Shin and calf muscles locking up during running or jumping is commonly caused by muscle cramps, overuse, dehydration, muscle fatigue, poor stretching, or low levels of minerals such as magnesium, potassium, calcium, or vitamin D. Repeated strain from high-impact sports can also lead to muscle tightness or stress-related injuries if the muscles are not recovering properly. Doctors may recommend electrolyte supplements, magnesium, calcium, vitamin D, or pain-relieving medicines depending on the cause and your test results. Proper warm-up, stretching before exercise, hydration, and gradual increase in training intensity are very important to prevent recurrence. Resting the muscles after heavy activity and wearing proper sports footwear may also help reduce strain on the shin and calf muscles. Please consult a doctor or sports specialist if the problem happens frequently, causes severe pain, swelling, weakness, or affects walking, as you may need evaluation for muscle imbalance, circulation problems, or stress injury.