People can get a “hammy” from stressing over semantics, but I would say in a 400m there is energy to make two significant “moves” during a race.
The first should be from the blocks: Sprint like a 200m runner for the first 50m. The purpose will be to establish the rhythm of your race and to get into the “lift” posture by 50m to establish the most biomechnically efficient posture. If you don’t have those two things in place by 50m, you keep trying. If you still don’t have those in place by 70m, you’ve probably blown the race already.
Once you’ve estblished the rhythm and mechanics, you go on auto-pilot and go through your personal check-list trying to correct any technical glitches (arm range, shoulder hunching) and trying to minimise tension which restricts movement range, speed and fuel efficiency.
Go through your 200m at 1sec or at best 0.8sec slower than your current best time for a one-off 200m race. That will allow you sufficient “cushion” to finish the race.
The second “move” or “acceleration”, or “kick” may be dictated by wind conditions or circumstances of your opponents or by your physical and mental strength on the day.
The second “move” usually comes around the waterjump, but may start anywhere down the backstraight or as late as the last moments of the bend entering the home-straight.
For fuel efficiency reasons primarily the second move should be like turning up the dial on a light dimmer, rather than like suddenly flicking a switch. Make it smooth, deliberate and powerful because that’s the move which will win or lose the race for you.
Arms are important throughout the race, but fast hands with a fairly full range of movement will yield best results, especially during the two “big moves” referred to.
The usual drop-off from the first 200m to the second 200m in the race is just under 2sec for a well conditioned 400m runner but for a bumped-up 200m sprinter just having a crack over 400m it can blow to 3.5sec. That’s a painful way to do it, but can still produce the occasional fast 400m.
No-one increases their speed over the last 200m as a whole. Not even Michael Johnson.
Most top 400m performers surge through the 3rd 100m - their critical second “move”.
But if you’re too far behind at the end of the first 200m and you’re up against top class 400m specialists, it’s going to be very difficult to walk your opponents down in the home straight.
That’s why the best option is to establish momentum early - within the first 70m and preferably by 50m and then concentrate on carrying your momentum through the race until you decide where to make the second “move”.
The effectiveness of the second “move” will largely be determined by the efficiency of the first.
If you work too hard through the first 200m, you will find your 300m time is good but your last 100m will be ugly and painful.
The race starts around the 300m, so you better be feeling fresh and you better be already in the medals frame at that stage.
The second “move” won’t last very long. It’s just a chance to re-accelerate, stave off the deceleration.
It’s important that during the whole race you hold a fast but “relaxed” rhythm. It’s that rhythm which will bring you home over the last 80m or so of the 400m race.
If you lean forward (whole-body, not from the waist) on the corners you can use them to accelerate a bit without spending any extra fuel.
This is important, especially when transitting from the backstraight into the bend. Runners who jam on the brakes, or drop their left hip coming out of or into a corner are signing up for major efficiency problems.
You may also want to “keep forward” during the last 80m, when some athletes tend to rock back onto their heels due to fatigue which slows them even more.
Then again…you could ignore everything and just go out and race a few 400m. You’ll quickly figure out how to survive them. Or maybe not.