Dr. Mitch Broser
Have you ever “pulled” a muscle? Often, I hear people pulling hamstrings, groins, backs and more. But what is a “pulled” muscle? What happens when you “pull” something? What is the best way to recover from a muscle “pull”?
Let’s review some basics first. With regards to the musculoskeletal system, there are 2 basics types a of tissues we will consider: muscle and connective tissue (aka fascia). Muscles and connective tissues physically work together to move bones relative to one another. The muscles, under the control of the nervous system, contract to pull and produce force, which produces human movement. Connective tissue does not actively contract, but it allows for force to be transmitted across larger areas, maximizing cumulative force produced from multiple muscles. This muscle-connective tissue relationship is seen at multiple scales (Fig. 1). Multiple muscles are wrapped together with connective tissue, like the quadriceps muscles (the group of muscles on the front of the thigh). An individual muscle belly is held together by a connective tissue layer call the perimysium. The muscle belly is made up a bunch of muscle fascicles, each bound together by connective tissue called perimysium. Finally, the fascicle is made up of a group of muscle fibers, each wrapped with endomysium, which is, you guessed it, connective tissue.
In some muscle bellies, less than 20% of the muscle fibers expand the entire distance between beginning and end of a muscle, while the remains +80% of muscle fibers are connected only by the endomysium. Connective tissue has a large force-transmitting/absorbing role, even within muscle bellies. However, connective tissue does not have the ability to quickly and actively react to high external forces (Wilke, 2019). When you load a muscle beyond its capacity quickly, the connective tissue is much more like to give before the actual muscle tissue.
In acute muscle injuries, tears isolated to muscle tissue are only found in 1/8 cases. Tears are much more commonly found in the connective tissues or at the junction between muscle and connective tissue, ie. the myotendinous junction (Wilke 2019). These tears can happen on a larger scale (epimysium) or smaller scale (endomysium). Wilke claims a better name for these injuries would be “myocollagenous strain injuries”, or injuries of the connective tissue.
The connective tissue exhibits a higher pain sensitivity than muscle, which could explain potential delays in return to play for athletes with connective tissue tears. DOMS (Delayed Onset Muscle Soreness, or that next-day workout soreness) seems to be from connective tissue rather than from the muscle itself. The “micro-tearing” you get from your strength training is happening in the connective tissue! DOMS is also associated with changes in neural drive. An altered afferent neurological feedback from connective tissue can contribute to reduced neural drive, limiting how hard you can contract a muscle. (Wilke, 2019).
Following acute injury to connective tissue, the immune response aims to phagocytose (eat and get rid of) injured cells and sensitize pain receptors. This comes with acute inflammation, which is typically short-lived and reversible. However, with prolonged/repeated loading, persistent inflammation may develop, resulting in ongoing tissue damage and increased pain sensitivity. Fibrosis, the accumulation of poor collagen tissue, can occur, tethering structures and inducing chronic compression in the tissues. (Zugel et. Al. 2018)
Connective tissue can get injured by too much force, but the appropriate force can optimize tissue healing and train tissues to get stronger and stronger. Studies have been done to look at how soft tissue therapy (aka myofascial release) effects the healing of tissue. Coa and colleagues revealed that lower-magnitude and longer-duration myofascial release (sustained force) is associated with accelerated studies of tissue tear closure rates, while higher-magnitude and short duration myofascial release did nothing, or further progressed the tearing. (Cao et al.).
When you pull a muscle, you have to determine the tissue that has actually be affected. Muscle and connective tissue are 2 very different types of tissue and damage to each should be addressed differently. In acute muscle strains, connective tissue is most commonly the damaged tissue. When not taken care of properly, fibrosis can collect, effecting the integrity of the connective tissue and your sensitivity to pain. In tissue healing, connective tissue responds to low levels of load over longer periods of time. In treatment and rehab, we have to be patient and be consistent.
References:
- Cao TV., Hicks MR., Zein-Hammoud M. & Standley PR. Duration and magnitudes of myofascial release in 3-dimensional bioengineered tendons: effect on wound healing. The Journal of the American Osteopathic Association, v.11 n.2. 2015.
- Wilke J., Hespanhol L. & Behrens M. Is it all about the fascia? A systematic review and meta-analysis of thee prevalence of extramuscular connective tissue lesions in muscle strain. The Ortho J of Sports Medicine. 2019.
- Zugel, et al. Fascia tissue research in sport medicine: from molecules to tissue adaptation, injury and diagnostic consensus statement. British Journal of Sports Medicine. 2018.