Shin splints are caused by repetitive stress on the shinbone and the tissue surrounding it, typically from running or other high-impact activities. The underlying problem is an accumulation of tiny, unrepaired damage in the bone of the lower leg, combined with inflammation of the membrane that wraps around the bone. Between 5% and 70% of runners experience shin splints depending on the population studied, making it one of the most common overuse injuries in sport.
What Happens Inside the Shin
The medical name for shin splints is medial tibial stress syndrome, and the process starts at the microscopic level. Every time your foot strikes the ground during a run, the tibia (your shinbone) bends slightly under load. That bending creates tiny amounts of damage in the outer layer of the bone, which is normal. Your body repairs this microdamage between sessions, and over time the bone actually gets stronger because of it. Shin splints develop when the rate of damage outpaces the rate of repair.
The bone is wrapped in a thin, nerve-rich membrane called the periosteum. Muscles in the back of your lower leg, especially the soleus (the deep calf muscle), attach to this membrane through connective tissue fibers. When those muscles contract repeatedly, they tug on the periosteum and create additional stress right where it connects to bone. This combination of bone bending and muscle pulling inflames the periosteum, producing the aching, diffuse pain along the inside of the shin that characterizes the condition.
Training Load Is the Biggest Trigger
The single most common trigger is doing too much, too fast. When you increase your running distance or pace sharply from one week to the next, the load on your tibia jumps before your bone and soft tissue have time to adapt. Research on recreational runners found that increasing weekly volume by more than 10% while also picking up pace was roughly 12% more likely to cause injury than holding steady or pulling back slightly. The bone needs time between sessions to recover its sensitivity to loading. After 24 hours of rest, about 98% of bone mechanosensitivity returns, which is why alternating running days with rest days is protective.
This explains why shin splints cluster in predictable groups: new runners building mileage for the first time, military recruits suddenly marching and running daily, and experienced runners returning after a break or ramping up for a race. The common thread is a rapid spike in repetitive impact before the body has adapted to handle it.
How Your Feet and Hips Play a Role
Foot mechanics are a well-documented risk factor. Overpronation, where the foot rolls inward excessively during each stride, increases stress on the inner edge of the tibia. One way to measure pronation is the navicular drop test, which checks how much the arch of the foot collapses when you stand. In a study of 77 cross-country runners, those with a navicular drop greater than 10 millimeters were nearly seven times more likely to develop shin pain than those below that threshold.
The speed of pronation matters too, not just the amount. Runners with shin splints tend to pronate faster, meaning the foot rolls inward more abruptly at impact. Weakness in the peroneal muscles on the outside of the lower leg or tightness in the posterior tibialis on the inside can both worsen this pattern by allowing the subtalar joint (the joint just below the ankle) to move through an excessive range.
The problem doesn’t always start at the foot. Increased internal rotation at the hip can change your running gait in ways that shift extra load onto the tibia. Essentially, anything upstream or downstream that alters how force travels through the lower leg can contribute.
Body Weight and Bone Density
A higher body mass index is a consistent, statistically significant risk factor. An evidence-based review found that people who developed shin splints had a meaningfully higher BMI than those who didn’t, though the absolute difference was modest. The proposed explanation is straightforward: more mass relative to height means more force on the tibia with every step, pushing closer to the threshold where microdamage accumulates faster than the bone can repair it. This doesn’t mean only heavier people get shin splints, but it does mean that carrying extra weight while ramping up impact activity raises the risk.
Lower bone mineral density likely amplifies this effect. Bone that is less dense to begin with has a lower threshold for microdamage, so the same training load is relatively harder on the tibia.
Worn-Out Shoes and Hard Surfaces
Running shoes lose their shock-absorbing capacity over time as the midsole foam compresses. The general recommendation is to replace running shoes every 500 to 700 kilometers (roughly 300 to 435 miles). Beyond that point, the cushioning degrades enough that more impact force transfers directly to your bones and joints. If you’re running 30 kilometers a week, that means new shoes roughly every four to six months.
Surface matters as well. Concrete and asphalt are unforgiving, returning nearly all of the impact energy back into your legs. Switching some runs to softer surfaces like trails, grass, or a track can reduce the cumulative load on the tibia without cutting your mileage.
How Shin Splints Differ From a Stress Fracture
Because shin splints and tibial stress fractures exist on the same spectrum of bone overload, telling them apart matters. Shin splint pain is typically diffuse, spreading across a broad area along the inside of the lower leg. Stress fracture pain is localized to one specific spot. Pressing along the shin with your fingertips can help: a stress fracture will produce sharp tenderness at a single point, while shin splint tenderness is spread out.
Another key difference is what happens during exercise. Shin splint pain often improves as you warm up and the tissues loosen, though it returns afterward. Stress fracture pain does not improve with continued activity and may worsen. Pain that persists at rest, stays pinpointed to one location, or doesn’t get better after scaling back activity warrants medical evaluation, because continuing to run on an undiagnosed stress fracture can lead to a complete break.
What Recovery Looks Like
Most shin splints involve the posteromedial (inner back) part of the tibial shaft, which is considered a low-risk location that heals without major complications. Recovery time varies widely depending on how long you trained through the pain before backing off, but most people see significant improvement within two to six weeks of reducing impact load.
Returning to running is a gradual process. A common protocol starts with alternating 30 to 60 seconds of easy jogging with 60 seconds of walking, then slowly increasing the running intervals over days and weeks. Running on alternate days rather than consecutive days gives bone cells time to regain their mechanosensitivity and continue adapting. Jumping straight back to previous mileage is the fastest route to a relapse.
Addressing the root cause during recovery makes a meaningful difference. If overpronation is a factor, motion-control shoes or custom orthotics can help. If the trigger was a sudden spike in training volume, a more conservative buildup plan prevents recurrence. Strengthening the calf muscles, particularly the soleus, and the muscles that control hip rotation reduces the traction forces on the periosteum that contributed to the problem in the first place.