I’ve long stated here that I count cycling as a major health benefit, both physically and mentally, and the more time goes on, the more strongly that idea is supported by the evidence of my own decades of self-monitoring.
Still, I had not ruled out some possible downsides. Those include development of an irregular heartbeat (which I’ve experienced under extreme training loads, gone when backing off).
But what I had not considered was low-level arteriosclerosis. Recently I had a CT heart calcium scan* score of 91 which is the 88th percentile for my age range (99 is the worst). That was a bit shocking and disappointing; I was expecting something like 0 to 5.
* I had the scan done because during my concussion, a CT scan of my head showed calcification in two major arteries in my brain.
So I saw a cardiologist and had my carotid arteries and heart scanned. They showed low level arteriosclerosis. However, my femoral arteries, listened-to by the cardiologist, have no auditory evidence of any issue.
The cardiologist pointed me to a study which suggests that the trauma of high volumes of intense exercise can induce low-level arteriosclerosis. As I understand it, the volume of blood being pushed through with great force in essence can irritate the artery walls, and this causes low-level inflammation, which leads to arteriosclerosis.
Update: coronary artery calcification might well be the result of magnesium deficiency and/or Vitamin K2 deficiency in many cases, those deficiencies preventing excess calcium from going into bones and allows it to build up within the body, including arteries.
Still, one gets all the upsides of exercise, so this theoretical downside concerns me little.
Conclusions: Participants in the >2000 MET-min/wk group had a higher prevalence of CAC and atherosclerotic plaques. The most active group, however, had a more benign composition of plaques, with fewer mixed plaques and more often only calcified plaques. These observations may explain the increased longevity typical of endurance athletes despite the presence of more coronary atherosclerotic plaque in the most active participants.
My minimum daily workout is about 1000 calories (kilocalories) at the crank = ~4000 KCal physiologically, assuming a physiological efficiency of 25% (I am 99% sure that I am at 25% or even 26% or 27%, based on the long habit of calculating calories to the gram of food, and my SRM power meter with at most 1% error).
MET (metabolic equivalent) = kcal / kg / hours
Note that "weight in kg" is just plain silly as it has a very large margin of error—8% body fat or 28%?
If I have this right, my base workout is as follows:
(4000 kg / 80 kg / (84 min/60 min/hour) ) = 35 MET hours = 2100 MET minutes per week (MINIMUM)