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Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 91 records · Page 5Linked to original sources
PubMed1996

Effects of heat and intermittent exercise on leukocyte and sub-population cell counts.

This study examined the combined effects of heat stress and intermittent exercise on circulating leukocyte and sub-population cell counts. Using a randomized-block design, 11 healthy male subjects [mean (SD) age = 29.1 (3.0) years maximal oxygen consumption (VO2max) = 47.6 (6.1) ml/(kg.min)] were assigned to four conditions. Each subject exercised on a cycle ergometer at 50% VO2max (two 30-min bouts, with 45 min rest between), or acted as his own control by sitting at 23 degrees C, or at 40 degrees C, 30% relative humidity, for 3 h. Blood samples taken prior to, during, and after each rest and exercise bout, and at corresponding times when sitting were used for Coulter cell counter and flow cytometric analysis. Sitting conditions did not produce any significant immunological changes. Intermittent exercise induced a biphasic response of granulocytosis, monocytosis and lymphocytosis, with a return to baseline between exercise bouts. One hour following the second exercise bout, samples showed a consistent granulocytosis, monocytosis and lymphocytosis (CD3+, CD4+, CD8+ and CD19+ cell counts). The second exercise bout produced a larger response than the first, further exacerbated when exercising at 40 degrees C. We conclude there is a synergism between heat and exercise exposure. An increase in core temperature and exercise stress recruit leukocytes into the peripheral circulation, with potentiation of the response during a second bout of exercise. However, while the increase of core temperature remains moderate, the disturbance of immune function does not appear to have great clinical significance.

Adult↗
PubMed1996

Determination of body heat storage: how to select the weighting of rectal and skin temperatures for clothed subjects.

Two methods of estimating body heat storage were compared under differing conditions of clothing and acclimation to heat. Sixteen male subjects underwent 6 consecutive days or two 6-day periods, separated by a 1-day rest period of heat acclimation, exercising 60 min.day-1 at 45%-55% of maximal aerobic power in a hot, dry environment (dry bulb temperature 40 degrees C; relative humidity 30%; and wind speed 0.3 m.s-1). Before and after acclimation, the subjects entered the same environment, wearing either normal light combat clothing or clothing protective against nuclear, biological, and chemical agents; they walked on a treadmill at 1.34 m.s-1, 0% slope continuously (n = 11 for normal clothing) or as repeated 15-min bouts of exercise followed by 15-min sitting rest (n = 5 for normal clothing and n = 16 for protective clothing). Average exposure times were 147 min (preacclimation) and 150 min (postacclimation) for continuous exercise and 150 min (both pre- and postacclimation) for intermittent exercise while wearing normal clothing, and 103 min (preacclimation) and 116 min (postacclimation) for intermittent exercise while wearing protective clothing. Heat storage was determined calorimetrically (from heat gains and heat losses) and thermometrically [using various weightings of rectal temperature (Tre) and mean skin temperature (Tsk)]. There were only minor (<5%) differences in estimated heat storage, whether calculations used a single specific heat (3.47 kJ.kg-1.degree C-1) or a value computed according to the subject's body composition. When wearing normal clothing, a formula with an invariant relative weighting for Tre to Tsk of 4:1 provided the best thermometric estimate of heat storage. When wearing protective clothing, the invariant relative weighting of 4:1 underestimated heat storage by 2%-12%; underestimation was attenuated by using respective relative weightings for a thermoneutral and hot environment of 2:1 and 2:1 or 4:1 and 9:1 before acclimation and 4:1 and 9:1 after acclimation. We conclude that the accuracy of thermometric estimates of heat storage can be improved by modifying the weighting factors according to environment, acclimation, and type of clothing.

Adult↗
PubMed1996

Effects of moderate endurance exercise and training on in vitro lymphocyte proliferation, interleukin-2 (IL-2) production, and IL-2 receptor expression.

