From the FCTM:
" A rolling takeoff procedure is recommended for setting takeoff thrust. It expedites
takeoff and reduces risk of foreign object damage or engine surge/stall due to a
tailwind or crosswind. Flight test and analysis prove that the change in takeoff roll
due to the rolling takeoff procedure is negligible when compared to a standing
takeoff.
Rolling takeoffs are accomplished in two ways:
• if cleared for takeoff prior to or while entering the runway, maintain
normal taxi speed. When the airplane is aligned with the runway
centerline, apply takeoff thrust by the method described below. There is
no need to stop the airplane prior to adding thrust.
• if holding in position on the runway, release brakes, then apply takeoff
thrust as described below.
Note: Brakes are not normally held with thrust above idle unless a static run-up
is required in icing conditions.
A standing takeoff procedure may be accomplished by holding the brakes until the
engines are stabilized, then releasing the brakes and applying takeoff thrust as
described below.
Note: Ensure the nose wheel steering wheel is released and the airplane is
tracking straight down the runway prior to thrust application.
Advance the thrust levers to just above idle (40%N1) as the airplane rolls onto the
runway at a slow taxi speed. Once the airplane is aligned with the runway, allow
the engines to stabilize momentarily then promptly advance the thrust levers to
takeoff thrust (autothrottle TO/GA). Allowing the engines to stabilize provides
uniform engine acceleration to takeoff thrust and minimizes directional control
problems. This is particularly important if crosswinds exist or the runway surface
is slippery. The exact initial setting is not as important as setting symmetrical
thrust.
Note: Allowing the engines to stabilize for more than approximately 2 seconds
prior to advancing thrust levers to takeoff thrust may adversely affect
takeoff distance."
I hope it helps
C