Exercise Library
Jackknife
Lying flat, you simultaneously fold your upper body and legs up to meet in a V shape, then lower back down under control. Both halves of the body work at once, making it a more demanding version of a basic sit-up.
Primary muscle
Primary: Rectus abdominis Secondary: Hip flexors
Equipment
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Category
Abs
Track This Exercise in the App
Log your jackknife sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.