If you pick up any fitness magazine these days, you’ll find that the old cardio prescription — 30–40 minutes of moderate-intensity running on a treadmill — is no longer the king of the fitness kingdom. While this basic form of exercise certainly has its merits, a growing body of research is steadily pushing recreational athletes toward a near-exclusive reliance on high-intensity interval training, or HIIT, as the main mode of cardio.
High-intensity interval training involves pushing yourself to near 100 percent effort on your chosen activity — running, for instance — in shorter, segmented bouts broken up by active recovery. In a typical HIIT running workout, you’d perform a short warm-up and then move into an all-out sprint for 30 seconds. This maximum effort would then be brought back to a slow jog or walk for a full minute. After that, the cycle would be repeated a number of times, usually for a span of 15–20 minutes total — a much more efficient use of your workout time than the endless treadmill runs of yesteryear.
But time efficiency isn’t the only gold star in the HIIT column: The productivity factor is crucial. Consider the basic fact that higher intensity exercise will almost always be better for you — it activates more fast-twitch muscle fiber, it burns more stored glycogen (sugar), and it nukes more calories. Well, if you perform say, ten 30-second sprints at 95% effort, that’s a total of five minutes that you ran at that pace. If you strung those all together, that’d make for a pretty impressive pace. But remember, you’re also working during your “rest” periods, even if at a slower pace, so the total impact of work performed is far greater than if you just took a leisurely jog for a few miles at a slower pace.
The research done on HIIT in the past few years has caused an upheaval in gyms everywhere, causing workout junkies to rethink their usual approach to cardio. Here are a few of the top reasons that HIIT may be the new cardio king.
HIIT makes you faster
Distance running traditionalists may scoff at the entire idea of HIIT, reasoning “if it ain’t broke, don’t fix it.” Well, just because it ain’t broke doesn’t mean it can’t use a tune-up.
A study performed at the University of Copenhagen (Denmark) showed that runners who used a form of HIIT shaved an average of one full minute off of their 10K times. The sprint-interval group decreased its total weekly mileage from 34.2 to 20.6 miles and added 2–3 sprint workouts per week. These workouts involved running eight to twelve 30-second sprints at roughly 95% effort with rest periods of three minutes in between. After nine weeks, this group was rewriting personal records left and right. The study author indicated that HIIT may increase levels of a protein that regulate the potassium that accumulates around muscle fibers and causes fatigue, but the cause isn’t nearly as impressive as the result. The bottom line is that HIIT can make you faster — even at longer distances.
HIIT makes you leaner
Whether you’re a weekend warrior or a PowerBar-sponsored elite athlete, there’s nothing wrong with getting a little leaner — and HIIT is in a league of its own when it comes to burning fat.
One study from Laval University (Ste-Foy, Quebec, Canada) reported that a 15-week HIIT program led to significantly more body fat loss than a 20-week continuous steady-state endurance program, despite the fact that the steady-state program burned about 15,000 calories more than the HIIT program. In a similar study conducted at East Tennessee State University, researchers found that subjects who followed an 8-week HIIT program lost 2% body fat, while those on a continuous steady-state treadmill program had no decrease in body fat.
How does HIIT do this? By significantly increasing your body’s resting metabolism following exercise, a phenomenon known as excess post-exercise oxygen consumption (EPOC). In other words, you continue to burn calories after working out, even when you’re home catching up with your DVR.
Another way HIIT works to keep you lean is because it focuses on your body’s fast-twitch muscle fibers, which have the greatest potential for strength and growth. This means more muscle is grown through this kind of training. Conversely, extended distance running can lead to muscle loss, as the body eats through glycogen and fat stores and goes on the hunt for more protein fuel (muscle). It’s the difference between sprinter’s legs, which are generally thick and muscular, versus marathoner’s legs, which tend to be leaner.
HIIT makes you healthier
In addition to the boosts in performance and body composition, research on HIIT is yielding some impressive potential health benefits.
In a study published in the March, 2009, issue of
The Journal of Strength and Conditioning Research, HIIT was shown to produce favorable changes in cholesterol in subjects that participated in an eight-week study. Another study, published in the
BioMed Central Endocrine Disorders Journal, showed HIIT to substantially improve insulin sensitivity in young men, heralding this type of training to be a potential method for prevention of Type II diabetes.
A HIIT for athletes
To get the most out of HIIT, try implementing 1–2 sessions per week to your usual workout schedule (see sample workout below). We know that the legions of long-run loyalists out there may be skeptical, but the facts are clear: These short-burst workouts train your body to perform better, look better, and last longer, helping you to be a standout, long after the competition starts to fade.
HIIT newbies, start here
Venture into high-intensity training with this sample running workout:
| Intensity | Duration |
| Walk | 2 min. |
| Slow jog | 2 min. |
| Sprint* | 10 sec. |
| Slow jog | 1 min. |
| Sprint | 10 sec. |
| Slow jog | 1 min. |
| Sprint | 10 sec. |
| Slow jog | 1 min. |
| Sprint | 10 sec. |
| Slow jog | 1 min. |
| Sprint | 10 sec. |
| Slow jog | 1 min. |
| Sprint | 10 sec. |
| Slow jog | 1 min. |
| Walk | 2 min. |
| TOTAL | 13 min. |
|
*For all of your sprints, aim for a speed that is anywhere from 75–95% of your max. As you progress, extend the duration of your sprints, eventually aiming for 30 seconds, or add additional intervals to your workout.
HIIT nutrition
Wondering what‘s the best way to fuel up for and recover from HIIT workouts? Well, the nutrition strategies for a HIIT training protocol would depend on training outcomes, and the frequency and intensity of the workout. In general, if the goal is to lose weight and improve body composition, certain aspects of sports nutrition should be employed. These are as follows:
- A calorie deficit (500 calories less per day to lose about 1 lb of weight per week)
- Aim for small, frequent meals to help keep your energy level up throughout the day
- Consume a lean protein source with every meal
- Have plenty of fiber on a daily basis, but not too much before a HIIT workout. (Aim for 20–35 grams per day)
- Do not fear carbs! You may not need as many carbs as your endurance runner friend, but extreme carb-deficient diets are not necessary or healthy. (2–4 grams per lb body weight per day is a good starting point)
- A low fat, but not non-fat diet, focusing on more healthful fats such as omega 3s
- Drink plenty of fluids (start each day with a large glass of water)
- Adequate post-workout nutrition, which includes a source of carbs and 15–25 grams of protein within 1 hour after your workout
- Don’t diet! Remember that you need to make long-term behavioral and nutritional changes that will last a lifetime. The goal should be to sustain a healthful weight and optimal nutritional status, rather than a short-term “diet” focus
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