Showing papers in "Medicine and Science in Sports and Exercise in 1999"

Economic costs of obesity and inactivity.

Abstract: Purpose: The purpose of this paper is to assess the economic costs of inactivity (including those attributable to obesity). These costs represent one summary of the public health impact of increasingly sedentary populations in countries with established market economies. Components of the costs of illness include direct costs resulting from treatment of morbidity and indirect costs caused by lost productivity (work days lost) and forgone earnings caused by premature mortality. Methods: We searched the Medline database for studies reporting the economic costs of obesity or inactivity, or cost of illness. From the identified references those relating to obesity or conditions attributable to obesity were reviewed. Chronic conditions related to inactivity include coronary heart disease (CHD). hypertension, Type II diabetes, colon cancer, depression and anxiety, osteoporotie hip fractures, and also obesity. Increasing adiposity, or obesity, is itself a direct cause of Type II diabetes, hypertension, CHD, gallbladder disease, osteoarthritis and cancer of the breast, colon, and endometrium. The most up-to-date estimates were extracted. To estimate the proportion of disease that could be prevented by eliminating inactivity or obesity we calculated the population-attributable risk percent. Prevalence based cost of illness for the U.S. is in 1995 dollars. Results: The direct costs of lack of physical activity, defined conservatively as absence of leisure-time physical activity, are approximately 24 billion dollars or 2.4% of the U.S. health care expenditures. Direct costs for obesity defined as body mass index greater than 30, in 1995 dollars, total 70 billion dollars. These costs are independent of those resulting from lack of activity. Conclusion: Overall, the direct costs of inactivity and obesity account for some 9.4% of the national health care expenditures in the United States. Inactivity, with its wide range of health consequences, represents a major avoidable contribution to the costs of illness in the United States and other countries with modern lifestyles that have replaced physical labor with sedentary occupations and motorized transportation.

Effects of physical inactivity and obesity on morbidity and mortality: current evidence and research issues.

Abstract: Purpose: The purpose of this review was to address three specific questions. 1) Do higher levels of physical activity attenuate the increased health risk normally observed in overweight or obese individuals? 2) Do obese but active individuals actually have a lower morbidity and mortality risk than normal weight persons who are sedentary? 3) Which is a more important predictor of mortality, overweight or inactivity? Methods: We initially identified more than 700 articles that included information on the exposure variables of body habitus (body mass index, body composition, or body fat pattern) and physical activity habits, and on outcomes such as morbidity or mortality. To be included in the review, we required that an article include an analysis of one of our outcomes by strata of the two exposure variables. We excluded review articles and reports of cross-sectional analyses. We used an evidence-based approach to evaluate the quality of the published data. Results: We summarized results from 24 articles that met all inclusion criteria. Data were available for the outcomes of all-cause mortality, cardiovascular disease mortality, coronary heart disease (CHD), hypertension, type 2 diabetes mellitus, and cancer. Summary results for all outcomes except cancer were generally consistent in showing that active or fit women and men appeared to be protected against the hazards of overweight or obesity. This apparent protective effect was often stronger in obese individuals than in those of normal weight or who were overweight. There were too few data on cancer to permit any conclusions. Conclusions: There are no randomized clinical trials on the topics addressed in this review. All studies reviewed were prospective observational studies, so all conclusions are based on Evidence Category C. The conclusions for the three questions addressed in the review are: 1) regular physical activity clearly attenuates many of the health risks associated with overweight or obesity; 2) physical activity appears to not only attenuate the health risks of overweight and obesity, but active obese individuals actually have lower morbidity and mortality than normal weight individuals who are sedentary, and 3) inactivity and low cardiorespiratory fitness are as important as overweight and obesity as mortality predictors. Research needs include extending current observations to more diverse populations, including more studies in women, the elderly, and minority groups, assessment methods need to be improved, and randomized clinical trials addressing the questions discussed in this review should be undertaken. Owing to size, complexity, and cost, these trials will need to be designed with valid noninvasive measures of subclinical disease processes as outcomes.

Design and analysis of research on sport performance enhancement.

Abstract: Design and analysis of research on sport performance enhancement. Med. Sci. Sports Exerc., Vol. 31, No. 3, pp. 472-485, 1999.Purpose:The purpose of this study was to assess research aimed at measuring performance enhancements that affect success of individual elite athletes in competitive ev

Exercise training-induced alterations in skeletal muscle antioxidant capacity: a brief review.

