Beijing 2008

Try and get a perfect start as this will max your speed bar straight away (if you try for the achievement in practice mode it won't matter if you false start). It's then just a matter of maintaining your speed for the whole 43 seconds (pause the game if you're getting tired). You can also use slo-mo in olympic mode to help you as it's a lot easier to build your speed back up.

I would pretty much follow Beanpotters suggestion, alternatively, I used slow motion just before pausing the game, this way you will lose less time/pace whilst hopping your finger from the analogue stick to the pause button.