In vivo muscle function vs speed I. Muscle strain in relation to length change of the muscle-tendon unit

We determined the influence of temperature on muscle function during jumping to better understand how the frog muscular system is designed to generate a high level of mechanical power. Maximal jumping performance and the in vivo operating conditions of the semimembranosus muscle (SM), a hip extensor, were measured and related to the mechanical properties of the isolated SM in the accompanying paper [Muscle function during jumping in frogs. II. Mechanical properties of muscle: implication for system design. Am. J. Physiol. 271 (Cell Physiol. 40): C571-C578, 1996]. Reducing temperature from 25 to 15 degrees C caused a 1.75-fold decline in peak mechanical power generation and a proportional decline in aerial jump distance. The hip and knee joint excursions were nearly the same at both temperatures. Accordingly, sarcomeres shortened over the same range (2.4 to 1.9 microns) at both temperatures, corresponding to myofilament overlap at least 90% of maximal. At the low temperature, however, movements were made more slowly. Angular velocities were 1.2- to 1.4-fold lower, and ground contact time was increased by 1.33-fold at 15 degrees C. Average shortening velocity of the SM was only 1.2-fold lower at 15 degrees C than at 25 degrees C. The low Q10 of velocity is in agreement with that predicted for muscles shortening against an inertial load.

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Computational modelling of muscle fibre operating ranges in the hindlimb of a small ground bird (Eudromia elegans), with implications for modelling locomotion in extinct species

PLoS Computational Biology ◽

10.1371/journal.pcbi.1008843 ◽

2021 ◽

Vol 17 (4) ◽

pp. e1008843

Author(s):

Peter J. Bishop ◽

Krijn B. Michel ◽

Antoine Falisse ◽

Andrew R. Cuff ◽

Vivian R. Allen ◽

...

Keyword(s):

Muscle Function ◽

Computational Models ◽

Fibre Length ◽

Computational Modelling ◽

Length Change ◽

Muscle Fibres ◽

Extinct Species ◽

Length Changes ◽

Experimental Findings

The arrangement and physiology of muscle fibres can strongly influence musculoskeletal function and whole-organismal performance. However, experimental investigation of muscle function during in vivo activity is typically limited to relatively few muscles in a given system. Computational models and simulations of the musculoskeletal system can partly overcome these limitations, by exploring the dynamics of muscles, tendons and other tissues in a robust and quantitative fashion. Here, a high-fidelity, 26-degree-of-freedom musculoskeletal model was developed of the hindlimb of a small ground bird, the elegant-crested tinamou (Eudromia elegans, ~550 g), including all the major muscles of the limb (36 actuators per leg). The model was integrated with biplanar fluoroscopy (XROMM) and forceplate data for walking and running, where dynamic optimization was used to estimate muscle excitations and fibre length changes throughout both gaits. Following this, a series of static simulations over the total range of physiological limb postures were performed, to circumscribe the bounds of possible variation in fibre length. During gait, fibre lengths for all muscles remained between 0.5 to 1.21 times optimal fibre length, but operated mostly on the ascending limb and plateau of the active force-length curve, a result that parallels previous experimental findings for birds, humans and other species. However, the ranges of fibre length varied considerably among individual muscles, especially when considered across the total possible range of joint excursion. Net length change of muscle–tendon units was mostly less than optimal fibre length, sometimes markedly so, suggesting that approaches that use muscle–tendon length change to estimate optimal fibre length in extinct species are likely underestimating this important parameter for many muscles. The results of this study clarify and broaden understanding of muscle function in extant animals, and can help refine approaches used to study extinct species.

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Fundamental Roles of Axial Stretch in Isometric and Isobaric Evaluations of Vascular Contractility

Journal of Biomechanical Engineering ◽

10.1115/1.4042171 ◽

2019 ◽

Vol 141 (3) ◽

Cited By ~ 4

Author(s):

