Red Rick said:
Interesting. So doing 400w on a flat road on a tt bike is somehow different than doing it on a road bike on a gradient.
It boils down to inertia (kinetic vs potential energy) and muscle activation, training, and body position.
On a climb your kinetic energy (movement) is being matched by a greater resistive force of gravity. You have less inertia due to the slower speed, and greater resistive force. On the flat, it's just wind resistance. Your muscles activate differently because (non-scientifically), they have to "catch up" to the power stroke on non-uphill surfaces. You can see this really simply by smashing up a small hill, watching power, then turn around and try to sustain that power on the descent. At first your brain says "WTF!?" and most people I know struggle to do it for sustained periods of time. If you persist, you can teach your legs how to pedal downhill. In my experience, TTing into a really strong, consistent headwind can allow much greater power generation more easily than a fast, tailwind TT section. Slower speed, more manageable muscle activation sequence.
This is one reason why people who can generate a lot of power doing sprints uphill don't necessarily win sprints in races -- the muscle activation of a flat or downhill sprint is very different. (Ignoring positioning and tactics and recovery etc). As is your position.
If people trained on the TT bike like they do when climbing, they would narrow the gap considerably between TT and climbing power, but they don't. People rarely go out with their mates on their TT bikes and hammer each other. Compare that to the weekend ride where you will hammer each other up every climb. You become good at what you train. I know a group who do TT together regularly and they are all capable TTers.
On a climb your posture is opened up - arms out (comapred to TT bike), hip angle increased, natural head position, maximum lung expansion possible. On the TT bike you are restricting lung expansion, arms together, compressing the hip angle, and typically restricting your wind pipe with an unnatural neck-head angle. There's also an aspect of the artery through the hip being compressed but I'm fuzzy on that one.