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Biomedical subjects

O Bar-Or

Publications and source records attributed to O Bar-Or.

At least 73 records · Page 4Linked to original sources
PubMed1993

Recovery of muscle power after high-intensity short-term exercise: comparing boys and men.

This study was conducted to determine whether boys differ from men in their ability to recover from high-intensity exercise. Two groups of volunteers, 8 prepubertal boys (9-12 yr) and 8 young men (19-23 yr), were similar in their peak oxygen uptake (49.6 +/- 6.6 vs. 51.1 +/- 6.6 ml.min-1 x kg-1), adiposity, and activity levels. On three different occasions subjects performed two consecutive 30-s all-out cycling tasks [Wingate anaerobic test (WAnT)], separated by a 1-, 2-, or 10-min recovery interval. In the boys, mean power reached 89.9 +/- 3.6% of the initial value after 1 min of recovery, 96.4 +/- 2.3% after 2 min, and 103.5 +/- 1.3% after 10 min. For the men, the values were 71.2 +/- 2.6, 77.1 +/- 2.4, and 94.0 +/- 1.3%, respectively (boys vs. men, P < 0.0001). Relative to the external work performed during the first WAnT, the boys had a higher net oxygen uptake (exercise--resting) during the test than the men (83.8 +/- 18.4 vs. 57.8 +/- 6.1 ml/kJ). After the WAnT, the net CO2 output and the respiratory exchange ratio were lower in the boys, and they recovered faster. It was concluded that boys recover faster than men from high-intensity short-term exercise. This may reflect a lower reliance on glycolysis during the WAnT in the boys, leading to less acidosis. It is also possible that the boys had a faster postexercise removal of metabolites.

Adult↗
PubMed1993

Comparison of three techniques for body composition analysis in cystic fibrosis.

Body composition analysis is an important component of nutritional assessment in cystic fibrosis (CF). No gold standard of measurement exists, and techniques applicable to healthy populations may be unsuitable for CF patients. We assessed lean body mass (LBM) in 12 children with CF by skinfold (SK) measurements, bioelectrical impedance analysis (BIA), and dual-photon absorptiometry (DPA) and repeated these measures in 10 subjects 6 mo later. SK and DPA measures in eight older CF patients and eight healthy controls were compared to evaluate any effect of disease on estimates of LBM by use of DPA. Good agreement between the measures was seen at baseline and 6 mo by use of concordance plots. However, the limits of agreement between measures ranged up to 19% of SK-derived LBM measures (baseline: SK and DPA, 2.63 to -3.93 kg; SK and BIA, 2.36 to -1.24 kg; BIA and DPA, 1.88 to -4.28 kg; 6 mo: SK and DPA, 2.10 to -3.58 kg; SK and BIA, 6.28 to -5.49 kg; BIA and DPA, 5.53 to -7.79 kg). The change in LBM over 6 mo did not correlate among the three measures. Only BIA change in LBM correlated with weight change (r = 0.716, P < 0.02), probably due to the inclusion of weight in the regression equations for determining LBM from impedance. The relationship between SK and DPA measures did not differ between the CF and control groups, suggesting that there was no effect of disease on the DPA measure. The results suggest that none of these methods is precise enough to follow short-term changes in the nutritional status of CF patients longitudinally.

Absorptiometry, Photon↗
PubMed1992

Voluntary dehydration and heat intolerance in cystic fibrosis.

Although exercise may be beneficial in cystic fibrosis (CF), patients' low tolerance to climatic heat stress means that physical exertion can increase morbidity and mortality. We postulated that the high salt content of CF patients' sweat and the consequent absence of body-fluid hyperosmolality during a long episode of sweating might deprive such patients of a thirst stimulus. Eight children with CF (four boys, four girls; aged 9.5-14.1 years) and eight controls, matched for age and sex, attended two randomly ordered sessions of exercise (cycling) in a chamber at 31-33 degrees C, relative humidity 43-47%. 20 min bouts of exercise (at 45% of predetermined maximum oxygen uptake) were interspersed with 25 min rest periods. At one session, chilled water was given every 15-20 min to replace fluid lost; at the other, drinking was guided by the child's thirst. At the thirst-guided session, CF patients drank much less than the controls did (0.80% vs 1.73% initial body weight) and lost twice as much fluid (1.57% vs 0.78% initial body weight). The recovery of heart rate after exercise was slower in CF patients, but there were no other signs of heat strain. The groups did not differ in any variable during the forced drinking session. We conclude that children with CF underestimate their fluid needs and undergo excessive dehydration during extended exposure to hot conditions.

