Interesting.. our Oly here in AZ got the swim cancelled last weekend and was turned into a DU. 5K, 25mi bike, 10K. It was my first duathlon as well. I was a little frustrated at first, but it ended up being one of my favorite races ever.

According to my coach, the best method is to add up the total running distance, then aim for a pace as if you were racing that distance. For example, 9.3mi of total running for this DU, so somewhere between 10K and 1/2 marathon pace overall. I consistently run 7:00/mi for 10K, and 7:30 for 1/2M.

I ran 7:12/mi for the first 5K and 7:30 for the final 10K. Mind you, I actually paced the first 5K on purpose. I let it rip in the final 10K and it happened to fall into a 7:30 overall pace. Still able to have the bike split I was aiming for and I was toast at the end of the event. Meaning, legs were giving out with about 1mi to go. As DrD said, my legs are trashed.. on Wednesday. IMO, aim for a 9-10mi running race pace overall, as my coach suggested.

Looking back, I think there is some benefit to holding back a little in that first 5K. I was about 1min slower in the DU than a standalone 5K. It took less than a mile to recover on the bike, and it left me with *barely* enough to run a strong (for me) 10K. I feel that if I had gone much harder in that first 5K, I would have broken apart towards the end in the final run and lost several minutes. Not saying I paced it perfectly, but I left enough in the tank to put in a hard run at the end, and luckily, run out of steam just near the end of the race.