Abstract: Cellular oxidants include a variety of reactive oxygen, nitrogen, and chlorinating species. It is well established that the increase in metabolic rate in skeletal muscle during contractile activity results in an increased production of oxidants. Failure to remove these oxidants during exercise can result in significant oxidative damage of cellular biomolecules. Fortunately, regular endurance exercise results in adaptations in the skeletal muscle antioxidant capacity, which protects myocytes against the deleterious effects of oxidants and prevents extensive cellular damage. This review discusses the effects of chronic exercise on the up-regulation of both antioxidant enzymes and the glutathione antioxidant defense system. Primary antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase will be discussed as well as glutathione, which is an important nonenzymatic antioxidant. Growing evidence indicates that exercise training results in an elevation in the activities of both superoxide dismutase and glutathione peroxidase along with increased cellular concentrations of glutathione in skeletal muscles. It seems plausible that increased cellular concentrations of these antioxidants will reduce the risk of cellular injury, improve performance, and delay muscle fatigue.

Cross-validation of three jump power equations

Abstract: Cross-validation of three jump power equations. Med. Sci. Sports Exerc., Vol. 31, No. 4, pp. 572-577, 1999. The vertical jump-and-reach score is used as a component in the estimation of peak mechanical power in two equations put forth by Lewis and Harman et al.Purpose:The purpose of the pres

Physical activity in the treatment of the adulthood overweight and obesity: current evidence and research issues

Abstract: WING, R. R. Physical activity in the treatment of the adulthood overweight and obesity: current evidence and research issues. Med. Sci. Sports Exerc., Vol. 31, No. 11, Suppl., pp. S547–S552, 1999.PurposeThe purpose of this paper is to review the evidence on the role of physical activity in the treat

Levels of physical activity and inactivity in children and adults in the United States: current evidence and research issues.

Abstract: Purpose: The purpose was to describe current levels of physical activity and inactivity among adults and young people in the United States. Methods: Estimates of participation in regular physical activity were derived from three national surveys for adults (National Health Interview Survey, National Health and Nutrition Examination Survey, and the Behavioral Risk Factor Surveillance System) and from the Youth Risk Behavior Survey for high school students. Results: Overall, 63.8% of high school students surveyed on the 1997 YRBS reported participating in vigorous physical activity for at least 20 min on 3 or more days per week. Participation in vigorous activity was higher for boys (72.3%) than girls (53.5%), whites (66.8%) compared with blacks (53.9%) and Hispanics (60.4%), and decreased with advancing grade. Among adults, 27.7% meet recommended levels of either moderate or vigorous physical activity, whereas 29.2% report no regular physical activity outside of their work. Gender differences in participation in physical activity are less pronounced than in youth, and age-related patterns were complex. Whites are more active than blacks and Hispanics, and persons with higher family incomes and more education report being more physically active. There have been only minor changes in reported participation in leisure time physical activity over the past 15 yr. Conclusion: National estimates of physical activity appear to be reliable and valid for adults but may be less so for adolescents and are poor measures for children. Research is needed to determine the role that objective monitoring with accelerometers may play in surveillance. Reliable and valid measures of occupational, household, and transportation-related physical activity and sedentary behaviors are needed to better characterize the range of activity that is associated with health.

Performance and muscle fiber adaptations to creatine supplementation and heavy resistance training.

Abstract: Performance and muscle fiber adaptations to creatine supplementation and heavy resistance training. Med. Sci. Sports Exerc., Vol. 31, No. 8, pp. 1147-1156, 1999.Purpose:The purpose of this study was to examine the effect of creatine supplementation in conjunction with resistance training on

Epidemiological patterns of musculoskeletal injuries and physical training

Abstract: Epidemiological patterns of musculoskeletal injuries and physical training. Med. Sci. Sports Exerc., Vol. 31, No. 8, pp. 1176-1182, 1999.Purpose:The purpose of this study was to identify rates of diagnosis-specific musculoskeletal injuries in U.S. Marine Corps recruits and to examine the ass

Laxity, instability, and functional outcome after ACL injury: copers versus noncopers.

Abstract: Laxity, instability, and functional outcome after ACL injury: copers versus noncopers. Med. Sci. Sports Exerc., Vol. 31, No. 2, pp. 210-215, 1999.Purpose:The purpose of this study was to determine the relationship among laxity, quadriceps strength, instability, and function in subjects with

Salivary IgA levels and infection risk in elite swimmers.

