Exercise induced leg pain

Anatomically speaking, the ‘leg’ is the region between the knee and the ankle. Chronic repetitive weight bearing exercise can be associated with painful conditions in this region. The sources of leg pain are varied, but the cause is often the same. While most body tissues have the capacity to adapt and strengthen in response to overload, overuse injuries typically occur when loads are increased more rapidly than the tissue capacity to adapt.

‘Shin splints’ is a lay term that has been used to describe a large number of fundamentally different exercise-induced leg injuries including tendinopathy, compartment syndrome and bone stress injuries. In light of the marked tissue-level differences between these conditions, clinical use of the term ‘shin splints’ is inappropriate and unhelpful for the purposes of diagnosis and management. Instead, each should be differentially diagnosed and managed.

Tendinopathy

What is tendinopathy?
Microtears in tendon that may cause inflammation in the tendon sheaths and surrounding tissue. Often incorrectly referred to as tendinitis.

How does it occur?
Over-training in repetitive movements, particularly over-stretching and eccentric loading (muscle contracting while being forced to lengthen). There may be a relationship between repetitive hyperpronation (excessive flattening of
the arch of the foot during locomotion) and tibialis posterior tendinopathy.

Region most affected
Tendon of tibialis posterior (deep muscle at the back), however, tibialis anterior (muscle at the front), the Achilles (the heel cord) and peroneal (muscles at the outside) tendons can also be affected.

Signs and symptoms
Pain, swelling and palpable crepitance (crunchy feeling) along the tendon during muscle contraction and stretch. For tibialis posterior tendinopathy, this can be mainly felt behind the “inside ankle bone” (medial malleolus.) Pain
occurs mainly at the start of and following exercise.

Prevention
Gradual increases in training. Methods to reduce hyperpronation may be helpful in tibialis posterior or anterior tendinopathy.

Treatment
Initially, avoid painful activities, but complete rest is not advised as tendon heals better when given mild, normal loading. Once inflammation and pain has subsided, stretch and strengthen the muscle associated with the tendon beginning with isometrics and graduating to eccentric loading.

Bone stress injuries

Medial Tibial Stress Syndrome – MTSS, stress reactions and stress fracture.

What is a bone stress injury?
A bone stress injury is a continuum of injury from inflammation of the periosteum (membrane surrounding bone), to bone microcracks, and finally to incomplete or complete cracks in bone in response to chronic loading of high magnitude and/or repetitions.

How does it occur?
Typically following inappropriately rapid increases in loading intensity or a change in the nature of the loading. Bone bending is a natural consequence of weight bearing. Chronic repetitive bending stimulates the tibia to increase its size by activating bone cells in its periosteum to lay down new bone. If increases in training intensity continues to occur during this process of adaptation, the periosteum can become inflamed (MTSS) or, microdamage can occur in the bone tissue. When this happens, bone cells can resorb the damaged bone and replace it with new bone, but there is a lag between resorption and formation.

If more loading occurs during the temporary window of reduced mass due to resorption, more damage is likely to occur and microdamage can progress to a crack or stress fracture. The injury may be compounded by simultaneous, repetitive muscle or fascial pull on the periosteum.

Being female, white, having low energy availability, low calcium and vitamin D, chronic use of corticosteroids and NSAIDS, and poor sleep are all associated with an increased risk of bone stress injury.

Other functional factors may increase risk of bone stress injury such as low step rate (long strides), reduced dorsiflexion range (moving the top of the foot towards the shin), and low leg muscle strength and endurance, but there is
great individual variation in risk.

Region most affected
Mid-to-distal region of the tibial shaft coinciding with the narrowest cross section, but stress injuries can also occur in the medial tibial condyle and in medial malleolus.

Signs and symptoms
Pain during weight bearing (particularly running and jumping) that does not ‘warm up’ as activity continues. Tenderness on palpation, which is diffuse along the medial tibial border in MTSS. Profound localised pain and focal tenderness as well as night pain is suggestive of a stress fracture. Can cause swelling, redness and warmth. MRI will typically show periosteal oedema (fluid-related swelling of the covering of the bone) in MTSS. The addition of endosteal (lining inside the bone) and sometimes marrow oedema (fluid-related swelling) is indicative of bone microdamage (microscopic cracking) or stress fracture.

Prevention
Wider bones resist bending better than narrower ones and are therefore less prone to injury, so preventative bone loading is key. Gradual training increases (<10% per week) and introducing other training modification gradually (different running surface, shoes, etc) is important. Addressing the risk factors listed above is recommended, particularly stabilising energy balance, 1000 mg calcium per day and 6 hours sleep a night.

Treatment

• Rest from painful activities (minimum 7 days – 15 days, depending on severity).
• A pneumatic brace may be indicated for stress fractures if painful when walking.
• Pool run and cycle to maintain aerobic fitness.
• Return to training gradually at a rate considerably lower than the rate at which the injury occurred and only if loading is pain free.
• Treadmill running, slower speed, and shorter strides will reduce loading during rehab.
• Do not stretch or strengthen muscles while symptomatic.

Typical tibial stress fractures typically heal within 4 to 8 weeks however stress fractures on the anterior (front) border of the tibia can take many months to heal and may require stimulation or grafting. It is not uncommon for tibial stress injuries to recur. If so, further rest is necessary, return to training must be at a much slower rate, and risk factors addressed.

Chronic Compartment Syndrome

What is chronic compartment syndrome?
A condition of leg muscle ischemia (lack of blood) occurring during exercise. It is relatively rare.

How does it occur?
Normally, during exercise, an elevated demand for oxygen induces increased flow of blood to the muscles, causing them to swell about 20%. If the sheaths of connective tissue (fascia) surrounding the muscles are unusually inelastic, this expansion is limited, and the increase in blood flow is prevented. Muscles starved of oxygen produce cramping pain.

Region most affected
The anterior (front) compartment. However, the deep posterior and peroneal (side) compartments may also be affected. The condition occurs in both legs in 90% of cases.

Signs and symptoms
Deep, diffuse, aching, cramping leg pain, swelling and tightness, leg muscle weakness, numbness in the leg and/or foot, reduced pulse at the front of the ankle, occasional muscle herniations
through fascial defects. Initially pain develops around 30 minutes into a moderate exercise bout but, with time, pain occurs earlier. If the activity is promptly ceased, pain resolves within 10-15 minutes. The diagnosis may be confirmed by compartment pressure testing during or immediately following exercise. Unlike muscle strain, tendinopathy, MTSS or stress fracture, symptoms are absent between exercise bouts, but those conditions can coexist complicating differential diagnosis.

Prevention
Nothing known to be effective.

Treatment
Acutely, immediate rest, leg elevation and icing. Fasciotomy (a surgical procedure involving the cutting of fascia in the leg to release thecompartments) is the only effective long term solution if a patient is to remain active. Rest, antiinflammatories and stretching are ineffective. Exercises that increase muscle bulk will compound the problem.

Conclusion

For most painful exercise-induced leg conditions, prevention, in the form of gradual changes in nature and intensity of training loads is the most effective form of management. Such loading gradation will avoid the accumulation of tissue injury at a rate that outstrips the body’s natural ability to adapt.