Stress fractures (tiny cracks in a bone) are most common in the weight-bearing bones of the lower leg and foot. Experiencing pain in your feet while walking/exercising which goes away while resting is said to be a sign.
While they are usually considered to be a sign of osteoporosis, they can also occur due to the lack of nutrients, poor footwear, certain sports, suddenly shifting from a sedentary lifestyle to intense training, and more.