I am a 44 year old male that have been a bit inactive the last years and am looking to get more fit. I have always been fond of running as a way to get some cardio, fresh air and reduce stress, but I am starting to get worried about my knees. One problem in this respect is that I am quite heavy (100 kg) although I have not much body fat.
I recently read "Your New Prime" by Craig Cooper. He is strongly opposed to long distance running for men over 40. In fact he advocates the 5k as an ideal bench mark distance as opposed to the marathon. That is if you can run the 5 km fast then you are healthy. If you can run the marathon fast you are not healthy. His reasoning is as follows: long distance running reduces musclemass and lower your testosterone levels. This is exactly the opposite of what you need since your muscle mass and testosterone levels decreases each year after 40.
This seems logical and plausible. I have verified his claims about muscle loss from age and long distance running from several other sources. However his suggestion about training towards the 5 k is not something I have found elsewhere. It sounds reasonable and practical but I have one worry: the force on knees and other joints increases with the speed. Not sure what is most dangerous for knees though: high volume or high intensity? The expression is high mileage knees, but on the other hand I would be worried about running a 100 m as fast as possible with little warmup in my age but not 20 years ago.
He also like so many other advocates high intensity training. There are lots of studies done in the last years showing how time effective this. Which is great, but high intensity sound possible dangerous. I have not seen any studies of possible harmful effect of hit such as possible irregular heartbeat.