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One recommendation resulting from the proceedings was for future research to describe the temporal relationship between motor development and physical activity Fulton et al. The assumption of this relationship is implied in multiple models of motor development Seefeldt, ; Clark and Metcalfe, ; Stodden et al. Two models that are commonly used to examine this relationship are Seefeldt's hierarchical order of motor skills development and the dynamic association model of Stodden and colleagues Seefeldt proposed a hierarchical order of motor skills development that includes four levels: reflexes, fundamental motor skills, transitional motor skills i.

With improved transitional motor skills, children are able to master complex motor skills e. At the end of this developmental period, children's vision is fully mature. The progression through each level occurs through developmental stages as a combined result of growth, maturation, and experience.

If children are able to achieve a level of competence above the proficiency barrier, they are more likely to continue to engage in physical activity throughout the life span that requires the use of fundamental motor skills. Conversely, less skilled children who do not exceed the proficiency barrier will be less likely to continue to engage in physical activity. For example, to engage successfully in a game of handball, baseball, cricket, or basketball at any age, it is important to reach a minimum level of competence in running, throwing, catching, and striking.

A thorough understanding of how this relationship changes across developmental stages is crucial for curriculum development and delivery and teaching practices. Lubans and colleagues recently examined the relationship between motor competence and health outcomes. They reviewed 21 studies identifying relationships between fundamental motor skills and self-worth, perceived physical competence, muscular and cardiorespiratory fitness, weight status, flexibility, physical activity, and sedentary behavior.

Overall, the studies found a positive association between fundamental motor skills and physical activity in children and adolescents, as well as a positive relationship between fundamental motor skills and cardiorespiratory fitness. Other research findings support the hypothesis that the most physically active preschool-age Fisher et al.

Rather, the hypothesis suggests that physical activity is influenced when a certain level of motor competence is not achieved and acknowledges that below the proficiency barrier, there is bound to be substantial variation in children's motor competence and participation in physical activity. The proficiency barrier is located between the fundamental and transitional motor skills periods. The transition between these two levels of motor competence is expected to occur between the early and middle childhood years.

Stodden and colleagues suggest that the relationship between motor competence and physical activity is dynamic and changes across time. The relationship between skills and physical activity is considered reciprocal. It is expected that as motor skills competence increases, physical activity participation also increases and that the increased participation feeds back into motor skills competence.

The reciprocal relationship between motor skills competence and physical activity is weak during the early childhood years ages because of a variety of factors, including environmental conditions, parental influences, and previous experience in physical education programs Stodden et al. Also, children at this age are less able to distinguish accurately between perceived physical competence and actual motor skills competence Harter and Pike, ; Goodway and Rudisill, ; Robinson and Goodway, ; Robinson, , and thus motor skills are not expected to strongly influence physical activity.

In older children, perceived competence is more closely related to actual motor skills competence. Older, low-skilled children are aware of their skills level and are more likely to perceive physical activity as difficult and challenging. Older children who are not equipped with the necessary skills to engage in physical activity that requires high levels of motor skills competence may not want to display their low competence publicly.

As children transition into adolescence and early adulthood, the relationship between motor skills competence and physical activity may strengthen Stodden et al. Investigators report moderate correlations between motor skills competence and physical activity in middle school—age children Reed et al. Okely and colleagues found that motor skills competence was significantly associated with participation in organized physical activity i.

A strength of the model of Stodden and colleagues is the inclusion of factors related to psychosocial health and development that may influence the relationship between motor skills competence and physical activity, contributing to the development and maintenance of obesity. Other studies have found that perceived competence plays a role in engagement in physical activity Ferrer-Caja and Weiss, ; Sollerhed et al.

Motor skills competence is an important factor; however, it is only one of many factors that contribute to physical activity. For instance, three studies have reported negative correlations between girls' motor competence and physical activity Reed et al. A possible explanation for these findings is that since girls tend to be less active than boys, it may be more difficult to detect differences in physical activity levels between high- and low-skilled girls.

It is also possible that out-of-school opportunities for physical activity are more likely to meet the interests of boys, which may at least partially explain sex differences in physical activity levels Le Masurier et al.

Previous research suggests that in general boys are more motor competent than girls Graf et al. One component of motor competence is the performance of gross motor skills, which are typically classified into object control and locomotor skills. Consistent evidence suggests that boys are more competent in object control skills, while girls are more competent in locomotor skills McKenzie et al. In light of these sex differences, it is important to examine the relationships of object control and locomotor skills with physical activity separately for boys and girls.

For boys, object control skills are more related to physical activity than are locomotor skills Hume et al. Three studies report a significant relationship between balance and physical activity for girls but not boys Reed et al. Cliff and colleagues suggest that object control and locomotor skills may be more related to boys' and girls' physical activity, respectively, because of the activity type in which each sex typically engages.

The relationship between motor competence and physical activity clearly is complex. It is quite likely that the relationship is dynamic and that motor competence increases the likelihood of participating in physical activity while at the same time engaging in physical activity provides opportunities to develop motor competence Stodden et al. Despite some uncertainty, the literature does reinforce the important role of physical education in providing developmentally appropriate movement opportunities in the school environment.

