MTSS (also known as shin splints) is characterised by pain at the posteromedial border of the tibia. It is thought to be the result of a imbalance between bony resorption and bone formation of the tibial cortex. Bony resorption takes place at a higher rate than bone formation (Magnusson et al. 2001). This theory has replaced the original theory that MTSS is caused by traction-related periostitis. MTSS is more common in women than in men, and hyperpronation of the foot during running is thought to be one of the main running-related risk factors (Reshef and Guelich 2012).

Two types of Achilles tendinopathy can be distinguished: insertional tendinopathy and mid-portion tendinopathy. Tendinopathy consists of a short acute inflammatory stage, but after some time it gradually becomes a degenerative condition (Abate et al. 2009). Chronic tendinopathy is characterised by a disorganised tendon structure, thickening of the tendon with increased ground substance and formation of peri- and intratendinous vascular sprouts and nerve endings (neurovascularisation). These changes, however, do apply to mid-portion tendinopathy whereas often the insertion site (enthesis) where the tendon connects to the bone is involved. Reasons why the osteotendinous junction is often affected are the low flexibility, the arrangement of fibres in relation to the direction of muscle force and a small insertion zone compared to muscle size (Renstrom and Hach 2005). Risk factors for Achilles tendinopathy related to running are a lateral rollover following heel strike and diminished forward force transfer underneath the foot (Van Ginckel et al. 2009). The later rollover may cause Achilles tendinopathy because of diminished shock absorption and increased stress on the lateral side of the tendon, whereas the diminished forward force may result in a reduced moment of the plantar flexors, which may be compensated by increased Achilles tendon forces, and thereby increased strain.

Patellofemoral pain syndrome (PFPS) is characterised by anterior knee pain in or around the patella, related to activity. PFPS is one of the most common causes for knee pain seen in primary care (Bahr et al. 2012). PFPS may result from increased cartilage and subchondral bon stress (Fredericson and Yoon 2006) and should be distinguished from patellar tendinopathy which involves the attachment of the patellar tendon to the patella. The risk factor that is most often associated with PFPS is weaker knee extension strength (Lankhorst et al. 2012b) Others factors for which there is some evidence that they are related to PFPS are a larger patellar tilt angle, lower peak torque knee extension, larger Q angle, larger sulcus angle, lower hip abduction strength and lower hip external rotation strength (Lankhorst et al. 2012a). Risk factors related to running are an excessive impact shock during heel strike and propulsion phase (Thijs et al. 2008), which results in high loads on the patellofemoral joint, and a less pronated position of the foot at heel strike and a more lateral rollover (Thijs et al. 2007), resulting in a supinated position of the foot and a less internally rotated tibia, leading to an increased Q angle, which would influence the patellar tracking and increase contact pressures.

Stress fractures of the lower leg and foot are typical in runners and are characterised by localised bone tenderness and oedema. In the lower leg, they occur most often in the distal and proximal part of the tibia and in the distal part of the fibula. In the foot they occur in the navicular bone and the metatarsals. The most common location for stress fractures among runners is the tibia (Lopes et al. 2012).

Stress fractures typically occur a few weeks to a few months after training has started (Bahr et al. 2012). Two theories, that are not mutually exclusive, exist about the aetiology of stress fractures (Sanderlin and Raspa 2003). According to the first theory, osteoclastic activity precedes osteoblastic activity by a few weeks, making the bone susceptible to injury during this period. The second theory finds the explanation for stress fractures in high stress on the bone at the insertion point of the muscles, which leads to bending stresses. A foot arch that deviates from normal may be a risk for tibial stress injuries (Barnes et al. 2008). Also, high vertical loading rates during running seem to be a risk factor for stress fractures in the tibia and metatarsals (Zadpoor and Nikooyan 2011).

This injury is also known as runner’s knee and is characterised by lateral knee pain near the lateral femoral condyle (Bahr et al. 2012). Repetitive friction between the iliotibial band and the femoral epicondyle is thought to be the cause of this condition, which is therefore termed ‘iliotibial band friction syndrome’. Some however have questioned this account and have argued that pain is caused by compression of the tissue between the tract and the epicondyle and have proposed ‘fascia lata compression syndrome’ as a more accurate name (Fairclough et al. 2007). Hip abductor weakness has been implicated in the onset of iliotibial band friction syndrome, although there is conflicting evidence regarding its role, and there is some evidence that early hip flexion and early knee flexion may be related to iliotibial band friction syndrome (van der Worp et al. 2012).

Plantar fasciitis is an enthesopathy that occurs at the proximal attachment of the plantar fascia to the calcaneus and is associated with heel pain. As in tendinopathy it is a degenerative condition, although lacking an initial inflammatory stage, and is therefore sometimes called ‘plantar fasciopathy’. Sometimes a heel spur is formed (Bahr et al. 2012). Risk factors for plantar fasciitis are increasing age, being female, increased body weight and running/playing on hard surfaces (Orchard 2012), whereas biomechanical running-related risk factors are higher impact peaks and loading rates (Pohl et al. 2009).

Besides these overuse injuries, acute injuries do also occurs in runners, although less often. Acute injuries, especially muscle injuries, are more common in sprinters and middle-distance runners than in long-distance runners (Lysholm and Wiklander 1987). Common acute RRIs are hamstring muscle injuries, gastrocnemius muscle injuries and ankle sprains (Table 49.2).

The incidence of RRIs is substantially high, and although there is a large body of literature on the subject of risk factors for RRIs, there is little consistency on the reporting of incidence, the aetiology and the risk factors of these injuries. The two most important factors for the occurrence of injuries in runners are higher running mileage and previous injury. Further research into specific injuries is required to determine the exact aetiology.