To understand CECS (or its much more serious relative, acute compartment syndrome) requires a beyond-basic knowledge of muscle anatomy and physiology. Muscles are bundled in a strong, thin, not very stretchy membrane called fascia—like casing on a sausage. Muscle use raises energy demand. An increase in energy demand is met by increased blood flow. Increased blood flow can cause a growth in muscle volume by as much as 20 percent, but because the fascia doesn’t expand, things get tight in the compartment. When things get tight, it’s harder for energy to get where it needs to go, so the entire limb starts underperforming. An underperforming forearm means an underperforming wrist, hand, and fingers.