An Intro to Tissue Healing & Adaptation

Understanding the physiological process of our tissues and how they heal is essential for determining an appropriate exercise program for individuals.  These programs can govern effective treatments for the affected tissues.  Unfortunately, providing an accurate and comprehensive bout of information would require writing a whole book.  To save time and address the important points of the overall tissue healing and adaptions, here are a few points to consider when deciding which exercises to perform:    

Average rate of tissue healing

Healing time varies from person to person and is dependent upon factors such as nutrition, age and mobility level. In general 50% of healing takes place in the first 2 weeks, 80% of healing occurs in the first 6 weeks and 100% of healing should occur within 12 weeks. To be more specific:

  • Muscles heal within 2-4 weeks
  • Tendons heal within 4-6 weeks
  • Bone heals within 6-8 weeks
  • Ligaments heal within 10-12 weeks
  • Cartilage can take up to 12 weeks to heal
  • Nerve grows back about 3-4mm per day.

These are just the general time frames to consider with obvious exceptions towards injuries that are more severe (e.g. stress fracture vs. a comminuted fracture). With those time frames in mind, it’s important to also understand the 3 phases that tissues undergo during the healing process.

3 Phases of Tissue Injury and Repair

  • Inflammatory Phase

    • Period that occurs during and/or after bleeding has stopped. Depending on the severity of the injury, it can last from 1 to several days. Fibroblasts are sent toward the injured area, capillary permeability increases causing edema in the tissue, and WBC permeate the area
  • Proliferation Phase

    • Since the fibroblasts are activated, the healing process has taken place. This phase typically occurs 4-5 days post-injury though can take up to 21 days. Granulation tissue can be formed with the combination of capillaries and fibroblasts invading the wound of an ulcer-like injury. New collagen fibers are starting to form along with weak scar tissue.
  • Remodeling Phase

    • This phase can take several months to more than a year. Collagen fibers are still being synthesized and the scar tissue strength is slowly adapting towards the demands placed on the tissue.

With that in mind, how are the tissues completely healed when the remodeling phase can take several months to more than a year? Like all great answers in physical therapy, it depends. As stated above, depending on the depth of injury can determine the length of time for tissues to completely heal. It’s up to the discretion of the medical professional (e.g. Physician, Physical Therapist, Occupational Therapist, etc.) to decide an appropriate time frame for placing certain stresses on those tissues. This leads us towards how the tissue adapts towards those stresses.

General adaptation syndrome

  • Alarm Phase

    • The alarm phase occurs when the body experiences a new stimulus. This sends a “shock” to the system causing the body to make adaptations towards the stimulus. Without this adaptation, improvements will not occur. During this phase, increased levels of soreness and stiffness are present. As the body adapts and begins to recover, it shifts over towards the resistance phase.
  • Resistance Phase

    • During this phase, the body has made physiological changes whereas the initial “shock” experienced during the alarm phase no longer causes negative responses towards the body.  The body has developed a “resistance”, as you will, towards the demands placed on it causing improvements to occur.  During this stage, a brief rebound effect will occur where performance actually improves. This is called the Supercompensation phase.  This is the true phase at which an individual should strive for during a workout program.  It can difficult to achieve and maintain this stage because of its brief activation. Resting too long will resort back to previous levels, and not resting enough can lead towards the exhaustion phase.
  • Exhaustion Phase

    • This final phase of stress is one to avoid whenever possible. This occurs when the stress levels become overbearing on the body causing a deterioration of improvements. Indicators of being in this stage include feelings of constant fatigue, soreness, plateauing, or being burnt out.  Other factors can play a role as well such as poor nutrition, exercising too much or too intensely, and even daily stressors.

Take Home Message

There are a wide variety of concepts that could have been discussed such as the stress-strain curve, nutritional guidelines that influence proper healing, scar tissue production, the SAIDs principle, the fundamental principles of the Physical Stress Theory, and many others. The purpose of this post is to provide the fundamental background of when healing takes place within different tissues and the process of how they adapt.  Keeping those concepts in mind will help determine an appropriate treatment plan and understanding protocols provided by physicians during a post-operative procedure. For ideas on developing an appropriate exercise plan, check out Phil’s post on Integrating Strength and Conditioning Principles in Physical Therapy. 

Thanks for taking the time to read!