scholarly journals Dynamics of Primate Oculomotor Plant Revealed by Effects of Abducens Microstimulation

2009 ◽  
Vol 101 (6) ◽  
pp. 2907-2923 ◽  
Author(s):  
Sean R. Anderson ◽  
John Porrill ◽  
Sokratis Sklavos ◽  
Neeraj J. Gandhi ◽  
David L. Sparks ◽  
...  
Keyword(s):  
Steady State ◽  
Muscle Activation ◽  
Isometric Force ◽  
Force Production ◽  
Rectus Muscle ◽  
Linear Component ◽  
Abducens Nucleus ◽  
In Series ◽  
Tension Increase ◽  
Movement Parameters

Despite their importance for deciphering oculomotor commands, the mechanics of the extraocular muscles and orbital tissues (oculomotor plant) are poorly understood. In particular, the significance of plant nonlinearities is uncertain. Here primate plant dynamics were investigated by measuring the eye movements produced by stimulating the abducens nucleus with brief pulse trains of varying frequency. Statistical analysis of these movements indicated that the effects of stimulation lasted about 40 ms after the final pulse, after which the eye returned passively toward its position before stimulation. Behavior during the passive phase could be approximated by a linear plant model, corresponding to Voigt elements in series, with properties independent of initial eye position. In contrast, behavior during the stimulation phase revealed a sigmoidal relation between stimulation frequency and estimated steady-state tetanic tension, together with a frequency-dependent rate of tension increase, that appeared very similar to the nonlinearities previously found for isometric-force production in primate lateral rectus muscle. These results suggest that the dynamics of the oculomotor plant have an approximately linear component related to steady-state viscoelasticity and a nonlinear component related to changes in muscle activation. The latter may in part account for the nonlinear relations observed between eye-movement parameters and single-unit firing patterns in the abducens nucleus. These findings point to the importance of recruitment as a simplifying factor for motor control with nonlinear plants.

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.

Activation heat and latency relaxation in relation to calcium movement in skeletal and cardiac muscle

1982 ◽  
Vol 60 (4) ◽  
pp. 529-541 ◽  
Author(s):  
Louis A. Mulieri ◽  
Norman R. Alpert
Keyword(s):  
Skeletal Muscle ◽  
Refractory Period ◽  
Muscle Activation ◽  
Slow Component ◽  
Isometric Force ◽  
Fast Component ◽  
Bathing Solution ◽  
Latency Relaxation ◽  
In Series ◽  
Activation Heat

Measurements of activation heat, initial heat, twitch tension, and latency relaxation were made using thin-layer, vacuum-deposited thermopiles and isometric force transducers, respectively. Experiments were performed on frog skeletal muscle fiber bundles and on rabbit right ventricular papillary muscles at 0, 15, and 21 °C in normal and 1.75× to 2.5× mannitol hyperosmotic bathing solutions. In skeletal muscle, activation heat, obtained by stretching to zero overlap, was only slightly affected by 1.75× hyperosmotic solution and consisted of a fast and a slow component. Both components have a refractory period and a relatively refractory period which can be demonstrated by double pulse stimulation. The twitch potentiators Zn2+ and caffeine increase the total activation heat and the magnitude and rate of the fast component. The temporal relation between the latency relaxation and activation heat is demonstrated. The latency relaxation is independent of the number of sarcomeres in series in a muscle. Activation heat and latency relaxation records from heart muscle are obtained in 2.5× hyperosmotic bathing solution. A model of excitation–contraction coupling is presented which indicates that (1) the downstroke of the latency relaxation monitors the functioning of the Ca2+ -permeability or debinding mechanism in the terminal cisternae, (2) the fast component of activation heat monitors the amount of Ca2+ bound to troponin C, and (3) the total amplitude of activation heat is a measure of the total quantity of Ca2+ cycled in a twitch.