These opportunities are the only means of engaging a large population of children and youth and providing them with the tools and opportunities that foster health, development, and future physical activity. Regular physical activity has no established effect on linear growth rate or ultimate height Malina, Although some studies suggest small differences, factors other than physical activity, especially maturity, often are not well controlled.

It is important to note that regular physical activity does not have a negative effect on stature, as has sometimes been suggested. Differences in height among children and adolescents participating in various sports are more likely due to the requirements of the sport, selection criteria, and interindividual variation in biological maturity than the effects of participation per se Malina et al.

Similarly, physique, as represented in somatotypes, does not appear to be significantly affected by physical activity during growth Malina et al. In contrast, components of weight can be influenced by regular physical activity, especially when the mode and intensity of the activity are tailored to the desired outcome. Much of the available data in children and adolescents is based on BMI, a surrogate for composition, and indirect methods based on the two-compartment model of body composition in which body weight is divided into its fat-free and fat components Going et al.

While studies generally support that physical activity is associated with greater fat-free mass and lower body fat, distinguishing the effects of physical activity on fat-free mass from expected changes associated with growth and maturation is difficult, especially during adolescence, when both sexes have significant growth in fat-free mass.

The application of methods based on the two-compartment model is fraught with errors, especially when the goal is to detect changes in fat-free mass, and no information is available from these methods regarding changes in the major tissue components of fat-free mass—muscle and skeletal tissue. Skeletal muscle is the largest tissue mass in the body. It is the main energy-consuming tissue and provides the propulsive force for movement. Postnatal muscle growth is explained largely by increases in cell size hypertrophy driving an increase in overall muscle mass.

The increase in muscle mass with age is fairly linear from young childhood until puberty, with boys having a small but consistent advantage Malina, , The sex difference becomes magnified during and after puberty, driven primarily by gender-related differences in sex steroids.

Muscle, as a percentage of body mass, increases from about 42 percent to 54 percent in boys between ages 5 and 11, whereas in girls it increases from about 40 percent to 45 percent between ages 5 and 13 and thereafter declines Malina et al. It should be noted that absolute mass does not decline; rather, the relative decline reflects the increase in the percentage of weight that is fat in girls. At least part of the sex difference is due to differences in muscle development for different body regions Tanner et al.

The growth rate of arm muscle tissue during adolescence in males is approximately twice that in females, whereas the sex difference in the growth of muscle tissue in the leg is much smaller. The sex difference that develops during puberty persists into adulthood and is more apparent for the musculature of the upper extremities.

Sex-related differences in muscular development contribute to differences in physical performance. Muscle strength develops in proportion to the cross-sectional area of muscle, and growth curves for strength are essentially the same as those for muscle Malina and Roche, Thus the sex difference in muscle strength is explained largely by differences in skeletal muscle mass rather than muscle quality or composition.

Aerobic endurance exercise has little effect on enhancing muscle mass but does result in significant improvement in oxygen extraction and aerobic metabolism Fournier et al. In contrast, numerous studies have shown that high-intensity resistance exercise induces muscle hypertrophy, with associated increases in muscle strength. In children and adolescents, strength training can increase muscle strength, power, and endurance.

Multiple types of resistance training modalities have proven effective and safe Bernhardt et al. These adaptations are due to muscle fiber hypertrophy and neural adaptations, with muscle hypertrophy playing a more important role in adolescents, especially in males.

Prior to puberty, before the increase in anabolic sex steroid concentrations, neural adaptations explain much of the improvement in muscle function with exercise in both boys and girls. The skeleton is the permanent supportive framework of the body. It provides protection for vital organs and is the main mineral reservoir. Bone tissue constitutes most of the skeleton, accounting for percent of body weight across the life span Trotter and Peterson, ; Trotter and Hixon, Skeletal strength, which dictates fracture risk, is determined by both the material and structural properties of bone, both of which are dependent on mineral accrual.

The relative mineral content of bone does not differ much among infants, children, adolescents, and adults, making up percent of the dry, fat-free weight of the skeleton Malina, As a fraction of weight, bone mineral the ash weight of bone represents about 2 percent of body weight in infants and about percent of body weight in adults Malina, Bone mineral content increases fairly linearly with age, with no sex difference during childhood.

Girls have, on average, a slightly greater bone mineral content than boys in early adolescence, reflecting their earlier adolescent growth spurt. The increase in total body bone mineral is explained by both increases in skeletal length and width and a small increase in bone mineral density Malina et al. Many studies have shown a positive effect of physical activity on intermediate markers of bone health, such as bone mineral content and density. Active children and adolescents have greater bone mineral content and density than their less active peers, even after controlling for differences in height and muscle mass Wang et al.

Exercise interventions support the findings from observational studies showing beneficial effects on bone mineral content and density in exercise participants versus controls Petit et al. The relationship between greater bone mineral density and bone strength is unclear, as bone strength cannot be measured directly in humans. Thus, whether the effects of physical activity on bone mineral density translate into similar benefits for fracture risk is uncertain Karlsson, Animal studies have shown that loading causes small changes in bone mineral content and bone mineral density that result in large increases in bone strength, supporting the notion that physical activity probably affects the skeleton in a way that results in important gains in bone strength Umemura et al.

