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Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 19 recordsLinked to original sources
PubMed2006

Relationship of bone health to yearlong physical activity in older Japanese adults: cross-sectional data from the Nakanojo Study.

INTRODUCTION: We determined associations between bone health and the quantity and quality of habitual physical activity in a cohort of 172 free-living Japanese aged 65-83 years (76 men, 96 women). METHODS: The number of steps taken and the intensity of physical activity were measured every 4 s throughout each 24-h period for 1 year, using a specially adapted accelerometer that distinguished up to 11 levels of physical activity (expressed in metabolic equivalents, METs). At the end of the year, a quantitative ultrasonic technique assessed each participant's osteosonic index (OSI, reflecting bone stiffness in the calcaneus). RESULTS: The data were significantly described by linear and exponential regression models which showed that in both sexes the OSI score increased with increasing daily physical activity, up to the observed maximum values of approximately 14,000 steps/day and 50 min/day at an intensity >3 METs. However, when data were categorized into quartiles of physical activity, OSI scores were not significantly greater in persons exceeding recommended minimum standards of habitual physical activity (corresponding to counts of around 6,900 and 6,800 steps/day and durations >3 METs of around 18 and 16 min/day in men and women, respectively). All who met such criteria (with the exception of a few women) had OSI scores above the threshold for a clinical diagnosis of osteoporosis. Multivariate-adjusted logistic regression analyses predicted that men and especially women who engaged in <6,800 steps/day and <16 min/day of moderate-intensity physical activity were, respectively, 4.9-8.4 and 2.2-3.5 times more likely to sustain fractures than those participating in >8,200 steps/day and >25 min/day of activity >3 METs. CONCLUSION: Causation cannot be inferred from a cross-sectional study. Nevertheless, we suggest that from the viewpoint of bone health, elderly people should be encouraged to engage in low- and moderate-intensity habitual physical activity, taking >7,000 steps/day with a duration >15 min/day at >3 METs.

Aged↗
PubMed2005

Chronic fatigue syndrome. A brief review of functional disturbances and potential therapy.

The chronic fatigue syndrome (CFS) is debilitating for both athletes and the general population. A review of etiology and mechanisms underlying functional disturbances is undertaken to provide a valid basis for therapeutic options. The review focuses on CFS as characterized by standard diagnostic criteria, building on previous reviews through use of articles identified by Medline search. Overtraining, a negative energy balance, excessive physical or environmental stress, disorders of personality and affect, dysfunction of the hypophyseal-pituitary adrenal axis, hormonal imbalance, nutritional deficits, immune suppression or activation and chronic infection have all been proposed as factors precipitating CFS, but none of these precipitants are observed consistently. Impairments of peak aerobic power and muscle strength, together with many functional disturbances, seem related to patient- or physician-imposed inactivity. Once CFS is established, treatment should aim at breaking the vicious cycle of effort avoidance, deterioration in physical condition and increasing fatigue through a combination of psychotherapy, general encouragement and a progressive exercise regimen.

Autoimmunity↗
PubMed2004

Cytokine induction during exertional hyperthermia is abolished by core temperature clamping: neuroendocrine regulatory mechanisms.

The immunomodulatory effects of physiological temperature change remain poorly understood and inter-relationships between changes in core temperature, stress hormones and cytokines during exertional hyperthermia are not well established. This experimental study was designed to examine how cytokine (tumour necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-12 and IL-1ra (receptor antagonist)) and hormone (epinephrine (Epi), norepinephrine (NE), growth hormone (GH) and cortisol (CORT)) responses are modified when the exercise-induced rise in core temperature is attenuated or exacerbated by immersion in a water bath. Ten men ((mean +/- SD) age: 26.9 +/- 5.7 years; height 1.75 +/- 0.07 m; body mass 76.0 +/- 10.9 kg; O(2 peak): 48.0 +/- 12.4 mL kg(-1) min(-1)) completed two 40-min cycle ergometer exercise trials at 65% O(2 peak) while immersed to mid-chest. Rectal temperature (T(re)) peaked at 39.1 +/- 0.03 and 37.5 +/- 0.13 degrees C during the hot (39 degrees C) and cold (18 degrees C) conditions, respectively. Blood samples were collected before, during (20- and 40-min) and after (30- and 120-min) exercise. Increases in circulating NE (>350%), Epi (>500%), GH (>900%), IL-12 (>150%) and TNF-alpha (>90%) were greatest after 40-min exercise in the heat. Substantial elevations of CORT (80%), IL-1ra (150%) and IL-6 (>400%) did not occur until after exercise was complete. Core temperature clamping decreased the rise in circulating stress hormone concentrations and abolished increases in plasma cytokine concentrations. These findings suggest that exercise-associated elevations of T(re) mediate increases of circulating stress hormones, which subsequently contribute to induction of circulating cytokine release.

