FES Control of Isometric Forces in the Rat Hindlimb Using Many Muscles

2013 ◽  
Vol 60 (5) ◽  
pp. 1422-1430 ◽  
Author(s):  
A. M. Jarc ◽  
M. Berniker ◽  
M. C. Tresch
Keyword(s):  
Isometric Forces

The platelet strip. I. A low-fibrin contractile model of thrombin-activated platelets

1985 ◽  
Vol 249 (3) ◽  
pp. C279-C287 ◽  
Author(s):  
L. Salganicoff ◽  
M. H. Loughnane ◽  
R. W. Sevy ◽  
M. Russo
Keyword(s):  
Platelet Rich Plasma ◽  
Human Platelets ◽  
Pharmacological Agents ◽  
Nylon Mesh ◽  
Giant Platelet ◽  
Activated Platelets ◽  
Full Relaxation ◽  
Platelet Aggregate ◽  
Thrombin Activation ◽  
Isometric Forces

The ultrastructure and contractile behavior of a new preparation of thrombin-activated human platelets is described. The preparation is referred to as the "platelet strip" because of its similarities to classical vascular smooth muscle strips. The platelet strip consists of a giant platelet aggregate 10 mm long, 4 mm wide, and 200 micron thick. To facilitate handling, the aggregate has a special high-compliance nylon mesh embedded in its mass. Each strip contains 7.3 X 10(8) platelets. Fibrin contamination is 150-fold lower than in platelet-rich plasma clots. Active isometric forces of up to 100 g/cm2 and 6-10 h viability are easily and reproducibly obtained. Platelet strips remain contracted after thrombin activation. The contraction is tonic and partial. Further small increases in force can be produced by depolarizing solutions or pharmacological agents, e.g., ADP, epinephrine, and endoperoxide analogues. These small increases are reversible on washout of the agents. Full relaxation is induced by agents such as prostaglandin E1 or papaverine, which increase adenosine 3',5'-cyclic monophosphate. However, after washout of these agents, recovery of tension is variable depending on the concentration of the drug and the degree of prestretching of the preparation.

scholarly journals Uptake of modified low-density lipoproteins alters actin distribution and locomotor forces in macrophages

2003 ◽  
Vol 284 (2) ◽  
pp. C555-C561 ◽  
Author(s):  
Celina V. Zerbinatti ◽  
Robert W. Gore
Keyword(s):  
Foam Cells ◽  
Force Transducer ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Force Frequency ◽  
Modified Low Density Lipoproteins ◽  
Generating Capacity ◽  
Induced Changes ◽  
Isometric Forces ◽  
Modified Forms

It is postulated that macrophage-derived foam cells accumulate in the arterial wall because they lose the ability to migrate after excessive ingestion of modified forms of low-density lipoproteins (LDL). To assess changes in locomotor force generating capacity of foam cells, we measured isometric forces in J774A.1 macrophages after cholesterol loading with oxidized (Ox-LDL) or aggregated (Agg-LDL) LDL using a novel magnetic force transducer. Ox-LDL loading reduced the ability of J774A.1 macrophages to generate isometric forces by 50% relative to control cells. Changes in force frequency consistent with reduced motility were detected as well. Agg-LDL loading was also detrimental to J774A.1 motility but to a lesser extent than Ox-LDL. Ox-LDL loading significantly reduced total actin levels and induced changes in the F-actin to G-actin distribution, whereas Agg-LDL loaded cells had significantly increased levels of total actin. These data provide evidence that cholesterol loading and subsequent accumulation decreases macrophage motility by reducing the cells' force generating capacity and that Ox-LDL appears to be more effective than Agg-LDL in disrupting the locomotor machinery.

scholarly journals Force enhancement after stretch of isolated myofibrils is increased by sarcomere length non-uniformities

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ricarda M. Haeger ◽  
Dilson E. Rassier
Keyword(s):  
Steady State ◽  
Sarcomere Length ◽  
Isometric Force ◽  
Force Production ◽  
Force Enhancement ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
State Force ◽  
Isometric Forces

