Fatigue, Foot Type, and Running Performance | Find Your Stride | Edinburgh Podiatrist

Why Fatigue Matters in Running Biomechanics

Fatigue is not merely a drop in power output, it fundamentally changes how the lower limb interacts with the ground. For runners, this means altered ground reaction forces (GRFs), delayed timing to peak forces, and modified muscle activation patterns. Clinically, these changes have been linked to common sports injuries such as plantar fasciitis, medial tibial stress syndrome, Achilles tendinopathy, and patellofemoral pain.

For podiatrists and sports clinicians, understanding how fatigue changes gait mechanics is essential for injury prevention, footwear prescription, orthotic design, and return-to-run decisions.

Fatigue changes how the lower limb interacts with the ground. For runners, this means altered ground reaction forces (GRFs), delayed timing to peak forces, and modified muscle activation patterns.

Pronated Feet Under Fatigue: What the Evidence Shows

A recent controlled laboratory study investigated runners with pronated feet versus those with neutral foot posture while running to fatigue at the heart rate deflection point (HRDP), a commonly used marker for sustainable aerobic intensity. The authors analysed GRFs and lower-limb muscle activity before and after fatigue.

Key findings relevant to practice:

1. Reduced Propulsive Force at Push-Off: Runners with pronated feet demonstrated significantly lower peak anterior GRF during push-off compared with neutral-foot runners. This suggests a less effective transfer of force into forward propulsion. An efficiency cost that may accumulate over distance.

   
   

2. Fatigue Further Decreases Push-Off Force in All Runners: Regardless of foot type, fatigue caused a measurable decline in propulsive GRF. For pronated feet, this compounds an already reduced push-off, potentially impairing running economy and speed.

   
   

3. Delayed Timing to Peak Forces: Individuals with pronated feet exhibited longer “time to peak” in multiple GRF components, indicating altered loading patterns that may increase tissue stress during stance.

   
   

4. Muscle Control May Deteriorate with Fatigue: The study reported fatigue-related changes in muscle activation, particularly in muscles involved in knee and foot control, suggesting reduced ability to stabilise joints during late stance.

Clinical interpretation:

Fatigue appears to magnify the apparent mechanical disadvantages of pronated foot posture, reducing propulsive efficiency and potentially increasing cumulative load on passive structures. This may help to explain why overuse injuries in runners have been linked with ‘excessive pronation’ in the past.

These conclusions are drawn from the peer-reviewed study by Fasihi and colleagues in Communications Medicine (2025) examining fatigue at HRDP in runners with pronated versus healthy feet  .

Performance Implications for Athletes

From a performance perspective, lower anterior GRF at push-off means less horizontal propulsion per stride. Over long distances, this can:

• Increase metabolic cost for a given pace

• Reduce stride efficiency

• Exacerbate asymmetries under fatigue

For competitive runners, even small decrements in propulsive force may influence pacing, late-race mechanics, and finishing kick.

Injury Risk: Connecting Mechanics to Pathology

Altered force patterns and delayed peak loading under fatigue can elevate stress in tissues that already tolerate high repetitive loads:

• Plantar fascia & structures supporting the medial arch: prolonged pronation with reduced muscular control

• Achilles tendon: altered timing of push-off and calf activation

• Tibia: changes in loading rate and impulse associated with stress reactions

• Knee: altered quadriceps and hamstring coordination during stance

Importantly, the study observed that fatigue reduced the foot’s ability to control joint motion, which may increase uncontrolled joint contact forces, an established mechanism in overuse sports injuries.

Practical Applications for Podiatrists and Clinicians

1. Gait Assessment Should Include Fatigue

Static assessment and short treadmill trials may underestimate risk. Consider evaluating runners after a sustained run or during longer sessions to reveal fatigue-related deviations.

2. Footwear and Orthotic Strategy

For runners with pronated feet:

• Motion-control or stability footwear may help maintain midfoot integrity under fatigue.

• Custom orthoses can be prescribed to improve lever arm efficiency during push-off and reduce excessive midtarsal motion.

3. Strength and Conditioning

Targeted strengthening of the following muscles/muscle groups can improve fatigue resistance and dynamic control.

• Intrinsic foot muscles

• Tibialis posterior

• Calf complex

• Proximal stabilisers (such as gluteus medius)

  
  

4. Load Management and Training Prescription

Use tools like HRDP or lactate threshold to structure training at sustainable intensities. Monitor for mechanical breakdown late in sessions, not just early-run form.

Take-Home Message

Fatigue changes how runners interact with the ground, and these changes are more pronounced in individuals with pronated feet. Reduced push-off force, delayed peak loading, and altered muscle activation under fatigue may compromise both running performance and injury resilience.

For athletes, optimising footwear, strength, and training structure can preserve efficiency. For clinicians, incorporating fatigue into assessment and intervention is key to reducing the burden of running-related sports injuries.

Citation

Fasihi, L., Siahkouhian, M., Jafarnezhadgero, A. A., & Fasihi, A. (2025). The effect of fatigue induced by running at heart rate deflection point in people with pronated versus healthy feet. Communications Medicine, 5:471. https://doi.org/10.1038/s43856-025-01176-z