How tension becomes muscle

Worth knowing because it tells you what is actually being trained, and it is the section where honesty about the evidence matters most.

#The chain

Load deforms integrin complexes at the costamere — transmembrane proteins that physically link the extracellular matrix to the cytoskeleton. That deformation recruits focal adhesion kinase.

Downstream, mTORC1 phosphorylates S6K1 and 4E-BP1, raising translational efficiency. The cell makes more contractile protein. Over weeks, satellite cells donate myonuclei so the fibre can support a larger cytoplasmic domain.

#Where the field is not closed

The route from FAK to mTORC1 is a leading proposal, not a settled pathway.

What is established, and it is the interesting bit: mechanical mTORC1 activation is insensitive to PI3K/Akt inhibition. Block the classic growth-factor pathway and mechanical loading still activates mTORC1. So the growth-factor route is not the carrier.

In parallel, mechanical stimulation activates diacylglycerol kinase-ζ, generating phosphatidic acid, which binds and activates mTOR directly. That one is well supported.

#Why tell you this

Because a program that presents every mechanism as settled is lying about a field that is not, and because the practical prescription does not depend on which proposal wins.

You do not need the pathway to be closed to know that tension drives growth. The intervention is the same either way: get fibres recruited, get them loaded, recover, repeat.

Be suspicious of anyone selling you a program on the strength of a mechanism diagram. The diagram is downstream of the training, not the reason it works.