About this episode
Dr. Megan Peach // #FitnessAthleteFriday // www.ptonice.com In today's episode of the PT on ICE Daily Show, Endurance Athlete division leader Megan Peach discusses the importance (or not!) of ground reaction force as it relates to running related injuries. Megan discusses research evaluating the association between ground reaction forces & running related injuries, noting that these forces do not seem to be directly linked to the onset of injuries. Furthermore, Megan shares that footwear that decreases ground reaction forces does not also seem to have an effect on the development of running related injuries. Megan cautions listeners to not worry too much about the manipulation of ground reaction forces in training or in rehab as the link to injury prediction seems to be poor. Take a listen to the episode or read the episode transcription below. 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Enjoy today's episode of the PT on ICE Daily Show. 01:26 MEGAN PEACH So what I want to talk about today is ground reaction force and how it relates to running related injuries. And we need to be a little bit cautious, I think, when we're talking about ground reaction force and how it relates to those injuries, because I think the popular opinion is that ground reaction force really is kind of the cause of running related injuries, or we need to address ground reaction forces when we're addressing running related injuries, or we need to reduce it And what the literature actually says is that it's not really the case. And so I'm going to give you a couple of examples from current literature that may tell a different story from popular opinion. So we'll start with a 2016 article. And this was actually a systematic review meta-analysis. So it pooled a lot of different studies. And what it looked at was the association of a ground reaction force with running-related injuries. What they found was that when they pooled all of the injuries together, loading metrics, so loading variables like ground reaction force or loading rate, were not necessarily related to running-related injuries when all of the injuries were pooled together. It was a bit of a different story when they individually looked at separate injuries. where they took out patellofemoral pain, they took out bone source injuries, they took out Achilles tendinopathy, for example. And what they found was that the vertical loading rate was associated with subjects or was related to the injury in subjects with tibial stress fractures. And so different outcomes there when we pool the running related injuries versus when we look at them individually. Another more recent study, so 2020 now. looked at about 125 injured runners, and they compared these runners to healthy controls. And what they found in this study was, contrary to the previous study, was that when they assessed the whole entire group of injured runners as a whole, so all of the injured running injuries together, what they found was that the impact variables, so vertical loading rate, ground reaction force. They were associated with running-related injuries when all of the subjects were pooled together. Different results when then they separated out the running injuries and looked at them individually. 03:59 IMPACT VARIABLES And so when they took groups of running-related injuries, groups of patellofemoral pain, groups of IT band syndrome, groups of Achilles tendinopathy, et cetera, what they found was that some injuries were associated with impact variables and some were not. And so the injuries associated with impact variables were our patellofemoral pain, our plantar fasciitis, And the injuries that were not associated with impact variables were tibial bone stress injuries, Achilles tendinopathy, and iliotibial band syndrome. So when we take a step back out of that space and think about our injured runner on the treadmill looking at their gait mechanics, when we have a injured runner with patellofemoral pain or plantar fasciitis, and they're on the treadmill, what we would expect to see in terms of faulty gait mechanics are faulty gait mechanics in the sagittal plane. So looking at that runner from the side, very typically or commonly we'll see clinical patterns of an overstride, we'll see a lack of knee flexion at initial contact, and we'll see an increased angle of inclination, so increased dorsiflexion at all at initial contact. in the runners with patella femoral pain and plantar fasciitis. So very common, not always. And it's not like that clinical pattern can't be seen in other injuries as well. It's just very common in those two injuries. And that makes a lot of sense because that clinical pattern is very much associated with increased ground reaction forces as well. So it would make sense that within this study, when we separate out all of the injuries and pull them as separate injuries and look at them, that those two specific injuries would be related to ground reaction force. When we also look at the other injuries, so IT band syndrome and Achilles tendinopathy, and we get those runners on the treadmill, we see different clinical patterns. So more likely in those runners, are we going to see movement faults from a different angle? We're likely to see um, faulty movement in more of the frontal plane and, and maybe kind of surrogate transverse plane movement faults as well. So we would likely see, um, increased femoral adduction, maybe internal rotation of the lower extremity, uh, potentially this crossover sign or a narrow, um, foot to center a mass, maybe over pronation. Those are very, very common mechanical faults that we might see with, um, your IT band syndrome and your Achilles tendinopathies. And so when we think about those movement patterns, those are much more associated with range of motion deficits. Maybe they have too much, maybe they have too little. Neuromotor control of that range of motion, maybe strength deficits in that frontal plane, but much less associated with the impact variables like ground reaction force and loading rate. So it makes sense from this study that those specific injuries, the IT band syndrome and the Achilles tendinopathy from like a clinical standpoint would be less related to ground reaction force than the other already previously mentioned injuries. So then when we take tibial bone stress injuries and we look at that, it's kind of in a group all of its own because when we look at bone stress injuries, and I'm talking more specifically to tibial because we just don't have enough information on the other common bone stress injuries like metatarsal or femoral. Most of the research right now is on tibial bone stress injuries in terms of biomechanics. And so when we consider a tibial bone stress injury and whether or not it's