This study was designed to examine immunological responses to an acute bout of cycle ergometry exercise before and after moderate endurance training. Previously sedentary males were randomly assigned to matched training (n = 9) or control (n = 6) groups. Training comprised 12 weeks during which supervised cycle ergometer exercise took place [30 min at 65-70% of maximal oxygen intake (VO2max), 4-5 days .week-1]. An acute bout of exercise (60 min; 60% VO2max) was performed initially and after the 12-week interval. Samples of peripheral venous blood were taken at rest, after 30 and 60 min of exercise, and at 30 and 120 min post-exercise. Training improved VO2max by an average of 20% (40.6 to 49.2 ml.kg-1.min-1). Relative to baseline and control measures, the resting concentration of (CD3-CD16+/CD56+) natural killer (NK) cells increased by 22% (P < 0.05). The resting count of total CD25+ [interleukin-2 receptor (IL-2R) alpha chain] lymphocytes did not change following training, but dual staining analysis showed a 100% increase in the fraction of CD16+ CD25+ NK cells (P < 0.05). Likewise the resting CD122+ (IL-2R beta chain) lymphocyte count increased 35% after training, the greatest increases (44%) being in CD16+ CD122+ NK cells (P < 0.05). Soluble IL-2R levels also increased 33% (P < 0.05) after training. Following acute exercise at the same relative intensity, trained individuals exhibited a larger increase in the NK cell count, reduced lymphocytopenia, and attenuation of exercise-induced suppression of lymphocyte proliferation and IL-2 production (P < 0.05). In addition, smaller increases in CD4 and CD8 counts during exercise were noted, but with faster recovery post-exercise (P < 0.05). Addition of recombinant IL-2 (rIL-2) to phytohemagglutinin-stimulated peripheral blood mononuclear cell cultures did not reverse exercise-induced suppression of cell proliferation, either before or after training. However, rIL-2 did augment the spontaneous blastogenesis of exercise and post-training samples relative to baseline (P < 0.05). We conclude that moderate endurance training is associated with sustained alterations in immune function, both at rest and when exercising. Further investigations are necessary to determine the impact on overall health and susceptibility to disease.

Adult↗
PubMed1996

Residual analysis in the determination of factors affecting the estimates of body heat storage in clothed subjects.

Body heat storage can be estimated by calorimetry (from heat gains and losses) or by thermometry [from changes (delta) in mean body temperature (T b) calculated as a weighted combination of rectal (Tre) and mean skin temperatures (T sk)]. If an invariant weighting factor of Tre and T sk were to be used (for instance, delta T b = 0.8.delta Tre + 0.2 delta T sk under hot conditions), body heat storage could be over- or underestimated substantially relative to calorimetry, depending on whether the subject was wearing light or protective clothing. This study investigated whether discrepancies between calorimetry and thermometry arise from methodological errors in the calorimetric estimate of heat storage, from inappropriate weightings in the thermometric estimate, or from both. Residuals of calorimetry versus thermometric estimates were plotted against individual variables in the standard heat balance equation, applying various weighting factors to Tre and T sk. Whether light or protective clothing was worn, the calorimetric approach generally gave appropriate estimates of heat exchange components and thus heat storage. One exception was in estimating latent heat loss from sweat evaporation. If sweat evaporation exceeded 650 g.h-1 when wearing normal clothing, evaporative heat loss was overestimated and thus body heat storage was underestimated. Nevertheless, if data beyond this ceiling were excluded from the analyses, the standard 4:1 weighting matched calorimetric heat storage estimates quite well. When wearing protective clothing, the same 4:1 weighting approximated calorimetric heat storage with errors of less than approximately 10%, but only if environmental conditions allowed a subject to exercise for more than 90 min. The best thermometric estimates of heat storage were provided by using two sets of relative weightings, based upon the individual's metabolic heat production (M in kilojoules per meter squared per hour): (4 - [(M - x).x-1].2): 1 for an initial, thermoneutral environment and (4 + [(M - x).x-1].5):1 for a final, hot environment, the optimal value of x lay between 450 and 500 kJ.m-2.h-1. We concluded that the accuracy of thermometric estimates of heat storage can be improved by modifying weighting factors of Tre and T sk according to the environment, type of clothing, and metabolic rate.

