A compression is the act of pressing, squeezing, or applying pressure to reduce the size or volume of something. The term shows up across medicine, physics, fitness, and emergency care, and in each context it refers to a slightly different application of the same basic principle: force pushing inward. Here’s what compression means in the situations you’re most likely to encounter it.
Compression in Physics
In physics, compression is a force that shortens or squeezes a material. When you push down on a spring or step on a sponge, you’re applying compression. Every solid and fluid resists compression to some degree, and scientists measure that resistance using a value called the bulk modulus: the ratio of the pressure applied to how much the material’s volume shrinks in response. Materials with a high bulk modulus, like steel, barely compress at all. Materials with a low bulk modulus, like rubber or foam, compress easily.
For objects shaped like rods, columns, or wires, the relevant measurement is how much the material shortens relative to the force applied along its length. This is the same principle at work when a concrete column supports a building or when a car’s suspension absorbs the weight of its passengers.
Compression Therapy for Circulation
In medicine, compression therapy uses external pressure (from bandages, stockings, or pneumatic devices) to improve blood flow in the legs. The underlying problem it addresses is simple: gravity works against the veins trying to push blood back up toward the heart. Over time, this can cause blood to pool, veins to stretch, and fluid to leak into surrounding tissue, resulting in swelling, varicose veins, or slow-healing wounds.
Compression garments counteract this by squeezing the leg and narrowing the veins, which speeds up blood flow, reduces vein diameter, and shifts pooled fluid back into central circulation. Therapeutic pressures in the range of 40 to 60 mmHg can meaningfully reduce swelling. The garments also reduce backflow through faulty vein valves and improve the leg’s natural pumping action during walking. People with chronic venous insufficiency, lymphedema, or leg ulcers are the most common users.
Compression therapy does have limits. People with significant peripheral artery disease, where blood supply to the legs is already restricted, need careful evaluation before using high-pressure garments. Current guidelines flag patients with an ankle-brachial index (a simple blood pressure ratio comparing the arm and ankle) between 0.5 and 0.8 as needing modified or cautious compression.
Cold Compression for Injuries
If you’ve ever iced a sprained ankle while wrapping it snugly, you’ve used cold compression. Applying cold to an injury slows the metabolic rate of surrounding tissue, which limits further damage in the first hours after an injury. Cold also constricts blood vessels, reducing the amount of blood that leaks into surrounding tissue and limiting swelling.
Adding compression on top of cold amplifies the effect. The combination cools tissue faster, reaches deeper layers, and speeds up the removal of excess fluid through the lymphatic system compared to cold alone. This is why devices that deliver both cold and pressure simultaneously are common in orthopedic recovery rooms and athletic training facilities.
Chest Compressions in CPR
During cardiopulmonary resuscitation, chest compressions are rhythmic pushes on the breastbone designed to manually pump blood through the heart when it has stopped beating on its own. The American Heart Association defines high-quality CPR as compressions at a rate of 100 to 120 per minute, pressed to a depth of at least 2 inches (5 centimeters) in adults, and at least one-third the depth of the chest in infants and children. Rescuers should aim for a chest compression fraction above 80%, meaning compressions are happening during at least 80% of the resuscitation effort with minimal interruptions.
Compression Fractures
A compression fracture happens when a bone collapses under pressure, most commonly in the vertebrae of the spine. These fractures are especially common in older adults with osteoporosis, where weakened bone can crack from something as minor as bending forward or coughing. The vertebra essentially loses height as it gets crushed.
Doctors grade compression fractures by how much height the vertebra has lost. A mild fracture involves 20% to 25% height loss, moderate means 25% to 40%, and severe is anything over 40%. Symptoms typically include sudden back pain that worsens with standing or walking. Multiple compression fractures over time can lead to a hunched posture and loss of overall height.
Nerve Compression
Nerve compression occurs when sustained pressure is applied to a nerve, disrupting its ability to send signals. Carpal tunnel syndrome is the most familiar example, where a nerve in the wrist gets squeezed inside a narrow passageway.
What happens inside a compressed nerve is a cascade of structural damage. First, the fluid normally cushioning nerve fibers gets squeezed out. Then the internal contents of the nerve fibers themselves start to deform and shift. The protective insulation around nerve fibers (myelin) can crack, separate into layers, and overlap in disordered patterns. In severe cases, nerve fibers can be sheared apart entirely. These changes are caused by mechanical forces, not just reduced blood supply, though prolonged compression can add blood-flow problems on top of the physical damage. The result is numbness, tingling, weakness, or pain in whatever area that nerve serves.
Compression Garments in Sports Recovery
Athletes commonly wear tight-fitting sleeves, socks, or full-body garments after hard training sessions. The goal is to reduce muscle swelling and inflammation, which in theory speeds recovery and reduces soreness. After high-intensity exercise, muscles accumulate markers of damage and inflammation. Compression garments apply gentle, sustained pressure that helps limit swelling and may reduce the severity of delayed-onset muscle soreness, the deep ache that peaks one to two days after a tough workout.
The practical effect is modest but consistent: less perceived soreness and a slightly faster return to normal muscle function. Athletes in sports with heavy eccentric loading (running downhill, plyometrics, heavy resistance training) tend to see the most benefit. The garments won’t prevent muscle damage, but they can make the recovery window a bit shorter and more comfortable.