Introduction

Running-related injuries frequently occur in experienced and novice runners, most often in the lower limb. The positive effects of participating in running should be addressed, as the benefits of running on the whole body are clear. To minimize the adverse effects of running (injuries) it is crucial to understand, both from a training and rehabilitation perspective, what happens in the lower limb during a running session. In this study, the authors looked at the influences of different types of running protocols on three frequently injured body regions. The information derived from this analysis can help guide training planning and rehabilitation.

Methods

This study examined 19 healthy participants who were injury-free and used to treadmill running. They were eligible if they were between 18 and 45, had a BMI of <26kg/m2, and were free from any injury in the last 3 months.

They were invited to participate in a test session where they completed different short one-minute runs while their data was collected. Retroreflective markers were placed at 26 locations. The ground reaction forces and lower body and trunk kinematics were recorded.

First, the participants completed an 8-minute run at 2.78 m/s for treadmill familiarization. Next, they ran 4 minutes at 3.33m/s to determine their preferred step frequency. They completed several 1-minute runs at different speeds and uphill or downhill slopes. The order of the runs was randomized. All the slope runs were performed at the speed of 2.78 m/s. Following the sloped runs, the participants ran at 3.33m/s using their preferred step frequency. Then they were asked to run at a higher step frequency (+10 steps per minute) and a lower step frequency (-10 steps per minute) by following the beat of a metronome.

Using the data from the retroreflective markers, a musculoskeletal model was constructed that contained 22 body segments, 37 degrees of freedom, and 80 muscles. The model was adapted to the body composition of each participant.

From this information the loads and damage at the patellofemoral joint, the tibia, and the Achilles tendon were determined. Since the amount of damage that tissues experience depends on the duration, magnitude, and frequency of loading the analysis took into account the following different loading parameters were calculated.

• Per-Step Peak Load: Reflects the maximum stress (on the patellofemoral joint and tibia) or strain (on the Achilles tendon) value per step.
  • The term “peak stress” or “strain” in this article refers to the highest level of pressure or deformation that our body tissues encounter during running. It’s basically the greatest force or stretch that our tissues have to bear
  • This peak stress or strain can provide information about the potential risk of injury to our bones and tendons. Understanding the peak stress or strain allows us to comprehend better the amount of load our bodily tissues are under and how it may affect their health and resilience
• Loading Impulse: As the amount of loading is dependent on the duration of loading, the loading impulse was calculated from the stress or strain over a gait cycle.
• Weighted Impulse: Stress or strain raised to an empirically derived exponent since the relationship between load and damage is nonlinear.
  • The weighted impulse considers different tissues’ vulnerability to harm and provides appropriate weights. This means that tissues that are more susceptible to injury are given more weight in the computation.
• Cumulative Impulse: Multiplied stress or strain impulse by the number of strides per kilometer to account for the frequency of loading

Results

The included participants were 10 males and 9 females on average 23.6 years old. They were on average 174 cm tall and weighed 67.2 kg.

When the different running conditions were examined, the following results were obtained.

1. Increases in speed
   • Increase the peak tibia and patellofemoral joint stress and the Achilles tendon strain
   • Decrease the impulse of the tibia and Achilles tendon
   • The impulse at the patellofemoral joint remains unchanged
2. Increases in the inclination of the treadmill (more uphill)
   • Decreases the peak patellofemoral joint stress
   • Increases the peak tibial peak stress and peak Achilles tendon strain
   • Decreases the patellofemoral joint impulse
   • Increases the impulse at the tibia and Achilles tendon
3. Decreases of the treadmill inclination (more downhill)
   • Increase the peak patellofemoral joint and tibial stress and impulse
   • Reduces the peak Achilles tendon strain and impulse
4. Increases in step frequency
   • Decreases the peak stress, strain and impulse at all three locations

As running consists of a high number of steps during each running bout, the authors calculated the cumulative load and the cumulative weighted impulse from the stress and strain impulses over the total number of strides taken.

The effect of higher running speeds:

• Increasing the running speed decreased the cumulative stress impulse of the patellofemoral joint and tibia and the cumulative Achilles tendon strain impulse
• Increasing the running speed, however, increased the cumulative weighted impulse at the patellofemoral joint

Inclination effects:

• Running steeper uphill decreases the patellofemoral cumulative stress impulse and weighted impulse, but increases both the tibial and Achilles tendon cumulative stress and strain impulses, and weighted impulses, respectively.
• Running more downhill increased patellofemoral and tibial cumulative stress impulses and weighted impulses but decreased the Achilles tendon cumulative strain impulse and weighted impulse.

Step frequency effects:

• When the step frequency was increased, this led to a decrease in the cumulative stress and strain weighted impulse of the patellofemoral joint and the Achilles tendon, but not for the tibia

Questions and thoughts

The authors wanted to calculate the amount of damage that tissues experience from the duration, magnitude, and frequency of loading. Although interesting to know, the article only considers the damage that running can bring to the patellofemoral joint, the tibia, and the Achilles tendon. It does not take into account the necessity of loading the joints and structures to remain healthy. As such, the protective effects that running can exert on these tissues are neglected. While I can certainly understand the necessity of knowing what running loads can do to our joints, the authors missed the opportunity to explain what to do to protect our joints. This is what I’ll try to do for you.

• Someone with Achilles tendon problems might find relief when running slower, running more downhill or avoiding uphill running, or by increasing the step cadence
• In case of patellofemoral joint problems, slower running, neutral or uphill running, or increasing the step cadence might work best
• With tibial problems, running slower, running on more flat surfaces, and increasing the step cadence are viable solutions

But is it all about damage?

While running is commonly regarded as a high-impact sport that may endanger joint health, evidence reveals that when done correctly and with good biomechanics, it can help protect the joints. Running can improve joint health by fostering positive adaptations, increasing cartilage synthesis, and maintaining joint integrity, potentially lowering the risk of injuries and degenerative disorders.

The results of this study help us understand what happens at the tibia, patellofemoral joint, and to the Achilles tendon. From the different options (speed, slope, and step frequency) we can understand how to best adapt running in case problems occur.

Talk nerdy to me

This study was conducted in a small sample and included only 19 participants. These people had no injuries or problems of their Achilles tendons, tibiae or patellofemoral joints and this may imply that the findings may differ from people suffering from pain or musculoskeletal conditions of these body regions.

By making a musculoskeletal model to estimate forces and loads across the body regions, the authors were able to use a very modern approach to calculate these dynamic 3D motions. However, the model also requires to make assumptions about for example the maximal muscle force, and therefore it remains an estimation.

Running was assessed using a treadmill, which may be different from outdoor running. The speeds were on the high end for recreational purposes, since the lowest speed was already at 10km/h and the fastest speed was 18km/h. The authors indicated that for many runners, these speeds were too demanding. Possibly this could have influenced the results.

Take home messages

This model determined the loads at the Achilles tendon, the tibia, and the patellofemoral joint. These locations were selected since they most frequently involve lower extremity running-related injuries. Understanding how different running conditions affect load and damage at common injury sites provides valuable insights for physiotherapists. By manipulating running speed, surface gradient, and cadence, clinicians can tailor rehabilitation programs to reduce load and prevent running-related injuries effectively.

Reference

Van Hooren B, van Rengs L, Meijer K. Per-step and cumulative load at three common running injury locations: The effect of speed, surface gradient, and cadence. Scand J Med Sci Sports. 2024 Feb;34(2):e14570. doi: 10.1111/sms.14570. PMID: 38389144. 

Related research

https://app.physiotutors.com/research-reviews/preventing-running-related-injuries/