Technique Summary

Form a stable base by placing your elbows on the pads and taking a firm grip of hand bars.  Lightly press your full back against the back of the machine.  Raise your knees to your chest by rounding your lower back.  Breathe out on the way up, breath in on the way down.

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Exercise Type: Compound (Isolation if you do leg raises or keep your knees bent through the full range of motion)

Primary Muscle: Rectus Abdominis (with emphasis on lower abs)

Secondary Muscle: Obliques, Rectus Femoris (one of quadriceps muscles), Tensor Fascia Lata

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Technique Details

According to a study conducted by the Biomechanics Lab at San Diego State University, the knee raises are the best popular exercise for your obliques and second best for your core abdomen.  That same study suggested that the knee raises work your obliques 3.1 times and your abdomen 2.12 times harder than the regular crunch.  This makes the knee raises our second favorite exercise after the bicycle crunch.

We also love the knee raises because they tend to put a lot less stress on your lower back.  Even with that in mind, it is still critical that you round your lower back as you try to achieve full contraction of your abs.  Doing so places more emphasis on your abs and prevents inter-vertebral discs from moving forward (which could lead to articular compression or shearing).

As you do this exercise, please focus on controlling the motion of your legs.  Throwing your knees/legs up to take advantage of momentum takes away from the development of your abs and could lead to injury.  Controlling your legs may become especially difficult in the negative phase of the exercise, when you are lowering your legs.  DO NOT let your legs swing on the bottom.  Do not let your legs go all the way down either.  You want to maintain pressure on your abdomen at all times.

Just as with other exercises, the knee raises can be modified to accommodate a range of fitness development.  The easiest alternative involves raising your knees to your chest.  You could add resistance by extending your legs out at contraction.  This means that you first raise your knees (this time only to a point where your thigh is parallel to the floor).  Then you extend your feet to make a straight line with your leg parallel to the floor (your feet will essentially make a 90 degree angle with your torso).  The most difficult alternative is keeping your legs straight throughout the motion.

The roman chair knee raises are also known as knee raises, leg raises, captain’s chair raises, roman chair raises, and knee up machine raises.