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PubMed1989

[Physical work capacity and ergometric indicators of the functional state of the cardiovascular system in sailors].

Examination of 194 sailors during the navigation period showed a decrease in their work capacity and deterioration of ergometric indices characterizing their cardiovascular activity. Decrease of chrono- and inotropic heart reserves, productivity of mechanical work and myocardium contraction function was pointed out. There were found out reduction in work economy and elevation of energy losses, the degree of which was associated with environmental conditions, work intensity and duration of continuous work.

Adult↗
PubMed1977

Fall in skin temperature during exercise.

During light work using the arm in a warm environment, skin temperatures of the arms and chest fell and remained at lower levels during work. The fall in skin temperature during work was not observed in a cool environment. The fall in skin temperature was nearly proportional to work intensity and was observed in both static and dynamic work. Leg work of moderate intensity produced an initial decline and a subsequent rise in skin temperatures of the hands, thighs and legs. A significant fall in skin temperature was observed not only in the foot but also in inactive regions such as the epigastrium. The mean skin temperature remained practically unchanged during work. The fall in skin temperature during work was not due to increased evaporative cooling, but was the result of segmental vasoconstriction probably caused as a reflex in the spinal cord by non-thermal afferents from exercising muscles or moving tissues. The effect of thermoregulatory vasodilation was reduced by the reflex vasoconstriction caused by non-thermal factors. The rise in internal temperature during work could be explained by decreased heat loss due to persistently lower skin temperature.

Adult↗
PubMed1974

Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates.

1. Glycogen depletion pattern in human skeletal muscle fibres was studied after bicycle exercise of varying intensity performed at different pedalling rates. Work intensities studied were equivalent to 30-150% of V(O) (2) max. with pedalling rates of 30-120 rev/min.2. Glycogen depletion increased dramatically with increasing exercise intensity; depletion was 2.7 and 7.4 times greater respectively at workloads demanding 64 and 84% V(O) (2) max. than at workloads calling for 31% V(O) (2) max. Even greater rates of glycogen utilization occurred at supramaximal loads.3. Slow twitch, high oxidative (ST) fibres were the first to lose glycogen (reduced PAS staining) at all workloads below V(O) (2) max. Progressive glycogen depletion occurred in fast twitch (FT) fibres as work continued. Large quantities of glycogen remained in the muscle after 3 hr of exercise at low exercise intensity. This was almost exclusively found in FT fibres. At workloads exceeding maximal aerobic power, there was an initial depletion of glycogen in both fibre types. Varying the pedalling rate and, thus, the total force exerted in each pedal thrust had no effect on the pattern of glycogen depletion in the fibres.4. Results point to primary reliance upon ST fibres during submaximal endurance exercise, FT fibres being recruited after ST fibres are depleted of glycogen. During exertion requiring energy expenditure greater than the maximal aerobic power, both fibre types appeared to be continuously involved in carrying out the exercise.

Adenosine Triphosphatases↗
PubMed2000

Structural and functional limits for oxygen supply to muscle.

Environmental oxygen is transported by the respiratory cascade to the site of oxidation in active tissues. Under conditions of heavy exercise it is ultimately the working skeletal muscle cells that determine the aerobic demand as over 90% of energy is spent in muscle cells. Oxygen is transported in the circulation bound to haemoglobin of erythrocytes while substrates are transported in the plasma. The supply of oxygen must be continuous because there are only minimal oxygen stores in the body of most mammalian species while substrates are stored in significant quantities both within muscle cells as also in organismic substrate stores. The pathways for oxygen and substrates ultimately converge in muscle mitochondria. In mammals, a structural limitation of carbohydrate and lipid transfer from the microvascular system to muscle cells is reached at a moderate work intensity (i.e. at less than 50% of VO2max). At higher work rates intracellular substrate stores must be used for oxidation. It is therefore not surprising to find larger intramyocellular carbohydrate and lipid stores in 'athletic' species as well as in endurance-trained human athletes. The transfer limitations for carbohydrates and lipids presumably occur on the level of the sarcolemma. These findings imply that the design of the respiratory cascade from lungs to muscle mitochondria has to be analysed with regard to satisfying the demand for oxygen of the working muscle cells. Substrate stores are replenished at low flux rates during periods of rest and are stored intracellularly. They are therefore locally available to mitochondria for aerobic work at high intensities.

