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At least 1,531 records · Page 85Linked to original sources
PubMed1991

Knees of trained long-distance runners: MR imaging before and after competition.

A previous report indicated that recreational runners had increased meniscal signal intensity and visible joint effusions on magnetic resonance (MR) images after jogging. Therefore, the knees of trained long-distance runners were evaluated by means of MR imaging before and after competition to determine the presence of any structural alterations, particularly changes in intrameniscal signal intensity and/or joint effusions. T1-weighted coronal, proton-density and T2-weighted sagittal, and short T1 inversion recovery sagittal images were obtained in five trained runners 24 hours before and within 24 hours after completion of a long-distance race (distance range, 17-50 miles). Pre- and postrace images were filmed and windowed with standardized techniques. All ligaments were normal before and after the race. No alteration in meniscal signal intensity was noted for any menisci, and there was no increase in joint fluid after running. These data indicate that the knees of trained long-distance runners do not demonstrate changes similar to those found in recreational runners, suggesting that these athletes may have adapted to the stresses of their activity.

Adult↗
PubMed1993

Higher levels of erythrocyte membrane fluidity in sprinters and long-distance runners.

Erythrocyte membrane fluidity was measured in male sprinters and long-distance runners by a spin-label method. The membrane fluidity was higher in long-distance runners than in sedentary subjects for both measurements by use of two stearic acid spin labels (SAL), 12- and 16-SAL, which represent the fluidity at two different depths of lipid bilayer. In the 12-SAL measurement, higher levels were also evident in sprinters than in sedentary subjects. Increases in the C20:5, C22:5, and total polyunsaturated acyl chains were evident in membrane phospholipids, whereas the C18 and total saturated acyl chains were decreased in long-distance runners compared with sedentary subjects. Only levels of C22:5 were higher in the sprinters than the sedentary subjects. Membrane cholesterol and phospholipid classes did not differ among the three groups. A higher level of erythrocyte membrane fluidity was observed in the athletes, more obviously in the long-distance runners, which was related to the altered phospholipid acyl chain composition. The change may contribute to the beneficial effects on erythrocyte functions related to microcirculation in athletes.

Adult↗
PubMed1997

Muscle capillarization O2 diffusion distance, and VO2 kinetics in old and young individuals.

The relationships between muscle capillarization, estimated O2 diffusion distance from capillary to mitochondria, and O2 uptake (VO2) kinetics were studied in 11 young (mean age, 25.9 yr) and 9 old (mean age, 66.0 yr) adults. VO2 kinetics were determined by calculating the time constants (tau) for the phase 2 VO2 adjustment to and recovery from the average of 12 repeats of a 6-min, moderate-intensity plantar flexion exercise. Muscle capillarization was determined from cross sections of biopsy material taken from lateral gastrocnemius. Young and old groups had similar VO2 kinetics (tau VO2-on = 44 vs. 48 s; tau VO2-off = 33 vs. 44 s, for young and old, respectively), muscle capillarization, and estimated O2 diffusion distances. Muscle capillarization, expressed as capillary density or average number of capillary contacts per fiber/average fiber area, and the estimates of diffusion distance were significantly correlated to VO2-off kinetics in the young (r = -0.68 to -0.83; P < 0.05). We conclude that 1) capillarization and VO2 kinetics during exercise of a muscle group accustomed to everyday activity (e.g., walking) are well maintained in old individuals, and 2) in the young, recovery of VO2 after exercise is faster, with a greater capillary supply over a given muscle fiber area or shorter O2 diffusion distances.

Adult↗
PubMed2001

Scaling peak VO2 to body mass in young male and female distance runners.

