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PubMed1989

A case study of stress and mass psychogenic illness in industrial workers.

Outbreaks of fainting, nausea, and weakness among several hundred workers led to an investigation of industrial conditions. Repeated and extensive monitoring failed to detect levels of any substance that might explain these reactions. In a subsequent investigation of the psychosocial environment, the authors used a combination of observations, inventories, and interviews to determine whether psychosocial factors might explain this phenomenon. A multiple regression analysis identified (in order of importance) work intensity, mental strain, work/home problems, education, and sex as independent predictors explaining 33% of the overall severity of illness. The work was high-pressured, repetitive, monotonous, and noisy. This profile is consistent with reports of mass psychogenic illness and with research indicating that such work can be distressing and unhealthy.

Age Factors↗
PubMed1998

Anaplerosis of the tricarboxylic acid cycle in human skeletal muscle during exercise. Magnitude, sources, and potential physiological significance.

In comparison to cardiac tissue, relatively few data are available regarding the concentrations of tricarboxylic acid cycle intermediates (TCAI) and the potential influence of TCAI pool size on the regulation of cycle flux in mammalian skeletal muscle. However, recent human exercise studies have confirmed the fundamental observation made in electrically-stimulated rodent muscle that moderate to intense contraction results in a net accumulation of TCAI. The increase in TCAI pool size, termed "anaplerosis," appears exponentially related to work intensity, although the relative changes in the individual cycle intermediates differ markedly. While a number of mechanisms could potentially contribute to the increase in TCAI, the reaction catalyzed by alanine aminotransferase appears primarily responsible for anaplerosis at the onset of exercise in humans. The expansion of the TCAI pool has been suggested to be important for aerobic energy provision, and various theories have been proposed which link the total concentration of TCAI with the capacity for TCA cycle flux during exercise. However, despite the recent advances which have been made with regard to the magnitude and potential source of TCAI expansion in humans, our understanding of the physiological significance of anaplerosis is limited. Indeed, it remains speculative whether the increase in TCAI pool size represents an important regulatory signal or is simply a consequence of the huge increase in metabolic flux which occurs during exercise.

Exercise↗
PubMed1996

Cardiovascular and peak VO2 responses to supine exercise: effects of age and training status.

Although stroke volume during exercise is affected by aging and posture, few studies have carefully examined the heart rate, blood pressure, and peak oxygen uptake (VO2) responses of older subjects to supine exercise. The present study examined these responses during graded supine cycling in younger (21-30 yr) and older (51-62 yr) untrained (Treadmill VO2max = 47.0 vs 32.3 ml.kg-1.min-1) and endurance-trained (66.3 vs 52.7 ml.kg-1.min-1) men (N = 6/group). All subjects had lower (P < 0.05) peak VO2 (ml.min-1) and peak heart rate responses during supine cycling compared with treadmill exercise. Additionally, the age-related reduction in peak VO2 (approximately 20-30%) was similar for supine compared with treadmill testing, even when normalized to fat-free leg volume and fat-free mass, respectively. However, at given absolute intensities (VO2) of supine exercise, heart rates were 10-15 beats.min-1 less (P < 0.05) in both older groups. Across relative supine work intensities (% of peak), systolic pressure increased most rapidly in the younger trained and older untrained groups. These findings suggest that the effects of aging on peak VO2 are similar during treadmill and supine exercise in both endurance-trained and untrained men. These data also indicate that the heart rate response to supine exercise is attenuated in healthy older men and contributes to their reduced peak VO2.

Adult↗
PubMed2001

Interval training for performance: a scientific and empirical practice. Special recommendations for middle- and long-distance running. Part I: aerobic interval training.

This article traces the history of scientific and empirical interval training. Scientific research has shed some light on the choice of intensity, work duration and rest periods in so-called 'interval training'. Interval training involves repeated short to long bouts of rather high intensity exercise (equal or superior to maximal lactate steady-state velocity) interspersed with recovery periods (light exercise or rest). Interval training was first described by Reindell and Roskamm and was popularised in the 1950s by the Olympic champion, Emil Zatopek. Since then middle- and long- distance runners have used this technique to train at velocities close to their own specific competition velocity. In fact, trainers have used specific velocities from 800 to 5000m to calibrate interval training without taking into account physiological markers. However, outside of the competition season it seems better to refer to the velocities associated with particular physiological responses in the range from maximal lactate steady state to the absolute maximal velocity. The range of velocities used in a race must be taken into consideration, since even world records are not run at a constant pace.

