Pushing and pulling?
Not all the energy you transmit to the pedals is transmitted instantly to the road. Some of it is stored in the resonant system that is you plus bike plus load
How it's stored, how it's then used or wasted, and how stored energy being brought back into play interferes constructively or destructively with energy you're inputting right now, and how that varies with your frequency of pedalling, your frequency of swaying the bike, how you naturally resist bike swau and how much the bike is loaded and how this all feeds into the steering, is a complex problem that contains now differentials than I want to tackle at this time of night. Save to say, you aren't 'just' moving a mass uphill, and the bike design can very much altar how much work you have to do.