How We Heal: Muscle Injuries

When muscles heal, they knit together with new connective tissue. This connective tissue is the dreaded scar tissue and is one of the main concerns when dealing with an injured muscle. The severity of the scar tissue depends on the immediate response to an injury and stewardship of the repair process, giving rise to a balancing act in which one goal is to maintain strength and restore function quickly and another is to minimize scar tissue.

How We Heal: Muscles

By: Nick Soleyn, PBC, Editor in Chief

There is a range of soft-tissue injuries that are not serious enough to require a doctor visit but are disruptive enough to daily life and training that we cannot ignore them. The distribution of these injuries clusters around tendinopathies and skeletal muscle injuries, and how we deal with them in the gym should change for each type of tissue involved. Last week, I wrote about how tendons heal and how the healing process underpins any rehab protocols. This article will talk about muscle injuries, the muscle repair process, and why certain treatments and protocols seem to work while others are dubious.

Muscle Injuries

There are three types of skeletal muscle injuries: contusions, strains, and lacerations. Lacerations are from external trauma, usually a crushing incident such as in a car accident or by cutting from a sharp object. These are the least common muscle injuries from daily-, sport-, or hobby-related activities and will usually require a visit to the doctor, making them also the least common type of injury that we deal with in the gym.

Contusions and strain make up around 90 percent of sports-related muscle injuries (Järvinen et al. 2005). A contusion is the result of an impact, compressive force on the muscle, causing a rupture at or near the site of impact. Contusions are common in combat sports and team sports where player-on-player contact is the norm (E.g., Hammami et al. 2018; Souza and Gottfried 2013). Strains come from a person’s own actions. Muscles are like ropes in that they apply force only by pulling. A strain occurs when the pull is either sudden and powerful enough or forceful enough to cause the muscle to tear, usually at a weak point in the structure (Järvinen et al. 2005). Strains are most common in big, multi-joint muscles at the distal meeting of muscle and tendon (the myotendinous junction or MTJ) (Souza and Gottfried 2013). So, some of the most common sports-related strains are in the rectus femoris of the quadriceps muscles, the semitendinosus of the hamstring muscle group, and the gastrocnemius of the calves (Järvinen et al. 2005).

Both muscles and tendons heal through a reparative process, which is distinct from a regenerative one. In a regenerative process, the healing tissue is identical to the surrounding, undamaged tissue. When bones heal, for example, they heal with new bone. In adults, when muscles and tendons heal, they knit together with new tissue. In muscles, the new tissue is more like the connective tissue that holds muscles together (the extracellular matrix) and less like the contractile portion of the muscle that was damaged. This connective tissue is the dreaded scar tissue and is one of the main concerns when dealing with an injured muscle. As a general rule, wider and denser scar tissue puts the person more at risk for future injuries. The severity of the scar tissue depends on the immediate response to an injury and stewardship of the repair process, giving rise to a balancing act in which one goal is to maintain strength and restore function quickly and another is to minimize scar tissue. The methods supporting each of these goals are in conflict at different times during the healing process.

That healing process, regardless of the underlying type of injury (laceration, strain, or contusion), happens in three phases: (1) the destruction and inflammatory phases, (2) the repair phase, and (3) the remodeling phase—with the repair and remodeling phases running mostly concurrently. The main distinguishing factor for the length and success of the repair process is the severity of the injury. Our focus is on relatively minor injuries that have not required a doctor visit or a referral to a medical professional.

The Destruction and Inflammation Phase (1­–3 Days)

The first phase of the repair process is marked by the rupture of portions of the contractile cells of the muscle, the formation of a hematoma, and the inflammatory cell response. We might think of this immediate response to injury as a kind of containment and cleaning action. Internal structures called contraction bands create a “system of fire doors,” preventing the spread of necrosis and keeping the damage local to the injury site (Järvinen et al. 2005). There is some evidence that delayed onset muscle soreness (DOMS), resulting from unfamiliar and high repetition eccentric movements, may lead to additional muscle protein degradation—hence the increased pain and inflammatory response (Hotfiel et al. 2018). Extreme DOMS can cause catastrophic muscle damage and may be accompanied by necrosis of the contraction band, leading to widespread cell death and possibly rhabdomyolysis (see, e.g., Câmara et al. 2019).

