Time Trial / Time Trialling / TT

sure, what i'm saying is that if two riders covered a course in exactly the same time but the first sprinted up the hills and the second sprinted down them the first rider would have used less energy. This is the reason riding hard on the climbs gets you a better time. Or am i confused? Here is another example...

if your riding a course with a head wind and a tail wind section which is totally flat is there any reason why you should vary your effort at all? You want to minimise your total effort, the only serious resistance to your movement is your speed relative to the air so surely you would aim to ride steady throughout so you were slower into the headwind and faster with the tail wind. Is there any physical advantage to riding harder into the head wind to avoid going slowly at that point?

Riding faster up hills uses MORE energy but you ride the course quicker. The idea is you should ride the harder parts a little bit harder and back off a little bit on the easier (tailwind, downhill) parts. Unless you're quite good at knowing your perceived exertion or watching a power meter it's usually best to stick with steady state. Lots of people will overcook things like climbs and then be forced to soft pedal descents.