Just like the world of fashion, the strength and conditioning universe is subject to ever-changing trends. As exercise science and training protocols evolve, what's "hot" one minute is "not" the next. Look into the mothball-laden closet of the strength and conditioning world, and you'll see soy protein, pre-workout static stretching, and sending girls to ellipticals and aerobics classes instead of the weight room. Low-fat diets are like the polyester leisure suits of strength and conditioning: outdated, and borderline harmful. There are always emerging trends in fitness (remember Tae Bo?) and nutrition (Atkins, anybody?), and it can be confusing to sort through the tried-and-trues and hot-new-fads to find the nuggets of scientific truth—especially as scientific methods are also changing with new studies and advances in technology!
Well, the Volt team has your back. Today we are going to unpack one of my favorite S&C trends: high-intensity interval training, otherwise known as HIIT. Fitness bootcamps, Insanity, SoulCycle, P90X, CrossFit, and Orange Theory Fitness all operate under the umbrella of HIIT training. But what exactly IS HIIT? How does it work? How do you do it? And—most importantly, for athletes—is HIIT really the best way to train for your sport? Or is it just another flash in the pan?
What is HIIT?
For the most part, HIIT is exactly what its acronym describes: exercise performed in short high-intensity work intervals, followed by moderate-intensity recovery intervals. The work intervals can be as brief as 5 seconds, or as long as 8 minutes—but they must be performed at 80% to 95% of your maximal heart rate (HRmax). The recovery intervals can last equally as long as the work intervals, and should be performed at around 40% to 50% of your HRmax. You can repeat the work/recovery intervals as such for anywhere from 20 minutes to an hour.
Let’s do the math! To find your HRmax, use the old rusty approximate equation of 220 minus your age (the standard deviation for this equation is +/- 12 beats per minute (BPM), so it’s not super accurate—but very easy to use!). If you were born in 1996, your HRmax is around 202 BPM. This means that, in order to perform a HIIT workout properly, your heart rate goal should be between 162 and 192 BPM during your work intervals, and between 82 and 101 BPM during your recovery intervals.
This is the crux of HIIT: the high-intensity intervals have to be really, REALLY intense! Like, sprinting full-speed intense. Like, kinda-wanna-puke intense. If your work intervals are NOT this intense, then you are NOT performing a HIIT workout. Many people miss out on the awesome benefits of HIIT training by not performing their work intervals at a high enough intensity—don't let that happen to you!
If you don’t have a HR monitor, and don’t feel like taking your sweaty pulse in the middle of exercise, you can also use the Talk Test to determine whether your work intervals are intense enough. You should be able to eek out a few words, but not carry on a conversation. If you can say the Pledge of Allegiance without pausing for breath after every line (I pledge allegiance / to the flag / of the United States / of America), then you aren’t working at 80% to 95% of your HRmax. During your recovery intervals, you should be able to talk or recite patriotic prose quite comfortably (once you stop gasping for breath).
The duration of the work intervals, recovery intervals, and the specific exercises performed can all be varied depending on your goals: as long as you are working HARD, it’s HIIT.
HIIT training has been shown to have some major health and fitness benefits. It can increase your maximal aerobic capacity (VO2max), anaerobic fitness (which recruits more fast-twitch muscle fibers), and insulin sensitivity—all while decreasing your blood pressure, cholesterol, body weight, and abdominal fat. And unlike endurance aerobic training, which can (in very high quantities over a long time) decrease muscle mass, HIIT training won't. If you are an athlete, you can utilize HIIT training to keep up your cardiovascular fitness if you're away from the gym or crunched for time, while still maintaining your important muscle mass.
Many have thought that the caloric and fitness benefits of HIIT come from the "after-burn" effect of EPOC (excess post-exercise consumption). The theory is that, because your body is working at such a high level during interval training, it takes the body longer to recover after a workout, thus burning more calories overall than steady-state aerobic exercise (like a 30-min jog). But the actual percentage of calories burned after HIIT is only about 15% of the total calories burned during your workout—compared to the EPOC of 7% after steady-state exercise. But since we are focusing on sport performance, calories aren't our currency. Instead, let's talk anaerobic exercise. (To read a well-written research review of EPOC from a calories-based approach, check out this article from nutritionist Lyle McDonald.)
