What is Gait Analysis?
Running is a great activity for cardiovascular exercise and stress relief, and is even better because all you need are a pair of shoes and a place to run. However, it can also be a source of pain and injury. Running injuries most frequently occur as a result of any combination of three common sources: First, running too much, or too quickly without slowly building the mileage; Second to blame is often having insufficient strength of the hips, legs and core; Third is form and the biomechanics of running, which can be related to underlying muscle deficiency. A gait analysis can be performed to identify running mechanical problems or errors.
During a gait analysis, brightly colored or reflective tape is often applied to several areas of the skin of the runner being analyzed to better visualize specific anatomic landmarks during the analysis. After a warm up, cameras are used to record the running movements from different angles, often a side view and frontal or rear view. The images captured are then reviewed frame by frame to determine if there are gait errors which may be contributing to pain or injury. Often multiple errors occur together. A plan is then created to help fix these errors with strengthening, physical therapy, and gait retraining.
While there are many different measurements that can be assessed, here we will discuss a few common gait abnormalities. We will first address the assessments visualized from a side and then a posterior view.
Side View
Foot Strike
There are three foot-strike patterns: a forefoot (or toe) strike, a midfoot strike and a rear foot (or heel) strike. Forefoot strike is most commonly seen while sprinting or wearing minimalist shoes. There is no conclusive evidence as to which of these patterns are best, but some studies have suggested that a heel strike pattern is associated with an increased risk of overuse injury, such as shin splints, runner’s knee or stress injury. A forefoot strike pattern has been shown to increase the stress on the foot and ankle, including the Achilles. While a rear foot strike pattern increases stress on the knees. When transitioning or training from rear foot to midfoot or forefoot striking, be careful to not overstress the foot and ankle, as they are not accustomed to the increased stress over long periods. In fact, preparing for this transition with adequate intrinsic foot strengthening exercises can help with a healthy transition.
Left: Forefoot strike, Middle: Midfoot strike; Right: Rearfoot strike
Tibia Angle
The moment that the weight of the runner impacts on the outstretched foot/leg is called the loading response phase. On frame-by-frame analysis this phase can be determined by the moment that shoe begins to deform after the initial contact. At this moment the angle of the tibia is assessed for excessive extension (or tibial overstride angle), which can exacerbate impact related injuries. A “normal” angle is considered vertical or slightly flexed (with the tibia angling posterior towards the heel). This angle allows the knee to more easily dissipate the impact forces of landing.
Left: Extended tibia, Middle: Vertical tibia, Right: Flexed tibia
Knee Flexion
During the stance phase, or the period of time where one foot supports the weight of the body, the angle of the knee of the planted foot is measured at the time of its maximal flexion. This angle generally reaches 45º although there is no specific cut off for normal. If the knee flexes significantly less than 45º there is likely reduced shock absorption, which may be associated with tibial stress fractures, patellar tendinitis and patellofemoral pain.
Left: Decreased knee flexion, Right: Appropriate knee flexion
Hip Extension
A common error is reduced hip extension of the trailing leg during late stance phase, or the moment before weight is transferred from the trailing to the leading foot. This finding often indicates reduced flexibility of the iliopsoas muscle. While there has been no defined optimal degree of hip extension, it can result from or lead to different running injuries including hip flexor and quad strains. Running at a faster pace can lead to stride modification in order to maintain the desired speed or cadence (foot turnover). The common compensations or stride modifications include increased lumbar extension (which strains the low back and further stretches or strains the hip flexor/iliopsoas), bounding to increase time in the air to make up for the decreased hip extension (which increases landing forces on impact), and excessive reaching to increase stride length (which also increased the impact landing force)
Left: Reduced hip extension, Right: Normal hip extension
Trunk Lean
The preferred angle of the trunk while running has not been presented with strong supporting evidence, and likely changes even in the same runner when running at different speeds. Generally, running experts recommend a forward leaning trunk. Increasing the trunk lean has been shown to decrease the stress across the patellofemoral joint.
