Thanks, that's really helpful. Even though I'm in relatively good shape, I don't think lockdown is good for aerobic fitness because I generally go from sitting down to relative high intensity.
I got a slightly flare up of my patella from a HM distance on Sunday so I might do a couple of test runs for MAF whilst I'm doing some strengthening physio. My main concern at the moment is getting too cold!
@Sainsburys_Ed figuring out the number isn't exactly taxing, so I guess I'll see how I get on with it.