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At least 19 recordsLinked to original sources

PubMed1992

Strength after bouts of eccentric or concentric actions.

This study examined the influence of an initial bout of eccentric or concentric actions and a subsequent bout of eccentric actions on muscular strength. Twenty-four healthy males, 24-45 yr old, were placed in three groups that performed eccentric actions in bouts 1 and 2 (ECC/ECC, N = 8), concentric actions in bout 1, and eccentric actions in bout 2 (CON/ECC, N = 8) or served as controls (N = 8). Bouts involved unilateral actions with the left and right quadriceps femoris. Ten sets of 10 repetitions with an initial resistance equal to 85% of the eccentric or concentric one repetition maximum (1 RM) were performed for each bout. Three minutes of rest were given between sets and 3 wk between bouts. Two weeks before bout 1 and 1, 4, 7, and 10 d after bouts 1 and 2, eccentric and concentric 1 RM were measured for the right quadriceps femoris and a speed-torque relation established for the left quadriceps femoris. Eccentric and concentric 1 RM decreased (P less than 0.05) 32% 1 d after bout 1 for group ECC/ECC. The speed-torque relation was down-shifted (P less than 0.05) 38%. Eccentric 1 RM and eccentric and isometric torque returned to normal 6 d later. Concentric 1 RM and torque at 3.14 rad.s-1 had not recovered on day 10 (-7% for both, P less than 0.05). Decreases in strength after bout 2 for group ECC/ECC only occurred on day (-9% for concentric 1 RM and 16% downshift of the speed-torque relation).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1978

Visual acuity at different retinal loci of eccentrically fixating functional amblyopes.

Visual acuity was measured in eccentrically fixating amblyopic subjects to determine the contribution of sensory (inhibitory) and motor (retinal-locus) components of the acuity loss. A unique aspect of this research involved the subjects' use of auditory feedback to control their unsteady and eccentric fixation while responding to flashed (800 msec) or continuously presented targets at various eccentricities in the visual field. All 4 amblyopic eyes had maximum visual acuity at the fovea; from there, the acuity declined approximately symmetrically into the nasal and temporal periphery. Foveal acuity for these amblyopic eyes was depressed from the acuity at the fovea of the normal eye. We conclude that Worth's explanation of eccentric fixation (eccentric fixation develops in an attempt by the amblyopic eye to fixate with a peripheral retinal locus having higher acuity than the fovea) cannot apply to our amblyopes. The acuity losses exhibited by the amblyopic eyes studied have a sensory (inhibition) component and a motor (retinal-locus) component, the sensory component being greater for small degrees of eccentric fixation and the motor component being greater for large amounts of eccentric fixation.

Acoustic Stimulation↗

PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine patterns. II. The far peripheral visual field (eccentricity 0 degrees-50 degrees).

Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6 degrees, 12 degrees, 21 degrees, 32 degrees, and 50 degrees on the nasal horizontal meridian. The field subtended 4 degrees X 4 degrees. Spatial frequencies ranged from 0.25 cpd up to the resolution limit, temporal frequencies from 0.1 Hz up to the CFF. Mean retinal illuminance was 10 trolands. We find for these conditions: (i) For any eccentricity there exists a unique combination of spatial frequency and velocity for which the threshold is a minimum. (Extremes are 2 cpd and 2 degrees s-1 at the fovea, and 0.5 cpd and 12 degrees s-1 at an eccentricity of 50 degrees. (ii) Acuity depends little on velocity, the CFF only little on spatial frequency. (iii) The higher the eccentricity, the higher the threshold for any drifting sine wave pattern. Except for this the qualitative threshold behavior as a function of spatial and temporal frequency is identical at the fovea and at eccentricities up to 50 degrees. The thresholds double every 12 degrees for spatial frequencies of 0.25-2 cpd. For a given spatial frequency the visual field is blind beyond a certain critical eccentricity. This critical eccentricity is a monotonically decreasing function of spatial frequency.

Adult↗

PubMed1978

Eccentric fixation in amblyopia: is reduced foveal acuity the cause?

