The Interaction of Compliance and Activation on the Force-Length Operating Range and Force Generating Capacity of Skeletal Muscle: A Computational Study using a Guinea Fowl Musculoskeletal Model

Synopsis A muscle’s performance is influenced by where it operates on its force–length (F–L) curve. Here we explore how activation and tendon compliance interact to influence muscle operating lengths and force-generating capacity. To study this, we built a musculoskeletal model of the lower limb of the guinea fowl and simulated the F–L operating range during fixed-end fixed-posture contractions for 39 actuators under thousands of combinations of activation and posture using three different muscle models: Muscles with non-compliant tendons, muscles with compliant tendons but no activation-dependent shift in optimal fiber length (L0), and muscles with both compliant tendons and activation-dependent shifts in L0. We found that activation-dependent effects altered muscle fiber lengths up to 40% and increased or decreased force capacity by up to 50% during fixed-end contractions. Typically, activation-compliance effects reduce muscle force and are dominated by the effects of tendon compliance at high activations. At low activation, however, activation-dependent shifts in L0 are equally important and can result in relative force changes for low compliance muscles of up to 60%. There are regions of the F–L curve in which muscles are most sensitive to compliance and there are troughs of influence where these factors have little effect. These regions are hard to predict, though, because the magnitude and location of these areas of high and low sensitivity shift with compliance level. In this study we provide a map for when these effects will meaningfully influence force capacity and an example of their contributions to force production during a static task, namely standing.

Download Full-text

The interaction of compliance and activation on the force-length operating range and force generating capacity of skeletal muscle

10.1101/580027 ◽

2019 ◽

Author(s):

S.M. Cox ◽

K.L. Easton ◽

M. Cromie Lear ◽

R.L. Marsh ◽

S.L. Delp ◽

...

Keyword(s):

Force Production ◽

Muscle Performance ◽

Operating Range ◽

Compliance Level ◽

Generating Capacity ◽

Low Sensitivity ◽

Fixed End ◽

Muscle Models ◽

No Activation ◽

Tendon Compliance

AbstractMuscle performance is influenced by where it operates on its force-length curve. Here we explore how activation and tendon compliance interact to influence muscle operating lengths and force-generating capacity. To study this, we built a musculoskeletal model of the lower limb of the guinea fowl and simulated the force-length operating range during fixed-end fixed-posture contractions for 39 actuators under thousands of combinations of activation and posture using three different muscle models: Muscles with non-compliant tendons, muscles with compliant tendons but no activation dependent shift in optimal fiber length (L0), and muscles with both compliant tendons and activation-dependent shifts in L0. We found that activation dependent effects altered muscle fiber lengths up to 40% and increased or decreased force capacity by up to 50% during fixed-end contractions. Typically, activation-compliance effects reduce muscle force and are dominated by the effects of tendon compliance at high activations. At low activation, however, activation-dependent shifts in L0 are equally important and can result in relative force changes for low compliance muscles of up to 60%. There are regions of the force-length curve in which muscles are most sensitive to compliance and there are troughs of influence where these factors have little effect. These regions are hard to predict, though, because the magnitude and location of these areas of high and low sensitivity shift with compliance level. Here we provide a map for when these effects will meaningfully influence force capacity and an example of their contributions to force production during a static task, namely standing.

Download Full-text

Force-length relation of isometric sarcomeres in fixed-end tetani

AJP Cell Physiology ◽

10.1152/ajpcell.1993.264.1.c19 ◽

1993 ◽

Vol 264 (1) ◽

pp. C19-C26 ◽

Cited By ~ 20

Author(s):

A. Horowitz ◽

G. H. Pollack

Keyword(s):

Sarcomere Length ◽

Production Capacity ◽

Force Production ◽

Length Change ◽

Optical Diffraction ◽

Tetanic Force ◽

End Conditions ◽

Linear Force ◽

Fixed End

The higher force observed in fixed-end tetani relative to sarcomere-isometric tetani is commonly attributed to sarcomere length inhomogeneity; sarcomeres in the end regions of the fiber shorten extensively at the expense of the central sarcomeres. By shortening, these sarcomeres supposedly attain higher force production capacity and can thus account for the extra force. However, the fibers could also contain sarcomeres that stay isometric throughout most of the tetanic force plateau. If such sarcomeres undergo slight shortening before their isometric phase, their force-length relation should be elevated (A. Horowitz, H. P. M Wussling, and G. H. Pollack. Biophys. J. 63: 3-17, 1992). These sarcomeres may therefore account for the higher force in fixed-end tetani. To test this possibility, single frog semitendinosus fibers were tetanized under fixed-end conditions. Sarcomere length change during the tetanus was measured at different locations along the fiber by optical diffraction. Fibers stretched to average sarcomere lengths between 2.2 and 3.2 microns contained sarcomeres that, except for some initial shortening during the early part of the tetanus, remained isometric. These sarcomeres were located between the ends and the central region of the fibers. Their force-length relation was higher than the linear force-length relation based on sarcomere length clamps by an average of 14% between sarcomere lengths of 2.4-3.2 microns. Thus slight (1-5%) shortening may explain the relatively higher fixed-end force-length relation.

