JJ, you asked about reasons to do GS. I think the most basic and fundamental answer would be to recover from high intensity work and increase work capacity. My current thinking on this is that higher volumes of extensive tempo are a more specific means of accomplishing this end, particularly for 400m runners (as Mike has written here in the past). However, I also feel that tempo work is much more apt to leave my athletes with lower leg and back pain due to the constraints of a 200m indoor track. As a result, it may be more pragmatic, if less utopian, to prescribe more GS and hurdle mobility work on recovery/work capacity days.
I'm having a tough time letting go of tempo, though I do believe that it will undoubtedly lead to more injuries than GS. I view the injury risk of GS as almost nill, but the potential benefit not nearly as high as with tempo. It's a cost/benefit analysis of sorts, with health winning out in my mind.
So, I'm leaning towards (for 400m types):
M – acc dev, weights
T – mobility, tempo, bodybuild exercises in wt. room
W – max velocity, weights
Th – mobility, GS
F – run/jump circuit, bodybuild exercises in wt. room
So we end up with one tempo day and one gs day. This is currently letting me sleep at night. I'd like to move towards intensive tempo on Thursdays, at which point I would cut the extensive tempo on Tuesdays and go with mobility/GS. After these days I would keep the jumps to a minimum in the Friday run/jump circuits, assuming we'll bring some fatigue into that day (especially after the first few sessions of intensive tempo).
Thoughts from the gallery?