Tensegrity, a combination of the words “tension” and “integrity”, is a principle that has been used in structural engineering for decades. More recently it has been used as a great principle in expressing how both human and horse fascia and internal structures work together.
Tensegrity is a simple concept with complexed implications. There have been a few different definitions given to this principle through history.
Fuller coined the term “Islands of compression in an ocean of tension.”
Emmerich gave this explanation, “Self-stressing structures consist of bars and cables assembled in such a way that the bars remain isolated in a continuum of cables. All these elements must be spaced rigidly and at the same time interlocked by the pre-stressing resulting from the internal stressing of cables without the need for external bearings and anchorage. The whole is maintained firmly like a self-supporting structure, whence the term self-stressing.”
Pugh merged these concepts with the following phrase. “A tensegrity system is established when a set of discontinuous compression components interacts with a set of continuous tensile components to define a stable volume in space.”
And Motro presented this description. “Tensegrity systems are systems whose rigidity is the result of a state of self-stressed equilibrium between cables under tension and compression elements.”
Levin discussed the efficiency of tensegrity structures in biological systems creating the term bio-tensegrity. His papers state that within these models structural material is only needed in areas of direct load, by carefully placing the compressive elements, tensegrity structures increase the resistance/weight ratio of traditional structures. These structures are also energy efficient, the system stores energy in the form of tension or compression meaning that when the structure needs to work it takes less energy to initiate because some energy is already stored in the structure. Levin also outlined other benefits to bio-tensegrities in his explanation of the spine, expressing how they are able to better withstand shear or bending forces over and above structures working in pure compression. Other of his papers discuss how tensegrity helps to explain how the body can withstand and exert forces over and above what conventional biomechanics and linear physics would suggest, while still remaining flexible. Tensegrity structures allow maximum work done with minimum energy expenditure and maximum structure within minimum space. With these benefits it makes logical sense that nature would favour these systems in its journey through evolution.
Juan and Tur summarise tensegrity comprehensively, some interesting terms from their conclusion being: an equilibrium of forces; proper stress vectors and the energy of the structure is the sum of the energies of each of its components. These are interesting phrases to provoke thought when applied to the relationship between the hoof and the rest of the tensegrity that is the horse.
Timoshenko and Young showed that tensegrity models can be applied to the musculoskeletal system of animals and the horse is certainly a biological tensegrity model. It is made up of segments, held together by continuous tension. The bones in the horse are suspended in a network of soft tissue, held in position by tension from muscles and fascia. The horses’ posture and conformation isn’t maintained by rigid joints and pure compression, but by this balance of tension across the horses entire musculoskeletal system.
Understanding how a tensegrity model reacts to stimulus helps to uncover how the horses’ fascia and other internal structures respond to stress. If you apply stress to one of these models you can see how the model distorts all over. They often will not break at the point of highest compression, the stress is dispersed over the whole structure and it concentrates, or breaks, at its weakest point. If you stretch the model everything stretches and again it will break at its weakest point.
As stated above, within the horse, one of the main components of the bio-tensegrity network is the fascia. Fascia is the connective tissue that runs throughout the horses’ body, connecting every single part of the horse with every other part. It’s a network of dense elastic tissue that supports, connects, separates and envelops the bones, organs, muscles, nerves and blood vessels. Myofascial lines in the horse have recently been documented by Elbrond and Shultz, while fascia extends throughout the entire horse forming part of the tensegrity structure, they also found chains of interconnected anatomical structures that functionally direct the basic motion patterns of the musculoskeletal system. fascia can thicken and strengthen in one direction to protect an injured body part, while lengthening in another direction to accommodate a new position. When fascia stretches or tightens as a response to stress, it affects all of the interconnected structures, for instance if it is stretched too far the nerves it contains can change from proprioceptive neurons, which are nerves that are responsible for telling the body where it is in space, to nociceptive nerves, which signal pain. It can create lines of tension, put pressure on blood vessels and nerves, and force the body to make compensations such as muscles working differently. This is how trauma or poor position and/or orientation of one and any part of the horse can result in pain or chronic irritation elsewhere. This relationship importantly includes the hoof and its fluid relationship with the entire musculoskeletal system.
In conclusion this foreword amalgamates the following articles nicely bringing some back round information to many of the principles they discuss.
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References
Motro. R, 2003, Tensegrity: Structural Systems for the Future,
R. Motro Tensegrity systems: the state of the art
Journal of Space Structures, 7 (2) (1992), pp. 75-83
R. Fuller, November Tensile-integrity structures, United States Patent 3063521, 1962.
D. Emmerich, April. Constructions de reseaux autotendantes, Patent No. 1.377.290, 1963.
A. Pugh An Introduction to Tensegrity
University of California Press (1976)
S. Levin The tensegrity-truss as a model for spinal mechanics: biotensegrity
Journal of Mechanics in Medicine and Biology, 2 (3) (2002)
S. Timoshenko, D. Young Cats’ Paws and Catapults: Mechanical Worlds of Nature and People
W.W. Norton and Company (2000)
Juan and Tur, 2008, Tensegrity Frameworks: static analysis review, Mechanism and Machine Theory, vol 43, issue 7, 859-881
Jericho Physio, https://www.jerichophysio.com/
Elbrond and Schultz, 2014, myofascial kinetic lines in horses, Equine Veterinary Journal