One garment, two jobs
A four-way woven shell that tracks the stride. It is joined to the liner at the waistband and nowhere else, so it moves independently of the leg.
A bonded compression liner, graduated firm through the quad and easier at the hem. It holds the muscle without the tourniquet feeling that makes most liners come off after an hour.
The two are fused rather than stitched through the high-friction zones. No ridge under load, no seam to work against on the inner thigh.
Why double compression
Three problems with the way training shorts are normally built, and what changes when you split the layers.
A single-layer tight ties the fabric over the quad to the fabric over the knee. Every stride drags one against the other. Splitting the layers lets the shell travel and leaves the liner where it was put.
Compression is only useful if it stays in contact. The bonded liner is anchored at the waistband and graduated down the leg, so it holds through the fourth set as well as the first.
The failure mode of a lined short is the liner climbing. Bonding the two layers at the waistband and nowhere else removes the mechanism that causes it.