Animals↗
PubMed1988

External load can alter the energy cost of prolonged exercise.

The present study was undertaken to examine the energy cost of prolonged walking while carrying a backpack load. Six trained subjects were tested while walking for 120 min on a treadmill at a speed of 1.25 m.s-1 and 5% elevation with a well fitted backpack load of 25 and 40 kg alternately. Carrying 40 kg elicited a significantly higher (p less than 0.01) energy cost than 25 kg. Furthermore, whereas carrying 25 kg resulted in a constant energy cost, 40 kg yielded a highly significant (p less than 0.05) increase in energy cost over time. The study implies that increase in load causes physical fatigue, once work intensity is higher than 50% maximal work capacity. This is probably due to altered locomotion biomechanics which in turn lead to the increase in energy cost. Finally, the prediction model which estimates energy cost while carrying loads should be used with some caution when applied to heavy loads and long duration of exercise, since it might underestimate the actual energy cost.

Adult↗
PubMed1999

Research challenges arising from changes in worklife.

Great challenges for occupational health research are set by the rapid changes in the world of work as a consequence of globalization, new technologies, demographic workforce changes, fragmentation of enterprises and work contracts, high time pressures, high demands for learning new skills, and growing worker mobility. The occupational health problems are of 2 types, the persistent and reemerging old problems of occupational injuries and diseases and new challenges from psychological stress, musculoskeletal disorders caused by computerized work, cognitive ergonomics in information-intensive work, the work ability of aging workers, and new trends in occupational allergies. The 3 roles of research, improvement of knowledge, improvement of understanding, and support of the development of work conditions in practice, all call for new initiatives in occupational health research. The new comprehensive strategy for the development and promotion of work ability has been found to respond effectively to these new needs.

Demography↗
PubMed1987

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

1. In ten young men the ventilatory, cardiovascular, catecholamine and metabolic responses to maximal dynamic leg exercise on a stationary bicycle were followed during partial neuromuscular blockade with tubocurarine. Maximal exercise was performed when the drug effect was at its maximum as well as during the subsequent reduction in the effect allowing a gradually increasing work intensity. The results were compared with those obtained during submaximal and maximal exercise performed without tubocurarine. Partial neuromuscular blockade decreased hand-grip strength to 41 +/- 1.1% (S.E. of mean) and the maximal work load to 27 +/- 2.4% of control values. Voluntary effort was maximal and the rate of perceived exertion was high at all levels of exercise with tubocurarine indicating a maintained intense central nervous motor command. 2. During maximal action of the drug oxygen uptake was 1.67 +/- 0.11 l/min while only 0.91 +/- 0.13 l/min (P less than 0.01) at the same work intensity without neuromuscular blockade. This difference may reflect a dominant reliance on fast-twitch muscle fibres when work was performed under the influence of tubocurarine. 3. Compared at a given oxygen uptake ventilation was higher during work with tubocurarine than during control exercise (e.g. 55 +/- 4.2 and 40 +/- 2.2 l/min, respectively (P less than 0.01), at a mean oxygen uptake of 1.9 l/min), while heart rate did not differ significantly (146 +/- 4.4 and 139 +/- 3.0 beats/min). With decreasing drug effect both variables increased towards the maximum values of 138 +/- 4.5 l/min and 183 +/- 3.9 beats/min, respectively, achieved in control experiments at an oxygen uptake of 3.8 +/- 0.2 l/min. Like heart rate the mean arterial blood pressure increased with increasing work load and was similar at a given oxygen uptake with and without tubocurarine. 4. During maximal exercise at peak tubocurarine effect plasma adrenaline and noradrenaline concentrations were smaller than during control maximum, 1.6 +/- 0.27 versus 3.4 +/- 0.55 nmol/l (P less than 0.01) and 7.5 +/- 1.3 versus 12.6 +/- 1.8 nmol/l (P less than 0.05), respectively. However, comparisons at identical oxygen uptake rates revealed that catecholamine responses were markedly enhanced during tubocurarine treatment. Also, blood lactate concentrations were smaller at peak tubocurarine action than during control maximum, 1.9 +/- 0.42 mmol/l and 6.1 +/- 0.49 mmol/l (P less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Mechanical efficiency of locomotion in females during different kinds of muscle action.

