The benefits of interval training as opposed to long endurance training.
Long Endurance Training
With continuous long endurance training such as long distance running (on the road or on the treadmill), you are routinely forcing your body to perform the same cardiovascular challenge, by repeating the same movement, at the same rate, over and over again, without variation, and without rest, which is unnatural for your body. Yet nature has designed your body to adapt to whatever environment you encounter. If you ask it to perform this activity repeatedly and routinely, it will gradually change the systems involved to meet the challenge more effectively.
But what adaptive changes does this activity cause?
The body’s primary adaptation will be to become more efficient at light, long, continuous, low output as you are asking it to repeatedly go non-stop for long distances, against low resistance, at a relatively slow speed.
One of the ways that your body adapts is by gradually rebuilding your heart, lungs, blood vessels and muscles as small as possible but still have the minimum energy required.
Forced, continuous, endurance exercise induces your heart and lungs to ‘downsize’, which will still allow you to go further, more efficiently, with less rest and less fuel.
Short bursts of exercise tell your body that storing energy as fat is inefficient, since you never exercise long enough to utilise much fat during each session. Carbohydrates, which are stored in muscle (as glycogen) rather than fat, burn energy at high rates. Exercising for short periods will use the glycogen and burn much more fat after exercising while you replenish the glycogen. This is based on Excess Post Oxygen Consumption or, in other words, the ‘after burn’ effect.
This can be explained as while exercising at a higher intensity, your body will use a lot more of its glycogen stores for energy, which will need to be replenished after exercise. This replenishing process requires energy and as the demand upon the body is now no longer high, it has time to utilise the Aerobic Energy System, which breaks down fat stores so you continue to burn fats for longer after a high intensity workout.
Take a look at these 2 examples:
Session 1: You do 20 minutes on the exercise bike at continuous pace with no rest. Your heart rate is a constant 60% of your maximum heart rate.
Session 2: You do 20 minutes on the exercise bike in numerous short bursts of 15-45 seconds while resting (recovering) in between. Your heart rate fluctuates between 60% and 80% of your maximum heart rate.
What happens in each session?
Session 1: You burn a total of 150 calories. 60% of those calories would come from fats and 40% from glycogen. This means you burned 90 calories from fats and 60 calories from glycogen.
Session 2: You burn a total of 250 calories as the demand is much greater. This time only 40% of those calories would come from fats and 60% from glycogen. This means you burned 100 calories from fats and 150 calories from glycogen.
What does this mean?
In the same amount of time, i.e. 20 minutes, you burned 100 more calories in session 2 plus more calories from fats even though the percentage using fats decreased. Session 2 also depleted your muscle glycogen, meaning you need to replenish your glycogen stores and repair muscles after your workout. What do we use as energy to do this? Fats! So with session 2, you get the ‘after burn’ effect up to 24-48 hours after your workout.
After a few months, your body stops storing fat because it simply doesn’t need it. This is the opposite of conventional advice, which tells you to burn fat during exercise. But this only makes matters worse. This tells your body to make and store more fat so you’ll have something to burn during your next workout. This is why so many people get frustrated when they don’t see results after months of spending hours at the gym.