Accelerating Skeletal Muscle Injury Regeneration

Man holds a leg in a cast

Muscle injuries are common in athletics, but there are steps to take to enhance recovery. Rest, ice, compression and elevation followed by specific muscle regeneration training have been shown to aid in muscle injury recovery. In addition, a study highlighting a novel biochemical means of speeding regeneration.

Muscle damage injuries are prevalent in athletes and, after strains, are the second leading cause of sports-related injuries (Muscle contusion injuries: current treatment options, 2001.  Beiner JM, Jokl P). A significant blow to muscle tissue can damage the muscle. Football players, by the nature of their sport, suffer a high frequency of muscle injuries. However, muscle damage is not limited to athletes because a severe impact will injure the muscle whether in the midst of competition or not. Nonetheless, a speedy regeneration of muscle tissue is likely of most consequence to the elite athlete.

Muscle injury symptoms include loss of muscle resistance and swelling at the injury site. It is important to understand how a muscle regenerates following injury. The diagram below illustrates the process of muscle healing. At day 2 following muscle injury macrophages remove broken muscle fibers while fibroblasts begin generation of connective scar tissue.  At day 3 satellite cells start regeneration of muscle tissue (a process that naturally occurs with muscle building as mentioned in a previous post on Exercise Medicine). By day 5 myoblasts have joined into tubes that will become active muscle fibers. On day 7 the myofibers begin protruding through the scar tissue formed by the fibroblasts. By day 14 the scar tissue is further reduced by regenerating myofibers. At day 21 days post-injury the connective scar tissue is nearly diminished by the fused muscle fibers.

muscle injury and regeneration

Although short-term treatment options for muscle injuries are well described in scientific literature, the sports medicine community has not agreed on a "one-size-fits-all" approach to long-term treatment (Muscle injuries: optimizing recovery, 2007. Tero Jarvinen, et al.). Although doctors used to prescribe muscle immobilization for muscle injuries, this is not common practice anymore due to the deleterious effects of continuous disuse. Instead, immobilization is recommended for the first 5 to 7 days following the injury.  Immobilization is succeeded by controlled use. Immediately following muscle injury, the protocol recommended is referred to as RICE: rest, ice, compression and elevation. Icing of the damaged area reduces inflammation. Elevation means keeping the damaged muscle above the heart to reduce blood pooling. The goal with all four treatments is to reduce the developing gap between damaged muscle tissue. This is accomplished by reducing interstitial fluid and bleeding at the internal injury site.

Three different muscle strengthening programs are recommended following initial recovery for controlled use of the muscle. The first training technique is isometric training and is to be commenced 3-7 days following muscle injury.  Isometric training is when tension increases but the muscle length remains constant. There is no joint movement. The load can be increased with muscle recovery. Once isometric training can be performed, pain-free isotonic training can be initiated. Isotonic training means the muscle length changes but the resistance on the muscle remains constant. The third training to be performed is isokinetic training, whereby the speed of the joint is constant. This is accomplished with special machines that vary resistance with the task.

An interesting study published last summer found that increased VEGF in the injured skeletal muscle of white rabbits improved muscle recovery (VEGF Improves Skeletal Muscle Regeneration After Acute Trauma and Reconstruction of the Limb in a Rabbit Model, 2012. Frey SP, et al.). VEGF, Vascular Endothelial Growth Factor, induces the proliferation of blood vessels or angiogenesis. The researchers treated rabbit limbs to ischemia (reduction of blood flow was accomplished with a tourniquet). Two interesting results came out of this study.  First, it was found that VEGF treatment accelerated the return of muscle force.  Second, VEGF treatment decreased resulting connecting tissue 40 days post-muscle damage. Recall that the connective tissue in this case is a form of scar tissue that is lost with muscle regeneration. The figure below shows the increase in muscle force in VEGF treated rabbits (top line) and rabbits not treated with VEGF (bottom line).

Muscles regenerate faster when treated with VEGF

However, as the authors note VEGF is expensive and human application cannot necessarily be extrapolated from rabbit models. In the meantime, if you are injured or treating someone injured the best bet is to follow the RICE plan followed by controlled strength training.

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