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Exercise of the Month: Jackknife with Halo® Trainer Plus

If you want to test your body’s endurance and strength — and work up a sweat — this exercise is worth trying. The jackknife with Halo® Trainer Plus with Stability Ball is a full-body workout that’s an excellent conditioning exercise for those advanced fitness enthusiasts looking for a challenge.

Instructors can progress the exercise as they see fit — getting the client to start first with knee tucks with a neutral spine, then progressing to incorporate spinal flexion with knee tucks. Finally, you can test your client’s balance and stability by having them hold the ball steady as they lift one leg at a time, eventually progressing to moving the ball in and out with their legs.

By using the Halo Trainer Plus, clients can maintain neutral alignment in their wrists, which may be a more comfortable position from which to support their body weight. Of course, if they’re more comfortable with their hands on the floor, they can still do this exercise from there.

Merrithew® Lead Instructor Trainer Sarah Jarvis breaks down the jackknife exercise and explains what elements to focus on while performing this challenging, but rewarding move.


  • Focus on obliques to stabilize and prevent the lower back from over-extending
  • Maintain engagement of the glutes and quads as the ball is moved in and out
  • Watch out for the elbows locking, scapulae winging and keep the gaze on the floor when in neutral spine
  • Start with the ball just below the knees and then progress to the ball starting lower down the shin

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