During this phase, the damaged muscle bleeds, which starts the formation of a hematoma and signals the inflammatory response that removes dead cells and starts the repair process. Much of the initial response to a muscle injury surrounds how we should deal with bleeding and pain, both of which may affect the healing timeline and the formation of scar tissue.

The Repair Phase (3­–4 Weeks)

During the repair phase, muscles will regenerate some of the damaged contractile tissues and form a connective tissue scar. Regeneration, as mentioned above, is the formation of new tissue of the same type as the original. Broadly, skeletal muscles have two components, myofibers (contractile tissue) and connective tissue, that “provides the framework that binds the individual muscle cells together during muscle contraction and embraces the capillaries and nerves within the muscle structure” (Järvinen et al. 2005). Myofibers do not themselves regenerate, but skeletal muscles contain a reserve of satellite cells that, in response to injury, grow and divide and then differentiate into myoblasts, which in turn give rise to new muscle cells (Baoge et al. 2012). “Eventually, the regenerating parts of the myofibers acquire their mature form with normal cross-striations and peripherally located myonuclei” (Järvinen et al. 2005). This limited regenerative capacity decreases as we get older.

At the same time as this regeneration starts, cells originating in the blood of the hematoma begin to form a connective tissue scar. This scar tissue acts like a “scaffolding,” giving the muscle strength to endure contractions, and it provides a connection site for invading cells called fibroblasts, which are connective tissue cells that will form the extracellular matrix (Id.). One concern with a healing muscle is the excessive proliferation of fibroblasts forming large and dense scar tissue. These pockets of scar tissue form new weak links within the muscle, which will later form new MTJs wherever scar tissue meets regenerated myofibers, leaving the person more prone to reinjury (especially muscle strains) adjacent to those MTJs in the future (Järvinen et al. 2005). Since the formation of scar tissue and the proliferation of fibroblasts is related to the amount of blood and the size of the hematoma, there is some motivation for treating bleeding as a first response to a muscle injury.

The Remodeling Phase (3–6 Months)

The remodeling phase is where a muscle completes its functional recovery. The regenerated muscle fibers mature, and the scar tissue contracts. It can take a while for the muscle to return to full strength, a time shortened by movement and exercise early in the healing process.

Common Treatments

The focus here has been on muscle injuries that are not severe enough to require a visit to the doctor or the ER but significant enough that they will affect a person’s daily function and training. These are the vast majority of muscle injuries that coaches and lifters encounter. Hopefully, this brief and superficial review of the muscle repair process helps highlight the issues that underly these muscle injuries: we want them to heal, of course, but we want them to heal as quickly as possible, with minimal loss of strength, and with minimal scar tissue. Here are some of the common treatments for muscle injuries and how they fit into this balancing act.

RICE (Rest, Ice, Compression, and Elevation)

As an immediate treatment, the RICE protocol has been the standard since the 1950s. Each component of the protocol limits bleeding at the injury site. That the RICE components limit bleeding is both rationale and justification for the protocol, since RICE has little direct data supporting it. Instead, each component has shown a tangential or theoretical value relating to the repair process outlined above:

(Rest) By limiting movement, resting the injured area can prevent the initial gap at the rupture site from growing, reducing the size of the hematoma. The closest proof of the efficacy of rest comes from studies on complete immobilization of injured muscles, which have shown similar benefits up to a point (Järvinen et al. 2005). (Ice) Similarly, studies have shown that early use of cryotherapy has also been associated with a smaller hematoma, supporting the use of ice as an immediate treatment. (Compression) Evidence for the benefits of compression has been less robust, but with ice and compression (applied for 15–20 minutes and repeated at intervals of 30–60 minutes), intramuscular blood flow should decrease, leading to a reduction of bleeding at the injury site. (Elevation) Similarly, elevation as a treatment is based on how the body works, “the elevation of an injured extremity above the level of the heart results in a decrease in hydrostatic pressure and, subsequently, reduces the accumulation of interstitial fluid” (Järvinen et al. 2005). All that said, RICE is still a standard treatment, and as long as the components are used in moderation (particularly rest and ice), they should help reduce bleeding and may improve outcomes with the formation of less scar tissue.

