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Biomedical subjects

O Bar-Or

Publications and source records attributed to O Bar-Or.

At least 91 records · Page 5Linked to original sources
PubMed1989

Voluntary and electrically evoked strength characteristics of obese and nonobese preadolescent boys.

Overweight and obese children demonstrate inferior motor performance for strength- and power-related activities requiring support or lifting of body weight. Our purpose here was to determine whether the inferior performance could be attributed to a lower strength to muscle area ratio in the obese. Eleven nonobese (16.6% fat) and 13 obese (35.5% fat) boys (9-13 years old) volunteered for the study. Peak torque was measured during voluntary isometric and isokinetic elbow flexion and knee extension at four joint angles and four velocities, respectively. The contractile properties, twitch torque, time to peak torque, and half-relaxation time were evoked for the elbow flexors by percutaneous stimulation. Elbow flexor and knee extensor cross-sectional areas (CSA) were determined by computed axial tomography taken at the mid-upper arm and mid-thigh, respectively. Isometric and isokinetic elbow flexion and knee extension strength normalized for body weight were significantly (p less than 0.05) higher in the nonobese compared to the obese boys. There were no significant (p greater than 0.05) differences, however, between groups for elbow flexor and knee extensor CSA or for absolute and relative (normalized for muscle CSA or the product of muscle CSA and height, the latter accounting for differences in moment arm length) isometric, isokinetic, or evoked twitch torque for elbow flexion or knee extension. Likewise, there were no differences between groups for the time-related contractile properties, time to peak torque, or half-relaxation time. These findings suggest that there is no difference in the intrinsic strength or contractile properties of the elbow flexor and knee extensor muscles between obese and nonobese pre-adolescent boys and that other factors, such as the handicapping effect of excess fat mass, probably account for the reduced motor performance of the obese child.

Analysis of Variance↗
PubMed1988

Anaerobic power of arms in teenage boys and girls: relationship to lean tissue.

The purpose of this study was to describe anaerobic peak and mean power characteristics of arms as a function of age, gender and body composition among 50 girls and 50 boys 14 to 19 years of age. Peak (PP) and mean power (MP) output were determined during arm cranking (Wingate anaerobic test). Fat-free weight (FFW) was estimated from skinfolds, and lean arm volume (LAV) was determined by water displacement, corrected for fat volume. PP and MP increased progressively and significantly (P less than 0.05) with age for boys but not for the girls. Boys had significantly larger absolute PP and MP outputs than girls at comparable ages. PP and MP corrected for lean tissue volume were greater in older than younger boys (P less than 0.05), but did not vary significantly with age for girls. Absolute (W) PP and MP were highly correlated with LAV (r = 0.82; r = 0.75) and FFW (r = 0.84; r = 0.78) among boys. The respective r values for girls were 0.60 and 0.49 (LAV); 0.78 and 0.60 (FFW). Absolute peak and mean power, respectively, were more highly correlated with LAV (r = 0.90; r = 0.84) and FFW (r = 0.90; r = 0.85) for the combined data for boys and girls than for similar gender specific comparisons. In conclusion, both anaerobic PP and MP of arms during adolescence are highly correlated with lean tissue volume and fat-free weight, particularly among boys.

Anaerobiosis↗
PubMed1986

Effect of training on anaerobic threshold, maximal aerobic power and anaerobic performance of preadolescent boys.

