When can i do cardio with broken fibula sprained ankle? i have airboot for another 3-4 weeks.

See details: That question needs to be addressed to the orthopedist who is treating you. That doctor has access to x rays and other clinical data that is necessary to provide a specific answer for you. As a rule, you can resume full activities when the fracture is totally healed and that is about 6 weeks.

Ankle fracture: Typically one has to wait 6 weeks for the fibula to heal. Before the airboot comes off a repeat xray has to confirm that the fibula has healed. Once that happens, then one has to be able to walk without any pain before a determination can be made about any cardio. If you access to the pool, one can start doing pool exercises much sooner since you are in semi-weightless environment.