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Preflexes are the latent capacities in the musculoskeletal system that auto-stabilize movements through the use of the nonlinear visco-elastic properties of muscles when they contract.^[1]^[2] Unlike stablization methods using neurons such as reflexes and higher brain control, it happens with minimal time delay. Its chief disadvantage is that it works only to stabilize the main movements of the musculoskeletal system.

Visco-elastic correction

Muscles possess nonlinear visco-elastic properties when they contract.^[3]^[4]^[5] This property can autocorrect movements when a muscle is forced to change its length, and at a velocity different to that with which it was originally commanded. Such automatic correction is useful when a commanded action is perturbated, for example, if a step goes into a hole as this causes the foot to unexpectedly stretch down. The nonlinear visco-elastic properties of muscles interact with these perturbation induced velocity and length differences such that they counteract directly, as they happen, the effects upon the body of the perturbation.

Evolutionary opportunity

Muscles contain many different systems on which the evolutionary selection of preflex stabilization can operate. The deltoid muscle, for example, consists of at least seven segments with different bone attachments and neural control.^[6] Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, aponeurosis, and a fascicle of active contractile and passive elements.^[3] Another source of variation is in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in pennate muscles.^[7] The complexities of the different visco-elastic length- and velocity-force relationships of these subparts provides the opportunity for the adaptive selection of structurally complex muscle biocomposites with highly task-tuned nonlinear visco-elastic length- velocity- force relationships. This nature of muscles to be composite structures thus provides the adaptive opportunity for evolution to modify the visco-elastic reactions of the musculoskeletal system so they counteract perturbations without the need for spinal or higher levels of control.

Examples

Leg step recovery

Quails like many other bipedal birds walk upon rough ground. When a quail's leg steps into a hole (a common disruption against which evolution has tuned the nonlinear visco-elastic properties of its musculoskeletal system), it will cause a momentarily uncommanded velocity and length change in the muscles that span its leg joints. This length/velocity discrepancy interacts with the nonlinear length- and velocity-force relationships that have evolved in response to such a disruption with the result that the leg extends further into the hole, and thus keeps the quail’s body stable and upright.^[8]

Leg wiping

It is the intrinsic musculoskeletal properties of a frog’s leg, not neurally mediated spinal reflexes, that stabilize its wiping movements at irritants when the leg movement is perpetuated.^[9]

Squat jumps

A human example of a preflex stabilization occurs when a person explosively jumps up from a squat position, and the leg muscles act to provide a minimal time delay against perturbations from the vertical ^[5] .

Notes

^ Blickhan R, Seyfarth A, Geyer H, Grimmer S, Wagner H, Gunther M. 2007. Intelligence by mechanics. Philos Transact A Math Phys Eng Sci 365: 199–220 PMID 17148057
^ Valero-Cuevas FJ, Yi JW, Brown D, McNamara RV, 3rd, Paul C, Lipson H. 2007. The tendon network of the fingers performs anatomical computation at a macroscopic scale. IEEE Trans Biomed Eng 54: 1161–6 PMID 17549909
^ ^a ^b Brown IE, Loeb GE. 2000. A reductionist approach to creating and using neuromusculoskeletal models. In Biomechanical and neurological control of posture and movements, ed. JMC Winters, P.E., pp. 148–63. New York: Springer ISBN 978-0471509080
^ Nishikawa K, Biewener AA, Aerts P, Ahn AN, Chiel HJ, et al. 2007. Neuromechanics: an integrative approach for understanding motor control. Integrative and Comparative Biology 47: 16–54 [1]
^ ^a ^b van Soest AJ, Bobbert MF. 1993. The contribution of muscle properties in the control of explosive movements. Biological Cybernetics 69: 195–204 PMID 8373890
^ Brown JMM, Wickham JB, McAndrew DJ, Huang X-F. 2007. Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. Journal of Electromyography and Kinesiology 17: 57–73 PMID 16458022
^ Azizi E, Brainerd EL, Roberts TJ. 2008. Variable gearing in pennate muscles. Proc Natl Acad Sci U S A 105: 1745–50 PMID 18230734
^ Daley MA, Biewener AA. 2006. Running over rough terrain reveals limb control for intrinsic stability. Proceedings of the National Academy of Sciences of the United States of America 103: 15681–6 PMID 17032779
^ Richardson AG, Slotine JJ, Bizzi E, Tresch MC. 2005. Intrinsic musculoskeletal properties stabilize wiping movements in the spinalized frog. J Neurosci 25: 3181–91 PMID 15788775

[1] Blickhan R, Seyfarth A, Geyer H, Grimmer S, Wagner H, Gunther M. 2007. Intelligence by mechanics. Philos Transact A Math Phys Eng Sci 365: 199–220 PMID 17148057

