45 Second Run
A key predictor to 800 meter performance is anaerobic capacity. In fact a 400 meter time is a tremendous predictor of 800 meter performance. (Anderson, Running Research, p. 3). The purpose of the 45 second test is to have your athlete run all out for 45 seconds on the track. Their whole purpose is to run as absolutely far as they possibly can. You then measure it out to the meter. The way I do this, is have a countdown timer and as soon as they hit 45 seconds, I put a cone down at where I saw their last step. Do not tell them to stop and have them walk back - watch it carefully. Then measure it out.
I had my athletes do the 45 second run on a week after their 15 minute Balke Test and did on a Monday so they were fresh. I did the 30m dash the same day just before the 45 second run. This tends to take a lot out of them if done right, so do not count on a whole lot more, workout wise, out of them after this.