Table of Contents

Component Description

The cardiovascular (CV) fitness component measured aerobic capacity through a submaximal treadmill test. The goals of this component are to provide: 1) nationally representative data on cardiovascular fitness for youth ages 12-15 years; 2) prevalence estimates of youth ages 12-15 years at risk due to poor physical fitness; and 3) data to study the association between cardiovascular fitness and other health conditions and risk factors, such as obesity, physical activity and dietary patterns.

Eligible Sample

Participants aged 12-15 years, who did not meet any of the exclusion criteria, were eligible for this component.

Participants are excluded from this component based on medical conditions, medications, physical limitations and safety limitations.

Protocol and Procedure

The treadmill protocol for the National Health and Nutritional Examination Survey National Youth Fitness Survey (NNYFS) for ages 12-15 years was conducted previously in NHANES 1999-2006 to measure aerobic capacity. The protocol specifically followed the NHANES 2004-2006 protocol.1  The protocol is a submaximal treadmill exercise test from which maximal oxygen consumption (VO2max) was estimated. Participants were assigned to one of five treadmill test protocols varying in grade and speed based on gender, age, BMI, and self-reported level of physical activity. Each of the protocols was designed so that the participant walks at all times. The test consists of a 2-minute warm up, two 3-minute exercise periods, and a 2-minute recovery period. The goal of each protocol is to elicit a heart rate that is approximately 75 percent of the predicted maximum (220 minus age) by the end of the test.

Heart rate was monitored continuously using an automated monitor with four electrodes connected to thorax and abdomen of the participant and was recorded at the end of warm-up, each exercise stage, and each minute of recovery. At the end of warm-up and each exercise stage, participants were asked to rate their perceived exertion using the Borg scale.

The main outcome of this component is the estimated VO2max, which is estimated using the heart rate at the end of each exercise period. Based on gender and age specific criteria, the estimated VO2max is categorized using Fitnessgram® criterion-referenced standards.2

Detailed descriptions of the protocol are provided in the NNYFS Treadmill Examination Manual3 available on the NNYFS website at: https://www.cdc.gov/nchs/data/nnyfs/treadmill.pdf

Quality Assurance & Quality Control

Examiners were regularly monitored by NCHS staff and field supervisors. Retraining sessions were conducted periodically with the examiners to reinforce the proper protocols and techniques. Inspection, calibration, and maintenance of the equipment and supplies were performed on a regular basis.

As part of on-going quality control practices, all data were reviewed systematically for logical or operational inconsistencies and examiner errors.

Data Processing and Editing

During the data processing, edits were made to ensure the logical consistency and analytic usefulness of the data. Extreme values were reviewed and cross-checked with other available data. When there was insufficient information to conclude that the values were invalid, they were retained in the data set.

Variable specific editing:

CVDEXSTS (CV fitness exam status)
This derived variable indicates the following for each participants:
1. VO2max estimated.
2. Tested but VO2max estimate missing - data obtained during the treadmill test were insufficient in calculating VO2max.
3. Did not participate in the treadmill test.

CVDEXCMT (Comment code for the exam status)
This derived variable denotes the reason the treadmill test was not done or data are missing. About 8% of participants who were eligible were excluded.

“0” – None: the exam was completed with no missing data point present.
“1” – Met exclusion criteria: exam was not done due to the participant met the exclusion criteria of the component other than pregnancy.
“3” – Refusal: participant refused to undergo or continue the test.
“4” – No time: the exam was not done because there was not enough time.
“5” – Technical problem: problems that occurred during the test with equipment, software applications, or technician error.
“6” – Met priority 1 stopping criteria: participant discomfort or distress observed by the health technician or reported by the participant that warranted an emergency stop of the protocol.
“7” – Met priority 2 stopping criteria: safety concerns arose during the test that warranted an early stop of the protocol.
“8” – Not able to calculate VO2max: heart rate obtained at the end of stage 2 lower than what obtained at the end of stage 1, or the difference between stages 1 and 2 heart rates is 5 beat/minute or less.
“90” – Other.

CVXPARC (Physical activity level)
This variable summarizes the responses from a series of questions and describes the participant’s typical physical activity level using the NASA/JSC physical activity scale.4 See the NHANES National Youth Fitness Survey (NNYFS) Treadmill Examination Manual Appendix D for further details.

CVDVOMAX (Predicted VO2max)
This derived variable designates predicted VO2max value calculated with the equation developed by Jackson et al.5 The prediction model is based on participant’s gender, age, body mass index, and self-reported level of physical activity. Predicted VO2max value is used in the determination of the exercise protocol for the treadmill test. See the NHANES National Youth Fitness Survey (NNYFS) Treadmill Examination Manual Appendix F for further details.

