Running Adaptations for PFP
This study investigated the effects of running adaptations for PFP
They let participants with PFP alter their running cadence and foot strike patterns
A higher cadence and a fore-foot strike pattern leads to less patellofemoral joint contact force and stress
Introduction
Patellofemoral pain (PFP) is a common condition limiting runners in their daily lives and training. Intrinsic and extrinsic factors have been linked to the development of PFP in runners. Since intrinsic factors are not always modifiable (patellar tracking or malalignment), much attention has been given to the extrinsic factors contributing to the development of PFP in runners. In their systematic review and meta-analysis, Alammari et al. (2023) found evidence for adding hip strengthening to relieve PFP and improve function. Yet, in some people, and especially runners, the development of the condition can be driven by excessive joint stress. Therefore, strategies to reduce the high-impact loading of running activities may positively influence PFP. Increasing cadence and reducing step width are factors that can be modified quite easily and the authors of this cross-sectional study wanted to explore the influence of these running adaptations in PFP.
Methods
In this cross-sectional study, the authors included male runners who suffered from PFP. They were between the ages of 18 and 45 and ran at least 15km weekly. PFP was diagnosed when they reported peripatellar pain of a non-traumatic onset for at least 6 weeks with a pain intensity of a minimum of 3/10 on the VAS scale during or after running. Additionally, they had to report knee pain with at least 3 of the following activities:
- Going up or down the stairs
- Kneeling
- Squatting
- Resisting knee extension
- Sitting for a prolonged time
To investigate the influence of foot strike pattern and running cadence on the knee joint, the resulting patellofemoral load was calculated by measuring knee joint angle and moments. Reflective markers were attached to the superior iliac spine, sacrum, greater trochanters, medial and lateral femoral epicondyles, medial and lateral malleoli, the first and fifth metatarsal heads, and the end of the big toes and heels.
Next, the participants completed six running trials where the cadence and foot strike patterns were adjusted to create 6 conditions:
- Running at a preferred cadence with a rearfoot strike
- Running at a preferred cadence with a forefoot strike
- Running at -10% of the preferred cadence with a rearfoot strike
- Running at -10% of the preferred cadence with a forefoot strike
- Running at +10% of the preferred cadence with a rearfoot strike
- Running at +10% of the preferred cadence with a forefoot strike
Results
Twenty male runners with PFP were included in the study and completed the running tests. They were on average 22,5 years old and had a symptom duration of nearly 12 weeks. Their preferred foot strike pattern was rear-foot strike and they ran with a cadence of 169 steps per minute.
They ran at an average speed of 2.71 m/s and the average step length in their preferred cadence was 1.01 meters.
Peak joint angle
The authors did not find an interaction effect between 3D peak knee joint angles, but they found a significant difference in peak knee flexion and internal rotation angles. A higher running cadence resulted in a lower knee flexion angle when it was compared to the preferred cadence.
The preferred cadence with both the rear-foot and fore-foot strikes resulted in a higher internal rotation angle compared to running with a lower cadence.
The forefoot strike reduces the knee flexion angle in all cadence conditions. With a forefoot strike, more adduction, and with a rearfoot strike, more abduction of the knee was found.
Peak joint moment
An increased cadence resulted in a lower peak knee extension moment for both the fore- and rear-foot strike patterns, compared to a lower cadence.
The increased cadence also gave less internal rotation moment compared to a lower cadence
Running with a forefoot strike increased the knee flexion moment and reduced knee extension moment and adduction moment compared to running with a rearfoot strike, irrespective of the running cadence.
Patellofemoral joint contact force and stress
The peak patellofemoral contact forces and stress during running were lower when the cadence was higher compared to when the participants ran at their preferred running speed, irrespective of the foot strike pattern. The forefoot strike pattern, on the other hand, resulted in lower peak patellofemoral joint contact force and patellofemoral stress compared to the rearfoot strike for all cadences.
Questions and thoughts
In summary, the study found that when the cadence was increased and when a fore-foot strike pattern was used, the peak patellofemoral joint contact forces were lower. This would imply that you can advise a runner with patellofemoral pain to increase their step rate and to land on their toes.
