Impact is good!

I recently wrote an article entitled “When exactly do injuries occur in walking and running?” that Paul Ingraham published Friday on his highly informative website on pain related issues. (Recall Paul recently wrote a guest post for OESH here). The article got some really nice attention over in the world of pain science this weekend. That spurred getting a phone call from an old colleague, Geoff Bove, Ph.D., a researcher who studies the neurophysiology of pain, who is also a practicing chiropractor. It was fun to catch up with Geoff, who has never been afraid to question dogma. We talked about how in the world, impact, that first little blip in force when the foot makes contact with the ground, could have been wrongly accused of causing harm for so many years. Unfortunately, dogma doesn’t always come from science. If you’re interested, I talk about this issue in full detail here on the post “The Rest of the Story” (which meanwhile has been getting a lot of excitement over in the running community). Go science!

All the time that impact has been wrongly accused in causing injuries, impact has not been given its due credit for (1) activating and exercising muscles and (2) stimulating healthy bone formation.

The impact force, which you can think of as a sharp tap, sends a neurological signal that triggers muscle activity throughout the foot and up the entire leg. The impact force also triggers modest vibrations in the foot and leg that further stimulate muscle activity. This muscle activity helps prepare the body to withstand the larger forces that can hurt bones and joints later when the foot is fully planted.

The impact force has a much higher frequency content than the force that occurs later when the foot is fully planted. (That’s just a fancier way of saying that the impact force is like a sharp tap.) That high frequency force, and the associated modest vibrations in bone that occur along with it, have been shown to uniquely stimulate and maintain healthy bone structure. For example, astronauts who are prone to weakened bones during prolonged weightlessness, are able to maintain bone health with regular sharp taps to their heels.

The bone thing is important in terms of helping prevent osteoporosis which all us women are at risk for getting when we’re older. But even in the short term, having strong bones is important for preventing stress fractures. I shared my thoughts here about how we’re prone to stress fractures at the time in the gait cycle when the foot is fully planted, when the forces through the stress fracture sites are at their greatest. So while the repetitive force that occurs when our foot is fully planted is what actually causes stress fractures, the repetitive force that occurs at impact builds bone to help prevent stress fractures.

Now back to what impact does for muscles. Ideally, we want to walk and run in a way that maximizes exercising our muscles, heart and lungs, while minimizing injury causing stresses to our joints and other injury prone areas. Impact does that for us. The nature of the force is such that it does not place damaging forces to the cartilage (which causes osteoarthritis) and actually helps bone health. Meanwhile, impact exercises muscle… which is what strengthens muscles, builds our cardiovascular health, and burns calories. What else could we ever want out of a little blip in impact force?

OESH is unique in that it is designed to not cushion impact. Rather, the sole is designed to compress and release much later in the gait cycle when your foot is fully planted, and all the stresses and strains in muscles, ligaments, tendons, joints, and bones are at their greatest.