The mechanical efficiencies (ME) of pure positive and pure negative work as well as of stretch-shortening cycle (SSC) exercise were investigated with a special sledge apparatus. The subjects were 20 young females who performed six different types of submaximal exercise: two of pure concentric exercise (positive work), two of pure eccentric exercise (negative work) and two SSC exercises. The work intensities were determined individually, from the recordings of distance obtained during a single maximal concentric exercise. Each exercise involved 60 muscle actions lasting a total of 3 min per testing condition. The MEs of pure positive work with intensities of 30% and 60% maximum (C30 and C60 respectively) were 15.5%, SD 2.6% and 14.3%, SD 1.9%, respectively. In pure negative work, when the dropping heights were 20 cm (E20) and 80 cm (E80), MEs were 28.4%, SD 6.9% and 47.9%, SD 10.1%, respectively. In SSC-exercise, the MEs during the positive phase of the take-off were 31.3%, SD 6.3% (E20/C90) and 35.0%, SD 7.0% (E80/C69). The total MEs in SSC-exercise were 29.1%, SD 4.0% (E20/C90) and 40.1%, SD 5.2% (E80/C60 x 100). In pure negative work, the increased stretching velocity increased the value of ME. In the concentric phase of SSC-exercise, the integrated electromyographic activity (iEMG) of vastus lateralis (VL) and vastus medialis (VM) muscles were lower (P less than 0.05) than in pure concentric work, when the mechanical work was the same (C60 vs E80/C60). During pure eccentric work, iEMGs were lower in comparison to the eccentric phase of SSC-exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Breath-by-breath gas exchange kinetics during constant-load work.

In order to study respiratory transients during exercise, we examined breath-by-breath gas exchange kinetics during constant-load work. Five male subjects performed cycle ergometer tests which 6 min of constant-load work (150, 200, 250W) followed 50W base-line work. VCO2 and VO2 measured at the mouth ((VCO2)E, (VO2)E) and estimated at the alveolar level ((VCO2)A, (VO2)A) were computed breath-by-breath. The kinetic parameter (time constant) of first- and second-order exponential model was estimated using non-linear least-squares method. Our results demonstrated that a relative stability of PETO2, PETCO2, and R at their control values in the first phase. Independent of work intensities, breath-by-breath variation in gas exchange measured at the mouth was larger than those in gas exchange estimated at the alveolar level both at a non-steady state and a steady state. The time constants of (VO2)A and (VO2)E were varied with increase of work load intensity.

Exercise Test↗
PubMed2002

The effects of speech production on physiologic responses during submaximal exercise.

PURPOSE: To investigate the effects of speech production on physiological responses during sub maximal exercise of various intensities. METHODS: Three constant levels running at work intensities corresponding to 65%, 75%, and 85% of the subjects' (N = 14) VO(2) max were performed with and without talking. These loads were chosen to represent the range of training intensities, which are most often used by the general population for improving cardiovascular fitness. During both sessions, various cardiopulmonary variables were measured breath-by-breath. RESULTS: Oxygen uptake, ventilation, breathing frequency, CO(2) production, total respiration cycle time, and expiration time decreased significantly while blood lactate, blood pressure, and end tidal CO(2) increased. There were no significant differences between talking and being silent in heart rate, inspiration time, and in tidal volume. CONCLUSIONS: Speech production during sub maximal exercise results in a significant reduction in minute ventilation and oxygen uptake with an accompanying elevation of lactic acid and blood pressure. These findings are of particular relevance for planning rehabilitation or training programs for ill as well as for healthy populations.

