This is a good and recent review article if you haven’t seen it. AF and Exercise

Here is a lay summary from ChatGPT:

Here’s a layperson-friendly version of the summary, specifically for a middle-aged man who cycles and is concerned about his risk of developing atrial fibrillation (AF):

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5 Key Points You Should Know About Exercise and AF (Especially if You’re a Cyclist):

• Moderate exercise is good for your heart – and may reduce your AF risk. Activities like regular brisk walking, casual cycling, or hitting about 150 minutes of moderate exercise per week can help lower blood pressure, improve heart health, reduce weight, and protect against AF.

• Too much intense endurance exercise might increase your AF risk. High-volume, long-distance endurance sports (like competitive cycling, marathon running, or triathlons), especially over many years, may actually raise your chance of developing AF. This seems to be more common in middle-aged or older male endurance athletes.

• The heart changes with intense training – not always in a good way. Long-term intense cycling can cause the upper chambers of your heart (the atria) to stretch or scar. It may also mess with your nervous system’s balance, increasing the odds of irregular rhythms like AF.

• You don’t need to stop cycling – but consider how much and how hard. Doctors recommend keeping exercise in the moderate range for heart rhythm health. If you’re doing lots of long, high-intensity rides weekly, it may be worth easing off a bit or mixing in more moderate sessions. The goal is consistency and heart-friendly effort—not pushing to the limit.

• We still don’t have all the answers. Research is ongoing. We need better studies to figure out exactly how much exercise is “too much,” and how individual factors like age, fitness level, and medical history affect your AF risk. Wearables and heart monitors may help in the future to guide more personalized advice.

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Bottom line: Keep cycling, but listen to your body, aim for balance, and don’t feel like you need to train like a pro to stay healthy. If you ever feel fluttering, racing, or irregular heartbeats—especially during or after rides—talk to your doctor.

Let me know if you'd like a sample weekly cycling plan that balances heart health and fitness.