There are many assumptions made about changes in muscle length, from calf muscles lengthening from practicing Downward Facing Dog to hamstrings and hip flexors shortening with prolonged sitting. While traditionally, literature has attributed increases in muscle extensibility observed after stretching to a mechanical increase in muscle length, a review by Weppler and Magnusson (2010) reports that a growing body of research refutes these mechanical theories, suggesting instead that the increases in muscle extensibility observed are predominantly due to modification in subjects’ sensation (often referred to as ‘stretch tolerance’). Findings from this review also suggest that muscles labeled as ‘shortened’ are lacking in extensibility rather than being short in terms of physical structure. A study by Krabak et al (2001) examined the passive ROM in patients before, during and after anesthesia and found that this increased significantly during anesthesia. This not only implicates nervous system contributions to muscle extensibility but also refutes the concept of ‘shortened’ muscle tissue.

There also tends to be a lot of assumptions made about muscle tightness. Tightness is a very vague term that means different things to different people. When someone talks about muscle tightness, they could be referring to a lack of extensibility of a muscle and the associated decreased range of movement, a dull ache in the region, ‘knots’ felt in muscle or even a sense of energetic congestion. There are many potential causes of muscle tightness and for most of us the exact root often remains unclear. Overusing a muscle group, underusing a muscle group, trauma and/or injury and psychological stress can all play a role here. It is also important to recognize that the human body is a tensile structure and we rely on tension to resist the force of gravity and to perform everyday tasks. So, while the words tension and tightness often have a negative connotation, they can have very significant functions. If we begin to alter our internal dialogue around tightness and take a more holistic approach to unwanted tightness by stretching, strengthening and decreasing our stress levels we might well notice that our perceived levels of tightness decrease.

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References:

Krabak, B., Laskowski, E., Smith, J., Stuart, M. and Wong, G. (2001) ‘Neurophysiologic Influences on Hamstring Flexibility: A Pilot Study.’ Clinical Journal of Sport Medicine 11, 4, 241-246.

Weppler, C. and Magnusson, P. (2010) ‘Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation?’ Physical Therapy 90, Issue 3, 438–449.