My best buddy and "twin separated at birth" texted me from the hospital yesterday. His watch detected an irregular heartbeat, so it contacted 911. He was helicoptered from the boonies to UCSD Medical.

This morning, he's "converted to sinus rhythm". A relief. Looks like classic atrial fibrillation, the bane of us aging endurance guys.

With all the riding I do, atrial fibrillation is the one thing I worry about the most. Risk increases with total training volume.

When exercise becomes risky for AF:

• > 2000 lifetime hours of exercise
• > 10 hours per week
• male

Check, check, and check.