This study examined age- and sex-associated variation in peak oxygen consumption (VO2) of young male and female distance runners from an allometric scaling perspective. Subjects were from two separate studies of 9- to 19-yr-old distance runners from the mid-Michigan area, one conducted between 1982 and 1986 (Young Runners Study I, YRS I) and the other in 1999-2000 (Young Runners Study II, YRS II). Data from 27 boys and 27 girls from YRS I and 48 boys and 22 girls from the YRS II were included, and a total of 139 and 108 measurements of body size and peak VO2 in boys and girls, respectively, were available. Subjects were divided into whole year age groups. A 2 x 9 (sex x age group) ANOVA was used to examine differences in peak VO2. Intraindividual ontogenetic allometric scaling was determined in 20 boys and 17 girls measured annually for 3-5 yr. Allometric scaling factors were calculated using linear regression of log-transformed data. Results indicated that 1) absolute peak VO2 increases with age in boys and girls, 2) relative peak VO2 (ml x kg(-1) x min(-1)) remains relatively stable in boys and in girls, 3) relative peak VO2 (ml x kg(-0.75) x min(-1)) increases throughout the age range in boys and increases in girls until age 15 yr, and 4) peak VO2 adjusted for body mass (ml/min) increases with age in boys and girls. The overall mean cross-sectional scaling factor was 1.01 +/- 0.03 (SE) in boys and 0.85 +/- 0.05 (SE) in girls. Significant age x sex interactions and significant scaling factors between sexes identify the progressive divergence of peak VO2 between adolescent male and female distance runners. Mean ontogenetic allometric scaling factors were 0.81 [0.71-0.92, 95% confidence interval (CI)] and 0.61 (0.50-0.72, 95% CI) in boys and girls, respectively (P = 0.002). There was considerable variation in individual scaling factors (0.51-1.31 and 0.28-0.90 in boys and girls, respectively). The results suggest that the interpretation of growth-related changes in peak VO2 of young distance runners is dependent upon the manner of expressing peak VO2 relative to body size and/or the statistical technique employed.

Adolescent↗
PubMed2005

Simple metric for scaling motor threshold based on scalp-cortex distance: application to studies using transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) is a unique method in neuroscience used to stimulate focal regions of the human brain. As TMS gains popularity in experimental and clinical domains, techniques for controlling the extent of brain stimulation are becoming increasingly important. At present, TMS intensity is typically calibrated to the excitability of the human motor cortex, a measure referred to as motor threshold (MT). Although TMS is commonly applied to nonmotor regions, most applications do not consider the effect of changes in distance between the stimulating device and underlying neural tissue. Here we show that for every millimeter from the stimulating coil, an additional 3% of TMS output is required to induce an equivalent level of brain stimulation at the motor cortex. This abrupt spatial gradient will have crucial consequences when TMS is applied to nonmotor regions because of substantial variance in scalp-cortex distances over different regions of the head. Stimulation protocols that do not account for cortical distance therefore risk substantial under- or overstimulation. We describe a simple method for adjusting MT to account for variations in cortical distance, thus providing a more accurate calibration than unadjusted MT for the safe and effective application of TMS in clinical and experimental neuroscience.

Adolescent↗
PubMed1984

Relations among threshold, spike height, electrode distance, and conduction velocity in electrical stimulation of certain medullospinal neurons.

This report describes how the threshold for extracellular, electrical stimulation of cell bodies in the rat's rostromedial medulla depends on the distance to the stimulating electrode. A monopolar microelectrode both delivered current pulses near medullospinal neurons and, after decay of the stimulus artifact, detected whether an orthodromic spike had occurred by collision of that spike with a suitably timed antidromic spike initiated at the thoracic spinal cord. The liminal current and the height of antidromic spikes were noted at a series of vertical electrode positions. Regression analysis was performed to determine whether threshold and the inverse of peak-to-peak spike height varied more as the radial distance or its square. The square relationship provided a much better fit for threshold and a marginally better fit for the inverse of spike height. The spatial decline in excitability (K2) averaged 859 microA/mm2, falling within the range of values found for fibers and cell bodies in other studies. The constant of spatial decline in spike height (C2) in millivolts per square millimeter was positively correlated with K2. Both C2 and K2 were negatively correlated with conduction velocity. From threshold distance curves fitted by regression analysis, the mean separation of sites of spike maxima and threshold minima along each electrode path was 16 micron; the estimated distance from these sites to, respectively, the loci of spike generation and spike excitation were positively correlated and similar. The variation of C2 and K2 with conduction velocity may be due either to an influence of the size and shape of the dendritic tree on the spatial decrement of excitability and spike height or to a confounding in the studied equations of the space-independent effect of the size of a cell body on spike height and excitability.

Action Potentials↗
PubMed1998

Human vestibuloocular reflex and its interactions with vision and fixation distance during linear and angular head movement.

