Runners and Bone Stress Injuries: Part 1

An osteon is the functional unit of the bone. Osteons contain osteocytes, the cells basically responsible for managing bone activity. Osteoblasts help build bone up, osteoclasts help break down bone. Lining all of this one the edge of the bone is the periosteum, a lining with blood supply. 

Now, we’ve got two types of bone: cortical and trabecular bone.

Why that matters:

Cortical Bone: 

• 80% of bone mass

• Low surface to volume ratio

• Higher stiffness and rigidity, transmits load well, withstands compression better than tensile loads

• Can handle high stress but low strain tolerance, aka poorly handles deformation

Trabecular/Cancellous: 

• 20% bone mass, shock-absorbing role

• Lower calcium more water contact, lots of surface area exposed to bone marrow and blood flow (big affected by energy availability)

• Absorbs and releases quickly; lower stress but high strain (can deform better)

Next, let’s define some bone terminology thrown about in the literature, and sometimes haphazardly in social media circles. 

• Stiffness: the material resistance to elastic deformation on a stress-strain curve

• Toughness= area under stress-strain curve 

• Strength= Measure of resistance to failure (damage)

• Inelastic deformation: a permanent change in form (not good for bone)

  
  

The above chart illustrates some of those terms pretty clearly. 

We have some primary forces acting on bone that we can choose, or are always obliged to, consider when selecting exercises and determining what’s causing a bony stress:

1. Muscular contraction: High impulse loading during dynamic loading that creates multiples of bodyweight forces. Muscles have a strong synergistic growth relationship with bones, i.e. better muscle cross-sectional area equates to better bone growth.

2. Impact loading: external forces like ground contact, partially absorbed and redistributed through joints, tendons, muscles, and bones. 

3. Gravity: We always have this occurring, as demonstrated by cases of astronauts on extended stays in orbit.  

And finally, the question we’ve taken some time to arrive at: What is a BSI? Bone stress injuries early on are essentially a reaction of the periosteum, which can evolve into bone marrow edema (swelling) and then into further damage of the bone on a structural level. This affects the integrity of the bone during loading activities. 

Picture: Bone marrow edema

BSIs develop more quickly in vivo (in living) rather than in vitro (in lab), as in vivo the bone is experiencing multiple force types simultaneously, which is not accounted for in vitro modeling studies. 

One big point I’d like to bring up: Matjevich et al (2019) demonstrated that ground reaction force metrics are not strongly correlated with tibial bone load when running across speeds and slopes. Give the paper a look: The vast majority of bone loading is due to muscular contractions, so peak tibial forces can vastly out measure GRFs, like 2-3xBW for GRFs versus peak distal end tibial force being 6-14x BW. What this can mean is the impact against the ground isn’t inherently a significant factor compared to the anticipated muscle contraction forces placed on bone.

Seeing some changes but still want a more individualized approach to your rehab? If you want to learn how to take control with some expert guidance and treatments to optimize your performance and longevity, then that’s exactly what we provide at Zenith Performance Physical Therapy. Call or text us at 562-502-1767 to schedule a free phone consultation and come in for an evaluation! 

1. Matijevich ES, Branscombe LM, Scott LR, Zelik KE. Ground reaction force metrics are not strongly correlated with tibial bone load when running across speeds and slopes: Implications for science, sport and wearable tech. PLoS One. 2019 Jan 17;14(1):e0210000. doi: 10.1371/journal.pone.0210000. PMID: 30653510; PMCID: PMC6336327.