To evaluate the effect of a 9-week interval training program on aerobic capacity, anaerobic capacity, and indices of anaerobic threshold of preadolescent boys, 28 10.2- to 11.6-year-old boys were tested. The test included laboratory evaluation of anaerobic capacity (Wingate anaerobic test) and evaluation of VO2 max and anaerobic threshold indices from a graded exercise test and measurement of blood lactate. The tests also included a 1200-m run to investigate the relationship of laboratory fitness indices, VO2 max, anaerobic threshold indices, and indices of anaerobic capacity to the performance of the run. It was found that in 10- to 11-year-old boys, a 9-week interval training increased the indices of anaerobic capacity: mean power by 10% and peak power by 14%. No change was found in percent fatigue. The training also increased VO2 max by 7% in absolute terms and by 8%/kg body weight. A significant increase was also found in the running velocity at the anaerobic threshold (running velocity at inflection point of lactate accumulation curve), but in relative terms (percent of VO2 max), the anaerobic threshold decreased by approximately 4.4%. It is concluded that proper training may improve maximal aerobic power and anaerobic capacity of preadolescent boys. It is also concluded that anaerobic threshold measures are less sensitive to the training regimen than VO2 max and that the 1200-m running performance is strongly associated with both aerobic and anaerobic capacities and less with the anaerobic threshold, which in preadolescent boys seems to be higher than in adults.

Anthropometry↗
PubMed1986

Anaerobic characteristics in male children and adolescents.

Only sparse information has been published on the effects of growth, development, and maturation on the ability to perform high intensity, short-term "anaerobic" tasks. Cross-sectional studies on Italian, African, British, and American females and males have indicated an age-related progression in the performance of the Margaria step-running test. Children had a distinctly lower mechanical power output than adolescents and young adults, both in absolute terms and when divided by body weight, or by fat-free mass. Data are presented on some 300 10- to 45-yr-old Israeli males who performed the Wingate anaerobic test by cycling or by arm cranking. Both the peak power at any 5-s period and the mean power throughout the test were lowest in the children, whether expressed in absolute power units or corrected for body weight. Performance progressed with age and reached the highest values at the end of the third decade for cycling and at the end of the second decade for arm cranking. This pattern is unlike that described for maximal O2 uptake per kg body weight which, in males, remains virtually unchanged from childhood to young adulthood. In females, maximal O2 uptake per kg is even higher in children than among adolescents or adults. Biochemical correlates of such a low anaerobic performance in children are their lower maximal lactate concentration in muscle and blood, lower rate of anaerobic glycolysis, and lower levels of acidosis at maximal exercise. The mechanisms for the relatively deficient anaerobic characteristics of children are not clear.

Acidosis↗
PubMed1986

Pathophysiological factors which limit the exercise capacity of the sick child.

While deficient exercise performance of sick children results from hypoactivity and detraining, it can also be caused by specific pathophysiological factors. These can affect one or more components of physical fitness. A low maximal aerobic power will result from a low maximal stroke volume, as in aortic stenosis or cardiomyopathy; a low maximal heart rate, as in congenital complete heart block or intake of beta-blockers; a low O2 content of the arterial blood, as in anemia or advanced cystic fibrosis; and a high O2 content of mixed-venous blood, as in muscle atrophy or severe malnutrition. A high O2 cost of locomotion, as in advanced obesity or cerebral palsy, will cause the patient to exert at a high percentage of his maximal aerobic power and thus fatigue easily. A subnormal muscle strength, as in progressive muscular dystrophy or juvenile rheumatoid arthritis, is sometimes the primary factor that limits the walking ability or other daily functions. Recent data suggest that local muscle endurance, as assessed by the Wingate anaerobic test, is particularly deficient in some neuromuscular diseases. Examples are muscular dystrophies and spastic cerebral palsy. The ratio of peak anaerobic power to peak aerobic power seems lower in such patients than in able-bodied controls.

Adolescent↗
PubMed1986

Role of the physician and physical education teacher in the treatment of obesity at school.

Obesity ranks as a leading chronic pediatric disorder, with estimates ranging from 10 to 25% of the childhood and adolescent population. Physical hypoactivity is prevalent among obese youth and may be an etiological factor. Physical training, with or without nutritional intervention, has been found effective for weight and body fat control. The purpose of this paper is to examine the role that the physician and physical education teacher can play in the treatment of obesity at school. Studies of school-based intervention programs utilizing exercise, nutrition and behavior modification are reviewed. Suggestions are outlined for school-based obesity programs.

Adolescent↗
PubMed1983

Load optimization for the Wingate Anaerobic Test.

