A Comparison of Medial Versus Lateral Hamstring Electromyographic Activity and Force Output During Isometric Contractions

1992 ◽  
Vol 2 (2) ◽  
pp. 47-55 ◽  
Author(s):  
Ira M. Fiebert ◽  
Jeannie M. Haas ◽  
Karen J. Dworkin ◽  
William G. LeBlanc
Keyword(s):  
Isometric Contractions ◽  
Electromyographic Activity ◽  
Force Output

scholarly journals Effects of different vibration frequencies, amplitudes and contraction levels on lower limb muscles during graded isometric contractions superimposed on whole body vibration stimulation

2019 ◽  
Vol 6 ◽  
pp. 205566831982746 ◽  
Author(s):  
Amit N Pujari ◽  
Richard D Neilson ◽  
Marco Cardinale
Keyword(s):  
Isometric Contraction ◽  
Vastus Lateralis ◽  
Whole Body Vibration ◽  
Biceps Femoris ◽  
Whole Body ◽  
Isometric Contractions ◽  
Electromyographic Activity ◽  
Mean Square ◽  
Body Vibration ◽  
Neuromuscular Activity

Background Indirect vibration stimulation, i.e., whole body vibration or upper limb vibration, has been investigated increasingly as an exercise intervention for rehabilitation applications. However, there is a lack of evidence regarding the effects of graded isometric contractions superimposed on whole body vibration stimulation. Hence, the objective of this study was to quantify and analyse the effects of variations in the vibration parameters and contraction levels on the neuromuscular responses to isometric exercise superimposed on whole body vibration stimulation. Methods In this study, we assessed the ‘neuromuscular effects’ of graded isometric contractions, of 20%, 40%, 60%, 80% and 100% of maximum voluntary contraction, superimposed on whole body vibration stimulation (V) and control (C), i.e., no-vibration in 12 healthy volunteers. Vibration stimuli tested were 30 Hz and 50 Hz frequencies and 0.5 mm and 1.5 mm amplitude. Surface electromyographic activity of the vastus lateralis, vastus medialis and biceps femoris were measured during V and C conditions with electromyographic root mean square and electromyographic mean frequency values used to quantify muscle activity and their fatigue levels, respectively. Results Both the prime mover (vastus lateralis) and the antagonist (biceps femoris) displayed significantly higher (P < 0.05) electromyographic activity with the V than the C condition with varying percentage increases in EMG root-mean-square (EMGrms) values ranging from 20% to 200%. For both the vastus lateralis and biceps femoris, the increase in mean EMGrms values depended on the frequency, amplitude and muscle contraction level with 50 Hz–0.5 mm stimulation inducing the largest neuromuscular activity. Conclusions These results show that the isometric contraction superimposed on vibration stimulation leads to higher neuromuscular activity compared to isometric contraction alone in the lower limbs. The combination of the vibration frequency with the amplitude and the muscle tension together grades the final neuromuscular output.

Activity of spindle afferents from cat anterior thigh muscles. II. Effects of fusimotor blockade

1985 ◽  
Vol 54 (3) ◽  
pp. 565-577 ◽  
Author(s):  
G. E. Loeb ◽  
J. A. Hoffer
Keyword(s):  
Stance Phase ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Muscle Spindles ◽  
Swing Phase ◽  
Knee Extensors ◽  
Electromyographic Activity ◽  
Force Output ◽  
Anterior Thigh ◽  
Proprioceptive Signal

