I don't dwell into running knowledge deeply nor know much about training, in fact I hated training when I was in my teens. I only know that if I don't push myself to do sprints or strides more often, soon I won't be able to do so. Sprints and strides used to be my favorite as it was second nature to me then. Now it is so hard, especially with age and a much-weakened core.
I am lucky to be living by a short segment of the super long Bund in Shanghai, which has a continuous stretch of park and pockets of tiny parks all over. And directly beside where I live, is a tiny park surrounded by a circular road that is slightly less than 1km, which I do my 1km intervals. There is also small stretch of straight polyurethane track paths (straight path covers approx. 300m) with roof beside (nearby with toilet and free drinkable hot and cold water provision) some 3km from where I live, which I do my 200-250m intervals. Along the long stretch of continuous park, there a few bridges which I can use to do upslope sprint intervals. If I run towards the famous bund direction, I will reach the suzhou creek some 9km away. If I turn the other direction, it will be a 10km run reaching another huge bridge crossing the river and a loop will be a 20km or HM for me.
As I mentioned, it is getting very tough for me and the 2:1 ratio is quite impossible for me due to slow recovery time. For the 1km intervals, I do a 1:1 ratio. As for the 200-250m, it takes approx. 40-45sec, and I will just walk back to the starting point (approx. 3-4mins) before starting again. Sometimes, I will rest a bit more to catch my breath. Normally I will prefer to see my HR drop within 120bpm before starting again.
One obvious difference now is the ability or rather lack of ability to garner the power whenever I want. Now that I have past the half-century mark, even when I could garner the power, it will be just a very short burst. For example, in my 200m sprint intervals, I will notice the deterioration in my form, core stability (hold the core upright and let the legs cycle naturally, good example is Asafa Powell) and drop in cadence around 100m mark and more by 150m mark. It is what it is, hence, the need to keep doing more of this to slow down the deterioration. And the need to do more strength training, which I am rather lazy to do so.
Once again, thank you for inviting me to take up cycling. I am considering an indoor cycling simulator for adverse weather (rain and punishing summer heat), but I need to clear a lot of things in the house before being able to do so. Craze in exploring new running shoes have reached saturation point, have to divert focus elsewhere on personal wellness.

Well, let's see how things develop.