Collagen:
Properties and Exercise Implications
Introduction to Collagen
Collagen is a vital structural protein present in bone, ligament, muscle, tendon, and skin.
The base collagen molecule is tropocollagen. Each tropocollagen is made up of three left-handed helices twisted into a right handed triple helix. These subunits self-assemble into collagen fibrils. Collagen fibrils are woven together to form a crimp pattern that allows for movement and recovery in an otherwise nonelastic tissue. Bundles of fibrils create collagen fibres.
During lengthening, collagen will absorb mechanical energy up to approximately 20% of its original length at which point rupture will occur.
Glycosaminoglycans (GAG’s) occupy the extracellular matrix and contribute to the structural integrity of cells, cell-cell communication, and lubrication in both the joints and soft tissues. GAG’s contribute to collagen’s viscoelastic properties which help it to absorb force, speed and compression.
Stimulus for Collagen Production
Modified tension is of utmost importance in the health and rehabilitation of collagen. Tension stimulates fibroblasts to produce collagen, GAG and hyaluronic acid. Tension to the collagen creates osmotic changes that draw nutrients in and transport wastes out. Tension is the stimulus that influences collagen fibre orientation. Repetitive loading leads to remodelling of the collagen matrix. Immobilization on the other hand causes atrophy and decreased elasticity.
Therapeutic Implications
Phases of healing: In the rest portion of the RICE protocol, modified tension will promote the optimal stimuli for repair, even on the day of injury. The concern of the clinician is to dose the therapeutic movement such that none of the new tropocollagen ionic bonds are broken. Rupture of collagen bonds will fire mechanoreceptors and cause pain. Pain therefore, is a good clinical guage to safe levels of tension. The therapist must also avoid metabolic overload of the healing tissues and leave enough energy in the system for protein synthesis and tissue repair after exercise. Early, painfree mobilization will prevent adhesions and scar tissue formation while promoting primary healing.
Therapeutic exercises will progress depending on the goal of the treatment. Concentric contractions are emphasized when the goal is to increase tissue vascularity. Isometrics are used when the goal is to apply stress while also promoting stability at a given range of motion. Eccentric exercises are prescribed to encourage collagen hypertrophy in conditions such as chronic tendinopathy.
Heat: Heat denatures collagen bonds as well as GAG’s. Tropocollagen bonding is dynamic to allow reformation after deformity. Excessive tension or excessive heating will open bonds between the tropocollagen molecules, allowing collagen to rupture with less tension. Heating collagen to 45 degrees causes rupture at 25% of the tension required when not exposed to temperature. When GAG’s are lost, collagen will also rupture under less tension. Elevation of body temperature through exercise will not heat collagen enough to lower its tensile strength. If we wish to break down collagen bonds then heat is appropriate. When formation of collagen bonds is the goal, then heat is not indicated.
References:
1. Grimsby O., Rivard J. Science, Theory and Clinical Application in Orthopaedic Manual Physical Therapy. Volume 1: Applied Science and Theory. Academy of Graduate Physical Therapy. Taylorsville 2008.
2. Kjaer M. et al. From mechanical loading to collagen synthesis, structural changes and function in human tendon. Scan J Med Sci Sports. 2009