Run Form and Energy Leaks
While running, the musculoskeletal system of the body acts like a compressible shock absorber. When your foot makes contact with the ground you compress the shock. When you push off the spring energy of the shock augments muscular force to make you go faster. You spring forward. This spring effect augments muscular force.
The spring works best when it is stiff and there are no energy leaks. Our body spring works best when almost all of the loading is in the sagittal plane.
Movement in the coronal plane is not well tolerated by the body and generally results in energy leaks (energy that is not returned as spring energy during push off but is instead wasted). Coronal plane movements are most likely to cause pain and injury. Your body has several mechanisms to control coronal plane movement while running and when these fail, pathological compensations can occur. Horizontal plane movements are normal when running but should not be excessive. The single leg push off creates a rotation moment that results in some horizontal plane movement. This is countered by arm swing and core strength. Less core strength and hip control will necessitate more arm swing, which costs more energy and reduces run economy.
In the picture above you see a runner loading the 3 major running springs. All of these springs operate primarily in the saggital plane (fore and aft). The ankle, knee, and hip springs are created by loading of the gastroc/soleus, quadriceps, and gluteus muscles respectively.
This is classic run cross over gait with knee valgus. Notice the knee caving in. The hip also moves out laterally and the opposite (non support side hip) drops. Instead of having a rigid spring, there are coronal plane energy leaks (hip out, knee in). Very little of this energy is going to be returned on push off. Also, the hip and knee are not well suited to accept these coronal plane (lateral) forces, so injury potential is high (i.e., IT band syndrome, patellar pain).
In this case there is less knee valgus but note how the hip is kicked out laterally, the opposite (non support side) hip drops, and the foot rotates out laterally. The lateral rotation of the foot (called increased foot progression angle) acts like a kickstand on a bike. A kickstand provides lateral stability to a bike to keep it from falling over. It is doing the same thing here. Normally that stability is provided by the gluteus medius and gluteus maximus. If they cannot do the job (due to weakness or weakness in other supporting muscles like the obliques), kickstanding is a common compensation. This can cause arch collapse and strain in the foot and may lead to plantar fasciitis or Achilles injuries. Again, this produces lateral force and wasted spring energy.
In the picture above, instead of loading a rigid spring, the runner is allowing his upper body to slouch. The spine is flexing forward, dissipating the spring energy instead of returning it during push off. This hunched over, head forward run posture is common. It typically causes heel striking, wasted energy, and lower back fatigue/pain.
The two pictures above show cases where sagittal plane movement can be inefficient. In this case, flexing of the spine, resulting in improper alignment, results in energy loss and bad run posture. This generally starts with a head forward run position. By pushing the head forward, the upper torso bends forward, the back arches excessively, and the hips rotate forward into anterior pelvic tilt. Not only does this spine collapse dissipate spring energy that is not returned on push off, but it also increases stress on the lower back and creates a hamstring dominant, rather than a gluteus dominant run form. The hamstrings start to take over the job of the gluteus maximus muscles, often leading to hamstring injuries. The excessive extension (hyperextension) of the lower back often leads to back pain.
All of these examples are compensations for either deficiencies in mobility (flexibility) or stability (strength) or due to chronic bad posture, which leads to both. When I think of applying strength training to running, I am not thinking about producing stronger muscles in order to get more propulsive force. I am thinking about creating a more stable structure to reduce energy leaks, and providing enough mobility to engage the right muscles and move through the appropriate range of motion.
Fixing run gait is a 2 step process:
1. First you have to gain enough strength in the right places to provide adequate stability and enough flexibility for adequate mobility. This removes the NEED for compensation.
2. Then you have to reprogram the bad movement patterns.
This is why simply trying to emulate good run form (i.e., Pose or Chi Running or any other) often does not work. It skips step #1