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PubMed1978

Lactate release in relation to tissue lactate in human skeletal muscle during exercise.

In four healthy volunteers, muscle lactate concentration and the release of lactate from the leg were determined at rest and at 4 and 12 min of sitting bicycle exercise at four intensities (30, 50, 70, and 90% of maximal oxygen uptake). The muscle biopsies were obtained by needle biopsy technique from m. vastus lateralis. The rate of lactate release was calculated from the femoral venous-arterial differences of lactate and the leg blood flow was determined by constant rate dye infusion. Both leg blood flow and leg oxygen consumption increased linearly with work intensity. The release of lactate rose approximately linearly with the muscle lactate concentration up to about 4-5 mmol/min but then the relationship revealed a clear leveling off. These results indicate a maximal level for the lactate release from the exercising muscles with a translocation hindrance for lactate within the muscles.

Adult↗
PubMed1983

Phases of progressive burnout and their work site covariants: critical issues in OD research and praxis.

The term "burnout" represents a significant perspective on how people respond to their work, but the attention paid to this phenomenon has largely been clinical and often anecdotal. In this article, the authors seek to expand the analysis of burnout in ways that permit comparative analysis, especially in large populations. This study specifically addresses three questions. First, does a paper-and-pencil instrument isolate domains of burnout that are relatively consistent between people-intensive work and the broader range of activities found in a commercial enterprise? Second, can we develop phases of progressive burnout? Third, can we test the efficacy of the burnout phases by searching for regularities in a panel of 22 variables commonly thought to tap the important facets of the work site? The author's analysis shows that we can answer these three central questions affirmatively, though occasionally with complex and potentially significant qualifications. The results of the analysis provide further evidence of the usefulness of a convenient instrument for measuring burnout and also suggest that behavioral scientists will find valuable a phase model that distinguishes regular and robust covariation by using a panel of variables thought to tap the important aspects of organizational life.

Analysis of Variance↗
PubMed1993

[A study on the primary prevention of essential hypertension (1). Evaluation of blood pressure response during exercise and effect of habitual exercise].

Hypertension is one of the risk factors of cardiovascular diseases, which are widely prevalent maladies that result in burdensome medical expenditures. Therefore, it is important to explore primary preventive measures for hypertension. Until recently, it was thought that exercise was a risk factor for hypertension, but recent reports have suggested that low-intensity physical training actually lowers blood pressure. However, habitual physical exercise has still not been clearly proven to prevent the development of hypertension. To clarify this point, one must first establish a method for predicting hypertension and second examine the possibility of preventing the development of hypertension by changing the subject's environment. In this study we have investigated a method for predicting hypertension by classifying blood pressure responses to increasing exercise intensity and the effect of habitual exercise on blood pressure response. This study was composed of three experiments. Experiment one involved female students (n = 42) and experiment two, male students (n = 38), in whom blood pressure response rates during exercise were recorded. In experiment three, the same group of female students (n = 23) was subjected to training in order to chart its effects on blood pressure response, both while exercising and while at rest. The exercises were performed with a bicycle ergometer in an upright position. There were four different degrees of work intensity. Blood pressure was measured using the auscultation method, with Riva-Rocci mercury measured by the same investigator. High blood pressure responses at rest were noted among some normotensive female and male students. The systolic blood pressure responses during the peddling exercise showed significant individual differences at the lowest work load; the distribution of the increment of the systolic blood pressure ratio at the lowest work load against the increment while resting showed two peaks. This result suggests that this increment ratio is an important variable related to the prediction of hypertension. The increment ratio showed no significant change in female students after three months of aerobic exercise. The high-response group showed high readings of the TPR indicator (MBP/VO2). Aerobic training was shown to be effective in significantly lowering the TPR indicator both at rest and during exercise. This result suggests that habitual exercise may contribute to preventing the development of hypertension.

Adult↗
PubMed2006

Differences in exercising limb blood flow variability between cardiac and muscle contraction cycle related analysis during dynamic knee extensor.