AbstractWhen a muscle is stretched during a contraction, the resulting steady-state force is higher than the isometric force produced at a comparable sarcomere length. This phenomenon, also referred to as residual force enhancement, cannot be readily explained by the force-sarcomere length relation. One of the most accepted mechanisms for the residual force enhancement is the development of sarcomere length non-uniformities after an active stretch. The aim of this study was to directly investigate the effect of non-uniformities on the force-producing capabilities of isolated myofibrils after they are actively stretched. We evaluated the effect of depleting a single A-band on sarcomere length non-uniformity and residual force enhancement. We observed that sarcomere length non-uniformity was effectively increased following A-band depletion. Furthermore, isometric forces decreased, while the percent residual force enhancement increased compared to intact myofibrils (5% vs. 20%). We conclude that sarcomere length non-uniformities are partially responsible for the enhanced force production after stretch.

Systematic Changes in Directional Tuning of Motor Cortex Cell Activity With Hand Location in the Workspace During Generation of Static Isometric Forces in Constant Spatial Directions

1997 ◽  
Vol 78 (2) ◽  
pp. 1170-1174 ◽  
Author(s):  
Lauren E. Sergio ◽  
John F. Kalaska
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Discharge Rate ◽  
Cell Activity ◽  
Force Production ◽  
Static Force ◽  
Force Output ◽  
Directional Tuning ◽  
Cortex Cell ◽  
Isometric Forces

Sergio, Lauren E. and John F. Kalaska. Systematic changes in directional tuning of motor cortex cell activity with hand location in the workspace during generation of static isometric forces in constant spatial directions. J. Neurophysiol. 78: 1170–1174, 1997. We examined the activity of 46 proximal-arm-related cells in the primary motor cortex (MI) during a task in which a monkey uses the arm to exert isometric forces at the hand in constant spatial directions while the hand is in one of nine different spatial locations on a plane. The discharge rate of all 46 cells was significantly affected by both hand location and by the direction of static force during the final static-force phase of the task. In addition, all cells showed a significant interaction between force direction and hand location. That is, there was a significant modulation in the relationship between cell activity and the direction of exerted force as a function of hand location. For many cells, this modulation was expressed in part as a systematic arclike shift in the cell's directional tuning at the different hand locations, even though the direction of static force output at the hand remained constant. These effects of hand location in the workspace indicate that the discharge of single MI cells does not covary exclusively with the level and direction of force output at the hand. Sixteen proximal-arm-related muscles showed similar effects in the task, reflecting their dependence on various mechanical factors that varied with hand location. The parallel changes found for both MI cell activity and muscle activity for static force production at different hand locations are further evidence that MI contributes to the transformation between extrinsic and intrinsic representations of limb movement.

scholarly journals Validity and Reliability of Isometric-Bench for Knee Isometric Assessment

2020 ◽  
Vol 17 (12) ◽  
pp. 4326
Author(s):  
Johnny Padulo ◽  
Nebojša Trajković ◽  
Drazen Cular ◽  
Zoran Grgantov ◽  
Dejan M. Madić ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Concurrent Validity ◽  
High Reliability ◽  
Low Cost ◽  
Isometric Strength ◽  
Systematic Bias ◽  
Validity And Reliability ◽  
Isokinetic Dynamometer ◽  
Isometric Forces ◽  
Flexion And Extension

There is a strong need for a new, probably cheaper, smaller, and more portable isometric dynamometer. With this aim, we investigated the concurrent validity and reliability of a low-cost portable dynamometer to measure the isometric strength of the lower limb. Seventeen young participants (age 16.47 ± 0.51 years) were randomly assessed on three different days for knee flexion and extension isometric forces with two different devices: a commonly used isokinetic dynamometer (ISOC) and a portable isometric dynamometer prototype (ISOM). No significant differences were observed between the ISOC and the ISOM (all comparisons p > 0.05). Test–retest comparison showed the ISOM to have high reliability (ICC 0.879–0.990). This study showed that measurements with the ISOM could be performed without systematic bias and with high reliability. The ISOM is a device that is able to assess knee isometric strength with excellent concurrent validity and reliability.

