The discussion in chapter 3 on growth and matu¬ration demonstrated that children are not smaller versions of adults. This concept translates into children exercising differently than adults do. The body makes two major adjustments during aero¬bic exercise (prolonged, rhythmic exercise like jogging, running, or cycling). First, muscles do their work during exercise by using fuel (food) and oxygen. The more intense the work, the more oxy¬gen and fuel used. The oxygen is used very rap¬idly, so the blood must deliver more oxygen (and fuel, too, but this is not a major issue at most lev¬els and durations of exercise) as work continues or increases. This means the lungs and heart must work harder. As a general rule, respiration and heart rate increase with the intensity of the exer¬cise. At some point, the circulatory system can no longer keep up in delivering oxygen and remov¬ing waste. Fatigue sets in quickly at that point, and work must be stopped or substantially reduced.
The second effect of exercise is production of heat. The body dissipates some heat by breath¬ing but most of it by sweating: The circulatory system increases blood flow to the skin, and the heat is lost by radiation and evaporation of sweat. Teachers need to be conscious of this process, particularly during hot and dry weather, when excessive sweating and evaporation may produce a loss in total body fluid. This can result in dehydra¬tion. Fluid lost should be replaced by regular water intake during heavy exercise In hot and dry weather. People of all ages are susceptible to dehydration. Children should always be permitted to drink as much water as they want to during and after exer¬cise. Water is as good a fluid replacement as any of the advertised commercial products. The USDA warns that children do not drink enough water and should be encouraged to drink water regardless of whether they are exercising, so encouraging children to drink water meets the demands of exercise and a more general nutritional need.
Children and adults handle heat and oxygen pro¬duction differently during exercise and physical activity. Children have higher resting heart rates than adults; this means that at rest children's hearts are working harder than adult's hearts. For example, a 6-year-old boy has a resting heart rate of 86 beats per minute (a girl's at the same age would be 88); by age 13, his resting heart rate would be 66 (hers would be 70). The maximum heart rate for a 6-year¬old is 215, as compared with 201 for a 13-year-old. The easiest way to estimate heart rate is to gently touch your fingers to the carotid artery and count the beats for 10 seconds, then multiply by 6. The carotid artery can be located by placing the fingers next to the Adam's apple (figure 6.2).
Blood pressure increases steadily during child¬hood and adolescence. Systolic pressure, the maximum pressure immediately after a heart beat, increases from 108 to 115 millimeters Hg during childhood and adolescence in boys, and in girls from 101 to 111 millimeters Hg (Hg is the symbol for the element mercury as read on the gauge). Diastolic pressure, the minimum pressure just before a heart beat, goes from 72 to 82 millime¬ters Hg in boys and 65 to 75 millimeters Hg in girls.
Respiration volume increases directly in relation to the intensity of exercise, but only about 50 to 60 percent of maximum aerobic power or maximum oxygen uptake (VO2max). Maximum aerobic power, maximum oxygen uptake, and VO2max are terms used to describe the upper limit of the cardio respiratory system in its ability to deliver oxygen to the body during exercise. At this point, respira¬tion increases very rapidly. The change from steady to rapid increase in respiration has been called the anaerobic threshold. The anaerobic threshold is the point at which the body can no longer keep up with the oxygen demands or the waste build-up in the muscles. The muscles are working without adequate oxygen, and in this state fatigue sets in very rapidly. Respiration response is the same for girls and boys. As children exer¬cise, respiration rate can provide information about level of fatigue. For example, a child who can talk easily while jogging is probably breath¬ing steadily; when respiration interferes with talk¬ing, the child is moving toward fatigue.
Anaerobic power, the ability to work without oxygen, is also lower in children than adults. This is because children have less of an important en¬zyme (phosophofructokinase or PFK) in their muscles; this enzyme allows the muscles to work without oxygen. Children will produce more PFK after puberty. Anaerobic power is important in activities such as sprinting.
Children also have a lower hemoglobin concen¬tration in the blood than adults. Since hemoglo¬bin is the part of blood that carries oxygen to the working muscles (e.g., in the heart and legs), chil¬dren transport less oxygen per unit of blood than adults. This means that children can do less work than adults. Hemoglobin content in the blood in¬creases at puberty; however, the increase is not as great in women as it is in men.
Children become more fit as a result of fitness training. The responses to training tend to be lower in children for several reasons:
- Children tend to be more fit at the onset, so training results in less improvement.