Left: Upright trunk posture, Right: Forward trunk lean
Overstriding
Overstriding is when a runner’s foot lands in front of the person’s center of mass. On video it can be evaluated when the runner is in loading response. A vertical line is drawn upward from the lateral malleolus to the height of the pelvis. This line should pass through the pelvis. If the line falls anterior to the pelvis it is an indicator of overstriding. An increased risk of tibial stress fractures has been found to be associated with overstriding.
Left: Overstriding, Right: Normal stride
Vertical Displacement
Vertical displacement is found by determining how much the body moves up and down while running. This can be done by comparing the pelvis at its highest level during float phase, or the moment both feet are off of the ground, and the lowest point during stance phase. Increased vertical movement is found in “bounders” who often have decreased hip extension, as previously discussed. Reducing the vertical displacement decreases the impact forces on the body and the work required to run. Decreasing the cadence, or step rate, by 10% has been shown to significantly reduce vertical displacement. When gait retraining, cues can be provided for the runner to look into the distance and try to keep the scenery as level as possible, which in turn attempt to prevent “bounding”.
Left: Large vertical displacement, or bounding, Right: Normal vertical displacement
Cadence
Cadence, or step rate, is important to assess in all runners. By counting the number of right or left foot strikes over 1 minute you obtain the “stride rate”, which when multiplied by 2 equals the “step rate” or cadence. There has been much debate as to the optimal cadence, and it is unlikely that there is an ideal number for all runners. Studies on running economy, or effectiveness while running, have show that a step rate of 180 is ideal, however this has not been backed by studies on injury mechanics. Increasing the step rate by 10% above the “preferred” rate was shown to decease stress in the foot and knee, decrease shin injury, and also help improve other mechanical running errors such as foot strike pattern, vertical displacement, and overstriding.
Posterior View
Base of Support, or Crossover
When viewing a runner from a posterior view, there should be a small space between the feet during steps. This gap varies depending on the speed while running. When the feet cross over or overlap when the feet are planted it creates a narrow base. A narrow base of support has been associated with tibial stress fractures, iliotibial band syndrome, and causing other mechanical running errors such as excessive hip adduction and over-pronation.
Left: Narrow base, Right: Normal spacing
Pronation
Mild pronation while running is normal and helps to distribute weight across the foot evenly. Excessive pronation of the foot can lead to tibial stress fractures, patellofemoral pain, and Achillies tendonopathy. It is difficult to measure foot pronation using 2D video. However it is linked to heel eversion, which is easier to evaluate and can be used to determine the amount of pronation present. It is also important to determine that heel eversion is not occurring too quickly. Many shoes and orthotics have been marketed as a solution to excessive pronation. Currently the evidence supporting such products is inconclusive.
Left: Over pronation, Right: Normal pronation
Knee Window
Many variables can impact the knees while running. Excessive hip internal rotation, hip adduction and excessive knee valgus, or angling of the knees towards each other, all have been found to contribute to running injuries. One way these variables can be assessed during a gait analysis is by evaluating the knee window. This is simply done by assessing if there is or is not a space between the knees at all times of the running cycle. A closed knee window can also be seen if there is excessive adduction, even if there is normal alignment of the hip, knee, and ankle.
Left: Closed knee window, Right: Normal knee window
Pelvic drop
Pelvic drop is often related to hip and core muscle weakness, specifically the hip abductor (gluteus medius, gluteus minimus) and hip extensor muscles (gluteus maximus, hamstring muscles). To assess pelvic drop the runner wears markers, which allow for visualization of the posterior superior iliac spine, or wear tight fitting clothes where the waistband can be used as a reference. When pelvic drop is present the pelvis will be fairly level at initial contact of the foot, but during stance phase there is a drop of the pelvis opposite of the foot contacting the ground. By strengthening hip abductors and extensors as well as core the risk of injury is reduced as there is adequate strength to stabile the body during take-off and landing phases of running.
Left: Excessive pelvic drop, Right: Level pelvis
By Dallin Erickson & Jon Minor, MD
References
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