NCHS Data Brief ■ No. 139 ■ December 2013

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

In 2008, the federal government released the Physical Activity Guidelines for 

Americans, which provide guidance on the types and amounts of physical 

activities that provide substantial health benefits for Americans of all ages. 

Regular physical activity reduces the risk of many adverse health outcomes 

and helps control the percentage of body fat in children and adolescents (1). 

This report provides the first nationally representative data on core, upper 

body, and lower body measures of muscle strength among U.S. children and 

adolescents aged 6–15 years by sex and age group. 

Keywords: muscle force • strength measurements • weight status • National 

Health and Nutrition Examination Survey

Were there differences in core muscle strength by sex and 

age group among children and adolescents? 

• There were no significant differences between younger girls and boys 

aged 6–11 years on the plank test, which is a measure of core body 

strength. Girls held the plank for 61 seconds and boys held it for 60 

seconds (Figure 1). 

Key findings

Data from the National 

Health and Nutrition 

Examination Survey, 

National Youth Fitness 

Survey

• There were no significant 

differences by sex in core, 

lower, or upper body measures 

of strength for younger 

boys and girls. In contrast, 

adolescent boys had higher 

values than adolescent girls on 

all measures of strength.

• Adolescent boys and girls 

had higher scores than younger 

boys and girls on the core and 

lower body strength measures 

and upper body strength as 

measured by the grip strength 

test.

• Adolescent boys completed 

more modified pull-ups, 

a measure of upper body 

strength, than younger boys. 

There was no significant 

difference in the number of 

modified pull-ups completed 

between adolescent and 

younger girls.

Measures of Muscular Strength in U.S. Children and 

Adolescents, 2012

R. Bethene Ervin, Ph.D.; Chia-Yih Wang, Ph.D.; Cheryl D. Fryar, M.S.P.H.;

Ivey M. Miller, R.T.R.; and Cynthia L. Ogden, Ph.D., M.R.P.

12–15 years

6–11 years

0 20 40 60

1

61

2

77

1

60

91

80 100

Boys

Girls

Figure 1. Number of seconds plank position held among children and adolescents aged

6–15 years, by sex and age group: United States, 2012

1

Significantly different from those aged 12–15 years in the same sex group, p < 0.05. 2

Significantly different from males in the same age group, p < 0.05.

NOTE: Access data table for Figure 1 at: http://www.cdc.gov/nchs/data/databriefs/db139_table.pdf#1.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, National Youth Fitness Survey.

Number of seconds
NCHS Data Brief ■ No. 139 ■ December 2013

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• There were significant differences between adolescent girls and boys aged 12–15 years on 

the plank test. Girls held the plank for 77 seconds, while boys held it for 91 seconds. 

• Adolescent boys and girls held the plank position longer than younger boys and girls.

Were there differences in lower body muscle strength by sex and age 

group among children and adolescents? 

• There were no significant differences between younger girls and boys on the knee extension 

test, which is a measure of lower body strength. Girls exerted a maximum of 44 pounds and 

boys exerted 43 pounds (Figure 2). 

• There were significant differences between adolescent girls and boys on the knee extension 

test. Girls exerted a maximum of 77 pounds, while boys exerted 86 pounds. 

• Adolescent boys and girls exerted more pounds of force on the knee extension test than 

younger boys and girls.

Figure 2. Maximum right knee extension force among children and adolescents aged 6–15 years, by sex and age 

group: United States, 2012

1

Significantly different from those aged 12–15 years in the same sex group, p < 0.05. 2

Significantly different from males in the same age group, p < 0.05.

NOTES: The knee extension score used was the maximum force exerted by the right knee. Access data table for Figure 2 at: 

http://www.cdc.gov/nchs/data/databriefs/db139_table.pdf#2.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, National Youth Fitness Survey.

0 20 40 60 80 100

Boys

Girls

Pounds

12–15 years

6–11 years

1

44

2

77

1

43

86
NCHS Data Brief ■ No. 139 ■ December 2013

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Were there differences in upper body muscle strength as measured by the 

modified pull-up by sex among children and adolescents? 

• There were no significant differences between younger girls and boys on the modified

pull-up, which is a measure of upper body strength. Girls performed four modified pull-ups 

and boys performed five (Figure 3). 

