5 minute plank and the 4 minute workout

O.k. so this is a short one, and a bit of a digression.  I found an online plan for the 5 minute plank, and I made it!

And these days I'm working on instituting the 4 minute workout in lots of versions ala Tom.  The 4 min. workout is 20 seconds on/spring and 10 seconds rest/walking.  Introduced to me as running, but Tom recently challenged me to do it with situps and pushups.  I can do it alternating (situps and then pushups).  Working my way toward doing the full 4 minutes with each.  Need a challenge?