Muscle stiffness in human ankle dorsiflexors: intrinsic and reflex components

1. The purpose of this study was to evaluate the mechanical response to stretch in normal human ankle dorsiflexors at different levels of voluntary contraction. In an active muscle, the total mechanical response is the sum of the intrinsic response from the contractile apparatus, the response from passive tissues, and the reflex mediated response. Each of these components was investigated. 2. The total incremental stiffness was defined as the ratio between the torque increment and the amplitude of the stretch. In 14 subjects the total stiffness increased from approximately 0.6 N.m/deg to approximately 2.5 N.m/deg at 50% of MVC and remained constant (+/- 10%) from 30 to 80% of MVC. 3. The contribution to incremental stiffness from intrinsic muscle properties was measured during electrical stimulation of the deep peroneal nerve at 7-50 Hz. Intrinsic stiffness increased linearly with torque from approximately 0.5 N.m/deg to approximately 2.5 N.m/deg at 80% of MVC. 4. The reflex component (total minus intrinsic stiffness) had a maximum of 0.5-1.5 N.m/deg at 30-50% of MVC and was approximately zero at no and maximal contraction. For intermediate levels of contraction the reflex increased the stiffness with 40-100% of the intrinsic stiffness in this flexor muscle. 5. The reflex contribution to total stiffness began approximately 50 ms after onset of stretch and peaked 150-300 ms after onset of stretch. 6. Total, intrinsic, and reflex mediated stiffness were all nearly independent of the amplitude of stretch in the range from 2 to 7 degrees. The higher stiffness observed for 1 degree stretches could be due to "short range stiffness" of the cross bridges. 7. Stretching of a contracting muscle generates large force increments even for moderate amplitudes of stretch. Approximately half of this force increment is due to the stretch reflex, which makes the muscle stiffer than predicted from the intrinsic stiffness. These findings in human flexor muscles are surprisingly similar to previous findings in extensor muscles of the decerebrate cat.

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The effects of pH on force and stiffness development in mouse muscles

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y87-280 ◽

1987 ◽

Vol 65 (8) ◽

pp. 1798-1801 ◽

Cited By ~ 3

Author(s):

J. M. Renaud ◽

R. B. Stein ◽

T. Gordon

Keyword(s):

High Frequency ◽

Small Amplitude ◽

Force Production ◽

Muscle Length ◽

Low Ph ◽

Muscle Stiffness ◽

Average Force ◽

Cross Bridge ◽

Effects Of Ph ◽

Cross Bridges

Changes in force and stiffness during contractions of mouse extensor digitorum longus and soleus muscles were measured over a range of extracellular pH from 6.4 to 7.4. Muscle stiffness was measured using small amplitude (<0.1% of muscle length), high frequency (1.5 kHz) oscillations in length. Twitch force was not significantly affected by changes in pH, but the peak force during repetitive stimulation (2, 3, and 20 pulses) was decreased significantly as the pH was reduced. Changes in muscle stiffness with pH were in the same direction, but smaller in extent. If the number of attached cross-bridges in the muscle can be determined from the measurement of small amplitude, high frequency muscle stiffness, then these findings suggest that (a) the number of cross-bridges between thick and thin filaments declines in low pH and (b) the average force per cross-bridge also declines in low pH. The decline in force per cross-bridge could arise from a reduction in the ability of cross-bridges to generate force during their state of active force production and (or) in an increased percentage of bonds in a low force, "rigor" state.

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Nonlinear behavior of muscle reflexes at the human ankle joint

Journal of Neurophysiology ◽

10.1152/jn.1995.73.1.65 ◽

1995 ◽

Vol 73 (1) ◽

pp. 65-72 ◽

Cited By ~ 92

Author(s):

R. B. Stein ◽

R. E. Kearney

Keyword(s):

Ankle Joint ◽

Stretch Reflex ◽

Maximum Voluntary Contraction ◽

Voluntary Contraction ◽

Voluntary Activation ◽

Random Perturbations ◽

Hydraulic Actuator ◽

Voluntary Activity ◽

Highly Nonlinear ◽

Human Ankle

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.

