HIIT for Conditioning, Health, & Fat Loss

Energy Systems Overview

HIIT’s benefits come from how it uses and benefits the body’s energy systems. Let’s quickly investigate the body’s energy systems.

Adenosine triphosphate (ATP) is the energy currency of the body. ATP breaks down into adenosine diphosphate (ADP) and a phosphate group. This reaction produces energy that the body uses.

For low intensity, long duration efforts your body pulls energy from its aerobic energy system. This is likely the energy system you’re using now, and the one your body uses most of the time.

When energy requirements increase, however, the body has two other energy systems to meet its energy requirements.

For extremely short duration, high intensity efforts (such as HIIT), your body uses its phosphagen system. This takes advantage of the ATP readily available in your muscles. It also benefits from creatine phosphate (CP). Creatine phosphate adds its phosphate group to ADP to produce another ATP and produce more energy.

This system only lasts about 10 seconds.

For high intensity, medium duration efforts, the body uses glycolysis. This is the breakdown of carbohydrates that produces energy less quickly than the phosphagen system but more quickly than the aerobic system’s oxidation.

This system lasts for maybe a couple minutes.

HIIT: Why & What?

High intensity interval training involves high intensity, low duration efforts with rest to allow for recovery in between intervals. During the interval, you will be using your phosphagen and glycolytic systems, but during the recovery both the glycolytic and aerobic systems will be providing ATP to replenish the ATP stored in your muscle.

Because high intensity training requires all your energy systems when you consider recovery, it improves all your energy systems.

Low intensity, long duration efforts do not provide the same benefits to high intensity.

This is similar to how strength benefits endurance but endurance does not benefit strength.

If you can do 40 push-ups, doing sets of push-ups will provide little to no benefit to your bench press. Improving your bench press, however, will help increase your push-up numbers.

High intensity interval training helps your heart health and prepares you for potential events in life that require heavy breathing efforts that are longer than a 5-rep set of squats.

How to Do HIIT

High intensity interval training exercises should be low skill and low impact.

This is where CrossFit often goes wrong, as they often perform high impact and high skill movements, such as high repetition, heavy Olympic lift variations for conditioning workouts.

When and how often should you perform high intensity interval training? How long should your work to rest ratio be? How many rounds should you do? The general guidelines are below:

• 15-20 seconds hard effort
• 1:3 to 1:4 work-to-rest ratio
• 5-10 rounds
• 2-3 times per week
• perform after your lifting

The above are rough guidelines. When you begin, just as with lifting, have your rest periods be longer, perform fewer rounds, and begin with only 2 times per week.

Some examples of good exercises or machines to use include sled pushes, stationary bike, or rower.

HIIT for Fat Loss

Why does high intensity interval training help improve fat loss?

These intervals don’t take much time to do, which is one of their benefits.

After you perform one of these workouts, however, your basal metabolic rate (BMR) will increase for about 24 hours after the workout.

What does this mean? You will burn more calories performing the same amount of activity after a HIIT workout than after an aerobic workout, even if the aerobic workout burned more calories.