Can you run a triathlon 1 week after you have your cast taken off?

Depends: On what was casted and reason for cast as well as your condition. You need to consult with your doctor.

What?: You didn't say what body part was casted. Regardless, my advise is no! after a limb has been in a cast even if the bone is healed the surrounding muscle/ ligaments are weakened from immobilization making them more vulnerable to injury. The bone too is somewhat more vulnerable to injury as it is still in the remodeling phase. Load bearing will help make it stronger but with gradual increased load.

Agree with Dr. Fagan: Even if your cast was on your upper extremity, triathalon is a whole body event. The upper extremity takes a large load during swimming and cycling (leaning on handlebars) events. I would not recommend participating so soon after cast removal.

Depends: Depends on where the cast was and if you are fully healed. Also depends on your risk factors. If ankle or leg, or wrist -- not worth it. If arm - maybe, though you will need it for support on the bike. Best idea -- Wait and train and do another one when you are fully recovered and trained. Good Luck -- choose wisely. (USAT Level I Certified Coach )

Not recommended: Your muscles will be a very weak from being in a cast and it may be more susceptible to trauma or injury. However, the person who can tell you for sure is your physician. Be patient.