Alexander W. Caulk ◽

Jay D. Humphrey ◽

Sae-Il Murtada

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Muscle Function ◽

Contractile Function ◽

Contractile Activity ◽

Comparison Of Methods ◽

Axial Stretch ◽

Smooth Muscle Function ◽

In Vivo Loading

Vascular smooth muscle cells (VSMCs) can regulate arterial mechanics via contractile activity in response to changing mechanical and chemical signals. Contractility is traditionally evaluated via uniaxial isometric testing of isolated rings despite the in vivo environment being very different. Most blood vessels maintain a locally preferred value of in vivo axial stretch while subjected to changes in distending pressure, but both of these phenomena are obscured in uniaxial isometric testing. Few studies have rigorously analyzed the role of in vivo loading conditions in smooth muscle function. Thus, we evaluated effects of uniaxial versus biaxial deformations on smooth muscle contractility by stimulating two regions of the mouse aorta with different vasoconstrictors using one of three testing protocols: (i) uniaxial isometric testing, (ii) biaxial isometric testing, and (iii) axially isometric plus isobaric testing. Comparison of methods (i) and (ii) revealed increased sensitivity and contractile capacity to potassium chloride and phenylephrine (PE) with biaxial isometric testing, and comparison of methods (ii) and (iii) revealed a further increase in contractile capacity with isometric plus isobaric testing. Importantly, regional differences in estimated in vivo axial stretch suggest locally distinct optimal biaxial configurations for achieving maximal smooth muscle contraction, which can only be revealed with biaxial testing. Such differences highlight the importance of considering in vivo loading and geometric configurations when evaluating smooth muscle function. Given the physiologic relevance of axial extension and luminal pressurization, we submit that, when possible, axially isometric plus isobaric testing should be employed to evaluate vascular smooth muscle contractile function.

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miR-206 family is important for mitochondrial and muscle function, but not essential for myogenesis in vitro

10.1101/796821 ◽

2019 ◽

Author(s):

Roza K. Przanowska ◽

Ewelina Sobierajska ◽

Zhangli Su ◽

Kate Jensen ◽

Piotr Przanowski ◽

...

Keyword(s):

Muscle Function ◽

Skeletal Muscle Regeneration ◽

C2c12 Myoblasts ◽

Skeletal Myoblasts ◽

Microrna Targets ◽

Microrna Family ◽

Differentiation Pathways

AbstractmiR-206, miR-1a-1 and miR-1a-2 are induced during differentiation of skeletal myoblasts and promote myogenesis in vitro. miR-206 is required for skeletal muscle regeneration in vivo. Although this microRNA family is hypothesized to play an essential role in differentiation, a triple knockout of the three genes has not been done to test this hypothesis. We report that triple KO C2C12 myoblasts generated using CRISPR/Cas9 method differentiate despite the expected de-repression of the microRNA targets. Surprisingly, their mitochondrial function is diminished. Triple KO mice demonstrate partial embryonic lethality, most likely due to the role of miR-1a in cardiac muscle differentiation. Two triple KO mice survive and grow normally to adulthood with smaller myofiber diameter and diminished physical performance. Thus, unlike other microRNAs important in other differentiation pathways, the miR-206 family is not absolutely essential for myogenesis and is instead a modulator of optimal differentiation of skeletal myoblasts.

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Effect of altering starting length and activation timing of muscle on fiber strain and muscle damage

Journal of Applied Physiology ◽

10.1152/japplphysiol.00524.2005 ◽

2006 ◽

Vol 100 (5) ◽

pp. 1489-1498 ◽

Cited By ~ 38

Author(s):

Timothy A. Butterfield ◽

Walter Herzog

Keyword(s):

Muscle Injury ◽

Tibialis Anterior Muscle ◽

Muscle Length ◽

Important Variable ◽

Cyclic Stretch ◽

Joint Torque ◽

Muscle Strain ◽

Fiber Dynamics ◽

Strain Magnitude

Muscle strain injuries are some of the most frequent injuries in sports and command a great deal of attention in an effort to understand their etiology. These injuries may be the culmination of a series of subcellular events accumulated through repetitive lengthening (eccentric) contractions during exercise, and they may be influenced by a variety of variables including fiber strain magnitude, peak joint torque, and starting muscle length. To assess the influence of these variables on muscle injury magnitude in vivo, we measured fiber dynamics and joint torque production during repeated stretch-shortening cycles in the rabbit tibialis anterior muscle, at short and long muscle lengths, while varying the timing of activation before muscle stretch. We found that a muscle subjected to repeated stretch-shortening cycles of constant muscle-tendon unit excursion exhibits significantly different joint torque and fiber strains when the timing of activation or starting muscle length is changed. In particular, measures of fiber strain and muscle injury were significantly increased by altering activation timing and increasing the starting length of the muscle. However, we observed differential effects on peak joint torque during the cyclic stretch-shortening exercise, as increasing the starting length of the muscle did not increase torque production. We conclude that altering activation timing and muscle length before stretch may influence muscle injury by significantly increasing fiber strain magnitude and that fiber dynamics is a more important variable than muscle-tendon unit dynamics and torque production in influencing the magnitude of muscle injury.

