What is the function of transport proteins in the plasma membrane?

Transport proteins allow substances through the membrane which cannot pass through the phospholipid bilayer throuh passive diffusion

These substances include:

Water-soluble molecules/polar molecules

Large molecules

So the transport proteins allow these molecules to pass through via facilitated diffusion

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.