- Children have higher resting and maximum heart rates, which limits the intensity of train¬ing (.7 x maximum heart rate = training heart rate).
- Children have less hemoglobin, which limits maximal oxygen uptake.
Exercise training produces three benefits for children and adults. First, hearts become stronger as a result of training as stroke volume (the amount of blood the heart can pump in one beat) increases. Second, more capillaries develop as a result of training, which provides a better supply of blood to the heart and working muscles. Third, better extraction of oxygen from the blood leads to improved enzymatic reactions. Recall that in order to benefit from training, children must ex¬ercise 3 days per week for at least 20 minutes per day for 10 or more weeks at the training heart rate. Training or target heart rates for various age groups are presented in table 6.2.
The relationship between the type of cardiovas¬cular (aerobic fitness exercise) used for training and the type of testing used is critical. A child who has trained regularly as a swimmer will have trained cardiovascular endurance, but if that child is tested using the mile run, the benefits may not show up in the test results. There are two reasons for this: First, the muscles used- for swimming (arms) and running (legs) are different, so muscle endurance may be low in the legs and detract from the child's performance. Second, the knowledge of how to pace for the mile run is critical and learned through practice. Failure to pace carefully is one reason many children do poorly on the mile run test. You may remember a classmate running full speed for the first part of the mile run, then stopping or at least slowing considerably for the rest of tile mile. The object of pacing in the mile run is to maintain a relatively constant speed with enough energy remaining to run faster at the end. Practice creates immediate improvements in test scores, which are not related to improved fitness.
Aerobic fitness tests fall into two categories: norm referenced and criterion referenced. Norm¬ referenced tests are based on the normal (bell¬ shaped) curve and compare one person to the group. Criterion-referenced tests use a standard and generally place people into two groups (pass and fail, or master and non master). Early fitness tests were norm referenced and used the levels of the best 5 to 15 percent as criteria for an award. Recent tests tend to be criterion referenced, with the criterion selected based on predicting health risk. The concept is that a student who is 10 years old and can run the mile in 9 minutes and 48 sec¬onds or less will have less health risk than a stu¬dent who runs the mile in 9 minutes and 49 sec¬onds or more. Unfortunately, the various tests use different standards for passing (Morrow, Jackson, Disch, and Mood 2000). For example, a 9-year-old boy would have to run the mile at different speeds to pass the various tests: FITNESSGRAM (12 min), Physical Best (10:30 min), President's National (8:31 min), and Presidential Tests (<10 min), re¬spectively. This is confusing and leads to contro¬versy about the level of fitness of youth in our country (Blair 1992). Further, there are gender dif¬ferences at each age for all tests, beginning at G years of age. The times for girls are 48 seconds or more greater (meaning that girls run more slowly and still pass) than boys at each age for each test (Wilkinson,Williamson, and Rozsdilsky 1996).
Careful consideration needs to be given to test selection, use, and interpretation. If we maintain separate, lower standards, the message we send to girls as young as G is this: Is girls' health less important than boys' health? Is there a biological reason to expect girls to perform more poorly when compared with boys? The answer to these questions is no. Prior to puberty, boys and girls are similar in ability, and their performance should be similar as should our expectations. The pass¬ing rates on the four tests are very different: FfTNESSGf2AM (84%), Physical Best (51 or 52%,), President's National (G3 or G5%), and Presidential Tests (21%), respectively (the passing percentage for boys is presented first; the passing percent¬age for girls is shown second, where there are dif¬ferences). By selecting the test, a teacher can ma¬nipulate the passing rate for all children. If we want to demonstrate that most of our students are fit, we should use the FITNESSGRAM. However, if we want to demonstrate a need for fitness, we should use the Presidential Test. Interpreting test results for students, parents, and administration must be done in terms of the test characteristics and the purpose of testing. Often, it is best on any test to compare scores for a particular child rather than to compare scores between children or to test cri¬teria alone. In this way, maintenance or improve¬ment, rather than awards and comparisons to highly variable standards, will be the focus of the discussion.
We must take care in the use of fitness training and testing, since there is no evidence that being fit or training for fitness actually "carries over" to adult physical activity. Tracking is a term used to describe whether a behavior or characteristic re¬mains constant across time. Unfortunately, no re¬lationship has been demonstrated between physi¬cal fitness as a child and adult fitness or activity (Bouchard, Shepard, and Stephens 1994). Further, school programs that train for fitness in children have had little success in maintaining fitness (or activity) levels once the program ended. There is little carry-over from during-school programs to out-of-school activity. Clearly, there are many chal¬lenges when planning and implementing a fitness program. The fact that there are challenges does not suggest that fitness is not important or valu¬able. However, the role of fitness and fitness test¬ing in physical education must be kept in perspec¬tive. The goal is maintaining good long-term health and providing a challenge for those students in¬terested in taking physical activity to the next level.
