Stretching may actually be a way to trick the brain into thinking that muscles are getting longer. Physiotherapists C. H. Weppler from Niederjosbach, Germany and S.P. Magnusson from the University of Denmark wrote an article that was published in Physical Therapy in 2010 that highlights the current theories explaining the properties of stretching and its effects upon muscles and joints. However, most of these theories are mechanical in nature with little or no consideration for neural and psychological factors that can cause the stretching sensation. These mechanical theories include viscoelastic deformation, increased sarcomeres in muscle fibers during a stretch, and neuromuscular relaxation. Although these theories are still taught to medical and fitness professionals, they have their limitations in explaining the underlying causes and effects of stretching.
For example, viscoelastic deformation refers to the elastic and water-like properties of muscles and how they can change with contraction. Even though static stretching increases range of motion in muscles and joints, the effects are transient and minimal. The muscle and joints eventually return to their original length and range of motion. “In one hamstring muscle study, a static stretch of 45 seconds duration was found to have no significant effect on the next stretch performed 30 seconds later,” Weppler and Magnusson wrote.
Weppler and Magnusson suggest that the sensory theory, which was first developed in the early 1990s by several researchers, can provide a more complete explanation of what is going on in the body during a stretch. In these early studies, the researchers did not observe a change in muscle length after stretching; rather, the only change observed was the increase of end-range joint angles and applied torque. “Because the end-point of these stretches was subject sensation, the only observable explanation for these results was that subject’s perception of the selected sensation occurred later in stretch application,” Weppler and Magnusson wrote. Thus, an “alteration of sensation,” not increase in muscle length, provided the increases in muscle extensibility. The authors pointed out that psychology could also play a factor in how experimental subjects perceive their flexibility. Their expectations of increased extensibility from stretching made them tolerate greater torque application and change their perception during the stretch. These findings only pertain to short-term stretching programs that are about three to eight weeks long. To date, no long-term stretching studies and findings have been reported.
Mainstream explanations and applications to improving flexibility are based mostly on the biomechanical or structural model, which does not make up a complete picture of how stretching tricks the brain to think that muscles and connective tissues are getting longer and joints have greater range of motion. The nervous system is ultimately the puppet master that controls muscle contraction, stiffness or painful sensations, and how tissues react to environmental stimuli. Licensed massage therapist Todd Hargrove, author of “Better Movement” and practices in Seattle, Washington, stated that if a muscle is given a general anesthetic, which knocks out the nervous system, then the muscle would feel no pain and can be stretched further than when the nervous system is on. He also mentioned that the nervous system protects the body from tissue damage, and stretching a muscle or joint too far will cause it to stiffen more. This can be counter-productive for people who think stretching can improve flexibility or performance.
In fact, a 2012 systematic review that examined 25 studies on the effectiveness of stretching on contractures may support Weppler, Magnusson, and Hargrove’s position. The study, which was published in Physical Therapy and conducted by Australian physiotherapists Owen M. Katalinic, Lisa A. Harvey, and Robert D. Herbert, revealed that stretching does not “produce clinically important changes” in pain, joint mobility, and other disorders in patients with neurological conditions, such as cerebral palsy, stroke, or spinal cord injury. Like Weppler and Magnusson’s study, researchers also found that the stretching effects had very little benefit to improve joint mobility since there were “little or no short-term or long-term effects of stretch.” The effects of the stretch is transient in which the tissues resume their normal state prior to the stretch in minutes.
“These results challenge long-held beliefs about contracture management and stretch,” Katalinic and colleagues wrote. Typical stretching that therapists do upon their patients may not be enough to elicit a change in tissue state. They added that people without neurological problems also had similar results from stretching. Based on the current evidence, perhaps it is really the brain and the rest of the nervous system that are playing tricks to make the muscles feel “stretched.”
By Nick Ng