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PubMed1986

The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises.

The mechanical efficiency of the leg extensor musculature of men and women was examined with a special "sledge ergometer". The subjects (ten males and ten females) performed pure positive work, pure negative work and a combination of negative and positive work (stretch-shortening cycle). The mechanical efficiency of pure positive work was on average 19.8 +/- 1.2% for female subjects and 17.4 +/- 1.2% for male subjects (t = 4.12, P less than 0.001), although the work intensity was equal in both groups. The mechanical efficiency of pure negative work was slightly lower in women than in men (59.3 +/- 14.4% vs 75.6 +/- 29.3%). The mechanical efficiency of positive work (eta +) in a stretch-shortening cycle exercise was 38.1 +/- 6.8% in men and 35.5 +/- 6.9% in women. The utilization of prestretch was better for female subjects at low prestretch levels, whereas males showed greater potentiation of elastic energy at higher prestretch levels. Regarding absolute Wel (work due to elasticity) values, male subjects showed greater (P less than 0.001) values than females (189 +/- 44 J vs 115 +/- 36 J, respectively). Fundamental differences in neuromuscular functions in men and women might cause the differences in the results obtained.

Adult↗
PubMed2003

Do ergonomics improvements increase computer workers' productivity?: an intervention study in a call centre.

This paper examines whether improving physical ergonomics working conditions affects worker productivity in a call centre with computer-intensive work. A field study was conducted at a catalogue retail service organization to explore the impact of ergonomics improvements on worker production. There were three levels of ergonomics interventions, each adding incrementally to the previous one. The first level was ergonomics training for all computer users accompanied by workstation ergonomics analysis leading to specific customized adjustments to better fit each worker (Group C). The second level added specific workstation accessories to improve the worker fit if the ergonomics analysis indicated a need for them (Group B). The third level met Group B requirements plus an improved chair (Group A). Productivity data was gathered from 72 volunteer participants who received ergonomics improvements to their workstations and 370 control subjects working in the same departments. Daily company records of production outputs for each worker were taken before ergonomics intervention (baseline) and 12 months after ergonomics intervention. Productivity improvement from baseline to 12 months post-intervention was examined across all ergonomics conditions combined, and also compared to the control group. The findings showed that worker performance increased for 50% of the ergonomics improvement participants and decreased for 50%. Overall, there was a 4.87% output increase for the ergonomics improvement group as compared to a 3.46% output decrease for the control group. The level of productivity increase varied by the type of the ergonomics improvements with Group C showing the best improvement (9.43%). Even though the average production improved, caution must be used in interpreting the findings since the ergonomics interventions were not successful for one-half of the participants.

Computers↗
PubMed1978

Oxygen consumption during constant-load exercise.

Previous investigators have reported that oxygen consumption (VO2) continues to rise after the initial 2- to 3-min transient period of exercise when work exceeds approximately 60% of VO2 max. The purpose of this investigation was to examine the possible causes of this slow rise in VO2. Eighteen subjects exercised for 20 min at 65% and at 80% of VO2 max on the bicycle ergometer. VO2, ventilation (VE), and respiratory exchange ratio were monitored by a continuous computer-based system. Blood lactate concentration and rectal temperatures were measured at 2- to 3-min intervals during the exercise. VO2 increased significantly from the 5th to 20th min of exercise in 81% of the tests at both levels of work intensity. The magnitude of the rise was not different for the two work loads. No evidence was found to support the lactacid explanation proposed for this rise. Increased temperature could account for 30% of the rise; the estimated cost of increased VE could account for 30 and 81% of the rise at the two work loads. The sum of these factors could account for 60 and 111% of the rise in VO2 at the 65 and 80% of VO2 max work loads.

Adult↗
PubMed1990

Association between muscle acetyl-CoA and acetylcarnitine levels in the exercising horse.