Abstract: The effects of exercise on the immune system has been shown to be dependent on the level of fitness of the subjects, the degree of intensity, and the duration of the exercise. A reduction in salivary IgA levels occurs after individual sessions of exercise. Purpose: The purpose of this study was to assess the relationship between changes in salivary IgA and training volume, psychological stress, and infection rates in a cohort of 26 elite swimmers over a 7-month training period and to compare the changes with a group of 12 moderately exercising controls. Methods: Salivary IgA concentrations were measured by an electroimmunodiffusion. Exercise gradings were assessed by a standardized aerobic-anaerobic rating system. Psychological stress/anxiety was evaluated by the Spielberger State-Trait Anxiety Inventory. Infections were physician-verified. Results: Salivary IgA levels showed an inverse correlation with the number of infections in both elite swimmers and moderately exercising control subjects. The pretraining salivary IgA levels in swimmers were 4.1% lower for each additional month of training and 5.8% lower for each additional infection. The posttraining salivary IgA levels in swimmers were not significantly correlated with infection rates but were 8.5% lower for each additional I km swum in a training session and 7.0% lower for each additional month of training. The number of infections observed in the elite swimmers was predicted from regression models by the preseason (P = 0.05) and the mean pretraining salivary IgA levels (P = 0.006). The trends in pretraining salivary IgA levels over the 7-month season, calculated as individual slopes of pretraining IgA levels over time, were also predictive of the number of infections (P = 0.03) in the swimmers. Conclusions: These results indicate that measurement of salivary IgA levels over a training season may be predictive for athletes at risk of infection.

The effects of progressive resistance training on bone density : a review

Abstract: Osteoporosis is a major public health problem that is characterized by low bone mass and increased susceptibility to fractures, primarily of the hip, spine, and wrist. It is estimated to cause 1.5 million fractures annually in the United States in people aged 50 yr and older. Physical activity, particularly weight-bearing exercise, is thought to provide the mechanical stimuli or "loading" important for the maintenance and improvement of bone health, whereas physical inactivity has been implicated in bone loss and its associated health costs. Both aerobic and resistance training exercise can provide weight-bearing stimulus to bone, yet research indicates that resistance training may have a more profound site specific effect than aerobic exercise. Over the past 10 years, nearly two dozen cross-sectional and longitudinal studies have shown a direct and positive relationship between the effects of resistance training and bone density. Conversely, a handful of other studies have reported little or no effect on bone density. However, these results may be partially attributable to the study design, intensity and duration of the exercise protocol, and the bone density measurement techniques used. High-intensity resistance training, in contrast to traditional pharmacological and nutritional approaches for improving bone health in older adults, has the added benefit of influencing multiple risk factors for osteoporosis including improved strength and balance and increased muscle mass.

Effects of ballistic training on preseason preparation of elite volleyball players.

Abstract: Effects of ballistic training on preseason preparation of elite volleyball players. Med. Sci. Sports Exerc., Vol. 31, No. 2, pp. 323-330, 1999.Purpose:The purpose of this study was to determine whether ballistic resistance training would increase the vertical jump (VJ) performance of already

Interval training at VO2max : effects on aerobic performance and overtraining markers