Adult↗
PubMed1981

The resident and the borderline in-patient: a supervisor's perspective.

The problems of residents working intensively with borderline inpatients in a general hospital psychiatric unit area described. The resident feels pressure because of inexperience with intensive psychotherapy, and the high visibility of working in a closely supervised team setting. The border line patient baffles the resident with his defensive activity characterized by splitting, erotization, idealization, and negative therapeutic response. These difficulties complicate supervision, necessitating the supervisor's alertness to being caught in team splits or collusion with the resident's unrealistic hopefulness or nihilism. Supervision must actively address the resident's countertransference and the supervisor's counterresponses. Clinical vignettes illustrate the various problems.

Borderline Personality Disorder↗
PubMed2001

[Changes in the work and life of bank employees with repetitive strain injury: RSI].

Nowadays, Repetitive Strain Injury (RSI) has been one of the most serious problems concerning workers' health. Aiming at analyzing the main changes in the work and life of RSI bearers from an RSI Bearers Association in Cascavel--Paraná, we developed this qualitative study. Semi-structured interviews were applied to nine bank employees. The first symptoms had appeared during the period of automation and introduction of new technology in the Brazilian financial system, which was when changes in work organization took place. The main elements in this process were the increase in work load, use of computers, overtime work, absence of intervals, monotony, repetitive actions, intense work and productivity control, pressure and tension. The aggravation of injuries affected productivity and caused dependence to carry out activities at work and out of it. A challenge lies in ensuring these worker's rights.

Adult↗
PubMed2002

Effects of creatine supplementation during recovery from rapid body mass reduction on metabolism and muscle performance capacity in well-trained wrestlers.

BACKGROUND: The aim of the study was to test the hypothesis that creatine supplementation with concomitant carbohydrate ingestion during recovery period after rapid body mass reduction accelerates the restoration of body mass and physical performance in well-trained wrestlers. METHODS: A double-blind, placebo-controlled cross-over study was conducted on five young healthy male wrestlers, who reduced their body mass by 4.5-5.3% in two series of investigations separated by one month. During 17 hrs recovery period they consumed controlled diet supplemented in random order with glucose (GL trial) or with glucose plus creatine (GL+CR trial). The capacity of the subjects to perform submaximal and maximal (W(max)) intensity work was measured using 5 min intermittent intensity test exercise at the Cybex II device before (Test 1) and after body mass loss (Test 2), also after the recovery (Test 3) on both trials. RESULTS: There was no effect of treatment on the extent of body mass regain during 17 hrs recovery. A significant increase (19.2%) in W(max) from Test 2 to Test 3 was observed in GL+CR trial whereas no change was evident with GL treatment. A strong correlation (r=0.92) was established between the whole body creatine retention and the extent of change in W(max) from Test 2 to Test 3. CONCLUSIONS: The results suggest that creatine supplementation with concomitant glucose ingestion during 17 hrs recovery from rapid body mass loss does not accelerate the restoration of body mass but still stimulates the regain of physical performance in maximal intensity efforts in well-trained wrestlers.

Adult↗
PubMed2005

[Work conditions and occupational features of female fur farmers].

The authors present some problems faced during use of "R 2.2.755-99" Manual in evaluating work conditions of female fur farmers. Gender approach appears necessary in evaluation of work conditions through physical, chemical, biologic factors and work intensity. The authors suggest evaluation scale for work conditions in influence of negative odorants on workers.

Adult↗
PubMed1991

Effort and dyspnoea during work of varying intensity and duration.