Human vestibuloocular reflex and its interactions with vision and fixation distance during linear and angular head movement. J. Neurophysiol. 80: 2391-2404, 1998. The vestibuloocular reflex (VOR) maintains visual image stability by generating eye movements that compensate for both angular (AVOR) and linear (LVOR) head movements, typically in concert with visual following mechanisms. The VORs are generally modulated by the "context" in which head movements are made. Three contextual influences on VOR performance were studied during passive head translations and rotations over a range of frequencies (0.5-4 Hz) that emphasized shifting dynamics in the VORs and visual following, primarily smooth pursuit. First, the dynamic characteristics of head movements themselves ("stimulus context") influence the VORs. Both the AVOR and LVOR operate with high-pass characteristics relative to a head velocity input, although the cutoff frequency of the AVOR (<0.1 Hz) is far below that of the LVOR ( approximately 1 Hz), and both perform well at high frequencies that exceed, but complement, the capabilities of smooth pursuit. Second, the LVOR and AVOR are modulated by fixation distance, implemented with a signal related to binocular vergence angle ("fixation context"). The effect was quantified by analyzing the response during each trial as a linear relationship between LVOR sensitivity (in deg/cm), or AVOR gain, and vergence (in m-1) to yield a slope (vergence influence) and an intercept (response at 0 vergence). Fixation distance (vergence) was modulated by presenting targets at different distances. The response slope rises with increasing frequency, but much more so for the LVOR than the AVOR, and reflects a positive relationship for all but the lowest stimulus frequencies in the AVOR. A third influence is the context of real and imagined targets on the VORs ("visual context"). This was studied in two ways-when targets were either earth-fixed to allow visual enhancement of the VOR or head-fixed to permit visual suppression. The VORs were assessed by extinguishing targets for brief periods while subjects continued to "fixate" them in darkness. The influences of real and imagined targets were most robust at lower frequencies, declining as stimulus frequency increased. The effects were nearly gone at 4 Hz. These properties were equivalent for the LVOR and AVOR and imply that the influences of real and imagined targets on the VORs generally follow low-pass and pursuit-like dynamics. The influence of imagined targets accounts for roughly one-third of the influence of real targets on the VORs at 0.5 Hz.

Adult↗
PubMed2000

Fetal binocular distance: no differences between ethnic groups.

OBJECTIVE: The aim of this study was to detect if interethnic differences for fetal binocular distance exist between the autochthonous Belgian population and immigrants from Turkey or Morocco, and to evaluate the need for different reference charts by ethnicity. METHODS: A prospective cross-sectional study was performed. In 246 pregnant women who presented for routine prenatal ultrasound between 18 and 40 weeks of gestation age the binocular distance was measured. Polynomial regression was performed for the three ethnic groups. RESULTS: The population consisted of 171 autochthonous Belgian women, 31 women from Turkish origin and 44 women from Moroccan origin. A statistically significant difference for the fetal binocular distance was noted between the Moroccan versus the autochthonous Belgian and Turkish fetuses (F test, p = 0. 047). The order of magnitude of this statistical difference is extremely small and does not result in clinical relevance. CONCLUSION: A small, but statistically significant difference exists for the fetal binocular distance between fetuses of Moroccan origin versus those of autochthonous Belgian or Turkish origin. This difference is of no clinical importance and there is no need to adapt reference charts for ethnicity when studying these three groups.

Adult↗
PubMed2003

Distances from the atlantal segment of the vertebral artery to the midline in children.

There are scant data in the literature regarding distances from the midline to the suboccipital segment of the vertebral artery, and to our knowledge, none addressing this measurement in the pediatric population. This study seeks to establish age-related distances (Y) from the laterally placed vertebral artery to the midline at the level of the posterior arch of the atlas in children. Measurements from the midline to the most medial portion of the vertebral artery at the level of the posterior arch of the atlas were made in 50 children who underwent CT imaging of the cervical spine. For all left sides, Y = 12-23 mm (mean 17 mm). For all right sides, Y = 10-25 mm (mean 17.5 mm). For girls, Y = 12-16 mm (mean 12.7 mm) for left sides and Y = 12-25 mm (mean 18.5 mm) for right sides. For boys, Y = 12-20 mm (mean 16 mm) for left sides and Y = 10-21 mm (mean 16.7 mm) for right sides. We have found that the most medial portion of the vertebral artery from the midpoint of the posterior arch of the atlas for all ages was approximately 17 and 17.5 mm for left and right sides, respectively. This distance was generally less for left sides, except in the 16-19 years age group. However, as a group, this distance did not vary more than 2.8 mm between left and right sides. These data should assist the neurosurgeon who operates in the suboccipital region in children.

