Use the Vertical Knee Raise Machine to Build Strong Abs

Captain's Chair
 Phil Walter/Getty Images

The vertical knee raise, often called the Captain's Chair exercise or the hanging knee raise, is a core exercise that lets you add variety to your ab workout while also taking it to a more advanced level. You perform the knee raise while you are suspended between two parallel bars.

The vertical knee raise came in second on the list of best exercises for the rectus abdominus. This is the conclusion of a study at San Diego State University that compared 13 common abdominal exercises in order to find which ones really strengthen the abs. Each exercise was ranked for muscle stimulation (measured with EMG) in the rectus abdominus, as well as the internal and external obliques.

How to Do the Vertical Knee Raise Exercise

  1. Position yourself on the dip/raise machine (described below), back against the pad and arms holding your body up by resting on the parallel bars. There should be hand grips to hold onto at the ends of the parallel bars, and there are usually foot bars to step up on to get into position.
  2. Allow your legs to dangle and then slowly lift your knees toward your chest. The motion should be controlled and deliberate as you bring your knees up until your thighs are parallel to the floor.
  3. Return your legs to the starting position, letting them down slowly—don't just drop them, or else you lose half the benefit of the exercise.

The Muscles Worked

If you're after the elusive six-pack abs, adding the vertical knee raise can help you along your way. It's not going to give you a six-pack by itself—in fact, having a six-pack has more to do with having low body fat than it does with working your abs, though this certainly is part of it—but the core muscles the vertical knee raise works are the ones that you show off: the rectus abdominus.

The rectus abdominus is responsible for spinal flexion and lets you do things like sit up from a lying position, pulling your chest down toward your hips. It runs through your torso, extending from your sternum down to your hips.

But that's not all the vertical knee raise works. It also targets your hip flexors. While your rectus abdominus is stabilizing your core during the exercise, it's your hip flexors that are doing the work of bringing up your knees.

The Knee Raise Machine

The vertical knee raise is most commonly performed on the dip or raise machine most gyms have. It includes a back pad that will help support you and keep you from swaying during the exercise. It will also likely have pads on each of the parallel bars where your elbows and forearms can rest in a comfortable and stable position. 

The captain's chair exercise was one of the few ab exercises on the "most effective" list that requires gym equipment. You will generally find a vertical knee raise machine in health clubs, or shop for one designed for home use.


You can vary the vertical knee raise while increasing the challenge and intensity by holding a weight between the knees. Start with very light weights for this to get accustomed to the higher load and to holding and controlling the weight between your feet.

You can also increase the intensity by lifting the legs laterally without bending the knees. This adds significant strain to your back, however, so exercise caution if you try this to avoid injury. 

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