How much strength training should I do

Integrating strength & mobility in your training program can have a positive impact on both injury prevention and performance.  Don't lose the primary focus though.

And ideally one should do 2 S&C sessions per week.

However, the focus should always be on developing sufficient running volume first.   

So here’s coach Karel’s take:

“The focus should always be on running first. Only when you’re at a reasonable volume first, you should incorporate strength training too.

For example, if you can run 7 hours a week comfortably, but have 9 hours available, you can add core stability and strength training.

Keep in mind: running IS strength training, running IS core stability.

But, of course, there are more effective ways to develop these if you have the time.”