I *think* I can see in principle what you mean. atleast partly.
I'm doing the movment by keying the timing I want, then enabling smoothing and tweaking graph. I think what you're saying is I'm applying a curve with exponential increase on every single keyfame I made and that gives the whole movement a start-stop feeling instead of an exponential increase for the whole thing.
for the most part I actually have different graphs for each frame to frame, and at the beggining I did notice the start stop thing you're talking about and try to fix it, but apparently my eye hasnt been sharp enough, so I'll keep an extra eye out for that :p
I hope that's what you meant, and what's going on. I hope it's NOT that I'm keying the momentum all wrong and it's just my sense of timing

thanks for the crit and the clarification

EDIT: I think I got to the crux of it. I have a sort of anticipation where he first lowers the axe, then he raises it. Then the actual attack starts and he bends his arm over his shoulder as he lurches forwards...this is the slow down you mean (?) and then increase speed again to deliver the blow, axe comes down pretty fast. is that what you mean?
I think that might come from the fact that when I was making the key where he swings over his shoulder is when I found the method of stretching stuff so I added a few keyframes there. it does kinda ruin the momentum :p.

I actually went and made a quick tweak. I basically moved what was happening when the axe was over his shoulder to when he had his arm outstretched, moving it from the middle of the action to the beggining if I got what you meant :p. The tweak removed some anticipation frames so the jump from low axe to axe way high is insane, but is this basically what you meant?