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Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 37 records · Page 2Linked to original sources
PubMed2001

Epinephrine causes a reduction in lymph node cell output in sheep.

The lymphatic system has a critical role in the return of fluids, proteins, and cells to the circulatory system. However, the effects of stress, including exercise, on this system have not been adequately studied. We investigated the effect of a physiological dose (1 mg) of epinephrine (Epi) on lymph flow, cell concentration, and lymphocyte subsets in efferent subcutaneous lymph in sheep. Blood leukocyte numbers, differential, lymphocyte subsets, and blood and lymph pools of lymphocytes were determined simultaneously. A significant acute increase in lymph flow was followed by a post-injection decrease in flow and cellular output. No changes in lymphocyte subsets or pools of lymphocytes were seen in either blood or lymph. The timing of elevated plasma and lymph concentrations of Epi and norepinephrine (NE) corresponded with the increased lymph flow. In conclusion, Epi injection caused no change in lymphocyte subset distribution, leukocyte concentration, or pools of lymphocytes. A decrease in lymph flow and cellularity was documented post-injection, indicating that lymphatic tissue has no role in the leukocytosis seen after Epi injection. Lymphocyte retention by lymph nodes, however, may contribute to post-injection lymphopenia.

Adrenergic alpha-Agonists↗
PubMed2001

Basic recruit training: health risks and opportunities.

The present review examines the impact of basic recruit training on health and lifestyle. Many of those recruited begin training with a less than optimal lifestyle with respect to fitness, smoking habits, alcohol consumption, drug abuse, and exposure to sexually transmitted diseases. Thus, there is scope to enhance training programs that address fitness and lifestyle, minimizing potential losses in health and efficiency from upper respiratory infections, musculoskeletal injuries, cardiac catastrophes, mental disturbances, and adverse responses to extreme environments.

Acute Disease↗
PubMed2000

The economic burden of physical inactivity in Canada.

BACKGROUND: About two-thirds of Canadians are physically inactive. As a risk factor for several chronic diseases, physical inactivity can potentially be a substantial public health burden. We estimated the direct health care costs attributable to physical inactivity in Canada, the number of lives lost prematurely each year that are attributable to a sedentary lifestyle and the effect that a reduction of 10% in inactivity levels (a Canadian objective for 2003) could have on reducing direct health care costs. METHODS: We calculated summary relative risk (RR) estimates from prospective longitudinal studies of the effects of physical inactivity on coronary artery disease, stroke, colon cancer, breast cancer, type 2 diabetes mellitus and osteoporosis. We then computed the population-attributable fraction (PAF) for each illness from the summary RR and the prevalence of physical inactivity (i.e., 62%) and applied the PAF to the total direct health care expenditures for 1999 and to the number of deaths in 1995 associated with each disease to determine the health care costs and lives lost prematurely that were directly attributable to physical inactivity. RESULTS: About $2.1 billion, or 2.5% of the total direct health care costs in Canada, were attributable to physical inactivity in 1999. A sensitivity analysis (simultaneously varying each of the health care costs and PAF by +/- 20%) indicated that the costs could be as low as $1.4 billion and as high as $3.1 billion. About 21,000 lives were lost prematurely in 1995 because of inactivity. A 10% reduction in the prevalence of physical inactivity has the potential to reduce direct health care expenditures by $150 million a year. INTERPRETATION: Physical inactivity represents an important public health burden in Canada. Even modest reductions in inactivity levels could result in substantial cost savings.

Adolescent↗
PubMed2000

Special feature for the Olympics: effects of exercise on the immune system: overview of the epidemiology of exercise immunology.

The application of epidemiological methods to exercise immunology is reviewed briefly, with particular reference to the possible influences of physical activity, exercise and training on susceptibility to upper respiratory infections. Available reports are arbitrarily rated in terms of limiting factors: the quality of the assessment of physical activity, the precision of diagnosis of upper respiratory infection and overall methodology. The pattern of physical activity has often been clearly established but, in part because of the problems associated with the competitive environment, assessments of infection and overall methodology have often been less than optimal. Although there is some evidence that susceptibility to infection is increased by either a single bout of very heavy activity or a period of heavy training, reports are far from unanimous, and in certain respects fail to meet the classical epidemiological criteria of a causal relationship. The issue is important to both the health and the success of the international competitor, and merits definitive investigation, using optimal methods to assess both activity patterns and infection.