Adult↗
PubMed1996

Exercise and cancer: linkages with obesity?

This review examines possible protection against various types of tumors from both occupational and leisure-time physical activity. A growing number of well-controlled studies suggest that both hard physical work and an active leisure reduce the overall incidence of cancer. Benefit is demonstrated most clearly for colonic tumors; here, benefit persists after control of the data for body mass index, and a likely mechanism is the speeding of colonic transit, with a resulting decrease in exposure to carcinogens. There are occasional reports of protection against tumors of the breast, reproductive tract, and other body organs. In some of these latter sites, potential mechanisms of protection include a suppression of sex hormone secretion and reduction of body fat depots, where androgens are converted to toxic estrogen derivatives. While vigorous athletic participation may well modulate hormone output, a reduction of body fat is a more likely explanation of any benefit from more moderate physical activity. Protection against cancer is unlikely to become a major argument for an active lifestyle, but it is nevertheless a useful byproduct of physical activity undertaken with other health objectives.

Adult↗
PubMed1996

The athlete's heart: is big beautiful?

Development of the concept of "athlete's heart" is traced through early clinical and radiographic studies to modern echocardiography and magnetic resonance imaging. It is noted that the lower limits of criteria for the diagnosis of a "pathological" enlargement of the heart have frequently been revised in an upward direction, as the prevalence of large hearts has been recognised in both endurance and power sports competitors who are in good health. Belief that hypertrophic cardiomyopathy is the commonest cause of sports related death in young adults is traced to weak diagnostic criteria and frequent republication of a very small group of cases. Although the existence of a congenital myocardial dystrophy is now well established, this condition is extremely rare, and has no particular predilection for athletes. Genetically based screening tests may become available in the future, but the exclusion of young adults from sports participation on echocardiographic criteria appears costly and ineffective. For most people, the development of a large heart is not a pathological sign--rather, it is a desirable outcome that will enhance performance on the sports field, and will allow longer independence in old age.

Cardiomegaly↗
PubMed1996

The place of perceived exertion ratings in exercise prescription for cardiac transplant patients before and after training.

OBJECTIVE: Heart rate provides a poor guide to exercise prescription after cardiac transplantation. This study explores whether the rating of perceived exertion (RPE) provides useful alternative information. METHODS: Borg's original categoric scale was applied to 36 male patients [T, age 47(SD 9 years] as they performed a progressive cycle ergometer test an average of seven months (range two to 23 months) after cardiac transplantation. The test was repeated after 16(7) months of progressive exercise centred rehabilitation. Sedentary but healthy controls [C, n = 45, age 45(7) years] performed a similar progressive cycle test. RESULTS: Initially, 13 RPE units corresponded to 66(12)% of peak VO2 in T and 50(11)% in C. Rehabilitation augmented peak VO2 (by 19%) and estimated lean body mass (by 3.5%) in the cardiac transplant patients. The increase of heart rate (HR) at 13 RPE units [delta HR = 10(17) beats.min-1] showed moderate correlations with gains of lean mass (r = 0.72) and gains of peak VO2 (r = 0.58). The relative oxygen intake at 13 RPE units remained unchanged at 68(12)% of peak VO2. CONCLUSIONS: Large inter-individual variations of RPE at a given VO2 limit the value of perceived exertion in exercise prescription. Ratings seem best restricted to fine tuning fixed distance/fixed speed exercise prescriptions in patients undergoing rehabilitation after cardiac transplantation.

Adult↗
PubMed1996

Associations between health behaviours and health related fitness.

