How Time Under Tension and Tempo Mitigate Stress Shielding

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In this listener Q&A episode, Brodie dives into four fascinating research-backed topics that every runner should understand — from aging performance to tendon rehab science:

• How running performance declines with age — and the key training interventions to slow it down
• Recovery potential after Achilles tendon rupture or tendinopathy, with or without surgery
• The true accuracy of MRI vs. CT scans for stress fractures and other running-related injuries
• Whether isometric exercises after a run can strengthen tendons and reduce “stress shielding”

Episode Summary

In this “Ask Brodie Anything” edition, Brodie tackles questions from listeners covering performance longevity, injury recovery, and the science behind imaging and tendon adaptation.

🏃‍♂️ 1. Aging & Running Performance

Brodie unpacks the 2019 paper “The Physiology and Biomechanics of the Master’s Runner” by Rich Willy, revealing:

• Performance decline typically begins around age 35, with VO₂ max dropping ~7% per decade.
• Active runners experience slower declines due to training volume and intensity.
• Step length decreases and cadence increases with age, while ankle power and tendon stiffness reduce, leading to slower speeds.
  🧩 Key takeaways:
• Maintain high-intensity interval sessions and training volume.
• Add heavy resistance training (2–3x per week) and plyometrics to preserve tendon stiffness and bone density.
• Use cross-training (ski erg, bike, rower) to build aerobic fitness while reducing joint stress.

🦶 2. Achilles Tendon Rupture: Can You Fully Recover?

Drawing from the 2016 World Congress on Sports Physical Therapy Consensus Statement, Brodie explains that:

• Return-to-sport rates range from 55–90% after 1 year of rehab.
• Surgical cases report 29–87% return, but recurrence rates remain high (27–44%).
• Recovery depends on age, injury severity, and rehab adherence.
  🧠 Brodie emphasizes that full recovery without pain or fear of re-injury is possible — but addressing psychological readiness is as vital as physical rehab.

🩻 3. MRI vs. CT for Stress Fractures

Brodie reviews a systematic review comparing imaging accuracy:

• CT scans: Sensitivity 32–38%, Specificity 88–98% → great for confirming, poor for ruling out.
• MRI: Sensitivity 68%, Specificity 99% → still the gold standard for stress fractures.
  👉 Clinical takeaway: A CT scan can confirm, but a negative CT often still needs MRI.
  Scans should be used only when clinically justified — chronic tendinopathies are best diagnosed via functional assessment, not imaging.

💪 4. Isometrics After Running: Useful or Overhyped?

Referencing tendon researcher Keith Baar, Brodie discusses “stress shielding” — when tendons redirect load away from damaged fibers.

• Post-run isometrics (3×20–30s holds) can help load fatigued tendons more evenly.
• But for true tendon remodeling, progressive heavy slow resistance remains essential.
• Alternatives like “creep loading” and time-under-tension exercises can also reduce stress shielding — no need to be fatigued to gain benefits.

🧩 Key Takeaways

• Stay strong as you age — resistance and high-intensity training slow decline.
• Achilles rehab success depends on gradual loading, not just surgery.
• MRI beats CT for stress fractures; be strategic about when to scan.
• Isometrics help, but heavy slow load is still the cornerstone of tendon rehab.

📚 Resources Mentioned

• Willy et al. (2019): The Physiology and Biomechanics of the Master’s Runner
• 2016 Consensus Statement on Return to Sport after Injury (World Congress in Sports Physical Therapy)
• Diagnostic Accuracy of Imaging Modalities for Lower Extremity Stress Fractures
• Keith Baar: Stress Shielding and Tendon Adaptation episode