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Do Ground Reaction Forces Reflect Bone Loads?

Karl Zelik, PhD and Emily Matijevich of Vanderbilt University are our guests for this Mountain Land Running Medicine Podcast. Dr. Zelik is an Assistant Professor in Mechanical Engineering and co-directs the Center for Rehabilitation Engineering & Assistive Technology (CREATE). CREATE aims to improve health, mobility, and independence for individuals with disabilities, and to enhance human capabilities beyond biological limits, by engineering, measuring, optimizing and understanding technologies that physically augment human performance. Emily Matijevich is a Mechanical Engineering PhD student working with Dr. Zelik. Emily’s research interests include musculoskeletal overuse injuries and opportunities for preventing these injuries with wearable technology and smart assistive devices. For her work, Emily is a recipient of a 2019 Women in Sports Tech Fellowship.


  • Ila R. Stewart

    June 28, 2019, 9:47 pm

    I want to thank Brian bay and Shane Dibiase and all staff members at the Holladay Mountain Land Physical Therapy and Rehabilitation. Due to a second neck injury I began to experience pain that became so intense I no longer had strength in my right arm. All of the fingers in my right hand would tingle and become numb. Severe pain would radiate from the vertebrates in the right side of my neck down through my arm and through my right hand. My right hand would become extremely cold and dark in color. I had strong frequent headaches that greatly interfered with each and every day.

    I met with a Neurologist here in Salt Lake City Utah. He went over an MRI with me and informed me that I had a pinched nerve causing weakness in my right shoulder and arm as well as the intense pain the cold and dark colored hand, and the numbness. My options were to have surgery to remove vertebra’s 3,4,5,and 6 and explained further the surgical procedure. The other option given me was to go into physical therapy and rehabilitation which is the option I chose but honestly felt little hope that this would relieve the severe pain and problems coming from my neck injury. I knew I would need the very best physical therapist and rehabilitation center where I would for certain receive the very best treatment plan that I felt through past experience Salt Lake City had to offer. Of course I’m speaking of the Mountain Land Physical Therapy and Rehabilitation in Holladay.

    I enter into a 6 week three days a week plan ordered by the Neurologist . My first appointment was a consultation with Brian Bay PT,DPT,Oct and a team member named Kallie . A plan was put in place and three days a week that plan was put into action. At my second appointment I had the opportunity to meet Brian’s assistance Shane Dibiase, PTA. With all of the staff members each visit became more and more hopeful for me. I began right from the beginning appointment improving. I faithfully done my physical therapy exercises each and every day at home as well as at the rehabilitation physicality. I began sleeping again with minimal pain and was able to drive my car longer distances and the dark cold tingling and numbing in my right hand stopped. The pain lessened it seemed with each visit. The frequent strong painful headaches left. This is the best part of all. I progressed so well I graduated seven visits early. All staff members not only helped me physically be on my way to pain relief and stronger muscles for safety but my mental well being had healed as well. Fun and professional all in one what more could an injured person ask for.

    Life happens and I may over do or what ever may be the case where I may need to return to receive further help. I do know from experience where I can receive Physical Therapy and Rehabilitation at it’s Best. Thanks Mountain Land Physical Therapy and Rehabilitation in Hollady, Utah you’re greatly appreciated!

  • Nathan Stern

    July 25, 2019, 1:18 pm

    Loved this episode. As good science should, it left me much more confused than before I listened to it. Some questions that came to mind:
    – What about the Zadpoor 2011 meta-analyses that showed peak loading rate and not peak GRFs were associated with tibial and metatarsal stress fractures? Granted it was only retrospective studies and the prospective studies have been mixed. Would it be even appropriate to group metatarsal and tibial bone stress injuries? If muscle activity is the largest contributor to bone stress then the muscles that attach to these bones respectively serve very different functions (ie plantar flexor prime mover vs multi-axial stabilization of the foot).
    – If muscle activity is truly the largest contributor to bone stress than one would expect slow weighted heel raises to be more provocative than a landing hard on the calcaneous or other impactful movements. As a new clinician I can not say if this holds water or not as I have not seen any tibial stress fractures.
    – How was it not mentioned in the podcast that this article has a poem in it??? Major style points.

  • Karl Zelik

    July 30, 2019, 8:41 am

    Thanks for listening, glad you enjoyed it! We had fun participating in this 🙂

    1) In Zadpoor 2011, half the studies reviewed actually reported that GRF loading rate was not different between the injured (stress fracture) and control (no stress fracture) groups (see Table 3 in that paper). So the results were quite mixed/variable even then. Furthermore, at the time there were just not that many studies to review on this topic. There are many more epidemiological studies now — about 3x as many. Dr. Ross Miller from the University of Maryland recently compiled this evidence and presented it at the American College of Sports Medicine conference earlier this year (2019), see link below. Main takeaway: when looking across >20 epidemiological studies there does not appear to be a compelling relationship/effect between loading rate and injury. This statement seems to hold for both prospective and retrospective studies based on current evidence. Link:

    2) In general I would not group injuries like tibial and metatarsal bone stress injuries. These are different locations in body which experience very different loading. As such, some running conditions (or techniques) may increase stress on one bone and decrease stress on the other.

    3) We did forget to mention the Limerick during the podcast 🙂 Glad you found it!

    All the best, Karl

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