Here are a few interesting articles on belt use and stabilisation of the 
spine.  Note that none of these studies involved any specific focus on the 
possible role played by TA (transversus Abdominis) in trunk stabilisation, 
but showed that increased Intra-abdominal Pressure (IAP) and activation of 
the back muscles suffices to achieve stabilisation under conditions of loaded 
lifting.

Note that one of the articles shows that belt wearing does not decrease 
activity of the trunk muscles while lifting, as is often claimed by those who 
oppose belt wearing.  Instead, the EMG activity of all 12 trunk muscles 
increases significantly in all three directions due to the increased IAP.

Another article showed that the activity of the oblique abdominal muscles 
when lifting decreased after isometric abdominal training, thereby suggesting 
that the typical type of slow abdominal exercise like "crunches" may have 

Another noteworthy observation is that maximum activity of the abdominal 
muscles appears long before the peak of the IAP, and that this lag between 
the two peaks may compromise lifting safety. On the other hand, if the IAP 
were to peak before the abdominal muscles, an inadequate "pressure wall" 
might exist to contain the increased pressure.  This finding might lend 
further weight to the recommendation that one should not exceed about 70% of 
one's maximum breath holding capability during heavy lifting (Vorobyev A  
"Textbook on Weightlifting"  1978).

------------------------

Miyamoto K et al   Effects of abdominal belts on intra-abdominal pressure, 
intra-muscular pressure  in the erector spinae muscles and myoelectrical 
activities of trunk muscles.   Clin Biomech (Bristol, Avon) 1999 Feb; 
14(2):79-87

Intra-muscular pressure of the erector spinae muscles increases significantly 
by wearing an abdominal belt during Valsalva maneuvers and during maximum 
isometric  lifting exertions, while maximum isometric lifting capacity and 
peak intra-abdominal pressure are not affected. Electrical activity of rectus 
abdominis increases significantly by wearing an abdominal belt during 
Valsalva maneouvres (after full inspiration) and during isometric leg 
lifting. 

It is concluded that wearing abdominal belts raises intra-muscular pressure 
of the erector spinae muscles and appears to stiffen the trunk. Assuming that 
increased intra-muscular pressure of the erector spinae muscles stabilizes 
the lumbar  spine, wearing abdominal belts may contribute to the 
stabilization during lifting exertions.
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Cholewicki J et al    Lumbar spine stability can be augmented with an 
abdominal belt and/or  increased intra-abdominal pressure.   Eur Spine J 
1999;8(5):388-95

The belt and raised IAP (Intra-abdominal pressure) increased trunk stiffness 
in all directions, but the results in extension lacked statistical 
significance. In flexion, trunk stiffness increased by 21% and 42% due to 40% 
and 80% IAP levels respectively; in lateral bending, trunk stiffness 
increased by 16% and 30%. The belt added between 9% and 57% to the trunk stiff
ness depending on the IAP level and the direction of exertion. In all three 
directions, the EMG activity of all 12 trunk muscles increased significantly 
due to the elevated IAP. 

The belt had no positive or negative effect on the activity of any of the 
muscles, with the exception of the thoracic erector spinae in extension and 
the lumbar erector spinae in flexion, whose activities decreased. The results 
indicate that both wearing an abdominal belt and raised IAP can each 
independently, or in combination, increase lumbar spine stability. However, 
the benefits of the belt must be interpreted with caution in the context of 
the decreased activation of a few trunk extensor muscles.
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Cresswell A, Blake P & Thorstensson A   The effect of an abdominal muscle 
training program on intra-abdominal pressure. Scand J Rehabil Med 1994 Jun; 
26(2):79-86

The effect of 10 weeks' specific abdominal strength training (resisted trunk 
rotations) on intra-abdominal pressure was investigated in 10 healthy males. 
Isometric rotational force, trunk flexor and extensor torque and 
intra-abdominal pressure were measured as well as intra-abdominal pressure 
responses to Valsalva manoeuvres, maximal pulsed pressures, drop jumps and 
trunk perturbations. 

Rotational strength increased 29.7% after training without significant change 
in intra-abdominal pressure. The isometric flexor strength did not change, 
while the extensor strength increased 11.0%. Valsalva and pulsed pressures 
increased 11.6 and 9.2%, respectively. The rate of intra-abdominal pressure 
development during pulsed pressures, drop jumps and trunk perturbations 
increased after training. The level of intra-abdominal pressure during the 
latter two tasks remained unchanged. 

It is  concluded that an increase in strength of the trunk rotators with 
training improves the ability to generate  higher levels of voluntarily 
induced intra-abdominal pressure and increases the rate of intra-abdominal 
pressure development during functional situations.  
 
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Hemborg B et al     Intraabdominal pressure and trunk muscle activity during 
lifting--effect of abdominal muscle training in healthy subjects.  Scand J 
Rehabil Med 1983;15(4):183-96

Twenty healthy young men went through intense isometric training of the 
abdominal muscles for five weeks. Before and after training the subjects were 
put through a standardized test programme, measuring the strength of 
abdominal and back muscles, and a series of lifts, 10, 25, and 40 kg, leg 
lifts and back lifts. The intraabdominal pressure (IAP), and the EMG activity 
of the oblique abdominal muscles, and of the erector spinae muscle were 
recorded. 

It was found  that: 

1.  The strength of the trunk flexors increased markedly after abdominal 
training. The activity of the oblique abdominal muscles when lifting 
decreased after abdominal training, i.e. motor unit recruitment was not 
improved.

2.  The IAP at lifting was not affected by abdominal training. 

3.  The activity of the oblique abdominal muscles was of no decisive 
importance to the IAP. 

4.  The strength of the back muscles increased, but the activity of the back 
muscles at lifts was not affected by abdominal training. In back lifts there 
was no detectable activity of the back muscles during the beginning of the 
lifting and during a great part of the lowering. 

5.  In back lifts the maximum activity of the abdominal muscles appeared long 
before the peak of the IAP, which may be of  importance with regard to the 
development of inguinal hernia.
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Cholewicki J, Juluru K & McGill S   Intra-abdominal pressure mechanism for 
stabilizing the lumbar spine. 
J Biomech 1999 Jan;32(1):13-7

Two distinct mechanisms for stabilising the spine were simulated separately 
and in combination. One was antagonistic flexor-extensor muscle coactivation 
and the second was abdominal muscle activation along with generation of IAP. 

Both mechanisms were effective in stabilizing the model of a lumbar spine. 
Both  mechanisms were also effective in providing mechanical stability to the 
spine model when activated simultaneously. The breath-holding IAP mechanism 
for stabilizing the lumbar spine appears preferable in tasks that demand 
trunk extensor moment such as lifting or jumping. This mechanism can increase 
spine stability without the additional coactivation of the erector spinae 
muscles of the back.
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Dr Mel C Siff
Denver, USA
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