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Physiology

Humans aren’t machines—we’re much more complicated. Exercise physiology involves changes in the body from exercise and rest.

From anaerobic threshold to environmental acclimatization, from FTP to PGC-1 alpha, we explore the science of human performance.

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Physiology > Endurance Training

An ultra-runner summits a mountain peak with the sun low in the sky behind him

An Ultra-Athlete’s Guide to RPE

An athlete’s rate of perceived exertion, or RPE, is one of the most underappreciated metrics. For ultra-athletes who are closely in touch with their bodies and minds, working with RPE is an essential component to training and racing.

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