Jack-kives are one of the exercises in the Muscle section of Wii Fit, where you do a kind of sit-up while lifting your legs. They are really good for the abs.

jackknives are in the strength training section. they are great for abs (among other things)

Hi!

I'm new here! I got tyhe wii fit for Christmas and am proud to say that I have been using it everyday! This is what I usually do for an ab workout focus:

In My Routine, set up your exersizes like this:

Yoga

Half Moon
Downward Facing Dog
Chair

Strength

Twists
Twists
Jackknife
Jackknife
(Jackknife-3 only if you are feeling ambitious)
Plank

Yoga
Bridge
Triangle
Half Moon

I find that if you do the jackknife or plank exercise before doing other exercises it helps to engage your ab muscles during those workouts as well.