AIM: Blood flow in peripheral conduit arteries during steady-state, dynamic exercise, can be estimated noninvasively with Doppler ultrasound, by measuring the conduit arterial diameter and the mean blood velocity averaged over consecutive cardiac beat-by-beat cycles (BB(cycle)) or muscle contraction-relaxation cycles (CR(cycle)). The precise impact fluctuations in the 1-BB(cycle)- or 1-CR(cycle)-rate may impose on the average blood flow measurements has previously not been clearly defined. The hypothesis investigated in the present study was that the blood flow measurements obtained, and its variability, during exercise, may differ between the 1-BB(cycle) and 1-CR(cycle) at incremental exercise intensities; as the BB(cycle)-measurements may be influenced by transient alterations in heart rate; whereas the CR(cycle)-measurements are dependent on the muscle contraction-relaxation frequencies independent of the exercise intensities per se. The main purpose was therefore to determine if fluctuations in blood flow for 1-BB(cycle) and 1-CR(cycle)varies at incremental exercise intensities (work rates) using the one-legged dynamic knee-extensor exercise (DKE) model. METHODS: Limb femoral artery blood flow (LBF) was determined, for 1-BB(cycle) and 1-CR(cycle), in 8 healthy male subjects during 4-min of steady-state DKE at 60 contractions per minute at 10, 20, 30 and 40 W. The variability of LBF was determined from the coefficients of variation (CVLBF). RESULTS: The CV(LBF) for the CR(cycle)-measurements at each work rate were similar (P=NS). The CV(LBF) for the BB(cycle)-measurements were higher (P<0.05) at 40 W compared to at 10 W. Furthermore, the CV(LBF) for the 1-BB(cycle) was higher (P<0.05) than for the 1-CR(cycle) at 30 and 40 W, despite almost identical mean LBF values for the BB(cycle)- and the CR(cycle)-measurements at each exercise intensity. CONCLUSIONS: The present data suggests that estimates of LBF at slightly higher exercise intensities such as above 30 W, for a few number of consecutive BB(cycle), renders a higher variability than for CR(cycle)-measurements. This may consequently result in slight over- and under-estimations of LBF compared to the CR(cycle)-measurement.

Adult↗
PubMed1995

Measurement of maximal oxygen consumption of thoroughbred horses at an altitude of 1250m using open-circuit flow-through calorimetry.

This study determined the maximal O2 uptake (VO2max) of Thoroughbred horses acclimatised to mild hypobaric conditions using a standard exercise test on a treadmill inclined at a 7% slope. The O2 uptake (VO2) versus speed relationship was linear below the exercise intensity required to attain VO2max. The VO2max of individual horses ranged from 143.5 to 172.6 ml/kg/min. The proportion of total variance for the VO2 versus speed relationship was greater than 0.992, and the coefficients of variation in repeated tests in individual horses ranged between 0.07 and 1.54%. The VO2 versus speed relationship attained a plateau at speeds above the VO2max, which ranged from 9.3 to 12.0 m/s. When work intensity was increased above that of the VO2max, there was no further increase in VO2, thus showing that a maximum had been attained.

Acclimatization↗
PubMed1983

[Regulation of the breathing pattern during muscle activity under normal and altered chemoreceptor stimulation].

The quantitative relations between the tidal volume and timing of the respiratory cycle (breathing pattern) in resting and with gradual muscular loads, were investigated in 16 healthy subjects under conditions of normal and altered chemoreceptive respiratory drive. The human breathing pattern during muscular exercise was shown to reflect the features of the central respiratory rhythmogenic mechanisms which depend on the interaction among stimuli of different modalities. In turn the effects of these stimuli are significantly modulated by the biomechanical factors and thus are subject to considerable individual variations: the augmentation of ventilation induced by increasing of work intensity is mainly due to the tidal volume rise or alternatively to the increased breathing frequency in the representatives of "tachypnoic" or "bradypnoic" breathing patterns, respectively.

