Midstance stability

One concept we emphasize with runners in the clinic at Sports and Spinal physical therapy is midstance stability. Research tells is that the middle point of a runner's stride is the point at which the ground reaction force up the leg is greatest. This point in the stride is appropriately termed "midstance". Think of it as after "initial contact", which is when a runner's foot first contacts the ground. Midstance comes when the foot is completely flat, and the opposite leg is swinging forward past the stance leg( see below). It is literally the middle point of the stride. Given the forces up the leg are largest at this time, we need to ensure that the runner's leg remain stable to the ground reaction forces. Even the slightest deviations, such as the kneecap turning inward, can dramatically increase strain to the involved tissues. The end result of this overload of stress could be one of the many mechanical problems runner's have such as ITB syndrome, or patellofemoral pain syndrome.

If I had just a few minutes to examine an injured runner, I would undoubtedly check their midstance stability. How would I do that you ask? Simple, just take the runner through a series of tests that evaluate how stable they are in midstance. A few of my favorite tests include:

1) Single leg balance: Ask a runner to stand on one leg while maintaining a balanced position. Typically, once a runner is set in a balanced position, I ask them to close their eyes.
I would like to see a runner maintain a balanced position for 30 seconds. My idea of a balanced position is where all components of the kinetic chain ( think from the foot up to the lower back) are stable, i.e. not teeter tottering. I will look at the foot/ankle to see if it remains in contact with the ground, or if the toes come off the ground. I will look at the knee to see that it maintains it position. A common deviation is the kneecap is turning inward and outward as the runner tries to maintain balance. I would look at the thigh bone to see if it is following the knee inward. The reason balance is so important is because it indicates a solid connection between the joints of the leg and the brain. We want the body to rely on the balance feedback it receives from the joints of the leg, versus just taking input from the vision and inner ear. The reason behind this desire is that is establishes a very quick feedback mechanism for the runner.

2) Single leg swing- This test takes the balance test above and makes it functional. I will ask a runner to stand on one leg and swing the opposite leg forward and back as if they were going through a running type motion. The test shows me how stable the runner is in a more dynamic fashion, one that mimics running. I will watch the leg the runner is standing on to look for instabilities. I will also watch the leg that is swinging to get a gross sense of range of motion of the hip. I will also look at how the swinging leg influences the lower back. I hip that is overly tight often results in a more stressful moment being imparted on the lower back. This is an important point we see time and time again in physical therapy : a stiff joint will typically adversely influence joints above and below.

3) Single leg squat- This is another functional test for runners. I ask the runner to stand on one leg. Once balanced, I ask the runner to squat to 45 degrees times 10 repetitions. Guess what I look for? You guessed it! I look for what is happen with the kinetic chain. Mainly what I look for is whether the chain stays stacked on top of itself. Notice the difference between the two images below. Obviously the B image is less stacked as the knee drifts toward midline, and the thigh rotates inward. Note how the torso is influenced also. I find that instabilities in the leg can influence any part of the leg, but can extend all the way up to the spine too.



4) Step down test-This test is similar to the single leg squat. I ask the runner to stand on top of a step. The test has a runner lowering one foot toward the floor. The foot comes slowly down to the floor without actually stepping off the step. I ask runners to do 10 reps on one side before they switch. I look at the chain just like I do in the squat test above. I often notice a runner doing fine with the squat test, only to flail on the step-down. Consider that the leg is being asked to do something different that just squat. The ankle is going through a greater range of motion which can be a limiting factor. The same applies to the knee.

Collectively, the above tests give me much useful information. They tell me how strong a runner is, how well they control their movements, where they are limited in flexibility, and ultimately what their MIDSTANCE stability is. This information can help me to understand why they are injured, and how I am going to help them recover.
I often cue runners to hold their foot in a "neutral " position such that the runner is actively maintaining the arch in their foot in a mid line position.