Physical fitness has been shown to be significantly related to the ability to do physical activities such as household chores, work, sports and dance in an effective and safe manner. Less than one-half (40%) of the adult population exercise on a regular basis and only one quarter have done so for five or more years. A higher percent of younger adults engage in regular exercise; however, over four-fifths of adults consider themselves as active or more active than other persons of the same age. The majority of adults are not knowledgeable regarding the specific requirements to strengthen the heart and lungs (frequency and duration of exercise and heart and breathing rate during exercise).
Based on household interviews of the civilian noninstitutionalized population, 40% of all ages of the U.S. population exercise or play sports regularly, 38% of females, 43% of males, 29% of those 65 years and over.
60% of the U.S. population does not exercise regularly.
Exercise prescription is based upon the frequency, intensity and duration of training, the mode of activity (aerobic in nature), the initial level of fitness and the progression of physical activity.
The current best estimate is that around 7%-8% of adults participate 3 or more times per week for 20 minutes or more per session in an activity that requires 60% or more V02 max.
Improvement in VO2, max is directly related to frequency, intensity and duration of training and ranges from 5%-25% depending upon quantity and quality of training.
The amount of improvement in V02 max tends to plateau when frequency of training is increased above 3 days per week; participation of less than 2 days per week does not show an adequate change in V02 max.
Programs that are conducted at least 3 days per week, for at least 20 minutes and of sufficient intensity and duration to expend a minimum of 300 kilocalories (Kcal) per exercise session are suggested as a threshold level for total body mass and fat weight loss.
The minimal threshold level for improvement in V02 max is approximately 60% of the maximum heart rate reserve (50% of V02 max).
In order to maintain the training effect, exercise must be continued on a regular basis.
A significant reduction in working capacity occurs after 2 weeks of detraining with participants returning to near pretraining levels of fitness after 10 weeks-8 months of detraining.
50% reduction in improvement of cardiorespiratory fitness has been shown after 4-12 weeks of detraining.
Endurance activities that require running and jumping may cause significantly more debilitating injuries to beginning exercisers than other nonweight bearing activities.
Although V02 max decreases with age, and total body mass and fat weight increase with age, evidence suggests that this trend can be altered with endurance training.
Studies evaluating circuit weight training (weight training conducted almost continuously with moderate weights, using 10-15 repetitions per exercise bout with 15-30 seconds rest between bouts of activity) showed little to no improvements in working capacity and V02 max.
It has been shown that endurance training less than 2 days per week, less than 50% of maximum oxygen uptake, and less than 10 minutes per day is inadequate for developing and maintaining cardiorespiratory fitness for healthy adults.
Skinfold measurements for body fat are significantly higher in today's youth than in measurements taken in the 1960s.
About 50% of today's youth do not receive "appropriate physical activity, i.e., activity most likely to ensure cardiorespiratory fitness and to establish life-long exercise patterns."
Approximately 80% of 5th- through 12th-graders take physical education classes. However, enrollment declines sharply, with 98% enrolled in 5th grade, but barely 50% in 12th grade.
An average physical education student attends classes 3.6 days per week: most students in elementary grades take classes only 1 or 2 days a week; only 36.3% of 5th- through 12-graders take daily classes.
The average youth gets more than 80% of his/her physical activity outside of the school physical education program. An average of 12-13 hours each week are spent in physical activity outside of class year round, compared to 2 or 3 hours in class.
In physical education classes, 47% of time is spent on lifetime activities (i.e., those that are likely to carry over into adulthood) compared to 63% of activity time outside of physical education.
Physical education teachers of younger students tend to rely heavily on relays and informal games, such as dodgeball and kickball, while teachers of older students rely heavily on organized sports and sports competitions.
For boys and girls, the top 5 physical education activities are basketball, calisthenics/exercises, volleyball, baseball/softball and jogging (distance running).
The top 5 activities outside of physical education for boys are: bicycling, basketball, tackle football, baseball/softball and swimming. For girls, they are swimming, bicycling, disco or popular dance, rollerskating and walking quickly.
Exercise patterns are highly seasonal. Activity in the winter and autumn months falls to half of the summer high. Youths have difficulty shifting activity from one season to the next or perpetuating activities despite change of season.
Several factors stand out in producing super-fit youths (those above the 75th percentile). These youths are enrolled in physical education, take classes more days per week than less fit youths and participate in a larger variety of activities. Outside of physical education, they find physical activity though a larger number of community organizations, have a more varied activity program and participate in more appropriate physical activities than others.
