Jackknives
This ab exercise mainly works your abs, with help from your obliques and hip flexors. Watch the demo video, then follow the tips below.
Rep Range
Time Based
How to do Jackknives
Begin on your back with arms straight down on the floor, using elbows to prop up your upper body. Extend legs in front. Bring both legs together feet touching each other, draw both knees to the chest at once.
Common mistakes
Avoid collapsing the elbows or not fully extending the legs after each repetition.
Breathing
Inhale when extending legs, exhale during the crunch.
Muscles worked
Primary Muscles
Abs
Secondary Muscles
Obliques, Hip Flexors