Treadmill exercise of 2-min duration and increasing intensity resulted in increased formation of acetyl-CoA and acetylcarnitine in working muscle of Thoroughbred horses. At high work intensities a plateau was reached for both acetyl-CoA (approximately 50 mumols/kg dry muscle) and acetylcarnitine (approximately 20 mmol/kg dry muscle). Postexercise concentrations were significantly (P less than 0.001) correlated; [acetylcarnitine] = 349.[acetyl-CoA] + 2.4. The results indicate that approximately 350 mumols acetylcarnitine were accumulated for every 1 mumol acetyl-CoA. Under the conditions of exercise used it is probable that most of the acetyl-CoA formed is generated through the intramitochondrial decarboxylation of pyruvate. The acetyl groups of acetyl-CoA are apparently redistributed throughout the whole cell through formation of acetylcarnitine, which readily transverses the mitochondrial membrane. Despite the redistribution, however, the close correlation between acetylcarnitine and acetyl-CoA would indicate that equilibrium was maintained and that neither acetylcarnitine transferase nor carnitine/acetylcarnitine translocase were rate limiting. There is some question as to whether the changes observed relate directly to exercise itself or to the state in muscle 10 s or more after exercise.

Acetyl Coenzyme A↗
PubMed1999

[Suffering and pleasure experienced by nurses working at an intensive care unit of a university hospital].

The purpose of this study is to grasp and to understand the nurses' social representations concerning their work in intensive care unit and the ways of expressing feelings of suffering and pleasure. Six nurses of the intensive care unit of medical, surgical and pediatric clinics were interviewed. The analysis of the social representations made possible the apprehension of the symbolic dimension of the work in the psycho-social (individual), social-dynamic (group) and institutional perspective. We verified that the work in intensive care unit brings pleasure to nurses despite of intense emotional constraint. This qualitative study allowed na in-depth reflection on the issue and made evident the need to deepen research. However, other investigations have to be carried out to deepen the subject on the subjective and symbolic dimension to subsidize the administration of human resources in nursing.

Attitude of Health Personnel↗
PubMed1997

[Recommendations and notes for Manual RP 2.2.-013-94, "Hygienic criteria in the evaluation of work conditions according to indicators of harmfulness and risks of industrial environment factors and hardness and intensity of the work process"].

Some modifications need to be set in Classification of work conditions, adopted in Manual R rho 2.2.013-94 "Hygienic criteria to evaluate work conditions through occupational hazards and jeopardy, work hardness and intensity". We suggest to modify maximal allowable levels of general vibration, local vibration and infrasound. A recommended formula characterizes total vibration dose received through exposure to several factors, calculates work duration in accordance with all acting hazards.

Aerosols↗
PubMed1988

Effects of increased muscle perfusion pressure on responses to dynamic leg exercise in man.

Ventilatory, cardiovascular and metabolic functions and work performance were studied in men performing incremental-load dynamic leg exercise until exhaustion. Part I: Responses to supine exercise were investigated in 8 subjects during exposure of the lower body to subatmospheric pressure at -6.67 kPa (-50 mm Hg) (Lower Body Negative Pressure, LBNP). Due to curtailment of stroke volume, cardiac output was reduced by LBNP over a wide range of work intensities, including heavy loads: ventilation, oxygen uptake and blood lactate concentrations increased with work load, but at lower rates than in the control condition. Part II: In 9 subjects, work performance was compared in three conditions: supine exercise with and without LBNP, and upright exercise. Performance in supine exercise was enhanced by LBNP, and was further improved in upright exercise. In supine exercise, the LBNP-induced reduction in blood lactate and enhancement of work performance are attributed to a more efficient muscle blood flow resulting from increased local perfusion pressure. This strongly suggests that the primary limitation of work performance was set by the peripheral circulation in working muscles rather than by cardiac performance. A similar mechanism may, in part, explain why work performance in dynamic leg exercise was greater in the upright than in the supine posture. It is also concluded that supine leg exercise during LBNP is a useful model of upright exercise, with regard to the central circulation and the circulation in working muscles.

Adult↗
PubMed1998

Effect of creatine supplementation during rapid body mass reduction on metabolism and isokinetic muscle performance capacity.