The purpose of the present study was to define the optimal loads (OL) for eliciting maximal power-outputs (PO) in the leg and arm modes of the 30s Wingate Anaerobic Test (WAnT). Eighteen female and seventeen male physical education students, respectively 20.6 +/- 1.6 and 24.1 +/- 2.5 years old, volunteered to participate. In each of the total five sessions, the test was administered twice on a convertible, mechanically braked cycle-ergometer, once for the legs and once for the arms. The five randomized, evenly-spaced resistance loads ranged from 2.43 to 5.39 Joule per pedal revolution per kg body weight (B. W.) for the legs, and from 1.96 to 3.92 for the arms. The measured variables were mean (MP x kg-1) and peak PO as well as absolute and relative measures of fatigue. A parabola-fitting technique was employed to define the optimal loads from the MP x kg-1 data. The resulting OL were 5.04 and 5.13 Joule x Rev-1 x kg B.W.-1 in the leg and 2.82 and 3.52 in the arm tests for the women and men, respectively. OL were shown to depend on PO magnitude. However, within a two-load span (0.98 Joule x Rev-1 x kg B.W.-1) about the OL, MP x kg-1 did not vary by more than 1.4% in the leg and 2.2% in the arm tests. It is suggested that although the WAnT is rather insensitive to moderate variation in load assignment, improved results could be obtained by using the stated OL as guidelines that may be modified according to individual body build, composition, and, particularly, anaerobic fitness level.

Adolescent↗
PubMed1983

Follow-up of normotensive men with exaggerated blood pressure response to exercise.

The early detection of hypertension is of foremost concern. It may be that individuals who are normotensive at rest but who show an exaggerated blood pressure (BP) response to exercise are at greater risk of developing hypertension in the future. From exercise tests, a group (ER) of healthy young males who were normotensive at rest (BP less than or equal to 140/90) but showed an exaggerated BP response to exercise (systolic BP greater than or equal to 200 mm Hg and/or diastolic BP 10 mm Hg to greater than 90 mm Hg) were selected. A control group (NR) with exercise BP values less than these were matched for age, weight/height, skinfold thickness, resting BP less than or equal to 140/90, resting heart rate, aerobic fitness level, physical activity, smoking history, and family history of hypertension. After a follow-up period of 5.8 years (range 3 to 14 years) eight of the subjects from the ER group were found to be hypertensive, whereas none of the NR group were hypertensive. Stepwise multivariate regression showed the exercise blood pressure to be the best predictor of future blood pressure of the parameters reviewed in this study. Exaggerated BP response to exercise may serve as an additional risk marker for hypertension.

Adolescent↗
PubMed1983

Maximal aerobic capacity of Canadian schoolchildren: prediction based on age-related oxygen cost of running.

Timed distance runs were administered to a random sample of 2,683 schoolchildren aged 7--16 years. Oxygen uptake was then measured during level treadmill running over a range of submaximal speeds in a randomly selected subsample of 134 children with approximately equal representation according to age and sex. The VO2--running speed relationship was found to be related to age with the younger children having a greater VO2 per kg body weight than the older children when running at the same absolute speed. Based on the relationship found between measured VO2max and VO2max predicted according to field test performance, corrected for age-related differences in running efficiency, VO2max was predicted for all 2,683 children. When expressed per kg of body weight, VO2max was highest in girls at age 11 (approximately 44 ml/kg) and in boys at age 14 (approximately 54 ml/kg); however, differences among ages were nonsignificant. At all ages VO2max for the boys was significantly higher than that for the girls. At all ages, values were higher than those previously reported for Canadian schoolchildren.

Adolescent↗
PubMed1983

Lactate in human skeletal muscle after 10 and 30 s of supramaximal exercise.