The Worth-Chavasse theory of amblyopia is briefly reviewed with particular attention to Worth's explanation that eccentric fixation develops in an attempt by the amblyopic eye to fixate with an eccentric retinal locus having higher acuity than the fovea. Three experiments are reviewed; these show that of 8 eccentrically fixating amblyopic eyes tested, 7 had foveal acuity that was higher than or equal to the acuity at the eccentric fixation locus. A fourth study is reviewed, however, which reports that 24 of 25 eccentrically fixating amblyopic eyes had highest acuity at the eccentric retinal locus. With only slight reservations, the conclusion from the first 3 experiments that eccentric fixation does not occur to improve acuity appears justified, but the contrary results of the fourth study, in which fixation was not controlled, cannot easily be dismissed. The importance of performing an experiment that accurately measures acuity across the retinas of amblyopic eyes with careful control of fixation and target location is stressed.

Amblyopia↗

PubMed1976

High reliability rates of spatial pattern analysis by vectorcardiogram in assessing the severity of eccentric left ventricular hypertrophy.

In 33 patients, including 12 control subjects and 21 with eccentric LVH, LV mass determined by angiocardiogram was correlated to 26 VCG measurements (Frank system) calculated from the scalar X, Y, and Z leads. The results demonstrated that the most reliable indices of VCG in assessing the severity of eccentric LVH determined by angiocardiogram were the magnitude of the spatial mean QRS vector and the time of the spatial maximal QRS vector ("spatial VAT"), of which correlation coefficients were 0.93 and 0.93, respectively. Such high correlation coefficients have never been obtained with the usual ECG analysis. These findings strongly suggest that (1) increased QRS voltage and usual prolonged QRS duration in eccentric LVH are due to an increase in LV mass, and (2) prolonged VAT observed in eccentric LVH is closely related to an anatomic alteration, namely, the greater distance of intra-ventricular conducting pathways as the result of LV dilatation, as an increase in LV mass is usually paralleled by the grade of the chamber enlargement in this type of LVH. Regarding the T loop, correlations between the LV mass and the VCG measurements were less as compared to those of the QRS loop. In general, T changes in moderate or severe LVH may be also related to a certain altered cardiac muscle state, in addition to an increase in LV mass. Angiocardiographic and light microscopic findings of a patient with eccentric LVH in whom a widened QRS-T angle was demonstrated to an extent much more than that expected with an increase in LV mass are presented and discussed. The spatial pattern analysis by VCG is very useful and reliable in assessing the severity of eccentric LVH.

Adolescent↗

PubMed1992

The influence of eccentricity on position and movement acuities as revealed by spatial scaling.

The rate of decline with increasing eccentricity of several position and movement acuities was measured using a method of spatial scaling. In this method all stimuli at each visual field location are simply magnified versions of each other. The influence of separation and eccentricity were dissociated by presenting stimuli on an iso-eccentric arc. For each task, the rate of decline in performance was quantified by the parameter E2 which represents the eccentricity at which stimulus size must double in order to maintain performance equivalent to that at the fovea. All tasks were found to obey the concept of spatial scaling in that performance at a given field location could be equated with performance at any other location simply by a change of scale. However, the rate at which performance deteriorated with eccentricity varied over an enormous range (over 100-fold) depending on the task itself. The advantage of such diverse peripheral gradients is clear; the goal is to establish the physiological mechanisms which underlie this phenomenon.

Discrimination, Psychological↗

PubMed1977

Changes in motor unit activity and metabolism in human skeletal muscle during and after repeated eccentric and concentric contractions.

This study was designed to investigate electromyographic (EMG), muscle glycogen and blood lactate changes in quadriceps muscle group during repeated 40 maximal eccentric and concentric contractions, and to follow the recovery in EMG, muscle glycogen and serum creatine kinase values during a 4 day period following the work test. The subjects were normal males and test order (eccentric or concentric) was randomly selected. The results indicated first, that the EMG parameters (IEMG, AMUP), muscle glycogen and blood lactate changed in a similar manner during the both fatigue loads. Despite the high tension work no selective depletion of glycogen could be observed in the slow or fast twitch muscle fibres in either type of work. The restoring of muscle glycogen occurred in a similar manner after the both fatigue loads, and no significant differences were present between eccentric and concentric works in the serum creatine kinase levels for a 2 days period. The eccentric work was associated with muscle soreness, which was strongest during the second day after the termination of the work test. The recovery of the EMG parameters were also delayed in eccentric fatigue. After concentric fatigue EMG-activity returned to normal values within 2 days.

Adult↗

PubMed1976

Receptive-field characteristics of neurons in cat striate cortex: Changes with visual field eccentricity.