Adult↗
PubMed2003

Test-retest errors and the apparent heterogeneity of training response.

Published reports have shown large apparent inter-individual differences of gains in maximal oxygen intake (VO(2max)) in response to a standard 20-week programme of aerobic conditioning that progressed to 75% of the individual's initial VO(2max). The observed gains of VO(2max) ranged from 0 to 1,000 ml min(-1), with a coefficient of variation (CV) of 8.4%. The present analysis evaluates the potential contribution of test-retest errors to these apparent large inter-individual differences in training response. The 2-day test-retest CV for VO(2max) readings in 742 healthy adults was initially 5.0%, dropping to 4.1% after training. Published training responses were estimated from the mean of paired measurements obtained before and after training if readings agreed by <5%, but from the highest of paired values if these differed by >5%. Taking account of the relative proportions of single and paired observations, the weighted VO(2max) data for the entire sample had an effective 2-day CV of 4.3% before and 3.4% after training. Assumption 1: if the 20-week test-retest error remained similar to the 2-day figure, measurement error would contribute a CV of 5.5% to apparent training responses, or (for the stated initial mean VO(2max) of 2,409 ml min(-1)) an SD of 132 ml min(-1). Assumption 2: if the 20-week CV was similar to that in other long-term studies (~5%), measurement error would contribute a CV of 6.1%, or a SD of 146 ml min(-1). The published data show a total SD of 202 ml min(-1) for apparent inter-individual differences in training response, with age, gender, race and baseline VO(2max) accounting for only 11% of this variance. After estimating the likely effect of test-retest measurement errors, the SD due to inter-individual differences would decrease to 138 ml min VO(2max) (assumption 1) or 123 ml min(-1) (assumption 2). We conclude that when estimating the extent of inter-individual differences in training response, allowance must be made not only for the minor effects of recognized covariates (age, gender, race and initial fitness), but also for the larger influence of test-retest measurement errors. Nevertheless, substantial inter-individual differences persist after making such adjustments. The most likely explanation of these differences is a familial aggregation of training responses.

Adaptation, Physiological↗
PubMed2003

Limits to the measurement of habitual physical activity by questionnaires.

Despite extensive use over 40 years, physical activity questionnaires still show limited reliability and validity. Measurements have value in indicating conditions where an increase in physical activity would be beneficial and in monitoring changes in population activity. However, attempts at detailed interpretation in terms of exercise dosage and the extent of resulting health benefits seem premature. Such usage may become possible through the development of standardised instruments that will record the low intensity activities typical of sedentary societies, and will ascribe consistent biological meaning to terms such as light, moderate, and heavy exercise.

Energy Metabolism↗
PubMed2002

The relationship between physical activity and self-image and problem behaviour among adolescents.

BACKGROUND: Although there are a vast array of studies which have demonstrated the psychological and physical health benefits of regular aerobic exercise for adults, few studies have focussed on children and adolescents. The current study examined associations between the extent of participation in endurance sport, and self-report data on self-image, physical and psychological health and overall lifestyle in a large representative sample of German high-school students. METHOD: Almost 1000 German adolescents (aged 14-18 years) were administered a comprehensive series of questionnaires aimed at assessing anxiety-depression, trait addiction, smoking and drinking behaviour, physical ill-health reports, and self-perception of self-image, parental acceptance and educational attainment. RESULTS: Regular practice of endurance exercise was related to a more favourable self-image. There was a strong association between participation in sports and the type of personality that tends to be resistant to drug and alcohol addiction. Physical exercise was further significantly related to scores for physical and psychological well-being. Adolescents who engaged regularly in physical activity were characterised by lower anxiety-depression scores, and displayed much less social behavioural inhibition than their less active counterparts. CONCLUSION: It is likely that discussion of recreational or exercise involvement may provide a useful point of entry for facilitating dialogue among adolescents about concerns relating to body image and self-esteem. In terms of psychotherapeutic applications, physical activity has many additional rewards for adolescents. It is probable that by promoting physical fitness, increased physical performance, lessening body mass and promoting a more favourable body shape and structure, exercise will provide more positive social feedback and recognition from peer groups, and this will subsequently lead to improvement in an individual's self-image.