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Botulinum toxin injection causes hyper-reflexia and increased muscle stiffness of the triceps surae muscle in the rat

Journal of Neurophysiology ◽

10.1152/jn.00452.2016 ◽

2016 ◽

Vol 116 (6) ◽

pp. 2615-2623 ◽

Cited By ~ 14

Author(s):

Jessica Pingel ◽

Jacob Wienecke ◽

Jakob Lorentzen ◽

Jens Bo Nielsen

Keyword(s):

Botulinum Toxin ◽

Muscle Force ◽

Botulinum Toxin Injection ◽

Contralateral Side ◽

Relative Increase ◽

Muscle Stiffness ◽

Triceps Surae ◽

Reflex Activity ◽

Muscle Properties ◽

Triceps Surae Muscle

Botulinum toxin is used with the intention of diminishing spasticity and reducing the risk of development of contractures. Here, we investigated changes in muscle stiffness caused by reflex activity or elastic muscle properties following botulinum toxin injection in the triceps surae muscle in rats. Forty-four rats received injection of botulinum toxin in the left triceps surae muscle. Control measurements were performed on the noninjected contralateral side in all rats. Acute experiments were performed, 1, 2, 4, and 8 wk following injection. The triceps surae muscle was dissected free, and the Achilles tendon was cut and attached to a muscle puller. The resistance of the muscle to stretches of different amplitudes and velocities was systematically investigated. Reflex-mediated torque was normalized to the maximal muscle force evoked by supramaximal stimulation of the tibial nerve. Botulinum toxin injection caused severe atrophy of the triceps surae muscle at all time points. The force generated by stretch reflex activity was also strongly diminished but not to the same extent as the maximal muscle force at 2 and 4 wk, signifying a relative reflex hyperexcitability. Passive muscle stiffness was unaltered at 1 wk but increased at 2, 4, and 8 wk ( P < 0.01). These data demonstrate that botulinum toxin causes a relative increase in reflex stiffness, which is likely caused by compensatory neuroplastic changes. The stiffness of elastic elements in the muscles also increased. The data are not consistent with the ideas that botulinum toxin is an efficient antispastic medication or that it may prevent development of contractures.

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Aging does not affect voluntary activation of the ankle dorsiflexors during isometric, concentric, and eccentric contractions

Journal of Applied Physiology ◽

10.1152/japplphysiol.01426.2004 ◽

2005 ◽

Vol 99 (1) ◽

pp. 31-38 ◽

Cited By ~ 74

Author(s):

Malgorzata Klass ◽

Stéphane Baudry ◽

Jacques Duchateau

Keyword(s):

Electrical Stimulation ◽

Compound Muscle Action Potential ◽

Voluntary Contraction ◽

Voluntary Activation ◽

M Wave ◽

Mechanical Responses ◽

Age Related ◽

Angular Velocities ◽

General Slowing ◽

Ankle Dorsiflexors

This study examines the age-related deficit in force of the ankle dorsiflexors during isometric (Iso), concentric (Con), and eccentric (Ecc) contractions. More specifically, the contribution of neural and muscular mechanisms to the loss of voluntary force was investigated in men and women. The torque produced by the dorsiflexors and the surface electromyogram (EMG) from the tibialis anterior and the soleus were recorded during maximal Iso contractions and during Con and Ecc contractions performed at constant angular velocities (5–100°/s). Central activation was tested by the superimposed electrical stimulation method during maximal voluntary contraction and by computing the ratio between voluntary average EMG and compound muscle action potential (M wave) induced by electrical stimulation (average EMG/M wave). Contractile properties of the dorsiflexor muscles were investigated by recording the mechanical responses to single and paired maximal stimuli. The results showed that the age-related deficit in force (collapsed across genders and velocities) was greater for Iso (20.5%; P < 0.05) and Con (38.6%; P < 0.001) contractions compared with Ecc contractions (6.5%; P > 0.05). When the torque produced during Con and Ecc contractions was expressed relative to the maximal Iso torque, it was significantly reduced in Con contractions and increased in Ecc contractions with aging, with the latter effect being more pronounced for women. In both genders, voluntary activation was not significantly impaired in elderly adults and did not differ from young subjects. Similarly, coactivation was not changed with aging. In contrast, the mechanical responses to single and paired stimuli showed a general slowing of the muscle contractile kinetics with a slightly greater effect in women. It is concluded that the force deficit during Con and Iso contractions of the ankle dorsiflexors in advanced age cannot be explained by impaired voluntary activation or changes in coactivation. Instead, this age-related adaptation and the mechanisms that preserve force in Ecc contractions appeared to be located at the muscular level.