Download Full-text

Computational Study of Body Force Production Process and Performance Improvement in Dielectric-Barrier-Discharge Plasma Actuator

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES AEROSPACE TECHNOLOGY JAPAN ◽

10.2322/tastj.16.550 ◽

2018 ◽

Vol 16 (6) ◽

pp. 550-555

Author(s):

Shintaro SATO ◽

Masayuki TAKAHASHI ◽

Naofumi OHNISHI

Keyword(s):

Performance Improvement ◽

Body Force ◽

Discharge Plasma ◽

Barrier Discharge ◽

Computational Study ◽

Force Production ◽

Dielectric Barrier Discharge Plasma ◽

Dielectric Barrier ◽

Barrier Discharge Plasma ◽

And Performance

Download Full-text

Can Mental Practice Increase Ankle Dorsiflexor Torque?

Physical Therapy ◽

10.1093/ptj/85.10.1053 ◽

2005 ◽

Vol 85 (10) ◽

pp. 1053-1060 ◽

Cited By ~ 34

Author(s):

Ben Sidaway ◽

Amy (Robinson) Trzaska

Keyword(s):

Treatment Options ◽

Force Production ◽

Mental Practice ◽

Control Group ◽

Physical Practice ◽

Practice Group ◽

Generating Capacity ◽

Abductor Digiti Minimi ◽

Group A ◽

Ankle Dorsiflexor

Abstract Background and Purpose. Mental practice has been shown to be effective in increasing the force production of the abductor digiti minimi muscle in the hand. The aim of this study was to determine whether mental practice could produce strength gains in the larger ankle dorsiflexor muscles, which are important during walking. Subjects. Twenty-four subjects were randomly assigned to a physical practice group, a mental practice group, or a control group (8 subjects per group). Methods. In the practice groups, subjects either physically or mentally practiced producing maximal isometric contractions for 3 sets of 10 repetitions, 3 times per week for 4 weeks. Changes in mean peak isometric torque normalized to body weight and the resulting percentage of improvement were analyzed across the 3 groups. Results. Differences in raw torque production after training in the 2 practice groups resulted in significant percentages of improvement for the physical practice group (25.28%) and the mental practice group (17.13%), but not for the control group (−1.77%). The 2 practice groups were not statistically different in their maximal torque-generating capacity after training. Discussion and Conclusion. These findings show that mental practice in people without impairments can lead to an increase in torque production similar to that produced by physical practice. Such a technique may prove to be a useful adjunct to traditional treatment options aimed at increasing muscle strength.

Download Full-text

Flight efficiency is a key to diverse wing morphologies in small insects

Journal of The Royal Society Interface ◽

10.1098/rsif.2021.0518 ◽

2021 ◽

Vol 18 (183) ◽

Author(s):

Thomas Engels ◽

Dmitry Kolomenskiy ◽

Fritz-Olaf Lehmann

Keyword(s):

Aerodynamic Force ◽

Computational Study ◽

Force Production ◽

Similar Efficacy ◽

Efficient Production ◽

Wing Membrane ◽

Aerodynamic Efficiency ◽

Energy Expenditures ◽

Insect Wings ◽

Lift And Drag

Insect wings are hybrid structures that are typically composed of veins and solid membranes. In some of the smallest flying insects, however, the wing membrane is replaced by hair-like bristles attached to a solid root. Bristles and membranous wing surfaces coexist in small but not in large insect species. There is no satisfying explanation for this finding as aerodynamic force production is always smaller in bristled than solid wings. This computational study suggests that the diversity of wing structure in small insects results from aerodynamic efficiency rather than from the requirements to produce elevated forces for flight. The tested wings vary from fully membranous to sparsely bristled and were flapped around a wing root with lift- and drag-based wing kinematic patterns and at different Reynolds numbers ( Re ). The results show that the decrease in aerodynamic efficiency with decreasing surface solidity is significantly smaller at Re = 4 than Re = 57. A replacement of wing membrane by bristles thus causes less change in energetic costs for flight in small compared to large insects. As a consequence, small insects may fly with bristled and solid wing surfaces at similar efficacy, while larger insects must use membranous wings for an efficient production of flight forces. The above findings are significant for the biological fitness and dispersal of insects that fly at elevated energy expenditures.