The purpose of this study was to evaluate the extent of anaerobic glycogenolysis, as indicated by intramuscular lactate concentration, after 10 and 30 s of supramaximal exercise and to compare male and female subjects in this regard. Fifteen males and seven females performed two cycle exercise bouts against a resistance which was standardized so that one pedal revolution resulted in 4.90 J work X kg body wt-1. A muscle biopsy was obtained after 10- and 30-s exercise bouts and analyzed for lactate concentration. The lactate concentrations averaged 36 and 61 mmol X kg dry wt-1 after the 10- and 30-s exercise bouts, respectively. The male subjects had higher (P less than 0.005) lactate concentrations and generated higher (P less than 0.001) power outputs for both exercise bouts. When the mean lactate concentrations were statistically adjusted after controlling for between-group variation in power output, no difference was evident between groups for the 10- or the 30-s lactate value. The results are evidence that pronounced lactate accumulation occurs during supramaximal exercise of a 10-s duration, suggesting that glycolysis can occur within this time frame. This is in contrast to the theory that glycolysis does not occur until endogenous phosphagen levels reach some critically low value, not thought to be obtainable within the first 10 s of supramaximal exercise.

Female↗
PubMed1982

Hemoglobin, hematocrit, and calculated plasma volume changes induced by a short, supramaximal task.

The influence of a short, supramaximal task of 30 s duration on plasma volume (PV) was tested in 14 female physical education students. Hemoglobin (Hb), hematocrit (Hct), and osmolality (Osm) were tested pre- and post-exercise. Performance of the exercise test, consisting of 30 s all-out pedaling against a load of 4.4 J/kg body weight per pedal revolution, brought about a significant elevation in the measured variables. The changes in Hct, Hb, and Osm were 3.14%, 0.92g X dl-1, and 9.58 mOs/kg-1, respectively. The changes in PV, calculated from the increase in Hct alone and from changes in Hct and Hb, was found to be -10.4% and -11.2%, respectively. It is suggested that very short periods of maximal exercise can bring about some 10% - 15% drop in PV. Mechanisms for this decrease are not clear. It could result from changes in tissue osmolality, filtration pressure, or opening up of collapsed capillaries.

Adult↗
PubMed1982

Changes in muscle metabolites in females with 30-s exhaustive exercise.

The purpose of this study was to quantify the changes in selected intramuscular metabolites associated with non-oxidative energy metabolism after performance of the Wingate Test (WT), a widely used, exhaustive, 30-s cycle test of short-time muscular power. Muscle biopsies were taken from the m. vastus lateralis of nine female physical education students at rest and immediately after performance of the WT. The concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), lactate, and glycogen were determined. The ATP decreased from 20.9 to 13.8; CP decreased from 62.7 to 25.1; lactate increased from 9.0 to 60.5; and glycogen decreased from 360 to 278 (all concentrations are mmol X kg-1 dry muscle). The absolute changes in CP and lactate were not as large as those reported in other exercise studies. Based on the metabolite changes, it was concluded that the WT is a satisfactory test of the maximal muscular power that can be generated from non-oxidative metabolism, but that the 30-s duration of the test probably does not tax the maximal capacity of such energy metabolism.

Adenosine Triphosphate↗
PubMed1982

Clinical implications of pediatric exercise physiology.

In recent years, there has been a surge of interest in health aspects of physical activity of children and preadolescents. The reasons of such interest are twofold: a) the great numbers of children who are exposed to high-level conditioning and competition regimens and, b) the recognition by Pediatrics that physical exercise can be a useful tool for pediatric diagnosis and an integral part of clinical management strategies. In an overview of the relationships between health and exercise, selected examples are given to illustrate the following pediatric topics: a) exercise as a diagnostic tool--invasive techniques (congenital heart defects); b) exercise as a diagnostic tool--non-invasive techniques (exercise-induced asthma, growth hormone deficiency); c) habitual activity of the sick child--diseases in which hypoactivity is inherent to the pathology (muscle dystrophies, cerebral palsy); d) habitual activity of the sick child--hypoactivity incidental to the pathology ("innocent murmur", hemophilia); e) deleterious, non-traumatic effects of acute exercise (diabetic hypoglycemia, heat strain); f) deleterious, non-traumatic effects of chronic exercise (menstrual cycle, over-use syndromes).

Adolescent↗
PubMed1981

Conditioning versus exercise in heat as methods for acclimatizing 8- to 10-yr-old boys to dry heat.

