Showing papers by "Roy J. Shephard published in 2003"

Regression to the mean. A threat to exercise science

Abstract: Regression to the mean (RTM) can bias any investigation where the response to treatment is classified relative to initial values for a given variable without the use of an appropriate control group. The phenomenon and resulting errors of interpretation have been recognised by clinicians in a number of disciplines. The causes of RTM include both intra-individual variance and measurement error. The magnitude of RTM can be estimated quite simply, given a knowledge of intra- and inter-individual variance. RTM can be avoided by using a fully controlled experimental design. Difficulties can also be minimised by making duplicate measurements prior to the experimental manipulation, the first measurement serving for classification, and the second (with randomly distributed variance) allowing an assessment of the response to treatment. Less satisfactorily, surrogate measurements (for example, plasma volume for maximal oxygen intake [VO2max]) can assess the bias introduced by an initial non-random sorting of study participants. The impact of RTM on the design and interpretation of investigations has as yet received little consideration by exercise scientists and sports physicians. The response to training is often related to initial measurements of a dependent variable such as heart size, ST segmental depression, fitness or level of physical activity. In particular, analyses of this type have been adduced to support the belief that the response to aerobic training is inversely related to an individual’s VO2max. In fact, RTM may account for a major part of this apparent relationship.

Effects of three different types of exercise on blood leukocyte count during and following exercise

Abstract: CONTEXT: High-intensity exercise causes tissue damage, production of stress hormones, and alterations in the function and quantity of various immune cells. Many clinical-physical stressors such as surgery, trauma, burns and sepsis induce a pattern of hormonal and immunological response similar to that of exercise. It has thus been suggested that heavy exercise might be used to cause graded and well-defined amounts of muscle trauma, thereby serving as an experimental model for inflammation and sepsis. OBJECTIVE: In order to explore whether some form of strenuous exercise might provide an useful model for the inflammatory process, we studied the effects of three different exercise protocols on blood leukocyte count during and following exercise. DESIGN: Four different experimental conditions, using a randomized-block design. SETTING: Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada. PARTICIPANTS: Eight healthy and moderately fit males. PROCEDURES: Participants were each assigned to four experimental conditions. Subjects performed 5 minutes of cycle-ergometry exercise at 90%, 2 hours of cycle-ergometry exercise at 60%, a standard circuit of resistance exercises with 3 sets of 10 repetitions at 60 to 70% of one-repetition maximum (1-RM) force at each of 5 different stations; or they remained seated for 5 hours. DIAGNOSTIC TEST USED: Flow cytometric analysis. MAIN MEASUREMENTS: Blood samples were analyzed for total leukocyte counts, total T cells, T helper/inducer cells, T suppressor/cytotoxic cells, B cells, cytolytic T cells, and natural killer cells. RESULTS: The peak aerobic and prolonged submaximal exercise induced similar alterations in cell counts. These changes were generally larger than those produced by the resistance exercise, although both resistance and peak aerobic exercise resulted in a significantly longer-lasting decrease in the CD4+/CD8+ ratio than the submaximal exercise bout did. CONCLUSION: The data suggest that, of the three exercise patterns tested, prolonged aerobic exercise induced the largest and most readily measured patterns of immune response. Nevertheless, the changes provided only a partial model for the clinical inflammatory process.

Adhesion molecules, catecholamines and leucocyte redistribution during and following exercise.

Abstract: The circulating blood normally contains no more than 1–2% of the body’s population of leucocytes. The numbers and phenotypes of circulating leucocyte subsets can change dramatically during and immediately following exercise. The surface expression of adhesion molecules makes an important contribution to such responses by changing patterns of cell trafficking. Alterations in the surface expression of adhesion molecules could reflect a shedding of molecules, selective apoptosis or differential trafficking of cells with a particular phenotype, effects from mechanical deformation of the cytoplasm, active biochemical processes involving cytokines, catecholamines, glucocorticoids or other hormones, or changes in the induction of adhesion molecules. The expression of adhesion molecules changes with maturation and activation of leucocytes. Typically, mature cells express lower densities of L-selectin (CD62L), the homing receptor for secondary lymphoid organs, and higher densities of LFA-1 (CD11a), the molecule associated with trafficking to non-lymphoid reservoir sites. The neutrophils and natural killer cells that are mobilised during exercise also express high levels of Mac-1 (CD11b), a marker associated with cellular activation. Possibly, exercise demarginates older cells that are awaiting destruction in the spleen. Plasma concentrations of catecholamines rise dramatically with exercise, and there is growing evidence that catecholamines, acting through a cyclic adenosine monophosphate second messenger system, play an important role in modifying the surface expression of adhesion molecules. Analogous changes can be induced by other forms of stress that release catecholamines or by catecholamine infusion, and responses are blocked by β2-blocking agents. Catecholamines also modify adherence and expression of adhesion molecules in vitro. Cell trafficking is modified by genetic deficiencies in the expression of adhesion molecules, but leucocyte responses to exercise and catecholamines are generally unaffected by splenectomy. A number of clinical conditions including atherogenesis and metaplasia are marked by an altered expression of adhesion molecules. The effects of exercise on these molecules could thus have important health implications.

Long-term cardiorespiratory results of exercise training following cardiac transplantation.

