After straining, spraining, or partially tearing a ligament, athletes often spend varying periods of time with the affected limb essentially 'unloaded', ie, in non-weight-bearing positions. This is understandable, since there is a concern that weight-bearing activity might increase inflammation, retard healing, or even further damage the unfortunate ligament, but sports-medicine experts have not been sure that such unloading strategies are totally optimal for healing. In fact, many sports-medicine therapists and doctors insist that 'loading' a recently hobbled ligament in a reasonable way, even after fairly severe ligamentous damage, actually enhances the healing process, forcing ligaments to recover in a manner which is best for strength, stability, and â€“ ultimately â€“ performance.
Which approach is correct? In an attempt to understand the differing effects of loading or unloading a ligament following injury, exercise scientists at the University of Wisconsin, the University of Houston, and the National Aeronautics and Space Administration-Ames Research Center in California recently surgically cut the medial collateral ligaments (MCLs) in the knees of laboratory rats. Three or seven weeks after the incisions, mechanical and morphological properties were measured in ligaments, muscles, and bones of weight-bearing and non-weight-bearing rats and were compared with the same properties in sham-operated rats ('Hindlimb Unloading Alters Ligament Healing', Journal of Applied Physiology, Vol. 94(1), pp. 314-324, 2003).
As it turned out, the ligament testing revealed that there were significant reductions in maximal force, stress tolerance, and elastic properties in the ligaments of animals which had their hind limbs suspended following the surgery to avoid weight-bearing activity. Strikingly, mineral density of the femur (the upper leg bone), femoral strength, calf-muscle mass, and the mass of the tibialis-anterior muscle group were all downplayed in the 'unloaded group'. In addition, collagen fibres in the MCLs of the surgery-treated, unloaded animals were misaligned (collagen is a protein, and collagen fibres form the main structural and supportive network of ligaments and tendons; if the fibres are not aligned properly, ligament strength is compromised).
As a result, the researchers concluded that 'stress levels from ambulation' (ie, from weight-bearing activity) are necessary to form structurally competent, continuous, collagen fibres in ligaments which are engaged in healing following an injury. The Wisconsin-Texas-California researchers noted that the results support their contention that leg unloading following injury or surgery actually impairs the healing of fibrous connective tissue. Naturally, one does not want to place so much force on a damaged ligament that healing is harmed, nor does one want to induce further damage by placing inappropriate forces on a ligamentous structure. However, judicious weight-bearing activity appears to be beneficial for even fairly traumatic injuries to ligaments; such exercise stimulates a process by which the collagen in ligaments forms structurally competent, continuous fibres which have the greatest possible strength and resistance to injury.