Abstract: Purpose: Between inefficient training and overtraining, an appropriate training stimulus (in terms of intensity and duration) has to be determined in accordance with individual capacities. Interval training at the minimal velocity associated with VO 2max (vVO 2max ) allows an athlete to run for as long as possible at VO 2max . Nevertheless, we don't know the influence of a defined increase in training volume at vVO 2max on aerobic performance, noradrenaline, and heart rate. Methods: Eight subjects performed 4 wk of normal training (NT) with one session per week at vVO 2max , i.e., five repetitions run at 50% of the time limit at vVO 2max , with recovery of the same duration at 60% vVO 2max , They then performed 4 wk of overload training (OT) with three interval training sessions at vVO 2max . Results: Normal training significantly improved their velocity associated with VO 2max (20.5 ± 0.7 vs 21.1 ± 0.8 km.h - 1 , P = 0.02). As a result of improved running economy (50.6 ± 3.5 vs 47.5 ± 2.4 mL.min -1 .kg -1 . P = 0.02), VO 2max was not significantly different (71.6 ± 4.8 vs 72.7 ± 4.8 mL.min -1 .kg -1 ). Time to exhaustion at vVO 2max ). was not significantly different (301 ± 56 vs 283 ± 41 s) as was performance (i.e., distance limit run at vVO 2max : 2052.2 ± 331 vs 1986.2 ± 252.9 m). Heart rate at 14 km.h - decreased significantly after NT (162 ± 16 vs 155 ± 18 bpm. P < 0.01). Lactate threshold remained the same after normal training (84.1 ± 4.8% vVO 2max ). Overload training changed neither the performance nor the factors concerning performance. However, the submaximal heart rate measured at 14 kmh -1 decreased after overload training (155 ± 18 vs 150 ± 15 bpm). The maximal heart rate was not significantly different after NT and OT (199 ± 9.5, 198 ± 11, 194 ± 10.4, P = 0.1 Resting plasma norepinephrine (veinous blood sample measured by high pressure liquid chromatography), was unchanged (2.6 vs 2.4 nm.L - 1 , P = 0.8). However, plasma norepinephrine measured at the end of the vVO 2max test increased significantly (11. 1 vs 26.0 nm.L - 1 , P = 0.002). Conclusion: Performance and aerobic factors associated with the performance were not altered by the 4 wk of intensive training at vVO 2max despite the increase of plasma noradrenaline.

Exercise training guidelines for the elderly.

Abstract: The capacity of older men and women to adapt to increased levels of physical activity is preserved, even in the most elderly. Aerobic exercise results in improvements in functional capacity and reduced risk of developing Type II diabetes in the elderly. High-intensity resistance training (above 60% of the one repetition maximum) has been demonstrated to cause large increases in strength in the elderly. In addition, resistance training result in significant increases in muscle size in elderly men and women. Resistance training has also been shown to significantly increase energy requirements and insulin action of the elderly. Purpose: We have recently demonstrated that resistance training has a positive effect on multiple risk factors for osteoporotic fracture in previously sedentary postmenopausal women. Methods: Because the sedentary lifestyle of a long-term care facility may exacerbate losses of muscle function, we have applied this same training program to frail, institutionalized elderly men and women. Results: In a population of 100 nursing home residents, a randomly assigned high-intensity strength-training program resulted in significant gains in strength and functional status. In addition, spontaneous activity, measured by activity monitors, increased significantly in those participating in the exercise program whereas there was no change in the sedentary control group. Before the strength training intervention, the relationship of whole body potassium and leg strength was seen to be relatively weak (r 2 = 0.29, P < 0.001), indicating that in the very old, muscle mass is an important but not the only determining factor of functional status. Conclusions: Thus, exercise may minimize or reverse the syndrome of physical frailty, which is so prevalent among the most elderly. Because of their low functional status and high incidence of chronic disease, there is no segment of the population that can benefit more from exercise than the elderly.

Overview of the determinants of overweight and obesity: current evidence and research issues.

Abstract: Overview of the determinants of overweight and obesity: current evidence and research issues. Med. Sci. Sports Exerc., Vol. 31, No. 11, Suppl., pp. S515-S521, 1999. Purpose: The prevalence of obesity has reached epidemic proportions in many countries around the world. However, the genetic and environmental factors contributing to obesity are incompletely understood. Methods: We reviewed studies relating to the regulation of energy balance and how these factors may contribute to the development of obesity. Results: Although it is widely believed that genetics contribute significantly to the variability in body fatness, the available data do not support a role for defects in resting metabolic rate, substrate metabolism, dietary induced thermogenesis, or the energy cost of physical activity as significant causes of obesity. Furthermore, it is safe to say that the human genotype has not changed substantially over the past two to three decades. Data from several national surveys indicate that over the past few decades, there has been either a slight increase or a very modest decline in total energy and fat intake. This suggests that decreases in physical activity are a major contributing factor. Panicipation in leisure time physical activity is low but has remained relatively constant. However, an increased reliance on technology has substantially reduced work-related physical activity and the energy expenditure required for daily living. Conclusion: The most likely environmental factor contributing to the current obesity epidemic is a continued decline in daily energy expenditure that has not been matched by an equivalent reduction in energy intake. Because daily energy expenditure is decreasing, it is difficult for most people to restrict intake to meet energy requirements, and more and more people are becoming obese. Thus, increasing physical activity may be the strategy of choice for public health efforts to prevent obesity.