The length dependency of maximum force development in rat medial gastrocnemius muscle in situ

2008 ◽  
Vol 33 (3) ◽  
pp. 518-526 ◽  
Author(s):  
Cornelis J. de Ruiter ◽  
Tinelies E. Busé-Pot ◽  
Arnold de Haan
Keyword(s):  
Muscle Activation ◽  
Isometric Force ◽  
Force Production ◽  
Time History ◽  
Medial Gastrocnemius ◽  
Force Output ◽  
Force Development ◽  
Activation Times ◽  
Maximal Isometric Force

During many movements (e.g., running, jumping, and kicking) there is little time for skeletal muscles to build up force, thus rapid force development is important. The length dependency of isometric force development was investigated in maximally activated rat medial gastrocnemius muscles in situ with intact blood flow at 35 °C. Depending on time available for muscle activation, the length dependency of force development was expected to differ from that of the maximal isometric force (Fmax) reached much later during the contraction. During isometric force development in intact muscle–tendon preparations, the contractile elements actually shortened. Therefore, similar to previous findings on shortening contractions, it was hypothesized that maximal rate of force development (MRFD) would be obtained at a length below the optimum (Lo) for maximal isometric force production. To measure the effect of the entire time history of activation, force time integrals (FTIs) for different activation times (10–50 ms) were also calculated. The highest MRFD was obtained 1.94 ± 0.42 mm below (p < 0.05) Lo. When expressed relative to Fmax obtained at each individual length, the optimum was found at Lo – 4.4 mm. For FTI 10 ms and FTI 20 ms, optimum length was obtained at ~2 and 1 mm above (p < 0.05) Lo, respectively, whereas the optima for FTI 30, 40, and 50 ms were ~1 mm below (p < 0.05) Lo. In addition, at short lengths (< Lo – 4 mm) and for all activation times FTIs were relatively more decreased than Fmax. In conclusion, length dependency of force output during rapid force development differed from that of maximal isometric force; specifically, MRFD was obtained 2 mm below Lo.

scholarly journals Force production and muscle activation during partial vs. full range of motion in Paralympic Powerlifting

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0257810
Author(s):  
Tanise Pires Mendonça ◽  
Felipe José Aidar ◽  
Dihogo Gama Matos ◽  
Raphael Fabrício Souza ◽  
Anderson Carlos Marçal ◽  
...  
Keyword(s):  
Range Of Motion ◽  
Muscle Activation ◽  
Isometric Force ◽  
Full Range ◽  
Pectoralis Major Muscle ◽  
National Level ◽  
Force Production ◽  
Muscle Thickness ◽  
Pectoralis Major ◽  
Post Exercise

Paralympic Powerlifting is a sport in which the strength of the upper limbs is assessed through bench press performance in an adapted specific bench. It is therefore essential to optimize training methods to maximize this performance. The aim of the present study was to compare force production and muscle activation involved in partial vs. full range of motion (ROM) training in Paralympic Powerlifting. Twelve male athletes of elite national level in Paralympic Powerlifting participated in the study (28.60 ± 7.60 years of age, 71.80 ± 17.90 kg of body mass). The athletes performed five sets of 5RM (repetition maximum), either with 90% of 1RM in full ROM or with a load of 130% 1RM in partial ROM. All subjects underwent both exercise conditions in consecutive weeks. Order assignment in the first week was random and counterbalanced. Fatigue index (FI), Maximum Isometric Force (MIF), Time to MIF (Time) and rate of force development (RFD) were determined by a force sensor. Muscle thickness was obtained using ultrasound images. All measures were taken pre- and post-training. Additionally, electromyographic signal (EMG) was evaluated in the last set of each exercise condition. Post-exercise fatigue was higher with full ROM as well as loss of MIF. Full ROM also induced greater. EMG showed greater activation of the Clavicular portion and Sternal portion of pectoralis major muscle and lower in the anterior portion of deltoid muscle when full ROM was performed. Muscle thickness of the pectoralis major muscle increased post-exercise. We concluded that training with partial ROM enables higher workloads with lower loss of muscle function.

