See i have this theory on fitness and i wouldn't mind some feedback on what others think of it. If you think its off then by all means let me know. Happy to hear others thoughts. My theory is not very clear cut (age wise) and is a vague in some area but here goes... I will start by saying that all theories are just that, a theory. Until it is proven, which this one isn't, well it's just someones thoughts based on their own observations/thoughts. I split it up into 3 stages based on age. The whole theory relates to body composition, muscle strength, flexibility, injury avoidance, and everything that sits in the fitness basket. SET UP STAGE: Between the ages of 10 and 20 (maybe up to roughly 25 years) is our set up stage. Prior to 10 years old anything can happen so I ignore that time of our lives. During the set up stage is when we set our body up for what it can be and how easy it will be later to maintain that level of fitness. That may be that it gets set up to run fast, lift heavy things, jump high, get fat etc. It's where the building blocks are laid. If the person is lazy or sedentary in the set up stage then the odds of getting to run fast or lift heavy things in stage 2 to 3 are greatly reduced. I'm not saying it cant be done but the chances are low for a couple of reasons. Firstly because the habits haven't been programmed into the mindset and secondly because it is much harder later to burn fat, build muscle, train muscle fibres to react at speed, and the metabolism slows which hinders the whole process. This is the stage the body will come back to if you lose your way later in life and hopefully your 'muscle memory' will help you get back in shape. All this can be overridden to some degree by very hard work and time later in life so if you missed the boat on stage 1, dont worry you can catch up to a degree. MAINTENANCE STAGE: Between the ages of 25 and 40 (and up to 45 depending on the person) is the maintenance stage. I believe that in this stage if you can maintain a healthy body (in a fitness sense) then in stage 3 you will be miles ahead of everyone else that didn't get stage 1 set up. If you slack off in this stage for a year or 3 then you should still relatively easily get it back with some work. If you slack off for 10 years then you will have probably lost the edge you had from stage 1 (the set up) and you are in the same boat of those that didn't set up properly. The habits you created and the building blocks physically laid in stage 1 will be your biggest asset and provide you with muscle memory to get back to good shape. If you succeeded in stage 1 then do your best in stage 2 to keep up a good level of fitness to benefit through to the end. HANG IN THERE STAGE: Beyond age 40 you are then in the 'hang-in-there' stage. This is where if you got it right in stage 1 and 2 life will be so much easier for you. You will have the right mindset and motivation to keep active. You will have less injuries, be more flexible and generally enjoy a greater overall health and quality of life. If you bummed out on stage 1 or 2 then all is not lost. Like giving up smoking when you are 60 is still a good idea, as is taking up exercise....its always a good idea. You can improve all parts of your fitness/health through regular exercise regardless of your age. My point in my theory is that if we start early and can maintain the momentum then you are gonna have a dream run. Hopefully this theory is not misinterpreted as doom and gloom. If you are over 40 and didn't get stages 1 and 2 down then there is always hope (re-read stage 3 again). My theory is aimed at the younger population in that if we can give them a reason to be active now then maybe they will understand that it will only make life later that much easier, and less of a burden on the health system. The whole theory may seem obvious but when i put to people i often get the response of 'well i sort of knew that but never acted on it'. By putting it out there it could just raise awareness and get people thinking more about it.