Braking force is the amount of energy that is directed into your leg, from front to back, when your foot first hits the ground. A good way to visualize this is to imagine you are running at full speed and have to stop suddenly. The maximum force you feel when you slam on the brakes is your peak braking force. This is relevant to you and I because peak braking force has been associated with an eight-fold increase in injury risk when the force is greater than 0.27 times body weight. Now, you and I can’t measure the force in relation to body weight. That is, unless you have a very expensive force treadmill in your basement that I don’t know about. In that case, invite me over to run on it. But, just because we cannot measure this precisely, it does not mean that this study is not of use.
But why can braking force be a problem? It can cause issues because your bones and tissues are not as effective at handing shear force (force that is applied sideways). Your bones and tissues are much better suited for handling force that is directed straight up and down, but not so much from front to back. So, we now see that if we would like to potentially avoid injury, we should be concerned with braking force.
Research Protocol and Findings
In a 20 study, researchers used a fancy force treadmill to measure peak braking force for athletes. Once they measured this, they put a video monitor up in front of the treadmill with a real-time graph that showed the runner the forces he or she was transmitting to the treadmill. Then, they told the runner to decrease the size of the force wave while running. They did not specify how – they just told runners to decrease the wave however they could.
So what happened? Well, the runners were quite effective at decreasing the amplitude of the wave and thereby decreasing peak braking force. In fact, they decreased the peak braking force by 15 percent. This amount of decrease then resulted in a five-fold decreased risk of running injury. That is a huge amount! Decreasing peak braking force by merely 15 percent decreased risk of injury by five times! That is some serious return on investment. But wait, we didn’t address how they decreased this peak braking force. Was it foot strike? Or knee bend? Actually, the runners increased their cadence by an average of seven percent and decreased step length by seven centimeters. So, they achieved less force transmission to their legs by increasing cadence and decreasing the length of their stride. So how does this apply to us? We don’t have a treadmill with a force plate and screen in front to change our pattern. Well, even if we don’t have the immediate feedback of a force plate, we do know how the athletes ultimately changed the forces. They increased cadence and decreased stride length. So, you and I can affect our cadence via a metronome on a phone or watch and decrease stride length by thinking about shorter, quicker steps. You can also use fancy foot pods or insoles that measure ground reaction force for a more concrete result.
What should our cadence be? Well, there is no ideal cadence, despite what you may read on the Internet. However, I have found in my practice that if we can get runners above 170 steps per minute, many issues will be resolved. Please note that you should not increase your cadence more than 15-20% at one time - it can hurt you!
So now we know that if we can reduce peak braking force, it may result in a decreased injury risk. As runners, we are always looking to decrease injury risk. But how do you know if you have a high peak braking force? That is a great question. This study only looked at runners who already had high peak braking forces, so those who were likely to become injured. If you are injury free, should you try to decrease your peak braking force? Perhaps, but that is a difficult question to answer in a blog. This is more appropriate for someone who has had recurring lower body injuries, stress fractures, tendon irritation, etc.
What about stride length? Don’t worry too much about the exact measurements of your stride. Just try to take shorter steps, and have your foot land underneath you.
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Keep running my friends, Ryan ____________________ 1. C Napier, et al. Real-Time Biofeedback of Performance to Reduce Braking Forces Associated With Running-Related Injury: An Exploratory Study. Journal of Orthopaedic & Sports Physical Therapy: 49:3, 136-144, 2019. #Precisionpt #precisionperformanceATL #physicaltherapy #atlantaphysicaltherapy #runningdoc #gaitretraining #triathlon#runningmedicine #PTfirst