How Quickly Do You Lose Cardio Fitness When Injured?

Getting injured is bad enough. Watching your fitness disappear because you can't train, makes it 10X worse.

VO2max starts dropping within the first week of inactivity. After four weeks, you can lose up to 20% of your aerobic capacity. Adaptations that took months to build, gone in a matter of weeks.

The standard advice is to do low-impact work your injury allows (e.g. swimming, cycling) which is good advice if your injury allows it. But what if it doesn't? And what if you wanted to optimise your recovery?

How IHHT can help for injury recovery and rehabilitation

IHHT (Intermittent Hypoxic-Hyperoxic Training) is an Oxygen Therapy protocol that triggers cardiovascular adaptation without any physical exertion. You sit in a chair, breathe through a mask for 40 minutes, and your body does the work.

Sessions alternate between low-oxygen air (around 10–12% O2, simulating altitude) and high-oxygen air (30–40% O2). The hypoxic phase sends a stress signal that drives the same biological responses as hard aerobic training: mitochondrial growth, new capillary formation, increased red blood cell production, better oxygen efficiency. The hyperoxic phase that follows floods the tissues with oxygen, reinforcing those adaptations.

It's the exact same mechanism why pro athletes train at altitude. And it's great for maintaining fitness during injury, because it doesn't requires you to move.