The feet endure the brunt of the stress during a run, and that’s why foot injuries are some of the most common types of injuries in runners. Minor injuries like blisters or missing toenails are most common, but running can also result in more serious conditions that cause a great deal of pain and may sideline a runner for weeks or even months. Here are a few of the most common causes of foot pain for runners:

Plantar fasciitis

Type of pain: Most often it’s a sharp, painful sensation in the heel of the foot but it may also manifest as an ache along the arch of the foot. The pain is usually most intense in the morning when the first steps of the day are taken or at the very beginning of a run.

Cause: Plantar fasciitis is an inflammation of the plantar fascia, a thick band of tissue that runs along the bottom of the foot. One of the most common causes of this condition is increasing the intensity or duration of training runs too rapidly. Running in shoes that don’t offer proper arch support may also injure the plantar fascia.

Heel Spur

Type of pain: A sharp pain in the heel or arch of the foot, almost identical to the discomfort caused by plantar fasciitis. It differs from plantar fasciitis pain, however, in that pushing on the front of the heel and pressing backwards will cause the pain to intensify.

Cause: This condition is also caused by an injury to the plantar fascia, but in the case of a heel spur the fascia actually tear away from the heel bone. This leaves blood behind, and over time that blood calcifies and forms a spur. The pain is caused by the flesh, tendons, and muscles in the area rubbing against the new piece of bone in the foot.

Extensor Tendonitis

Type of pain: Acute soreness on top of the foot. The pain will likely become more severe if downward pressure is applied to the toes while trying to raise them.

Cause: The extensor tendons run along the top of the foot and are responsible for raising and straightening the toes as well as helping to move the entire foot. When those tendons become inflamed—usually from wearing improper shoes, a tight Achilles tendon, or tight or weak calf muscles—it can result in extensor tendonitis.

Stress Fracture

Type of pain: Soreness on the top of the foot, similar to that found in extensor tendonitis. With a stress fracture, however, the pain will become more intense with impact. Hopping on the injured foot, for example, will likely result in a sharp pain in the affected area.

Cause: Stress fractures occur most often when the duration and intensity of training is increased too rapidly. A misstep on a run, such as landing on a rock or in a pothole, may also cause a stress fracture.