Adult↗
PubMed1979

Influence of skin temperature on sweating and aerobic performance during severe work.

Two male subjects were measured over a range of work intensities at dry-bulb temperature (Tdb) = 21 degrees C (relative humidity, rh less than 50%) and at approximately 65 and 85% VO2max for 1 h at Tdb at 5,10,15,21, and 25 degrees C with high convective airflow (2.5-5 m/s). The results showed that mean skin temperature (Tsk) was related to Tdb and unaffected by rh over the range studied. Tsk was dependent on the relative work load and was 2.5 degrees C lower at 85% than 65% VO2max in the cooler environments. During submaximal work the relative sweat rate (Msw expressed as %Mse, max) was a linear function of rectal temperature (Tre) and Tsk for each subject and thus %Msw, max could be predicted from these two variables with a standard deviation of +/- 12%. For a given Tsk, Tre appeared to rise to meet the requirement of heat loss by stimulating set %Msw response. However, during severe work (85% VO2max) this mechanism appeared to become saturated, Tre (except for a very narrow prescriptive range) was dependent on Tdb. These results suggest that under moderate environmental conditions the maximal aerobic and evaporative (cooling) power outputs of an individual are closely matched and only during extremely hard work does thermoregulation become passive and effectively physical (rather than physiological) in nature.

Body Temperature Regulation↗
PubMed2006

Cardiologists are living through exciting times. The example of postconditioning to protect the human heart during revascularization.

The exciting work the group of Jennings, published in Circulation in 1986, has established a new and powerful form of cardioprotection, whereby exposure to short bouts of repeated ischemia interspersed by reperfusion protects from a subsequent prolonged and potentially very serious major ischemic attack. Similar protection by postconditioning can be achieved by short bursts of ischemia just after the onset of mechanical reperfusion in acute myocardial infarction. Of interest, it has taken almost 20 years of intense work to bring all the important preconditioning ideas to clinical reality in the form of postconditioning. Once cardiologists are fully awoken to the idea of attacking reperfusion induced myocardial cell death, then this area will be set to develop as a major and novel target in the therapy of acute myocardial infarction.

Cardiology↗
PubMed2003

Impaired leg vasodilation during dynamic exercise in healthy older women.

The purpose of the present study was to test the hypothesis that leg blood flow responses during leg cycle ergometry are reduced with age in healthy non-estrogen-replaced women. Thirteen younger (20-27 yr) and thirteen older (61-71 yr) normotensive, non-endurance-trained women performed both graded and constant-load bouts of leg cycling at the same absolute exercise intensities. Leg blood flow (femoral vein thermodilution), mean arterial pressure (MAP; radial artery), mean femoral venous pressure, cardiac output (acetylene rebreathing), and blood O2 contents were measured. Leg blood flow responses at light workloads (20-40 W) were similar in younger and older women. However, at moderate workloads (50-60 W), leg blood flow responses were significantly attenuated in older women. MAP was 20-25 mmHg higher (P < 0.01) in the older women across all work intensities, and calculated leg vascular conductance (leg blood flow/estimated leg perfusion pressure) was lower (P < 0.05). Exercise-induced increases in leg arteriovenous O2 difference and O2 extraction were identical between groups (P > 0.6). Leg O2 uptake was tightly correlated with leg blood flow across all workloads in both subject groups (r2 = 0.80). These results suggest the ability of healthy older women to undergo limb vasodilation in response to submaximal exercise is impaired and that the legs are a potentially important contributor to the augmented systemic vascular resistance seen during dynamic exercise in older women.

Adult↗
PubMed2003

Maternal employment and overweight children.

This paper seeks to determine whether a causal relationship exists between maternal employment and childhood weight problems. We use matched mother-child data from the National Longitudinal Survey of Youth (NLSY) and employ econometric techniques to control for observable and unobservable differences across individuals and families that may influence both children's weight and their mothers' work patterns. Our results indicate that a child is more likely to be overweight if his/her mother worked more hours per week over the child's life. Analyses by subgroups show that it is higher socioeconomic status mothers whose work intensity is particularly deleterious for their children's overweight status.