Adolescent↗
PubMed1992

Anaerobic endurance and peak muscle power in children with spastic cerebral palsy.

The aim of this study was to provide information on anaerobic muscle endurance (mean power) and peak muscle power in children with spastic cerebral palsy. We measured peak power and mean power of the upper and lower limbs in 29 boys and 20 girls, aged from 6 to 14 years, by means of the Wingate Anaerobic Test. In addition, the physical components (physical capacity, upper limb, and lower limb) of a system used for evaluating function in the physically disabled were assessed. Of the 49 subjects, 46 and 37 successfully completed the arm and leg Wingate Anaerobic Test, respectively. Compared with norms for age and gender (healthy, nonathletic children), peak and mean power in the patients, even when corrected for body weight, were distinctly subnormal. The performance of subjects with quadriplegia was 3 to 4 SDs below the mean for controls. Twenty-five of diplegic and hemiplegic subjects had values below 2 SDs. When the data were analyzed according to the severity of the cerebral palsy, with the use of the physical capacity, upper limb, and lower limb score, those children with moderate to severe cerebral palsy had values for mean and peak power of the arm and leg 3 to 4 SDs below the normal mean. Values for children with only mild cerebral palsy also fell below the mean, but the data were more scattered, especially for the leg. The lower muscle performance may reflect both quantitative and qualitative differences in the upper- and lower-limb muscles, due to altered innervation and, in the more severely affected children, disuse.

Adolescent↗
PubMed1992

Total energy expenditure and spontaneous activity in relation to training in obese boys.

Obese boys [n = 10, aged 10-11 y, average percent body fat (%BF) 32.4] were given a regimented training program (4 wk, 5 1-h sessions, 45 min cycling/wk at 50-60% of predetermined VO2max) to investigate whether they modify their energy expenditure by reducing or augmenting their spontaneous physical activities. No change was observed in mean weight (52.7 vs 52.9 kg), %BF based on 2H- and 18O-dilution and densitometry (32.4 vs 31.7), sleeping metabolic rate (5.83 vs 5.68 MJ/24 h), and spontaneous activity by heart rate recording (percent time of light intensity: 85.3 vs 83.6; medium: 11.2 vs 12.4; and heavy: 3.5 vs 3.9) and activity questionnaires (861 vs 821 min physical activity/wk). There was a 12% increase in average daily metabolic rate by doubly labeled water, half of which can be explained by the energy cost of training and the rest by an increase in energy expenditure outside the training hour. In conclusion, training leads to an appreciable augmentation in the overall energy expenditure of obese children, even with a lack of change in spontaneous physical activity.

Adipose Tissue↗
PubMed1992

Thermoregulation during rest and exercise in the cold in pre- and early pubescent boys and in young men.

Eight minimally dressed pre- and early pubescent boys (age 11-12 yr) and 11 young adult men (age 19-34 yr) rested for 20 min and exercised on a cycle ergometer for 40 min at approximately 30% of their maximum oxygen consumption (VO2max) at 5 degrees C. To quantify the added increase in metabolic rate because of cold, a separate test was carried out at 21 degrees C at rest and at equal work rates as in the cold. Both groups were similar in subcutaneous fat thickness and VO2max per kilogram body weight. Rectal temperature increased slightly during the exposure to the cold, but no significant difference was observed between the boys and men. In the cold, the boys had lower skin temperatures than the adults in their extremities but not in the trunk. The boys increased their metabolic rates in the cold more than did the men. As a result, the boys maintained their core temperature as effectively as the adults. Similar age-related differences in thermoregulatory responses to cold were observed when two boys and two men with equal body sizes were compared. Our results suggest that there may be maturation-related differences in thermoregulation in the cold between children and adults.

Adult↗
PubMed1992

Swimming and asthma. Benefits and deleterious effects.