The relatively recent application of peripheral quantitative computed tomography for estimating bone strength in youth has also provided some results suggesting an increase in bone strength with greater than usual physical activity Sardinha et al. The intensity of exercise appears to be a key determinant of the osteogenic response Turner and Robling, Bone tissue, like other tissues, accommodates to usual daily activities.

Far fewer randomized controlled trials RCTs examining this relationship have been conducted in children than in adults, and there is little evidence on dose response to show how the type of exercise interacts with frequency, intensity, and duration. Taken together, however, the available evidence supports beneficial effects of physical activity in promoting bone development Bailey et al.

Physical activity may reduce osteoporosis-related fracture risk by increasing bone mineral accrual during development; by enhancing bone strength; and by reducing the risk of falls by improving muscle strength, flexibility, coordination, and balance Bloomfield et al.

Early puberty is a key developmental period. Approximately 26 percent of the mineral content in the adult skeleton is accrued during the 2 years around the time of peak height velocity Bailey et al. This amount of mineral accrual represents approximately the same amount of bone mineral that most people will lose in their entire adult lives Arlot et al. The increase in mineral contributes to increased bone strength.

Mineral is accrued on the periosteal surface of bone, such that the bone grows wider. Increased bone width, independent of the increased mineral mass, also contributes to greater bone strength. Indeed, an increase of as little as 1 mm in the outer surface of bone increases strength substantially. Adding bone to the endosteal surface also increases strength Parfitt, ; Wang et al.

Increases in testosterone may be a greater stimulus of periosteal expansion than estrogen since testosterone contributes to wider and stronger bones in males compared with females. RCTs on this issue are few, although the available data are promising McKay et al. Thus, impact exercise begun in childhood may result in lasting structural changes that may contribute to increased bone strength and decreased fracture risk later in life Turner and Robling, ; Ferrari et al. Adipocytes are distributed throughout the body in various organs and tissues, although they are largely clustered anatomically in structures called fat depots, which include a large number of adipocytes held together by a scaffold-like structure of collagen and other structural molecules.

In the traditional view of the adipocyte, the cell provides a storage structure for fatty acids in the form of triacylglycerol molecules, with fatty acids being released when metabolic fuel is needed Arner and Eckel, The role of adipocytes in regulation of energy balance and in carbohydrate and lipid metabolism and the potential effects of physical activity on adipocyte function are of particular interest here, given growing concerns related to pediatric and adult obesity Ogden et al.

Adipocytes increase in size hypertrophy and number hyperplasia from birth through childhood and adolescence and into young adulthood to accommodate energy storage needs. In total the adipose organ contains about 0. There is wide interindividual variation, however, and the difficulty of investigating changes in the number and size of adipocytes is obvious given the invasiveness of the required biopsy procedures; understandably, then, data on these topics are scarce in children and adolescents.

Also, since only subcutaneous depots are accessible, results must be extrapolated from a few sites. Based on such information, the average size of adipocytes has been reported to increase two- to threefold in the first year of life, with little increase in nonobese boys and girls until puberty Malina et al. A small increase in average adipocyte size at puberty is more obvious in girls than in boys.

There is considerable variation in size across various subcutaneous sites and between subcutaneous and internal depots. The number of adipocytes is difficult to estimate. Available data suggest that the cellularity of adipose tissue does not increase significantly in early postnatal life Malina et al. Thus, gain in fat mass is the result of an increase in the size of existing adipocytes. From about years of age and continuing through early and middle childhood, the number of adipocytes increases gradually two- to threefold.

With puberty the number practically doubles, followed by a plateau in late adolescence and early adulthood. The number of adipocytes is similar in boys and girls until puberty, when girls experience a greater increase than boys. The increases in the number of adipocytes during infancy and puberty are considered critical for enlargement of the adipose tissue organ and for the risk of obesity.

Since size and number are linked, the number of adipocytes can potentially increase at any age if fat storage mechanisms are stimulated by chronic energy surfeit Hager, ; Chumlea et al. Energy expenditure through regular physical activity is a critical element in preventing energy surfeit and excess adiposity. While cellularity undoubtedly is strongly genetically determined, regular physical activity, through its contribution to energy expenditure, can contribute to less adipocyte hyperplasia by limiting hypertrophy.

Fat distribution refers to the location of fat depots on the body. The metabolic activities of fat depots differ, and small variation can have a long-term impact on fat distribution. Differences in metabolic properties across depots also have clinical implications. Visceral adipose tissue in the abdominal cavity is more metabolically active reflected by free fatty acid flux than adipose tissue in other areas Arner and Eckel, , and higher amounts of visceral adipose tissue are associated with greater risk of metabolic complications, such as type 2 diabetes and cardiovascular disease Daniels et al.

In contrast, subcutaneous fat, particularly in the gluteofemoral region, is generally associated with a lower risk of cardiometabolic disease. Age- and sex-associated variations in fat distribution contribute to age- and sex-associated differences in cardiometabolic disease prevalence.

