Overview of Tissue Healing Process
Healing is a complex process that can be defined as the process in which dead or injured tissue is replaced by living tissue that consists of the stages of the three broad stages of inflammation, fibroplasia or proliferation, and scar formation (A.T. Still University, 2017) The stages are not isolated incidents. Instead they overlap and happen simultaneously.
Before the healing process begins hemostasis, the process of which the body controls bleeding, occurs. In hemostasis, blood vessels vasoconstrict and begin forming blood clots composed of collagen, thrombin, and fibronectin, which act as a type of scaffolding to prevent pathogens from entering the cell, stimulates the release of cytokines and growth factors from the platelets, which initiates the inflammation process (Rand & Gelhorn, 2016) The Inflammation is the first stage of healing and happens hours after injury and can last for several months if the injury is mismanaged. The goal of inflammation is to eliminate any pathogens and remove damaged tissue components. It is the first response to injury and in it pathogens are destroyed and is vital to tissue repair. Pro-inflammatory molecules that are released increase vasodilation, permeability, and the migration of cells (Rand & Gelhorn, 2016). This decreases lymphatic drainage and forms the swelling associated with inflammation. Pathogens and dead cells are cleaned up from the site by neutrophils which digest collagen and break down the extracellular matrix (Rand & Gelhorn, 2016). As the number of neutrophils increase and new cells migrate to the tissue, inflammation begins to decrease, and leads to the beginning of the next phase. The goal of inflammation is to eliminate any pathogens and remove damaged tissue components, so tissue can be repaired (Schreml, Szeimies, Prantl, Landthaler, & Babilas, 2010)
Fibroplasia is a multi-stepped phase that begins about a week after initial injury. The goal of this phase is to repair injured tissue through forming a fibrous scar (A.T. Still University, 2017). Fibroplasia begins around the fourth day after injury. In this stage fibroblasts move to the injured area to begin synthesizing collagen type III fibers to serve as a temporary connective tissue replacement (Rand & Gelhorn, 2016). Type II collagen fibers are laid down at the same time which can be filled with new blood vessels. After the new collagen fibers are laid down, the wound begins to contract. The margins of the wound begin to shrink as myofibroblasts combine with the collagen fibers (A.T. Still University, 2017). After some time, scar tissue begins to form where less stable type III collagen fibers are replaced by stronger, more stable collagen type I fibers. Blood vessels are reabsorbed, and active fibroblasts disappear.
The last stage of healing is scar formation and maturation. The goal of this stage to repair the tissue to be as similar as before injury. (A.T. Still University, 2017). Scar formation and maturation begins around week three post injury and can continue up to a year. In this stage the extracellular matrix is strengthened, and collagen deposition is thickened and becomes more organized around the lines of stress in the tissue (Rand & Gelhorn, 2016). Scar maturation can take up to a year but the strength of the tissue, the force it can generate, and the force the tissue can withstand, will never be as strong as uninjured tissue.
It is important to know the stages of healing for fitness practitioners to train around an injury. Most post rehabilitative training takes place in the scar formation and maturation stage. It is best for fitness professionals to view an injury as neuromuscular dysfunction as more restrictive protocols negatively impacts normal movement patterns by inhibiting the neuromuscular system (Joyce & Lewindon, 2016). It is more important to focus on what the client can do instead of what they cannot do as coordinated movement patterns and muscular control as this protects the joints from further injury. For example, an ACL deficient client may not be able to squat with a large load a couple months post injury, but they can perform the motion with the assistance of suspension trainer or in a pool. This allows the client to allow strengthen the ankle, knee, and hip musculature, while learning a fundamental movement pattern, and minimizing strain to the ACL. After an injury to a tissue it is forever weakened. The injured client is load compromised and the client’s tissue cannot take the same out of training stress or competition as it could previously (Joyce & Lewindon, 2016). If the client quits strength training, their neuromuscular system switches off its protective mechanisms, and increases chances of injury. Knowing the types of injured tissue is important. Injured tendons and ligament immature scar tissue has a random alignment of collagen fibers. Loading the tissue in controlled manner, along the lines of tension will help promote healing, by promoting parallel fiber alignment found in uninjured tissue (A.T. Still University, 2017).
A time-based approach to returning to competition is flawed. People heal at different rates based on the client’s age, vascularity, nutrition, adherence to rehabilitation protocols, gender, severity of injury, hormonal factors, and genetics (Hildebrand, Gallant-Behm, Kydd, & Hart, 2005). One person may take a long time to be functional post injury, while another person may be ready much sooner. Instead returning to play should be based on specific criteria based on their injury and goal. A criteria-based approach allows a client to achieve competency by increasing biomechanical demand and specificity (Joyce & Lewindon, 2016). For example, in ACL rehabilitation, Panariello, Stump, and Maddalone (2016) recommend a client only discharged once a client meets the criteria of having the strength, active and passive range of motion, and power of the injured leg be >90% of the healthy leg, while possessing the capabilities of their sport or tasks. In Panariello et al.’s (2016) plan the client progresses from flexibility, range of motion, and light strengthening, to building functional strength and power, and lastly to plyometric drills. This progression allows the client to protect their knee graft while building neuromuscular control and strength to return to their sport or activity. Testing and assessment should be done relatively frequently to asses which training interventions are needed for the client. A criteria-based approach is more sensible than a time-based approach in returning from an injury.
Athletes must be monitored once returning from injury. The athlete’s injured tissue is forever compromised and cannot take as much stress as before. The fitness professional should make sure the athlete has proper biomechanics when training. For example, the athlete with an ACL injury needs exercises that reduce frontal and transverse forces like stiff legged kettlebell swings, and single leg landing drills (Joyce & Lewindon, 2016). The fitness professional also needs to manage fatigue, as a fatigue reduces a muscles capacity to generate force, joint proprioception, and the athletes form. Injured tissue tends to experience fatigue more quickly. A coach can minimize fatigue with planned training variations and by focusing on the quality of movement and not number of reps. If the athlete is too fatigued to perform the exercise with quality form, they increase their chance of injury through improper distribution of forces. It is better for the athlete to perform two repetitions well, than twelve with poor form. In this case rest periods can be increased between sets, or load can be decreased. Lastly the athletes tissue tolerance should be increased though activities that meet the demands of their activity. To decrease reoccurrence of hamstring strains, a tennis player can perform single leg bridges which will increase the muscles ability to generate force, which will increase the hamstrings force tolerance (Joyce & Lewindon, 2016).
A.T. Still University. (2017, January 05). Soft tissue repair [Video file].
Hildebrand, K. A., Gallant-Behm, C. L., Kydd, A. S., & Hart, D. A. (2005). The basics of soft tissue healing and general factors that influence such healing. Sports Medicine and Arthroscopy Review, 13(3), 136-144.
Joyce, D., & Lewindon, D. (2016). Sports injury prevention and rehabilitation: Integrating medicine and science for performance solutions. Londres: Routledge.
Panariello, R. A., Stump, T. J., & Maddalone, D. (2016). Postoperative rehabilitation and return to play after anterior cruciate ligament reconstruction. Operative Techniques in Sports Medicine, 24(1), 35-44.
Rand, E., & Gelhorn, A. C. (2016). The healing cascade: Facilitating and optimizing the system. Regenerative Medicine, 27(4), 765-781.
Schreml, S., Szeimies, R., Prantl, L., Landthaler, M., & Babilas, P. (2010). Wound healing in the 21st century. Journal of the American Academy of Dermatology,63(5), 866-881.