Contribution of a sedentary lifestyle and inactivity to the etiology of overweight and obesity: Current evidence and research issues

Abstract: PURPOSE: The etiology of overweight and obesity is clearly multifactorial, but ultimately it is determined by the long-term balance between energy intake and expenditure. This review will consider the effects on body weight and the risk of obesity of sedentary lifestyles, within the context of dietary habits. METHODS: The data from ecological, cross-sectional, and prospective studies that have assessed physical activity and dietary intake and their relationship to body weight were reviewed. RESULTS: Ecological analyses imply that the increase in the prevalence of obesity is more strongly related to lower levels of physical activity than higher energy intakes. However, there is a paucity of pertinent data from cross-sectional or prospective studies. There is some evidence that both a high proportion of dietary fat and low levels of physical activity may increase the likelihood of weight gain. However, even the most comprehensive studies are unable to account for more than a small proportion of the interindividual variance in weight gain, so it is difficult to usefully assess their relative importance. Furthermore, there are insufficient data that pertain to "sedentary lifestyles" to segregate any putative effect from a protective effect of exercise. All the data in this review is NHLBI Evidence category C. CONCLUSIONS: This review provides clear evidence that low levels of physical activity are associated with an increased risk of weight gain and obesity. On balance, the evidence is suggestive of a causal link, but the experimental designs are too weak is provide conclusive evidence. The potential effect of interactions between diet and activity have largely been ignored. To make progress in this area, a number of key issues need to be resolved with regard to the methodology, study design, and statistical analysis of prospective epidemiological studies. In the meantime, data need to be drawn from other sources, particularly those studies designed to elucidate the mechanism of action of diet and physical activity in the etiology of obesity, to establish rational interventions to guide public health policies.

Prescription of resistance training for health and disease.

Abstract: When prescribed appropriately, resistance training is effective for developing fitness, health, and for the prevention and rehabilitation of orthopedic injuries. Because resistance training is an integral component in the comprehensive health program promoted by the major health organizations (e.g., American College of Sports Medicine, American Heart Association, American Association of Cardiovascular and Cardiopulmonary Rehabilitation, Surgeon General's Office), population-specific guidelines have recently been published. The current research indicates that, for healthy persons of all ages and many patients with chronic diseases, single set programs of up to 15 repetitions performed a minimum of 2 d x wk(-1) are recommended. Each workout session should consist of 8-10 different exercises that train the major muscle groups. Single set programs are less time consuming and more cost efficient, which generally translates into improved program compliance. Further, single set programs are recommended for the above-mentioned populations because they produce most of the health and fitness benefits of multiple set programs. The goal of this type of program is to develop and maintain a significant amount of muscle mass, endurance, and strength to contribute to overall fitness and health. Patients with chronic diseases (e.g., arthritis) may have to limit range of motion for some exercises and use lighter weights with more repetitions.

Shoe inserts and orthotics for sport and physical activities

Abstract: The purposes of this paper were to discuss the perceived benefits of inserts and orthotics for sport activities and to propose a new concept for inserts and orthotics There is evidence that inserts or orthotics reduce or prevent movement-related injuries However, there is limited knowledge about the specific functioning an orthotic or insert provides The same orthotic or insert is often proposed for different problems Changes in skeletal movement due to inserts or orthotics seem to be small and not systematic Based on the results of a study using bone pins, one may question the idea that a major function of orthotics or inserts consists in aligning the skeleton Impact cushioning with shoe inserts or orthotics is typically below 10% Such small reductions might not be important for injury reduction It has been suggested that changes in material properties might produce adjustments in the muscular response of the locomotor system The foot has various sensors to detect input signals with subject specific thresholds Subjects with similar sensitivity threshold levels seem to respond in their movement pattern in a similar way Comfort is an important variable From a biomechanical point of view, comfort may be related to fit, additional stabilizing muscle work, fatigue, and damping of soft tissue vibrations Based on the presented evidence, the concept of minimizing muscle work is proposed when using orthotics or inserts A force signal acts as an input variable on the shoe The shoe sole acts as a first filter, the insert or orthotic as a second filter, the plantar surface of the foot as a third filter for the force input signal The filtered information is transferred to the central nervous system that provides a subject specific dynamic response The subject performs the movement for the task at hand For a given movement task, the skeleton has a preferred path If an intervention supports/counteracts the preferred movement path, muscle activity can/must be reduced/increased Based on this concept, an optimal insert or orthotic would reduce muscle activity, feel comfortable, and should increase performance

