Yes I had already come across the news that marathon sessions are proving to be bad. When I do steady state cardio I do it only for 46 minutes including warmup & cooldown.
What raised the question in my mind is that when I'm sitting on that killing machine (recumbent cycle) I fear and going all out, both cardiovascular system and the thigh muscles are in top action, so I thought the latter might be similar in effect to the leg press weight training.
I haven't read any articles on HIIT raising blood pressure that high.
However, I'm not sure they really have their arms around the issue yet. For example, did you know that 1/3 of strokes occur when people are defecating? It turns out squatting can raise blood pressure significantly even w/o weights.http://news.bbc.co.uk/2/hi/health/1399412.stm
Our bodies were born for walking and, of course, can handle significant running, climbing and other activities that involve our own body weight
. As mentioned about, you can go too far with this of course.
Now, before, I say anything else, I should point out that cardio is actually prescribed, if you will, by one study on weight lifters. A little cardio done after weights preserved arterial function:http://www.ncbi.nlm.nih.gov/pubmed/17872406
But that doesn't answer your question about intensity. I guess my only comment is that I have not seen any studies showing high intensity cardio an hurt or age arteries and I doubt they will find any since this is part of our past. Futhermore, this is verifed, I think, by the fact that a number of studies show that higher intensity cardio improves arterial parameters in many cases:http://heart.bmj.com/content/78/1/22.short
"Non-invasive measurement of endothelial function: effect on brachial artery dilatation of graded endothelial dependent and independent stimuli."http://cardiovascres.oxfordjournals.org/content/67/1/161.short
"Moderate vs. high exercise intensity: Differential effects on aerobic fitness, cardiomyocyte contractility, and endothelial function"