Passive and active mechanical properties of the superficial and deep digital flexor muscles in the forelimbs of anesthetized Thoroughbred horses

The activation of a muscle depends on the function that it is performing and on the architectural properties of that muscle; the two are inextricably linked. Activation conditions such as activation timing, duration and amplitude can be varied throughout a cyclical movement (such as locomotion) and the length change of the whole muscle tendon unit (MTU) can also be varied. Architecturally, muscles have a range of fibre lengths, maximum force-producing capabilities and stiffness of the series elastic element (SEE). In the present work we use a model to explore the relationship between power output and efficiency of a muscle across a range of contraction conditions. We have also examined the mechanical and energetic effects of changing muscle architecture within the model. Our results indicate that whilst there are clear optimal conditions for achieving maximum power output and maximum efficiency, the design of the muscle allows high levels of both to be achieved over a range of activation conditions. This range changes with both SEE compliance and the amplitude of the cyclical length change. The results suggest that a compliant SEE allows a muscle to function closer to the maximum of both power output and efficiency. In addition, by varying the amplitude of the activation level, the efficiency can theoretically remain unchanged, whilst the power output can be modulated.

Section: Discussionmentioning

confidence: 99%

Effects of series elasticity and activation conditions on muscle power output and efficiency

Lichtwark

Wilson

2005

“…The ligaments were represented as passive elastic structures. The force-length curve of each tendon and ligament was modeled by fitting a third-order polynomial function to experimental data reported in the literature (Jansen et al, 1993a;Jansen et al, 1998;Kostyuk et al, 2004;Lochner et al, 1980;Meershoek et al, 2001;Swanstrom et al, 2004;Swanstrom et al, 2005a;Swanstrom et al, 2005b;Weller, 2006). The lengths, moment arms and tendon wrapping directions of each muscle and ligament were calculated using a software program called OpenSim (Delp et al, 2007).…”

Section: Musculoskeletal Modelingmentioning

confidence: 99%

“…This approach has been used extensively to determine musculoskeletal function in human movement (Pandy and Zajac, 1991;van Soest et al, 1993;Zajac, 1993;Pandy, 2001;Shelburne et al, 2004;Shelburne et al, 2006;Pandy and Andriacchi, 2010); however, relatively few studies have applied this approach to the study of equine locomotion (Biewener, 1998;Meershoek et al, 2001;Merritt et al, 2008;Swanstrom et al, 2005a;Wilson et al, 2001). Detailed models of isolated muscle-tendon preparations have been used to study the interactions between the active and passive properties of an actuator (Swanstrom et al, 2005b), but few studies have used models of the musculoskeletal system to evaluate muscle and joint loading during gait. Biewener presented the most comprehensive model of the distal forelimb developed to date (Biewener, 1998).…”

Section: Introductionmentioning

confidence: 99%

Relationship between muscle forces, joint loading and utilization of elastic strain energy in equine locomotion

Harrison

Whitton

Kawcak

et al. 2010

Self Cite

SUMMARYStorage and utilization of strain energy in the elastic tissues of the distal forelimb of the horse is thought to contribute to the excellent locomotory efficiency of the animal. However, the structures that facilitate elastic energy storage may also be exposed to dangerously high forces, especially at the fastest galloping speeds. In the present study, experimental gait data were combined with a musculoskeletal model of the distal forelimb of the horse to determine muscle and joint contact loading and muscle-tendon work during the stance phase of walking, trotting and galloping. The flexor tendons spanning the metacarpophalangeal (MCP) joint -specifically, the superficial digital flexor (SDF), interosseus muscle (IM) and deep digital flexor (DDF) -experienced the highest forces. Peak forces normalized to body mass for the SDF were 7.3±2.1, 14.0±2.5 and 16.7±1.1Nkg -1 in walking, trotting and galloping, respectively. The contact forces transmitted by the MCP joint were higher than those acting at any other joint in the distal forelimb, reaching 20.6±2.8, 40.6±5.6 and 45.9±0.9Nkg -1 in walking, trotting and galloping, respectively. The tendons of the distal forelimb (primarily SDF and IM) contributed between 69 and 90% of the total work done by the muscles and tendons, depending on the type of gait. The tendons and joints that facilitate storage of elastic strain energy in the distal forelimb also experienced the highest loads, which may explain the high frequency of injuries observed at these sites.

“…Animal and human skeletal muscles cover a broad range of tendon length-to-fibre length ratios (Zajac, 1989;Biewener and Roberts, 2000). As a consequence, the fixed-end compliance of skeletal muscle varies considerably (Biewener and Roberts, 2000): horse superficial digital flexor 81% (Brown et al, 2003;Swanstrom et al, 2005), human medial gastrocnemius 35% (Narici et al, 1996) cat medial gastrocnemius 28% (Griffiths, 1991), guinea fowl lateral gastrocnemius 13% (Buchanan and Marsh, 2001), frog semitendinosus 11% (Lieber et al, 1991(Lieber et al, , 1992, hopping mouse gastrocnemius 6% (Ettema, 1996) and rat gastrocnemius 5% (Ettema, 1996). Experimental findings support distinct mechanical and functional roles for tendons of low and high series compliance (Biewener et al, 1981;Ettema, 1996).…”

Section: Introductionmentioning

confidence: 99%

Additional in-series compliance reduces muscle force summation and alters the time course of force relaxation during fixed-end contractions

Mayfield

Launikonis

Cresswell

et al. 2016

There are high mechanical demands placed on skeletal muscles in movements requiring rapid acceleration of the body or its limbs. Tendons are responsible for transmitting muscle forces, but, because of their elasticity, can manipulate the mechanics of the internal contractile apparatus. Shortening of the contractile apparatus against the stretch of tendon affects force generation according to known mechanical properties; however, the extent to which differences in tendon compliance alter force development in response to a burst of electrical impulses is unclear. To establish the influence of series compliance on force summation, we studied electrically evoked doublet contractions in the cane toad peroneus muscle in the presence and absence of a compliant artificial tendon. Additional series compliance reduced tetanic force by two-thirds, a finding predicted based on the force-length property of skeletal muscle. Doublet force and force-time integral expressed relative to the twitch were also reduced by additional series compliance. Active shortening over a larger range of the ascending limb of the force-length curve and at a higher velocity, leading to a progressive reduction in forcegenerating potential, could be responsible. Muscle-tendon interaction may also explain the accelerated time course of force relaxation in the presence of additional compliance. Our findings suggest that a compliant tendon limits force summation under constant-length conditions. However, high series compliance can be mechanically advantageous when a muscle-tendon unit is actively stretched, permitting muscle fibres to generate force almost isometrically, as shown during stretch-shorten cycles in locomotor activities. Restricting active shortening would likely favour rapid force development.