Double Thresholds and other such workouts

The “double threshold” workout is taking over the world! From Jakob Ingebrigtsen to all kinds of runners in Flagstaff, they are being applied with a lot of success.
As always happens, with success comes emulation. Other pros and collegiate runners have already picked up on these workouts and they are filtering down through to high school and amateur adult runners.
Is this a good idea, though?
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