Should you permanently alter everyone’s running technique to spare the patellofemoral joint? Of course not. However, the results of this study give an interesting insight into the biomechanics of running and the implications of altering the running technique on the patellofemoral joint. Burke et al., (2021) and Dillon et al. (2023) independently indicated that foot strike patterns were not associated with running injuries. As such, these running adaptations should not be prescribed as primary prevention but rather can serve as a way to temporarily alter load and manage the condition.
The knee extensor moment is a biomechanical metric that measures the torque created by the knee extensor muscles during activities. It is critical in actions that require knee extension, such as gait propulsion, jumping, and weight-bearing tasks. The quadriceps muscles’ and the lever arm’s combined force are used to compute the knee extensor moment. The knee extensor moment has been used in studies to characterize patellofemoral joint dynamics during various actions. Variations in the knee extensor moment have also been linked to variations in knee joint loading, muscle activation patterns, and joint stability. An increase in the knee extensor moment results in increased patellofemoral joint force and stress while lowering patellofemoral joint stress and peak knee extensor moments can improve pain and function in people with patellofemoral discomfort (Anderson et al., 2022). Furthermore, the quadriceps muscle strength, which contributes to the knee extensor moment, has been demonstrated to alter patellofemoral kinematics, indicating a function in patellofemoral pain treatment (Zhang et al., 2021).
- The results of this study indicate that increasing the running cadence lowers the knee extension moment, aka, the quadriceps should produce less force compared to running at lower cadences, and as such the patellofemoral joint stress is reduced.
- Running with a forefoot strike increased the knee flexion moment. The knee flexion moment is critical in running because it absorbs the impact of each stride and propels the body forward. The knee flexion moment assists in progressively bending the knee as the foot strikes the ground, allowing the leg to absorb the shock generated by the impact. This bending action distributes the pressures applied to the knee joint.
- The knee internal rotation moment refers to the force that causes the lower leg to rotate inwards at the knee joint. Running at an increased cadence gave less internal rotation moment compared to a lower cadence.
- When a 10% increase in running cadence was combined with a forefoot strike the patellofemoral joint stress was reduced by 42%. The reason for this would be that the knee flexion and ground reaction forces are reduced during the stance phase. This would lower the activation of the quadriceps and as such, the patella gets less contact stress with the patellar groove.
Talk nerdy to me
Running shoes were standardized across the participants. Standardization of the shoes is necessary to compare the individuals against each other to limit the influence of the shoes they wear on the data that is collected. The study did, on the other hand, not take into account other anatomical differences between the participants. For example, someone with knee varus will display different biomechanics than someone with a neutral knee or valgus alignment. Similarly, alterations of patellar configuration can lead to alterations in peak joint contact stress. The standardized shoes are a good option to make the comparisons more uniform, but I can imagine that running with a shoe you’re not familiar with would feel weird and uncomfortable and this could also alter running biomechanics at the knee joint.
Although the running adaptations for PFP were altered and showed that an increase in cadence and a fore-foot strike were beneficial, this study did not investigate the relationship between the patellofemoral joint contact forces and pain. As such, it cannot advise on reducing PFP. The results of this study can merely give insight into the results of the running adaptations for PFP on a biomechanical level. Yet, other studies seem to support the theory behind reduced patellofemoral stress and decrease in pain.
Briani et al., (2022) concluded that when women experienced PFP, they adopted movement strategies to distribute more loads to the hip joint than to the knee joint, which was hypothesized to avoid or manage the pain. This supports the hypothesis that reduced patellofemoral contact stress due to running adaptations will likely decrease pain.
Take home messages
Running adaptations for PFP could include an increased cadence and a fore-foot strike. Together, these adaptations can reduce the loads exerted on the patellofemoral joint and as such this could help manage the condition. With these adaptations, runners with PFP could be able to keep running, despite suffering from this condition. As PFP can be a longstanding condition, these simple alterations in running technique avoid people to refrain from their preferred sport, possibly by finding a way to manage pain.
Reference
Additional references
THE ROLE OF THE VMO & QUADS IN PFP
Watch this FREE 2-PART VIDEO LECTURE by knee pain expert Claire Robertson who dissects the literature on the topic and how it impacts clinical practice.
