Creep

“Connective tissues demonstrate properties of extensibility. The dense regular connective tissues are viscoelastic displaying both viscous and elastic rheologic properties with both time and frequency dependent properties.”
Wainwright SA, Biggs WD, Curry JD, Gosline JM. Mechanical design in organisms. London: Edward Arnold, Princeton University Press;1976. Dorrington K. In: Vincent JFV, Currey JD,eds. The theory of viscoelasticity in biomaterials. 1980: 289-314 Cambridge University Press.

“Mechanical creep, defined as elongation of tissue beyond it’s intrinsic extensibility resulting

from a constant load over time.”
Wilhelmi BJ, Blackwell SJ, Mancoll JS, Phillips LG. Creep vs. Stretch: A review of viscoelastic properties of skin. Ann Plast Surg. 1998; 41:215-219

“A property common to extensible soft tissues is that they become stiffer as they are extended due to the reorientation of collagen fibers. A stretch of a magnitude of 3-8% causes tearing and inflammation while applying a lesser stretch of 1-1.5% (load deformation) will have a similar affect.”
Currier DP, Nelson RM. Dynamics of human Biologic Tissues Philadelphia:FA Davis Co; 1992

“Sitting with the back slouched for as little as 20 minutes can result in increased laxity of the posterior spinal ligaments. It may take 30 minutes or more for these ligaments to regain their previous level of stiffness.”
McGill SM, Brown S. Creep response of the lumbar spine to prolonged full flexion. Clinical Biomechanics. 1992; 7: 43-46.

“It was concluded that sustained static or cyclic loading of lumbar viscoelastic tissues may cause micro-damage in the collagen structure, which in turn reflexively elicit spasms in the multifidus as well as hyperexcitability early in the recovery when the majority of the creep recovers. The micro-damage, however, results in the time dependent development of inflammation. In all cases, the spasms, initial and delayed hyperexcitabilities represent increased muscular forces applied across the intervertebral joints in an attempt to limit the range of motion and unload the viscoelastic tissues in order to prevent further damage and to promote healing. It is suggested that a significant insight is gained as to the development and implications of a common idiopathic low back disorder as well as to the development of cumulative trauma disorders.”
M. Solomonow, a, R. V. Barattaa, B. -H. Zhoua, E. Burgera, A. Zieskeb and A. Gedaliac Muscular dysfunction elicited by creep of lumbar viscoelastic tissue_a Occupational Medicine Research Center, Bioengineering Laboratory, Department of Orthopaedic Surgery, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA_b Department of Pathology, Louisiana State University Health Sciences Center, New Orleans, LA

70112, USA_c Departments of Pediatrics and Rheumatology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA _Received 24 July 2002; revised 14 November 2002; accepted 19 November 2002. ; Available online 22 May 2003.

“Static flexion of the lumbar spine with constant load applied to the viscoelastic structures for 20 minutes and for 50 minutes resulted in development of spasms and inhibition in the multifidus muscles (e.g., deep erector spinae) and in creep of the supraspinous ligament in the feline model. The development of spasms and inhibition was not

dependent on load magnitude. It is suggested that occupational and sports activities which require prolonged static lumbar flexion within the physiological range can cause a “sprain”-like injury to the ligaments, which in turn reflexively induce spasms and inhibition in some erector spinae muscles. Such disorder may take a long time to recover, in the order of days to weeks, depending on the level of creep developed in the tissues.”
M. Solomonow, , B. Zhou, R. V. Baratta, M. Zhu and Y. Lu Neuromuscular disorders associated with static lumbar flexion: a feline model _Occupational Medicine Research Center and Bioengineering Laboratory, Department of Orthopaedic Surgery, Louisiana State University Medical Center, New Orleans, LA 70112, USA _Received 12 April 2001; revised 16 August 2001; accepted 28 September 2001 Available online 28 November 2001.