Body Mass Index↗
PubMed1976

A comparative study of the physical performance capacity of rural and urban Burmese women aged 19-24 years.

A comparative study of the physical performance capacity of 32 Burmese women aged 19-24 years of the rural and urban area was conducted. Difference in physique was found between the two groups. Maximal oxygen uptake of the rural group was 39.21 ml/kg/min and that of the urban group was 32.32 ml/kg/min, the difference being significant at 0.1% level. Maximal oxygen pulse and maximal work load were significant only at 2% and 5% levels respectively. Though maximal ventilation in the rural group had a higher mean value it was not significant. These showed a higher cardiorespiratory fitness in the rural group, which was attributable to their high work intensity of 55.13% of the maximal aerobic power. However, a positive training effect of habitual physical activity on muscle strength could not be observed in this study.

Adult↗
PubMed1987

[Specialist, physical therapy and social work management status of older children and adolescents with cerebral palsy].

In face of catamnestic examinations at a group of 61 older children and juveniles with infantile cerebral palsy we can see, that an optimal attendance by medical specialists, physiotherapists and social workers is not reached yet in each case. 39 patients (64 p.c.) are provided by a specialist regularly, 35 patients (57.4 p.c.) regularly get a physiotherapeutic treatment and 33 patients (54.1 p.c.) are often only sporadically attended by social workers. Serious disabled children, who are nursed only in their families, bring particular problems. In the authors opinion a decisive improvement of attendance is possible. For that purpose a more intensive work of "Dispensaries for disabled children and juveniles" in connexion with a consistent utilization of the socialist legislation is necessary.

Adolescent↗
PubMedDate not supplied

Commercial porters of eastern Nepal: health status, physical work capacity, and energy expenditure.

The purpose of the study was to compare full-time hill porters in eastern Nepal with part-time casual porters engaged primarily in subsistence farming. The 50 porters selected for this study in Kenja (elevation 1,664 m) were young adult males of Tibeto-Nepali origin. Following standardized interviews, anthropometry, and routine physical examinations, the porters were tested in a field laboratory for physiological parameters associated with aerobic performance. Exercise testing, using a step test and indirect calorimetry, included a submaximal assessment of economy and a maximal-effort graded exercise test. Energy expenditure was measured in the field during actual tumpline load carriage. No statistically significant differences were found between full-time and part-time porters with respect to age, anthropometric characteristics, health, nutritional status, or aerobic power. Mean VO2 peak was 2.38 +/- 0.27 L/min (47.1 +/- 5.3 ml/kg/min). Load-carrying economy did not differ significantly between porter groups. The relationship between VO2 and load was linear over the range of 10-30 kg with a slope of 9 +/- 4 ml O2/min per kg of load. During the field test of actual work performance, porters expended, on average, 348 +/- 68 kcal/hr in carrying loads on the level and 408 +/- 60 kcal/hr in carrying loads uphill. Most porters stopped every 2 min, on average, to rest their loads briefly on T-headed resting sticks (tokmas). The technique of self-paced, intermittent exercise together with the modest increase in energy demands for carrying increasingly heavier loads allows these individuals to regulate work intensity and carry extremely heavy loads without creating persistent medical problems.

Adult↗
PubMed1975

The physiological responses to walking uphill under hot environment.

