I agree with @Rittyrib, @XelaM and @titchy . Universities are primarily interested in your grades and other stuff is only relevant insofar as you can use it to show that you're a good fit for the course. Here's an extract from a Telegraph article a few years back:
"Sixth formers have long been advised that playing the harp or captaining the school chess team could persuade admissions tutors to award them that elusive university spot. But the suggestion that non-academic pursuits could make any difference to pupils' applications is a myth, according to Mike Nicholson, director of undergraduate admissions at Oxford.
Mr Nicholson said students would be better off devoting more time to their studies than trying to bolster their personal statements through charity work or Duke of Edinburgh awards...Mr Nicholson told the Times Educational Supplement: "It really doesn't matter if you haven't got any friends or hobbies or if you don't do any charitable work ...[Acceptance] is a purely academic judgement."
He said universities were only interested in "enthused, engaged and excellent" candidates, rather than "second-rate historians who happen to play the flute".
Current advice from Oxford is:
"Tutors at Oxford are only interested in your academic ability and potential. They want to see that you are truly committed to the subject or subjects you want to study at university but it’s not enough just to say that you have a passion for something: you need to show tutors how you have engaged with your subject, above and beyond whatever you have studied at school or college. This can include any relevant extra-curricular activities...There’s a myth that Oxford is looking for the most well-rounded applicants, and that you will only be offered a place if you have a long list of varied extra-curricular activities. In fact, extra-curricular activities are only helpful in so far as they demonstrate the selection criteria for your course.
If you are applying to other universities as well as to Oxford (you can make five choices on your UCAS form) then you may need to find out whether the other universities have different selection criteria. If they do, then you might want to provide some information about your extra-curricular interests – but keep it to a minimum. The space in your personal statement is limited, so think carefully about what you want to include.
Do I need experience of work and travel?
We understand that not everyone has the opportunity to do work experience or to go travelling so these activities are not a requirement for any of our courses. Tutors won’t be impressed by your connections, or the stamps in your passport, but they will be impressed by how you’ve engaged with your subject."
I doubt very much that many admissions tutors are bothered about your physical fitness.