Why Going Slow Makes You Go Fast
Simple explanations to important changes in physiology
To explain how low intensity exercise makes you faster, I’m going to cover:
The body’s 2 main energy systems
Fat burning vs. Carb burning intensities
What Mitochondria are & how Z2 influences them
Lactate and what happens when our muscles fatigue
The 2 Main Energy Systems
Aerobic: Zone 1 and Zone 2
Anaerobic: Zone 3, Zone 4 and Zone 5
*There are technically 3, with 2 types of Anaerobic, but in this context we can simplify to just Aerobic vs. Anaerobic
Aerobic means “with oxygen” and is done at a conversational pace (or easier). Muscles have full supply of oxygen to function as needed.
Anaerobic means “without oxygen.” Breath is labored. Muscles don’t get as much oxygen as they need, so the body starts burning carbs for fuel (this is called Glycolysis).
Key distinction between Aerobic and Anaerobic:
Exercising in Aerobic zones improves Anaerobic zones.
Exercising in Anaerobic zones DOES NOT improve Aerobic zones.
When we go slow, we improve all intensities of fitness.
When we go fast, we only improve high intensity.
This is the simple answer to why going slow helps you go fast.
Now we’ll dive more into the science of fat vs. carb fueling, mitochondria and lactate.
Fat Burning vs. Carb Burning
Here are 2 visuals that help understand how the body burns Fat at low intensity and Carbs (glucose) at high intensity.
Visual 1: relationship between Fat burning and Carb burning as intensity (and Heart Rate) rises.
Visual 2: brief explanation of how the body functions differently at low intensity (Z1 & Z2) vs. moderate/high intensity (Z3, Z4 & Z5).
Howard Luks has a lot of great info on Z2 in the context of longevity and performance.
Mitochondria are the “powerhouse of the cell” and a key indicator of overall health. The healthier the mitochondria, the healthier the person.
Aerobic exercise (Z1 and Z2) increases our number of mitochondria and improves two important functions:
their ability to use fat as fuel
their ability to shuttle lactate (and use it as fuel)
Metabolic flexibility = ability to use both fat and carbs as fuel
Mitochondria dysfunction = inability to use fat as fuel; results from sedentary lifestyle/no aerobic exercise and manifests as Type 2 Diabetes, heart disease, etc.
Aerobic exercise helps increase our ability to burn fat as fuel (via mitochondria).
Lactate is a byproduct of the body using significant carbs (glucose) as fuel.
It is accompanied by a Hydrogen ion (this is what causes muscle fatigue).
Building a strong Aerobic base helps extend the intensity range where we trigger carb burning, and get a subsequent rise in lactate.
In athletes with a strong aerobic base (and healthy mitochondria), mitochondria can shuttle lactate back into the cell to be used as fuel.
In athletes with limited (or no) aerobic base, mitochondria function is impaired, lactate (and Hydrogen ion) accumulates and muscle fatigue becomes insurmountable.
Having a well trained aerobic base lets us work at higher intensity before switching from carb to fat burning.
This delays lactate accumulation while also improving our ability to maintain effort with lactate present.
Aerobic (Z1 & Z2) exercise improves Anaerobic fitness (Z3, Z4 & Z5). The inverse is not true.
Aerobic exercise increases our ability to use fat as fuel at higher intensities
When the body switches to relying on carbs for fuel, lactate (w/ accompanying Hydrogen ion) accumulates in the blood. This causes muscle fatigue.
Athletes with well developed Aerobic fitness (and well functioning mitochondria) can shuttle lactate into muscle cells and use lactate as fuel, and minimize effects of fatigue
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