Well-trained subjects (n = 6) were studied before and after losing a mean 3.0%-4.3% of body mass to determine whether muscle performance could be maintained or even enhanced by dietary creatine supplementation. During a 5-day period of loss of mass the subjects were randomly assigned to a creatine or placebo supplemented diet. All the subjects were measured before and after loss of mass on both supplements for isokinetic peak torque (PT) and work at peak torque (W(PT)) of knee extensors, also for intermittent high intensity working capacity of the same muscle group. The latter test consisted of submaximal isokinetic knee extensions at an angular velocity of 1.57 rad x s(-1) for 45 s at the rate of 30 contractions each min (submaximal work, Ws max) followed by 15-s maximal effort (maximal work, Wmax). Total duration of the test was 3 min. Haematocrit was measured and haemoglobin, ammonia, lactate, glucose and urea concentrations were analysed in blood samples obtained at rest and after cessation of muscle performance tests. The results indicated that creatine supplementation in comparison with placebo treatment during rapid body mass reduction may help to maintain muscle PT and W(PT)1 at high angular velocities, not influencing Wmax and the rate of fatigue development during Wmax, but affecting adversely Ws max. Within the limitations of the present study the reasons for the partially detrimental effect of creatine administration remain obscure, but it is suggested that impaired creatine uptake in muscle during body mass loss as well as creatine induced changes in muscle glucose and glycogen metabolism may be involved.

Adult↗
PubMed1987

Plasma beta-endorphin immunoreactivity during graded cycle ergometry.

The present study was undertaken to define the response of plasma beta-endorphin immunoreactivity (ir-BE) to exercise of increasing intensity. Nineteen healthy males performed continuous exercise for 32 min on a cycle ergometer, comprised of 8-min bouts at %VO2max approximating 25, 50, and 75% of maximal exercise. Venous blood samples were collected before exercise (T = -20 and 0 min), during exercise (T = 8, 16, 24, and 32 min), and in recovery (T = +15, +30 min). Ir-BE in plasma was measured by radioimmunoassay using Immuno Nuclear assay kits. Plasma ir-BE level (pg X ml-1) was not altered from pre-exercise (18.3 +/- 1.3) after 8 min of exercise at 25 and 50% VO2max intensity; however, ir-BE rose significantly after 8 min of 75% VO2max work intensity (27.1 +/- 2.4) and was further elevated at maximal exercise (74.1 +/- 8.6). Ir-BE level remained elevated 15 min (60.9 +/- 8.1) and 30 min (35.2 +/- 5.2) post-exercise. The response pattern was further characterized by a significant (P less than 0.05) inter-individual variation, both at rest and during exercise; also, regression analysis indicated the ir-Be levels attained at maximal exercise were inversely related to the relative VO2max (ml X kg-1 X min-1) of the subject (predicted ir-BE = 248.2 - 3.39 VO2max; r = -0.397, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

[Energy requirements of miners engaged in open-pit coal mining].

It has been found that according to the value of daily energy consumption the coal miners engaged in open-cast mining should be referred to group III-IV of work intensity. The determining component of daily energy consumption is energy consumption during the working period the value of which depends on the character of working activity and duration of the working shift. The method of strict evaluation of the calorific value of the food taken and the control of body mass is acceptable for the assessment of daily energy consumption.

Body Weight↗
PubMed1985

Maximal perfusion of skeletal muscle in man.