CVAPROT and CVDPROT (Assigned exercise protocol and the actual protocol used in stages 1 and 2)
Each participant was assigned to one of five protocols based on the predicted VO2max. The original protocol used in NHANES 1999-2004 had 8 different protocols. In NHANES 2003-2004, exercise protocols 1, 2 and 8 were eliminated for all participants 12-19 years. This procedure was followed by NNYFS. Participants who were assigned to exercise protocol 1 or 2 were re-assigned to protocol 3, and persons who used to be assigned to exercise protocol 8 were re-assigned to protocol 7. According to the procedure, if the heart rate in warm-up is greater than 60% of the predicted maximal heart rate (PMHR), the assigned exercise protocol is decreased by 1 for the remainder of the treadmill test (the exception being if the protocol was already at the lowest possible one). When the heart rate in warm-up is less than 50% of the PMHR, the assigned protocol is increased by 1 for the remainder of the test (the exception bring if the protocol is already at the highest possible protocol). The variable CVAPROT denotes the exercise protocol that was originally assigned to the case while variable CVDPROT reflects the actual exercise protocol used in stage 1 and stage 2 after the adjustment during warm-up. See the NHANES National Youth Fitness Survey (NNYFS) Treadmill Examination Manual , Sections 3.7.18.1 and 3.7.18.2 for further details.

CVDESVO2 (Estimated maximal oxygen uptake)
This derived variable designates the main outcome of the component: VO2max (ml/kg/min). It is estimated by extrapolation using measured heart rate responses to known levels of exercise workloads, assuming the relation between heart rate and oxygen consumption is linear during exercise.6 See the NHANES National Youth Fitness Survey (NNYFS) Treadmill Examination Manual , Appendix G for further details.

CVDFITLV (Cardiovascular fitness level) - change
The level of cardiovascular fitness is categorized based on gender-age specific cut-points of estimated VO2max. The reference standards used for adolescents ages 12-15 years are based on the criteria used in the FITNESSGRAM program.2 See Treadmill Examination Manual , Appendix H for further details.

Analytic Notes

The NNYFS examination sample weights should be used to analyze the cardiovascular fitness data. Please refer to the NNYFS Analytic Guidelines for details on the use of sample weights and other analytic issues.

Due to the nature of the submaximal test, some estimates obtained in this component may appear extreme compared to data obtained from more direct measures. Analysts need to carefully examine the data distribution and consider whether or not it is appropriate to include or exclude extreme values in a given analysis.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number
Target:
Both males and females 12 YEARS - 15 YEARS

CVDEXSTS - CV fitness exam status

Variable Name:
CVDEXSTS
SAS Label:
CV fitness exam status
English Text:
CV fitness exam status
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 VO2max estimated 451 451
2 Tested but VO2max estimate missing 12 463
3 Not done 29 492
. Missing 0 492

CVDEXCMT - Comment code for CV fitness exam status

Variable Name:
CVDEXCMT
SAS Label:
Comment code for CV fitness exam status
English Text:
Comment code for CV fitness exam status
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 None 451 451
1 Met exclusion criteria 22 473
3 SP refusal 1 474
4 No time 4 478
5 Data acquisition problem 3 481
6 Met priority 1 stopping criteria 2 483
7 Met priority 2 stopping criteria 6 489
8 Not able to calculate VO2max 3 492
99 Other 0 492
. Missing 0 492

CVDEXLEN - Length of CV fitness exam (min)

Variable Name:
CVDEXLEN
SAS Label:
Length of CV fitness exam (min)
English Text:
Length of the CV fitness exam (minutes)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
5.48 to 43.57 Range of Values 463 463
. Missing 29 492

CVDPMHR - Predicted maximal heart rate (per min)

Variable Name:
CVDPMHR
SAS Label:
Predicted maximal heart rate (per min)
English Text:
Predicted maximal heart rate (per minute)
English Instructions:
Predicted maximal heart rate = 220 - (Age at interview)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
205 to 208 Range of Values 492 492
. Missing 0 492

CVDESVO2 - Estimated maximal O2 uptake (ml/kg/min)

Variable Name:
CVDESVO2
SAS Label:
Estimated maximal O2 uptake (ml/kg/min)
English Text:
Estimated maximal oxygen uptake (ml/kg/min).
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
23.17 to 92.6 Range of Values 451 451
. Missing 41 492

CVDFITL2 - Cardiovascular fitness level

Variable Name:
CVDFITL2
SAS Label:
Cardiovascular fitness level
English Text:
Cardiovascular fitness level
English Instructions:
The level of cardiovascular fitness is categorized based on gender-age specific cut-points of estimated VO2max. (See CV Fitness Procedures Manual, Appendix I for details.)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Healthy fitness zone 197 197
2 Needs improvement - some risk 69 266
3 Needs improvement - high risk 185 451
. Missing 41 492