NSAIDs

Here, I will only point out what NSAIDs are used for and some challenges to their traditional use. NSAIDs are used to reduce pain and for their anti-inflammatory effects. Because inflammatory cells are important to the repair process, there is some thought that NSAIDs may negatively affect healing. Evidence of either benefits or harm to the repair process has been conflicting (Rahusen, Weinhold, and Almekinders 2004). Also, apart from their effect on inflammation, NSAIDs have potential pros and cons:

“NSAIDs would not have a greater effect on the pain of a muscle injury than paracetamol, but they have more side effects including asthma exacerbations, gastrointestinal and renal side effects, hypertension, and other. However, NSAIDs also have beneficial effects. The inflammatory process can be excessive and cause edema, resulting in anoxia and further cell death. This can be prevented by the administration of low-dose NSAIDs.” (Baoge et al. 2012)

One study says that NSAID use should be restricted to 48 hours after the initial injury (Rahusen, Weinhold, and Almekinders 2004). Others, however, argue for short-term use, at least in minor injuries (Järvinen et al. 2007):

“Despite the lack of direct human evidence, the effects of NSAIDs have been quite well documented experimentally. A short-term use of different NSAIDs in the early phase of healing has been shown to lead to a decrease in the inflammatory cell reaction with no adverse effects on the healing process or on the tensile strength or ability of the injured muscle to contract. Furthermore, the NSAIDs do not delay myofiber regeneration. However, it seems that the use of NSAIDs should be restricted to the early phases of muscle repair as their long-term use might have undesired effects on the regenerating skeletal muscle, although these detrimental effects were not reported in the most thorough experimental study.”

NSAIDs continue to be standard practice for athletic injuries and are used widely (see, e.g., Qazi et al. 2019).

Immobilization vs. Early Mobilization

There is an idea that early mobilization (i.e., “walking it off”) will prevent functional loss and preserve muscle strength. However, with any muscle injury, there is a risk of an additional rupture caused by too-early mobilization. In our discussion above, we talked about the “fire door” system that helps keep the damage local to the initial injury site. That containment needs to happen without interruption to reduce the risk of a larger connective tissue scar due to increased bleeding. Accordingly, the common recommendation is immediate and short-term immobilization following a muscle injury. Immobilization should be limited to a few days during the destruction and early repair phase, allowing bleeding to stop and the connective tissue scar to provide strength to the muscle without risking additional damage.

Progressive Resistance

Pain is the guide in the most common treatment recommendations. Generally, these will recommend progressing from isometric holds to full range of motion movements to resistance training. Each stage is performed until there is no pain, and then the person moves on to either more movement or more resistance until the muscle has returned to full strength.

How Strength Training Fits into the Picture

As barbell enthusiasts, it is common for us to look to barbell training as an answer to just about every ailment the human body can suffer, and that isn’t without some good reasoning. Barbell training gets us moving, uses regular movement patterns, is great exercise, and of course, it builds muscle and bones and even improves functions of most of the tissues of the body. So, when we suffer a muscle injury, it is almost natural to look at strength training for rehab.

One of the most popular treatment protocols is the Starr rehab method, outlined by Matt Reynolds in this article and named for the legendary strength coach Bill Starr. It goes something like the following:

  1. Wait three to four days until the pain starts to decrease.
  2. Lift, using a movement for which the injured muscle is a prime mover. Start by performing at light weights for high reps.
    • An injured hamstring, for example, might have the lifter performing three sets of 25 reps of the deadlift with just an empty bar, using perfect form.
    • If the lifter cannot maintain perfect form, they need to back off and let the healing process progress before starting the protocol.
  3. Repeat the light weight and sets of 15-25 reps every day for about ten days.
  4. Add weight and decrease reps until back to previous working weights in the five-rep range.

The Starr protocol should be the main work for that muscle, and the lifter should limit other heavy lifting during their rehab.

Note that the Starr protocol fits nicely into the repair process. The injury gets three to four days to stop bleeding and begin the repair process. Following common recommendations, this short period should be marked by rest and/or immobilization of the site, and the lifter may want to treat the injury with the RICE protocol during these few days.