The second effect of exercise is production of heat. The body dissipates some heat by breath¬ing but most of it by sweating: The circulatory system increases blood flow to the skin, and the heat is lost by radiation and evaporation of sweat. Teachers need to be conscious of this process, particularly during hot and dry weather, when excessive sweating and evaporation may produce a loss in total body fluid. This can result in dehydra¬tion. Fluid lost should be replaced by regular water intake during heavy exercise In hot and dry weather. People of all ages are susceptible to dehydration. Children should always be permitted to drink as much water as they want to during and after exer¬cise. Water is as good a fluid replacement as any of the advertised commercial products. The USDA warns that children do not drink enough water and should be encouraged to drink water regardless of whether they are exercising, so encouraging children to drink water meets the demands of exercise and a more general nutritional need.
Children and adults handle heat and oxygen pro¬duction differently during exercise and physical activity. Children have higher resting heart rates than adults; this means that at rest children's hearts are working harder than adult's hearts. For example, a 6-year-old boy has a resting heart rate of 86 beats per minute (a girl's at the same age would be 88); by age 13, his resting heart rate would be 66 (hers would be 70). The maximum heart rate for a 6-year¬old is 215, as compared with 201 for a 13-year-old. The easiest way to estimate heart rate is to gently touch your fingers to the carotid artery and count the beats for 10 seconds, then multiply by 6. The carotid artery can be located by placing the fingers next to the Adam's apple (figure 6.2).
Blood pressure increases steadily during child¬hood and adolescence. Systolic pressure, the maximum pressure immediately after a heart beat, increases from 108 to 115 millimeters Hg during childhood and adolescence in boys, and in girls from 101 to 111 millimeters Hg (Hg is the symbol for the element mercury as read on the gauge). Diastolic pressure, the minimum pressure just before a heart beat, goes from 72 to 82 millime¬ters Hg in boys and 65 to 75 millimeters Hg in girls.
Respiration volume increases directly in relation to the intensity of exercise, but only about 50 to 60 percent of maximum aerobic power or maximum oxygen uptake (VO2max). Maximum aerobic power, maximum oxygen uptake, and VO2max are terms used to describe the upper limit of the cardio respiratory system in its ability to deliver oxygen to the body during exercise. At this point, respira¬tion increases very rapidly. The change from steady to rapid increase in respiration has been called the anaerobic threshold. The anaerobic threshold is the point at which the body can no longer keep up with the oxygen demands or the waste build-up in the muscles. The muscles are working without adequate oxygen, and in this state fatigue sets in very rapidly. Respiration response is the same for girls and boys. As children exer¬cise, respiration rate can provide information about level of fatigue. For example, a child who can talk easily while jogging is probably breath¬ing steadily; when respiration interferes with talk¬ing, the child is moving toward fatigue.
Anaerobic power, the ability to work without oxygen, is also lower in children than adults. This is because children have less of an important en¬zyme (phosophofructokinase or PFK) in their muscles; this enzyme allows the muscles to work without oxygen. Children will produce more PFK after puberty. Anaerobic power is important in activities such as sprinting.
Children also have a lower hemoglobin concen¬tration in the blood than adults. Since hemoglo¬bin is the part of blood that carries oxygen to the working muscles (e.g., in the heart and legs), chil¬dren transport less oxygen per unit of blood than adults. This means that children can do less work than adults. Hemoglobin content in the blood in¬creases at puberty; however, the increase is not as great in women as it is in men.
Children become more fit as a result of fitness training. The responses to training tend to be lower in children for several reasons:
- Children tend to be more fit at the onset, so training results in less improvement.
- Children have higher resting and maximum heart rates, which limits the intensity of train¬ing (.7 x maximum heart rate = training heart rate).
- Children have less hemoglobin, which limits maximal oxygen uptake.
