I have just done a triathlon with my disabled son, Benjamin (team-bee.blogspot.co.uk)
While we were training I started to try to calculate the energy requirements for the event, because I was worried about running out of glycogen before the end. Most of the calculation methods can not take account of weather - especially wind, so I am starting to wonder how to make a power meter for our bike. I can either go for strain gauges in the cranks, which is likely to be difficult mechanically, or I am wondering if I can just use my heart rate.
I have just got a Garmin 610 sports watch with heart rate monitor. It uses a wireless protocol called 'ant'. I'll have to look at how good heart rate is as a surrogate for power output.
I may have to go to a gym to calibrate myself against a machine that measures work done...a winter project I think!