There is a big difference between the Starr Protocol and common clinical treatments, however, and that is pain. The Starr protocol is intentionally uncomfortable and will likely hurt. Also, while loading should be done very gradually and patience is an absolute requisite to the protocol, loading is not based on an absence of pain. A good tell on whether loading is appropriate for this protocol is whether the lifter can lift with perfect form or whether pain or dysfunction causes them to move awkwardly. In the latter case, it’s important to hold back or slow down progress.

Note that the Starr protocol is not the be-all and end-all of soft tissue rehab. It would be a mistake to perform the Starr protocol on an injured tendon or other connective tissue. Rather, the Starr protocol is a good example of using progressive resistance training to help speed healing, prevent atrophy, and reduce scar tissue (when timed correctly), but the timeline and the process for other connective tissue injuries will be different. Treat muscles like muscles, tendons like tendons, and use the repair processes to help inform decisions on how training can fit into the overall rehab picture.


References

Baoge, L., E. Van Den Steen, S. Rimbaut, N. Philips, E. Witvrouw, K. F. Almqvist, G. Vanderstraeten, and L. C. Vanden Bossche. 2012. “Treatment of Skeletal Muscle Injury: A Review.” ISRN Orthopedics 2012 (April): 1–7. https://doi.org/10.5402/2012/689012.

Câmara, Nakita, Eva Sierra, Antonio Fernández, Cristian Manuel Suárez-Santana, Raquel Puig-Lozano, Manuel Arbelo, and Pedro Herráez. 2019. “Skeletal and Cardiac Rhabdomyolysis in a Live-Stranded Neonatal Bryde’s Whale With Fetal Distress.” Frontiers in Veterinary Science 6 (December): 476. https://doi.org/10.3389/fvets.2019.00476.

Hammami, N., S. Hattabi, A. Salhi, T. Rezgui, M. Oueslati, and A. Bouassida. 2018. “Combat Sport Injuries Profile: A Review.” Science & Sports 33 (2): 73–79. https://doi.org/10.1016/j.scispo.2017.04.014.

Hotfiel, Thilo, Jürgen Freiwald, Matthias Hoppe, Christoph Lutter, Raimund Forst, Casper Grim, Wilhelm Bloch, Moritz Hüttel, and Rafael Heiss. 2018. “Advances in Delayed-Onset Muscle Soreness (DOMS): Part I: Pathogenesis and Diagnostics.” Sportverletzung · Sportschaden 32 (04): 243–50. https://doi.org/10.1055/a-0753-1884.

Järvinen, Tero A. H., Teppo L. N. Järvinen, Minna Kääriäinen, Hannu Kalimo, and Markku Järvinen. 2005. “Muscle Injuries: Biology and Treatment.” The American Journal of Sports Medicine 33 (5): 745–64. https://doi.org/10.1177/0363546505274714.

Järvinen, Tero A.H., Teppo L.N. Järvinen, Minna Kääriäinen, Ville Äärimaa, Samuli Vaittinen, Hannu Kalimo, and Markku Järvinen. 2007. “Muscle Injuries: Optimising Recovery.” Best Practice & Research Clinical Rheumatology 21 (2): 317–31. https://doi.org/10.1016/j.berh.2006.12.004.

Qazi, Taimoor H., Georg N. Duda, Melanie J. Ort, Carsten Perka, Sven Geissler, and Tobias Winkler. 2019. “Cell Therapy to Improve Regeneration of Skeletal Muscle Injuries.” Journal of Cachexia, Sarcopenia and Muscle 10 (3): 501–16. https://doi.org/10.1002/jcsm.12416.

Rahusen, Frank T. G., Paul S. Weinhold, and Louis C. Almekinders. 2004. “Nonsteroidal Anti-Inflammatory Drugs and Acetaminophen in the Treatment of an Acute Muscle Injury.” The American Journal of Sports Medicine 32 (8): 1856–59. https://doi.org/10.1177/0363546504266069.

Souza, Jaqueline de, and Carmem Gottfried. 2013. “Muscle Injury: Review of Experimental Models.” Journal of Electromyography and Kinesiology 23 (6): 1253–60. https://doi.org/10.1016/j.jelekin.2013.07.009.

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