[2] Valero-Cuevas FJ, Yi JW, Brown D, McNamara RV, 3rd, Paul C, Lipson H. 2007. The tendon network of the fingers performs anatomical computation at a macroscopic scale. IEEE Trans Biomed Eng 54: 1161–6 PMID 17549909

[brown-3] Brown IE, Loeb GE. 2000. A reductionist approach to creating and using neuromusculoskeletal models. In Biomechanical and neurological control of posture and movements, ed. JMC Winters, P.E., pp. 148–63. New York: Springer ISBN 978-0471509080

[4] Nishikawa K, Biewener AA, Aerts P, Ahn AN, Chiel HJ, et al. 2007. Neuromechanics: an integrative approach for understanding motor control. Integrative and Comparative Biology 47: 16–54 [1]

[van_Soest-5] van Soest AJ, Bobbert MF. 1993. The contribution of muscle properties in the control of explosive movements. Biological Cybernetics 69: 195–204 PMID 8373890

[6] Brown JMM, Wickham JB, McAndrew DJ, Huang X-F. 2007. Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. Journal of Electromyography and Kinesiology 17: 57–73 PMID 16458022

[7] Azizi E, Brainerd EL, Roberts TJ. 2008. Variable gearing in pennate muscles. Proc Natl Acad Sci U S A 105: 1745–50 PMID 18230734

[8] Daley MA, Biewener AA. 2006. Running over rough terrain reveals limb control for intrinsic stability. Proceedings of the National Academy of Sciences of the United States of America 103: 15681–6 PMID 17032779

[9] Richardson AG, Slotine JJ, Bizzi E, Tresch MC. 2005. Intrinsic musculoskeletal properties stabilize wiping movements in the spinalized frog. J Neurosci 25: 3181–91 PMID 15788775

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 ==Evolutionary opportunity==
-Muscles enable the [[Adaptation (biology)|evolutionary selection]] of preflex stabilization due to their heterogeneity. This gives them a highly composite and evolvable internal visco-elastic structure. While such internal heterogeneity is ignored in the descriptions given in most textbooks, it is considerable both at the gross and the muscle fiber levels. The [[Deltoid muscle|deltoid muscle]], for example, consists of at least seven segments with different bone attachments and neural control.<ref>Brown JMM, Wickham JB, McAndrew DJ, Huang X-F. 2007. Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. Journal of Electromyography and Kinesiology 17: 57–73 {{PMID|16458022}}</ref> Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, [[Aponeurosis|aponeurosis]], and a [[Muscle fascicle|fascicle]] of active contractile and passive elements.<ref name="brown"></ref> Another composite factor is the variation in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in [[Pennate|pennate]] muscles.<ref>Azizi E, Brainerd EL, Roberts TJ. 2008. [http://www.pnas.org/content/105/5/1745.full.pdf+html Variable gearing in pennate muscles.] Proc Natl Acad Sci U S A 105: 1745&ndash;50 {{PMID|18230734}}</ref> The potential heterogeneity of the different visco-elastic length- and velocity-force relationships of these subparts provides the opportunity for the adaptive selection of structurally complex muscle biocomposites with highly task-tuned nonlinear visco-elastic length- velocity- force relationships. This nature of muscles to be composite structures thus provides the adaptive opportunity for evolution to modify the visco-elastic reactions of the musculoskeletal system so they counteract perturbations without the need for spinal or higher levels of control.
+Muscles contain many different systems on which the [[Adaptation (biology)|evolutionary selection]] of preflex stabilization can operate. The [[Deltoid muscle|deltoid muscle]], for example, consists of at least seven segments with different bone attachments and neural control.<ref>Brown JMM, Wickham JB, McAndrew DJ, Huang X-F. 2007. Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. Journal of Electromyography and Kinesiology 17: 57–73 {{PMID|16458022}}</ref> Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, [[Aponeurosis|aponeurosis]], and a [[Muscle fascicle|fascicle]] of active contractile and passive elements.<ref name="brown"></ref> Another source of variation is in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in [[Pennate|pennate]] muscles.<ref>Azizi E, Brainerd EL, Roberts TJ. 2008. [http://www.pnas.org/content/105/5/1745.full.pdf+html Variable gearing in pennate muscles.] Proc Natl Acad Sci U S A 105: 1745&ndash;50 {{PMID|18230734}}</ref> The complexities of the different visco-elastic length- and velocity-force relationships of these subparts provides the opportunity for the adaptive selection of structurally complex muscle biocomposites with highly task-tuned nonlinear visco-elastic length- velocity- force relationships. This nature of muscles to be composite structures thus provides the adaptive opportunity for evolution to modify the visco-elastic reactions of the musculoskeletal system so they counteract perturbations without the need for spinal or higher levels of control.
 == Examples ==