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FORCE SUMMATION AND TWITCH POTENTIATION CAPACITY IN HUMAN ANKLE PLANTAR- AND DORSI-FLEXOR MUSCLES

Journal of Musculoskeletal Research ◽

10.1142/s0218957714500158 ◽

2014 ◽

Vol 17 (04) ◽

pp. 1450015

Author(s):

Yoichi Ohta ◽

Kengo Yotani

Keyword(s):

Muscle Function ◽

Pulse Train ◽

Maximum Voluntary Contraction ◽

Voluntary Contraction ◽

Twitch Potentiation ◽

Flexor Muscles ◽

Human Ankle ◽

Before And After ◽

Isometric Torque ◽

Plantar Flexor Muscles

Purpose: The present study aimed to clarify inter-individual correlation between the magnitudes of force summation and the post-activation potentiation (PAP), in human ankle plantar- and dorsi-flexor muscles. Methods: We analyzed 10 male participants plantar-flexor muscles and the 12 male participants dorsi-flexor muscles using a database from a previous study. Before and after maximum voluntary contraction, we measured the amount of isometric torque evoked by a single, double- and triple-pulse train stimulus. Results: The magnitude of PAP was significantly positively correlated with the magnitude of force summation in both the plantar- and dorsi-flexor muscles. Conclusions: The present study confirmed the correlation between the magnitudes of force summation and PAP in human ankle plantar- and dorsi-flexor muscles. This suggests that muscle characteristics affecting the force summation capacity depend on the PAP, to some degree. These results suggest that the combination of both parameters might enhance the usefulness of evaluating changes in muscle function using intrinsic contractile properties.

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Adaptations in human neuromuscular function following prolonged unweighting: I. Skeletal muscle contractile properties and applied ischemia efficacy

Journal of Applied Physiology ◽

10.1152/japplphysiol.01402.2005 ◽

2006 ◽

Vol 101 (1) ◽

pp. 256-263 ◽

Cited By ~ 75

Author(s):

Brian C. Clark ◽

Bo Fernhall ◽

Lori L. Ploutz-Snyder

Keyword(s):

Lower Limb ◽

Strength Loss ◽

Contractile Properties ◽

Plantar Flexor ◽

Postactivation Potentiation ◽

Flexor Muscle ◽

Muscle Properties ◽

Cross Sectional ◽

Lateral Gastrocnemius

Strength loss following disuse may result from alterations in muscle and/or neurological properties. In this paper, we report our findings on human plantar flexor muscle properties following 4 wk of limb suspension (unilateral lower limb suspension), along with the effect of applied ischemia (Isc) on these properties. In the companion paper (Part II), we report our findings on the changes in neurological properties. Measurements of voluntary and evoked forces, the compound muscle fiber action potential (CMAP), and muscle cross-sectional area (CSA) were collected before and after 4 wk of unilateral lower limb suspension in adults ( n = 18; 19–28 yr). A subset of subjects ( n = 6) received applications of Isc 3 days/wk (3 sets; 5-min duration). In the subjects not receiving Isc, the loss in CSA and strength was as expected (∼9 and 14%). We observed a 30% slowing in the duration of the CMAP, a 10% decrease in evoked doublet force, a 12% increase in the twitch-to-doublet force ratio, and an altered postactivation potentiation response (11% increase in the postactivation potentiation-to-doublet ratio). We also detected a 10% slowing in the ability of the plantar flexor to develop force during the initial phase of an evoked contraction, along with a 6% reduction in in vivo specific doublet force. In the Isc subjects, no preservation was observed in strength or the evoked muscle properties. However, the Isc group did maintain CSA of the lateral gastrocnemius, as the control subjects’ lateral gastrocnemius atrophied 10.2%, whereas the subjects receiving Isc atrophied 4.7%. Additionally, Isc abolished the unweighting-induced slowing in the CMAP. These findings suggest that unweighting alters the contractile properties involved in the excitation-contraction coupling processes and that Isc impacts the sarcolemma.

