Fascia

Fascia is the connective tissue that wraps and separates muscles, organs and nerves throughout the body. It ranges from thin loose layers that allow tissues to slide against each other to dense sheets such as the iliotibial band and the plantar fascia.

It has real mechanical functions. It transmits some force between muscles, contributes to elastic energy storage during running, and provides a continuous structure that gives the body's soft tissue a degree of tensional integrity.

It is also richly innervated, which is likely more important than its mechanical role for how it is experienced. Fascia contains sensory nerve endings, so it contributes to proprioception and to pain perception.

The gap between that and popular fascia content is wide. Claims that foam rolling releases adhesions, that fascia can be lengthened by a few minutes of pressure, or that fascial restrictions explain unrelated symptoms run far ahead of the evidence. Dense fascia requires forces far beyond what a hand or a roller can apply.

That does not make foam rolling useless. It produces short term increases in range of motion and modest reductions in soreness, and the current explanation is neurological, a change in the nervous system's tolerance to stretch, rather than structural change in the tissue.

Two conditions people meet by name sit here: plantar fasciitis, better understood as a degenerative overload problem of the plantar fascia, and iliotibial band syndrome, which responds to load management and hip strength rather than to attempts at stretching a structure that barely lengthens.

In practice, roll if it feels useful before training, and treat load management and strength as the interventions that change tissue.