What it is
The muscles of the lower leg sit in four compartments wrapped in tough tissue (fascia): the front, the outside, and the shallow and deep back of the calf. In CECS, repeated exercise brings on pain and tightness in one or more compartments, and it eases when you stop. The NHS describes symptoms that come on gradually with exercise and go away when you rest.
The usual explanation is that pressure builds inside a compartment that can't expand enough during exercise. A 2026 review points out that this has never been proven, so the cause is still debated.
Sources 1, 2, 3, 4
Who gets it
Mostly young, active people whose sport repeats the same movement, especially running and marching. Of 1,411 people referred to a Dutch specialist centre with exercise-related leg pain, 698 had CECS on testing, and it was commonest at about 20 to 25 years. In US service members it is diagnosed at about 0.49 per 1,000 people a year.
In people under 50 at that centre, 59% had the front compartment involved and 53% the deep back compartment (some had both), and only 22% had it in one leg. It isn't only a young person's problem: 1 in 7 diagnosed were 50 or older. They more often had it in one leg (45%) and in the front compartment (82%), and most of them did no sport beyond walking or hiking.
Sources 5, 6, 7, 1
How it's recognised
In a consensus of 27 civilian and military experts, all those who finished agreed it is likely when someone does an activity that repeats the same muscle action, has pain and tightness during it, stops or avoids that activity, and has the symptoms brought on when examined after exercise. Cramp, weakness and pins and needles can happen but weren't seen as essential.
In a Dutch running study, people's pain came on within the first 15 minutes of running and settled within 15 minutes of stopping. The American Academy of Orthopaedic Surgeons (AAOS) adds numbness, a foot that slaps down when running, and visible muscle bulging. Almost all the experts (96%) didn't use X-rays or MRI (magnetic resonance imaging) scans to confirm it; scans are used to rule out other causes such as a stress fracture.
Sources 3, 8, 1
The pressure test helps, but isn't a clear yes or noStrong evidence
A specialist can measure the pressure in a compartment with a needle before and after exercise. The trouble is that the usual cut-offs overlap with healthy people: in a review of 38 studies, all but one of the common criteria overlapped the range in people without symptoms, and several studies found pressures in people without symptoms that would have counted as positive. Another review of 32 studies found a clear gap only for the reading 1 minute after exercise.
Experts agree the 1-minute reading is the most useful, but not on the cut-off: 54% use the most widely quoted criteria (the Pedowitz criteria) or part of them, and 38% use their own. So a high reading supports the diagnosis when the story fits, a borderline one settles little, and a normal one doesn't rule it out: when people with ongoing symptoms were tested again, 3 of 20 compartments that had been normal before now met the criteria.
Sources 9, 10, 3, 11, 12
Compartment syndrome, shin splints, a stress fracture or narrowed arteries?
These can feel alike, and shin splints and CECS often happen together: about half the people in one Dutch running study had both, and in a Dutch military programme people with both did as well as those with CECS alone.
- CECS: tightness and pain in the muscle, building at about the same time or distance in each run and easing within minutes of stopping, often in both legs.
- Shin splints: a tender strip along the inner edge of the shin bone, during and after running. The shin splints guide covers it.
- Stress fracture: one spot on a bone you can point to, sore with every step and later at rest or at night. The stress fracture guide covers it.
- Narrowed leg arteries (peripheral arterial disease): an ache in the calf or thigh on walking that goes after a few minutes' rest, more likely if you smoke or have diabetes. In 84 people over 50, CECS came on later in exercise (about 15 minutes against 4), and stopping exercise fully relieved the arterial pain in everyone but not in most people with CECS.
- Popliteal artery entrapment, a rare problem with the artery behind the knee, can mimic deep calf CECS. In 69 people, tingling in the foot and symptoms in both legs pointed to the artery problem.
Sources 3, 8, 7, 13, 14, 15
How it usually goesEmerging evidence
Left as it is, it tends to stay: in 12 soldiers who were diagnosed but not operated on, all still had the same symptoms about 4 years later, and 16 of 21 legs still met the pressure cut-off. It is usually not an emergency, though: in 191 service members on Dutch conservative programmes, none developed acute compartment syndrome.
Sources 16, 17, 18
Acute compartment syndrome: the emergency
Acute compartment syndrome is different and dangerous: pressure rises fast enough to cut off the blood supply to the muscle. The NHS says it usually starts suddenly, after an injury or a bandage or cast that is too tight, and needs surgery as soon as possible. The British Orthopaedic Association's standard names pain far worse than the injury explains, and pain when the muscle is stretched, as the key signs. The AAOS calls numbness and paralysis late signs.
Rarely, it follows very hard exercise that breaks down muscle, without any injury. In 7 young male athletes it took an average of 97 hours to diagnose, 4 were missed at first, and 2 of those 4 were left with lasting nerve damage and loss of function. In one case report, the pain and a foot drop began the day after a hard workout.
Sources 2, 19, 1, 20, 21