Five subjects exercised with the knee extensor of one limb at work loads ranging from 10 to 60 W. Measurements of pulmonary oxygen uptake, heart rate, leg blood flow, blood pressure and femoral arterial-venous differences for oxygen and lactate were made between 5 and 10 min of the exercise. Flow in the femoral vein was measured using constant infusion of saline near 0 degrees C. Since a cuff was inflated just below the knee during the measurements and because the hamstrings were inactive, the measured flow represented primarily the perfusion of the knee extensors. Blood flow increased linearly with work load right up to an average value of 5.7 l min-1. Mean arterial pressure was unchanged up to a work load of 30 W, but increased thereafter from 100 to 130 mmHg. The femoral arterial-venous oxygen difference at maximum work averaged 14.6% (v/v), resulting in an oxygen uptake of 0.80 l min-1. With a mean estimated weight of the knee extensors of 2.30 kg the perfusion of maximally exercising skeletal muscle of man is thus in the order of 2.5 l kg-1 min-1, and the oxygen uptake 0.35 l kg-1 min-1. Limitations in the methods used previously to determine flow and/or the characteristics of the exercise model used may explain why earlier studies in man have failed to demonstrate the high perfusion of muscle reported here. It is concluded that muscle blood flow is closely related to the oxygen demand of the exercising muscles. The hyperaemia at low work intensities is due to vasodilatation, and an elevated mean arterial blood pressure only contributes to the linear increase in flow at high work rates. The magnitude of perfusion observed during intense exercise indicates that the vascular bed of skeletal muscle is not a limiting factor for oxygen transport.

Adult↗
PubMed1998

The influence of PaO2, pH and SaO2 on maximal oxygen uptake.

Influence of arterial oxygen pressure (PaO2) and pH on haemoglobin saturation (SaO2) and in turn on O2 uptake (VO2) was evaluated during ergometer rowing (156, 276 and 376 W; VO2max, 5.0 L min-1; n = 11). During low intensity exercise, neither pH nor SaO2 were affected significantly. In response to the higher work intensities, ventilations (VE) of 129 +/- 10 and 155 +/- 8 L min-1 enhanced the end tidal PO2 (PETO2) to the same extent (117 +/- 2 mmHg), but PaO2 became reduced (from 102 +/- 2 to 78 +/- 2 and 81 +/- 3 mmHg, respectively). As pH decreased during maximal exercise (7.14 +/- 0.02 vs. 7.30 +/- 0.02), SaO2 also became lower (92.9 +/- 0.7 vs. 95.1 +/- 0.1%) and arterial O2 content (CaO2) was 202 +/- 3 mL L-1. An inspired O2 fraction (F1O2) of 0.30 (n = 8) did not affect VE, but increased PETO2 and PaO2 to 175 +/- 4 and 164 +/- 5 mmHg and the PETO2-PaO2 difference was reduced (21 +/- 4 vs. 36 +/- 4 mmHg). pH did not change when compared with normoxia and SaO2 remained within 1% of the level at rest in hyperoxia (99 +/- 0.1%). Thus, CaO2 and VO2max increased to 212 +/- 3 mL L-1 and 5.7 +/- 0.2 L min-1, respectively. The reduced PaO2 became of importance for SaO2 when a low pH inhibited the affinity of O2 to haemoglobin. An increased F1O2 reduced the gradient over the alveolar-arterial membrane, maintained haemoglobin saturation despite the reduction in pH and resulted in increases of the arterial oxygen content and uptake.

Adult↗
PubMed1994

Cardiovascular responses during one- and two-legged exercise in middle-aged men.

Eight healthy and regularly physically active men, 44-69 years old, performed one- and two-legged dynamic knee extension exercise at increasing work intensities, including one leading to exhaustion. Leg blood flow increased linearly in relation to work rate, reaching a peak value of 5.1 +/- 0.4 l min-1. With a mean weight of quadriceps femoris of 2.2 +/- 0.1 kg, a peak perfusion of 2.3 +/- 0.1 l kg-1 min-1 was attained. The maximal leg oxygen uptake was 0.72 +/- 0.07 l min-1 (0.33 +/- 0.03 l kg-1 min-1). At submaximal work the elevation in limb oxygen uptake accounted for between 70 and 100% of the rise in pulmonary oxygen uptake. Comparing two- with one-legged knee extension the cardiac output was 1.5 l min-1 higher at each work level, reaching 13.7 +/- 0.7 and 12.3 +/- 1.0, respectively at exhaustion, leaving 3.5 and 7.2 l min-1 of blood flow to the remaining body (cardiac output--leg blood flow). The mean arterial pressure was 119 +/- 5 mmHg at rest and increased to 155 mmHg for both test modes at the maximal work rate. The femoral arterial and venous plasma concentrations of lactate, ammonia and noradrenaline were significantly higher for two-legged as compared with one-legged exercise at the maximal load performed. However, the rate of release per leg, for both lactate and ammonia, did not differ between the two test conditions. It is concluded that physically active middle-aged men, with a well-retained muscle mass, can maintain a high skeletal muscle perfusion, similar to that of young males. However, the blood flow is achieved with a higher mean arterial pressure and an elevated sympathetic activity, as reflected by noradrenaline in plasma and spillover from the exercising limb.

