I've been a competitive runner ever since I was just 10 years old and over the past 30 years or so, I've competed in countless races ranging from 800 metre track races to 100 hundred mile trail events, and more recently, a 24 hour race where one runs as far as possible in that limited time frame. Every single race has been different and every single race has meant pushing myself to my limits to get the best result I am capable of on the day. I've trained hard, I've raced hard, there have been times when I've completely surprised myself and been over the moon with my result, and there have been times when I've felt extremely disappointed and frustrated at a performance where I've felt I could have done much better. I like to think that I'm physically and mentally strong, but how do you measure that strength? Even now, after hundreds of races over the years, I am still not 100% certain about my true limits - at what point do I finally admit that I...