Exercise↗
PubMed1997

Ventilatory response to positive and negative work in patients with chronic obstructive pulmonary disease.

In healthy subjects, oxygen consumption and cardiorespiratory responses are lower during eccentric exercise (negative work, Wneg) than during concentric exercise (positive work, Wpos) at the same work load. The aim of the present study was to investigate the ventilatory response to Wneg in patients with chronic obstructive pulmonary disease (COPD). The study population consisted of 12 subjects with COPD [forced expiratory volume in 1 s (FEV1) mean (SD): 1.5 (0.4) 1, 46 (16)% of predicted]. Concentric and eccentric exercise tests (6 min exercise; interval > or = 1 h) were performed in random order at constant work loads of 25 and 50% of the individual maximal (positive) work capacity. Expired ventilation per minute (VE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were 30% lower during Wneg than during Wpos for both work intensities. The breathing reserve during 25% Wneg was 11 (8)% and during 50% Wneg was 18 (14)% higher than during Wpos at corresponding work loads (P < 0.01). VE/VO2 and VE/VCO2 were similar during Wpos and Wneg. Arterial carbon dioxide tension (PaCO2) increased by 0.1 (0.4) kPa during 50% Wneg and by 0.7 (0.5) kPa during 50% Wpos (P < 0.01). During 50% Wneg' perceived leg effort (modified Borg scale) tended to be higher than perceived breathlessness (2.4 (1.2) vs. 2.0 (1.1). It was concluded that in subjects with COPD, the ventilatory requirements of Wneg were considerably lower than those of Wpos at similar work loads up to 50% of maximal work capacity. During Wneg, the ventilatory reserve was higher and gas exchange was less disturbed as a result of a lower VO2 and VCO2.

Carbon Dioxide↗
PubMed1995

Quantitation of progressive muscle fatigue during dynamic leg exercise in humans.

There is virtually no published information on muscle fatigue, defined as a gradual decline in force-generating capacity, during conventional dynamic (D) leg exercise. To quantitate progression of fatigue, we developed 1) a model featuring integration of maximal voluntary static contraction (MVC) of knee extension (KE) muscles with ongoing DKE and 2) a device that allows frequent rapid transfer between DKE isolated to the quadriceps femoris muscles and measurement of KE MVC. Eight healthy men performed graded and submaximal constant work rate one-leg DKE to exhaustion while seated. Work rate, a product of a contraction rate (1 Hz), force measured at the ankle, and distance of ankle movement from 90 degrees to 150 degrees of KE, was precisely controlled. Lack of rise in myoelectric activity in biceps femoris of the active leg during DKE and MVC was consistent with restriction of muscle action to quadriceps femoris. The slope of the linear relationship between O2 uptake and work rate was 13.7 ml O2/W (r = 0.93). This slope and the increase of heart rate relative to increasing work intensity agreed with published values for D leg exercise. Test-retest values for O2 uptake were similar (P > 0.05) for matched DKE work rates. To track fatigue, MVC (90 degrees knee angle) was performed every 2 min of DKE. After 4 min of DKE at work rates corresponding to (mean +/- SE) 66 +/- 2, 78 +/- 2, and 100% of peak DKE O2 uptake, MVC fell to 95 +/- 3, 90 +/- 5, and 65 +/- 7%* of MVC of rested muscle, respectively (*P < 0.01 from previous work rates). Virtually identical declines in MVC were observed by the end of graded work rate DKE and submaximal constant work rate DKE tests. Quantitation of progressive muscle fatigue during D leg exercise provides a framework to study the effects of a variety of interventions on the fatigue process and may permit unique insights into the involved mechanisms.

Adolescent↗
PubMed1990

Is hypoxia a stimulus for synthesis of oxidative enzymes and myoglobin?

