Shin splints happen when the repetitive impact of running creates more stress on your shinbone than it can repair between workouts. The bone develops tiny microcracks, the tissue lining the bone becomes inflamed, and you feel that familiar aching along the inner edge of your shin. It’s one of the most common running injuries, affecting anywhere from 16% to 35% of runners depending on the population studied, with even higher rates among recreational marathon runners.
What’s Actually Happening Inside Your Shin
Your tibia (shinbone) is designed to absorb impact. Every time your foot strikes the ground while running, the tibia bends slightly under load and then rebounds. Your body normally handles this by continuously remodeling bone tissue, laying down new material where stress occurs. Shin splints develop when you’re running enough that the microdamage accumulates faster than your bone can repair it.
This creates two overlapping problems. First, tiny cracks form in the outer layer of the bone as its internal structure fails at the microscopic level. Second, the periosteum, a thin tissue wrapping the bone’s surface, becomes inflamed. The calf muscles that attach along the inner border of the tibia pull on this tissue with every stride, adding traction stress on top of the impact stress. The soleus (a deep calf muscle) and the flexor digitorum longus (a muscle that controls your toes) attach directly to the area where shin splint pain concentrates. Interestingly, the tibialis posterior muscle, long thought to be the main culprit, doesn’t actually attach to the pain site at all.
A layer of connective tissue called the deep crural fascia also anchors along the upper two-thirds of the inner shin border and may contribute to the pulling forces involved.
Why Some Runners Get Them and Others Don’t
Shin splints aren’t random. Several measurable physical traits raise your risk. The strongest biomechanical predictor is something called navicular drop, which is how much the arch of your foot collapses when you stand on it. People who developed shin splints had, on average, about 2 mm more navicular drop than those who didn’t. When your arch flattens excessively, your lower leg loses some of its ability to absorb ground forces efficiently, and more stress transfers directly into the tibia.
Greater ankle flexibility in the downward (pointing your toes) direction is another risk factor, possibly because it changes your foot-strike pattern. Runners with more range of motion at the hip in outward rotation also showed higher rates, though the exact mechanism isn’t fully understood. Higher BMI is consistently linked to shin splints as well, which makes sense: more body weight means more force on the bone with every step.
Women develop shin splints at higher rates than men. This may partly relate to bone mineral density differences, particularly in female athletes who experience menstrual irregularities, which can reduce bone density over time. Lower lean muscle mass in the lower leg is another contributing factor.
Experience matters too. Runners with more years of consistent training are less likely to develop shin splints later in their careers, likely because their bones have adapted to the loading over time. Newer runners are especially vulnerable because their bones haven’t yet remodeled to handle the forces of regular running.
Training Mistakes That Trigger Shin Splints
Training errors are the leading cause of preventable running injuries, and the pattern is almost always the same: too much, too soon, too fast. A study tracking 873 new runners over one year found that those who increased their weekly mileage by more than 30% over a two-week period had significantly higher injury rates than those who kept increases under 10%. The lowest injury rates belonged to runners who followed that familiar 10% rule, adding no more than 10% to their weekly distance at a time.
It’s not just mileage. Suddenly adding speed work, hill repeats, or extra running days can all spike the load on your shins before the bone has time to adapt. Returning to running after a break is a particularly high-risk window because the bone loses some of its conditioned resilience during time off.
Your Shoes and Running Surface
Running shoes lose their shock-absorbing capacity over time. The general recommendation is to replace them every 500 to 700 kilometers (roughly 300 to 430 miles). As the midsole foam compresses and breaks down, less impact gets absorbed by the shoe and more transmits into your lower leg. If you can’t remember when you bought your current pair, that’s probably a sign.
Hard surfaces like concrete deliver more impact per stride than asphalt, trails, or tracks. If you’re running exclusively on sidewalks and noticing shin pain, mixing in softer surfaces can reduce the cumulative stress on your tibia.
Shin Splints vs. Stress Fractures
Shin splints and tibial stress fractures exist on a spectrum of bone overload, and telling them apart early matters. With shin splints, pain typically shows up during running (especially at faster speeds) and fades once you stop. You generally won’t feel it while walking around or doing daily activities. The pain spreads across a few inches along the inner shin rather than concentrating at one specific point.
Stress fractures behave differently. The pain starts during running but eventually persists during walking and even at rest. It tends to localize to one precise spot that’s tender when you press on it. If your shin pain is getting worse over time, hurting during normal activities, or pinpointing to a single location, that warrants imaging to rule out a fracture.
How to Reduce Your Risk
Strengthening the muscles that support your tibia is one of the most direct things you can do. Calf raises performed on a step, lowering your heel past the edge and raising back up, build the soleus muscle that attaches along the shin’s pain zone. Three sets of 12 to 15 repetitions on each leg is a standard starting point. Single-leg soleus bridges, where you place the ball of your foot on a step edge and lift your hips, target the same area from a different angle.
Hip and glute strength also plays a role because weak hips allow your leg to rotate and collapse inward during the landing phase of running, increasing tibial stress. Building strength in your hip rotators helps control that chain of movement from the top down.
Beyond strength work, the most effective prevention strategy is simply managing your training load. Build mileage gradually, take rest days seriously, and don’t stack multiple new stressors (more miles, faster pace, new shoes, harder surface) in the same week. If you’re a newer runner, your bones need several months of consistent, moderate running to develop the density required for higher volumes. Patience during that adaptation period is what separates runners who push through shin splints repeatedly from those who stop getting them altogether.