Hydraulic

460 kg squat, sumoman

This is 1014 lbs. 400-lb squats would not have prepared me for supporting 1014 lbs.

According to one of my HIT books (or rather one I used to own, because I got rid of all of them) supporting 900 lbs on the back is really too much. The argument was that heavyweight powerlifters squatted this much and they weighed 300 lbs and that plus 900 lbs was enough to crush the vertebrae of a normal man. The HIT book recommended no more than 400 lbs full squats for safety.

Clearly I am not normal… or maybe HITers simply don’t know what they are going on about. Yes, it must be the latter.

Scientists had the same problem. When they first calculated how much weight the spine should be able to lift they were somewhat surprised to discover that it shouldn’t be able to hold as much as it actually did, it also puzzled them that the force on the discs was a lot less than the calculations indicated. This is the sort of calculation they did:

Thus F equals 300 Newtons. The force squashing the disc between the 2 vertebrae (the ones by the arrows) being 2022.4 N at an angle of 8.5°.

The same principle could also be applied if the force was applied vertically:

So F equals 857.1 N and the disc force equals 2857.1 N.

Of course the reason that their calculations didn’t reflect reality was that they failed to take into account the hydraulic effect of the torso. Thus:

So F equals 1289.6 N but the disc is being stretched by 1532.2 N at an angle of 57.3°. 40 kN.m² (about 300 mmHg) applied over the 300 mm diameter disc (A = πr²) equals 2827.4 N.

Similarly:

So F equals 3684.5 N and the disc force equals 2857.1 N.

Discussion

Lets compare the figures;

Note that in each example the model’s back muscles are taken to exert a maximum force of 2000 N. This is the combined force of the muscles acting at this level rather than just being a single muscle connecting the spinous processes.

When doing a hyperextension type move the person can support 300 N, his vertebral disc is exposed to 2022.4 N at an angle of 8.5°. With hydraulic support he is able to support 1289.6 N but the force on his vertebral disc is negative 1532.2 N at an angle of 57.3° – which may explain the restorative effects of hyperextension type moves.
When doing a squat type move the person can support 857.1 N, his vertebral disc is exposed to 2857.1 N of force. With hydraulic support he is able to support 3684.6 N but the force on his vertebral disc is still 2857.1 N.

The figures and diagrams though illustrative are roughly in line with those that occur in the body thus they clearly show the dramatic difference that hydraulic support can offer, there is however much debate as to exactly how much support IAP offers.

The muscular effort from hydraulic support comes from the transverse muscles of the waist and torso, the force that these muscles exert has been referred to as ‘hoop’ tension. This support is partly hydraulic (fluid based) as well as partly gaseous (air based) – thus maximal support is offered when the breath is held.

It should be noted the hoop tension depends on muscular effort, thus one literally flexes the muscles all around the waist and torso to maintain the pressure. Note also that my model suggest that this hoop tension offers greater lifting ability than the back muscles alone.

The length of the spine in a vertical support lift doesn’t come into the calculation unless there is a horizontal component. Thus if the spine were to lean from the vertical or bend like a bow this would have to be taken into account

An experienced lifter will use as much IAP (and ITP (intra-thoracic pressure)) as possible – in a squat for example this pressure is very noticeable and even more noticeable when a belt is donned.

Note that in all the calculations that forces must be balanced and torques must be balanced.

Belt Up

Quite often you will hear that people say that one should not wear a belt because the waist muscles will get weak.

Obviously this is drivel.

A belt offers no elastic recoil (it being inelastic), instead it acts like an extra set of transverse abdominals. This doesn’t mean the abdominals take a break instead it means that the rest of the muscles (the back and hips for example) can work harder. The abs also have something to brace themselves against so they can work harder.

The result of all this working harder is that greater forces are generated by the squatting muscles (for example by the back and hips) so that greater weight is used. Even the abs work harder and generate more force because they have something to brace (push) against. Yes I said push. Muscles contract but when they contract in a hoop the overall effect is of pushing the spine straight and pushing against the belt. Your neck and face will also bulge with the extra pressure generated. The capillaries in your eyes and skin may burst.

I’ve found that it is important not to do the belt up too tight or else this will simply make the waist too narrow. There needs to be a balance between maximising the waist area and maximising IAP so as to maximise the overall lifting torque at the spine.

You will find that later on when you can squat more, that you can take off your belt and squat more than your previous beltless squat.