Shin splints
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The cause of shin splints is usually overused muscle, either an acute injury or DOMS (delayed-onset muscle soreness). The muscle pain is caused by any activity that involves running or jumping. An individual not accustomed to running may experience pain in the shin muscles the next day even after a single, short bout of intense running. There may even be immediate discomfort in the muscles from a build-up of lactic acid.
Shin pain may also be the result of inflammation of connective tissue such as periosteum (periostitis). The pain may be caused by a stress fracture in the bone or some other problem like osteosarcoma. Pain in the lower leg may also be referred from a distant area of the body, such as pressure on the sciatic nerve (sciatica) near the foot joint. If a bone problem is suspected, a bone scan can be useful in confirming the diagnosis.
The purpose of the muscles of the anterior shin is to dorsiflex the foot (raise the toe). It may not be obvious why a muscle which raises the toe can be stressed or injured by running, given that it is not responsible for propulsion. The reason is that unskilled runners overstride, and land heavily on the heel with each footstrike. When this happens, the forefoot rapidly slaps down to the ground. Effectively, the foot, which is dorsiflexed prior to making contact with the ground, is forcefully extended. This forceful extension of the toe causes a corresponding rapid stretch in the attached muscles. A reflex in the muscles responds, causing a powerful contraction. It is this eccentric contraction which leads to muscle soreness and possible injury to the muscle, tendon or connective tissue.
In a similar way, improper pronation of the foot during the footstrike can also cause pain in the muscles which oppose pronation, on the inside or outside of the shin. In proper pronation the foot strikes the ground on the outside of the heel and then rolls toward the inside of the foot approximately 5%. The ideal degree of pronation varies slightly with the individual. It is determined by factors such as the height of the arch (a higher arch has more clearance for pronation than a low arch) and the flexibility of the arch. In over pronation, the foot rolls in too far. The result is that the foot pushes off almost entirely from the big toe, causing excessive strain on the big toe and the outside of the shin. In contrast, under pronation, occurs when the foot does not roll enough. This causes the entire weight of the foot strike to concentrate on too small of an area on the outside of the foot which places a corresponding strain on the shin.
It is also commonly believed that a contributing cause of shin muscle pain in some cases is the relative weakness of the muscles on the anterior of the lower leg compared to those in the calf. In this case exercises that preferentially strengthen the anterior muscles may help alleviate or avoid shin splints. The shin pain is attributed to a forced extension of the muscle, in this case by the opposing calf muscles which "overpower" the shin.
A problem which can mimic anterior shin splints is chronic compartment syndrome (CCS). This is a serious problem which can lead to significant loss of function in the lower leg. CCS occurs when swelling within the indistensible anterior compartment of the leg reduces blood flow. This relative lack of blood, ischemia, can cause more swelling and generate a positive feedback loop. In severe cases the result can be acute compartment syndrome (ACS) which requires emergency surgery to prevent ischemic muscle necrosis, muscle death due to lack of blood.
Think of CCS when pain worsens steadily during exercise rather than improving as the ligaments and muscles warm. Tingling in the foot is a particular red flag; it indicates compression of the nerve.
If you suspect CCS seek medical attention before continuing to train. If you suspect ACS seek medical attention immediately night or day.
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[edit] Treatments and remedies
[edit] Acute treatment
The immediate treatment for shin splints is rest. Running and other strenuous lower limb activities like soccer should be avoided until the pain subsides and is no longer elicited by activity. In conjunction with rest, anti-inflammatory treatments such as icing and drugs such as NSAIDs may be suggested by a doctor or trainer, though there is some controversy over their effectiveness. Some people will use acupuncture to treat shin splints though there has not been any conclusive or comprehensive study in the effects of acupuncture on shin splints.
[edit] Training
Like any muscle, the muscles of the anterior shin can be trained for greater static and dynamic flexibility through adaptation, which will diminish the contracting reflex, and allow the muscles to handle the rapid stretch. The key to this is to stretch the shins regularly. However, static stretching might not be enough. To adapt a muscle to rapid, eccentric contraction, it has to acquire greater dynamic flexibility as well. One way to work on the dynamic flexibility of the anterior shin is to subject it to exaggerated stress, in a controlled way. If the muscle is regularly subject to an even greater dynamic, eccentric contraction than during the intended exercise, it will become more capable of handling the ordinary amount of stress. Experienced long-distance runners practice controlled downhill running as a part of training, which places greater eccentric loads on the quadriceps as well as on the shins. A professional trainer or coach, or perhaps a sports medicine doctor, should be consulted before engaging in this type of training.
[edit] Form
The long-term remedy for muscle-related pain in the shin is a change in the running style to eliminate the overstriding and heavy heel strike.
Most competitive runners do not strike the ground heel first. Sprinting is performed on the toes, as is middle-distance running. In long-distance running, the footstrike should be flat, though some elite long-distance runners will retain their forefoot strike acquired from years of competing in track-and-field.
Correcting the footstrike begins with posture. A hunched forward posture leads to a heel strike. The following grossly exaggerated diagrams illustrate:
( ) <-- head
\
\ <-- forward bend
/
\_/
O < -- heel
<--- facing direction
( ) <--- head
/
/ <-- backward bend
\
\
O <-- heel
_/
In both postures, the center of gravity is directly over the foot. Physics requires this, because it is the condition which prevents a body from falling over. An object falls over when its center of gravity shifts too far one way or the other outside of the range of its supporting base. Arching the back shifts the body's center of gravity toward the rear, so that the legs must tilt forward to compensate, bringing the weight to the toes. Bending forward at the waist has the opposite effect: the legs tilt back at the ankle, shifting weight to the heels.
During running, the center of gravity changes dynamically. Because much of the time there is a drive leg extending backward, the torso appears to tilt forward to compensate for this. This forward tilt is similar to what happens in a standing position when one leg is raised from the ground and extended backward. Inexperienced runners witness this forward tilt in professional athletes and imitate it by bending at the waist, which isn't the same thing. In the forward tilt, the torso and extended leg still form a straight line, or even a slight backward curve:
0 <-- head \-- \/\ \ \ /\ \ straight line / \ \ \ ---\ --
[edit] Footwear
Stress on the shin muscles can also be somewhat alleviated by footwear and choice of surface. Runners who strike heavily with the heel should look for shoes which provide ample rearfoot cushioning.[dubious — see talk page] Such shoes may be referred to as "stability" or "motion control" shoes. The so-called "neutral" shoes for bio-mechanically efficient runners may not have adequate support in the heel, because the runners for whom these shoes are intended do not require it. When their cushioning capability degrades, the shoes should be replaced. The commonly recommended replacement interval for shoes is 500 miles or 800 kilometers. Excessive pronation can be reduced by extra supports under the arch. Running shoes which have a significant supporting bump under the arch are called "motion control" shoes, because they work by limiting the pronating motion. Also shoes with cushion shock features and shoe inserts can help prevent further problems.
