Ab Killer, Abdominal Exercise Machine, Best Ab Workout, Do the Math

The Ab Killer utilizes the Roller Body Arch principle. The body forms an arch. Because the Ab Killer is on wheels it is free to roll away. What this means is that there is no friction at this point to hold the body in it's arch position. The body can only maintain it's arch position by creating tension in the abdominal muscles. Muscles work by pulling or creating tension. That's what they do. By holding this position you are loading your abdominal muscles and forcing them to hold up the arch. The calculation to the right calculates the tension required for a person of my height and build, to hold this position.

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27 x 1000 - 36 x 300 = T x 150
T = 16200/150

T = 108 kg

T = 238 lb

When you are doing a crunch, you are using your abs to lift your torso off the ground in a similar manner to erecting a pole with a rope. Your spine is that pole and your abs the rope. Now the torso has a certain mass, and a centre of gravity, and therefore your abdominal muscles need to develop a specific amount of tension to get things moving. For a person of my height and a person of my build my abs need to generate 145 lbs of tension to make it happen.

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At 0 degrees: T x 150 = 36 x 275

T = 66 kg max.

T = 145 lb

At 45 degrees: T x 150 = 36 x 275 x 0.707

T = 47 kg

When you are working out on the Ab Killer Max and doing slightly forward flys on your toes you are putting a whopping 325 lbs of tension into those abs ... Ouch!

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45 x 725 - 36 x 290 = T x 150
T = 22185/150

T = 148 kg

T = 325 lb

What these calculations show is that the Ab Killer loads the abdominal muscles 64% more than the maximum tension created when doing sit ups or crunches. When doing the Max workout on the Ab killer Max you are putting more than double the amount of tension into your abs. What also needs to be taken into account is that when doing crunches, this maximum tension position is quite difficult to maintain, and once off the ground the abdominal tension falls away significantly. On the other hand when using the Ab Killer it is relatively easy to maintain the maximum tension position. This demonstrates the efficiency of the principle.

For the purpose of our calculation we have used a model who is 178cm, 5'10" tall and weighs 73kg, 160lbs. Although the reality is more complex, we have chosen some simplifications that will be pretty close approximations. We have assumed for simplicity that the spine is a hinge opposite the belly button or navel. We have estimated the mass of the upper body and lower body, between knees and navel, and a centre of gravity for each.

Warranty: Machine: Full 2 year replacement warranty. Knee Mat: no warranty

Disclaimer: The Roller Body Arch Position loads the lower back in compression to the same degree as it loads the abdominal muscles in tension. When exercising on the Ab Killer the user needs to do so initially with care and discretion.