Girls have more subcutaneous fat than boys at all ages, although relative fat distribution is similar. After a rapid rise in subcutaneous fat in the first few months of life, both sexes experience a reduction through age 6 or 7 Malina and Roche, ; Malina and Bouchard, ; Malina, Girls then show a linear increase in subcutaneous fat, whereas boys show a small increase between ages 7 and 12 or 13 and then an overall reduction during puberty.

The thickness of subcutaneous fat on the trunk is approximately one-half that of subcutaneous fat on the extremities in both boys and girls during childhood. The ratio increases with age in males during adolescence but changes only slightly in girls. In males the increasing ratio of trunk to extremity subcutaneous fat is a consequence of slowly increasing trunk subcutaneous fat and a decrease in subcutaneous fat on the extremities.

In girls, trunk and extremity subcutaneous fat increase at a similar rate; thus the ratio is stable Malina and Bouchard, As a consequence, the sex difference in the distribution of body fat develops during adolescence. It is important to note that changes in subcutaneous fat pattern do not necessarily represent changes in abdominal visceral adipose tissue.

Tracking of subcutaneous fat has been investigated based on skinfold thicknesses and radiographs of fat widths in males and females across a broad age range Katzmarzyk et al. Results indicate that subcutaneous fat is labile during early childhood. After age 7 to 8, correlations between subcutaneous fat in later childhood and adolescence and adult subcutaneous fat are significant and moderate.

Longitudinal data on tracking of visceral adipose tissue are not available, but percent body fat does appear to track. Thus children and especially adolescents with higher levels of body fat have a higher risk of being overfat at subsequent examinations and in adulthood, although variation is considerable, with some individuals moving away from high fatness categories, while some lean children move into higher fatness categories.

In cross-sectional studies, active children and adolescents tend to have lower skinfold thicknesses and less overall body fat than their less active peers Loftin et al. Longitudinal studies indicate small differences in fatness between active and inactive boys and girls. Although some school-based studies of the effects of physical activity on body composition have reported changes in BMI or skinfolds in the desired direction Gortmaker et al.

High levels of physical activity are most likely needed to modify skinfold thicknesses and percent body fat. In adults, visceral adipose tissue declines with weight loss with exercise. In contrast, in a study of obese children aged , a 4-month physical activity program resulted in minimal change in abdominal visceral adipose tissue but a significant loss in abdominal subcutaneous adipose tissue Gutin and Owens, In adults, decreases in fatness with exercise are due to a reduction in fat cell size, not number You et al.

Given that adipocyte hypertrophy may trigger adipocyte hyperplasia Ballor et al. Regular physical activity also affects adipose tissue metabolism so that trained individuals have an increased ability to mobilize and oxidize fat, which is associated with increased levels of lipolysis, an increased respiratory quotient, and a lower risk of obesity Depres and Lamarche, The ability to perform sustained activity under predominantly aerobic conditions depends on the capacity of the cardiovascular and pulmonary systems to deliver oxygenated blood to tissues and on the ability of tissues primarily skeletal muscle to extract oxygen and oxidize substrate.

By age 2 the systems are fully functional, although young children lack the cardiorespiratory capacity of older children and adults because of their small size Malina et al. Children's aerobic capacity and consequently their ability to exercise for longer periods of time increase as they grow.

Maximal aerobic power liters per minute increases fairly linearly in boys until about age 16, whereas it increases in girls until about age 13 and then plateaus during adolescence Malina et al. Changes with age and sex differences are explained largely by differences in the size of the relevant tissues.

Dimensions of the heart and lungs enlarge with age in a manner consistent with the increase in body mass and stature Malina et al. The increase in the size of the heart is associated with increases in stroke volume blood pumped per beat and cardiac output product of stroke volume and heart rate, liters per minute , despite a decline in heart rate during growth. Similarly, increase in lung size proportional to growth in height results in greater lung volume and ventilation despite an age-associated decline in breathing frequency.

The general pattern of increase as a function of height is similar in boys and girls. In both, lung function tends to lag behind the increase in height during the adolescent growth spurt. As a result, peak gains in lung function occur about 2 years earlier in girls than in boys.

Blood volume is highly related to body mass and heart size in children and adolescents, and it is also well correlated with maximal oxygen uptake during childhood and adolescence Malina et al. Blood volume increases from birth through adolescence, following the general pattern for changes in body mass. Both red blood cells and hemoglobin have a central role in transport of oxygen to tissues.

Hematocrit, the percentage of blood volume explained by blood cells, increases progressively throughout childhood and adolescence in boys, but only through childhood in girls. Hemoglobin content, which is related to maximal oxygen uptake, heart volume, and body mass, increases progressively with age into late adolescence.

Males have greater hemoglobin concentrations than females, especially relative to blood volume, which has functional implications for oxygen transport during intense exercise. Growth in maximal aerobic power is influenced by growth in body size, so controlling for changes in body size during growth is essential. Although absolute liters per minute aerobic power increases into adolescence relative to body weight, there is a slight decline in both boys and girls, suggesting that body weight increases at a faster rate than maximal oxygen consumption, particularly during and after the adolescent growth spurt Malina et al.

