Patellofemoral Joint Stress during Running with Alterations in Foot Strike Pattern

Déjà vu? Been there, done that? Different Running Techniques Load Different Tissues Differently. Its 6 of one and half a dozen of the other. Etc

We aleady know that increasing the cadence reduces knee loads; and leaning forward at the hip decreases knee loads but increases hip loads whereas leaning forward at the ankles also decreases knee loads but increased ankle loads; and running barefoot decreases knee loads (but was that becasue of the ‘barefoot’ or the increased cadence?); and that forefoot striking decreased knee loads and increased ankle loads whereas rearfoot striking increased knee loads and decreased ankle loads. Now we have this new study to add to the mix:

Patellofemoral Joint Stress during Running with Alterations in Foot Strike Pattern.
Nathan Vannatta, C.; Kernozek, Thomas W.
Medicine & Science in Sports & Exercise; September 8, 2014
Purpose: This study aimed to quantify differences in patellofemoral joint stress which may occur when healthy runners alter their foot strike pattern from their habitual rearfoot strike to a forefoot strike in order to gain insight on the potential etiology and treatment methods of patellofemoral pain.
Methods: Sixteen healthy female runners completed twenty running trials in a controlled laboratory setting under rearfoot strike and forefoot strike conditions. Kinetic and kinematic data were used to drive a static optimization technique to estimate individual muscle forces to input into a model of the patellofemoral joint to estimate joint stress during running.
Results: Peak patellofemoral joint stress and the stress-time integral over stance phase decreased 27% and 12%, respectively, in the forefoot strike condition (p<0.001). Peak vertical ground reaction force increased slightly in the forefoot strike condition (p<0.001). Peak quadriceps force and average hamstring force decreased while gastrocnemius and soleus muscle forces increased when running with a forefoot strike (p<0.05). Knee flexion angle at initial contact increased (p<0.001), total knee excursion decreased (p<0.001), and no change occurred in peak knee flexion angle (p=0.238). Step length did not change between conditions (p=0.375), but the leading leg landed with the foot positioned with a horizontal distance closer to the hip at initial contact in the forefoot strike condition (p<0.001).
Conclusion: Altering one’s strike pattern to a forefoot strike results in consistent reductions in patellofemoral joint stress independent of changes in step length. Thus, implementation of forefoot strike training programs may be warranted in the treatment of runners with patellofemoral pain. However, it is suggested that the transition to a forefoot strike pattern be completed in a graduated manner.

The déjà vu about this study is the confirmation that you can’t decrease the load in one tissue without increasing it in another (ie decrease knee loads and increase ankle loads and increased ground reaction force), but this study does add a new perspective.

Firstly, though there are a couple of issues:

  • it was an acute intervention, so we do not know if the results would be the same if they transitioned to a forefoot strike and were habituated to it
  • its was in healthy runners and not those with symptoms
  • the sample size was 16; I do not have a problem with it, but the fan boys who objected to the result of other studies that they don’t like because they only had 16 participants will automatically reject this study for that reason.

What new perspective did this study add? For me, it was that stride length was not different between the two conditions. This implies that cadence was the same for both conditions. With a forefoot strike, typically the cadence increases which it didn’t in this study. A previous study has shown a reduction in knee loads with increased cadence and another previous study showed that knee loads were lower when running barefoot vs shod, but it was not clear in the later study that if the loads were really reduced by the ‘barefoot’ or if they were reduced by the increased cadence that typically accompanies barefoot running. From the above study it appears that you can reduce knee loads by forefoot striking and not change the cadence.

Somewhat surprisingly, ground reactions forces increased in the forefoot strike condition, which is the opposite of all the rhetoric and propaganda about the benefits of forefoot striking.

As mentioned above and it should not need to be pointed out, as I have done it enough times before when commenting on similar studies, is that this was not a clinical trial on patellofemoral pain syndrome. It was a lab based study on asymptomatic healthy female runners. The results may or may not be different in those with patellofemoral pain syndrome. As I said in the post on foot orthotics and Achilles loads:

This reminds me of the keynote address that Dr Peter Cavanagh gave at the, I think, Footwear Biomechanics meeting in Stellenbosch in 2009 (…sorry Peter, if I mixed up meetings!). Peter admonished biomechanists for leaving their work at the lab door and not taking it through to clinical trials. He used examples where a range of different interventions that showed promise in the lab failed to deliver in a clinical outcome study in the field. He also gave similar examples of interventions that were showing promise in the lab (like the study above) and were being widely used in clinical practice based on that rationale from the lab based studies, but had not yet been subjected to clinical trials. … at least that is my interpretation of what Peter was saying.

This is applicable here as we are getting an increased number of these lab based studies on increasing and decreasing loads in various tissues, but this has not yet been seen though to clinical trials in those with pathology.

As always, I go where the evidence takes me until convinced otherwise… and yes you can change the running technique to reduce the load in one tissue, but at the cost of increasing it at another.

Nathan Vannatta C, & Kernozek TW (2014). Patellofemoral Joint Stress during Running with Alterations in Foot Strike Pattern. Medicine and science in sports and exercise PMID: 25202853

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