Not long ago I wrote a post about the benefits of running backwards. This post is a follow-up, discussing the biomechanical and structural reasons that running backwards addresses so many of the typical muscular imbalances that lead to back and knee pain.

It is my firm belief that mere training tips don’t constitute real answers. As with all forms of training, running backwards only does what it does because of how it develops certain mechanical systems and components. It is important to know what those components are or how they are developed, in case we’ve discovered a new and amazing way to “beat” the mechanical requirements of a technique running backwards—therefore precluding ourselves from reaping the benefits of our training.

Problems at the knee can be addressed by looking at the hip or even beyond, because the knee, like any other part of the body, doesn’t exist in isolation. When we push against the ground, the same amount of mechanical energy (the reaction of our action, according to Newton’s Third Law) flows into our body.

That’s why it’s a requirement for all of us, regardless of race, creed, or nationality, to lead with our hips as we throw a punch. Kinetic energy travels through the knee in a straight line, and if a lower or upper muscle doesn’t pull correctly to align the knee with this vector, we will experience knee pain.

Changing the way a particular muscle fires will change how the body interacts with mechanical energy, resulting in a change of the center of gravity (CoG). In other words, lateral knee pain (and the majority of mechanical running injuries) are reducible to problems with the location of the CoG, and problems in the body’s “mechanical solution”—i.e. the patterns of muscle firings it uses to “solve” the problem of moving in the world.

It is usually imbalances between the front and rear muscles which typically hamper the conduction of mechanical energy. Rear muscles typically have a mechanical advantage over the front muscles; they can move bones a much greater distance with the same amount of force. This means that when there is any imbalance, it tends to be that the rear muscles that are too tight, while the front muscles are too weak.

The body looks a lot like a series of bows put together: The lower back is curved forwards, held taut by the lower back muscles. The same happens with the legs: all the thickest tendons and strongest muscles are at the back, which means that the body as a whole will be curved forwards. Think of a bow: pulling a bowstring may take a lot of force, but suppose there was an identical bowstring running along the front of the bow. In order to curve the bow forwards (in the wrong direction) instead of back, it would take far, far more force. In order to maintain both groups of muscles balanced, it is usually the front muscles that must be trained.

That said, the body’s natural shape, especially while running, is to be curved like a bow. The important thing is to prevent excessive curvature, which manifests as stiffness in the back muscles and pain in the rear tendons. The form of many of the world’s fastest runners exemplifies this bow-like structure quite clearly, as is the case with Haile Gebrselassie, the Ethiopian former Marathon world record holder:

Thanks to these structural regularities, mechanical requirements of running backwards coincide quite neatly with how to solve the frontal/rear mechanical imbalance.

First and most importantly, we have to stay on our feet. This is otherwise known as not falling. Although it seems obvious and perhaps painfully simple, the mechanical and cognitive requirements of remaining in balance center around maintaining the COG in the proper place: running backwards without falling means that the body must find a mechanical solution where its CoG doesn’t move too far back in relation to the center of the hips.

Balance is much more central to running backwards than it is to running forwards because we can’t use our eyes effectively for that purpose. Therefore, the burden falls onto our proprioception: we are able remain in balance only by increasing how much we listen to our body. Because our focus is distributed across the entire body, muscle movement naturally increases. This increase allows the body to deal with mechanical energy more effectively, which by implication means that the CoG is becoming more ideally located.

To keep our balance while running backwards, we have to engage the frontal muscles in the majority of the effort of moving the body. If, on the other hand, we tried to engage our rear muscles, we would would find ourselves pushing against the ground with our heels, forcing ourselves out of balance. Try it—you’ll see.

The motion patterns necessary to run backwards contrast starkly with regular running, where the frontal muscles are the majority movers until the leg travels back past the midline of the body, at which point the rear muscles begin to take over. When we run backwards, the rear muscles never get a chance to take over: we land on our forefoot at the midline of our body and then our leg travels forwards in relation to our body. This is pure frontal muscle exertion.

It’s important to note that when running backwards, the CoG never moves forwards, and yet the frontal muscles become stronger. Usually, the muscles develop around the CoG: if it shifts to the right, we will see the outer muscles of our right leg and the inner (right) muscles of our left leg strengthen. When we run, our CoG ideally moves forwards and our frontal muscles strengthen. On the other hand, when we run backwards, our frontal muscles strengthen because we’re negating the mechanical advantage that our rear muscles have over our frontal muscles. (Running backwards is kind of like insisting on pulling the bowstring on the wrong side of the bow; that bow will become less and less curved over time, as the “wrong-side” bowstring becomes more dominant).

Therefore, running or jogging backwards is an excellent cool-down exercise to do, especially after a long run when you can feel your hamstrings and calves tightening up. It will loosen them—but not because you’re stretching the muscles and tendons. By using the frontal muscles in this way, you will force the back muscles to do more than just move; you’ll force them to communicate with the frontal muscles, re-establishing the correct motion patterns. Because the muscles will remain much more supple and mobile during recovery, they will receive more blood flow (and nutrients) overall, and the proper neuromuscular patterns will become strengthened throughout recovery and not just during training.