Changes in maximal oxygen consumption during growth tend to be related more closely to fat-free mass than to body mass. Nevertheless, sex differences in maximal oxygen consumption per unit fat-free mass persist, and maximal oxygen consumption per unit fat-free mass declines with age. Improvements in cardiorespiratory function—involving structural and functional adaptations in the lungs, heart, blood, and vascular system, as well as the oxidative capacity of skeletal muscle—occur with regular vigorous- and moderate-intensity physical activity Malina et al.

Concern about the application of invasive techniques limits the available data on adaptations in the oxygen transport system in children. Nevertheless, it is clear that aerobic capacity in youth increases with activity of sufficient intensity and that maximal stroke volume, blood volume, and oxidative enzymes improve after exercise training Rowland, Training-induced changes in other components of the oxygen transport system remain to be determined.

Physical fitness is a state of being that reflects a person's ability to perform specific exercises or functions and is related to present and future health outcomes. Historically, efforts to assess the physical fitness of youth focused on measures designed to evaluate the ability to carry out certain physical tasks or activities, often related to athletic performance. In more recent years, the focus has shifted to greater emphasis on evaluating health-related fitness IOM, a and assessing concurrent or future health status.

Health- and performance-related fitness, while overlapping, are different constructs. Age- and sex-related changes in the components of both are strongly linked to the developmental changes in tissues and systems that occur during childhood and adolescence. Although genetic factors ultimately limit capacity, environmental and behavioral factors, including physical activity, interact with genes to determine the degree to which an individual's full capacity is achieved. Cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition are components of health-related fitness historically assessed in school-based fitness assessment programs IOM, a.

These components of health-related fitness are considered important since they can be linked to the risk of cardiometabolic disease and musculoskeletal disability, chronic hypokinetic-related diseases. Cardiorespiratory aerobic endurance reflects the functioning of the pulmonary and cardiovascular systems to deliver oxygen and the ability of tissues primarily skeletal muscle to extract oxygen from the blood. Defined clinically as the maximum oxygen consumption during a maximal graded exercise test, in practice it is usually measured indirectly as performance on a field test of endurance, such as 1- or 2-mile run time IOM, a.

During childhood, aerobic capacity approximately doubles in both boys and girls, although girls on average possess a lower capacity. Males continue to improve during adolescence, up to ages , while aerobic capacity plateaus around age 14 in females Malina et al.

Favorable associations have been found between aerobic endurance and high-density lipoproteins, systolic blood pressure, diastolic blood pressure, BMI, measures of fatness, arterial stiffness, and measures of insulin sensitivity Boreham et al. Some evidence suggests a decline in aerobic endurance among U.

Aerobic exercise has been shown to increase cardiorespiratory endurance by about percent in youth Malina et al. The programs that produce this benefit involve continuous vigorous- or moderate-intensity aerobic activity of various types for minutes per session at least 3 days per week over a period of at least months Baquet et al. Muscle strength is defined as the highest force generated during a single maximum voluntary contraction, whereas muscle endurance is the ability to perform repeated muscular contraction and force development over a period of time.

Muscle strength and endurance are correlated, especially at higher levels of force production. Muscle strength is proportional to the cross-sectional area of skeletal muscle; consequently, strength growth curves parallel growth curves for body weight and skeletal muscle mass Malina et al.

Both males and females show impressive increases in muscle strength from childhood to adolescence. Strength in children increases linearly, with boys having a slight advantage over girls. However, these sex differences are magnified during the adolescent years as a result of maturation Malina and Roche, Differences in muscle strength between boys and girls become more apparent after puberty, primarily as a result of the production of sex steroid hormones.

In boys the increase in strength during adolescence lags behind the growth spurt by at least a year peak height velocity , which may explain why some boys experience a brief period of clumsiness or awkwardness during puberty, as they have not yet acquired the muscle strength necessary to handle the changes associated with their larger bodies. Muscle strength increases at its greatest rate approximately 1 year after peak height velocity in boys, whereas for girls the strength spurt generally occurs during the same year as peak height velocity Bar-Or, A compelling body of evidence indicates that with resistance training children and adolescents can significantly increase their strength above that expected as a result of normal growth and maturation, provided that the training program is of sufficient intensity, volume, and duration Committee on Sports Medicine Fitness, Both boys and girls can benefit, and strength gains in children as young as have been reported Faigenbaum et al.

Gains in muscle strength of about 30 percent are typical, although considerably larger gains have been reported. Adolescents make greater gains than preadolescents in absolute strength, whereas reported relative percent above initial strength gains in strength during preadolescence and adolescence are similar. As in adults, training adaptations in youth are specific to the muscle action or muscle groups that are trained, and gains are transient if training is not maintained Faigenbaum et al.

Youth resistance training, as with most physical activities, does carry some degree of risk of musculoskeletal injury, yet the risk is no greater than that associated with other sports and activities in which children and adolescents participate Council on Sports Medicine Fitness, ; Faigenbaum et al. A traditional area of concern has been the potential for training-induced damage to growth cartilage, which could result in growth disturbances. However, a recent review found no reports of injury to growth cartilage in any prospective study of resistance training in youth and no evidence to suggest that resistance training negatively impacts growth and maturation during childhood and adolescence Faigenbaum et al.

