Shin splints is a broad term for exercise-related shin pain. It often follows a change in running load, but bone stress injury and other problems can also cause lower-leg pain.
If pain becomes more localised, starts earlier in runs, affects walking, or continues at rest, do not keep testing it with another run. Reducing the provoking load and getting an appropriate assessment is more useful than assuming every shin problem just needs tougher muscles.
WHEN TO GET HELP
Severe pain, marked swelling or worsening pain with ordinary walking warrants medical advice promptly.
Further reading
This is general information, not a diagnosis or an individual rehabilitation plan. An assessment may change the advice that is right for you.