The effect of speed, surface gradient, and cadence on 3 common injury locations

How does increasing running speed affect injury prone sites such as the patellofemoral joint, tibia, and Achilles tendon?

To answer this question it’s essential to first understand the various methods that can be used to measure tissue load. This includes looking at peak loads, the impulse (or the area under the load-time curve), weighted impulse, and cumulative impulse measures. Cumulative measures account for the fact that higher speeds generally result in longer step lengths and fewer steps, potentially leading to a decrease in the cumulative load on tissues. In other words, even though the load per step may increase, the overall load over multiple steps may decrease because we take fewer steps at higher speeds. Cumulative measures thus account for the number of steps to complete a given distance. Weighted impulse measures account for the fact that a larger load does much more damage than multiple applications of a small load. This idea can be understood using the following example: if I had to hit you on your head with a hammer either once with a force of 100 kg, or 1000 x with a force of 0.1 kg, which would you choose? Likely the option of 1000 very gentle taps rather than one big hit as you intuitively know the latter induces more damage. By exponentially weighting the impulse values we also account for the larger damage induced by larger loads.

In summary, the cumulative weighted impulse is therefore probably the more interesting outcome to consider. Therefore, now I can finally answer your question regarding the effect of speed on patellofemoral joint, tibia, and Achilles tendon loading.

Our analysis shows that cumulative damage tends to increase with running speed, despite the reduction in the number of steps needed to cover a distance. This is because each step at a higher speed causes more damage to tissues.

This trend is especially noticeable in the patellofemoral joint, where damage significantly increases with speed. Similarly, the Achilles tendon shows a notable increase in damage as speed increases. While the tibia also experiences an increase in damage, it was not statistically significant. The overall evidence therefore suggests that higher running speeds can increase the risk of cumulative damage to various tissues, underscoring the importance of cautious speed management in running practices to minimize injury risks.

What is the impact of uphill and downhill running on the loading and damage of the common injury site listed above?

Here I will focus again on just the cumulative weighted impulse outcome as discussed before. For the patellofemoral joint, uphill running appears to reduce cumulative damage, potentially lowering the risk of related injuries. Conversely, downhill running increases the cumulative damage to this joint, suggesting a higher risk of patellofemoral injuries.

When examining the tibia, both uphill and downhill running elevate the cumulative damage compared to running on flat surfaces. This indicates an increased risk of injury to the tibia regardless of the incline direction.

As for the Achilles tendon, uphill running exacerbates cumulative damage, which intuitively makes sense as it involves landing more on the front of the foot, placing greater force and strain on the Achilles tendon. On the other hand, downhill running seems to reduce the accumulated damage relative to level running, potentially offering some relief to the Achilles tendon in this aspect.

These findings highlight the importance of understanding the biomechanical impacts of varying running terrains, particularly for athletes and individuals seeking to manage injury risks while training on different inclines. For example, rapidly changing running terrains could introduce running injuries at different locations, depending on the exact nature of the terrain. With this information, such injuries may be mitigated.

How does modifying step frequency influence the load and potential damage of these sites?

When considering the impact of step frequency on running, increasing the number of steps per minute at a constant speed (for example, 12 kilometres per hour) decreased the cumulative damage across all investigated structures. This means that by taking more steps at the same speed, the overall damage to tissues is reduced, despite the increased number of steps needed to cover a specific distance. This insight is particularly relevant for runners looking to optimize their technique to minimize injury risk, highlighting the potential benefits of adjusting step frequency to protect against cumulative tissue damage.

Are there any significant differences in the way different structures (patellofemoral joint, tibia, Achilles tendon) respond to changes in running conditions (speed, gradient, cadence)?

This study highlights the complex interplay between running technique modifications, such as changes in slope or speed, and the resulting impacts on tissue damage. We found that adjustments aimed at reducing damage to one tissue might inadvertently increase damage to another tissue. This phenomenon, previously unexplored, was a focal point of our research, particularly examining how variations in running speed, slope and step frequency affect cumulative damage across different structures.