1. Receptive-field properties of 214 neurons from cat striate cortex were studied with particular emphasis on: a) classification, b) field size, c) orientation selectivity, d) direction selectivity, e) speed selectivity, and f) ocular dominance. We studied receptive fields located throughtout the visual field, including the monocular segment, to determine how receptivefield properties changed with eccentricity in the visual field.2. We classified 98 cells as "simple," 80 as "complex," 21 as "hypercomplex," and 15 in other categories. The proportion of complex cells relative to simple cells increased monotonically with receptive-field eccenticity.3. Direction selectivity and preferred orientation did not measurably change with eccentricity. Through most of the binocular segment, this was also true for ocular dominance; however, at the edge of the binocular segment, there were more fields dominated by the contralateral eye.4. Cells had larger receptive fields, less orientation selectivity, and higher preferred speeds with increasing eccentricity. However, these changes were considerably more pronounced for complex than for simple cells.5. These data suggest that simple and complex cells analyze different aspects of a visual stimulus, and we provide a hypothesis which suggests that simple cells analyze input typically from one (or a few) geniculate neurons, while complex cells receive input from a larger region of geniculate neurons. On average, this region is invariant with eccentricity and, due to a changing magnification factor, complex fields increase in size with eccentricity much more than do simple cells. For complex cells, computations of this geniculate region transformed to cortical space provide a cortical extent equal to the spread of pyramidal cell basal dendrites.

Animals↗

PubMed1992

Eccentric and concentric torques of knee and elbow extension in young and older men.

The purpose of this study was to compare the strength of knee extensors and elbow extensors in young and older men under conditions of eccentric loading and concentric contractions. Twelve men ages 23 to 32 years and 12 ages 60 to 75 years were tested at two angular velocities of movement, 90 and 180 degrees.s-1, on a KinCom isokinetic dynamometer. Compared to young men, older men had lower concentric peak torque values for elbow (31%) and knee (32%) extensors (p less than 0.05). The older group showed lower eccentric peak torques on all elbow comparisons (21% lower), and for knee extension at the slower velocity (20%). At the faster velocity, knee extension eccentric peak torque did not differ from that of younger men. Differences between the age groups were significantly less for the eccentric muscle action than for the concentric one. The observation of maintained eccentric strength in older men, particularly at fast velocity, warrants research in defining the mechanism.

Adult↗

PubMed1992

Red-green and yellow-blue opponent-color responses as a function of retinal eccentricity.

Using the hue cancellation technique, I measured the spectral sensitivities of red-green (r-g) and yellow-blue (y-b) opponent-color responses of two color-normal observers at 0 (fovea), 3.3, 10, 21, and 31 degrees along the horizontal meridian of the temporal retina. The stimulus size as a function of retinal eccentricity was varied according to the cortical magnification factor. I found that the net spectral sensitivity (i.e. corrected for macular pigment) of the r-g channel was approximately constant as a function of retinal eccentricity. On the other hand, the net spectral sensitivity of the y-b channel was not constant. For the y-b channel I found a constant spectral sensitivity as a function of eccentricity when no macular correction was made. This means that the y-b system changes its yellow and blue responses with eccentricity to counterbalance the effects of macular pigment.

Adaptation, Ocular↗

PubMed1992

Contrast sensitivity as a function of spatial frequency, viewing distance and eccentricity with and without spatial noise.

Using computer graphics and a two-alternative forced-choice method we measured threshold contrast as a function of viewing distance, spatial frequency, and eccentricity for gratings with and without added, white two-dimensional spatial noise. Our experiments showed that in spatial noise contrast sensitivity was independent of viewing distance as long as contrast sensitivity was lower with noise than without. With increasing spatial frequency (f) the grating area (A) was reduced in order to keep the relative grating size (Af2) constant. At all spatial frequencies the test gratings thus had the same amount of detail and contour. Noise spectral density was reduced in direct proportion to grating area in order to keep the physical signal-to-noise ratio constant. An increase in spatial frequency was thus accompanied with reductions in grating area and noise spectral density similar to those produced by a corresponding increase in viewing distance. In agreement, contrast detection in spatial noise was found to be independent of spatial frequency as long as contrast sensitivity was lower with noise than without. The effect of increasing eccentricity on visual performance can be compensated for by reducing the viewing distance (M-scaling). Hence, without M-scaling the effect of increasing eccentricity is similar to that of increasing viewing distance. In agreement, we found that contrast sensitivity in spatial noise was independent of eccentricity as long as contrast sensitivity was lower with noise than without.

