I've spent the last 11 years limiting the intensity of my exercise out of necessity, and I've lost all my fitness as a result.
Some, not all, I venture to suggest, because if you’d lost it all then low-medium intensity cycling would be beyond you.
Someone obviously thinks they know more about my exercise than I do.
I was under the impression that I hadn't been able to exercise at much above about 100bpm for over a decade, with no cycling at all for over two years. Cardiologists used to keep telling me that atrial fibrillation was no reason to stop exercise (and it isn't, for some patients) but every time I resumed I ended up back on an ambulance. You would have thought that after 10 such trips they would have got the message, but apparently not. The sudden cessation of cycling altogether occurred because I got frustrated at 8 years of losing fitness, and tried to return to training nearer to the way I used to. Just prior to this I was still able to walk 12-15 miles a day on the Oxfordshire Way provided I kept to a gentle pace, now my limit is about 2 hours gentle walking a week at 80-85bpm, which just enough to fetch groceries from Tesco.
The simple bottom line is that the maximum level of exercise I can tolerate is lower than what it takes to maintain my fitness, and I think that the reason for the fitness loss is that it takes intensity not duration to maintain fitness.
the advice I received from a cardiologist was that the overall health benefits of cycling, including age-appropriate spells of intense effort, so vastly outweigh any specific cardio risk that comes with it
What are you trying to do, contradict me with my own argument?
The Schnohr study I quoted says that mortality rate is reduced more by increasing intensity than by increasing duration. The large volumes of exercise that come with chronic endurance training are a risk for developing arrhythmia.
ACSM Guidelines for Exercise Testing and Prescription recommend just 500-1000 METminutes a week for optimum health, a lot less than a typical cycling enthusiast. At my most enthusiastic I was averaging 6000-8000 METmins/wk.
cardio risk isn’t worth worrying about except in the case of a person with specific health conditions.
Specific health conditions like atrial fibrillation and a history of chronic overtraining, you mean?
The chap was a keen cyclist himself
John Mandrola is a keen cyclist, and an atrial fibrillation patient. He's also a consultant electrophysiologist (a cardiologist who specialises in treating heart arrhythmias).