A series of human experiments on walking uphill under radiant heat in addition to hot environment were carried out and the safety conditions for walking uphill from the standpoint of physiological response were determined. Experiments were carried out on three healthy adult males aged 21 years, walking uphill on a motor-driven treadmill with the aim of walking at a speed of 45 m/min, 55 m/min and 65 m/min and with a slope gradient of 0 degrees, 5 degrees and 10 degrees. The load weight used was 30, 40 and 50 percent of the body weight for each combination of speed, gradient and load weight. The subjects were exposed to a radiant heat of 1.3 cal/cm2.min, using 12 exsiccating infrared lamps, with a room temperature of 33 degrees C, a relative humidity of 60% and an airflow of 0.7 m/sec. The following results were obtained by estimating the physiological response (heart rate, respiration rate, rectal temperature and RMR (relative metabolic rate)) to different degrees of walking conditions during the 10-minute exercise: 1) The work intensity (RMR) of uphill walking with a certain load weight under hot environment can be changed by varying the walking speed and the load weight according to the slope gradient. 2) As there exists a gap between RMR 5 and 6 in parallel with the other physiological responses, it is preferable to keep the walking condition under RMR 6, as viewed from the change of the other walking conditions. 3) The heart rate as an indicator of the work load must be kept below 130 beats/min for a safe uphill walking of under RMR 6.

Adult↗
PubMed1986

Prediction modeling of physiological responses and human performance in the heat.

Over the last two decades, our laboratory has been establishing the data base and developing a series of predictive equations for deep body temperature, heart rate and sweat loss responses of clothed soldiers performing physical work at various environmental extremes. Individual predictive equations for rectal temperature, heart rate and sweat loss as a function of the physical work intensity, environmental conditions and particular clothing ensemble have been published in the open literature. In addition, important modifying factors such as energy expenditure, state of heat acclimation and solar heat load have been evaluated and appropriate predictive equations developed. Currently, we have developed a comprehensive model which is programmed on a Hewlett-Packard 41 CV hand held calculator. The primary physiological inputs are deep body (rectal) temperature and sweat loss while the predicted outputs are the expected physical work--rest cycle, the maximum single physical work time if appropriate, and the associated water requirements. This paper presents the mathematical basis employed in the development of the various individual predictive equations of our heat stress model. In addition, our current heat stress prediction model as programmed on the HP 41 CV is discussed from the standpoint of propriety in meeting the Army's needs and therefore assisting in military mission accomplishment.

Acclimatization↗
PubMed2005

Dyspnea, ventilatory pattern, and changes in dynamic hyperinflation related to the intensity of constant work rate exercise in COPD.

STUDY OBJECTIVE: We undertook the present study to investigate the perception of dyspnea (with respect to changes in end-inspiratory and end-expiratory lung volumes), during four different levels of high-intensity constant work rate exercise (CWRE) in patients with severe COPD. DESIGN: Crossover descriptive study with consecutively recruited subjects. SETTING: Tertiary university hospital. PATIENTS: Twenty-seven subjects with severe COPD (mean [+/- SD] age, 65 +/- 5 years of age; mean FEV1, 43 +/- 8% predicted; and mean inspiratory capacity [IC]; 74 +/- 14% predicted). MEASUREMENTS AND RESULTS: Subjects randomly performed four high-intensity CWRE tests (conducted at 65%, 75%, 85%, and 95% of their symptom-limited peak work rate). Dyspnea, leg fatigue, and IC were determined every 2 min during exercise with breath-by-breath gas exchange and ventilatory measurements. There was a good correlation between the resting IC percent predicted and the oxygen uptake (V(O2)) peak (r = 0.64 to 0.69 between the IC percent predicted and V(O2) peak at the four work rates). There were significant differences (p < 0.01) in mean respiratory rate (33 +/- 6, 35 +/- 6, 37 +/- 6, and 38 +/- 6 min), peak dyspnea score (5.9 +/- 1.3, 6.3 +/- 1.4, 6.8 +/- 1.2, and 6.9 +/- 1.6), minute ventilation (45.0 +/- 8.7, 43.8 +/- 7.7, 43.1 +/- 8.7, and 42.8 +/- 8.0 L/min), leg fatigue (4.8 +/- 1.3, 5.1 +/- 1.3, 5.7 +/- 1.4, and 5.8 +/- 1.4), and end-tidal carbon dioxide partial pressure (4.41 +/- 0.36, 4.53 +/- 0.33, 4.66 +/- 0.31, and 4.76 +/- 0.24 kPa), respectively, for tests conducted at 65%, 75%, 85%, and 95% of their symptom-limited peak work rate, and in mean end-expiratory lung volume ([EELV] 4.55 +/- 0.44, 4.69 +/- 0.43, and 4.79 +/- 0.43 L), respectively, for tests conducted at 65%, 75%, and 85% of their symptom-limited peak work rate. In multivariable analysis, the factors that were independently correlated with dyspnea (p < 0.05) were EELV, peak inspiratory flow, and leg fatigue/discomfort. CONCLUSION: In COPD subjects with flow limitation at rest, the perception of dyspnea increased nonlinearly with the magnitude of high-intensity CWRE in association with a faster respiratory pattern and an increase in EELV. At the highest work rates, it appeared that a reduction in tidal volume and ventilation peak may have limited the tolerance to exercise.