Abstract: The long-term influence of exercise training after heart transplantation remains unclear. Accordingly, we performed a 12-year follow-up study of 36 patients who underwent heart transplantation. Findings for survivors were compared with those of age-matched controls over the same period. Comparisons were also made between survivors and deceased patients. The sample comprised 36 men (aged 47 ± 9 years) and a group of healthy age-matched controls. The patients received 16 months of outpatient exercise training; physiologic data were collected initially and at discharge. At 12 years, further data were collected on 20 of 23 survivors and their controls; 3 of the survivors were unavailable for final assessment, and 13 patients had died in the interim. The survivors’ peak oxygen intake (VO2peak) increased 26% after training and decreased 0.39 mlkg−1min−1 per year (27.9 ± 7 to 23.7 ± 6), which was a similar rate as the controls (0.37 mlkg−1min−1 per year; 33.7 ± 7 to 29.2 ± 7). Lean body mass (LBM) increased 3 kg by 16 months and a further 2.5 kg by 12 years, but ultimately was 3 kg below the controls. Although there was no difference in entry data between deceased patients and survivors, the latter attained greater gains in VO2peak and LBM over the 16 months of training. Thus, in heart transplantation patients who undergo training, gains in exercise capacity are lost over 12 years at a rate commensurate with normal aging. A reduced training response in VO2peak and LBM contributes to a poorer prognosis.

Tracking of physical fitness from childhood to adulthood

Abstract: The purpose of the present study was to investigate the tracking of selected aspects of physical fitness (peak handgrip force, sit-ups, aerobic fitness, and blood pressure) from childhood to adulth...

New insights in the prescription of exercise for coronary patients.

Abstract: Prescribing exercise for cardiac patients is comparable in many ways to prescribing medications; that is, one recommends an optimal dosage according to individual needs and clinical status. Recent research has shown that it is more accurate to prescribe exercise as a percentage of the oxygen uptake reserve (VO2R), which is the difference between resting and maximal or peak oxygen consumption, rather than as a percentage of the VO2 max. Moreover, it appears that a minimum of 1600 kcal/week of leisure-time physical activity may halt the progression of coronary artery disease, whereas regression may be achieved with a gross energy expenditure of 2200 kcal/week. Upper body and resistance training have also been shown to be safe and effective for clinically stable patients. Aerobic capacity serves as an independent predictor of all cause and cardiovascular mortality in patients referred to an outpatient cardiac rehabilitation program, with each 1 metabolic equivalent increase in aerobic fitness conferring an approximate 10% reduction in mortality. The goal of preventing recurrent cardiac events is, to a large extent, based on sustained compliance to multifactorial interventions, which can be influenced by numerous socioeconomic and clinical variables, and enhanced by home-based or group cardiac rehabilitation programs that are designed to circumvent or attenuate barriers to participation and adherence, so that many more individuals may realize the benefits that secondary prevention can provide.

BMI in the Trois-Rivières study: child-adult and child-parent relationships.

Abstract: This study evaluated intraindividual child-adult and interindividual child-parent relationships of body mass index (BMI) using data from the Trois-Rivieres semilongitudinal study of growth and development. Intraindividual correlations between age 12 and 35 years were substantial (r(2) = 36% of variance in women, 30% of variance in men). Interindividual child-parent correlations for mothers and fathers age 36.6 +/- 0.4 and 39.5 +/- 0.4 years, respectively, were very low to low for daughters age 12 years (r = 0.09, NS and 0.34, P < 0.001 vs. father and mother, respectively) but all very low for sons age 12 years (r = 0.07, NS and 0.16, NS vs. father and mother, respectively). A multiple regression analysis predicted adult BMI from the individual's BMI at 10, 11, 12 years plus the maternal and paternal BMIs as calculated from self-reported heights and weights. The BMI at age 12 years was a better predictor of adult BMI than the parental BMI in both men and women (P < 0.001) and multivariate analysis revealed that this index at age 12 years was the sole significant predictor of adult BMI for both men and women. The results from our study do not support the hypothesis that parental BMI is a stronger predictor of adult BMI than childhood BMI. However, useful information for the prediction and prevention of adult overweight can be obtained from the BMI at age 12 years. Our results suggest that environmental influences may be the major factor in the present obesity epidemic.

Supervision of occupational fitness assessments.

Abstract: Controversy continues regarding an appropriate level of supervision for occupational fitness assessments. A bout of vigorous physical activity can augment the immediate risk of a cardiac catastroph...

Boosting of Performance in the Athlete with High-Level Spinal Injury

Abstract: Autonomic dysreflexia is a common response to painful stimuli following high level spinal injuries. Loss of normal control of sympathetic reflexes leads to large increases in blood pressure, accompanied by headache and occasional more dangerous sequelae. Although now officially banned, intentional dysreflexia ("boosting") is still exploited by some competitors to gain an unfair advantage. It is thus important to consider physiological mechanisms, consequences for health and performance, and methods of controlling this abuse. Boosters perceive the practice as frequent, performance enhancing, and of low immediate risk. Effective methods of eliminating the practice may include more stringent control of competitors, evaluating and publicizing short-and long-term risks, and countering arguments that boosting is an ethically acceptable method of restoring a normal physiological response.