OBJECTIVE: To examine relations between health behaviours and health related fitness. METHODS: Subjects were a convenience sample of 350 healthy adults (172 men, 178 women). Covariance analysis adjusted data for significant influences of age and socioeconomic status. Obesity was assessed by anthropometry and body density. Cardiovascular fitness was assessed and various metabolic measurements were made. Questionnaires on physical activity and health related behaviours were completed. RESULTS: Cigarette abstinence was associated with a small abdominal circumference (men) and a low trunk/extremity skinfold ratio (women). Obesity indices (body mass index, total skinfolds, percent fat, and abdominal circumference) were negatively associated with perceived fitness. Leisure activity and exercise frequency were also negatively linked to some obesity indices. Blood glucose, cholesterol, HDL-cholesterol, and triglycerides were favourably influenced by perceived activity, exercise frequency, and perceived fitness, but not by exercise intensity. Abstinence from coffee was associated with a low cholesterol/HDL ratio (men only). Principal component, discriminant, and multiple logistic regression analyses showed only weak clustering of habitual physical activity with other positive health behaviours. CONCLUSIONS: Although multiphasic health promotion programmes are economical, favourable interactions between individual programme elements seem likely to be quite limited.

Adolescent↗
PubMed1996

Quality of life and cardiorespiratory function in chronic heart failure: effects of 12 months' aerobic training.

OBJECTIVE: To examine the long-term benefits and safety of aerobic training in patients with chronic heart failure. DESIGN: Non-randomised control trial with 52 weeks follow up. SETTING: Outpatient cardiac rehabilitation referral centre. PATIENTS: Patients with compensated chronic heart failure (mean (SD) age 62 (6) years, New York Heart Association stage III, initial resting ejection fraction 22 (7)%). Experimental group of 17 men, 4 women; control group 8 men, 1 woman. INTERVENTIONS: Experimental group: progressive, supervised aerobic walking programme for 52 weeks. CONTROL GROUP: standard medical treatment. MAIN OUTCOME MEASURES: Six-minute walk distance, progressive cycle ergometer test to subjective exhaustion, disease-specific quality of life questionnaire, and standard gamble test, all measured at entry, 4, 8, 12, 16, 26, and 52 weeks. RESULTS: Control data showed no changes except a small trend to improved emotional function (P = 0.02 at 12 weeks only). Fifteen of the 21 patients completed all 52 weeks of aerobic training; two withdrew for non-cardiac reasons (16, 52 weeks). Three were withdrawn because of worsening cardiac failure unrelated to their exercise participation (4, 4, 8 weeks), and one had a non-fatal cardiac arrest while shopping (16 weeks). Gains of cardiorespiratory function plateaued at 16-26 weeks, with 10-15% improvement in six-minute walk, peak power output, and peak oxygen intake linked to gains in oxygen pulse and ventilatory threshold and reductions in resting heart rate. Marked improvements in quality of life followed a parallel course. CONCLUSIONS: Aerobic training is safe and beneficial in compensated chronic heart failure. Gains in aerobic function and quality of life persisted over a programme lasting 52 weeks.

Aged↗
PubMed1996

Endurance exercise with and without a thermal clamp: effects on leukocytes and leukocyte subsets.

To test how leukocyte responses to endurance exercise were modified by clamping body temperature, nine men (27.3 +/- 6.0 yr) completed four 80-min immersions to midchest at water temperatures of 23 or 39 degrees C; two tests included 40-min of cycle ergometer exercise at 65% of aerobic power. When the subjects were exercising, rectal temperature peaked at 39.1 +/- 0.4 degrees C in the warm water and 37.8 +/- 0.3 degrees C in the cool water. When the subjects were sitting in warm water, rectal temperature closely matched the core temperature during exercise in cool water, whereas when they were sitting in cool water, rectal temperatures decreased to 36.4 +/- 0.6 degrees C. Total and differential white cell counts were determined by using a Coulter counter, and cortisol and growth hormone concentrations were determined by radioimmunoassay; all data were adjusted for changes of blood and plasma volumes. Heat clamping during exercise substantially reduced the rise in white cell, lymphocyte, and granulocyte counts but not the increase in monocyte count. Clamping also abolished previously observed associations between cell counts and cortisol and weakened associations with growth hormone concentrations (D. A. McCarthy and M. M. Dale. Sports Med. 6: 333-363, 1988). We conclude that both exercise and a rise of core temperature contribute to the changes in white cell and subset counts during and immediately after moderate exercise. Both cortisol and growth hormone concentrations appear to be mediators of these responses.