Adult↗
PubMedDate not supplied

[Work-related musculoskeletal diseases in dental professionals. 1. Prevalence and risk factors].

The past two decades have witnessed a sharp rise in the incidence of work-related musculoskeletal disorders (WMSD). All occupations are involved; in dental professionals (dentists, dental hygienists and dental auxiliaries) this problem occurs in 54-93% of subjects, with higher risk in elderly subjects and women. Spine, shoulder, elbow and hand are mostly involved. Prevention of WMSD is becoming crucial and requires the identification and modification of risk factors. Individual characteristics of the worker--such as gender, age, stature, physical condition, strength, etc.--may contribute to the occurrence of these musculoskeletal disorders. Moreover, the specific occupation and work organisation may be the source of ergonomic hazards. Awkward postures, prolonged repetitive movements, intense work schedules or fast work pace represent important risk factors for WMSD. Sometimes the dentist's workstation is not suited to the specific professional characteristics and an ergonomic improvement is needed. Finally, factors connected with professional equipment (such as vibrations, or sharp and hard surfaces causing pressure points) may also contribute to generating WMSD in dental professionals.

Aged↗
PubMed1994

[Endothelins. I. Physiology].

At the beginning of 1988 in Japan in a unique manner a new peptide substance derived form the endothelium was described, so far the most powerful vasoconstrictor substance-endothelin. This started an information boom which soon led to evidence of other substances of this group, naturally related substances; the detailed structure of all endothelins was established, gradually these substances were synthetized, very sensitive radioassays for their estimation were developed. Experimental and clinical work on endothelins and their effects penetrate at present all spheres of medicine and intensive work is under way, focused on their use in the treatment of diseases as widespread as hypertension, vasospastic disorders, atherosclerosis, bronchial asthma, renal failure, etc. These findings are becoming the basis of a medical sub-discipline which can be described by the term of vascular wall endocrinology. In the first part of the review the author submits information on the chemical structure, synthesis and secretion of endothelins, on their plasma levels, mechanism of intracellular action and experimental effects. In the second part the author reviews findings on the participation of endothelins in the pathogenesis of cardiovascular and renal diseases. Their role in the control of volume homeostasis and in the genesis of the preeclamptic syndrome is discussed, as well as effects on the CNS and other organs, and the author reflects on the general impact of contemporary findings on endothelins in medicine and on possibilities of their perspective practical use.

Amino Acid Sequence↗
PubMedDate not supplied

Comparison of the views of junior doctors, consultants and managers on work and training.

OBJECTIVE: To determine the views of junior hospital doctors on their working conditions, NHS reforms and training, and to compare their views with those of consultants and managers. SUBJECTS: A questionnaire was distributed to 52 junior doctors, 19 consultants and 14 middle or senior grade managers in an acute NHS trust. CONCLUSIONS: Junior doctors had strong feelings about several areas covered in the questionnaire; in particular, more structured training without the requirement to undertake a higher degree would be welcomed. Shift systems are unpopular and the reduction of 'non-medical' tasks with a reduction in work intensity is perceived to be more important than further reductions in hours available for work.

Attitude of Health Personnel↗
PubMed1996

The use of ratings of perceived exertion for exercise prescription in patients receiving beta-blocker therapy.

