Exercise guide
Side Jackknife
The Side Jackknife is a bodyweight abdominal exercise performed from a side-lying position. The abdominals are the listed primary focus, with no secondary muscle group assigned in the exercise row. Bringing the upper and lower body toward one another creates the working action, while the side position makes balance and a controlled return part of every repetition.
Training context
How to keep the Side Jackknife controlled
The Side Jackknife has a relatively compact range, so a rushed repetition can replace abdominal control with momentum. Set the side of the body comfortably on the floor and organize the arm positions before lifting. Move the torso and legs toward one another without rolling onto the back.
This exercise can fit as direct abdominal work near the end of a session or inside a bodyweight routine. Record repetitions for each side and use the same version when comparing workouts. Stop the set when the side-lying position changes or the return becomes a drop onto the floor.
Technique overview
Keep the movement stacked over one side
Lie on one side with enough space for the legs and torso to move. Set the lower arm where it can help with balance without pushing the entire repetition. Bring the upper body and legs toward one another through a range you can control, pause briefly, and lower without dropping. Complete the chosen work on both sides, using a smaller range if that helps the body remain on its side.
Treat this as an overview and use a range, pace, and setup you can control.