Adult↗

PubMed2026

Effects of essential amino acid supplementation on musculotendinous recovery following eccentric plantar flexor exercise: a randomized controlled trial.

BACKGROUND: Exercise-induced muscle damage (EIMD) resulting from eccentric contractions leads to transient impairments in muscle function. Essential amino acids (EAAs) stimulate muscle protein synthesis and may support recovery following damaging exercise. However, limited research has examined the effects of EAAs on muscle function following eccentric plantar flexor exercise. The purpose of this study was to examine the effects of EAA supplementation on indirect markers of muscle and musculotendinous recovery following EIMD. METHODS: Thirty-six recreationally active males (age: 21.2 ± 2.7 years) were randomly assigned to an EAA group (10 g of EAAs), placebo (10 g of maltodextrin), or control (no supplementation). Supplements were consumed 30 minutes before and immediately after an eccentric plantar flexor protocol (4 × 50 repetitions followed by one set to failure) and during the 72 hours recovery period. Indirect markers of muscle damage were assessed pre-exercise, immediately post-exercise, and 24, 48, and 72 hours post-exercise, consisting of perceived soreness (NPRS), pain pressure threshold (PPT), calf muscle thickness and Achilles tendon thickness (ultrasound), and calf circumference. RESULTS: The eccentric protocol elicited responses consistent with EIMD, including increased soreness (p < 0.001), increased calf muscle thickness and circumference (p < 0.001), and reduced PPT (p = 0.018). EAA supplementation attenuated soreness at 24 hours compared with placebo. Calf muscle thickness increased following exercise in both groups; however, swelling returned to baseline by 72 hours in the EAA group but remained elevated in placebo (Condition × Time, p < 0.001). Achilles tendon thickness decreased immediately post-exercise (p = 0.005) but was not influenced by supplementation. CONCLUSIONS: EAA supplementation modestly reduced soreness and was associated with faster recovery of muscle swelling but did not influence tendon morphology within 72 hours.

Humans↗

PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine wave patterns. I. The near peripheral visual field (eccentricity 0 degrees-8 degrees).

Contrast detection thresholds for moving spatial sine wave gratings were obtained, at the fovea, and at eccentricities of 1 degree, 2 degrees, 4 degrees, 6 degrees, and 8 degrees on the nasal horizontal meridan, for two subjects. The target field subtended 30 X 30 minutes of arc. The spatial frequency range extended from 2 cpd up to the spatial resolution limit, the temporal frequency range from 0.1 Hz up to the CFF. Mean retinal illuminance was 10 trolands. We find for these conditions: (i) Contrast detection thresholds are higher, the higher the spatial and/or temporal frequency of the stimulus. (ii) Acuity appears to be independent of the temporal frequency, the CFF appears to be independent of the spatial frequency. (iii) The higher the eccentricity, the higher the contrast detection threshold for any drifting sine wave pattern. The threshold doubles roughly any 2 degrees-3 degrees for spatial frequencies of 2-20 cpd, except that the visual field for a given fineness of grating is blind beyond a certain critical eccentricity. This critical eccentricity is a monotonically decreasing function of the spatial frequency of the grating. These measurements do not support the hypothesis that coarse patterns are preferentially detected at extrafoveal sites in the visual field.

Adult↗

PubMed1979

Study of eccentric fixation with secondary visual feedback.

Secondary visual feedback (2VFB) is a visual signal derived from continuous measurement of eye position and provides an extra artificial indication of the point of gaze. 2VFB may be eccentrically displaced and subjects are able to visually superimpose 2VFB onto a visual target signal and thus achieve and maintain eccentric fixation. Initial transient patterns of movement depend upon training but even naive subjects can achieve eccentric fixation within the first 40 s of such a task. Individual strategies and idiosyncratic patterns are exaggerations of normal control and fixational eye movements. The variance of maintained fixation increases with eccentricity and appears to be related to visual acuity as well as to precision of ocular motor control.

Biofeedback, Psychology↗

PubMed1975

Indoleamines and the eccentric cells of the limulus lateral eye.

