Get off the sofa: time is running out to locate the Roger Bannister lurking inside every one of us "There isn't a magical age when your fitness suddenly goes downhill," he says. It depends a lot on your lifestyle and level of activity. However there is a strong relationship between your aerobic capacity (maximum oxygen uptake) and endurance performance. From 30 years onwards, if you have a sedentary lifestyle your aerobic capacity will fall by about 10 per cent per decade, but if you are still involved in physical training you can offset the rate of decline. An active 50-year-old can have a similar aerobic capacity to a sedentary 30-year-old. Quick, jump off the sofa. Reassuringly, your mind too can play some part in delaying the race to the bottom. Not so much in the determination to achieve a particular time, but in the determination to haul your large rump out of a comfortable bed at six o'clock in the morning, or to push yourself to the limit in a race. This can, though, only take you so far. As Tong bluntly puts it: "If I offered you £1,000 to run your five kilometres faster than you did last week, you probably could. However, you would never be able to run faster than Usain Bolt. You cannot achieve performances that your body isn't physiologically designed for. And, as the years creep by, it becomes more and more difficult to improve even the performances your body is physiologically designed for. A 65-year-old runner is unlikely to be able to run as fast as he could at 60, even if he substantially increases his training. And the 50-year-old endurance runner, that sinewy man you see running home from work with a bag on his shoulders and a trainer-addiction in his eye, will lose 10 per cent of his aerobic capacity over the next decade, despite all his frequent exercising. Tong knows how it feels to read this and feel sad. Nothing can stop it unfortunately. I am 50 myself, it is a bit depressing when you see your performance decreasing but the message to get across is that lifelong exercise is good for you. And that running in itself is a pleasure. There are still opportunities to test yourself when you are older without feeling a fool. Veterans races abound and the Saturday morning parkrun computes your age-adjusted score - because for some the competitive gene never dies. Bannister himself continued running for fun until a car accident crushed his ankle in 1975. Invalided out, he took up walking until 2011 when he discovered some running shoes designed for Kenyan athletes made out of old car tyres. They suited him. In an interview with this paper last year he reported being 80 and happy on a diet of weights, walking and running twice a week. It is a lesson for puddings and would-be gazelles everywhere.