jcwoijfea;d wrote:
I'll echo what a few others have mentioned - interval workouts are good and sustainable as long as they are part of a well-rounded training program.
In the workouts the OP mentioned, the intervals in questions are likely 5k pace at the slowest. They are fine, useful workouts, but I think twice per week is too much. I would recommend workouts along those lines once every 10 days or every 2 weeks. Fill the other workout days with progression runs, tempo work (continuous or reps), fartlek, top-end speed work, etc. to be a better rounded runner, and not get stale on that narrower band of stimulus.
As a writer who interviews Olympic runners and scholastic coaches I have found some very accomplished coaches who pushed too hard at times. It only takes one workout or race to push the runner over the edge. I heard one coach say about a regular season race "that meet was his state championship." Why run 10 X 400 at your top paces with a short interval at mid-season? Save it for the championships if you can.