Long story short i had ankle problems which turned out to be tight tendons and very bad flexibility, been stretching alot and doing yoga ect to improve this, now my ankle is fixed ive got adsc in 2 weeks in which ive had to up my cardio running 1.5 in around 8.45 regularly
knees have started to ache ...

Not worth worrying about at 14, to pass my selection i played for a football team,tennis,hockey ect all keep you ticking over but none push you, at 15 i joined a gym had weight progammes circuits ect for strength,

if you are a generally fit person at this age cardio is easy to improve i passed my ...