High intensity interval training (HIIT) is a well-documented strategy for improving health, building lean muscle, burning fat and increasing endurance. A HIIT workout alternates between short work intervals (70 to 90 percent max heart rate) and rest periods (60 to 65 percent max heart rate).

One major benefit of HIIT? Some research has indicated that HIIT can also help exercisers reverse the progression of certain chronic diseases such as Type II diabetes. Another great benefit of HIIT is a significantly reduced time commitment. Shorter workouts leave more time for other obligations.

However, customizing HIIT to the individual is essential to realize these benefits.

The Personal Metric

Effective and safe HIIT with a heart rate monitor is based on the very personal metric of heart rate rather than a cookie cutter metric of volume loads, time or sets.

Using a heart rate monitor correctly, you can turn any workout routine into a HIIT session, from a treadmill workout to strength training with free weights.

Many interval trainers put their clients through a series of predetermined drills or numbered sets. This can work great for some advanced exercisers, but for a beginner or even a long-time exerciser unused to HIIT such a routine may actually be harmful. Driving the heart rate too high and keeping it there too long can spike the production of stress hormones, tax the immune system, and increase the chance of injury.

Rather than building the cardiovascular system, overdoing these workouts can be detrimental to heart health and a tax on the endocrine system.

Heart Rate Monitors

Monitoring the heart rate is the best way to optimize your HIIT workout and customize it to individual fitness levels. Using a state of the art monitor is essential for an accurate reading.

Suunto (a sister company of Precor) makes a great product with a range of styles from a basic wearable belt to an ultra-modern watch with all the bells and whistles. The data-obsessed will have a lot of fun with this cool tool, which can track weather reports, sync with apps and record calories burned and miles trekked. You can even sync your Suunto with the Movescount app to join a worldwide training community.

Some concept training goes a long way in helping people to train with a device. Though HR zones and recovery times are built into some of the settings, to get an individual number your client should take their heart rate upon waking in the morning, before any strenuous activity or caffeine. This resting heart rate will be the base rate on which optimal HIIT zones are built.

Maximum Heart Rate Formula

Help your clients personalize their monitor's manual settings to reflect their body's personal resting heart rate. The device will crunch the numbers for them, but it's always helpful to run through the most updated formula. Originally, “220-age” gave a good approximation for the client's maximum heart rate (MHR). Also keep in mind that formulas only provide an approximation in terms of the amount of calories your body is burning.

Now, however, the Journal of the American College of Cardiology published a study recommending “208 – (age * 0.7)” as a more accurate measure for maximum.

(208 – (age * 0.7)) x 70 percent = low zone (208 – (age * 0.7)) x 85 percent = high zone

The optimal HIIT zone will be between the low and high zones. While a seasoned athlete may work up to the 90 percent range, the average exerciser should keep below the 85 percent range.

Treadmills for HIIT

A treadmill is the perfect place to begin working with these numbers, alternating hill walking, slow jogging with intense sprints and slow walking (active rest). Note that some individuals will not need to sprint in order to drive their heart into the upper range; in some cases a steep hill or even brisk walking will be adequate.

The shorter intervals (15 to 20 seconds) will actually require longer rests, as the shorter burst allow a greater expenditure of energy. While the rest period will typically have a ratio of 2:1 and even 3:1 for beginners, don't rely on time but, rather, on heart rates instead.

Active rest periods should last until the heart rate is safely back in the 60 to 65 percent range.

Mixing it up and keeping the intervals varied works best for building muscle and conditioning the cardiovascular system.

Once people are comfortable using their device and transitioning between intervals, active rest and more steady intervals, they can design virtually any kind of workout to utilize HIIT principles.

Bodyweight Training

Bodyweight moves such as lunges, squats, jumps and planks alternating with sprints, jumping rope and specialized foot work are excellent workouts and can be adapted to challenge a varied group.

Group training will look a little different than a synchronized class because everyone will be following their natural rhythms. Because it is somewhat self-led, this structure will allow trainers to work closely with individuals on essentials such as form and proper alignment.

Together with a warm-up, a HIIT workout should wrap up quickly, in about a half hour. If this seems too short, add in a movement recovery session that focuses on functional balance, core and flexibility training.

We're excited about personalized HIIT sessions and can't wait to hear what workouts you create. Let us know some of your favorite HIIT workouts!