Adult↗
PubMed1996

Nutritional, immunologic and psychological responses to a 7250 km run.

OBJECTIVE: Health, nutritional status, aerobic power, mood state and immune function were studied over 112 days of aerobic activity (a 7250 km cross-Canada run). TYPE OF STUDY CASE REPORT: a healthy nulliparous 43 yr old woman ran 65 km/day for 112 days at a 7.9 km/h pace. MEASURES: Food intake, Profile of Mood State and Beck Depression Inventory were monitored weekly. Resting lymphocyte subsets and cytokines were determined before the run, at 3324, 5700 and 7250 km, and after recovery. Clinical data, ventilatory threshold, maximal oxygen intake and immune responses to maximal exercise were obtained before and after the run. OBJECTIVE: Health, nutritional status, aerobic power, mood state and immune function were studied over 112 days of aerobic activity (a 7250 km cross-Canada run). TYPE OF STUDY CASE REPORT: a healthy nulliparous 43 yr old woman ran 65 km/day for 112 days at a 7.9 km/h pace. MEASURES: Food intake, Profile of Mood State and Beck Depression Inventory were monitored weekly. Resting lymphocyte subsets and cytokines were determined before the run, at 3324, 5700 and 7250 km, and after recovery. Clinical data, ventilatory threshold, maximal oxygen intake and immune responses to maximal exercise were obtained before and after the run. RESULTS: Early muscle pain was treated with Ibuprofen. A mild paronychia responded to saline soaks, and exercise-induced asthma necessitated inhalation of fenoterol hydrobromide, beclomethasone diproprionate and ipatropium bromide. Food intake, (16.7 MJ/day), was 4.3 MJ/day less than expenditure, covered by metabolizing 16.7 kg of tissue (81.4% fat, 18.6% lean tissue). Ventilatory threshold and aerobic power showed little change. Initial psychological data showed tension and lack of confidence. Depression increased when crossing the Rockies, and there was anger and lack of vigor after the event. The CD8 count was low throughout; the CD25 count increased, but the CD16/56 count, IL-6 and TNF-alpha decreased over the run. Three weeks later, IL-6 had increased, but TNF-alpha remained low. CONCLUSIONS: Given substantial fat reserves, an exercise-induced energy deficit of 4.3 MJ/day can be sustained for 112 days without significant adverse consequences for immune function.

Adult↗
PubMed1996

Lung volumes of Igloolik Inuit and Volochanka nGanasan.

BACKGROUND: Acculturation to a 'modern' lifestyle has apparently speeded the aging of FVC and FEV1.0 in the Inuit (6). To test this hypothesis further, we compared lung function between Igloolik Inuit and less acculturated nGanasan in Volochanka. METHODS AND MATERIALS: FVC and FEV1.0 were measured by Stead-Wells spirometer (13.5 L lightweight bell) on 210M and 157F Inuit, and by 7.8 L dry gas wedge spirometer on 80M and 66F nGanasan. Subjects were aged 11-60 years. RESULTS: The Inuit and the nGanasan were both some 10 cm shorter than the urban norms, but the ratio of sitting to standing height was normal. Cigarette smoking began around 13-14 yr, reaching a prevalence of 80% in Inuit males and females, 78% in nGanasan males, and 56% in nGanasan females. Inuit lung volumes exceeded urban norms as children and young adults, but had a steep age coefficient even after excluding subjects with a history of respiratory disease. The nGanasan had smaller lung volumes as young adults, but a less rapid decline of function with age. CONCLUSIONS: High lung volumes in young adults probably reflect the continued physical fitness levels of circumpolar residents. The steep age coefficients for the Inuit cannot be explained simply by aging of a cohort with previous respiratory disease. The nGanasan have little advantage of smoking habits or fitness, but do not have snowmobiles. Operation of these vehicles may increase the inhalation of arctic air, and/or cause vertebral damage with resulting alterations of FVC and FEV1.0.

