Jackknife sit-up exercise instructions and video

Use the jackknife sit-up to develop your hip flexors and abdominal muscles, as well as to improve the strength of your core.

Jackknife sit-up exercise instructions and video

Side Jackknife, Exercise Videos & Guides

Jackknife Sit Up - How to Instructions, Proper Exercise Form and

Jackknife Exercise How to Tutorial by Urbacise

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Forget sit-ups — you only need a pair of dumbbells and 7 exercises

How to do a Jackknife Sit-Up

How to Do a Jackknife - Howcast

How to do a Jackknife Sit-Up

The 16 Best Oblique Exercises to Fire Up the Sides of Your Abs