Work-dependent deactivation of a crustacean muscle

1999 ◽  
Vol 202 (18) ◽  
pp. 2551-2565 ◽  
Author(s):  
R.K. Josephson ◽  
D.R. Stokes
Keyword(s):  
Muscle Activation ◽  
Isometric Force ◽  
Carcinus Maenas ◽  
Stimulus Frequency ◽  
Force Production ◽  
Muscle Length ◽  
Background Level ◽  
Shortening Velocity ◽  
Shortening Deactivation ◽  
Work Done

Active shortening of respiratory muscle L2B from the crab Carcinus maenas results in contractile deactivation, seen as (1) a decline of force during the course of isovelocity shortening, (2) a reduction in the rate of force redevelopment following shortening, (3) a depression of the level of isometric force reached following shortening, and (4) an accelerated relaxation at the end of stimulation. The degree of deactivation increases with increasing distance of shortening, decreases with increasing shortening velocity, and is approximately linearly related to the work done during shortening. Deactivation lasts many seconds if stimulation is maintained, but is largely although not completely removed if the stimulation is temporarily interrupted so that the force drops towards the resting level. Deactivation for a given distance and velocity of shortening increases with increasing muscle length above the optimum length for force production. Stimulating muscle L2B at suboptimal frequencies gives tetanic contractions that are fully fused but of less than maximal amplitude. The depression of force following shortening, relative to the force during an isometric contraction, is independent of the stimulus frequency used to activate the muscle, indicating that deactivation is not a function of the background level of stimulus-controlled muscle activation upon which it occurs. Deactivation reduces the work required to restretch a muscle after it has shortened, but it also lowers the force and therefore the work done during shortening. The net effect of deactivation on work output over a full shortening/lengthening cycle is unknown.

A Comparison of Ballistic-Movement and Ballistic-Intent Training on Muscle Strength and Activation

2007 ◽  
Vol 2 (4) ◽  
pp. 386-399 ◽  
Author(s):  
Nicole A. Dinn ◽  
David G. Behm
Keyword(s):  
Reaction Time ◽  
Muscle Activation ◽  
Isometric Force ◽  
Movement Time ◽  
Force Production ◽  
Training Group ◽  
Pectoralis Major ◽  
Ballistic Movement ◽  
Ctrl Group ◽  
Elastic Resistance

Purpose:Studies have both supported and refuted the concept that it is the intent to perform ballistic contractions that determines velocity-specific gains in resistance training. The purpose of this investigation was to determine whether ballistic intent is as effective as ballistic movement in improving muscle activation, force, movement time, and reaction time.Methods:Subjects completed 8 wk of punch training. A dynamic (DYN) group trained with elastic resistance bands, and the isometric (ISO) group trained with an unyielding strap. A control (CTRL) group was also tested. Pretesting and posttesting measures included isometric force; electromyography (EMG) of triceps, biceps, pectoralis major, and latissimus dorsi; movement and reaction time of both arms; and a quick-hands test of coordination.Results:Triceps iEMG increased by 63% in the ISO group (P = .03). Pectoralis major iEMG increased by 65% in the DYN group (P = .007). Movement time decreased 17.6% in the DYN training group (P = .001). Isometric force did not improve in either training group or in the CTRL group.Conclusions:Because of its specificity of movement, dynamic training might be a more appropriate method to improve punching speed for martial artists and boxers. The intent to contract explosively over a short duration does not appear to be beneficial in increasing force production or speed of movement in punching.

Mysteries of Muscle Contraction

2008 ◽  
Vol 24 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Walter Herzog ◽  
Timothy R. Leonard ◽  
Venus Joumaa ◽  
Ashi Mehta
Keyword(s):  
Steady State ◽  
Experimental Evidence ◽  
Active Component ◽  
Isometric Force ◽  
Force Production ◽  
Myosin Filament ◽  
Passive Component ◽  
Cross Bridge ◽  
The Cross ◽  
State Force

According to the cross-bridge theory, the steady-state isometric force of a muscle is given by the amount of actin–myosin filament overlap. However, it has been known for more than half a century that steady-state forces depend crucially on contractile history. Here, we examine history-dependent steady-state force production in view of the cross-bridge theory, available experimental evidence, and existing explanations for this phenomenon. This is done on various structural levels, ranging from the intact muscle to the myofibrillar and isolated contractile protein level, so that advantages and limitations of the various preparations can be fully exploited and overcome. Based on experimental evidence, we conclude that steady-state force following active muscle stretching is enhanced, and this enhancement has a passive and an active component. The active component is associated with the cross-bridge kinetics, and the passive component is associated with a calcium-dependent increase in titin stiffness.

