Injured runner series: causes of running injuries - part D: Biomechanics

Introduction

The final post in this series covers biomechanical influences on injury risk.  I want to set expectations before diving in. The relationship between running biomechanics and injury is far less clear than most runners, coaches, and therapists assume. As a rehab specialist, I can make a reasonable case that biomechanics matter after injury occurs. How much they matter prospectively,  meaning before an injury develops, is a much harder question to answer. Keep that in mind throughout.

Three Foundational Points

In terms of biomechanics, I think three pieces of knowledge are required as starting points to understand when and how biomechanics influence injury risk. 

1. It has been well established that static posture (quadriceps angle, arch height)  does not influence injury risk, though it will likely influence running biomechanics, just not in a way that is consequential for injury (1,2) 

2. Dynamic foot posture also does not appear to influence injury risk, contrary to popular belief. This is true even when hyper-pronators run in neutral shoes (3). 

3. Muscle, not ground reaction force, is the main contributor to tissue loads while running (4)

What Actually Predicts Injury Risk

With that foundation in place, the research becomes more useful. Kliethermes et al. (5,6)  identified a clinical prediction model for bone stress injuries (BSI) that includes: 

• Reduced step rate

• Increased center of mass (COM) excursion

• Peak vertical ground reaction force

• Vertical GRF impulse. 

Joachim et al. (7) added to this in 2023, finding that pre-season Vertical COM displacement was a significant risk factor for BSI development in collegiate cross-country runners.

Importantly, all of these variables - COM excursion, peak vertical GRF, GRF impulse, and vertical COM displacement - can be meaningfully influenced by changes in step rate (cadence). That's what makes cadence such a practical clinical tool, something we'll return to in a future post.

The Foot Strike Debate

Notice what's missing from the list above: foot strike pattern.

Foot strike influences where injuries occur, but not how often they occur overall (8). Think of it as a load redistribution, not a load reduction. Rearfoot striking increases stress at the tibiofemoral and patellofemoral joints (knee). Forefoot striking shifts load to the ankle, specifically the achilles tendon and plantar fascia.

Prospectively changing foot strike carries two risks: it may shift load onto tissues that haven't yet adapted, and it often reduces running economy. Neither outcome is desirable  (9).

Injury-Specific Application

There are clear, case-specific situations where biomechanical intervention is appropriate, particularly once injury has occurred and the goal is load management.

Take two common examples:

• Achilles tendinopathy or shin splints: The priority is reducing plantar flexion loading. This means discouraging a forefoot strike, reducing speed work, and limiting uphill running.

• Patellofemoral pain: The priority is offloading the knee. A forefoot strike may actually help here, alongside reduced speed work and avoidance of downhill running — though uphill running is generally tolerated.

The throughline is tissue-specific loading, not universal biomechanical correction.

Practical Takeaways

• Static and dynamic posture are useful to observe, but shouldn't drive injury risk assessment.

• Footwear should be prescribed based on comfort, not to correct postural "faults." Retroactive footwear changes to temporarily reduce load during rehab can be appropriate — proactive prescription is not well-supported.

• Muscle force is the primary driver of tissue stress. Biomechanical targets should reflect this.

• The most clinically relevant kinematic variables are: COM excursion, vertical COM displacement, peak vertical GRF, GRF impulse, and step rate.

• In a gait analysis, three starting points are most informative: (1) trunk movement in all three planes, (2) step rate, and (3) foot contact position relative to the center of mass.

How I Actually Use This in Practice

As a physical therapist, I use biomechanical assessment as a tool for managing tissue loads in the rehab process. As a screening tool, I use it to get a lens into how a runner moves, not really to gather a list of things to correct. 

As a coach, I rarely assess it in any formal sense. The one exception is cadence. I'll check a runner's cadence through Garmin Connect or Strava and address it when: they're newer to running and don't have ingrained patterns where changing cadence will negatively impact performance, if they have an injury history where cadence changes could shift long-term risk, or they have a prior history of lower limb bone stress injuries.

The evidence here will continue to evolve, and my clinical opinions will evolve with it. 

Thanks for reading!