Mine was after around a week i noticed i could push myself a little harder...

Say i was normally doing 150kg leg presses, 5 sets of 8, i found i could almost "Suddenly" do 6 or 7 sets... Same went for curls and presses... quite wierd i found at teh time...

May all be Physcological, you never really know for sure if the chage was actually physical within you, if you follow?