Swimming is a common pastime activity and competitive sport for patients with asthma. One reason for such popularity may be the low asthmogenicity of swimming compared with landbased activities. Review of available evidence suggests that swimming induces less severe bronchoconstriction than other sports. The mechanisms for this protective effect of swimming are not clear, but there is some experimental evidence intimating that it results in part from the high humidity of inspired air at water level, which reduces respiratory heat loss (and possibly osmolarity of airways mucus). Beneficial roles of horizontal posture and of water immersion have been tested but not confirmed. Swimming poses two potentially deleterious effects to the patient with asthma. One is the exaggerated parasympathetic tone due to the 'diving reflex', that has been shown to trigger bronchoconstriction. The other is airway irritation because of chlorine and its derivatives. Swimming as a training modality has definite benefits for the patient with asthma. These include an increase in aerobic fitness and a decrease in asthma morbidity. There is no conclusive evidence, however, that swim training causes a decrease in the severity or frequency of exercise-induced bronchoconstriction.

Asthma↗
PubMed1992

Sweat electrolyte loss during exercise in the heat: effects of gender and maturation.

Humans may lose large amounts of water and electrolytes from sweat during prolonged exercise in a hot climate. Gender and maturational differences for the total sweat electrolyte losses have not been reported. The purpose of this study was to compare sweat electrolyte losses of prepubescent (PP), pubescent (P) and young adult (YA) males and females, under the same environmental conditions and relative exercise intensities. Twenty-five females (8 PP, 9 P, 8 YA) and 26 males (10 PP, 8 P, 8 YA) cycled for two 20-min bouts at 50% of their peak VO2 in a climatic chamber (42 degrees C, 18% relative humidity). Sweat was collected from a plastic bag attached to the lower back. Total body sweat loss was calculated from the differences in nude body weight corrected for fluid intake, urine, and respiratory water loss. Sweat [Na+] and [Cl-] tended to increase with maturation while sweat [K+] was lower in YA compared with that of PP. Children had a lower sweating rate than YA, even when corrected for body surface area. As a result, total Na+ and Cl- losses per kg body weight from sweat (mEq.kg-1.h-1) were higher in YA compared with those of PP and P; however, no maturational difference was found in K+ losses. Within the same maturational group, there were no gender differences in any of the electrolyte losses. These results may be useful in recommending "optimal" fluid-electrolyte drinks for children exercising in the heat.

Adolescent↗
PubMed1992

Sweat gland response to exercise in the heat among pre-, mid-, and late-pubertal boys.

Sweating rate (SR) of boys is lower than that of men. To assess the association between the response of individual sweat glands and physical growth and maturation, three groups of circumpubertal boys cycled at 50% VO2max in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 16 were classified as prepubertal (PP, Tanner 1), 15 as midpubertal (MP, Tanner 2-4), and five as late-pubertal (LP, Tanner 5). Population density (PD) of the heat-activated sweat glands, the mean area of sweat drops (DA), and the proportion of skin covered by sweat (%A) were measured by skin photography and computer-assisted imaging analysis. Other measurements included rectal and skin temperatures (Tre, Tsk, respectively), heart rate (HR), and total body SR. The rise in HR, Tre and Tsk did not differ among groups. Whole body SR was significantly higher in the LP group compared with PP (PP = 4.95 +/- 0.23, MP = 5.79 +/- 0.20, LP = 6.70 +/- 0.42 ml.min-1.m-2) (mean +/- SEM). PD was significantly higher in the PP group (PP = 128 +/- 8, MP = 97 +/- 9, LP = 74 +/- 9 glands.cm-2), while DA was higher in the LP group (PP = 5.47 +/- 0.59, MP = 6.92 +/- 0.47, LP = 12.83 +/- 1.41 microns2.10(4)). %A did not differ among groups. The calculated SR per gland was higher among the LP groups compared with the less mature ones (PP = 4.6 +/- 0.3, MP = 7.2 +/- 0.8, LP = 9.6 +/- 1.0 nl.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Thermoregulatory responses of pre-, mid-, and late-pubertal boys to exercise in dry heat.