scholarly journals Motor Cortex Neural Correlates of Output Kinematics and Kinetics During Isometric-Force and Arm-Reaching Tasks

2005 ◽  
Vol 94 (4) ◽  
pp. 2353-2378 ◽  
Author(s):  
Lauren E. Sergio ◽  
Catherine Hamel-Pâquet ◽  
John F. Kalaska
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Isometric Force ◽  
Arm Movements ◽  
Population Level ◽  
Emg Activity ◽  
Hand Motion ◽  
Arm Reaching ◽  
Direction Of Movement ◽  
Isometric Forces

We recorded the activity of 132 proximal-arm-related neurons in caudal primary motor cortex (M1) of two monkeys while they generated either isometric forces against a rigid handle or arm movements with a heavy movable handle, in the same eight directions in a horizontal plane. The isometric forces increased in monotonic fashion in the direction of the force target. The forces exerted against the handle in the movement task were more complex, including an initial accelerating force in the direction of movement followed by a transient decelerating force opposite to the direction of movement as the hand approached the target. EMG activity of proximal-arm muscles reflected the difference in task dynamics, showing directional ramplike activity changes in the isometric task and reciprocally tuned “triphasic” patterns in the movement task. The apparent instantaneous directionality of muscle activity, when expressed in hand-centered spatial coordinates, remained relatively stable during the isometric ramps but often showed a large transient shift during deceleration of the arm movements. Single-neuron and population-level activity in M1 showed similar task-dependent changes in temporal pattern and instantaneous directionality. The momentary dissociation of the directionality of neuronal discharge and movement kinematics during deceleration indicated that the activity of many arm-related M1 neurons is not coupled only to the direction and speed of hand motion. These results also demonstrate that population-level signals reflecting the dynamics of motor tasks and of interactions with objects in the environment are available in caudal M1. This task-dynamics signal could greatly enhance the performance capabilities of neuroprosthetic controllers.

The strength of the corticospinal coherence depends on the predictability of modulated isometric forces

2013 ◽  
Vol 109 (6) ◽  
pp. 1579-1588 ◽  
Author(s):  
Ignacio Mendez-Balbuena ◽  
Jose Raul Naranjo ◽  
Xi Wang ◽  
Agnieska Andrykiewicz ◽  
Frank Huethe ◽  
...  
Keyword(s):  
Sensory Feedback ◽  
Muscle Activation ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Visuomotor Task ◽  
Gamma Range ◽  
Cortical Motor ◽  
Contralateral Hand ◽  
Hand Motor Area ◽  
Isometric Forces

Isometric compensation of predictably frequency-modulated low forces is associated with corticomuscular coherence (CMC) in beta and low gamma range. It remains unclear how the CMC is influenced by unpredictably modulated forces, which create a mismatch between expected and actual sensory feedback. We recorded electroencephalography from the contralateral hand motor area, electromyography (EMG), and the motor performance of 16 subjects during a visuomotor task in which they had to isometrically compensate target forces at 8% of the maximum voluntary contraction with their right index finger. The modulated forces were presented with predictable or unpredictable frequencies. We calculated the CMC, the cortical motor alpha-, beta-, and gamma-range spectral powers (SP), and the task-related desynchronization (TRD), as well as the EMG SP and the performance. We found that in the unpredictable condition the CMC was significantly lower and associated with lower cortical motor SP, stronger TRD, higher EMG SP, and worse performance. The findings suggest that due to the mismatch between predicted and actual sensory feedback leading to higher computational load and less stationary motor state, the unpredictable modulation of the force leads to a decrease in corticospinal synchrony, an increase in cortical and muscle activation, and a worse performance.

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