We have all had patients present to us describing that some muscle “just feels tight.” Often a perplexing finding on these patients is the lack of correlation to this sensation of being “tight” and loss of motion. Some patients who show no perception of tightness show large losses of range of motion while some individuals who feel tight show normal range. What is going on here? It may very well be a protective neural mechanism creating a sense of tightness to constrain a perceived threat during dynamic activity. One of these threats to the CNS may occur when a muscle is impaired in production of muscular force at greater muscle lengths. Notably, these individuals have terrible abilities to eccentrically lengthen their muscle to the same degree to which you can stretch them passively (perhaps relating to gamma motor neuron activity.. a thought for another day.) So let me give the example of the patient who presents with a sense of “tight” hamstrings. These individuals never seem to be able to appropriately hip hinge to the same degree of hip flexion as you can passively take them in the analogous position of a supine hamstring stretch. What I believe could be occurring in these individuals is that the perceived “tightness” is actually protective stiffness created from a subconscious response to perceived threat. This threat may arise as a shift away from the optimal actin-myosin overlap represented in the plateau section of the length tension relationship (see image below.) As you move further right on the graph there is less available distance to elongate before potential fibril damage may occur…an understandable “threat.”
What is required in these individuals is a shift of the plateau of the length tension relationship towards greater muscle elongation. To do this there are two practical tools available: stretching and eccentric exercise. Stretching has gotten a bad rap lately. Acutely, stretching improves range of motion but typically for only a very short period of time (<60 minutes) with the most likely mechanism simply an increase in tolerance to stretch rather than any biomechanical effects(See study.) Furthermore, stretching has come under scrutiny due to extensive literature demonstrating no improvement in injury rates and a decrease in muscle performance following stretching. However, a recent literature review by Behm, Blazevich, Kay, and McHugh (See study) found that while static and PNF stretching did result in small (-3.7 to -4.4%) change in muscle performance this change is both dose dependent and able to be avoided. Stretches held less than 60 seconds resulted in only a 1.1% decrease in performance with greater than 60 seconds resulting in a 4.6% decrease. Additionally, performance decrease only occurs if the muscle is tested immediately after stretching with deficits in muscle performance effectively ameliorated with dynamic activity before exercise. Chronically, stretching programs can cause lasting improvement in range of motion(See study) likely, in part, from the serial addition of sarcomeres, termed sarcomerogenesis, observed in several animal studies(See study, See study.)
So despite lackluster effects with acute bouts of stretching, stretching programs do appear to have a place in rehabilitation, though eccentric exercise may prove more beneficial in improving range of motion through sarcomerogenesis. A 2012 review by Kieran O’Sullivan (See study) demonstrated that eccentric exercise programs are effective at increasing both range of motion and serial addition of sarcomeres. Eccentric training allows muscular adaptation which can decrease injury risk and improve force production at greater degrees of muscle elongation (See study, See study.) I always attempt to modulate threat perception using active muscle contraction at various joint ranges which is, in my opinion, why PNF techniques work so nicely at improving motion. So while eccentric and stretching programs may both produce improvements in muscle length and flexibility (See study), it would make sense that eccentric exercise should be included with its ability to directly promote the ability to generate eccentric force at greater muscle length and for possible threat inoculation. Keep in mind this is about one factor that may contribute to threat, there are a multitude of others including constraining movement at a nearby body segment that are certainly as or more plausible. In any case, if you don’t utilize eccentric training for range of motion improvement, for that, you should consider incorporating it into your repertoire.