Researchers found that the hold, forcing a detainee to bend over while seated, can massively cut lung capacity.
They placed 40 volunteers in chairs and then leaned them forward, bringing their face close to the lap. They used arm holds and applied a small amount of force to prevent the volunteer from attempting to return to a normal sitting position. In the worst cases, the lungs' capacity was almost halved.
"Imagine that from the perspective of the security staff. They feel you struggle and they will feel that you are getting angry. They will apply more force to manage your resistance. It becomes a vicious circle."
Restraint technique could be fatal, research suggests. BBC.