To compare two situations with similar magnitudes of mitochondrial substrate flux but different blood oxygen contents, one-legged training was employed. Ten healthy subjects trained one leg under normobaric conditions and the other under hypobaric conditions. At each session the subjects trained each leg for 30 min. The absolute work intensity was the same for both legs and was chosen to correspond to 65% of the average (right and left) pretraining one-legged maximal work capacity. There were three to four training sessions per week for 4 wk. Muscle biopsies from each leg were taken before and after training and analyzed for fiber types, capillaries, myoglobin, and oxidative and glycolytic enzymes. The most striking finding was a greater increase of citrate synthase activity under hypobaric conditions than under normobaric conditions. In addition, the myoglobin content increased in the leg trained under hypobaric conditions, whereas it tended to decrease in the normobarically trained leg. Because both legs were trained at the same intensity, the oxygen turnover and the substrate flux through the carboxylic acid cycle and the respiratory chain must have been of similar magnitude. Thus a difference in substrate flux is less likely to have caused the differences in enzyme activities and myoglobin content between training under normobaric and hypobaric conditions. Instead, the stimulus seems to be related to the blood oxygen content or tension.

Adult↗
PubMed2002

Return to work after spinal cord injury: a review of recent research.

This manuscript reviews recent research on return to work (RTW) for individuals who sustain spinal cord injury (SCI), including the effects of demographics variables, occupational characteristics, workplace accommodations, quality of life, physical functional limitations, and other variable. Demographic variables that influence RTW for persons with SCI include age at injury onset, chronological age, gender, education, ethnicity, marital status, and per-injury work intensity. Others include satisfaction, and adjustment to sustaining SCI. In an effort to enhance employment opportunities for individuals with disabilities including SCI, Ticket to Work Incentive Improvement Act of 1999 (TWILA) has been passed by Congress and some states have begun implementing targeted initiatives through the State Partnership Systems Change Initiatives (SPI). Future research directions are recommended in light of recent legislative initiatives.

Activities of Daily Living↗
PubMedDate not supplied

[Results of medical studies in relation to the program of the second space flight on the orbital complex "Mir"].

In 1987, the USSR cosmonauts Y. V. Romanenko (326 days), A. I. Laveikin (approximately 176 days), and A. P. Alexandrov (approximately 160 days) made a space mission on Mir. (A. I. Laveikin showed specific cardiovascular responses to exercise tests and was therefore replaced with A. P. Alexandrov). The most important medical result of this mission was that Yu. V. Romanenko, who remained in orbit for 3 months longer than anyone before, working intensively, did not exhibit any changes that were qualitatively different from those observed in previous long-duration space flights. The health status and work performance of other crewmembers were also good, although each of them showed individual responses. The postflight recovery period went smooth.

Adaptation, Physiological↗
PubMed2005

[Physiologic and hygienic characteristics of college teachers work].

First series of studies covered analysis of lecture with registering number of words and movements complementary to them. The series 2 determined occupational activities of college teacher, according to contemporary hygienic classification, as highly intensive work requiring physiologic and managerial correction.

Adaptation, Physiological↗
PubMed1989

Effect of active warming-up on thermoregulatory, circulatory, and metabolic responses to incremental exercise in endurance-trained athletes.

The influence of 10 min warming-up at 40% VO2 max on thermal, circulatory, and metabolic responses to an incremental exercise to exhaustion as well as on the anaerobic threshold at the blood lactate level of 4 mmol.l-1 (AT) and the individual anaerobic threshold (IAT) was investigated in eight cross-country skiers. During exercise preceded by warming-up, the mean skin temperature (T sk) and external auditory canal temperature (Tac) did not change significantly in contrast to exercise without warming-up, producing a rise in both T sk and Tac (by approx. 1.2 degrees C and 1.1 degrees C, respectively). Warming-up did not alter the course of the rectal temperature changes during exercise. With warming-up skin humidity rose immediately after the beginning of exercise, whereas the onset of sweating without warming-up appeared much later at higher work intensities. Warming-up did not change the circulatory and ventilatory responses to incremental exercise and the oxygen uptake (VO2) either at submaximal or maximal work loads. With warming-up a significant increase was found in the threshold work load both at the AT and the IAT. The data demonstrated that warming-up has an advantageous effect on the efficiency of thermoregulation in endurance-trained athletes producing an early sweating response to the incremental exercise that results in attenuation of hyperthermia. An increase in the anaerobic threshold during incremental exercise preceded by warming-up may indicate an enhancement of the endurance capacity subsequent to warming-up.

