This IM set asks you to come up with drills "on the fly." The idea is that you should start each swim without pre-thinking what your drills will be. Come up with the drills as you push off the wall, and try not to repeat the same drill more than once or twice. FIns are optional throughout the set. The effect is a little like downhill skiing or slalom — you have to stay mentally awake!
1 X 400 IM (25 kick/25 drill/25 kick/25 drill in each stroke)
2 X 300 IM (25 drill/25 drill/25 swim in each stroke)
3 X 200 IM (25 kick/25 drill in each stroke)
4 X 100 IM (#1 and #3: drill the fly and breast; swim back and free) (#2 and #4: swim the fly and breast; drill back and free)