Physical Activity

"At least one-third of all cancers are attributable to poor diet, physical inactivity, and overweight.  Thus, if our goal of reducing cancer incidence by 25% in the United States by 2015 is to be reached, cancer prevention efforts must include strong programs for healthy eating and physical activity. Such programs will also help to reduce the incidence of many other chronic diseases."

 – DiLeep G. Bal, MD, MS, MPH President, American Cancer Society

Healthy People 2010 Objectives

• Increase the proportion of adolescents who engage in moderate physical activity for at least 30 minutes on 5 or more of the previous 7 days from 20% to 30%
• Increase the proportion of adolescents who engage in vigorous physical activity that promotes cardiorespiratory fitness 3 or more days per week for 20 minutes or more minutes per occasion from 64% to 85%
• Increase the proportion of the nation's public and private schools that require daily physical education for all students from 17% to 25% for middle schools and from 2% to 5% for senior high schools.
• Increase the proportion of adolescents who participate in daily school physical education from 27% to 50%.
• Increase the proportion of adolescents who spend at least 50% of school physical education class time being physically active from 32% to 50%
• Increase the proportion of children and adolescents who view television 2 or fewer hours per day from 60% to 75%
• Increase the percentage of children and adolescents aged 5-15 years who walk to school less than 1 mile from 28% to 50%.
• Increase the percentage of children and adolescents aged 5-15 years who bike to school less than 2 miles from 2.2% to 5% ⁷

Importance of Physical Activity

Regular participation in moderate physical activity is an integral component of a healthy lifestyle.  Benefits include

• aerobic endurance and muscular strength.
• improvement of blood lipid profiles.
• reduction in risk of developing diabetes.
• Promotes development of optimal peak bone mass (physical activity may be even more important than calcium in determining peak bone density)^.80
• Enhances self-esteem and self-confidence.
• Decreases feelings of anxiety and stress.
• Improves behavioral conduct.
• Promotes social skills.
• Provides an opportunity for children to set and strive for personal, achievable goals.^81,82

Decreased physical activity and increased physical inactivity are major contributors to the current child and adolescent obesity epidemic.⁸³ 

Time spent watching television is associated with obesity and decreased physical inactivity.  Decreasing time spent in sedentary activities can increase physical activity levels and is an effective obesity intervention.⁸¹   Lifetime physical activity habits develop and persist into adulthood.⁸⁴

Physical Activity Guidelines

Physical activity recommendations for adolescents issued by the International Consensus Conference on Physical Activity Guidelines for Adolescents

• All adolescents should be physically active daily, or nearly every day, as part of play, games, sports, work, transportation, recreation, physical education, or planned exercise, in the context of family, school, and community activities.
  
  
• Adolescents should engage in three or more sessions per week of activities that last 20 minutes of more at a time and that require moderate to vigorous levels of exertion.
  
  
• Physical activity guidelines for children issued by the National Association for Sport and Physical Education consider the special developmental needs and abilities of younger children.
  
  
• Elementary school-age children should accumulate at least 30-60 minutes of age-appropriate and developmentally appropriate physical activity from a variety of activities on all, or most, days of the week.
  
  
• An accumulation of more than 60 minutes, and up to several hours per day, of age-appropriate and developmentally appropriate activity is encouraged.
  
  
• Some of the child's activity each day should be in periods lasting 10 to 15 minutes or more and include moderate and vigorous activity.  This activity will typically be intermittent in nature, involving alternating moderate to vigorous activity with brief periods of rest and recovery.
  
  
• Children should not have extended periods of inactivity. ⁸³

Physical Inactivity Recommendations

The American Academy of Pediatrics recommends that television viewing be limited to no more than 1-2 hours of quality programming per day due to the association of television viewing with eating disorders and obesity.⁸⁵ 

It is evident that children and adolescents spend a significant amount of time watching television and videos and playing computer games.

According to Nielson Media Research, the average child or adolescent watches about three hours of television per day exclusive of time spent watching videos and playing video games.⁸⁵

Over half of high school students report watching two or more hours of television per day.⁸⁶  

A recent study reported that the average child spends 6.5 hours per day using various forms of media.⁸⁵ 

Current Levels of Physical Activity

Due to budgetary constraints and demands for increased academics, schools are not adequately preparing students for lifetime physical activity.  According to the 1999 Youth Risk Behavior Surveillance System, a significant portion of high school students in the United States do not meet physical activity recommendations. ^83,86

Approximately two-thirds engaged in regular vigorous physical activity.

Approximately one-quarter participated in regular moderate activity.

