Taken from the link you sent
You can exercise in a public outdoor place:
by yourself
with the people you live with
with your support bubble (if you are legally permitted to form one)
in a childcare bubble where providing childcare
or, when on your own, with 1 person from another household
This includes but is not limited to running, cycling, walking, and swimming. Personal training can continue if participants are from the same household or support bubble. It can also continue if it is one-on-one, although this should only take place in a public outdoor place, and not in someone’s private home or garden.
This part
or, when on your own, with 1 person from another household