Hi .. Good work Sandy, I am 52 and after playing sport until i was 45 I quit and didnt do anything !!!!
Anyway - four weeks ago I started 10 k trainer and got my bulky 110kg off the couch and just started
I am a big guy - 6'2" .. sore knees , feet etc
But ... I just do what i am told -some days I hate the 10k girls voice but most of the time she isn't too demanding
You are brave doing the 25 k - but good on you .!!
Anyway - I have found that it is best I stop pushing myself too hard - that was my instinct at first ... but now I just do it at a comfortable pace and go as slow as I like .. As long as you do what you are told it WILL WORK ...
Good luck .. you may be surprised about how much better you feel in all aspects of life