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Power output from a flight muscle of the bumblebee Bombus terrestris. I. Some features of the dorso-ventral flight muscle

Journal of Experimental Biology ◽

10.1242/jeb.200.8.1215 ◽

1997 ◽

Vol 200 (8) ◽

pp. 1215-1226 ◽

Cited By ~ 2

Author(s):

R Josephson ◽

C Ellington

Keyword(s):

Flight Muscle ◽

Bombus Terrestris ◽

Low Frequency ◽

Muscle Strain ◽

Optimal Length ◽

Tetanic Force ◽

Tethered Flight ◽

Wing Stroke ◽

Tetanic Tension

1. Isometric contractions from the asynchronous dorso-ventral flight muscle of the bumblebee Bombus terrestris were slow and rather weak. The twitch duration (onset to 50 % relaxation) was approximately 300 ms at 30 °C and 170 ms at 40 °C. The maximum tetanic tension was approximately 40 kN m-2; the ratio of twitch force to tetanic force was approximately 0.2. 2. The unstimulated muscle was quite resistant to stretch, with a low-frequency stiffness of 730 kN m-2 at muscle lengths close to that of the muscle in vivo. The lengthtension curve for active tetanic tension (that is the increase in tension above the passive level during stimulation) was very narrow, with a half-width equal to only 17 % of the optimal length. 3. The muscle strain during tethered flight was approximately 2 % peak-to-peak, occasionally reaching 3 %. Strain amplitude increased with wing stroke frequency. The thoracic vibration frequency of escape buzzing, during which the wings are not extended but are folded over the abdomen, was approximately twice that of tethered flight but the muscle strain was similar to that of flight.

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Fatigue alters in vivo function within and between limb muscles during locomotion

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2008.1734 ◽

2008 ◽

Vol 276 (1659) ◽

pp. 1193-1197 ◽

Cited By ~ 8

Author(s):

Timothy E Higham ◽

Andrew A Biewener

Keyword(s):

Muscle Function ◽

Contractile Function ◽

Force Generation ◽

Whole Body ◽

Activation Patterns ◽

Reduction In Force ◽

Numida Meleagris ◽

Limb Kinematics ◽

Specific Alteration

Muscle fatigue, a reduction in force as a consequence of exercise, is an important factor for any animal that moves, and can result from both peripheral and/or central mechanisms. Although much is known about whole-limb force generation and activation patterns in fatigued muscles under sustained isometric contractions, little is known about the in vivo dynamics of limb muscle function in relation to whole-body fatigue. Here we show that limb kinematics and contractile function in the lateral (LG) and medial (MG) gastrocnemius of helmeted guineafowl ( Numida meleagris ) are significantly altered following fatiguing exercise at 2 m s −1 on an inclined treadmill. The two most significant findings were that the variation in muscle force generation, measured directly from the muscles' tendons, increased significantly with fatigue, and fascicle shortening in the proximal MG, but not the distal MG, decreased significantly with fatigue. We suggest that the former is a potential mechanism for decreased stability associated with fatigue. The region-specific alteration of fascicle behaviour within the MG as a result of fatigue suggests a complex response to fatigue that probably depends on muscle–aponeurosis and tendon architecture not previously explored. These findings highlight the importance of studying the integrative in vivo dynamics of muscle function in response to fatigue.

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Adaptation to chronic length change in explanted airway smooth muscle

Journal of Applied Physiology ◽

10.1152/japplphysiol.01180.2002 ◽

2003 ◽

Vol 95 (1) ◽

pp. 448-453 ◽

Cited By ~ 33

Author(s):

Jahanbakhsh Naghshin ◽

Lu Wang ◽

Peter D. Paré ◽

Chun Y. Seow

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Culture Media ◽

Length Change ◽

Functional Change ◽

Muscle Stiffness ◽

Airway Narrowing

It has been shown that airway smooth muscle in vitro is able to maintain active force over a large length range by adaptation in the absence of periodic stimulations at 4°C (Wang L, Paré PD, and Seow CY. J Appl Physiol 90: 734–740, 2001). In this study, we show that such adaptation also takes place at body temperature and that long-term adaptation results in irreversible functional change in the muscle that could lead to airway hyperresponsiveness. Rabbit tracheal muscle explants were passively maintained at shortened and in situ length for 3 and 7–8 days in culture media; the length-tension relationship was then examined. The length associated with maximal force generation decreased by 10.5 ± 3.8% (SE) after 3 days and 37.7 ± 8.5% after 7 or 8 days of passive shortening. At day 3, the left shift in the length-tension curve due to adaptation at short lengths was reversible by readapting the muscle at a longer length. The shift was, however, not completely reversible after 7 days. The results suggest that long-term adaptation of airway smooth muscle could lead to increased muscle stiffness and force-generating ability at short lengths. Under in vivo condition, this could translate into resistance to stretch-induced relaxation and excessive airway narrowing.

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