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Endurance time characteristics of human ankle dorsiflexors and plantarflexors

European Journal of Applied Physiology and Occupational Physiology ◽

10.1007/bf00854968 ◽

1995 ◽

Vol 71 (2-3) ◽

pp. 124-130 ◽

Cited By ~ 3

Author(s):

A. V. Shahidi ◽

P. A. Mathieu

Keyword(s):

Endurance Time ◽

Human Ankle ◽

Ankle Dorsiflexors

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Molecular Mechanisms of Muscle Tone Impairment under Conditions of Real and Simulated Space Flight

Acta Naturae ◽

10.32607/actanaturae.10953 ◽

2021 ◽

Vol 13 (2) ◽

pp. 85-97

Author(s):

Boris S. Shenkman ◽

Andrey K. Tsaturyan ◽

Ivan M. Vihlyantsev ◽

Inessa B. Kozlovskaya ◽

Anatoliy I. Grigoriev

Keyword(s):

Space Flight ◽

Molecular Mechanisms ◽

Simulated Microgravity ◽

Muscle Tone ◽

Muscle Stiffness ◽

Hindlimb Suspension ◽

Gravitational Unloading ◽

Muscle Stretch ◽

Intrinsic Muscle ◽

Intrinsic Stiffness

Kozlovskaya et al. [1] and Grigoriev et al. [2] showed that enormous loss of muscle stiffness (atonia) develops in humans under true (space flight) and simulated microgravity conditions as early as after the first days of exposure. This phenomenon is attributed to the inactivation of slow motor units and called reflectory atonia. However, a lot of evidence indicating that even isolated muscle or a single fiber possesses substantial stiffness was published at the end of the 20th century. This intrinsic stiffness is determined by the active component, i.e. the ability to form actin-myosin cross-bridges during muscle stretch and contraction, as well as by cytoskeletal and extracellular matrix proteins, capable of resisting muscle stretch. The main facts on intrinsic muscle stiffness under conditions of gravitational unloading are considered in this review. The data obtained in studies of humans under dry immersion and rodent hindlimb suspension is analyzed. The results and hypotheses regarding reduced probability of cross-bridge formation in an atrophying muscle due to increased interfilament spacing are described. The evidence of cytoskeletal protein (titin, nebulin, etc.) degradation during gravitational unloading is also discussed. The possible mechanisms underlying structural changes in skeletal muscle collagen and its role in reducing intrinsic muscle stiffness are presented. The molecular mechanisms of changes in intrinsic stiffness during space flight and simulated microgravity are reviewed.

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Self–Myofascial Release: No Improvement of Functional Outcomes in “Tight” Hamstrings

International Journal of Sports Physiology and Performance ◽

10.1123/ijspp.2015-0399 ◽

2016 ◽

Vol 11 (5) ◽

pp. 658-663 ◽

Cited By ~ 3

Author(s):

Robert W. Morton ◽

Sara Y. Oikawa ◽

Stuart M. Phillips ◽

Michaela C. Devries ◽

Cameron J. Mitchell

Keyword(s):

Maximum Voluntary Contraction ◽

Knee Extension ◽

Voluntary Contraction ◽

Muscle Stiffness ◽

Therapeutic Modality ◽

Myofascial Release ◽

Joint Range Of Motion ◽

Joint Range ◽

Torque Development

Purpose:Self–myofascial release (SMR) is a common exercise and therapeutic modality shown to induce acute improvements in joint range of motion (ROM) and recovery; however, no long-term studies have been conducted. Static stretching (SS) is the most common method used to increase joint ROM and decrease muscle stiffness. It was hypothesized that SMR paired with SS (SMR+SS) compared with SS alone over a 4-wk intervention would yield greater improvement in knee-extension ROM and hamstring stiffness.Methods:19 men (22 ± 3 y) with bilateral reduced hamstring ROM had each of their legs randomly assigned to either an SMR+SS or an SS-only group. The intervention consisted of 4 repetitions of SS each for 45 s or the identical amount of SS preceded by 4 repetitions of SMR each for 60 s and was performed on the respective leg twice daily for 4 wk. Passive ROM, hamstring stiffness, rate of torque development (RTD), and maximum voluntary contraction (MVC) were assessed pre- and postintervention.Results:Passive ROM (P < .001), RTD, and MVC (P < .05) all increased after the intervention. Hamstring stiffness toward end-ROM was reduced postintervention (P = .02). There were no differences between the intervention groups for any variable.Conclusion:The addition of SMR to SS did not enhance the efficacy of SS alone. SS increases joint ROM through a combination of decreased muscle stiffness and increased stretch tolerance.

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