Two heat-acclimatization protocols were studied in 8- to 10-yr-old boys: exercise in dry heat (WH, n = 9) and exercise in neutral climate (W, n = 9). Five 90-min acclimatization sessions were conducted within a 12-day period. Base-line (BL) and criterion (CT) tests sessions were held at 43 degrees C db and 24 degrees C wb, with three 20-min exercise bouts at approximately 40 Ws. With acclimatization, the WH group showed a significant reduction in heart rate (HR) (11.4 beat x min-1), mean skin temperature (0.64 degrees C), and an increase in the population density of heat-activated sweat glands (HASG) (25.2 glands x cm-2). The W group showed a significant reduction in HR (13.4 beat x min-1) and rectal temperature (0.24 C). Total sweat rate per body surface area did not increase significantly in either group. However, the sweat rate relative to rise in core temperature increased in both groups. No significant differences were found between the two acclimatization procedures in any of the variables studies except for the HASG, which showed a greater increase in the WH group. It is suggested that in 8- to 10-yr-old boys physiological changes compatible with heat acclimatization could be achieved either by exercise in heat or by mere physical conditioning (approximately 65% of VO2max), in neutral climate. It is postulated that age-related factors associated with the thermoregulatory system prevent children from deriving full effectiveness of exercise-in-heat acclimatization protocol as used in this study.

Acclimatization↗
PubMed1980

Climatic heat stress and performance in the Wingate Anaerobic Test.

To determine climatic effects on performance of the Wingate Anaerobic Test, 28 children (10.2-12.2 years old) were each tested in three different climates: Neutral (22-23 degrees C, 55-60% R.H.), hot-dry (38-39 degrees C, 25-30% R.H.), and warm-humid (30 degrees C, 85-90% R.H.). The test is an all-out 30 s cycle-ergometer-pedalling in which mean as well as peak power outputs are determined. The children stayed in the climatic chamber for 45 min prior to the test. Mean power, relative to body weight, was higher in the boys after the warm-humid exposure compared with the hot-dry one (P < 0.05). No other differences were found. Inter-climate correlations of weight-relative power outputs were 0.83-0.92 and 0.82-0.86 for mean power in the girl and boy groups, respectively, and 0.33-0.72 and 0.49-0.75 for peak power, in the same order. The corresponding values for absolute power outputs were always higher. Reasons why the single detected inter-climate difference is likely to have been a happenstance are discussed, and it is suggested that comparable environmental exposures do not appreciably affect performance of the Wingate Anaerobic Test by children and young adolescents. The practicality and reliability of this test is, therefore, well maintained in "field situations" where climate cannot be strictly controlled.

Child↗
PubMed1980

Breathing dry or humid air and exercise-induced asthma during swimming.

Recent studies have shown the relevance of air humidity to the provocation of bronchoconstriction by running. The present study was undertaken to ascertain whether the humid air breathed during swimming could explain the protective effect of swimming on the asthmatic. Nine asthmatic children 9--15 years old swam while inspiring dry (15--35% R.H.) or humid (80--90% R.H.) air administered in a random order, a week separating the two sessions. The exercise challenge was an 8-min tethered swim at a metabolic rate (VO2) of 29 ml.kg-1.min-1, minute ventilation (VE) of 34 L.min-1, and a heart rate (HR) of 161 beats.min-1. Ambient air and water temperature were 28 +/- 2 degrees C and 27 +/- 2 degrees C, respectively. Pulmonary functions were tested pre and post swimming. Exercise VE, VO2 and HR were similar under the two conditions. No reduction in any of the pulmonary functions (FVC,FEV1.0,MMEFR,MBC) was found after 5 and 10 minutes following the swimming exercise in either of the conditions. In contrast, a treadmill run of similar metabolic and ventilatory intensity induced bronchoconstriction when room air was dried to 25--30% R.H. It is suggested that, unlike running, swimming is of low asthmogenicity even when inspired air is dried to 25--30% at neutral temperatures.

Adolescent↗