My coach recently suggested that we adjust my workouts to focus on speed rather than distance, so I thought that I'd adjust my nutrition to match. Normal on my long bike rides I take Cliff Shot blocks, which are my preferred food, and Gatorade (a single bottle).
On Saturday, with a two hour ride and 30 minute run brick scheduled, and coming off a short race where I used Gu, I decided to take 4 Gu, the same Gatorade, and give the workout a go. The ride was simple- 1 hour in B, 30 minute time trial in C, 30 minutes in B, and the run in B. I decided to aim for a 42 mile ride that would take me out to Madison and up towards Durham from Hammonassett, with enough legitimate climbing to make it a serious 2 hour ride and also prepare me on the off chance we went up to Lake Placid.
Much as in a long race, your nutrition rarely hurts you while you are still on the bike. It can happen, but it's infrequent. The ride went well. I got the 42 miles in at the 1:56 mark, including over 22.4 for the time trial on rolling terrain, pulled into my driveway, tossed my helmet and shoes, put my running shoes and cap on and started run.
The run is hard, with a hill right at the beginning, and two other decent hills in about 33 minutes, although I was aiming for about 31 minutes with a solid B effort. The initial climb always makes you feel gassed and you have to remind yourself that you've gotten off the bike and climbed, that there's a downhill around the corner...
No reason to bore anyone actually reading this with the actually blow by blow of a thirty minute training run, so in short- I was gassed on the run. I did run a solid B pace, but it felt like an uneven C pace.
Verdict- Gu might be all right for a sprint race of about an hour, it simply isn't up to a two and a half hour race or workout without other supplemental nutrition that makes me wonder why you'd choose it as part of your nutrition suite. Now of course, that's just me. And just me is sticking with Clif Blocks.