Exercise training produces three benefits for children and adults. First, hearts become stronger as a result of training as stroke volume (the amount of blood the heart can pump in one beat) increases. Second, more capillaries develop as a result of training, which provides a better supply of blood to the heart and working muscles. Third, better extraction of oxygen from the blood leads to improved enzymatic reactions. Recall that in order to benefit from training, children must ex¬ercise 3 days per week for at least 20 minutes per day for 10 or more weeks at the training heart rate. Training or target heart rates for various age groups are presented in table 6.2.
The relationship between the type of cardiovas¬cular (aerobic fitness exercise) used for training and the type of testing used is critical. A child who has trained regularly as a swimmer will have trained cardiovascular endurance, but if that child is tested using the mile run, the benefits may not show up in the test results. There are two reasons for this: First, the muscles used- for swimming (arms) and running (legs) are different, so muscle endurance may be low in the legs and detract from the child's performance. Second, the knowledge of how to pace for the mile run is critical and learned through practice. Failure to pace carefully is one reason many children do poorly on the mile run test. You may remember a classmate running full speed for the first part of the mile run, then stopping or at least slowing considerably for the rest of tile mile. The object of pacing in the mile run is to maintain a relatively constant speed with enough energy remaining to run faster at the end. Practice creates immediate improvements in test scores, which are not related to improved fitness.
Aerobic fitness tests fall into two categories: norm referenced and criterion referenced. Norm¬ referenced tests are based on the normal (bell¬ shaped) curve and compare one person to the group. Criterion-referenced tests use a standard and generally place people into two groups (pass and fail, or master and non master). Early fitness tests were norm referenced and used the levels of the best 5 to 15 percent as criteria for an award. Recent tests tend to be criterion referenced, with the criterion selected based on predicting health risk. The concept is that a student who is 10 years old and can run the mile in 9 minutes and 48 sec¬onds or less will have less health risk than a stu¬dent who runs the mile in 9 minutes and 49 sec¬onds or more. Unfortunately, the various tests use different standards for passing (Morrow, Jackson, Disch, and Mood 2000). For example, a 9-year-old boy would have to run the mile at different speeds to pass the various tests: FITNESSGRAM (12 min), Physical Best (10:30 min), President's National (8:31 min), and Presidential Tests (<10 min), re¬spectively. This is confusing and leads to contro¬versy about the level of fitness of youth in our country (Blair 1992). Further, there are gender dif¬ferences at each age for all tests, beginning at G years of age. The times for girls are 48 seconds or more greater (meaning that girls run more slowly and still pass) than boys at each age for each test (Wilkinson,Williamson, and Rozsdilsky 1996).
Careful consideration needs to be given to test selection, use, and interpretation. If we maintain separate, lower standards, the message we send to girls as young as G is this: Is girls' health less important than boys' health? Is there a biological reason to expect girls to perform more poorly when compared with boys? The answer to these questions is no. Prior to puberty, boys and girls are similar in ability, and their performance should be similar as should our expectations. The pass¬ing rates on the four tests are very different: FfTNESSGf2AM (84%), Physical Best (51 or 52%,), President's National (G3 or G5%), and Presidential Tests (21%), respectively (the passing percentage for boys is presented first; the passing percent¬age for girls is shown second, where there are dif¬ferences). By selecting the test, a teacher can ma¬nipulate the passing rate for all children. If we want to demonstrate that most of our students are fit, we should use the FITNESSGRAM. However, if we want to demonstrate a need for fitness, we should use the Presidential Test. Interpreting test results for students, parents, and administration must be done in terms of the test characteristics and the purpose of testing. Often, it is best on any test to compare scores for a particular child rather than to compare scores between children or to test cri¬teria alone. In this way, maintenance or improve¬ment, rather than awards and comparisons to highly variable standards, will be the focus of the discussion.
We must take care in the use of fitness training and testing, since there is no evidence that being fit or training for fitness actually "carries over" to adult physical activity. Tracking is a term used to describe whether a behavior or characteristic re¬mains constant across time. Unfortunately, no re¬lationship has been demonstrated between physi¬cal fitness as a child and adult fitness or activity (Bouchard, Shepard, and Stephens 1994). Further, school programs that train for fitness in children have had little success in maintaining fitness (or activity) levels once the program ended. There is little carry-over from during-school programs to out-of-school activity. Clearly, there are many chal¬lenges when planning and implementing a fitness program. The fact that there are challenges does not suggest that fitness is not important or valu¬able. However, the role of fitness and fitness test¬ing in physical education must be kept in perspec¬tive. The goal is maintaining good long-term health and providing a challenge for those students in¬terested in taking physical activity to the next level.
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