We exhaust ourselves when we work too hard to rest and too gently to grow.

coach Zone 2 training stimulates the protein PGC-1alpha to build new mitochondria, making muscles highly efficient at burning fat instead of limited sugar.

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Quiz

Which cellular structures, often called the powerhouses of the cell, multiply during Zone 2 training?

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Quiz

What is the primary fuel source your body burns when exercising in Zone 2?

coach Wearable heart-rate data helps athletes avoid the unproductive middle intensity of training.

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Quiz

What is a major downside of spending too much training time in Zone 3?

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Quiz

Why is Zone 3 often referred to as the 'gray zone' by sports coaches?

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Fun Fact

Mitochondria power: Consistent endurance training can double the volume of mitochondria in your muscle cells in just six weeks, supercharging your energy.

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Quiz

What type of metabolism does your body rely on when exercising in Zone 5?

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Quiz

What is the term for the maximum rate at which your body can consume oxygen during exercise?

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Glossary

maximum heart rate (noun)
The highest number of beats per minute that a person's heart can safely reach during exercise. In 1970, researchers William Haskell and Samuel Fox developed the classic formula to estimate this physiological limit.