Runner's knee, or patellofemoral syndrome, is a common running injury that is often described as a dull pain at the front of the knee joint. The patellofemoral joint is a diarthrodial plane joint with no secure articulation with the tibia or femur. The patella is embedded in the quadriceps tendon and acts as a mechanical pully to increase the torque of the quadriceps for knee extension. 

Patellofemoral Syndrome has several causes that are generally agreed upon. Weak hip abductors/flexors, tight quadriceps, genu valgus or genu vara, overuse, and rapid changes in training load are all common reasons for this pain to develop.

Taking a deeper look, patellofemoral syndrome's causes are normally linked to abnormal patellar groove pathing. The patella will rub harder on either side of the superior tibial condyles causing degradation of cartilage, inflammation, and damage to the bone.

Rehab strategies for treating runner's knee generally recommend rest and strengthening the quadriceps and gluteus medius.

Stress fractures are injuries to the bone that manifest as micro-fractures or increased stress on certain areas of bone visible on x-rays or MRIs. The most common stress fractures related to running are on the metatarsals, navicular, tibia, and sacroiliac joint. Without imaging, stress fractures are usually diagnosed when the individual reports extremely severe point tenderness on a bony structure. 

Stress fractures have two main causes, overuse and under-fueling. Overuse stress fractures occur as a result of sudden drastic changes in training load that the body is unable to recover from. Stress fractures related to under-fueling generally come about as a result of the athlete failing to meet the nutritional requirements of their training. 

Normal training for running requires the bones of the lower extremity to be exposed to forces that are much higher than normal daily activities. Because of this, the body needs extra time to rebuild after being exposed to this stress. After a long period of time without proper recovery, stress fractures can develop. 

Treatment of stress fractures almost always requires some amount of time off from running. Additionally, crutches, boots, or other ambulatory devices might be prescribed by a doctor to reduce the stress on the affected bone. In some cases, the athlete may need to be cast or require surgical intervention. 

Achilles Tendinopathy is a broad group of injuries that are related to the function of the Achilles tendon. The Achilles is the point of termination for the gastrocnemius and soleus muscles, the primary plantar flexors of the ankle, a group of muscles also known as the triceps surae. Commonly there are two types of tendinopathy that affect the Achilles, high and low tendon pain. The high tendon pain affects the musculotendinous junction and the low tendon pain affects the connection between the calcaneus and the Achilles tendon. 

The most common causes of Achilles tendinopathy are a sudden increase in training load, shoe/running surface selection, pes planus, and weak plantar flexors.

Achilles tendon injuries are uniquely dangerous due to the high amount of force that is sent through it during a running stride. Too much damage to the tendon can cause a sudden rupture which is one of the hardest running injuries to recover from and almost always requires surgery. 

As a result, treatment for Achilles tendinopathy is generally very reserved and slow. Generally beginning with a break from activity. Then rehab will progress slowly until a pain-free range of motion can be achieved before applying any stress to the muscles up the chain.