• There were significant differences between adolescent girls and boys in the number of 

modified pull-ups completed. Girls completed 4 modified pull-ups, while boys completed 10.

• There was no significant difference between younger and older girls in the number of 

modified pull-ups they could complete; however, adolescent boys completed twice as many 

modified pull-ups as the younger boys.

Figure 3. Number of modified pull-ups completed among children and adolescents aged 6–15 years, by sex and age 

group: United States, 2012

1

Significantly different from males in the same age group, p < 0.05. 2

Significantly different from those aged 12–15 years in the same sex group, p < 0.05. 

NOTE: Access data table for Figure 3 at: http://www.cdc.gov/nchs/data/databriefs/db139_table.pdf#3.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, National Youth Fitness Survey.

02468 10 12

Boys

Girls

Number completed

12–15 years

6–11 years

4

1

4

2

5

10
NCHS Data Brief ■ No. 139 ■ December 2013

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Were there differences in upper body muscle strength as measured by the 

grip strength test by age group among children and adolescents? 

• There were no significant differences between younger girls and boys on grip strength, 

which is a measure of upper body strength. Girls squeezed 68 pounds and boys squeezed

71 pounds (Figure 4).

• There were significant differences between adolescent girls and boys on grip strength. Girls 

squeezed 116 pounds on the grip strength test, while boys squeezed 143 pounds.

• Adolescent boys and girls had higher scores on the grip strength test than younger boys and 

girls.

Figure 4. Combined grip strength force among children and adolescents aged 6–15 years, by sex and age group:

United States, 2012

1

Significantly different from those aged 12–15 years in the same sex group, p < 0.05. 2

Significantly different from males in the same age group, p < 0.05.

NOTES: The combined grip strength score was the sum of the largest readings from each hand. Access data table for Figure 4 at: 

http://www.cdc.gov/nchs/data/databriefs/db139_table.pdf#4.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, National Youth Fitness Survey.

0 20 40 60 80 100 120 140 160

Boys

Girls

Pounds

12–15 years

6–11 years

1

68

2

116

1

71

143
NCHS Data Brief ■ No. 139 ■ December 2013

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Summary

This report provides the first nationally representative estimates of strength for U.S. children aged 

6–11 years and adolescents aged 12–15 years by sex and age group. The measures of muscle 

strength examined in this study were the plank (measures core muscles around the trunk and 

pelvis), modified pull-up (measures upper body strength), knee extension (measures lower body 

muscle strength), and grip strength (measures upper body muscle strength). 

Consistent with other research (2–5), these results demonstrated that adolescent boys had more 

strength than adolescent girls as reflected by higher scores on all measures of strength, but there 

were no significant differences between the sexes for younger children. Also, adolescent boys and 

girls had more strength or higher scores on most of the measures of strength than younger aged 

boys and girls. These sex and age differences are likely the result of physical changes that occur 

during puberty. Researchers have attributed these changes in strength to changes in height and 

weight as well as an increase in muscle mass in puberty (2,4,6). 

Definitions

Plank: This exercise works core muscles around the trunk and pelvis. Participants begin by lying 

face-down on a mat. The participant lifts his or her body off the mat, keeping his or her toes and 

forearms resting on the mat and his or her back straight. The objective of the exercise is to hold 

this position without movement for as long as possible.

Modified pull-up: This exercise measures upper body strength. Participants lie on their back 

with outstretched arms under a horizontal bar above their fingers. The participant grasps the bar 

with an overhand grip while maintaining a straight body with his or her heels on the floor. The 

participant raises and lowers his or her body as many times as possible so that his or her chest 

touches a band hanging 8 inches down from the bar.

Knee extension force: This exercise measures lower body strength. Participants are seated in 

a testing chair with their legs hanging over the edge of the seat. The participant’s hips, thighs, 

and trunk are restrained with web belts to limit use of other muscles during the test. A hand-held 

dynamometer (HHD) is placed on the shin just above the ankle. The participant presses his or her 

leg forward into the HHD as hard as possible. Each leg was tested; maximum force was recorded. 

