Originally Posted by taras0000

The problem that most riders have when it comes to the seated transition, is that they drop into the saddle too quickly. Most people coming from a road background are used to being out of the saddle at "full extension". In other words, their legs are about 95-98% at full extension the whole time they are out of the saddle. A freewheel allows you to do this because you can stomp up and down. On a fixed gear, you have to be able to pedal through the top and bottom as well. You can't do that at full extension. You have to be able to "run on the pedals" and this is done at 90-95% extension. With experience, you can extend more. It's all about being able to train the proper neural sequences, and just comes with practice. You can watch riders accelerating in match sprints to once they are up to top speed.

You can do this drill in a light gear, riding at 120-130 rpm seated, and raising yourself off the saddle an inch or so, without dropping leg speed. As you get better, you rise higher off the saddle, and drop back down, doing it slowly over the course of about 10-15 pedal strokes (5-8 seconds, 5 seconds should be enough). You can do this as a warm-up in a light gear before a workout, just doing a few reps or so. It's purely a technique thing at first, but you will need to up it to race gear at some point with the exercise after you've gotten smooth enough.

Try a slower drop into the saddle next time you're at the track and see if it helps.