The National Children and Youth Fitness Study (NCYFS) shows that boys can do more sit-ups and chin-ups, can stretch farther and have less body fat as they reach the older teens.
For girls, abdominal strength and flexibility appear to improve with age. Although girls' body fatness increases with age, this pattern decelerates around age 15. Upper body strength remains consistently low. On the mile walk/run, girls' performance appears to peak at around 14, decline slightly and level off in the older teens. This overall pattern of continued improvement for both boys and girls runs contrary to the common belief that performance on fitness tests levels off for boys and declines for girls in early adolescence.
In the 1985 National School Population Fitness Survey (NSPFS) girls scores in the V-sit reach ranged form 1 1/2 inches to 3 inches better than boys. With the exception of ages 8 and 16 girls generally improved with age group. 40% of boys ages 6 through 15 could not reach beyond their toes. Boys over 13 showed steady improvement by age, but still lagged behind the girls about 2 to 1 1/2 inches.
Approximately 50% of girls ages 6 through 17 and 30% of boys ages 6 through 12 could not run a mile in less than 10 minutes, according to the NSPFS.
Regular, vigorous and prolonged physical activity is generally accepted as essential for an effectively functioning cardiorespiratory system. The term "appropriate physical activity," as typical defined and as adopted by the NCYFS, refers to exercise involving large muscle groups in dynamic movement for periods of 20 minutes or longer, 3 or more times weekly, at an intensity requiring 60% or more of an individual's cardiorespiratory capacity. The NCYFS shows that approximately half of boys and girls in grades 5 through 12 are achieving at least the minimum weekly requirement. By measuring appropriate physical activity 3 ways, the NCYFS found that 58.9% engage in appropriate physical activity year round, 46.9% engaged in 1 or more lifetime activities to achieve year round appropriate physical activity and 41.0% perceive that they regularly exert themselves during exercise (sweating and breathing hard). The segment of the population engaging in appropriate physical activity, and by any measure, fluctuates with the seasons, falling off sharply in the fall and winter months and climbing again in spring and summer.
According to the self-report survey, the typical youth is exposed to (i.e., participates in at least 3 times) 21.3 different activities over a year's time outside the physical education class (primarily the community). The variation in activities drops as children grow older. The average youth has opportunities to participate in physical activity through two different community organizations, with only 18.2% not performing a physical activity through community organizations. Among community organizations, the leading sources of physical activity are churches and other places of worship, parks and recreation programs, local team sports and private organizations (e.g., health clubs).
Public and Professional Awareness
40% of the U.S. population think a person should exercise 3-4 days to strengthen the heart and lungs.
52% think a person should exercise more than 25 minutes on each occasion so that the heart and lungs are strengthened.
The medical care setting is an important location for the promotion of physical activity.
The President's Council on Physical Fitness and Sports provides physical fitness and sports leadership training, motivational support and exercise program material to youth-serving organizations and information and editorial copy to newspapers, magazines and trade journals on the benefits of regular exercise.
National Health and Nutrition Examination Survey (NHANES) III planners are currently examining the feasibility and desirability of an improved set of exercise and fitness questions for the NHANES III in fiscal year 1988.
The Behavioral Risk Factor Surveillance System (BRFSS) is an ongoing surveillance system. At the present time, 24 states are participating in the BRFSS to determine leisure time activity and other health related habits of adults.
National polls and data from selected population groups suggest that the amount of time spent by adults in vigorous leisure time activity has increased in the past 10-20 years. The data do not allow a quantitative estimate of the increase. If a change has occurred, the data are insufficient to determine if all demographic groups have participated.
Most surveys of leisure time physical activity show that adults (18 years and older) most commonly report the activities of walking, swimming, calisthenics, bicycling and jogging or running. Variation in definition of participation precludes any assessment or national trends in the absolute or relative frequencies of these activities. No information is available about participation in public recreation programs in community facilities.
The NCYFS shows that American young people have become fatter since the 1960s. For both boys and girls, the NCYFS sample had median skinfold sums that were 2-3 millimeters thicker than in the 1960's sample studied by the National Center for Health Statistics. Average triceps skinfold thickness was significantly greater in the NCYFS for 13 or 16 age/sex groups.