Injuries typically occur in unsupervised settings and when inappropriate loads and progressions are imposed. In addition to the obvious goal of gaining strength, resistance training may be undertaken to improve sports performance and prevent injuries, rehabilitate injuries, and enhance health. Appropriately supervised programs emphasizing strengthening of trunk muscles in children theoretically benefit sport-specific skill acquisition and postural control, although these benefits are difficult to study and thus are supported by little empirical evidence Council on Sports Medicine Fitness, Similarly, results are inconsistent regarding the translation of increased strength to enhanced athletic performance in youth.

Limited evidence suggests that strength-training programs that address common overuse injuries may help reduce injuries in adolescents, but whether the same is true in preadolescents is unclear Council on Sports Medicine Fitness, Increasing evidence suggests that strength training, like other forms of physical activity, has a beneficial effect on measurable health indices in youth, such as cardiovascular fitness, body composition, blood lipid profiles and insulin sensitivity Faigenbaum, ; Benson et al.

Some work has shown that muscle fitness, reflected in a composite index combining measures of muscle strength and endurance, and cardiorespiratory fitness are independently and negatively associated with clustered metabolic risk Steene-Johannessen et al. Moreover, children with low muscle strength may be at increased risk of fracture with exercise Clark et al. Finally, muscle hypertrophy, which adds to fat-free mass, contributes to resting metabolic rate and therefore total daily energy expenditure.

Resistance training may be particularly useful for raising metabolic rate in overweight and obese children without the risk associated with higher-impact activities Watts et al. At all ages, girls demonstrate greater flexibility than boys, and the difference is greatest during the adolescent growth spurt and sexual maturation.

Perhaps the most common field measure of flexibility in children and youth is the sit-and-reach test IOM, b of low-back flexibility. Low-back flexibility as measured by this test is stable in girls from age 5 to 11 and increases until late adolescence. In boys, low-back flexibility declines linearly starting at age 5, reaching its nadir at about age 12, and then increases into late adolescence.

The unique pattern of age- and sex-associated variation is related to the growth of the lower extremities and the trunk during adolescence. In boys the nadir in low-back flexibility coincides with the adolescent growth spurt in leg length.

In both boys and girls, the increase during adolescence coincides with the growth spurt in trunk length and arm length, which influences reach. Flexibility in both males and females tends to decline after age 17, in part as a result of a decline in physical activity and normal aging. The principal health outcomes hypothesized to be associated with flexibility are prevention of and relief from low-back pain, prevention of musculoskeletal injury, and improved posture. These associations have been studied in adults, with equivocal results Plowman, Although flexibility has long been included in national youth fitness tests, it has proven difficult to establish a link between flexibility and health IOM, a.

In contrast to other fitness components that are general or systemic in nature, flexibility is highly specific to each joint of the body. Although appropriate stretching may increase flexibility, establishing a link to improved functional capacity and fitness is difficult. A few studies suggest that improvements in flexibility as measured by the sit-and-reach test may be related to less low-back pain Jones et al.

Consequently, the Institute of Medicine IOM Committee on Fitness Measures and Health Outcomes in its recent report elected to forego recommending a flexibility test for a national youth fitness test battery pending further research to confirm the relationship between flexibility and health and to develop national normative data IOM, a. Body composition is the component of health-related fitness that relates to the relative amount of adipose tissue, muscle, bone, and other vital components e.

Most feasible methods for assessing body composition are based on models that divide the body into fat and fat-free all nonfat constituents components Going et al. Although fat mass and adipose tissue are not equivalent components, fat mass is easier to estimate than adipose tissue, and it is correlated with performance and disease risk.

In settings in which estimation of body fat is difficult, weight-for-height ratios often are used as surrogates for body composition. Indeed, definitions of pediatric overweight and obesity have been based on BMI, calculated as weight in kilograms divided by height squared.

Child and adolescent obesity defined by BMI remains at all-time highs. Population surveys indicate that approximately 33 percent of all boys and girls are overweight, and nearly one in five are obese Ogden and Flegal, The tendency for excess fatness to persist from childhood and adolescence into adulthood Daniels et al.

The increase in prevalence of obesity is undoubtedly due to a mismatch between energy intake and expenditure. Population surveys have shown that few children and youth meet recommended levels of daily physical activity see Chapter 2. Prospective studies have shown a significant and inverse relationship between habitual physical activity and weight gain Berkey et al. These relationships are better established in adults than in children and youth, although even in preschool children, low levels of physical activity, estimated from doubly labeled water, were found to be indicative of higher body fat content Davies et al.

While studies of exercise without caloric restriction generally show only small effects on body weight, significant albeit moderate reductions of body fat are generally reported Eisenmann, Moreover, even in the absence of significant weight loss, exercise has beneficial effects on risk factors for cardiometabolic disease Ross and Bradshaw, ; Gutin and Owens, Changes in weight for height with growth and maturation for U. Current growth curves were derived from U. In boys and girls, BMI declines during early childhood, reaching its nadir at about ages , and then increases through adolescence.

A gender difference emerges during puberty, with males gaining greater fat-free mass than females. Physical activity and BMI are inversely correlated in children and adolescents, although the correlations are modest Lohman et al. Indeed, when studied separately, fat mass index FMI, or fat mass divided by height squared and fat-free mass index FFMI, or fat-free mass divided by height squared are both inversely related to physical activity.

