Let’s go for over 45’s. It was going to be over 50’s but I’m not there yet. 45 isn’t really that old at all (neither is 50), However, we can’t escape from science, and if you’ve reached this milestone or further, you’ve probably noticed that your body doesn’t quite do as it’s told (or certainly what it was told to do 20 years ago). The rules of training change a little as the years go by!