Adolescent↗
PubMed1996

Effects of enhanced physical education on lung volumes of primary school children.

OBJECTIVE: To test the impact of an enhanced physical education programme upon the growth and development of static and dynamic lung volumes of primary schoolchildren. EXPERIMENTAL DESIGN: Quasi-experimental three factor design (treatment x gender x urban vs rural environment) with students evaluated over each of 6 years of primary school. SETTING: Entire classes from State schools in urban and rural environment. PARTICIPANTS: All willing students aged 7-12 years in selected classes; initially 546 students, with 4% drop-out rate per year. INTERVENTION: Five hours of additional physical education per week, taught by specialist. MEASURES: Body dimension (height, body mass), aerobic power (treadmill to exhaustion), forced vital capacity (FVC), one second forced expiratory volume (FEV1.0). RESULTS: Small but statistically significant influences of treatment, gender (M > F) and environment (rural > urban) which could not be explained by body size. Both FVC and FEV1.0 conform closely to cubic functions of height in metres: Boys FVC = 0.93 (H)3, FEV1.0 = 0.79 (H)3. Girls FVC +/- 0.85 (H)3, FEV1.0 = 0.76 (H)3. CONCLUSIONS: A regular physical education programme can enhance lung volumes in primary school students. Norms should allow for gender differences, and reflect the potential attainment of students receiving adequate physical training and living in an area of low air pollution.

Child↗
PubMed1996

Asphyxial death of a young skier.

OBJECTIVE: Review of the cause of death in fatal downhill skiing accidents is important to prevention: this report concerns a boy found dead with his head buried in powder snow. EXPERIMENTAL DESIGN: Case history of an 11-year-old boy who was found dead 4 hours following descent of a steep ski slope. SETTING: Treatment by mountain rescue team and hospital emergency room. PATIENT: A boy who was discovered immersed head first in one meter of powder snow, with no sign of an avalanche or struggling, and no vital signs. The differential diagnosis included concussion + asphyxia, cervical injury, loss of consciousness from other causes, and hypothermia. INTERVENTIONS: Standard cardio-pulmonary resuscitation, rewarming by bladder irrigation and extracorporeal circulation. RESULTS: The rectal temperature, initially 29.4 degrees C, fell further to 23.3 degrees C during evacuation in a heated ambulance. On hospital admission, a blood sample showed creatine kinase 5306 units, K+ 16 mM, pH 6.38, PaCO2 223 Torr, and PaO2 67 Torr. There was no ECG rhythm, and radiography revealed pulmonary edema but no cervical malignment. Emergency measures normalized blood gases, but did not restore cardiac action. CONCLUSIONS: Death was caused by asphyxia, secondary to mild concussion. The public needs education on the dangers of deep powder snow. Adventurous skiers should wear helmets, and should not ski alone on steep mountainsides.

Asphyxia↗
PubMed1995

Effects of 6 versus 12 days of heat acclimation on heat tolerance in lightly exercising men wearing protective clothing.

This study investigated the influence of 6 versus 12 days of heat acclimation on the tolerance of low-intensity exercise in the heat while wearing protective clothing. Sixteen young men were acclimated by treadmill walking (50% of each subject's maximal aerobic power for 60 min.day-1) in a climatic chamber [40 degrees C dry bulb (db), 30% relative humidity] for either 6 consecutive days or two 6-day periods, separated by a 1-day rest. Before and after heat acclimation, the subjects performed a heat-exercise test (1.34 m.s-1, 0% grade; 40 degrees C db, 30% relative humidity), either under control conditions [wearing normal light combat clothing (continuous exercise; n = 5)] or when wearing protective clothing resistant against nuclear, biological, and chemical (NBC) agents (repeated bouts of 15-min walk + 15-min rest; n = 8). Criteria for halting the test exercise were a rectal temperature (Tre) of 39.3 degrees C, a heart rate (fc) > or = 95% of the subject's observed maximum, unwillingness of the subject to continue, or the elapse of 150 min. Heat acclimation decreased overall test values of Tre, fc, and mean skin temperature for both control and protective clothing conditions. When wearing normal combat clothing, acclimation responses were about twice as large after 12 than after 6 days, but the response was not increased by longer acclimation when wearing NBC protective clothing. Both 6 and 12 days of acclimation increased tolerance times in NBC protective clothing by about 15 min [from 97 (4) to 112 (6) min and from 108 (10) to 120 (10) min for 6 and 12 days, respectively]. We conclude that the physiological strain and limitation of heat-exercise tolerance imposed by wearing NBC protective clothing are not reduced if heat acclimation is prolonged from 6 to 12 days.