Adolescent↗
PubMed2002

Naive and memory T cell subsets are differentially mobilized during physical stress.

This study examined the naive and memory phenotypic profiles of CD4+ and CD8hi T cells that were mobilized to the peripheral circulation during a combination of aerobic exercise and heat stress, determining expression of the adhesion molecules CD62L and CD11a on the recruited cells. Twelve recreationally active males (age 27.1 +/- 5.3 yr, height 1.77 +/- 0.08 m, mass 76.9 +/- 12.0 kg, VO2peak 43.9 +/- 6.7 mL x kg(-1) x min(-1)) completed a 40 min bout of cycle ergometry at 65 % of VO2peak while immersed to mid-chest in a water bath at 39 degrees C. Venous blood samples were collected before (T0), during (T40) and 30 min after (T70) exposure to combined exercise and heat stress. Specimens were analyzed by three-colour flow cytometry for CD4+ and CD8hi T cell expression of CD45RO, CD11a and CD62L. Some 80 % of the CD4+ T cells that were mobilized were of the CD45RO memory phenotype, with the numbers of CD11alo and CD62L+ cells increasing more than those of CD11ahi and CD62L- cells. For the CD8hi cells, there was a more equal recruitment of CD45RO- naive (43 %) and CD45RO+ memory (57 %) cells. The majority (84 %) of recruited CD8+ cells were CD11ahi; there was a trend to predominance of CD62L- cells (57 %) for the memory subset, but with almost equal recruitment of CD62L+/- for the naive subset. We conclude that the exercise + heat stress induced trend to an increase in CD4+ T cells is linked in some way to memory phenotype; it cannot be explained simply by a high density expression of CD11a and lack of the lymph node homing receptor (CD62L). Furthermore, although mobilization of CD8hi T cells is not linked to memory phenotype, a high density expression of CD11a and a lack of the lymph node homing receptor are important determinants of CD8hi T cell mobilization.

Adult↗
PubMed2002

Exercise under hot conditions: a major threat to the immune response?

It seems likely that the disturbances of immune response induced by prolonged competitive exercise are exacerbated if athletes also face the stress of hot environmental conditions. We have investigated this question by manipulating the exercise-induced increases of body temperature in a climatic chamber and by submersion of exercisers in a large water-bath. Hot conditions increase the stress of a given bout of exercise, as assessed by personal perceptions, objective (heart rate variability) measures of autonomic nerve balance, and the secretion of "stress" hormones, with a parallel increase in effects upon critical lymphocyte subsets. Changes in the immune response show substantial correlations with plasma concentrations not only of epinephrine (which modulates the adhesiveness of peripherally sequestered lymphocytes), but also with norepinephrine. The latter hormone may mobilize leukocytes from the spleen and lymph glands, or it may act by increasing cardiac output and thus intravascular shear forces. Given the cumulative impact of various environmental stressors upon the immune system, every effort should be made to minimize the athlete's exposure to stresses other than the exercise to be performed. In some circumstances, the use of medications to reduce the overall stress response may also be warranted.

Body Temperature Regulation↗
PubMed2001

Differential cell adhesion molecule expression and lymphocyte mobilisation during prolonged aerobic exercise.

