MTTS, more precisely known as MTSS (medial tibial stress syndrome), is the medical term for what most people call shin splints. It’s an overuse injury that causes pain along the inner edge of the shinbone, typically in the lower two-thirds of the leg. Among runners, prevalence ranges from about 10% in collegiate cross-country athletes to nearly 70% in recreational marathon runners, making it one of the most common exercise-related leg injuries.
If you searched “MTTS” looking for the Vietnamese social enterprise Medical Technology and Transfer Service, that’s a separate organization based in Hanoi that designs low-cost neonatal care devices for hospitals in developing countries. The rest of this article covers the injury.
What Happens Inside the Shin
The pain of MTSS comes from the membrane covering the shinbone (the periosteum) becoming irritated where calf muscles attach to it. The soleus, a deep calf muscle, is the most likely culprit. It anchors directly to the inner border of the tibia, and repetitive pulling at that attachment site creates inflammation along a broad strip of bone rather than at a single point.
A second muscle called the flexor digitorum longus, which helps control your toes, also attaches in this zone and contributes to the stress. Interestingly, the tibialis posterior, a muscle long suspected in shin splints, doesn’t actually attach to the injury site in most people. The condition exists on a continuum with stress fractures: the same forces that cause MTSS, if they continue to accumulate, can eventually damage the bone itself.
How It Feels
The hallmark of MTSS is a dull, aching pain along the inner edge of the lower leg that shows up during or after exercise and improves with rest. The tender area typically stretches more than 5 centimeters along the bone. This is one of the key ways it differs from a stress fracture, which tends to produce sharp, pinpoint tenderness in a spot smaller than 5 centimeters.
Pain from MTSS doesn’t come with cramping, burning in the back of the calf, or numbness and tingling in the foot. If you’re experiencing those symptoms, something else is likely going on, such as compartment syndrome or nerve compression. Severe swelling, redness, or loss of pulse in the foot are also not typical of shin splints and warrant prompt medical attention.
Who Gets It
MTSS is overwhelmingly a running injury, but it’s also common in military recruits and anyone whose training involves repeated impact on hard surfaces. Incidence in military populations runs between about 11% and 35%, depending on the study. Among recreational runners, nearly half may develop the condition at some point.
A meta-analysis of runner studies identified several clear risk factors:
- Previous shin splints: Having had MTSS before makes you 3.7 times more likely to get it again.
- Female sex: Women are about 1.7 times more likely to develop the condition than men.
- Less running experience: Newer runners are significantly more prone, likely because their bones and soft tissues haven’t adapted to the repetitive load.
- Higher BMI: More body weight means more force transmitted through the shin with each stride.
- Flat feet: A navicular drop greater than 10 millimeters (a measure of how much the arch collapses under weight) roughly doubles the risk.
- Prior orthotic use: Runners who had previously used shoe inserts were 2.3 times more likely to develop MTSS, possibly because orthotic use signals pre-existing foot and leg problems.
In men specifically, increased outward rotation of the hip also showed a strong association with the injury.
How It Differs From a Stress Fracture
Because MTSS and tibial stress fractures exist on the same spectrum of bone stress injury, telling them apart can be tricky. The practical differences come down to the pain pattern. MTSS produces a broad, diffuse tenderness you can feel by running your fingers along several inches of the inner shinbone. A stress fracture hurts in one precise spot.
MTSS pain typically eases once you stop exercising and warm up again the next session before returning. Stress fracture pain tends to get worse with each bout of activity and can eventually hurt during normal walking. If rest isn’t improving your symptoms over a couple of weeks, or if the pain is becoming more localized and intense, imaging may be needed to rule out a fracture.
Recovery and Getting Back to Activity
The first and most important step is reducing the load on the shin. That usually means cutting back on running volume, switching temporarily to low-impact activities like cycling or swimming, and avoiding hard surfaces. Most cases of MTSS improve within two to six weeks of relative rest, though more stubborn cases can take several months.
Returning to full activity works best as a graded process. Start with light aerobic exercise that doesn’t provoke symptoms, such as 5 to 10 minutes of walking or easy cycling. If that goes well, progress to moderate jogging and brief running over the next several days. From there, build toward sport-specific drills and higher-intensity work before returning to competition. The key rule: if symptoms return at any stage, drop back to the previous level and give it more time.
Addressing the underlying risk factors matters as much as managing the acute pain. Strengthening the calf muscles (especially the soleus) through exercises like seated calf raises can improve the shin’s tolerance for load. Runners with significant arch collapse may benefit from supportive footwear or custom inserts. Gradually increasing weekly mileage rather than making large jumps gives bone and connective tissue time to adapt, which is especially important for newer runners who face the highest risk.