Christopher Coulson: I'd be interested to hear whether a comparative performance formula I've devised makes real sense or whether I'm only imagining that it's a useful guide. I modestly call it the Coulson Performance Factor (CPF) and I devised it because I wanted to incorporate the training variables of time, distance and heart rate in a single indicator of comparative fitness. The CPF is supposed to answer the question: is it a sign of greater fitness (a) to do 6174 metres in 30 minutes at an average heart rate of 137.3, or (b) to do 14188 metres in 65 minutes at an average heart rate of 148.8? I believe the answer can be calculated using the CPF formula: 500m split time (in seconds)/metres per heartbeat = CPF A lower CPF means greater fitness. In the test case, if the CPF is meaningful, session (b) is indicative of greater fitness because its CPF is 93.66 as opposed to (a)'s 97.26. Or am I fooling myself? What do you think?Terry O'Neill: Your idea is interesting and I will discuss it with some of my mates at Loughborough Human Performance dept. The first thing that strikes me is that when you compare different distances, the balance between the aerobic and anaerobic contribution to the overall effort changes. Also it is different between individuals, and so someone who has a high anaerobic contribution would appear to be less fit when doing the longer distances whereas it is not a question of fitness but suitability.For example; if you asked Linford Christie to run the 5,000 metres, he would either not be able to complete it or it would take him a long time. You could not conclude that he was not fit only that he was not fit for the task he was set.When comparing the 30 and 60 minute pieces it is not so bad, but when you start to get down to 2,000 metre times then it could be different. With all that said, I think it is a pretty safe way to monitor your own progress and as time goes on you will build up data and maybe refine it.