Chronically implanted electrodes and nerve cuff catheters were used to record the activity of individual muscle spindle afferents during treadmill walking as low doses of lidocaine were infused around the femoral nerve to progressively block gamma motoneuron activity. Both primary and secondary endings from both the monarticular knee extensors and the biarticular hip/knee muscles of the anterior thigh showed large decreases in afferent activity, usually well before changes in the electromyographic activity, force output, or length and velocity were seen in the parent muscles. This decline in the proprioceptive signal feeding back onto the spinal cord, which we presume to have involved most of the spindles supplied by the femoral nerve, did not cause noticeable irregularities or instability of the walking gait. At the peak of the fusimotor blockade, spindle afferents from knee extensor muscles lost about half of their usually brisk activity during the near-isometric contraction of the stance phase. Significant decreases in the response to passive stretch during the flexion phase also occurred. At the peak of the fusimotor blockade, spindle afferents from the biarticular muscles lost all of their activity during the rapidly shortening swing phase and about half of their activity during the rapidly lengthening stance phase. For both monarticular and biarticular muscle spindles, the activity decreases in stance and swing phase often occurred at distinctly different stages of the progressive fusimotor blockade, indicating several different sources of fusimotor control. From these data, we infer that the sensitivity of most spindle afferents is substantially influenced by fusimotor activity during phases of both extrafusal activity and extrafusal silence. At least some of this influence appears to come from fusimotor neurons whose recruitment is independent of the extrafusal recruitment. The extent and type of fusimotor effects on spindle afferent sensitivity (dynamic or static) appear to be specialized for the mechanical events that tend to occur during those phases.

Electromyography of Superficial and Deep Neck Muscles During Isometric, Voluntary, and Reflex Contractions

2006 ◽  
Vol 129 (1) ◽  
pp. 66-77 ◽  
Author(s):  
Gunter P. Siegmund ◽  
Jean-Sébastien Blouin ◽  
John R. Brault ◽  
Sofia Hedenstierna ◽  
J. Timothy Inglis
Keyword(s):  
Neck Muscles ◽  
Head Movements ◽  
Isometric Contractions ◽  
Data Sets ◽  
Electromyographic Activity ◽  
Complex Data ◽  
Force Direction ◽  
Complex Data Sets ◽  
Splenius Capitis ◽  
Muscle Activations

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45deg intervals) from the neutral posture; (ii) 50N isometric contractions with a slow sweep of the force direction through 720deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular–kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models’ muscle geometry, physiology, and feedforward/feedback neuromechanics.

scholarly journals Sources of Signal-Dependent Noise During Isometric Force Production

2002 ◽  
Vol 88 (3) ◽  
pp. 1533-1544 ◽  
Author(s):  
Kelvin E. Jones ◽  
Antonia F. de C. Hamilton ◽  
Daniel M. Wolpert
Keyword(s):  
Motor Unit ◽  
Isometric Force ◽  
Force Production ◽  
Motor Command ◽  
Force Variability ◽  
Isometric Contractions ◽  
Linear Scaling ◽  
Force Output ◽  
Extensor Pollicis Longus ◽  
Isometric Force Production

It has been proposed that the invariant kinematics observed during goal-directed movements result from reducing the consequences of signal-dependent noise (SDN) on motor output. The purpose of this study was to investigate the presence of SDN during isometric force production and determine how central and peripheral components contribute to this feature of motor control. Peripheral and central components were distinguished experimentally by comparing voluntary contractions to those elicited by electrical stimulation of the extensor pollicis longus muscle. To determine other factors of motor-unit physiology that may contribute to SDN, a model was constructed and its output compared with the empirical data. SDN was evident in voluntary isometric contractions as a linear scaling of force variability (SD) with respect to the mean force level. However, during electrically stimulated contractions to the same force levels, the variability remained constant over the same range of mean forces. When the subjects were asked to combine voluntary with stimulation-induced contractions, the linear scaling relationship between the SD and mean force returned. The modeling results highlight that much of the basic physiological organization of the motor-unit pool, such as range of twitch amplitudes and range of recruitment thresholds, biases force output to exhibit linearly scaled SDN. This is in contrast to the square root scaling of variability with mean force present in any individual motor-unit of the pool. Orderly recruitment by twitch amplitude was a necessary condition for producing linearly scaled SDN. Surprisingly, the scaling of SDN was independent of the variability of motoneuron firing and therefore by inference, independent of presynaptic noise in the motor command. We conclude that the linear scaling of SDN during voluntary isometric contractions is a natural by-product of the organization of the motor-unit pool that does not depend on signal-dependent noise in the motor command. Synaptic noise in the motor command and common drive, which give rise to the variability and synchronization of motoneuron spiking, determine the magnitude of the force variability at a given level of mean force output.

