Have you heard of a Czechoslovakian exercise physiologist named Vladimir Janda, MD? He came up with an ab exercise that truly isolates the abdominals. Dr. Janda claims the crunch does not isolate the abs. He claims that it's impossible to completely eliminate hip flexor recruitment during the crunch.
When you do a traditional ab crunch, you work a muscle called the Iliopsoas or hip flexor. This muscles job is to bring the knee into the chest. When you do a sit up or crunch you are primarily working the Iliopsoas.
The Janda sit-up inactivates the hip flexors because you are contracting the hamstrings and glutes. The result, according to Dr. Janda, is true isolation of the abdominal muscles.
The hip flexor is tied neurologically to the hamstrings. If you contract the hamstrings, your brain neurologically turns off the hip flexor. This effectively isolates the abs and obliques when you do a crunch.
Janda sit-ups, when done properly, SUCK! They are really hard to do because they completely isolate the abdominal muscles by taking the hip flexors out of the movement.
If you have a training partner, you can test the Janda sit up out for yourself. Lie on the floor in the crunch position. Your partner kneels down by your feet and places their hands on the back of your legs by the calf muscles. Your training partner then pulls the back of your legs up and away from you at a 45 degree angle, while you resist by contracting your hamstrings and by pulling your legs in towards your glutes. This tension takes the hip flexor out of the crunch movement. NOW TRY AND DO A CRUNCH!
If you can do one of these the very first time you try the Janda sit up, you are either doing it wrong, or you are one strong MoFo!
What if you train at home, alone, and have no training partner? You could buy the Ab Pavelizer, invented by Pavel Tsatouline:
The Ab Pavelizer allows you to do the Janda sit up, solo. BUT, this thing costs $97, plus shipping. Once again my handy chain set up I made for my dumbbell spotting system can be used to make a homemade ab pavelizer or janda sit up:
The sabre spotter on my powertec rack is in the number nine hole position; one chain with two 3/8 spring links and one 5/16 link is looped behind the front upright of the rack and held up by the sabre spotter; last but not least you need a 3/4" x 36" pipe conduit from my homemade calf machine, an Olympic bar pad, and you have a homemade ab Pavelizer to do Janda sit ups!
You want this homemade janda sit up device to pull your legs up and back by the calf muscles:
Contract your hamstrings by pulling your legs in towards your glutes, try and do a crunch, and you will work your abs in a way you probably haven't done before, TRULY ISOLATED!
IF you do these correctly, you will have a hard time doing one rep. If this is the case, reach up and grab onto the pipe for assistance, pull yourself up, and practice lowering yourself back onto the floor without holding onto the pipe (negative reps).
I can't believe how many uses I've found for this simple chain set-up or just parts of this arrangement:
Remember to keep tension on the glutes and hamstrings throughout the entire movement by pulling back against the Olympic pad. If full reps are too difficult, begin with negative half-reps. Try to do at least four or five reps per set. When this becomes easy, hold a weight plate on your chest.
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