Everyday we work with athletes, clients, and patients who present with an injury or condition involving an injury to a muscle, nerve, ligament, tendon, or bone. One of the most powerful tools we have to accelerate the healing of this injury is exercise. The goal of rehab course is to expedite tissue healing to improve physical function. As nearly every rehabilitation intervention introduces force to the affected tissues, therapists must have an appreciation of how those mechanical responses influence biological signals to result in tissue healing.
To better understand how exercise works let’s use a more common issue you are familiar with and have experienced.
When you get sick with symptoms including nausea, fever, chills, and body aches; you visit your physician and they prescribe some medication like an antibiotic. That medication prescribed has a certain dosage.
250 mg, twice daily, for 10 days.
That dosage will have a cellular response within your body to overcome the symptoms to assist in “healing” your body. Antibiotics work either by killing bacteria or halting their multiplication so that the body’s immune system can fight off the infection. Cells communicate with other cells to accomplish that.
With physical medicine physical therapists will prescribe exercise to help promote tissue healing.
Dosage is one of the most important things to consider. How much and how often? That largely depends on age, level of acuity, tissue type, body region, level of irritability or sensitivity, and other factors at play. This is where physical therapists form a collaborative relationship with you to determine. You being the expert of your body and sensations. Physical therapist being the experts in exercise prescription.
The how it works is all about MECHANOTRANSDUCTION.
Check out the two videos below to see different loading strategies to create tissue healing in the achilles tendon!
Physiologically, what stimulates tissue repair of articular cartilage, muscles and tendons is called mechanotransduction. Which is the process by which the body converts mechanical loading into cellular responses.
It can be broken down into three phases:
1) Mechanocoupling: This is the physical load cells undergo while in repair. The physical load is transferred into chemical signals which stimulate cellular changes.
2) Cell-Cell Communication: When one cell is stimulated, other cells in the area (whether directly stimulated by the initial mechanical stimulus or not) will undergo a cellular response.
3) Effector Response: When a cell is mechanically stimulated through compression, distraction, etc., several processes will occur intrinsically to allow change to occur.
Different tissue types will respond differently to the physical load.
When a tendon is trying to heal, there is up-regulation of insulin-like growth factor, other growth factors, and cytokines which allows for cellular proliferation and tissue remodeling. Because healing is occur at the cellular level, too much stress OR too little stress on the tendon tissue could cause an alteration in the up-regulation, not allowing the tendon to rehabilitate optimally. The research up-to-date shows that tendons responds positively to “controlled loading.” Research focusing on the type and intensity of controlled loading (eccentrics, assisted, resisted) is still ongoing.
The authors Khan and Scott state that “muscle offers one of the best opportunities to exploit and study the effects of mechanotherapy” because of how muscle tissue responds to loading. We know there is an overload of mechanogrowth factor (MGF) released when load is induced on the muscle force. This in turn causes muscle cell hypertrophy due to a cell-to-cell communication with nearby satellite cells. At this point, the research shows that early loading after a brief immobilization period is essential for minimizing atrophy and restoring normal cellular structure of the muscles.
Articular cartilage is comprised of a large population of mechanosensitive cells. It is hypothesized that by repetitively stimulating the articular cartilage with a low load/high repetition exercise dosage, better outcomes will result. One study assessing full thickness cartilage defects following periosteal transplantation demonstrated that individuals who used continuous passive motion (low load/high repetitions) had greater outcomes than those who did not receive this intervention. As with all things, research is ongoing.
When assessing bone healing, osteocytes are the primary mechanosensors. A recent study looking at individuals following a distal radius fracture had stronger bone growth if they received intermittent compression as an adjunct to the standard of care (compression & gripping exercises). The pneumatic compression allowed for extra stimulation of the bone cells and an increased healing rate. This is Wolf’s Law. The bone adapting to load. A small, relatively weak bone can become larger and stronger in response to the appropriate load through the process of mechanotransduction.
Physical Therapy exercise will always be a staple in conservative treatment for the regeneration of injured tissues. Utilize a Physical Therapist to learn how to best manage your injury and how to utilize specific exercise parameters in get back to life and sports. There is a lot more going on beneath the skin and at the local tissue level to promote healing to that nagging ache and injury!
If you are currently dealing with a nagging injury come see us so we can prescribe the right exercise and right dosage to see mechanotransduction in action! Your body is amazing and with our collaboration we can help achieve your goals and get your life and activity back!
Just fill out the form below and an expert doctor of physical therapy will contact you!
Khan and Scott. (2009) “Mechanotherapy: how physical therapists’ prescription of exercise promotes tissue repair.”
British Journal of Sports Medicine. 2009; 43: 247-251. Web. 5 Dec. 2013.
Thompson WR, Scott A, Loghmani MT, Ward SR, Warden SJ. Understanding Mechanobiology: Physical Therapists as a Force in Mechanotherapy and Musculoskeletal Regenerative Rehabilitation. Phys Ther. 2016;96(4):560-569. doi:10.2522/ptj.20150224