Why HIIT can’t replace all of your easy cardio

Intervals are efficient, but doing every cardio session hard limits recovery and aerobic volume.

High-intensity intervals can improve VO2 max and performance with relatively little training time, but that does not make easy cardio obsolete. Hard intervals create substantial muscular, metabolic and nervous-system fatigue, so the amount you can recover from is limited—especially alongside strength training.

Lower-intensity cardio lets you accumulate more aerobic work with less fatigue. It supports adaptations such as increased mitochondrial density, capillary growth and improved fat oxidation while placing less stress on your joints and glycogen stores. Easy sessions also build the aerobic base that helps you recover between hard intervals and repeated lifting sets.

HIIT is best treated as a concentrated dose, not the entire prescription. Keep most cardio at a conversational pace and add one or two interval sessions per week when recovery and your goals allow.

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