I got on a computrainer and did a 41k with 2 big hills and some small rollers, I finished in 1 hour 10 mins, and averaged 244 watts.

But when I looked into the profile I was running on, it was setup for a rider weight of 133kg. My time was up so I could only coax a short 3 mile run with the weight set to the proper 77kg (or should I be adding in the bike/clothes etc?)... when I did this it felt as if the wattage was much higher for the same effort - I averaged 290 watts for the 3 miles on spent legs (and I wasn't burnt out at the end) and when it was set to 133kg I could barely get it up to 290 watts with totally fresh legs, let alone sustain it for any period of time.

I've tried to find how the computrainer uses weight... what I see is that it uses it to calculate the resistance - which sounds like to me if I put out 250 watts I would just go slower set to 133kg vs 77kg (especially on the hills), but I'm not sure if the wattage reading would be different - I know it absolutely matters on my trainer at home and a weight change very much alters the power readings relative to my effort, but thats not a computrainer.

Anyone know how this works? I may go back and compare the readings/feeling to two extremes, like 20kg and 150kg.. but maybe someone has already done this/knows what would happen? Maybe there would be a way to calculate what the difference would be if the weight was set correctly?