Grip strength: This exercise measures upper body strength. Grip strength was measured using a 

handgrip dynamometer. While standing, the participant squeezes the handle of the dynamometer 

as hard as possible. Each hand was tested; maximum force was recorded. 
NCHS Data Brief ■ No. 139 ■ December 2013

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Data source and methods

Data from the National Health and Nutrition Examination Survey (NHANES), National Youth 

Fitness Survey (NNYFS) were used for these analyses. 

NNYFS was a nationally representative survey of the resident noninstitutionalized U.S. 

population aged 3–15 years. NNYFS excluded all children in supervised care or custody in 

institutional settings and any other U.S. citizens residing outside the 50 states and the

District of Columbia. It consisted of questionnaires administered in the home followed by a 

standardized physical examination in specially equipped mobile examination centers (MECs). 

The examination included physical activity and fitness tests, body measurements, and an 

in-person, 24-hour dietary recall interview conducted in the NNYFS MEC. 

The NNYFS sample was selected using a complex, multistage, probability sampling design. The 

survey was conducted in conjunction with the 2012 NHANES, with the NNYFS sample selected 

from an independent sample of dwelling units within the segments selected for NHANES. The 

sample design did not include oversampling by race and ethnicity.

Sample weights, which account for the differential probabilities of selection, nonresponse, 

and noncoverage, were incorporated into the estimation process. The standard errors of the 

percentages were estimated using Taylor series linearization, a method that incorporates the 

sample weights and sample design.

Differences between groups were evaluated using a t statistic at the p < 0.05 significance level. 

Test for trends by weight status were evaluated using linear regression, and the significance level 

was set at p < 0.05. All differences reported are statistically significant unless otherwise indicated. 

Statistical analyses were conducted using the SAS System for Windows (release 9.3; SAS 

Institute Inc., Cary, N.C.) and SUDAAN (release 11.0; RTI International, Research Triangle Park, 

N.C.).
NCHS Data Brief ■ No. 139 ■ December 2013

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About the authors

R. Bethene Ervin, Chia-Yih Wang, Cheryl D. Fryar, Ivey M. Miller, and Cynthia L. Ogden are 

with the Centers for Disease Control and Prevention’s National Center for Health Statistics, 

Division of Health and Nutrition Examination Surveys. 

References

1. U.S. Department of Health and Human Services. 2008 Physical activity guidelines for 

Americans. 2008. Available from: http://www.health.gov/PAGuidelines. 

2. Macfarlane TS, Larson CA, Stiller C. Lower extremity muscle strength in 6- to 8-year-old 

children using hand-held dynamometry. Pediatr Phys Ther 20(2):128–36. 2008.

3. Beenakker EAC, van der Hoeven JH, Fock JM, Maurits NM. Reference values of maximum 

isometric muscle force obtained in 270 children aged 4–16 years by hand-held dynamometry. 

Neuromuscul Disord 11(5):441–6. 2001.

4. Bäckman E, Odenrick P, Henriksson KG, Ledin T. Isometric muscle force and anthropometric 

values in normal children aged between 3.5 and 15 years. Scand J Rehabil Med 21(2):105–14. 

1989.

5. Eek MN, Kroksmark A-K, Beckung E. Isometric muscle torque in children 5 to 15 years of 

age: Normative data. Arch Phys Med Rehabil 87(8):1091–9. 2006.

6. Lundgren SS, Nilsson JÅ, Ringsberg KAM, Karlsson MK. Normative data for tests of 

neuromuscular performance and DXA-derived lean body mass and fat mass in pre-pubertal 

children. Acta Pædiatr 100(10):1359–67. 2011.
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Suggested citation

Ervin RB, Wang C-Y, Fryar CD, et al. 

Measures of muscular strength in U.S. 

children and adolescents, 2012. NCHS data 

brief, no 139. Hyattsville, MD: National 

Center for Health Statistics. 2013.

Copyright information

All material appearing in this report is in 

the public domain and may be reproduced 

or copied without permission; citation as to 

source, however, is appreciated.

National Center for Health 

Statistics

Charles J. Rothwell, M.S., Acting Director

Jennifer H. Madans, Ph.D., Associate 

Director for Science

Division of Health and Nutrition 

 Examination Surveys

Kathryn S. Porter, M.D., M.S., Director