Personal Achievement - beating your own times and distances set doing a previous exercise can make you feel good about yourself, cycling for an extra mile, running for an extra 5 minutes or scoring one more goal than your mate will put you on your way to a healthier body and an improved level of fitness.
Making friends - The more activities you do and become part of (new clubs and teams) will enable you to meet new people and create new friendships with people you may not have met or thought could be you friends.
Health - Exercise doesn't only just increase your levels of fitness but it also builds up your muscles and enables your bones to develop and grow.
Fun - It may be hard to believe but its true, KEEPING FIT AND HEALTHY IS FUN!! Everybody has that feeling of 'I am too tired' or 'I will do some exercise tomorrow' getting over that feeling means you are half way to a healthier body.
Reduces Boredom - Exercising is a great way to reduce boredom, if you are sat at home thinking about what to do with yourself, why not put your tracksuit and trainers on and go for a jog.