At midday on the 21st September I will toe the line of the 400m race track at the Tooting Bec Athletics Stadium. Once that starting bell goes I won't stop moving - short of an undiscovered and long dormant volcano erupting in South London - for 24 hours.

After nearly two decades of being involved in sport, I have reached my athletic zenith - running around in a circle for 1440 minutes. For 43,200 seconds I will turn left and for 43,200 further seconds I will be turning right - the organisers are merciful enough to switch the direction of running every 6 hours.

Even to those who know me and the obscene, borderline ludicrous struggles I have put my body through over the years will think I've crossed the rubicon with this challenge. So why do it? I turned to ultra-running in part because of the love of moving and in part because the pyschological, let alone the physiological demands, are incomparably rewarding. Knowing I can take one step to the left and get off the track at any point and quit makes this challenge something extra special.

But far above all of those selfish reasons, I am doing it to support a wonderful charity - Level Water. They make sure that disabled kids get a fair start in sport by providing one-to-one swimming lessons for children who would not be able to access swimming otherwise. It is then up to them how far they take their sport. You can read more about their great work here: http://www.levelwater.org

I have been extremely fortunate to meet so many remarkable people and collect a lifetimes worth of wonderful memories through my sport over the years. Whether you run, swim, cycle or jump, everyone should have the same opportunity to access sport. 

I hope you will help me and Level Water deliver on that promise.