The chart above shows what approximate "exercise zones" correspond to your HR while exercising. (The zones have to do with how your body creates the energy molecule ATP—we will save a more in-depth discussion of these zones for an upcoming post.) As you can see, when you are working at 80%+ of your HRmax, it puts you in the Anaerobic Zone.
While endurance athletes work primarily in the aerobic zone (although they still benefit from anaerobic training for their sport), athletes whose sport involves short, high bursts of speed or strength work in the anaerobic zone. This makes HIIT training well-suited for training for these anaerobic sports. Especially because the main mode of exercise during HIIT isn't strength training, but rather aerobic forms of exercise (performed at a much higher, anaerobic intensity). So football players can incorporate HIIT sprint work into their training without detriment to their sport performance. Long-distance slow running might give you similar cardiovascular benefits, but HIIT training won't decrease your muscle strength—and can be accomplished much quicker. Plus, since HIIT modalities can be sport-specific exercises (think hill sprints, plyometrics, etc.), HIIT can help make you better at your sport overall.
Hill sprints are a great form of high-intensity conditioning! Sprinting uphill is advantageous for promoting a number of sport performance factors. Regular hill sprinting can help increase lower body muscle mass, improve work capacity, lower body fat, improve overall sprint mechanics, and help to increase acceleration. And let's not forget: you'll develop some serious mental fortitude depending the hill's grade (steepness), length, and the amount of rest you take in-between each bout. Love seeing the #VoltFamily get better every day!! #Repost @middwlacrosse ・・・ Hills and stadium day! So psyched for our first NCAA game this Sunday!! @middathletics
Why Not HIIT?
All benefits aside, here's my dose of tough love: just because HIIT is good for you doesn’t mean you should do it. I’m talking specifically to athletes here, or anyone training their body for a specific task or event (triathlon, 10k, etc.). One tenet of strength and conditioning science that has not grown outdated over the years is the principle of Specificity, Overload, and Progression. OK, that’s three tenets, but they act together as one to make up the core of sports-specific training. To train properly for your sport, your training must be SPECIFIC to that sport (meaning all exercises must be selected based on relevance to the movements in your sport); your training must OVERLOAD your muscles (in order to produce adaptation, the body must be challenged beyond its current state); and your training must PROGRESS as your body continues to adapt to new training stimuli. These principles are the tried-and-tested kind, and they provide the foundation for Volt programming. The problem with HIIT training is that it doesn’t always fit into the Specificity-Overload-Progression model of sport-specific training.
Let’s say you’re a collegiate distance runner. Your sport involves long periods of aerobic endurance activity, and requires great core stability and single-leg strength for athletic success. A HIIT workout involving intervals of squat jumps probably isn’t the right choice for you for a couple reasons. One, squat jumps aren't sport-specific: jumps involve force production by both legs at once, unlike running, and while squat jumps are beneficial for aerobic health and muscular strength they are not as effective for distance runners as sprints, or other single-leg HIIT movements. Two, distance athletes live in the aerobic zone: their training should involve more aerobic exercise than anaerobic. HIIT training doesn’t always equal sport-specific training.
That being said, HIIT can certainly be a useful tool in athletic development. For athletes needing to lose body fat without losing muscle, a HIIT workout as a finisher to your sport-specific strength training session can be very effective. (Check out our Volt Met Con Finishers on your daily workout page.) And athletes whose sports rely more heavily on anaerobic metabolism can utilize HIIT training to increase their anaerobic threshold. My point here is this: it all depends on your goals. And if your goal is to train on a well-rounded program designed specifically for your chosen sport, HIIT training simply may not be for you.
It’s no surprise that HIIT training is the mode du jour of today’s casual exercisers. It’s quick, effective, and fun (if you call hitting 192 bpm during your workout “fun”). Computer programmers can come home from a 10-hour workday and fit in a HIIT workout before dinner. Elderly exercisers can use HIIT protocols on low-impact exercises to help increase their cardiovascular fitness. Nursing moms can do a HIIT workout while their baby naps, and still have time for a shower afterward! But for serious athletes focused on performing well at one sport, HIIT might not be all it’s cracked up to be. I for one think this trend is here to stay, but you never know what next season will hold—even in exercise science.
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Learn more about Christye and read her other posts | @CoachChristye