Adolescent↗
PubMed1986

Training responses of two age groups during treadmill walking.

The purpose of the present study was to use a previously developed treadmill walking test to determine training-induced changes within and between two groups of untrained men during a six week training period. One group consisted of seven middle-aged (mean age, 41.3 yr), and the second group consisted of seven young adult (mean age, 19.9 yr), men. Heart rates following training were significantly lower at all work intensities for the middle-aged men (p less than 0.005) whilst for the young adults only the 12.5% and 15% (p less than 0.025) work levels were significantly lower. Blood lactic acid concentrations (p less than 0.005), Respiratory Exchange Ratios (p less than 0.05), Ventilatory Equivalents (p less than 0.005) and mean Two Mile times (p less than 0.005) were all significantly lower after training for the older age group but this was not so for the younger adult group. The oxygen cost of the walking test was lower for four of the workloads of the middle-aged, but only for the final workload (p less than 0.005) for the young adults, after training. The performance test did not disadvantage the middle-aged subjects yet the results demonstrated that the test provided a common means of reflecting the training state of the two groups whether the level of activity took place on the treadmill or on the track.

Adolescent↗
PubMed1989

Norepinephrine spillover from skeletal muscle during exercise in humans: role of muscle mass.

The purpose of this study was to determine the effect of increasing muscle mass involvement in dynamic exercise on both sympathetic nervous activation and local hemodynamic variables of individual active and inactive skeletal muscle groups. Six male subjects performed 15-min bouts of one-legged knee extension either alone or in combination with the knee extensors of the other leg and/or with the arms. The range of work intensities varied between 24 and 71% (mean) of subjects' maximal aerobic capacity (% VO2max). Leg blood flow, measured in the femoral vein by thermodilution, was determined in both legs. Arterial and venous plasma concentrations of norepinephrine (NE) and epinephrine were analyzed, and the calculated NE spillover was used as an index of sympathetic nervous activity to the limb. NE spillover increased gradually both in the resting, and to a larger extent in the exercising legs, with a steeper rise occurring approximately 70% VO2max. These increases were not associated with any significant changes in leg blood flow or leg vascular conductance at the exercise intensities examined. These results suggest that, as the total active muscle mass increases, the rise in sympathetic nervous activity to skeletal muscle, either resting or working at a constant load, is not associated with any significant neurogenic vasoconstriction and reduction in flow or conductance through the muscle vascular bed, during whole body exercise demanding up to 71% VO2max.

Adult↗
PubMed1996

Oxygen deficit: a measure of the anaerobic energy production during intense exercise?

Several findings in studies of whole-body exercise indicate that the energy provided from anaerobic sources during intense whole-body exercise cannot be quantified from oxygen deficit determinations when energy demand for the supramaximal exercise is estimated from a linear relationship between work intensity and energy production during submaximal exercise. It is likely that the energy demand during high-intensity exercise is underestimated by this procedure; these errors are probably greatest for very high power outputs (shorter exercise time to exhaustion). It is clear that further studies are needed to characterize the energy demand during intense exercise before the oxygen deficit can be used as a measure of the anaerobic energy production.

Anaerobic Threshold↗
PubMed1990

Mechanical efficiency during cycling in prepubertal and adult males.

Previous studies have indicated that values for mechanical efficiency during cycle exercise in prepubertal subjects are similar to those in adults. Few studies have directly compared these groups, however, and earlier reports did not consider the importance of assessing efficiency at similar relative exercise intensities. Nineteen prepubertal boys and 21 college men underwent cycle exercise testing for determination of delta efficiency (the energy required to increase workload), related to both absolute work load and relative work intensity (percent VO2max). No significant differences in either of these measures were observed between the two groups. Mean delta efficiency between workloads of similar relative intensity was 23.2% for the prepubertal subjects and 22.5% for the adults (p greater than .05). Between equal absolute workloads the values were 23.2 and 26.5%, respectively (p greater than .05). These findings support earlier contentions that the efficiency of muscular contraction during exercise is comparable in pre- and post-pubertal subjects.