During exercise in a hot climate, children have been reported to have a less effective temperature regulation capability, compared with adults. It is likely that the transition from a child-like to an adult-like response occurs during puberty. To assess the association between the thermoregulatory response and physical maturation, three groups of circum-pubertal boys cycled at 50% VO2max (three 20-min bouts with 10-min rests), in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 10 were classified as prepubertal (PP), 13 as midpubertal (MP), and eight as late pubertal (LP). Measurements included rectal and skin temperatures (Tre, Tsk), heart rate (HR), sweating rate (SR), oxygen consumption (VO2), and forearm blood flow (FBF). Tre, Tsk, and HR increased with time, with no significant difference among groups. Relative VO2 (ml O2.kg-1) was similar among groups. FBF was consistently higher in PP compared with LP. In spite of the higher SR (PP = 4.9 +/- 0.2, MP = 5.7 +/- 0.3, LP = 6.6 +/- 0.4 ml.min-1.m-2) (mean +/- SEM) among LP compared with PP, the rate of heat storage (PP = 5.5 +/- 0.4, MP = 5.3 +/- 0.4, LP = 6.8 +/- 0.3, kJ.h-1.kg-1) was also significantly higher among those in the LP group. Three of eight LP did not complete the session due to high Tre, while two of the 10 PP were unable to complete the session even though the physiologic heat strain was not high. The results suggest that the transition from a child-like to an adult-like thermoregulatory effectiveness in a hot, dry climate may occur at a somewhat later stage, but not during puberty.

Adolescent↗
PubMed1991

Sweat lactate in exercising children and adolescents of varying physical maturity.

This study attempts to explain some of the individual variability in sweating pattern by comparing prepubescents and pubescents. Sweating rate and muscular anaerobic capacity are higher in adults than in children; thus we hypothesized that sweat gland anaerobic metabolism, as reflected by lactate excretion, might be higher with advanced physical maturity (PM). Lactate concentration in sweat ([LAC]sw) was measured at various stages of PM in boys who exercised in the heat. The subjects were divided into three groups on the basis of Tanner staging: prepubertal (PP, n = 16), midpubertal (MP, n = 15), and late pubertal (LP, n = 5). Subjects cycled at 50% of maximal O2 uptake for three 20-min bouts, with 10-min rest periods, in 42 degrees C and 18% relative humidity. Sweat samples were harvested, and population density of activated sweat glands was determined after each exercise bout. [LAC]sw during bout 1 was higher in PP than in LP [PP = 22.2 +/- 2.2, MP = 19.5 +/- 1.4, LP = 14.3 +/- 1.3 (SE) mmol/l]. In all groups, [LAC]sw decreased during subsequent bouts, and there were no intergroup differences in [LAC]sw during bout 3 (PP = 11.2 +/- 0.4, MP = 10.6 +/- 0.5, LP = 9.7 +/- 0.2 mmol/l). [LAC]sw was inversely related to sweating rate. Lactate excretion rate per gland was greater with the increase in PM (PP = 61.0 +/- 8.2, MP = 79.1 +/- 11.3, LP = 99.9 +/- 11.0 pmol/min; P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Aldosterone and prolactin response to exercise in the heat in circumpubertal boys.

Thermoregulatory responses to exercise in the heat, especially sweating pattern, differ between children and adults. To determine whether such differences may be related to hormonal responses and to assess the possible association between this response and physical maturation, three groups of circumpubertal boys cycled at 50% of maximal O2 uptake (three 20-min bouts with 10 min of rest between bouts) in 42 degrees C at 20% relative humidity. On the basis of Tanner staging, 11 were prepubertal (PP), 12 midpubertal (MP), and 7 late pubertal (LP). Water ingestion was encouraged to minimize dehydration. Venous blood was sampled before and immediately after the session. Changes in heart rate, rectal temperature, and percent decrease in plasma volume did not differ among groups. There was no change in plasma osmolality in any of the groups. Resting testosterone concentrations were higher with increased level of physical maturity (PP = 0.4 +/- 0.1, MP = 8.2 +/- 1.9, LP = 13.8 +/- 1.2 nmol/l; P less than 0.05). In all groups, both aldosterone (ALD) and prolactin (PRL) markedly increased after exercise in the heat (ALD: PP = 161 +/- 40 vs. 1,289 +/- 263, MP = 173 +/- 47 vs. 1,245 +/- 153, LP = 250 +/- 76 vs. 1,681 +/- 400 pmol/l; PRL: PP = 8.1 +/- 1.2 vs. 24.9 +/- 4.2, MP = 8.8 +/- 1.0 vs. 22.0 +/- 8.9, LP = 8.4 +/- 0.8 vs. 39.0 +/- 3.6 micrograms/l; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

New muscle power test in neuromuscular disease. Feasibility and reliability.