The lateral eye of the horseshoe crab, Limulus polyphemus, was studied by fluorescence microscopy according to Falck and Hillarp and microspectrofluorometry for identifying neuronal monoamines. After the formaldehyde treatment, the eccentric cells and their axons have a yellowish, rapidly fading fluorescence, such as is seen with 5-hydroxytryptamine. The microspectrofluorometric analysis was compatible with the fluorescence being caused by an indole, which could not be definitely identified, however. The eccentric cells have the ability to accumulate indoleamines such as 5-hydroxytryptamine, 6-hydroxytryptamine and 5,6-dihydroxytryptamine. Their axons were best demonstrated after being loaded with 6-hydroxytryptamine. Characteristic varicose terminals were seen in the neuropil, often arranged in clusters. Other terminals, possibly originating from the eccentric cells, were also seen among the pigment cells in the basal part of the ommatidia.

Animals↗

PubMed1975

Mean QRS, ventricular gradient and left ventricular mass in patients with eccentric left ventricular hypertrophy.

The spatial ventricular gradient (G) and the mean QRS-T angle were examined in 12 patients with angiographically determined eccentric left ventricular hypertrophy (LVH), as compared with 12 normal control subjects. In these 24 patients, a high significant correlation (r = 0.88) was obtained between the magnitude of the spatial mean QRS and LV mass. Although correlations were obtained between the magnitude of the spatial G or the spatial mean QRS-T angle and LV mass, they were lower (r = 0.56, 0.71 respectively). The magnitude of the spatial G (0.190 +/- 0.049 MVSec) in the eccentric LVH group increased significantly (p less than 0.001) in comparison with the control value (0.105 +/- 0.032 mVSec), while in the eccentric LVH group, decreased G/QRS (p less than 0.02), decreased T/QRS (p less than 0.05), and increased QRS-T angle (p less than 0.02) were observed. Furthermore, decreased G/QRS and widening of the QRS-T angle were observed in cases of LVH only. In cases of mild or moderate LVH, normal G/QRS ratios with definitely increased G magnitude and normal QRS-T angle were observed. It is concluded that the magnitude of the spatial mean QRS closely relates to an increase in LV mass. Therefore, should the magnitude of G increase proportionally to an increase in total muscle volume in ideal hypertrophy, then the widening of the QRS-T angle observed in LVH would be due not only to the large ARS complex but also to an alteration in the ventricular gradient.

Adolescent↗

PubMed1978

A motor theory for monocular eccentric fixation of amblyopic eyes.

A motor theory is proposed to explain monocular eccentric fixation of amblyopic eyes. Clinical observations that suggest the involvement of a motor anomaly related to strabismus are cited. The model proposes that potentiation (after discharge) of the agonist muscle in strabismus results in a nonregistered error of monocular fixation of the amblyopic eye. The position error goes undetected as a result of reduced sensitivity of the amblyopic eye. Evidence is cited for normal muscle potentiation in nonamblyopic eyes. A suggestion is made that amblyopia be considered both a sensory and a motor disorder. The sensory disorder is the reduced acuity at the fovea of the amblyopic eye. The motor disorder is muscle potentiation that causes the amblyopic eye to fixate with an eccentric retinal region that has lower acuity than the fovea. A distinction is made between motor anomalies that have a sensory basis, such as unsteady fixation in anisometropic amblyopia, and motor anomalies that have a motor basis, such as eccentric fixation in strabismic amblyopia.

Amblyopia↗

PubMed1992

Changes in plasma zinc following high force eccentric exercise.

This study was done to determine whether eccentric exercise that causes muscle damage will produce an increase in plasma levels of zinc. Changes in total plasma zinc concentration (Zn) were examined following an eccentric and concentric exercise of the forearm flexors. Eight female subjects performed 24 maximal concentric actions (CON) with one arm and 10-14 days later performed 24 maximal eccentric actions (ECC) with the other arm. Maximal isometric force, elbow joint angles at a relaxed (RANG) and flexed position (FANG), muscle soreness, and plasma creatine kinase activity (CK) were measured as indicators of muscle damage. Zn levels were determined at the same time as CK. Maximal isometric force, RANG, FANG, and muscle soreness showed large changes after ECC but little if any change after CON. CK increased significantly after ECC but did not change after CON. Neither ECC nor CON showed significant changes in Zn following exercise. It is concluded that exercise-induced muscle damage does not appear to produce an increase in plasma zinc levels.

Adult↗