This study was undertaken to determine the cell adhesion molecule profile of CD4+, CD8hi and CD56+ lymphocytes, which are mobilised to and from the peripheral blood during and after prolonged aerobic exercise. Ten healthy males (21-35 years old) were tested on two occasions, separated by at least 14 days. On the first occasion, subjects were examined in a rested state but did not exercise. On the second occasion, the same subjects were examined at the same time of day before, during and after 2 h of exercise at 65% of peak oxygen consumption. Blood samples obtained at rest (t0), during (at 0.5, 1, 1.5 and 2 h, t0.5, t1, t1.5 and t2, respectively) and after (at 4 and 24 h, t4 and t24, respectively) exercise were analysed by two-colour flow cytometry for CD4+, CD8hi and CD56+ cell surface expression, and density of CD62L, CD49d and CD11a. At t2, circulating concentrations of CD56+, CD8hi and CD4+ lymphocytes had increased (P < 0.05) by 330%, 105% and 30%, respectively. The majority of CD4+, CD8hi and CD56+ lymphocytes mobilised to the blood at t2 were CD62L- and CD11ahi, although populations of CD4+ and CD56+ cells that expressed CD62L+ and CD11alo were also mobilised. Changes in subset concentrations at t0.5 were positively associated (r = 0.63; P < 0.01) with their corresponding mean surface density of CD11a at t0. Our findings suggest that the differential mobilisation of lymphocytes during prolonged aerobic exercise is linked to the surface expression of CD11a (i.e. lymphocyte-function-associated antigen-1). However, mechanisms unrelated to CD11a expression also appear to be involved.

Adult↗
PubMed2001

Absolute versus relative intensity of physical activity in a dose-response context.

PURPOSE: To examine the importance of relative versus absolute intensities of physical activity in the context of population health. METHODS: A standard computer-search of the literature was supplemented by review of extensive personal files. RESULTS: Consensus reports (Category D Evidence) have commonly recommended moderate rather than hard physical activity in the context of population health. Much of the available literature provides Category C Evidence. It has often confounded issues of relative intensity with absolute intensity or total weekly dose of exercise. In terms of cardiovascular health, there is some evidence for a threshold intensity of effort, perhaps as high as 6 METs, in addition to a minimum volume of physical activity. Decreases in blood pressure and prevention of stroke seem best achieved by moderate rather than high relative intensities of physical activity. Many aspects of metabolic health depend on the total volume of activity; moderate relative intensities of effort are more effective in mobilizing body fat, but harder relative intensities may help to increase energy expenditures postexercise. Hard relative intensities seem needed to augment bone density, but this may reflect an associated increase in volume of activity. Hard relative intensities of exercise induce a transient immunosuppression. The optimal intensity of effort, relative or absolute, for protection against various types of cancer remains unresolved. Acute effects of exercise on mood state also require further study; long-term benefits seem associated with a moderate rather than a hard relative intensity of effort. CONCLUSIONS: The importance of relative versus absolute intensity of effort depends on the desired health outcome, and many issues remain to be resolved. Progress will depend on more precise epidemiological methods of assessing energy expenditures and studies that equate total energy expenditures between differing relative intensities. There is a need to focus on gains in quality-adjusted life expectancy.

Adult↗
PubMed2001

Sepsis and mechanisms of inflammatory response: is exercise a good model?

OBJECTIVES: The immune changes induced by a bout of prolonged and vigorous exercise have been suggested to be a useful experimental model of sepsis and the inflammatory response. Available literature was reviewed to evaluate this hypothesis. METHODS: Literature describing the immune response to various patterns of exercise was compared with data on the immune changes observed during sepsis and inflammation. RESULTS: Although there are qualitative similarities between the immune responses to exercise and sepsis, the magnitude of the changes induced by most forms of exercise remains much smaller than in a typical inflammatory response. Indeed, the exercise induced changes in some key elements such as plasma cytokine concentrations are too small to be detected reliably by current technology. CONCLUSIONS: If exercise is to provide a valid model of sepsis and the inflammatory response, it will be necessary to focus on subjects who are willing to exercise extremely hard, to use the pattern of exercise that has the greatest effect on the immune system, and to combine this stimulus with other psychological, environmental, or nutritional stressors.

Anti-Inflammatory Agents↗
PubMed2001

Physical activity assessment options within the context of the Canadian Physical Activity, Fitness, and Lifestyle Appraisal.

The Canadian Physical Activity, Fitness, and Lifestyle Appraisal (CPAFLA) is a standardized battery of tests that is commonly used to assess asymptomatic individuals. This paper reviews evidence concerning the reliability, validity, and utility of the procedure currently used to assess habitual physical activity in the CPAFLA and surveys available physical activity assessment options. Special considerations related to age, gender, ethnicity, seasonal variations, and within-week variance are discussed. The potential assessment options are discussed with consideration given to the logistical and pragmatic constraints inherent in the CPAFLA. New technologies for future assessment of physical activity are briefly presented and recommendations for future research forwarded.