With FMI controlled, however, FFMI is positively related to physical activity, indicating that, for a given level of body fat, individuals with more fat-free mass are more active Lohman et al. BMI cut-points for defining overweight and obesity have historically been based on age- and gender-specific population distributions of BMI. Recent work has shown good correspondence between BMI standards and percent fat standards that are referenced to health criteria Laurson et al. These new standards should prove useful for identifying children and adolescents at risk for higher levels of cardiometabolic risk factors.

Direct measures of body fat as a percent of weight provide a better index of adiposity and health risk than BMI Zeng et al. Recently, percent fat growth curves were established for representative samples of U. Median percent fat for boys aged ranged from 14 to 19 percent and for girls across the same ages 15 to 28 percent. In both boys and girls, percent fat increases slowly during early childhood, with girls having a consistently greater relative fatness than boys after ages In girls, percent fat increases gradually throughout adolescence in the same manner as fat mass.

In boys, percent fat increases gradually until the adolescent growth spurt and thereafter gradually declines until about age , reflecting the rapid growth in fat-free mass relative to fat mass. After age 17, percent fat in males gradually increases again into adulthood. The increased prevalence of child and adolescent obesity as defined by BMI presumably also reflects increased adiposity, although the degree is not certain as population-based estimates of percent fat have only recently been developed Laurson et al.

Health-related percent fat standards recently were developed by determining levels of body fat associated with greater occurrence of chronic disease risk factors defined by metabolic syndrome Going et al. In boys and girls aged , body fat above percent and above percent, respectively, was predictive of metabolic syndrome.

Physical activity is inversely correlated with percent body fat Rowlands et al. In youth, as in adults, the effects of exercise without caloric restriction are modest and are influenced by the initial level of body fat and the duration and regimen of exercise Going, Experimental studies have documented reductions in percent body fat with aerobic exercise, especially in children and adolescents who are overweight or obese at the initiation of an exercise program Davis et al.

Regular physical activity also affects adipose tissue metabolism Gutin and Owens, Individuals who engage in aerobic endurance exercise training have an increased ability to mobilize and oxidize fat, which is associated with increased levels of lipolysis Depres and Lamarche, Similar information on adipose tissue metabolism in children and youth is lacking, although one can reasonably expect similar adaptations in older adolescents.

The tendency for risk factors for cardiometabolic disease to cluster, now called metabolic syndrome, is well recognized in adults Alberti and Zimmet, Similar clustering occurs in older children and especially adolescents Cook et al. There is as yet no accepted definition of metabolic syndrome for use in pediatric populations Jolliffe and Janssen, Typically, adult definitions are extrapolated to children and adolescents, with appropriate adjustments of the thresholds for the defining variables.

Perhaps the most common approach is to emulate the National Cholesterol Education Program NCEP , which defines metabolic syndrome as exceeding thresholds on three of five components: waist circumference, blood pressure systolic or diastolic , blood lipids high-density lipoprotein [HDL] and triglycerides , and blood glucose levels NIH, The concept of metabolic syndrome is useful as it provides an integrated index of risk, and it recently was used to derive health-related percent-body-fat standards Laurson et al.

Based on NHANES data, the prevalence of metabolic syndrome varies with the degree of obesity, and it is estimated at percent of children and adolescents Cook et al. Youth with metabolic syndrome have an increased risk of type 2 diabetes and cardiovascular disease. In adults a loss of percent of body weight through calorie restriction and exercise has been shown to reduce the risk of cardiometabolic disease by improving risk factors Diabetes Prevention Program Research Group, ; Ross and Janiszewski, In particular, weight loss results in reduced visceral adipose tissue, a strong correlate of risk Knowler et al.

Even without significant weight loss, exercise can have significant effects in adults by improving glucose metabolism, improving lipid and lipoprotein profiles, and lowering blood pressure, particularly for those who are significantly overweight Ross and Bradshaw, Similar benefits have been observed in adolescents. A growing body of literature addresses the associations of physical activity, physical fitness, and body fatness with the risk of metabolic syndrome and its components in children and especially adolescents Platat et al.

Studies in adults have shown that higher levels of physical activity predict slower progression toward metabolic syndrome in apparently healthy men and women Laaksonen et al. Few population studies have focused on these relationships in children and adolescents, and the use of self-reported activity, which is imprecise in these populations, tends to obscure associations. In a large sample of U. Moreover, for each component of metabolic syndrome, prevalence was generally lower with higher physical activity levels, and adolescents with low physical activity levels had the highest rates of all metabolic syndrome components.

Mean clustered risk score decreased across increasing fifths quintiles of cardiorespiratory fitness in both males and females. The most significant decline in risk score was observed from the first lowest to the second quintile Other studies, using the approach of cross-tabulating subjects into distinct fitness and fatness categories, have examined associations of fitness and fatness with metabolic syndrome risk Eisenmann et al.

Although different measures of fitness, fatness, and metabolic syndrome risk were used, the results taken together across a wide age range 7—18 show that fitness modifies the influence of fatness on metabolic syndrome risk. That many adult chronic health conditions have their origins in childhood and adolescence is well supported Kannel and Dawber, ; Lauer et al.