Download Full-text

Doublet potentiation in the triceps surae is limited by series compliance and dynamic fascicle behavior

Journal of Applied Physiology ◽

10.1152/japplphysiol.00403.2015 ◽

2015 ◽

Vol 119 (7) ◽

pp. 807-816 ◽

Cited By ~ 8

Author(s):

Dean L. Mayfield ◽

Glen A. Lichtwark ◽

Neil J. Cronin ◽

Janne Avela ◽

Andrew G. Cresswell

Keyword(s):

Force Production ◽

Muscle Length ◽

Triceps Surae ◽

Ultrasound Images ◽

Lateral Gastrocnemius ◽

Nonlinear Force ◽

Series Compliance ◽

Fixed End ◽

High Series ◽

Stimulation Of

Activation of skeletal muscle twice in quick succession results in nonlinear force summation (i.e., doublet potentiation). The force contributed by a second activation is typically of augmented amplitude, longer in duration, and generated at a greater rate. The purpose of this study was to examine force summation in a muscle attached to a compliant tendon, where considerable internal shortening occurs during a fixed-end contraction. The triceps surae of 21 ( Experiment 1) and 9 ( Experiment 2) young adults were maximally activated with doublet stimulation of different interstimulus intervals (ISIs) (5-100 ms) at several muscle lengths. Ultrasound images acquired from lateral gastrocnemius and soleus muscles allowed quantification of dynamic fascicle behavior. Force summation was muscle length dependent. Force augmentation was limited to a short muscle length. Lateral gastrocnemius and soleus fascicles underwent large amounts of active shortening and achieved high velocities in response to doublet stimulation, dynamics unfavorable for force production. Summation amplitude and the sensitivity of summation to ISI were dramatically depressed in the triceps surae after comparison to muscles with less fixed-end compliance. We propose that the internal shortening permitted by high series compliance limited force augmentation by offsetting and/or interfering with activation and cross-bridge processes driving augmentation. High series compliance may also reduce the sensitivity of the summated response to ISI, an assertion supported by predictions from a Hill-type muscle model. These muscles may exhibit greater force augmentation during more accustomed stretch-shorten tasks (i.e., hopping), where the compliance of the Achilles tendon actually enables near-isometric fascicle behavior.

Download Full-text

Effects of long-term exercise on the biomechanical properties of the Achilles tendon of guinea fowl

Journal of Applied Physiology ◽

10.1152/jappl.2001.90.1.164 ◽

2001 ◽

Vol 90 (1) ◽

pp. 164-171 ◽

Cited By ~ 99

Author(s):

Cindy I. Buchanan ◽

Richard L. Marsh

Keyword(s):

Biomechanical Properties ◽

Guinea Fowl ◽

Cross Sectional ◽

Tendon Stiffness ◽

Mechanical Fatigue ◽

Downhill Running ◽

Numida Meleagris ◽

Tendon Compliance

The purpose of this study was to determine the effect of long-term exercise on tendon compliance and to ascertain whether tendons adapt differently to downhill running vs. running on a level surface. We carried out this investigation on the gastrocnemius tendon of helmeted guinea fowl ( Numida meleagris) that were trained for 8–12 wk before commencing experimental procedures. We used an in situ technique to measure tendon stiffness. The animals were deeply anesthetized with isofluorane during all in situ procedures. Our results indicate that long-term exercise increased tendon stiffness. This finding held true after normalization for the cross-sectional area of the free tendon, likely reflecting a change in the material properties of the exercised tendons. Whether training consisted of level or downhill running did not appear to influence response of the tendon to exercise. We hypothesize that the increased stiffness observed in tendons after a long-term running program may be a response to repeated stress and may function as a mechanism to resist tendon damage due to mechanical fatigue.

Download Full-text

Muscular Resistance to Varus and Valgus Loads at the Elbow

Journal of Biomechanical Engineering ◽

10.1115/1.2834755 ◽

1998 ◽

Vol 120 (5) ◽

pp. 634-639 ◽

Cited By ~ 48

Author(s):

T. S. Buchanan ◽

S. L. Delp ◽

J. A. Solbeck

Keyword(s):

Applied Load ◽

Musculoskeletal Model ◽

Maximum Flexion ◽

Significant Contributor ◽

Pronator Teres ◽

Flexion Extension ◽

Flexion Moment ◽

Generating Capacity

Although the contributions of passive structures to stability of the elbow have been well documented, the role of active muscular resistance of varus and valgus loads at the elbow remains unclear. We hypothesized that muscles: (1) can produce substantial varus and valgus moments about the elbow, and (2) are activated in response to sustained varus and valgus loading of the elbow. To test the first hypothesis, we developed a detailed musculoskeletal model to estimate the varus and valgus moment-generating capacity of the muscles about the elbow. To test the second hypothesis, we measured EMGs from 11 muscles in four subjects during a series of isometric tasks that included flexion, extension, varus, and valgus moments about the elbow. The EMG recordings were used as inputs to the elbow model to estimate the contributions of individual muscles to flexion-extension and varus-valgus moments. Analysis of the model revealed that nearly all of the muscles that cross the elbow are capable of producing varus or valgus moments; the capacity of the muscles to produce varus moment (34 Nm) and valgus moment (35 Nm) is roughly half of the maximum flexion moment (70 Nm). Analysis of the measured EMGs showed that the anconeus was the most significant contributor to valgus moments and the pronator teres was the largest contributor to varus moments. Although our results show that muscles were activated in response to static varus and valgus loads, their activations were modest and were not sufficient to balance the applied load.

Download Full-text