H.I.I.T. Explained – How To Maximize Fat Loss

Choose Your Conditioning Wisely

So that we better understand how to train for maximum conditioning and fat loss, we need to understand exactly where the body gets the energy it needs to condition in the first place.

Very simply, the body draws from a pool of ATP (or Adenosine Triphosphate) for ALL of its energy needs, regardless of the intensity or duration of the exercise. It has several pathways that it uses to make ATP, but it’s important to note, that regardless of how it’s made, the body pulls from the same “pool” (or reservoir) of ATP.

What is ATP?

The vast majority of chemical energy in our cells is used to generate ATP, which yields its energy through the loss of a phosphate, becoming adenosine DI-phosphate. It’s a complicated process, but for our purposes here’s what you need to know: at low levels of energy demand (easy breathing, low heart rate) – you watching this video, for example – ATP is provided primarily by the “aerobic” oxidation of fatty acids and other fuels.

The process is regulated to supply the small amount of ATP needed for energy use at this low level of activity. As long as energy demands remain low, the aerobic/oxidation pathway’s steady ATP deposit into the ATP pool is enough to supply the body with the energy it needs.

ATP to ADP

However, if high levels of energy are suddenly demanded – like if you were attacked by a tiger while watching this video – the small amount of available ATP is very quickly depleted. The high energy demands make heavy, quick withdrawals from the ATP pool, turning it into ADP, and the ADP is then quickly re-synthesized (back to ATP and into the pool) from the breakdown of creatine phosphate (CP).

But these on-hand stores (from pre-stored ATP and CP) are depleted in seconds as the intense exercise creates a surge of energy demand that exceeds the low level of production by the aerobic processes, i.e. the intense exercise makes withdrawals from the pool faster and in greater amounts than the aerobic/ oxidation pathway can deposit. This requires that energy production be stepped up to refill the pool faster, and in greater amounts than the aerobic/oxidative system can manage.

Glycolysis to the Rescue

The solution is found in glycolysis, the first part of the process where carbohydrates are used to generate ATP. Muscle cells use glucose in the cell as well as glucose released from the breakdown of stored glycogen in the muscle (glycogenolysis) to produce relatively large amounts of ATP quite quickly. If the intensity level remains high, this pathway can continue to supply enough ATP to the pool to meet energy demands for upwards of two minutes. However, if the intense exercise continues longer than a couple of minutes, the ATP production by this pathway will be exceeded by the energy demand

Since both the immediate energy stores (stored ATP & CP) and glycolysis do not require oxygen, they are referred to as “anaerobic.” But the pathways can operate in this fashion in the short term only; we cannot train in longer time periods at these levels of intensity. Glycolysis runs down quickly, and it produces lactate that builds up, as it cannot be converted to energy fast enough by the slower aerobic pathways.

Ultimately, the oxygen-requiring pathways must complete the oxidation of carbohydrates and supply sustained energy from other substances such as fatty acids. The aerobic pathways ramp up over an exercise session to higher production levels and can produce ATP at a moderate rate nearly endlessly.

Energy Systems Explained

Now, there are several things to understand about how Energy System Pathways work together. First, they all fill the same ATP pool that the body draws from for its energy needs. Second, the energy pathways overlap. For example, when intense exercise begins and is sustained for a period of time, such that the aerobic/oxidative pathways cannot supply the pool with sufficient amounts of ATP, the aerobic system does not shut down and stop just because glycolysis is needed to supply the pool with adequate ATP.

On the contrary, the aerobic system ramps up and runs at capacity along with the glycolytic system to help supply the ATP pool. These pathways function together. Aerobic production fills the immediate “anaerobic” energy supply of stored ATP and CP. Rapid glycolysis during periods of high demand refills this same pool (400m run). Glycolysis under lower demand (jogging) fills the pool but the lactate produced is processed by the aerobic pathways instead of building up. More intense exercise simply has the potential to outstrip our ability to keep up the readily usable ATP supply, as well as our ability to deal with the lactate produced under anaerobic conditions. This is why your all-out sprint turns into an increasingly uncomfortable fast run and then eventually into a jog.

What is High Intensity Interval Training (H.I.T.T.)?

This is fairly easy to understand when the intense exercise is constant and continual in duration. However, what happens when short, high intensity intervals are used, commonly referred to as HIIT?

HIIT intervals will use components of all three primary energy systems. The amazing thing about HIIT conditioning in the anaerobic-glycolytic pathway is that your body will burn an enormous amount of calories, both during and after exercise, because your metabolism remains elevated for up to 24 hours after the training. There will actually be an up-regulation of aerobic, anaerobic, and ATP enzyme activity, meaning that all 3 energy systems will become more efficient at generating energy and burning calories.

Very simply, training primarily in the anaerobic-glycolytic pathway makes ALL the energy pathways more efficient, including aerobic oxidation because high-intensity exercise requires high output of all the energy systems. But this is not a two-way street. Training aerobically for endurance will not lead to equal up-regulation of stored ATP and CP or anaerobic glycolytic enzyme activity because aerobic training does not stress these systems. Training at high intensities, for short intervals, with recovery periods, is king when it comes to conditioning.

H.I.T.T. Explained – How To Train Using HIIT

So how do we do this practically? Low Impact, Low Skill. Something like pushing a prowler or sled, rowing on a C2 rower, swimming, or hard sprints on an exercise bike like a Rogue Echo or Assault bike.

We like to do hard sprints in the 15-20 second range, followed by nearly complete recovery (which at first might put you in the 2 min range, but eventually can probably be reduced to 45-60 seconds of rest) so that you end up somewhere in the 1:3 work to rest ratio (so 15 seconds on, 45 seconds off, or 30 seconds on, 90 seconds off).

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