related to ground reaction forces. We have to look at the forces on that bone. And so ground reaction force is just one component of the force, the total force on that bone. And it's the external load. When we look at the internal load, it comes from muscles. And so when we're talking about the tibia specifically, we're generally talking about the soleus because it's directly attached to that tibia. And when the soleus contracts, it imparts this internal load directly onto that bone. So it's considered an internal load. When we look at the differences between the external load and the internal load, the external load during running activity or the ground reaction force is generally about two and a half to three times body weight of that runner. But when we look at the internal load, it's upwards of eight times body weight for that specific runner compared to the two and a half times for external load. So you can see how the internal load in a tibial bone stress injury is going to play a much greater role in the development of that bone stress injury than the actual external load coming from that ground reaction force. So again, the results from this study suggest that ground reaction force doesn't really play a big role in, um, tibial bone stress injuries. And that is consistent with the rest of the literature as well. Um, there was a systematic review about a decade ago, looking at ground reaction forces in, um, bone stress injuries, tibial and metatarsal and their conclusions were, um, supportive of this result as well, where they found that ground reaction force is really not related to the development of, um, bone stress injuries in runners, as well as more recent literature has basically corroborated that and their results are very, very similar. Now, a more recent study, so one published just last year actually, looked at 800 runners Um, now that's, that's insane for our running study that those are huge, huge numbers. And so initially I was thinking, okay, this was a survey study. Like they sent out a survey to a bunch of runners and they got it back and they figured out some results from the study, but no. they actually got 800 runners and put them on a treadmill, did their motion capture, and then evaluated it all for ground reaction force and biomechanics. And so that's a tremendous amount of work, a tremendous amount of data, and really interesting results as well. And so really, the big purpose of this more recent study was to look at um, risk factors, uh, for running related injuries in two different shot conditions. And so one shoe was a, uh, like a hard cushions shoe and one shoe was a softer cushion shoe. And so they're looking at the differences in risk factors between those two different shoes and, um, interesting results. So while they did find, uh, different risk factors based on the different shoe condition, what they didn't find was any of the loading variables, so there were numerous in this study, but the big ones are ground reaction force and loading rates. And they did not find any association with the loading variables and in either of the shoe conditions and risk for injury. So basically, what they're saying here is that regardless of the type of shoe that that runner is wearing, or those 800 runners are wearing, 10:41 GROUND REACTION FORCE & RUNNING RELATED INJURIES Ground reaction force did not play a role in the development of that injury, which is super, super interesting because I think often we associate different shoes with different ground reaction forces as well, but that's not necessarily the case. And that's not what the literature is telling us. And so. all of this literature combined. And certainly this is not all the literature. It's not all encompassing. And these are, these are just four different studies. Um, so take that with a grain of salt, but I think there's, there's this popular belief out there that, um, ground reaction force is very closely related to the development of bone stress or not, sorry, not bone stress, but running related injuries, regardless of the type of running related injury. And I think we can look at studies two different ways. And so In one way, we can look at the study as a whole and take all of the running-related injuries and pool them together, and then look at the results from there. But those results tend to be very, very different from when we separate out running-related injuries and say, okay, what do the patellofemoral pain injuries look like, and what are the mechanics for Achilles tendinopathy, and how are they different from IT band syndrome? And when we do that, we actually get very different results, not only for the biomechanics, but for the ground reaction force as well. And so, you know, contrary to popular belief, I don't think impact variables like ground reaction force are a very good predictor for running related injury, nor may they be. And again, this is different per injury. So they may be something to address in injuries that are definitely related to ground reaction forces like patellofemoral pain, plantar fasciitis, plantar fasciosis. But ground reaction force may not be the best thing to try to address with other types of injuries like bone stress injuries or Achilles tendinopathy or IT band syndrome. And I think the main goal here is just to get the point across that it's not the only metric, and quite often we don't actually have access to that information anyways in a clinical setting. It's more in a lab based setting, but we need to look at that whole runner. So we need to not only address if we are addressing ground reaction force, but address the range of motion, address other running biomechanics, address the strength, address the neuromotor control, so that we can basically address that runner as a whole. Okay, that's all I have for you today. I hope that was helpful. I hope you have a wonderful Friday and a wonderful weekend. Don't forget, if you want to sign up for Rehab of the Injured Runner online, our last cohort of 2023, make sure you get in there. Go ahead and sign up today. All right, have a good one. Until next time. 14:39 OUTRO Hey, thanks for tuning in to the PT on Ice daily show. If you enjoyed this content, head on over to iTunes and leave us a review and be sure to check us out on Facebook and Instagram at the Institute of Clinical Excellence. If you're interested in getting plugged into more ice content on a weekly basis while earning CEUs from home, check out our virtual ice online mentorship program at ptonice.com. While you're there, sign up for our Hump Day Hustling newsletter for a free email every Wednesday morning with our top five research articles and social media posts that we think are worth reading. Head over to ptonice.com and scroll to the bottom of the page to sign up.