Acclimatization↗
PubMed1995

Determination of body heat storage in clothing: calorimetry versus thermometry.

Two methods of estimating body heat storage were compared under differing conditions of clothing, training, and acclimation to heat. Six male subjects underwent 8 weeks of physical training [60-80% of maximal aerobic power (VO2max) for 30-45 min.day-1, 3-4 days.week-1 at < 25 degrees C dry bulb (db)] followed by 6 consecutive days of heat acclimation (45-55% VO2max for 60 min.day-1 at 40 degrees C db, 30% relative humidity)]. Nine other male subjects underwent corresponding periods of control observation followed by heat acclimation. Before and after each treatment, subjects walked continuously on a treadmill (1.34 m.s-1, 2% grade) in a climatic chamber (40 degrees C db, 30% relative humidity) for an average of 118 min (range 92-120 min) when wearing normal light combat clothing and for an average of 50 min (range 32-68 min) when wearing protective clothing resistant to nuclear, biological, and chemical agents. The heat storage was determined calorimetrically (by the balance of heat gains and losses) and thermometrically [by the conventional equations, using one or two set(s) of relative weightings for the rectal temperature (Tre) to mean skin temperature (Tsk) of 4:1 and 4:1, 2:1 and 4:1, or 2:1 and 9:1 in thermoneutral and hot environments, respectively]. Tsk was calculated from 12-site measurements, weighted according to the regional distribution of body surface area and the first eigenvectors of principal component analysis. There were only minor differences (< 5%) between the heat storage values calculated by given weighting factors for Tre and Tsk, whether the individual coefficients were derived from estimates of regional surface area or principal component methodologies. When wearing normal clothing, no significant differences were found between the two estimates of heat storage (calorimetry vs thermometry with an invariant relative weighting of 4:1) in any experimental condition, with one specific exception: when wearing protective clothing, thermometry underestimated the heat storage by 24-31%. This under-estimation was attenuated by using two sets of relative weightings of 2:1 and 4:1 or 2:1 and 9:1. The results suggest that when subjects wearing protective clothing are transferred from thermoneutral to hot environments, the accuracy of thermometric estimates of heat storage can be improved by using two sets of weighting factors for Tre and Tsk.

Adult↗
PubMed1995

Exercise, aging and immune function.

Aging leads to a diminution of resting immune function, increasing the risk of infection, tumor development and auto-immune diseases. The production of interleukin-2 is decreased, sometimes with a decrease of total T cell count, and often with changes in T cell subsets and proliferative responses to mitogens. However, natural killer cell activity remains unchanged. In theory, moderate exercise should help to reverse the adverse effects of aging upon the immune system. However, there have been relatively few studies comparing the immune responses of young and older individuals to acute exercise and to training. A single bout of moderate exercise seems to be well tolerated by the elderly. The NK cell response is much as in younger individuals, but perhaps because of a low initial proliferative capacity, older subjects show less stimulation of lymphocyte proliferation by moderate activity and less suppression with exhausting exercise. Perhaps because resting immune function is less than in the young, moderate training programs seem to stimulate immune function to a greater extent than in young subjects. The proliferative response of the T cells is enhanced in elderly rodents whereas in young animals it is suppressed. Moreover, the resting NK cell activity of elderly human subjects seems to be increased by training. Nevertheless, the therapeutic use of exercise must be cautious in the elderly, since aging also enhances susceptibility to over-training.

Aging↗