Adolescent↗
PubMed2000

Exercise and training in women, Part I: Influence of gender on exercise and training responses.

Exercise and training responses in women are briefly reviewed. Part I of the paper considers the influence of gender on such responses. The average woman has a smaller inherent aerobic power and less muscular strength than a man, reflecting sociocultural influences, physical size, body composition, and hormonal milieu. Nevertheless, the best-trained women can out-perform sedentary men. The handicap of the average woman is offset by a lighter body mass and a tendency to metabolize fat rather than carbohydrate during exercise. A lack of anabolic hormones may limit training increases of muscle bulk in the female. A low initial fitness may enhance the scope for training tolerance, but it also limits tolerance of conditioning. Nevertheless, women seem less vulnerable than men to exercise-induced sudden death and overtraining. Part II of the review considers the influence of the menstrual cycle and pregnancy upon exercise and training responses. Physical activity programmes for young women should take account of possible pregnancy. Potential dangers to the foetus include an excessive rise of core body temperature, a decrease of maternal blood sugar, and foetal hypoxia. Nevertheless, regular moderate exercise generally has a favourable impact upon pregnancy outcomes.

Cardiovascular Physiological Phenomena↗
PubMed2000

Exercise and training in women, Part II: Influence of menstrual cycle and pregnancy.

This part of the review considers the impact of the menstrual cycle and pregnancy upon exercise performance, together with the implications of continued, regular exercise for the developing foetus. Specific issues that are covered include changes in physical performance over the menstrual cycle; the impact of training on the menstrual cycle; a need for awareness of potential pregnancy; alterations in fitness, performance, circulatory, respiratory and metabolic function during pregnancy; potential hazards to the foetus from hyperthermia and hypoxia; a recommended physical activity programme for the pregnant woman; and the impact of continued exercise upon pregnancy outcomes.

Exercise↗
PubMed2000

Exercise elevates plasma levels but not gene expression of IL-1beta, IL-6, and TNF-alpha in blood mononuclear cells.

Physical activity induces a subclinical inflammatory response, mediated in part by leukocytes, and manifested by elevated concentrations of circulating proinflammatory cytokines, including interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha). However, the source of the cytokines that appear during exercise remains unknown. In this study, we examined exercise-induced changes in plasma cytokine concentrations and their corresponding mRNA expression in peripheral blood mononuclear cells. Ten healthy [peak oxygen uptake = 48.8 +/- 6.5 (SD) ml. kg(-1). min(-1)] but untrained men [age = 25 +/- 5 (SD) yr] undertook 3 h of exercise (cycling and inclined walking) at 60-65% peak oxygen uptake. Circulating leukocyte subset counts were elevated during and 2 h postexercise but returned to normal within 24 h. Plasma concentrations of IL-1beta, IL-6, and TNF-alpha peaked at the end of exercise and remained elevated at 2 h (IL-6) and up to 24 h (IL-1beta and TNF-alpha) postexercise. Cytokine gene expression in circulating mononuclear cells was measured by using the reverse transcriptase-polymerase chain reaction; mRNA accumulation did not change with exercise. In conclusion, mRNA accumulation of IL-1beta, IL-6, and TNF-alpha in circulating mononuclear cells is not affected by 3 h of moderate endurance exercise and does not seem to account for the observed increases in plasma cytokines.

Adult↗
PubMed2000

Adhesion molecule expression in acute and chronic exercise.

Adhesion molecules expressed on leukocytes and the vascular endothelial lining include the selectins, integrins, members of the immunoglobulin superfamily, and mucins. The changes in their expression that develop with acute and chronic exercise are briefly reviewed. Adhesion molecules are thought to modulate leukocyte trafficking, accounting for changes in the counts and possibly also the functional activity of various leukocyte subsets during and following an acute bout of physical activity. Some of the changes in the surface density of adhesion molecules can be explained through the action of epinephrine and other humoral factors on their expression, but an influence of sympathetic nerve terminals on cells sequestered in the spleen and liver, and an influx into the general circulation of leukocytes of differing phenotype also appear to be involved.