Both biological e. Coexistence of cardiometabolic risk factors, even at young ages Dubose et al. Landmark studies from the Bogalusa Heart Study Berenson et al. The benefits of exercise for prevention and treatment of cardiometabolic disease in adults are well described Ross et al. Prospective studies examining the effects of exercise on metabolic syndrome in children and adolescents remain limited, and it is important to refrain from extrapolating intervention effects observed in adults to youth, although one might reasonably assume the benefits in older adolescents to be similar to those in young adults.

Indeed, based on the inverse associations of physical activity and physical fitness with metabolic syndrome Kim and Lee, and on the available intervention studies, some experts have recommended physical activity as the main therapeutic tool for prevention and treatment of metabolic syndrome in childhood Brambilla et al.

Comparative studies in adults have shown that the effect of exercise on weight is limited and generally less than that of calorie restriction Brambilla et al. Moreover, the relative effectiveness of diet and exercise depends on the degree of excess fatness Brambilla et al. Comparative studies in children and youth are few, as behavioral interventions in overweight children and adolescents commonly combine exercise and dietary restriction, making it difficult to disentangle their independent effects.

Nonetheless, diet and exercise have different effects on body composition: While both contribute to fat loss, only exercise increases muscle mass and thus has a direct effect on metabolic health. Exercise also may have important benefits even without significant modification of body composition Bell et al.

Experimental studies in overweight and obese youth have shown that exercise leads to reductions in visceral fat Owens et al. Results from experimental studies of the effects of exercise on lipids and lipoproteins Stoedefalke et al.

Bradshaw finds him on the shower floor when she gets home, but it's too late—Big dies in her arms. Big lived what many would call an extravagant lifestyle — including cocktails, cigars, and big steaks — and was at serious risk as he had a previous cardiac event in Season 6," she said Dr. Steinbaum is referring to an incident in which Big had surgery to open a blocked artery, the Wall Street Journal reports.

Riding his Peloton Bike may have even helped delay his cardiac event. But that wasn't it. The company shared a commercial on Sunday, showing Big alive and well—seemingly having faked his own death. The two agree to "take another ride" as in, another Peloton class before a voiceover comes in: "And just like that, the world was reminded that regular cycling stimulates and improves your heart, lungs, and circulation, reducing your risk of cardiovascular diseases. Cycling strengthens your heart muscles, lowers resting pulse, and reduced blood fat levels.

He's alive. The initial scene, though, was upsetting—not just for Carrie and Big supporters, but for anyone who has heart disease , or knows someone who has. But before you decide to swear off your cardio routine, for fear of exacerbating a previously-diagnosed heart issue, it's important to look at the facts surrounding exercise particularly cardiovascular exercise and heart health. First and foremost: Cardiovascular exercise is a major part of maintaining heart health—even and sometimes especially if you've dealt with issues in the past.

Overall, the American Heart Association AHA recommends all adults get at least minutes of moderate-intensity aerobic activity per week, or 75 minutes of vigorous aerobic activity. You can "gain even more benefits" by simply being active for at least minutes per week. There are loads of reasons why cardiovascular exercise specifically is good for you: It can lower your blood pressure and cholesterol levels, help control blood sugar, and prevent diabetes—all of which can protect you against heart disease, Sadiya Khan , MD, assistant professor of cardiology and epidemiology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician, tells Health.

Even if you've already been diagnosed with heart disease or had a previous cardiac event, your doctor will still probably recommend that you exercise on a regular basis. According to the National Library of Medicine MedlinePlus , exercise can make your heart muscle stronger if you have heart disease, and it can help you be more active without chest pain or other symptoms.

That said, you shouldn't jump right into a new workout routine after a cardiac event or diagnosis without first consulting your health care provider—you'll want to get the OK from them to make sure the exercise you'd like to do is safe for you. MedlinePlus says that's especially important if you have recently had a heart attack; have been having chest pain or pressure, or shortness of breath ; have diabetes, or if you've recently had a heart procedure or surgery.

Once you've gotten the OK from your doctor to start an exercise, program, there are additional steps you can take to make sure you're keeping your heart safe while making it healthy. The first major tip? Start slowly. Making sure you take time to warm up and cool down after a workout is important too—five minutes is a good amount of time to aim for. And you'll also want to take enough rest periods with water!

You can write off a character but not the value of cardio apple macbook pro srbija

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You can write off a character but not the value of cardio You can further improve its accuracy by using these tips. The mastery of fundamental motor skills is strongly related to physical activity in children and adolescents Lubans et al. When you have considered these heart sound variations, move on to consider the gaps between the heart sounds. In contrast, components of weight can be influenced by regular physical activity, especially when the mode and intensity of the activity are tailored to the desired outcome. This tendency to avoid or resist social interactions can make it challenging to find a sense of belonging and shared interests with others, as well as cause type D individuals increased distress when faced with group tasks or projects that require them to collaborate with others. For example, while walking your pet, let the arm with your watch swing freely while the other holds the leash. Block, MD.
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You can write off a character but not the value of cardio heath hunter

How To STOP Cardio From Killing Your Gains (3 WORST Mistakes You’re Making)

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