We studied the feasibility, reliability, and reproducibility of an "all-out" 30-second cycling or arm cranking test of muscle power and muscle endurance (the Wingate Anaerobic Test) in 66 girls and boys aged 5 to 18 years old who had cerebral palsy or a myopathy. The arm and leg tests, given in duplicate, were feasible in 94% and 61% of subjects, respectively. Reliability coefficients exceeded .95 in patients with spastic cerebral palsy and myopathies and were somewhat lower in those with athetotic cerebral palsy. Means and SDs were similar in both trials. We conclude that the Wingate Anaerobic Test is feasible, highly reliable, and reproducible in these patients.

Adolescent↗
PubMed1990

Voluntary strength, evoked twitch contractile properties and motor unit activation of knee extensors in obese and non-obese adolescent males.

The purpose of this study was to determine whether neural and/or muscular factors contributed to the inferior strength-related motor performances of obese adolescents. Subjects were 10 non-obese (14.6% fat) and 11 obese (32.3% fat) males matched for age (15-18 years), level of maturity (Tanner stages IV and V), lean body mass, and height. Peak torque (PT) was measured during maximal voluntary isometric (IS) and isokinetic (IK) knee extension (KE). Peak twitch torque (TT), time to peak torque (TPT), and half-relaxation time (HRT) of the knee extensors were elicited by percutaneous electrical stimulation. The interpolated twitch technique was used to determine the extent of motor unit activation (% MUA) during maximal voluntary IS KE. Knee extensor cross-sectional area (CSA) was determined by computed axial tomography taken at the mid-thigh. All strength and area measurements were made on the right side of the body. Obese subjects had significantly (P less than 0.05) lower maximal voluntary IS and IK KE strength normalized for body weight, and significantly lower % MUA during IS KE. There were no significant differences (P greater than 0.05) between groups for absolute or normalized (for the product of muscle CSA and height) ISPT, IKPT, and TT, knee extensor CSA, or TPT and HRT. These results suggest that reduced MUA and a lower strength per mass ratio (due to excess fat) are probably important contributing factors to the poorer motor performances of the obese, especially for complex motor tasks involving large muscle groups and the support or moving of body weight.

Adolescent↗
PubMed1990

Effects of humid air breathing during arm or treadmill exercise on exercise-induced bronchoconstriction and refractoriness.

Although it has been reported that inhibitory prostaglandins may be a causal factor in exercise refractoriness, it is still unclear whether exercise-induced bronchoconstriction (EIB) and/or other specific "exercise factors" are necessary to trigger their release and render a subject refractory to subsequent exercise. The purpose of this study was to determine whether non-EIB-producing exercise with the legs or arms could produce refractoriness to a standard treadmill challenge. Eight asthmatic subjects with EIB completed three sessions consisting of two exercise challenges separated by a 30-min rest. In all sessions, the second challenge was done on a treadmill while breathing dry air. Conditions for Challenge 1 were the following: Session A = treadmill, dry air; Session B = treadmill, humid air; Session C = arm cranking, humid air. All three conditions produced a significant degree of refractoriness. There was a tendency for the percent protection index to be greater for Session A; however, no significant differences were found among the three sessions. Therefore, it can be concluded that although both exercise and bronchoconstriction may play a role in producing the refractory period, neither severe bronchoconstriction nor intense exercise with the same muscle groups are required to produce refractoriness.

Adult↗
PubMed1990

Use of the Borg scale in exercise prescription for overweight youth.

Twenty overweight children, ages 9-15 years, participated in a study on the usefulness of the Borg 6-20 perceived exertion (RPE) scale as a means for exercise prescription. As a criterion measure, they cycled at four intensities, based on pre-determined % peak power, giving RPE ratings at each load. During two return visits subjects were asked to set the resistance on the ergometer (cycle tasks) and to walk or run around an oval track (track tasks) at intensities they perceived as RPE = 7, 10, 13 and 16. HR-on-RPE regressions were compared among the criterion, cycle and track tasks. Cycle and track lines differed from the criterion (p less than .001). Subjects were, however, able to discriminate among each of the RPE prescriptions on the cycle. They overestimated intensities on the track tasks. We conclude that overweight children need additional instruction in using the Borg scale for exercise prescription.

Adolescent↗