Moderate exercise during growth in prepubertal boys: changes on bone mass, size, volumetric density, and bone strength: a controlled prospective study

Abstract: Cross-sectional studies of elite athletes suggest that growth is an opportune time for exercise to increase areal bone mineral density (BMD). However, as the exercise undertaken by athletes is beyond the reach of most individuals, these studies provide little basis for making recommendations regarding the role of exercise in musculoskeletal health in the community. To determine whether moderate exercise increases bone mass, size, areal, and volumetric BMD, two socioeconomically equivalent schools were randomly allocated to be the source of an exercise group or controls. Twenty boys (mean age 10.4 years, range 8.4-11.8) allocated to 8 months of 30-minute sessions of weight-bearing physical education lessons three times weekly were compared with 20 controls matched for age, standing and sitting height, weight, and baseline areal BMD. Areal BMD, measured using dual-energy X-ray absorptiometry, increased in both groups at all sites, except at the head and arms. The increase in areal BMD in the exercise group was twice that in controls; lumbar spine (0.61 +/- 0.11 vs. 0.26 +/- 0.09%/month), legs (0.76 +/- 0.07 vs. 0.34 +/- 0.08%/month), and total body (0.32 +/- 0.04 vs. 0.17 +/- 0.06%/month) (all p < 0.05). In the exercise group, femoral midshaft cortical thickness increased by 0.97 +/- 0. 32%/month due to a 0.93 +/- 0.33%/month decrease in endocortical (medullary) diameter (both p < 0.05). There was no periosteal expansion so that volumetric BMD increased by 1.14 +/- 0.33%/month, (p < 0.05). Cortical thickness and volumetric BMD did not change in controls. Femoral midshaft section modulus increased by 2.34 +/- 2. 35 cm3 in the exercise group, and 3.04 +/- 1.14 cm3 in controls (p < 0.05). The growing skeleton is sensitive to exercise. Moderate and readily accessible weight-bearing exercise undertaken before puberty may increase femoral volumetric BMD by increasing cortical thickness. Although endocortical apposition may be a less effective means of increasing bone strength than periosteal apposition, both mechanisms will result in higher cortical thickness that is likely to offset bone fragility conferred by menopause-related and age-related endocortical bone resorption.

Childhood and adolescent physical activity patterns and adult physical activity.

Abstract: Purpose: A major research priority is the influence of childhood and adolescent physical activity patterns on adult physical activity. The research in this area is inconsistent. Therefore, the purpose of this study was to evaluate the relationships among specific components of physical activity during childhood and adolescence and exercise habits in adulthood. Methods: We analyzed preteen and teenage experiences, individual and team sports, and several psychosocial variables. One hundred and five male volunteers completed questionnaires about their current (estimated energy expenditure (EE)) and historic physical activity and a treadmill stress test. Results: Based on correlations and regression analyses, without and with controlling for potentially confounding variables (treadmill run time and sum of skinfolds), the frequency of being forced to exercise and the frequency of being encouraged to exercise during the preteen years were inversely related to adult physical activity. Being forced to exercise during the preteen years was more related to participation in individual sports than to participation in team sports or both individual and team sports. Conclusions: Being forced to exercise during childhood may have potentially negative consequences for later activity. The findings indicate that experiences related to participation in activity during childhood and adolescence may influence adult physical activity. The implications of our findings are discussed and future research is recommended.

The obesity epidemic in children and adults: current evidence and research issues.

Abstract: Purpose: The term epidemic of obesity implies that obesity is a characteristic of populations. not only of individuals. The purpose of this paper is to review evidence on obesity in populations and to identify future research issues. Methods: To examine recent increases in the population prevalence of overweight or obesity, a literature search was undertaken. Results: Trends in overweight or obesity among adults showed considerable variability internationally. Some countries, including Canada, Finland (men), New Zealand, the United Kingdom, the United States, and Western Samoa showed large increases in prevalence (>5 percentage points), whereas several other countries showed smaller or no increases. Overweight is also increasing among children and adolescents, at least in some countries. It is not clear what the expected prevalence of overweight or obesity might be in the current environment, and these findings may be most usefully viewed as shifts in the distribution of a population characteristic. The reasons for these shifts are not clear. The health implications of these shifts are also not clear, in part because trends in cardiovascular risk factors do not always parallel trends in obesity. Of the classic epidemiologic triad of host, agent, and environment, the environment has often received the least attention. Conclusions: The economic, social, and cultural factors that influence the distribution of body mass index in a population are not well understood. Future research needs include continued monitoring of trends in obesity and in related health conditions and observational studies to examine the causes of these trends. Public health research should aim at defining realistic goals and strategies to improve health in an environment conducive to high levels of overweight and obesity.