The 1985 National School Population Fitness Survey reported that, in general, the performance of youth in 1985 was not much different from that of youth in 1975. The study supports a large body of related evidence that increased emphasis is required to improve the levels of youth physical fitness.
The typical student reports spending over 80% of his/her physical activity time outside physical education class. Activity time peaks in the summer, falls off rapidly in the fall and winter months and resumes at a more typical level in the spring. Year round, the average student spends 760 minutes (or slightly under 13 hours) per week in sports, active games and exercises. The activity patterns of girls and younger students are disproportionately affected by changes in the weather.
The average physical education class lasts 46.7 minutes, for an average weekly activity time of 141 minutes. Students are exposed to an average of 11.8 different activities over a year's time, with slightly less than half the time spent on lifetime activities.
The greater the number of physical activities in which students have participated (at least 3 times) in the past year and the greater the variety in the types of community organizations through which they have participated, the better the performance on physical fitness tests.
Enrollment in physical education drops off as students grow older. From an enrollment level of 97% in grades 5 and 6 enrollment tapers off until it approaches 50% in grades 11 and 12. For 12th-grade girls, enrollment is under 50%. Among students enrolled in physical education, daily participation is the modal frequency, but only 36.3% of students in grade 5 through 12 take physical education daily.
The effects of physical activity on several diseases of public health importance are summarized.
A number of well designed and carefully analyzed observational studies have shown the incidence of coronary heart disease to be approximately 2-fold higher among sedentary men than among men who regularly participate in vigorous leisuretime or occupational physical activity. A careful review of the data strongly supports the conclusion that these effects are not attributable to the selection of a more active lifestyle by men who are healthier to begin with. It seems prudent to believe that vigorous activity so defined (i.e., dynamic and rhythmic use of large muscle groups 3 or more times per week, 20 or more minutes per session, and at 60% or more V02 max) does reduce the risk of Coronary Heart Disease.
Cross-sectional surveys and prospective studies limited in magnitude and design suggest that physical activity prevents the development and aids in the control of hypertension. The effect, if actually present, appears to be modest, only a few millimeters of mercury reduction in systolic pressure. Applied over the whole population, however, the effect on morbidity and mortality may be substantial.
Walking, running and other weight-bearing activity correlate with bone density. Data sufficient to estimate the magnitude of the expected reduction in osteoporosis related morbidity (e.g., hip fractures in the elderly) are not available.
Physical activity reduces blood glucose levels, increases insulin receptors and increases the effect of insulin. A crosssectional study of a population on a Pacific island noted a higher prevalence of diabetes among sedentary than among active population; the association was independent of obesity. No other data are available with which to estimate whether habitual physical activity might prevent or postpone the development of noninsulin-dependent diabetes or its complications. Clinical observations suggest that physical activity improves glucose control in children with insulin-dependent diabetes mellitus. However, no data are available to estimate changes in the rate of the complication of diabetes.
Clinical depression is common with prevalence estimates ranging from 3-4 to 5%-10% about 15% of whom (or 20,000 per year) will die from suicide. The antidepressant effects of exercise are widely accepted, yet have been demonstrated in only 2 controlled studies. Data are not available with which to estimate the benefits from improved function and lower incidence of depresessive episodes among depressed patients.
No controlled studies have been done on patients with anxiety disorders. Among nonclinical populations, experimental studies of acute and chronic vigorous exercise have consistently shown a reduction in temporary anxiety states, less consistently a reduction in permanent anxiety traits and improvements not necessarily better than other interventions such as meditation or eating. The data do not allow an estimate of the magnitude of these effects on morbidity or mortality.
Exercise has been reported to improve self concept, social skills and behaviors associated with IQ measurement in mentally retarded individuals. The potentially associated reduction in medical costs has not been estimated.
One study reported higher abstinence rates after three months among alcoholics in a treatment program that included exercise than alcoholics from another program.
Cross sectional surveys and clinical trials consistently support the observation that physical activity has a beneficial effect on weight control. Although the effect is firmly established, no estimates have been made concerning the benefits which accrue in terms of reduced morbidity and mortality.
Adverse Health Effects
Physical activity is associated with a variety of acute musculoskeletal injuries. However, virtually no data are available with which to estimate the incidence of adverse acute or chronic musculoskeletal, psychological or metabolic effects. It should be noted, however, that improved muscular strength, muscular endurance and flexibility are associated with improved fitness and may reduce injury in physical activity at work and in recreation.