The ratings of perceived exertion (RPE) scale has received widespread acceptance for gaining a subjective estimate of work intensity and as a means of monitoring and regulating exercise intensity across a variety of populations. The original premise for the use of the scale was its high correlation with heart rate (HR). Although individual correlations between HR and RPE in individuals on beta-blocker therapy are probably as high as in untreated individuals, there is evidence to suggest that the RPE response is mediated at a given work rate, particularly at higher absolute work rates. The variation in the RPE response appears to be mediated by the type of beta-blocker therapy administered. In the interests of safety it is necessary for the exercise specialist to develop at least a basic understanding of the mechanism and effects of beta-blocker therapy as they relate to exercise prescription. beta-Blocking drugs cause a decrease in HR and cardiac output at rest and during exercise, a decrease in myocardial contractility and a decrease in coronary and muscle blood flow. These effects can initiate premature fatigue and apprehension in the exercising patient. In the light of these responses, the RPE scale provides important information and may be used to increase the accuracy of monitoring and the prescription of exercise intensity in the cardiac population. While results regarding the use and accuracy of the scale during beta-blocker treatment are equivocal, this appears to be due mainly to variations in dosage of the drug, the mode, intensity and duration of exercise and the health status of the individuals used. Overall, the RPE scale appears to be an appropriate monitoring tool, particularly when it is used after a learning period. It is concluded that nonselective beta-blockade therapy increases RPE, particularly localised RPE. This could be attributed to a decreased blood flow and oxygen delivery to the muscle and altered glycolytic metabolism, which increases local muscle fatigue. There is no evidence to suggest a decrease in the total level of oxygen consumption at given work rates. However, as beta-blocker therapy reduces the maximal oxygen consumption (VO2max) attainable, this serves to increase the exercise intensity at all work rates. Thus, for a given absolute work rate, the RPE response is higher. However, when the work rate is expressed as a proportion of the VO2max attainable during beta-blockade, the differences in RPE are minimised or disappear. Although the evidence is not conclusive, it appears that cardioselective beta-blocker therapy does not have such profound effects on the RPE response, compared with nonselective beta-blocker therapy, when this is expressed as a proportion of VO2max. However, localised RPE tends to be higher for nonselective beta-blocker therapy. Thus, the evidence indicates that RPE can be used to estimate exercise intensity, provided the specific effects of the type of beta-blocker therapy on local and central fatigue (and local and central RPE) are taken into account. Studies which have examined the effects of an endurance training programme during beta-blocker therapy have shown that RPE are decreased at given work rates after training. This has been observed for cardioselective and nonselective beta-blocker therapy, and local and central RPE. There is also some evidence to suggest that the RPE can be used as the controlling variable to regulate the exercise response. Patients on cardioselective beta-blocker therapy produce similar exercise intensities to other cardiac patients who are not receiving beta-blocker treatment.

Adrenergic beta-Antagonists↗
PubMed1986

Effect of acute exercise on plasma immunoreactive-atrial natriuretic factor.

The effect of acute exercise on plasma immunoreactive-atrial natriuretic factor (IR-ANF) was studied in 5 healthy young males subjected to graded exercise on a bicycle ergometer at four different work intensities (approx. 30, 50, 70, and 90% VO2max respectively). Except for the final exercise period, which was continued until exhaustion, all the others were of 30 min duration. Venous blood samples were obtained in the last 2 min of each exercise period. The plasma IR-ANF response to exercise was similar to that of heart rate and systolic blood pressure in that mild exercise in the first stage (corresponding to approx. 30% VO2 max) caused a striking increase of plasma IR-ANF concentrations with a further augmentation in the next stages and a levelling off at exhaustion. Plasma arginine-vasopressin (AVP) and aldosterone (ALDO) rose significantly only in the last two stages, and the highest concentrations were observed at exhaustion. In conclusion, acute exercise stimulates ANF secretion in proportion to the intensity of exercise, while concomitant increases in plasma AVP and ALDO occur only when the work load exceeds the blood lactate (BLA) threshold.

Adult↗