Adolescent↗
PubMed2006

Myoneural junctions of extraocular muscles: distances from the orbital rim and widths.

PURPOSE: To examine both the distances from the orbital rim to the myoneural junctions (MNJs) and the widths of the MNJs of all extraocular muscles. METHODS: Six orbits of 3 post-mortem cadavers were used. The cadavers (1 female and 2 males) were all Japanese with an average age of 76.3 years. The MNJs of the extraocular muscles and their motor nerves were exposed, and then the distance from the orbital rim to each MNJ and the width of each MNJ were examined. RESULTS: The distance from the orbital rim to each MNJ in the 6 extraocular muscles ranged from 24.4 to 33.6 mm and the width of each MNJ ranged from 5.0 to 8.5 mm. CONCLUSIONS: It is essential for orbital surgeons to understand both the distance from the orbital rim to MNJs and the widths of MNJs. This information not only aids the understanding of MNJ damage, but also prevents iatrogenic nerve impairment during orbital surgery.

Aged↗
PubMed1986

Factors influencing the frequency of consanguineous marriages in Japan: marital distance and opportunity of encounter.

The inbreeding coefficients (F) were estimated according to marital distance between birthplaces and the opportunity of encounter. As for marital distance, the F-value was the highest for the shortest distance (0.00252), whereas the F-values were similar in the other distance classes (0.00072-0.00097). As for opportunities of encounter, the F-value was 30-37 times higher in the group for friendship from the time of childhood (0.00986) than in those for school, workplace and social gatherings (0.00033) and for chance meetings (0.00027).

Consanguinity↗
PubMed1991

Family distances as a measure of hidden consanguinity. A reappraisal.

We compared the family distances of patients with autosomal recessive disorders with those of a random control group and a matched control group. Only in the great-grandparental generation were weak-significant differences found. We also found that the family distances of persons with an urban origin were significantly larger than those of persons with a rural origin. In our study, family distance seems to be a more powerful measure of hidden consanguinity than the parental distance.

Chromosome Aberrations↗
PubMed1994

Contrasting chimpanzees and bonobos: nearest neighbor distances and choices.

In an effort to understand factors underlying differences in the social organization of Pan troglodytes and P. paniscus, we measured the nearest neighbor distances and choices for chimpanzees in Kibale National Park, Uganda, and for bonobos in Lomako Forest, Zaire. We assume that the spatial organization of a set of individuals should reflect the underlying relationships between them. Bonobos were found to have smaller nearest neighbor distances than chimpanzees. The distribution and variability of the distances suggested that chimpanzees have a more restricted range of nearest neighbor distances than bonobos, avoiding situations of very close proximity. Selection of the sex of the nearest neighbor by a focal animal differed between the species. For example, male bonobos rarely had another male as their nearest neighbor, while male chimpanzees frequently did. Similarly, male bonobos tended to move apart when observed together, while it was female chimpanzees who tended to move apart when together. These observations are considered with respect to the nature of the social interactions in these species.

Animals↗
PubMed1977

Distance correction for precordial electrocardiographic voltage in estimating left ventricular mass: an echocardiographic study.

This study was undertaken to assess both the relation between echocardiographic measurement of left ventricular (LV) mass and commonly used electrocardiographic criteria for LV hypertrophy and the effect of the distance from the center of LV mass to the anterior chest wall on precordial voltage. Echocardiograms and standard 12-lead electrocardiograms were obtained on 100 persons, ages 3 to 79. The correlation coefficients of echocardiographically determined LV mass with ECG precordial voltage (SV1 + RV5 or V6), the Estes point score system, and a VL4 wave voltage were .686, .721, and .531, respectively. Extrapolating from the dipole nature of the heart, the precrodial voltage was multiplied by the square of the chest wall to mid-LV distance to correct for the loss of energy across the distance from LV to recording electrode. Utilizing this correction, a much improved precordial voltage estimation of LV mass (r = .846) was obtained. We conclude that the distance of the center of LV mass from the chest wall influences the amplitude of recorded precordial voltage and that correction for this influence improved the correlation of precordial voltage with LV mass.