Hyponatremia in ultradistance triathletes.

Abstract: Hyponatremia in ultradistance triathletes. Med. Sci. Sports Exerc., Vol. 31, No. 6, pp. 809-815, 1999.Purpose:Hyponatremia ([plasma sodium] <135 mmol·L−1) is a potentially serious complication of ultraendurance sports. However, the etiology of this condition is still uncertain. This observat

Effect of physical training on total and visceral fat in obese children.

Abstract: PURPOSE: Children with high levels of total body fat mass (TFM) and visceral adipose tissue (VAT) have elevated levels of certain risk factors for coronary artery disease and non-insulin-dependent diabetes mellitus. We tested the hypothesis that controlled physical training, without dietary intervention, would have a favorable impact on VAT and percent body fat (%BF) in obese children. METHODS: A volunteer sample of 74 obese children, 7-11 yr of age, accepted random assignment to physical training or control groups. Before and after 4 months of intervention, measurements were obtained for VAT, TFM, %BF, daily physical activity, and cardiovascular fitness. The intervention involved 4 months of controlled physical training 5 d x wk(-1), 40 min per session, at a mean heart rate (HR) of 157 beats x min(-1). The estimated energy expenditure (EE) per training session was 925+/-201 kJ. RESULTS: Compared with the control group, the physical training group declined significantly in %BF (delta = -2.2%) (P < 0.01), TFM (delta = -3.1%) (P < 0.01), and subcutaneous abdominal adipose tissue (delta = - 16.1%) (P < 0.05), and increased significantly in fat-free mass (delta = +6.1%) (P < 0.05) and moderate-to-very hard physical activity (delta = +14.1%) (P < 0.05). The increase in VAT was significantly less in the physical training group (delta = +0.5%) as compared with that in the control group (delta = +8.1%) (P < 0.05). CONCLUSIONS: This study showed that during physical training obese children: 1) were capable of participating in a substantial amount of high intensity physical training over a 4-month period: 2) accumulated significantly less VAT as compared with nonexercising controls; and 3) experienced other beneficial changes in total and regional body composition.

Comorbidities of overweight and obesity: current evidence and research issues

Abstract: Purpose: The evidence with regard to the relationship of obesity with medical comorbidities was assessed and priority research issues identified. Methods: The existing literature in English was surveyed. Results: The evidence is overwhelming on the association of obesity to a number of medical conditions. These include: insulin resistance, glucose intolerance, diabetes mellitus, hypertension, dyslipidemia, sleep apnea, arthritis, hyperuricemia, gall bladder disease, and certain types of cancer. The independent association of obesity seems also clearly established for coronary artery disease, heart failure, cardiac arrhythmia, stroke, and menstrual irregularities. The relationship between central (or upper body) obesity and the above conditions is positive for most of them but with a lesser number of studies. Most of the fat distribution studies have been done using anthropometric measurements rather than the more accurate magnetic resonance imaging or computer tomographic scans. Priority research issues include the following: more definitive data on the relation of central fat to comorbidities; the proportional importance of subcutaneous versus visceral fat in producing comorbidities; the relationship between obesity and psychiatric disease; the genetics of the relationship between obesity and each of the comorbidities; the independent contribution of diet and of sedentariness to the development of each of the comorbidities: the impact of gender, race, intensity, and duration on these associations. Conclusions: The evidence for the relationship of obesity to a number of comorbidities is strong, though the strength of the relationship varies with the condition. Much more research is necessary on causation and on what other factors may play an interactive role.

Knee joint kinematics during the sidestep cutting maneuver: potential for injury in women.

