No description available.

Physiological and psychological indicators of stress were measured in a cohort of 20 female nurses working 12 hour, 7.5 hour and 'nine to five' shift patterns in intensive care units conducted over a period of four years. Saliva samples were collected by each subject at four specified times during each shift over a period for one week and repeated every few months. Two consecutive days were used to compare days on duty, days off duty and the first day at work following days off. Salivary cortisol levels were measured by RIA. Secretory immunoglobulin A (SIgA), also a physiological indicator of stress, was determined with an indirect sandwich ELISA using a monoclonal antibody. Salivary cortisol levels of nurses were higher and SIgA levels lower prior to starting 12 hour shift following a day off compared with nurses working other shifts. Simultaneous psychological measures obtained by selfreports of perceived demands, coping and moods showed these nurses did not perceive themselves to be stressed. The findings of the study suggest that nurses working 12 hour shifts prepare for work differently perhaps in anticipation of long hours of work. Furthermore, salivary cortisol levels were considerably higher compared with those cited in studies of acute stress under laboratory conditions. In contrast, 20 nurses undertaking an academic examination, considered an acute stressful event, reported increased anxiety and mental and emotional demands and had higher salivary cortisol concentrations prior to the event, albeit lower than the longitudinal study. SIgA levels were lower prior to the examination but not significantly so. A positive correlation between cortisol and SIgA levels was apparent, however, only 6 months later when the subjects no longer perceived themselves to be stressed.

No description available.

No description available.

Results of the first investigation into possible acclimatisation to cold and thermal status of Antarctic divers are presented. Over a year, on average one subject dived on alternate days and the other four subjects once a week. Divers wore 7mm or 10mm wet suits in water ca-1^oC. Mean dive duration was 30min, and mean depth of immersion 9m. Surface mean wind speed was 10 knots and mean ambient temperature -2^oC. Over the year subjects rectal and skin temperatures, and thermal comfort were monitored before, during and after immersion on 26 dives. Severe body cooling (Hall 1972) occurred on 75%, rectal temperature decreased to below normal (although never to clinically hypothermic levels) and there was a marked, exponential drop in skin temperature. End-of-dive finger temperatures were always at a level at which impairment of function would be expected. Divers were usually uncomfortably cold at the end of dives. During the year repeated monthly measurements were made of: skinfold thickness, body weight, body fat weight and fat-free mass: basal metabolic rate: rectal and skin temperatures, metabolic rate, shivering, thermal comfort, adrenaline, noradrenaline and cortisol excretion during immersion to the neck in water at 20^oC for one hour: time of onset of cold-induced vasodilatation, temperature and pain responses of left index finger immersed at 0^oC for half an hour. Differences between the responses of divers at different months of the year and between divers and nondivers were tested by analysis of variance. It was found that divers shivered less and had less thermal discomfort (by verbal rating scales) than nondivers (as they had similar metabolic rates this suggests greater nonshivering thermogenesis). It was also found that divers extracted more oxygen from inspired air while immersed to the neck than nondivers. In both divers and nondivers there was a winter increase of skinfold thickness and body fat weight and a winter decrease of fat-free mass, and while these may be an adaptation to cold, it is possible that other stimuli were responsible. No significant differences were found between any of the other parameters tested. Monthly measurements of physical fitness, and time spent outside and in various activities indicated that these were not important complicating factors in the acclimatisation studies. A comparison of Antarctic dives and laboratory cold water immersions showed that while dives led to a greater fall of peripheral temperature and lower peripheral thermal comfort the laboratory immersions led to a greater fall in rectal temperature and trunk skin temperature. In this thesis, it is proposed that while Antarctic divers were subject to considerable thermal stress there was little evidence of cold acclimatisation.

A study was made on seventeen young men at a Polar scientific research station over a period of one year. Serial observations were made of body composition, energy expenditure and performance. Weather recordings were carried out in order to determine the influence of seasons on the various parameters described and an attempt made to ascertain any groupings of the individuals. Body composition was recorded weekly by weighing and by skinfold thickness measurements that were subsequently converted into total body fat estimations. Both these parameters increased predominantly during the first six months. Activity patterns derived by personal diary recall showed that on average ten per cent of time was spent outside, with a variation between summer and winter. Mean energy expenditure derived from these figures was at a level of 3600 kcal/day. This compares favourably with results from previous polar expeditions and distinction is made between a static and a travelling scientific station. Discussion is centred on a proposed stress triad that includes isolation, darkness and severe weather. Various combinations of these environmental stresses are considered and an evaluation is made of their effects on performance that was measured using a cycle ergometer. It is shown that the group became significantly more fit over the year and that the correlation between fitness change and energy expenditure is poor. The influence of body composition on fitness is considered and a re-appraisal is made of cold acclimatization. It is confirmed that Man on a static scientific research station spends only a small proportion of time outside and the conclusion is drawn that Antarctica now, with the facilities of modern building insulation techniques and specialised clothing, together with an adequate diet, is a desirable habitat for Man who may soon colonize the region to exploit natural resources.