Regular participation in vigorous physical activity dropped from 73% of 9^th grade students to 61% of 12^th grade students.

Just over half performed strengthening exercises regularly. About half did not play on any sports teams during the year.

Nearly half were not even enrolled in a physical education class; enrollment in physical education drops from 79% in 9^th grade to 37% in 12^th grade.

Only 29% attended daily physical education classes compared to 42% in 1991.

Ethnic/racial Variations in Physical Inactivity Patterns

National studies have reported that minority children and adolescents watch more television than white children.

Percent of Adolescents Watching > 2 hours of television per day, YRBS, 1999.

(Source: Centers for Disease Control and Prevention, 2000.)

About one-third of White, alf of Mexican American, and three-fourths of Black high school students watch two or more hours of television per day.

NHANES III, 1988-1999 provides information on television viewing habits of children and youth.⁸⁷

Overall, almost half of US children aged 8-16 years watched more than 2 hours of television a day. 

More Black (65%) and Mexican American youth (53%) watched television for three or more hours per day than White children (37%).

Three times more Black and 1.5 times more Mexican American children watched 5 or more hours of television per day than White children.⁸⁷

The National Longitudinal Study of Adolescent Health also noted racial/ethnic disparities in physical inactivity. ⁸⁸

White adolescents had lower inactivity hours than minority adolescents, especially Black adolescents.

Ethnic Variations in Physical Activity Patterns

The Youth Risk Behavior Survey found racial/ethnic disparities in physical activity patterns.

Percentage of high school students who participated in physical activity, and strengthening exercises by race YRBS, 1999.

(Source: Centers for Disease Control and Prevention. CDC Surveillance Summaries. January 9, 2000. MMWR 2000;49(No. SS-5).)

Minority youth, especially African American, are less likely to engage in regular vigorous or moderate activity and strengthening exercises.

Data on physical activity patterns is available from the NHANES III.

Participation in Physical Activity Most Days Among US Children Aged, 8-16, NHANES III 1988-1994

(Source: Crespo et al, 2001)

Only 56.7% of US children are active 5 or more days per week.

White boys had the highest prevalence (72.4%) and Black girls the lowest (41.8%) of being active five or more days per week.

Some data are available on physical activity of school age children from different racial/ethnic groups from smaller studies. 

A study of 43 Pima Indian children and 42 Caucasian children (mean age just under 10 years) found that Pima Indian children watched more television and were less physically active than Caucasian children.⁸⁹

A study of 2410 3^rd graders in four states reported an average of 90 minutes per day of moderate to vigorous physical activity, with 12.8% spending less than 30 minutes and 36.6% less than 60 minutes per day.  These children spent an average of 120 minutes per day engaged in sedentary activity.  Black and Hispanic children spent less time participating in moderate to vigorous physical activity than white children.  However, time spent in sedentary activity did not differ by ethnicity.⁸⁴

Black girls spent less time than did white girls on the weekend with heart rate 125% and 150% above basal levels. ⁹⁰ 

A study of girls in grades 5 through 12 in Massachusetts reported lower physical activity levels among Hispanics and Asian than other ethnic groups. 

Possible explanations provided for this difference are that strenuous physical activity may not be considered feminine, a greater emphasis on academics, and a cultural acceptance of a larger body size.⁹¹  

Factors Contributing to Lack of Physical Activity

Factors contributing to lack of physical activity:

• Use of automobile for transportation even for very short trips.
• Although an estimated 38 million young people participate in youth sports programs, participation declines substantially as children progress through adolescence.  One study found that attrition from youth sports programs was occurring among 10-year-olds and peaked among 14- to 15-year-olds⁸³
• Decreased school physical education requirements.
• Time spent in sedentary activities.
• Technology.⁸³
• Parental inactivity^.92

Environmental factors contributing to physical activity include ⁸¹

• Safe places for children to play and be physically active.
• Access to community physical activity programs.
• Access to activity equipment such as bike trials, skates, balls.
• Access to physical activity facilities such as parks, recreation centers, and gyms.
• Time spent outside.
• Parental role modeling and support such as transportation to a sports facility or practice and purchase of equipment.

A study of school environment and physical activity found that fewer than 2% of girls and 6% of boys were physically active during unstructured time.  Physical activity increased when there were improvements to activity areas and adult supervision of activities.⁹³ 

A 3-year follow-up of 5th grade CATCH participants found that the intervention resulted in decreases in percent calories from fat and saturated fat, decreased consumption of foods high in fat and sodium, and increased daily vigorous activity.⁹⁴