Adolescent↗
PubMed1989

Randomized placebo-controlled, double-blind trial of ketanserin in claudicants. Changes in claudication distance and ankle systolic pressure. PACK Claudication Substudy.

The effect of ketanserin on intermittent claudication (measured by treadmill walking distance and ankle systolic pressure) was assessed in 594 patients, a subset of the 3,899 patients who composed a double-blind study of the effect of ketanserin on cardiovascular events. Complete data sets at the beginning and end of 1 year's treatment with ketanserin or placebo were available in 436 patients. There was no difference between the groups in the improvement in pain-free treadmill walking distance. The placebo effect on treadmill walking distance increased continuously for at least 1 year at the rate of about 15% every 6 months. There was no significant change in either group in the ankle systolic pressure at the end of the treatment period but in the group given ketanserin, brachial systolic pressure was decreased and the ankle to arm systolic pressure ratio therefore increased. There was only a very weak association between treadmill walking distance and ankle to arm systolic pressure ratio both at the beginning and in terms of change over 1 year. Therefore, this pressure ratio is probably not a useful way of assessing the effects of medical treatment of claudication.

Blood Pressure↗
PubMed2006

The involvement of the inferior parietal cortex in the numerical Stroop effect and the distance effect in a two-digit number comparison task.

The neural mechanism of number representation and processing is currently under extensive investigation. In this functional magnetic resonance imaging study, we designed a number comparison task to examine how people represent and compare two-digit numbers in the brain, and whether they process the decade and unit digits in parallel. We manipulated the decade-unit-digit congruency and numerical distance between the pairs of numbers. We observed both Stroop-like interference and the distance effect in the participants' performance. People responded more slowly to incongruent pairs of numbers and pairs of a smaller distance. The inferior parietal cortex showed common and distinct patterns of activation for both attentional selection and number comparison processes, and its activity was modulated by the Stroop-like interference effect and the distance effect. Taken together, these results support both parallel and holistic comparison of two-digit numbers in the brain.

Adolescent↗
PubMed1992

Does pentoxifylline prolong the walking distance in exercised claudicants? A placebo-controlled double-blind trial.

The aim of this study was to test whether in claudicants oral pentoxifylline, given for twelve weeks in addition to physical exercise, prolongs the walking distance more than placebo plus exercise. Forty outpatients were randomized into group A (2 x 600 mg oral pentoxifylline per day) or group B (placebo). Both groups received the same exercise program in addition. The maximal and painfree walking distances and blood viscosity were measured. Intergroup differences in terms of blood viscosity reached the level of significance only after twelve weeks (p = 0.006 at shear rate of 94.5 s-1), but values of group A continuously decreased and those of group B continuously increased. After one and eight weeks, but not after twelve weeks, the maximal walking distances were significantly longer in group A than in group B. At no point were there significant intergroup differences in terms of painfree walking distance. The data suggest that pentoxifylline is clinically effective in claudicants even when given in addition to exercise. The benefit of drug plus physical therapy compared with exercise alone could be observed mainly in the first weeks of treatment and may wear off during long-term therapy.

Administration, Oral↗
PubMedDate not supplied

Cricothyroid distance and vocal pitch. Experimental surgical study to elevate the vocal pitch.

To establish an experimental basis for surgical approximation of the anterior cricothyroid distance which aims at raising the vocal pitch, the relationship between vocal pitch and the cricothyroid distance was analyzed in voices produced with excised human larynges (four male and two female larynges). Within the framework of the experimental conditions, the following conclusions were drawn: 1) The vocal pitch expressed in semitones was almost linearly related to the cricothyroid distance, with an increase of 0.15 to 0.90 semitones per milimeter of cricothyroid approximation. 2) The rise in vocal pitch reached a plateau when the force applied to shorten the cricothyroid distance reached 30 to 50 gm.

Cricoid Cartilage↗