Canada↗
PubMed2001

Intracellular monocyte and serum cytokine expression is modulated by exhausting exercise and cold exposure.

This study tested the hypothesis that exercise elicits monocytic cytokine expression and that prolonged cold exposure modulates such responses. Nine men (age, 24.6 +/- 3.8 y; VO(2 peak), 56.8 +/- 5.6 ml. kg(-1). min(-1)) completed 7 days of exhausting exercise (aerobic, anaerobic, resistive) and underwent three cold, wet exposures (CW). CW trials comprised </=6 h (six 1-h rest-work cycles) exposure to cold (5 degrees C, 20 km/h wind) and wet (5 cm/h rain) conditions. Blood samples for the determination of intracellular and serum cytokine levels and circulating hormone concentrations were drawn at rest (0700), after exercise (approximately 1130), and after CW (~2000). Whole blood was incubated with (stimulated) or without (spontaneous) lipopolysaccharide (LPS; 1 microgram/ml) and stained for CD14 monocyte surface antigens. Cell suspensions were stained for intracellular cytokine expression and analyzed by flow cytometry. The proportion of CD14(+) monocytes exhibiting spontaneous and stimulated intracellular expression of interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha increased after exercise, but these cells produced less IL-1beta and TNF-alpha after CW when CW was preceded by exhausting exercise. Serum cytokine concentrations followed a parallel trend. These findings suggest that blood monocytes contribute to exercise-induced cytokinemia and that cold exposure can differentially modulate cytokine production, upregulating expression of IL-6 and IL-1 receptor antagonist but downregulating IL-1beta and TNF-alpha. The cold-induced changes in cytokine expression appear to be linked to enhanced catecholamine secretion associated with cold exposure.

Adult↗
PubMed2001

The cytokine response to physical activity and training.

Cytokines are soluble glycoproteins that are produced by and mediate communication between and within immune and nonimmune cells, organs and organ systems throughout the body. Pro- and anti-inflammatory mediators constitute the inflammatory cytokines, which are modulated by various stimuli, including physical activity, trauma and infection. Physical activity affects local and systemic cytokine production at different levels, often exhibiting striking similarity to the cytokine response to trauma and infection. The present review examines the cytokine response to short term exercise stress, with an emphasis on the balance between pro- and anti-inflammatory mechanisms and modulation of both innate and specific immune parameters through cytokine regulation. The effects of long term exercise on cytokine responses and the possible impact on various facets of the immune system are also discussed, with reference to both cross-sectional and longitudinal studies of exercise training. Finally, the validity of using exercise as a model for trauma and sepsis is scruti- nised in the light of physiological changes, symptomatology and outcome, and limitations of the model are addressed. Further studies, examining the effect of exercise, trauma and infection on novel cytokines and cytokine systems are needed to elucidate the significance of cytokine regulation by physical activity and, more importantly, to clarify the health implications of short and long term physical activity with respect to overall immune function and resistance to infection.

Aging↗
PubMed2001

Chronic fatigue syndrome: an update.

The chronic fatigue syndrome is characterised by a fatigue that is disproportionate to the intensity of effort that is undertaken, has persisted for 6 months or longer, and has no obvious cause. Unless there has been a long period of patient- or physician-imposed inactivity, objective data may show little reduction in muscle strength or peak aerobic power, but the affected individual avoids heavy activity. The study of aetiology and treatment has been hampered by the low disease prevalence (probably <0.1% of the general population), and (until recently) by a lack of clear and standardised diagnostic criteria. It is unclear how far the aetiology is similar for athletes and nonathletes. It appears that in top competitors, overtraining and/or a negative energy balance can be precipitating factors. A wide variety of other possible causes and/or precipitating factors have been cited in the general population, including psychological stress, disorders of personality and affect, dysfunction of the hypothalamic-pituitary-adrenal axis, hormonal imbalance, nutritional deficits, immune suppression or activation and chronic infection. However, none of these factors have been observed consistently. The prognosis is poor; often disability and impairment of athletic performance are prolonged. Prevention of overtraining by careful monitoring seems the most effective approach in athletes. In those where the condition is established, treatment should aim at breaking the vicious cycle of effort avoidance, deterioration in physical condition and an increase in fatigue through a combination of encouragement and a progressive exercise programme.

Exercise↗