bending moment from e.g. the dead lift (DL) is transfered as a couple of forces. one compressive and one tensile. in the absence of axial loading the compressive and the tensile forces are equal in magnitude. typically the case in the bottom position of the DL.
spinal health is dependent on which part is generating the compressive force.
basically, there are 2 options to generate the compressive force, either the compressive force is generated in the spine (passive) or it is generated in the abdomen (active).
the longer lever between the abdomen and the erectors compared to the lever between the erectors and the spine results in a corresponding reduction of the magnitude of force required in the couple of forces that resists the bending moment if the abdomen generates the compressive force.
bracing is the widespread word for the technique to make the abdomen generate the compressive force. bracing transfers compressive forces from the spine to the abdomen and shear forces to the oblique abdomen.
failing to brace properly in the DL, thus results in a spinal compressive load combined with shear load, moreover due to the shorter lever the magnitude of force in the couple of forces will be higher. to my knowledge of the spine, is that it is not built and it cannot be trained to take substantial load and therefore this scenario must be avoided. this, IMO, is the single most important thing in lifting. IMO also, failing to brace properly might be the root cause for most back injuries in lifting ever.
It is more important to brace properly than to keep the spine in perfect alignment!
on one hand, if you fail to brace properly even if your spine is in perfect neutral alignment during a heavy lift, it will be loaded with compressive and shear forces and that is bad. on the other hand, if you brace properly but your spine is not in perfect neutral alignment your spine will be unloaded anyway and this is good.
i know two ways to discern proper bracing from improper bracing before disaster strikes.
one way is to gauge the sensory feedback from the erectors. proper bracing results in lowering of the erectors tensile force while improper bracing results in increasing of the said force. this is deceptive, as one might judge high tensile forces in the erectors as something desirable, but getting them at the cost of a compressive force in the spine is bad. typically, one could see this happening with a beginner that overextends at the lockout of a dead lift.
the other way i know of how to discern proper bracing from improper is by gauging the sensory feedback from the abdomen. the abdomen should feel really tensed and activated.
i’m sure hog already knows this, i got sort of carried away when i started to write, apologies for preaching to the choire, just felt i could contribute with something finally.