Observations on force enhancement in submaximal voluntary contractions of human adductor pollicis muscle

2005 ◽  
Vol 98 (6) ◽  
pp. 2087-2095 ◽  
Author(s):  
Ali E. Oskouei ◽  
Walter Herzog
Keyword(s):  
Steady State ◽  
Muscle Activation ◽  
Isometric Force ◽  
Fiber Type ◽  
Voluntary Contraction ◽  
Adductor Pollicis ◽  
Postactivation Potentiation ◽  
Force Enhancement ◽  
Adductor Pollicis Muscle ◽  
Voluntary Contractions

It has been observed consistently and is well accepted that the steady-state isometric force after active muscle stretch is greater than the corresponding isometric force for electrically stimulated muscles and maximal voluntary contractions. However, this so-called force enhancement has not been studied for submaximal voluntary efforts; therefore, it is not known whether this property affects everyday movements. The purpose of this study was to determine whether there was force enhancement during submaximal voluntary contractions. Human adductor pollicis muscles ( n = 17) were studied using a custom-built dynamometer, and both force and activation were measured while muscle activation and force were controlled at a level of 30% of maximal voluntary contraction. The steady-state isometric force and activation after active stretch were compared with the corresponding values obtained during isometric reference contractions. There was consistent and reliable force enhancement in 8 of the 17 subjects, whereas there was no force enhancement in the remaining subjects. Subjects with force enhancement had greater postactivation potentiation and a smaller resistance to fatigue in the adductor pollicis. We conclude from these results that force enhancement exists during submaximal voluntary contractions in a subset of the populations and suggest that it may affect everyday voluntary movements in this subset. On the basis of follow-up testing, it appears that force enhancement during voluntary contractions is linked to potentiation and fatigue resistance and therefore possibly to the fiber-type distribution in the adductor pollicis muscle.

scholarly journals Sensorimotor Impairments and Reaching Performance in Subjects With Poststroke Hemiparesis During the First Few Months of Recovery

2007 ◽  
Vol 87 (6) ◽  
pp. 751-765 ◽  
Author(s):  
Joanne M Wagner ◽  
Catherine E Lang ◽  
Shirley A Sahrmann ◽  
Dorothy F Edwards ◽  
Alexander W Dromerick
Keyword(s):  
Upper Extremity ◽  
Acute Phase ◽  
Muscle Activation ◽  
Isometric Force ◽  
Force Production ◽  
Subacute Phase ◽  
Healthy Control ◽  
Sensorimotor Impairment ◽  
Isometric Force Production ◽  
Speed Accuracy

Background and Purpose Little is known about the relationship between upper-extremity (UE) sensorimotor impairment and reaching performance during the first few months after stroke. The purpose of this study was to examine: (1) how measures of UE sensorimotor impairment are related to the speed, accuracy, and efficiency of reaching in subjects with hemiparesis during the subacute phase after stroke and (2) how impairments measured during the acute phase after stroke may predict the variance in reaching performance a few months later. Subjects and Methods Upper-extremity sensorimotor impairments and reaching performance were evaluated in 39 subjects with hemiparesis at 2 time points: during the acute phase (8.7±3.6 [X̅±SD] days) and the subacute phase (108.7±16.5 days) after stroke. Ten subjects who were healthy (control subjects) were evaluated once. Regression analyses were used to determine which impairments were the best predictors of variance in reaching performance in the subacute phase after stroke. Results Only a small amount of variance (&lt;30%) in reaching performance was explained at the subacute time point, using either acute or subacute impairments as predictor variables. Of the impairments measured, UE strength deficits were the strongest, most consistent predictors of the variance in reaching performance during the first 3 months after stroke. Discussion and Conclusion Surprisingly, the detailed clinical assessment of UE sensorimotor impairment, measured at the acute or subacute phase after stroke, did not explain much of the variance in reaching performance during the subacute phase after stroke. The findings that UE strength deficits (ie, decreased active range of motion and isometric force production) were the most common predictors of the variance in reaching performance during the first 3 months after stroke are consistent with the current viewpoint that impaired volitional muscle activation, clinically apparent as UE weakness, is a prominent contributing factor to UE dysfunction after stroke.

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