Fatigue responses of human triceps surae muscles during repetitive maximal isometric contractions

2000 ◽  
Vol 88 (6) ◽  
pp. 1969-1975 ◽  
Author(s):  
Yasuo Kawakami ◽  
Kenji Amemiya ◽  
Hiroaki Kanehisa ◽  
Shigeki Ikegawa ◽  
Tetsuo Fukunaga
Keyword(s):  
Plantar Flexion ◽  
Triceps Surae ◽  
Peripheral Fatigue ◽  
Isometric Contractions ◽  
Electromyographic Activity ◽  
Full Extension ◽  
Flexor Muscles ◽  
Human Triceps Surae ◽  
Triceps Surae Muscles ◽  
Plantar Flexor Muscles

Nine healthy men (22–45 yr) completed 100 repetitive maximal isometric contractions of the ankle plantar flexor muscles in two knee positions of full extension (K0) and flexion at 90° (K90), positions that varied the contribution of the gastrocnemii. Electromyographic activity was recorded from the medial and lateral gastrocnemii and soleus muscles by using surface electrodes. Plantar flexion torque in K0 was greater and decreased more rapidly than in K90. The electromyographic amplitude decreased over time, and there were no significant differences between muscles and knee joint positions. The level of voluntary effort, assessed by a supramaximal electrical stimulation during every 10th contraction, decreased from 96 to 70% ( P < 0.05) with no difference between K0 and K90. It was suggested that a decrease in plantar flexion torque was attributable to both central and peripheral fatigue and that greater fatigability in K0 than in K90 would result from a greater contribution and hence more pronounced fatigue of the gastrocnemius muscle. Further support for this possibility was provided from changes in twitch torque.

scholarly journals Speed-Dependent Reductions of Force Output in People With Poststroke Hemiparesis

1999 ◽  
Vol 79 (10) ◽  
pp. 919-930 ◽  
Author(s):  
David A Brown ◽  
Steven A Kautz
Keyword(s):  
Lower Extremity ◽  
Muscle Activity ◽  
Mechanical Work ◽  
Elderly Subjects ◽  
Electromyographic Activity ◽  
Vastus Medialis ◽  
Force Output ◽  
Paretic Side ◽  
Vastus Medialis Muscle ◽  
Work Done

Abstract Background and Purpose. Movement is slow in people with poststroke hemiparesis. Moving at faster speeds is thought by some researchers to exacerbate of abnormal or unwanted muscle activity. The purpose of this study was to quantify the effects of increased speed on motor performance during pedaling exercise in people with poststroke hemiparesis. Subjects. Twelve elderly subjects with no known neurological impairment and 15 subjects with poststroke hemiparesis of greater than 6 months' duration were tested. Methods. Subjects pedaled at 12 randomly ordered workload and cadence combinations (45-, 90-, 135-, and 180-J workloads at 25, 40, and 55 rpm). Pedal reaction forces were used to calculate work done by each lower extremity. Electromyographic activity was recorded from 7 lower-extremity muscles. Results. The main finding was that net mechanical work done by the paretic lower extremity decreased as speed increased in all subjects. The occurrence of inappropriate muscle activity on the paretic side, however, was not exacerbated in that the vastus medialis muscle on the paretic side did not show a consistent further increase in its prolonged activity at higher speeds. The mechanics of faster pedaling resulted in greater net negative mechanical work because, at higher pedaling rates, the prolonged vastus medialis muscle activity is present during a greater portion of the cycle. Conclusion and Discussion. The lessened force output by the paretic limb is mainly the result of the inherent mechanical demands of higher-speed pedaling and not due to exacerbation of impaired neural control.

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