Abstract: There is a paucity of data describing female lower limb biomechanics during "high risk" movements linked to noncontact ACL injury. This study compared, across gender, knee kinematics associated with sidestepping maneuvers to provide insight into why women display a significantly higher incidence of this injury than do men.Thirty participants (16 men, 14 women) had bilateral knee joint kinematic data recorded while sidestepping. A custom software package (JTMOTION) quantified maximum, minimum, and range of motion during stance for each of the three clinical knee joint rotations (flexion/extension, adduction/abduction and external/internal rotation) over 20 (leg x condition x trial (5)) trials.Gender differences possessed limited clinical significance with all maximum values well within safe ranges of knee motion. Women did, however, display increased intertrial variability for axial rotation patterns during cutting compared with men. This variability was thought to be unaffected by gender, with experience level found statistically (P < 0.01) to be the major determinant of knee kinematic variability during sidestepping. Hence, the level of exposure to sidestep cutting may have a large impact on the subsequent risk of ACL injury when when one performs these maneuvers.Gender differences in knee motions during cutting did not contribute to the increased risk of noncontact ACL injury in women compared with men. The reasons for this increased incidence, therefore, remain unclear. The potential relationship between gender and other parameters linked to ACL injury such as joint geometry, ligament morphology, and physical conditioning requires further investigation.

Exercise and cellular innate immune function.

Abstract: Epidemiological evidence suggests a link between the intensity of exercise and infectious and neoplastic disease. One likely way by which exercise exerts its effect on cancer and infection is by altering the function of the immune system. Cells of the innate immune system (i.e., macrophage [Mphi], natural killer [NK] cell, and polymorphonuclear neutrophils [PMN]) are first-line defenders against cancer and infectious disease by nature of their phagocytic, cytolytic, and antimicrobial properties. The purpose of this review is to define the role of cells of the innate immune system (i.e., Mphi, PMN, and NK cells) in infection and cancer, present current information regarding the effects of acute and chronic exercise on the quantification and functional activities of these cells, and briefly to discuss potential mechanisms as to how exercise affects these cells and describe how these changes may potentially affect susceptibility to infection and cancer. The effects of exercise on the number, functions, and characteristics of cells of the innate immune system are complex and are dependent several factors, including 1) the cell function or characteristic being analyzed; 2) the intensity, duration and chronicity of exercise; 3) the timing of measurement in relation to the exercise bout; 4) the dose and type of immunomodulator used to stimulate the cell in vitro or in vivo; and 5) the site of cellular origin. Further studies are needed to determine whether the exercise-induced changes in immune function alter incidence or progression of disease. Likewise, the mechanisms as to how exercise alters innate immune function are as yet unresolved.

Effects of different interval-training programs on cycling time-trial performance.

Abstract: Effects of different interval-training programs on cycling time-trial performance. Med. Sci. Sports Exerc., Vol. 31, No. 5, pp. 736-741, 1999.Purpose:We have investigated the effect of varying the intensity of interval training on 40-km time-trial performance in 20 male endurance cyclists (p

Physical activity in the treatment of childhood overweight and obesity: current evidence and research issues.

Abstract: Purpose: This paper reviews the utility of exercise as a treatment for overweight and obese children and adolescents. Methods: Computer database searches identified 13 studies that met the following criteria for inclusion: 1) obese children or adolescents were provided either different types of exercise programs or an exercise program compared with a no-exercise control. 2) subjects were randomly assigned to groups or assigned by matching on demographic and anthropometric variables, and 3) the exercise program was at least 2 months in duration. Results: The only area in which there were a sufficient number of studies to make a quantitative analysis was the comparison of diet versus diet plus exercise programs, which suggested that exercise adds to the effect of diet in the short-term treatment of pediatric obesity. There was not enough research to evaluate the effects of exercise alone. The majority of findings indicate fitness changes are greater for subjects provided exercise alone or exercise combined with diet in comparison with subjects provided no exercise (control) or diet alone. Conclusions: Research on effects of exercise or physical activity in pediatric obesity treatments are encouraging and may be important for improving treatment outcome for obesity and comorbid conditions. Recommendations for future research are presented.

Ground reaction forces, bone characteristics, and tibial stress fracture in male runners.

Abstract: Ground reaction forces, bone characteristics, and tibial stress fracture in male runners. Med. Sci. Sports Exerc., Vol. 31, No. 8, pp. 1088-1093, 1999.Purpose:Tibial stress fracture is a common overuse running injury resulting from repetitive mechanical loading. This research project aimed t