400m S-L questions

[Charlie_Francis]

@Sam_S

I have noticed there isn’t much attention paid to speed endurance in the CF400 S-L template. I am a 400m/200m runner and plan to use a double periodisation model for my upcoming season, with a greater emphasis on my 200m running in the first competition period. As I still want to be able to run a good 400, would I be risking overuse injuries if I extended the speed day into the section section of the program (weeks 7-12) as stand alone a speed endurance session (at the expense of the strength endurance), or would I be better off sacrificing a special endurance day? Typically I respond very well to special endurance training and speed endurance can be something of a weakness for me.
Alternatively – Does split special endurance runs (e.g. 4x80m, 3x100m, 2x150m off short recoveries) have a carry on effect into speed endurance abilities? Obviously they are all at 95-100% of max speed so theoretically at least one of the runs is going to be of very high quality and thus have a benefit to speed endurance (or so I would think). If this is true, then, would this set up still allow me to progress my speed endurance abilities without creating a specific speed endurance day?
[If it is of any use I am 19 years old, in my second year of full time training (PRs: 21.5, 47.97-underdone in the 400 department for sure). I would like to be running 21.0-21.1 in order to increase my speed reserve to take my 400 time down to low 47s-46s in the coming year.]

No SE?? SE can come from split-runs as well as continuous runs. If you investigate what Mennea was doing you’ll see his split 60s, similar to what you see, yielded plenty of SE - enough for the WR in the 200m. Check the rest breaks vs intensity vs number of runs… It’s all in how you perform it.