Our findings revealed a significant increase in cumulative damage to both the Achilles tendon and the patellofemoral joint with higher running speeds, a trend more pronounced than the damage increase observed in the tibia. Additionally, manipulating step frequencies showed a universal reduction in cumulative damage across all three structures, without a significant difference in the effect’s magnitude related to the step frequency change.

Examining slope effects, we discovered that running on steeper uphill gradients increases cumulative damage to the Achilles tendon more than to the tibia. Interestingly, the increase in Achilles tendon damage with uphill running exceeds the reduction of damage to the patellofemoral joint. Thus, recommending uphill running to mitigate patellofemoral injuries might inadvertently heighten the risk for Achilles tendon injuries due to the disproportionate increase in tendon damage. In other words, we might increase the risk of Achilles tendon injuries more than the decrease we cause in patellofemoral injury risk.

Conversely, running on steeper downhill slopes tends to significantly reduce Achilles tendon damage compared to the increase in damage observed in the femoral joint. This nuanced understanding of how running conditions affect tissue integrity emphasizes the need for a balanced approach when advising modifications to running habits, especially for clinicians aiming to minimize injury risks while addressing specific tissue vulnerabilities.

What does this mean for coaches designing training programs aimed at injury prevention and performance enhancement?

For coaches and athletes alike, understanding the implications of running speed and terrain on injury risk is crucial. Our research highlights that faster running speeds tend to increase cumulative damage across all studied tissues, although with only a marginal impact on the tibia. This suggests that slowing down, while maintaining total distance, may effectively reduce the risk of running-related injuries. Supporting evidence from large cohort studies also links higher running speeds to an increased likelihood of various injuries.

Another critical area of focus is the impact of running on different gradients, specifically uphill and downhill running. While downhill running has been observed to have lower peak vertical ground reaction forces and ankle joint moments compared to level running, leading some to propose its utility in reducing loading on certain structures during rehabilitation, our findings paint a more complex picture. Although downhill running may indeed result in lower cumulative damage to the Achilles tendon, it conversely increases damage to both the tibia and the patellofemoral joint. This underscores the importance of approaching gradient running with caution, as the reduction in damage to one tissue may be offset by increased damage to another, potentially elevating the overall injury risk rather than mitigating it.

These insights are pivotal for those involved in running training and rehabilitation, emphasizing the need for a balanced and informed approach to training regimens that consider the nuanced effects of speed and terrain on the body’s tissues.

How should recovery and rehabilitation strategies be adjusted after injuries to these specific locations?

Exploring the effects of gradient running, particularly uphill and downhill, unveils nuanced implications for injury risk management. Downhill running, noted for its reduced peak vertical ground reaction forces and ankle joint moments compared to level running, has been posited as a potentially lower-impact activity. This perspective suggests it might be beneficial for reducing loading on specific structures, possibly during rehabilitation phases.

However, our research provides a more detailed perspective. While downhill running does indeed result in lower cumulative damage to the Achilles tendon—indicating reduced impact—it concurrently increases damage to both the tibia and the patellofemoral joint. This finding prompts a cautionary approach to incorporating gradient running into routines, especially for rehabilitation or injury prevention. The reduction in Achilles tendon damage achieved through downhill running could be outweighed by the increased damage to other tissues, potentially elevating the overall risk of injury.

This insight underscores the importance of a comprehensive understanding of how different running practices impact the body. It suggests that while modifying running environments (such as gradients) can alter the load on specific tissues, it may inadvertently increase the risk elsewhere, emphasizing the need for careful consideration and balance in training and rehabilitation programming to genuinely lower the risk of injury.

These questions were based on the article publised by Bas and his colleagues, “Per-step and cumulative load at three common running injury locations: The effect of speed, surface gradient, and cadence.”