking 2 miles per hour could qualify as a "sprint" if you are morbidly obese. Running a 6-minute mile might not qualify as HIIT if you are in superb physical condition.
The key ingredient in a HIIT workout is that should feel hard. You absolutely should feel tired after your exercise session. You should feel like you simply cannot go on any more. Your arms should hurt. Your legs should hurt. Your lungs should hurt. Muscle exhaustion should be real. You can feel a seven-minute workout, done properly, for a week.
Does HIIT Training Carry Over into Everyday Life?
High-intensity exercise sounds find for elite athletes, but does it offer any benefits to the rest of us. Dr. Zoran Milaović and colleagues at the University of Nis in Serbia took a look at the literature in a meta-analysis they published in the journal Sports Medicine. They confirmed that HIIT sessions increase the maximum volume of oxygen (VO2 max) used by athletes. Dr. Charlotte Jelleyman, an exercise physiologist at the University of Leicester in England took a look at the literature on HIIT and glucose use in another meta-analysis they published in the journal Obesity Reviews. They concluded that blood glucose levels were better controlled after HIIT than after continuous exercise or no exercise at all.
Favors People Who Are Out of Shape
Dr. Håkan Westerblad, a muscle and exercise physiologist at the Karolinska Institute in Stockholm, go so far as to say that HIIT actually is more beneficial who are in poor shape than for athletes. Westerblad and his colleagues designed a study to find out why.
The Swedish researchers examined 18 recreationally active but not "athletic" men and male endurance athletes who did six rounds of 30-second bursts of high-intensity cycling followed by four minutes of rest. After the workout, the scientists took biopsies of the working muscles in the participants’ legs.
When a muscle cell receives a nerve signal to contract, tiny pumps called ryanodine receptors open. They release calcium into the fluid inside the cell, causing it to contract. When this happens across all the cells of a muscle, the whole muscle contracts.
After a HIIT workout, the ryanodine receptors in the muscles of men who weren't in top shape tended to leak. They generated a steady drip of calcium into the fluid of the cell. This made the cell continue to contract long after the exercise session was over. It caused the muscle cell to remodel itself for greater endurance, but it also caused the muscle cell to continue to require glucose, keeping blood glucose levels lower. For diabetics, the message is (and diabetics can test their blood sugar levels after HIIT workouts and verify) that working out for just a few minutes to the edge of endurance keeps blood sugar levels under control far longer than easier, milder, non-painful exercise.
Endurance athletes, on the other hand, didn't have a breakdown in ryanodine receptors after heavy workouts. Their ryanodine receptors were not changed by the HIIT session, and they did not get incremental benefits from the workout. It's as if they were too fit for HIIT.
If You Would Benefit from HIIT, How Do You Motivate Yourself to Do It?
People who exercise all the time, it turns out, don't really need high-intensity interval training. It's people who don't do a lot of exercise who really need to workout hard. But the fact is, if you don't already work out hard, chances are you don't want to. Maybe you would prefer not to work out at all. What can you do to motivate yourself to do the exercise you need to do?
One of the principles of HIIT is that it doesn't really make a lot of difference which exercise you do as long as you perform it at maximal effort. Hate treadmills? Do a stationary bike. Ellipticals not for you? Try using weight machines set for the maximum you can push or pull for 10 seconds. You won't burn enough calories to lose weight. In fact, you might gain weight as you gain muscle. But your metabolic fitness will improve.
Work out until it hurts--and then rest. You can see changes in your muscle strength, your endurance, and, if you are diabetic, in your blood sugar numbers in as little as six sessions. That's just two weeks. That's just 3 hours of exercise. It's a real price to pay, but it's a small price to pay for greatly improved metabolic health.
Biddle SJ, Batterham AM. High-intensity interval exercise training for public health: a big HIT or shall we HIT it on the head? Int J Behav Nutr Phys Act. 2015 Jul 18;12(1):95. doi: 10.1186/s12966-015-0254-9. Free full text.
Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med. 2015 Oct;45(10):1469-81. doi: 10.1007/s40279-015-0365-0. Abstract.
Photo credit: By U.S. Navy photo by Mass Communication Specialist 2nd Class Michelle Kapica [Public domain], via Wikimedia Commons.