If you can afford it, you may be able to nonverbally signal to onlookers that you are there for Serious Running by showing up in a Serious Running outfit with corresponding accessories.
Thanks, that would be a simple solution. It seems rather obvious now, I just nod, mutter 'good morning/afternoon' and run on... which they accept as a response without question because I'm there for Serious Running!
My family's relatively well off, and my birthday is coming up, so the cost isn't likely to be a problem unless it's very expensive. I'll check out the sports store next time I'm in town and see what sort of kit they have available. Thanks again.
An exercise:
Name something that you do not do but should/wish you did/are told you ought, or that you do less than is normally recommended. (For instance, "exercise" or "eat vegetables".)
Make an exhaustive list of your sufficient conditions for avoiding this thing. (If you suspect that your list may be non-exhaustive, mention that in your comment.)
Precommit that: If someone comes up with a way to do the thing which doesn't have any of your listed problems, you will at least try it. It counts if you come up with this response yourself upon making your list.
(Based on: Is That Your True Rejection?)
Edit to add: Kindly stick to the spirit of the exercise; if you have no advice in line with the exercise, this is not the place to offer it. Do not drift into confrontational or abusive demands that people adjust their restrictions to suit your cached suggestion, and do not offer unsolicited other-optimizing.
To alleviate crowding, Armok_GoB has created a second thread for this challenge.