Tissue Healing

The following is an exclusive excerpt from the book Essentials of Strength Training and Conditioning-4th Edition with Web Resource, published by Human Kinetics. All text and images provided by Human Kinetics.

The process of returning to competition following injury involves the healing of the injured tissues and the preparation of these tissues for the return to function. To better understand the role of the strength and conditioning professional during rehabilitation and reconditioning, it is necessary to review the general phases of tissue healing following musculoskeletal injury (22, 24). The timing of the events occurring within each phase of tissue healing differs for each tissue type and is affected by a variety of systemic and local factors, including age, lifestyle, degree of injury, and the structure that has been damaged. However, all tissues follow the same basic pattern of healing (table 22.1).

>> The process of returning to competition following injury involves healing of the injured tissues, preparation of these tissues for the return to function, and use of proper techniques to maximize rehabilitation and reconditioning.

Inflammatory Response Phase

Inflammation is the initial reaction to injury (22, 24) and is necessary in order for normal tissue healing to occur. Both local and systemic inflammation occur during the inflammatory response phase, allowing the eventual healing and replacement of damaged tissue. During the inflammatory phase, several events transpire that contribute to both tissue healing and an initial decrease in function. The injured area becomes red and swollen due to changes in vascularity, blood flow, and capillary permeability. After tissues are damaged, a locally hypoxic environment leads to a certain amount of tissue death that allows the release of several chemical mediators, including histamine and bradykinin. These substances further increase blood flow and capillary permeability in this local area, thereby allowing edema, the escape of fluid into the surrounding tissues. Edema inhibits contractile tissues and can significantly limit function. Tissue debris and pathogens are removed from the injured area by increased blood flow and a process called phagocytosis; phagocytosis allows the release of macrophages, which search for and remove cellular debris that may slow healing.

The inflammatory substances present during this phase may result in stimulation of pain fibers, causing the injured athlete to sense pain, further contributing to decreased function. This phase typically lasts two to three days following an acute injury but may last longer with a compromised blood supply and more severe structural damage. Though the inflammatory phase is critical to tissue healing, if it does not end within a reasonable amount of time, the phases that follow may not occur, thereby delaying the rehabilitation process. Typically this phase lasts less than one week.

Fibroblastic Repair Phase

Once the inflammatory phase has ended, tissue repair begins (22, 24); the fibroblastic repair phase is characterized by catabolism (tissue breakdown) and replacement of tissues that are no longer viable following injury. In an attempt to improve tissue integrity, new capillaries and connective tissue (scar tissue) form in the area. Type III collagen is randomly deposited along the injured structure and serves as the framework for tissue regeneration. This newly formed tissue is weaker than the original tissue; thus optimal strength of the new tissue is not yet achieved. Collagen fibers are strongest when they lie longitudinally to the primary line of stress, yet many of the new fibers are positioned transversely, which limits their ability to efficiently transmit force. This phase of tissue healing begins as early as two days after injury and may last up to two months.

Maturation–Remodeling Phase

The weakened tissue produced during the repair phase is strengthened during the maturation–remodeling phase of healing (22, 24). Production of collagen fibers has shifted to a stronger Type I collagen, allowing the newly formed tissue the opportunity to improve its structure, strength, and function. With increased loading, the collagen fibers of the newly formed scar tissue begin to hypertrophy and align themselves along the lines of stress (18). The thicker and more optimally aligned collagen fibers become stronger, allowing a return to function. Although strength of the collagen fibers and healing tissue improves, this tissue is not as strong as the tissue it has replaced. Tissue remodeling in the maturation–remodeling phase can last months to years after injury (22, 24, 32).

>> Following injury, all damaged tissues go through the same general phases of healing: inflammation, repair, and remodeling. The timing of the events occurring within each phase of tissue healing differs for each tissue type and is affected by a variety of systemic and local factors, including age, lifestyle, degree of injury, and the structure that has been damaged. Characteristic events define each phase and separate one phase from another.

Developed by the National Strength and Conditioning Association (NSCA), Essentials of Strength Training and Conditioning-4th Edition with Web Resource, is the fundamental preparation text for the Certified Strength and Conditioning Specialist^® (CSCS^®) exam as well as a definitive reference that strength and conditioning professionals will consult in everyday practice. The book is available in bookstores everywhere, as well as online at the NSCA Store.