Jack Knife - Exercise How-to - Skimble Workout Trainer

Right Side Plank Crunches - Exercise How-to - Skimble

Killer core exercise: Jackknife (aka V-up) with weights

How to perform the Jack Knife Sit Up - Physitrack

Single Leg Jack Knife by Mimi K. - Exercise How-to - Skimble

How to Do a Jackknife

Alternate Single Leg Jack Knife by Daniel Dutta - Exercise How-to - Skimble

Mountain Climbers - Exercise How-to - Skimble Workout Trainer

Jackknife by Dennis Richardson - Exercise How-to - Skimble

Straight Leg Jackknife by Gracie D. - Exercise How-to - Skimble

How to Do a Jack Knife Sit Up: 9 Steps (with Pictures) - wikiHow

Jack Knife - Exercise How-to - Skimble Workout Trainer

Weighted Jackknife by Al B. - Exercise How-to - Skimble

Weighted Jackknife by Al B. - Exercise How-to - Skimble

Weight Bent Leg Jackknife by Gracie D. - Exercise How-to - Skimble

Side Jackknife (Exercises.com.au)