Adult↗
PubMed1975

Limitations to maximum oxygen uptake in arms, leg, and combined arm-leg ergometry.

Our purpose was to study the effect of arm, leg, and combined arm-leg ergometry on the oxygen uptake (Vo2), cardiac output (Q), ventilation, and anaerobic threshold (AT) of three healthy men. At submaximum work intensities, Vo2 was not significantly different in the three tasks, but differences were observed for heart rate, ventilation, and Q. The AT was reached at progressively higher work rates in arm, leg and combined arm-leg ergometry, respectively. The Vo2 max in arm ergometry averaged 68 percent of the Vo2max in leg ergometry and 60 percent of Vo2 max in combined arm-leg ergometry. Two subjects with Vo2max's less than 45 ml/kg-min had a mean Vo2max in combined arm-leg ergometry 19 per cent higher than in leg ergometry. A third subject, with a Vo2max greater than 50 ml/kg-min, showed no change. Differences in Vo2max were primarily due to the differences in Q. Skeletal muscle blood flow appears to be a critical factor in the limitation of Vo2max in arm or leg ergometry.

Adult↗
PubMed2000

Self-rated health and occupational conditions in Russia.

A low level of health promotion and disease prevention awareness in Russia, such as disregard for personal health during periods of well-being or illness, have contributed to a decline in general population health over the past decade. The relationship of working conditions and health awareness was explored among a sample of adults in Russia. This research project was conducted, July-August, 1998, in the city of Kazan. Data was collected by probability sampling of addresses and personal interview. Working conditions influence general public and family health. The occupation of the spouse contributed significantly to family conflicts, and financial problems ranked first as the cause of marital conflict. Due to lack of material resources, one-third of respondents, even though employed, reported being dissatisfied with the quality of their nutritional status and one-fifth with the lack of leisure time. Although more than two-thirds were satisfied with their work, every fifth did not consider their wages sufficient, every fourth wanted to change occupations, and every third was afraid of being fired. The majority of employed respondents reported low salaries, worked a full 8-hour day at their primary occupations and one-fifth had a second job. Younger people were especially prone to disregard their health with intensive work schedules. About half of respondents reported being exposed to toxic health hazards in their past or current jobs. Almost one-fifth agreed to work at hazardous occupations because of higher salaries. Social status, indicated by a higher education, was associated with having the opportunity to chose work in more favourable circumstances, and consequently with less health risks. In summary, the research demonstrated that health was an instrumental value in Russia, exploited as a economic resource not only during periods of well-being but also during illness, by individuals not seeking preventive or timely health care because of the fear of losing their jobs.

Adult↗
PubMedDate not supplied

[The evaluation of the physiological workload in the Brazilian legislation should be revised! The case of garbage collectors in Rio de Janeiro].

The physiological workload (PW) involved in garbage collection was assessed in a probabilistic sample of 70 Rio de Janeiro city garbage collectors to determine the adequacy of Brazilian labor legislation regarding classification of work. PW was measured as energy expenditure (EE) and heart rate (HR) during total work time (TT) and actual time (AT) in garbage collection on 4 consecutive days. Median EE values were 288.4 and 319.1 kcal.h-1 during TT and AT, respectively, indicating moderately intense work according to Brazilian legislation. However, PW was considered heavy when work classifications based on individual response to work were used: 1) ratio of EE and resting metabolic rate was above 5.0, indicating heavy workload according to the WHO; 2) mean percentage of maximal EE was higher (36.2 and 41.1% for TT and AT, respectively) than the limit for garbage collection (30%) suggested as maximal for Dutch workers; and 3) percentage of maximal HR reserve was also higher than 30% (32.2 and 37.5% for TT and AT, respectively). These results indicate the need for a revision of the workload classification in the Brazilian legislation to take individual workers' characteristics into account.

Adult↗