Aged↗
PubMed1987

Regional distribution of blood flow of dogs during graded dynamic exercise.

The regional blood flow response to progressive treadmill exercise was measured with radioactive microspheres in 25 untrained mongrel dogs. Incremental increases in work intensity resulted in corresponding increases in blood flows to the gracilis, gastrocnemius, semimembranosus, and semitendinosus muscles of the hindlimb and to the heart. During maximal exercise, blood flow was greatest in the semimembranosus muscle and lowest in the semitendinosus muscle (342 and 134 ml-1.100 g tissue-1.min-1, respectively). Exercise produced a decrease in blood flow to the temporalis muscle, which was classified as nonlocomotive in function. Blood flows to the stomach, pancreas, and large intestine decreased at the lowest exercise work load and remained diminished throughout the continuum to maximal exercise. Blood flows to the small intestine and spleen were maintained during submaximal exercise but were reduced by 50% at maximal O2 consumption (VO2max). No changes in blood flows to the kidneys, adrenal glands, liver, and brain were found. These results demonstrate that 1) renal blood flow is maintained at resting levels during exercise in untrained dogs; 2) blood flow changes in the various organs of the splanchnic region of dogs during exercise are heterogeneous; and 3) blood flows to the working skeletal muscles of dogs progressively increase with increasing work loads up to VO2max.

Animals↗
PubMed1985

The physiologic sequelae of chronic dynamic exercise.

The physiologic results of acute dynamic exercise include complex neurologic, hormonal, pulmonary, and cardiovascular adjustments that provide an integrated response perfectly matching oxygen supply with oxygen demands. Long-term repeated bouts of dynamic exercise of sufficient intensity and duration yield predictable changes in anatomy and physiology. These changes affect active skeletal muscle and the heart. Changes in skeletal muscle include an increased capillary blood volume, increased mitochondrial density, increased oxidative pathway enzymes, and more efficient regulation of blood flow. These adaptations result in an increased oxidative capacity and more favorable fuel utilization. Oxygen extraction increases, accounting for up to 50 per cent of the increased maximal oxygen consumption, and endurance improves. Following chronic dynamic exercise the heart beats slower and has a larger stroke volume at rest and throughout a broad range of work intensities. The maximal cardiac output increases substantially, accounting for up to 50 per cent of the increased maximal oxygen consumption. The metabolic and biochemical changes found in skeletal muscle are not found in cardiac muscle. Changes found in isolated cardiac muscle do not always correlate with heart performance. The separation of central and peripheral factors in assessing heart performance is difficult because preload and afterload are major determinants of heart function and are altered by chronic dynamic exercise. Ischemia is a major stimulus for the development of coronary collateral vessel development in animals. Because dynamic exercise does not induce ischemia in normal humans, collateral vessel development may only occur in those with coronary heart disease. However, there is no convincing evidence that chronic dynamic exercise results in physiologically important coronary collateral vasculature in patients with angina. Improved work capacity is predictable following chronic dynamic exercise in patients with coronary heart disease. Although the rate pressure product that produces angina does not change following training, heart rates are lower at matched absolute workloads and the maximal consumption of oxygen increases. Changes in heart function are largely secondary to peripheral changes in these patients.

Animals↗