Patellofemoral Joint and Achilles Tendon Loads during Running

Continuing Education Physical Therapy
August 14, 2016
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Evidence-Based Practice | Issue 4-2016

Patellofemoral Joint and Achilles Tendon Loads during Overground and Treadmill Running

Article.  Willy, Richard W., et al., Patellofemoral Joint and Achilles Tendon Loads during Overground and Treadmill Running, Journal of Orthopaedic & Sports Physical Therapy 2016; 8(3):  1-30.

Purpose. The purpose of this study was to compare measures of loading to the patellofemoral joint and Achilles tendon across treadmill and overground running in healthy, uninjured runners.  

Study Design. Controlled Laboratory Study


  • Subjects
    • 18 healthy runners ran at their self-selected speed on an instrumented treadmill and overground while three-dimensional running mechanics were sampled.
    • All participants were required to be habitual runners, free of any lower extremity surgeries and injury-free for at least the previous three months.  
    • Participants were limited to 18-35 years of age to limit heterogeneity in biomechanics and Achilles tendon properties that may be introduced by a greater age range.  
    • Participants had to be comfortable with treadmill running defined as a score of at least “8” on a visual analog scale.
    • Factors previously related to patellofemoral pain and Achilles tendinopathy in runners include injury history, age, strength deficits, training errors, structural issues, biological sex and biomechanical overloading.  
    • Participants were conservatively determined to be necessary to adequately power this study.
    • 18 recreational runners (9 males, 9 females) from a large university and area running clubs.
      • A musculoskeletal model derived peak load, rate of loading and estimated cumulative load per 1 kilometer of continuous running for patellofemoral joint and Achilles tendon for each condition.
      • Data were analyzed via paired T-tests and Pearson’s correlations to detect differences and assess relationships, respectively, between the two running mediums.
      • Potential differences in joint kinetics exist suggesting that there are differences in loading characteristics of the patellofemoral joint and Achilles tendon between overground and treadmill running.  
  • Data Collection
    • Visual Analog Scale
      • Fifty-six reflective markers were affixed to the bilateral lower extremities, pelvis and trunk of each participant.
      • 3-dimensional running mechanics were sampled for 10 seconds at each participant’s self-selected running speed.
      • Ground reaction forces and marker trajectories were sampled at 1000 Hz by the instrumental treadmill and a 200 Hz by a 10-camera motion capture system.  
      • The treadmill running trial was not longer than 5 minutes of sustained running and an approximately 10-minute rest period was provided to each runner between the end of the treadmill testing and initiation of overground testing to minimize fatigue.
      • 3-D overground running mechanics were samples as runners traversed a 25-meter runway at their same selected running speed used during the treadmill running.  
      • Each runner practiced execution of the overground trials for several minutes to accommodate to the overground collection procedures, including establishment of running speed and runway starting position.  
      • Marker trajectories and ground reaction forces were sampled with the exact same parameters as those utilized during the treadmill trial.  


  • No differences were found and there was excellent correlation for gait speed between overground and treadmill running for our participants.  
  • Step length was significantly shorter during treadmill running compared with overground running.  This difference was associated with a moderate effect size yet had an excellent correlation between two running modes.  
  • Stance duration was not different and was highly correlated between the two running conditions.  
  • Peak knee flexion and peak knee extensor moment were not different between the two running modes.
  • Peak patellofemoral joint reaction force, peak patellofemoral joint stress was also not different between conditions.
  • The peak plantar flexor moment was significantly greater and not correlated during treadmill running compared with overground running.  
  • Achilles tendon force, tendon loading rate, tendon force impulse per stance, and estimated cumulative Achilles tendon force per 1 kilometer of continuous running were all significantly greater during treadmill running.  

Clinical Relevance

  • Loads placed on the knee and patellofemoral joint are not different between overground and treadmill running.
  • Loads placed on the ankle, specifically the Achilles tendon are significantly greater with treadmill running than overground training.  
  • Clinicians may use this information to guide patients safely back to running activities after injury or surgery.
  • Clinicians may strongly consider recommending overground running activities over treadmill training for those with risk factors for Achilles pathology or previous injury/surgery.