This study quantified the separate contributions of the intensity of exercise and its duration to muscular effort and dyspnoea during cycle ergometry. Six normal subjects estimated the perceived intensity (Borg scale 0-10) of peripheral muscular effort and dyspnoea during incremental exercise to their maximum work capacity (Wcap). On separate days, the same subjects exercised to endurance or 60 min at work rates rated for leg effort on the initial incremental test as: 2 ("slight", 33.1 +/- 1.45% Wcap) (mean +/- SE); 3 ("moderate", omission 83.6 +/- 3.87% Wcap). Perceived leg effort increased by a factor of 4.4 (2(2.13)) with a doubling of work rate and by 1.3 (2(0.39)) with a doubling of duration, as expressed by: Leg effort = k x %Wcap2.13 x Time0.39 (r2 = 0.87) Perceived dysponea increased 5.3-fold with a doubling of work rate and by 1.4-fold with a doubling of duration: Dysponea = k x %Wcap2.41 x Time0.47 (r2 = 0.75) Changes in work intensity, rather than duration, dominated symptom magnitudes such that in the performance of a given task, halving the intensity and doubling the duration of activity reduces the maximal intensity of muscular effort and dyspnoea to less than a third.

Adult↗
PubMed1987

Influence of age on VDU work.

This study was conducted in a data processing centre with intensive work load. The keying speed and typing errors were monitored daily by the management for performance appraisal. The average keying speed of the operator was about 10,000 key strokes per hour. A survey on the subjective symptoms and feelings of fatigue of 68 experienced data entry operators revealed that there was no significant difference as far as physical health was concerned for the 42 young(18-30 years old) and 26 older operators (31-45 years old). However, there was a higher prevalence of visual strain and musculo-skeletal complaints among the older workers. A follow up study on the performance of 22 operators for 5 years showed that there was a significant reverse correlation between age and keying speed, r = 0.74 (p less than 0.01). A lower but significant correlation was also noted for typing errors and age, r = 0.50, (p less than 0.05). These results suggest that age has a significant influence on speed, accuracy and health of VDU operators. When discussing the ergonomics approach to VDU work, attention must be paid to the effect of this factor.

Adult↗
PubMed1977

Influence of water temperature on thermal, circulatory and respiratory responses to muscular work.

Different muscular exercises have been executed on a bicycle ergometer during immersion in water, the temperature of which varied between 20 and 40 degrees C. During submaximal works, O2 consumption was not modified by the temperature of the water. On the other hand, body temperature (rectal and muscular) are clearly influenced by environment. The temperature of the quadriceps varies from 37.7-38.5 degrees C when the bath temperature rises from 20-40 degrees C during the same work intensity corresponding to 1/3 of the individual maximal work capacity. The rectal temperature was always lower about 0.5 degrees C. Ventilation and heart rate underwent modifications which were significantly accentuated in hot water. Maximal O2 consumption does not reach its highest level in cold water. The low muscular temperature observed in these conditions seems to limit the aerobic metabolism and the working of the muscles. Maximal O2 consumption then rises in parallel with the increase in bath temperature and in body temperatures. In very hot water however (40 degrees C), when rectal temperature rises unduly, the circulatory demand linked to thermolysis becomes excessive, and maximal O2 consumption decreases.

Adult↗
PubMed1976

Maximal oxygen uptake during exercise with various combinations of arm and leg work.

Oxygen uptake (VO2) was determined in 10 males during the following types of maximal exercise (work time: about 5 min): uphill running, bicycling, arm work (cranking), and combined arm work and bicycling (A + L). The A + L exercise was performed in four different ways, the arms doing 10%, 20%, 30%, or 40% of the same total rate of work; and also with the maximal bicycle work load plus either maximal or submaximal arm work. VO2 was the same in running as in all types of A + L exercise, except when the arm work load was 10% and 40% of the total rate of work, where VO2 was 2.5% (P less than 0.05) and 9.4% (P less than 0.001) lower, respectively. Bicycle VO2 was lower than VO2 in running but equal to A + L VO2 when arm work intensity was 40% of the total rate of work. It is concluded that VO2 during maximal exercise a) to a certain extent depends on the exercising muscle mass, b) is lower than the oxygen-consuming potential of the muscles involved in A + L exercise, and c) in A + L exercise is influenced by the ratio of arm work to total rate of work and the subject's fitness for arm work and bicycling.

Adult↗