Exercise leads to bone growth. That's an irrefutable fact of biology and one of the most important tools for preventing and reversing osteoporosis. While we can observe that this is true– and scientists have been observing it for generations– the mechanisms by which this incredible process occurs are still being discovered.
Today we'll look at a brand new study that digs deep into the question of how new bone is created as a result of the pressure that we exert on our bones when we exercise.
Get ready to zoom way in to the microscopic cells that are responsible for building bone. What you’ll learn there can help you make choices that maximize your bone growth and ensure your strength and well-being.
What We Know About Bone Formation
We know that exercise stimulates bone formation. Surgeon and anatomist Julian Wolff observed this law of biology in the late 19th century, which is why we call it Wolff's Law. That law observes that in a healthy person or animal, bone will adapt to the loads under which it is placed.
We call that load mechanical load. Mechanical load describes the pressure that our muscles exert on our bones to create movement or resist pressure. Weight-bearing exercise places a mechanical load on your bones.
Bones sense this pressure with the help of osteocytes, the most abundant bone cells in the adult skeleton. Found in mineralized bone matrix,osteocytes are mechanosensitive, meaning they are sensitive to mechanical pressure.1
When osteocytes sense pressure, they respond by releasing compounds called paracrine factors, which interact with stem/stromal cells in bone. These cells are progenitor cells with the ability to mature into cells with different functions. The paracrine factors send a message to the stem/stromal cells to develop into cells that will create new bone mass, like osteoblasts. This bone-creating process is called osteogenesis.1
The process described above is how exercise results in new bone growth. We could also break it down into a chain of communication that looks like this:
- You do weight-bearing exercise, which engages your muscles
- Your osteocytes sense the pressure that your muscles are exerting on your bones
- Your osteocytes respond by releasing paracrine factors
- The paracrine factors signal stem/stromal cells to become cells that create new bone
- Osteogenesis begins at the site of the pressure
New bone is formed in response to the pressure that muscle places on bone. This occurs because osteocytes sense mechanical pressure, then release compounds called paracrine factors that signal progenitor cells to become bone-forming cells that carry out the process of osteogenesis, which is the creation of new bone.
Study Reveals The Mechanism Of Communication
Although the chain of events described above is well known, scientists were less certain of how each event in the chain connected to the next one. That's what a team of Irish scientists set out to discover.
They performed an experiment in which they applied mechanical pressure to osteocytes in a lab and observed the results.
They found that when the osteocytes secrete paracrine factors, those compounds use extracellular vesicles to interact with stem/stromal progenitor cells, driving them to the process of osteogenesis. These extracellular vesicles are activated by this osteocyte response to mechanical pressure and are a previously unconfirmed part of the bone formation process.1
Extracellular vesicles are not pathways that are continually present. They are created by osteocytes along with the paracrine factors so that those factors can reach the stem/stromal cells that will then develop into cells that can conduct osteogenesis.1
This remarkable ability of osteocytes to both create the signal for osteogenesis to commence, and to create the means of sending that signal is a major step forward in understanding how exercise creates new bone.
A group of Irish scientists observed what happens when osteocytes experience mechanical load. They discovered that not only do those osteocytes secrete paracrine factors, but they also create extracellular vesicles that allow for the signals contained in those factors to reach the progenitor cells that will begin the process of osteogenesis.
What This Means To You
Every time you go for a walk, lift a bag of groceries, or perform an exercise routine, you're engaging an intricate and ancient system of building bone. It's a solution to bone loss that lives inside of us, the complexity of which is still being discovered by scientists at the top of their field.
You have the power to engage this process anytime you want. Use that power. Activate the bone-building pathways, the osteocytes, the extracellular vesicles, and set them to their purpose: building strong and healthy new bone.