Cell Adhesion↗
PubMed2000

Immune function and incidence of infection during basic infantry training.

The effect of an 18.5-week infantry training program on health status was studied in 23 male military personnel (aged 22.0 +/- 0.5 years, mean +/- SE). Aerobic power, body composition, and immune function (including natural killer cell activity, mitogen-stimulated lymphocyte proliferation, in vivo cell-mediated immunity, and secretory immunoglobulin A levels) were measured in subjects at the beginning and end of the course. Subjects self-reported their symptoms of sickness in health logs using a precoded checklist. Data from this study indicate that subjects became leaner and maintained, but did not increase, their aerobic fitness by the end of the course. Cell function was enhanced significantly; however, in vivo cell-mediated immunity remained the same, and levels of secretory immunoglobulin A were lower by the end of the course. The incidence of infection remained stable throughout the course. These results indicate that the current pattern of infantry training does not have an adverse effect on the health status of recruits.

Adult↗
PubMed1999

Impact of three different types of exercise on components of the inflammatory response.

It was hypothesized that muscle injury would be greater with eccentric than with all-out or prolonged exercise, and that immune changes might provide an indication that supplements the information provided by traditional markers such as creatine kinase (CK) or delayed-onset muscle soreness. Eight healthy males [mean (SE): age = 24.9 (2.3) years, maximum oxygen consumption (VO2(max)) = 43.0 (3.1) ml x kg(-1) x min(-1)] were each assigned to four experimental conditions, one at a time, using a randomized-block design: 5 min of cycle ergometer exercise at 90% VO2(max) (AO), a standard circuit-training routine (CT), 2 h cycle ergometer exercise at 60% VO2(max) (Long), or remained seated for 5 h. Blood samples were analyzed for CK, natural killer (NK) cell counts (CD3(-)/CD16(+)56(+)), cytolytic activity and plasma levels of the cytokines interleukin (IL)-6, IL-10, and tissue necrosis factor alpha (TNF-alpha). CK levels were only elevated significantly 72 h following CT. NK cell counts increased significantly during all three types of exercise, but returned to pre-exercise baseline values within 3 h of recovery. Cytolytic activity per NK cell was not significantly modified by any type of exercise. Prolonged exercise induced significant increases in plasma IL-6 and TNF-alpha. We conclude that the lack of correlation between traditional markers of muscle injury (plasma CK concentrations and muscle soreness rankings) and immune markers of the inflammatory response suggests that, for the types and intensities of exercise examined in this study, the exercise-induced inflammatory response is modified by humoral and cardiovascular correlates of exercise.

Adult↗
PubMed1999

How much physical activity is needed for good health?

The Harvard Alumni study is reviewed critically with a view to resolving the apparent conflict between the conclusions drawn from this research and the current consensus on optimal patterns of physical activity for health. The optimal energy expenditure reported for the Harvard data set is less than at first appears, since the estimated expenditures are gross rather than net values. Further, the optimal energy expenditure has been over-estimated, because too high a cost was assumed for stair climbing, and sport involvement may also have been over-reported. The data do not as yet allow the assertion that benefit is obtained only from vigorous physical activity, and there seems little conflict with the current consensus on the benefits of moderate physical activity.

Energy Metabolism↗
PubMed1999

Biology and medicine of soccer: an update.

Recent literature on the biology and medicine of soccer (primarily since 1990) has been accumulated by a combination of computer searching of relevant databases and review of the author's extensive files. From a total of 9681 papers, 540 were selected for closer scrutiny and 370 are discussed in the present review. These articles cover patterns of play and the resulting energy demands, the nutritional requirements of soccer, the anthropometric, physiological, biochemical and immunological characteristics of successful players, the influence of environmental stressors (heat, cold, hypoxia and time zone shifts), special features of female and junior competitors, selected issues in training, and the incidence and prevention of injuries. The information presented has important implications for the safety and success of soccer players; the challenge is now to ensure that this information is understood and acted upon by coaches and individual team members.