A study has been undertaken to determine the energy balance and thermal stress of skidoo drivers in Antarctica, and to compare them in those respects with dog sledgers. A background study of the variation over a year in various physiological parameters in some of the travellers studied was also carried out. 1. Resting metabolic rate. blood pressure, and pulse rate, body weight and skin fold thickness were measured monthly over a period of one year in six men living on a scientific base in Antarctica. Percentage body fat was determined from body weight and skin fold thickness. Skin fold thickness and percentage body fat were greater than that to be expected in the U.K.: other parameters did not differ significantly from accepted norms. Most of the parameters measured showed similar patterns cf variation: high values in spring or summer, falling in winter, with a small-peak after midwinter, rising again in autumn. There was a significant reduction in skin fold thickness and body fat over the year, but no significant change in other parameters. 2. Energy intake, expenditure and balance, weight loss and fat loss were determined in men travelling overland in Antarctica. Thirteen trips, seven by skidoo and six by dog sledge, each of approximately eleven days, were studied. Energy deficit was found on all trips. Energy intake, expenditure, and deficit were significantly greater on dog trips. Weight loss and fat loss were also greater, but the differences were not statistically significant. 3. Skin temperature was measured and thermal comfort, shivering, sweating, clothing and activity were recorded on ten day trips, six by dog sledge, and four by skidoo. Skin temperatures on dog runs were lower and more variable than on skidoo runs, and differences between central and peripheral temperatures greater. Thermal discomfort, shivering and sweating were more common on dog runs.

The purpose of the study was to examine the proposition that adaptations of skeletal muscle are more important determinants of the ability to sustain submaximum exercise than maximum oxygen uptake (V0₂ max). The metabolic response to exercise was compared in 2 groups of runners with differing V0₂ max values. Trained female runners, despite their lower V0₂ max values, showed lower respiratory exchange ratio values (R) and higher post-exercise concentrations of plasma fat metabolites than active male subjects. This was so when subjects ran at a common absolute speed and when each individual ran at a speed equivalent to 60% V0₂ max. Six weeks of training on the cycle ergometer resulted in a 16% increase in V0₂ max but a 250% increase in endurance performance, i.e. time to exhaustion at 80% V0₂ max. During standard, submaximum exercise oxygen uptake, ventilation, heart rate, R values and blood lactate concentration were lower post-training than pre-training. The concentrations of plasma fat metabolites during and after exercises were not influenced by training. Training one leg and not the other resulted in 20% and 10% increase in V0₂ max but 340% and 150% increases in endurance for the trained leg (TL) and the untrained leg (UTL) respectively. The increases in both variables were significantly greater for the TL than for the UTL. Changes in submaximum V0₂, ventilation, R values and blood lactate concentration were mainly restricted to exercise with the TL but the reduction in heart rate was similar for each leg. Plasma FFA, glycerol and citrate concentrations during exercise were unchanged for either leg. The role of citrate in the training-induced interaction of fat and carbohydrate metabolism was investigated. Artificial elevation of plasma citrate concentrations by ingestion of citrate did not decrease blood lactate concentrations during exercise. After short-term fasting citrate accumulated in the myocardium but not in skeletal muscles in the rat. Plasma citrate concentration was a poor predictor of muscle citrate concentration in these circumstances. When subjects were exhausted after single-leg exercise at 80% V0₂ max muscle glycogen concentration decreased by 70% and muscle lactate concentration was increased 10-fold. Training halved the rate of glycogen depletion, decreased muscle lactate concentration and resulted in a decrease in R values only during exercise with the TL. The trend towards an increase in muscle citrate concentration was restricted to trained muscle. The experiments showed that absolute values of V0₂ max could be dissociated from the metabolic characteristics of endurance training and that V0₂ max is an insensitive indicator of training improvements in submaximum endurance. Peripheral adaptations are the dominant influence on the ability to sustain submaximum exercise but training only one leg can cause some systemic change which influences both V0₂ max and endurance for the UTL. The mechanism of the training-induced interaction of fat and carbohydrate metabolism remains unclear.

No description available.

This thesis describes the experimental work carried out to further the understanding of the mechanisms involved in the process of fretting fatigue. The design and construction of a rig to enable a controlled fretting action to be applied to a push-pull type of fatigue specimen is discussed. Special consideration is given to the form of the fretting contact geometry with regard to the generated stress field, and the reasons behind the final choice of a circular Hertzian contact are given. The investigation of the effects of various parameters on the fatigue life of the specimen are reported. The parameters chosen for the investigation were the slip amplitude, the bulk stress and the normal load. Examination of the developing fretting damage was carried out ty interrupting the tests at prescribed intervals. The subsequent observations made of the surface and sue-surface damage are illustrated by optical and scanning electron micrographs. Two distinct forms of damage are proposed, these have been termed type I and type II fretting fatigue damage. Type I damage is considered to be by crack nucleation from the conjoint action of the bulk and surface stress fields. These cracks were found to nucleate in the direction of maximum shear at the edge of the fretting contact, and at the position where the alternating tensile stress was largest. The subsequent direction of propagation of these cracks, determines whether or not fatigue failure of the specimen will occur. The type I fretting damage process, is noted to have been responsible for every case of catastrophic fatigue failure of the test specimens. Type II fretting damage was found at the centre of the fretting contact area, where the hydrostatic stress and surface shear traction are maximum. The material in this region was found to have undergone extensive microstructural alteration. White etching layers with a hardness in excess of 1300Hv (more than four times the original hardness) are reported. An extensive literature survey is presented which shows no previous evidence of white etching layers forming under clean fretting conditions. The white layers are shown to have important consequences on the rate of wear, thus it is postulated that under certain conditions fretting wear and fretting fatigue may be linked ty the same mechanism, i.e. white etching layer formation. The white etching layers are also discussed in terms of their potential for nucleating fatigue cracks, this phenomenon is illustrated by a service failure from a diesel engine.