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Originally Posted by
Mark Rippetoe
LSD is really not good for humans. Middle distance efforts and sprints can be quite useful for metabolic conditioning, and CrossFit makes good use of them. If you are working up through your novice SS progression, I'd recommend holding off a while until your initial plateau is reached; this linear strength improvement will be more valuable in the long term than met/con, which is easier to obtain and comes more efficiently when you are strong. If you are already an intermediate-level trainee, you could add a sprint day to your week, and then add your middle distance day a month or two later after you have had time to adapt the rest of your training to the added work.