How to Break 50 Seconds for the 400 Meters

I watched this video and it basically told me what was needed to break 50 sec.

To find your 400 time, take your best 200 time, double it, and then add 4 seconds. The first 200 must be ran in 24 sec., and then the second 200 in 26 sec. A workout that was proposed was 3 x 150m fly times (when you start 10 meters back behind the 150 mark), with full recovery of 10-15 min. To break 50, I need to get my 150m time down to 16.5 sec.

That being said, I need to work hard and continue to push myself because this goal will NOT be a easy one.

Here is a link to the video