Adult↗
PubMed1999

Daily primary school physical education: effects on physical activity during adult life.

PURPOSE: The purpose of this investigation was to study the influence of a daily primary school physical education program on physical activity (PA) level, attitudes toward physical activity, and perceptions of barriers to physical activity during adulthood. METHODS: We compared two groups: 1) an experimental group of men and women (N = 147) who had received five physical education sessions per week throughout their 6 yr of primary school education in the early 1970s; and 2) a control group, drawn from the data bank of the Québec Health Survey, and matched for age, gender, and socioeconomic profile (N = 720). Experimental and control subjects filled out an identical questionnaire about their current physical activity level, their attitudes toward PA, and their perceptions of barriers to PA. The control group was stratified to obtain the same sociodemographic profile as the experimental group. RESULTS: Our principal results were: 1) a frequency distribution that showed a higher rate of physical activity in experimental women than in control women; 2) similar intentions to exercise and attitudes toward exercise in the experimental and control groups, with no differences in opportunities for exercising or in the support received from their family and friends; and 3) a lower prevalence of regular smokers in experimental men than in control men. There were also some differences in the types and frequency of physical activities selected between experimental and control subjects. CONCLUSION: Our results strongly suggest that daily physical education at the primary school level has had a significant long-term positive effect on the exercise habits on women, despite similar perceived barriers, attitudes, and intention to exercise in the two groups. The program has also had a significant health effect in men, substantially reducing the risk of becoming a regular smoker. Because the program was not specifically designed to promote health, we hypothesize that a health-oriented physical education program could have an even stronger effect.

Adult↗
PubMed1999

Identifying bottlenecks in endurance performance: the conductance theorem.

The various transport processes that contribute to human endurance performance, such as oxygen intake, elimination of carbon dioxide, lactate and heat, and the delivery of metabolic fuels, can all be represented by conductance analogues. The use of such models is helpful in identifying bottlenecks within each of these systems, and in comparing parallel systems such as the intake of oxygen and the elimination of carbon dioxide. However, in order to make the models manageable, many simplifications are necessary, and corresponding caution is needed in drawing inferences from conductance analogues.

Adaptation, Physiological↗
PubMed1999

Indomethacin inhibits circulating PGE2 and reverses postexercise suppression of natural killer cell activity.

Natural killer (NK) cells are important in combating viral infections and cancer. NK cytolytic activity (NKCA) is often depressed during recovery from strenuous exercise. Lymphocyte subset redistribution and/or inhibition of NK cells via soluble mediators, such as prostaglandin (PG) E2 and cortisol, are suggested as mechanisms. Ten untrained (peak O2 consumption = 44.0 +/- 3.5 ml. kg-1. min-1) men completed at 2-wk intervals a resting control session and three randomized double-blind exercise trials after the oral administration of a placebo, the PG inhibitor indomethacin (75 mg/day for 5 days), or naltrexone (reported elsewhere). Circulating CD3(-)CD16(+)/56(+) NK cell counts, PGE2, cortisol, and NKCA were measured before, at 0.5-h intervals during, and at 2 and 24 h after a 2-h bout of cycle ergometer exercise (65% peak O2 consumption). During placebo and indomethacin conditions, exercise induced significant (P < 0.0001) elevations of NKCA (>100%) and circulating NK cell counts (>350%) compared with corresponding control values. With placebo treatment, total NKCA was suppressed (28%; P < 0.05) 2 h after exercise, and a postexercise elevation (36%; P = 0.02) of circulating PGE2 was negatively correlated (r = 0.475, P = 0.03) with K-562 tumor cell lysis. NK counts were unchanged in the postexercise period, but at this stage CD14(+) monocyte numbers were elevated (P < 0.0001). Indomethacin treatment eliminated the postexercise increase in PGE2 concentration and completely reversed the suppression of total and per CD16(+)56(+) NKCA 2 h after exercise. These data support the hypothesis that the postexercise reduction in NKCA reflects changes in circulating PGE2 rather than a differential lymphocyte redistribution.

Administration, Oral↗