CVXPARC - Physical activity readiness code

Variable Name:
CVXPARC
SAS Label:
Physical activity readiness code
English Text:
Physical activity readiness (PAR) code
English Instructions:
The PAR code was determined by a series of questions to describe the participant's typical physical activity level. (See CV Fitness Procedures Manual, Appendix E)
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 7
Code or Value Value Description Count Cumulative Skip to Item
0 Little or no regular recreation, sport or physical activity and avoids walking or exertion 6 6
1 Little or no regular recreation, sport or physical activity but walks for pleasure and occasionally exercises 27 33
2 Participating regularly in recreation or work requiring modest physical activity for 10 to 60 minutes per week 90 123
3 Participating regulalry in recreation or work requiring modest physical activity for more than 60 minutes per week 102 225
4 Participating regularly in heavy physical activity for less than 30 minutes per week 7 232
5 Participating regularly in heavy physical activity for 30 - 60 minutes per week 37 269
6 Participating regularly in heavy physical activity for 1 - 3 hours per week 68 337
7 Participating regularly in heavy physical activity for more than 3 hours per week 126 463
. Missing 29 492

CVDVOMAX - Predicted maximal O2 uptake (ml/kg/min)

Variable Name:
CVDVOMAX
SAS Label:
Predicted maximal O2 uptake (ml/kg/min)
English Text:
Predicted maximal oxygen uptake (ml/kg/min)
English Instructions:
Predicted VO2max = 56.363 + [1.921 x CVXPARC] - [0.381 x RIAAGEYR] - [0.754 x CVABMI] + [10.987 x (F=0, M=1)] . This is used in the determination of the exercise protocol used in the treadmill test.
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 100
Code or Value Value Description Count Cumulative Skip to Item
36.06 to 76.12 Range of Values 463 463
. Missing 29 492

CVAPROT - Assigned exercise protocol

Variable Name:
CVAPROT
SAS Label:
Assigned exercise protocol
English Text:
Assigned exercise protocol
English Instructions:
See CV Fitness Procedures Manual, Section 3.7 and Appendix H
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 9
Code or Value Value Description Count Cumulative Skip to Item
3 to 6 Range of Values 463 463
. Missing 29 492

CVDPROT - Exercise protocol used in stage 1 and 2

Variable Name:
CVDPROT
SAS Label:
Exercise protocol used in stage 1 and 2
English Text:
Exercise protocol used in stage 1 and stage 2 after adjustment for warm-up heart rate
English Instructions:
If the heart rate in Warm-up is greater than 60 % of the predicted maximal heart rate (PMHR), the assigned exercise protocol is decreased by 1 for the remainder of the treadmill test. If the heart rate in Warm-up is less than 50 % of the PMHR, the assigned exercise protocol is increased by 1 for the remainder of the treadmill test. This variable reflects the actual exercise protocol used in stage 1 and stage 2 after the adjustment for heart rate during warm-up. (See CV Fitness Procedures Manual, Sections 3.12 and 4.5)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3 to 7 Range of Values 463 463
. Missing 29 492

CVATEM1 - Pre-test room temperature (degrees F)

Variable Name:
CVATEM1
SAS Label:
Pre-test room temperature (degrees F)
English Text:
Pre-test room temperature (degrees Fahrenheit)
English Instructions:
Measured by a digital thermometer directly integrated with the computer system. If temperature is not captured automatically, the temperature can be read off the monitor and entered manually.
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 140
Code or Value Value Description Count Cumulative Skip to Item
62.4 to 77 Range of Values 462 462
. Missing 30 492

CVAHUM1 - Pre-test room humidity (%)

Variable Name:
CVAHUM1
SAS Label:
Pre-test room humidity (%)
English Text:
Pre-test room humidity (%)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
18.7 to 73.9 Range of Values 460 460
. Missing 32 492

CVATEM2 - Post-test room temperature (degrees F)

Variable Name:
CVATEM2
SAS Label:
Post-test room temperature (degrees F)
English Text:
Post-test room temperature (degrees Fahrenheit)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
63.9 to 76.6 Range of Values 462 462
. Missing 30 492

CVAHUM2 - Post-test room humidity (%)

Variable Name:
CVAHUM2
SAS Label:
Post-test room humidity (%)
English Text:
Post-test room humidity (%)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
21.9 to 72.7 Range of Values 460 460
. Missing 32 492

CVAWS1 - Warm-up speed (mph)

Variable Name:
CVAWS1
SAS Label:
Warm-up speed (mph)
English Text:
Warm-up speed (miles per hour)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 3.7
Code or Value Value Description Count Cumulative Skip to Item
2.2 to 3.7 Range of Values 463 463
. Missing 29 492

CVAWG1 - Warm-up grade (% incline)

Variable Name:
CVAWG1
SAS Label:
Warm-up grade (% incline)
English Text:
Warm-up grade (% incline)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 14.5
Code or Value Value Description Count Cumulative Skip to Item
2 to 5.5 Range of Values 463 463
. Missing 29 492

CVDWTIM - Amount of time spent in warm-up (min)

Variable Name:
CVDWTIM
SAS Label:
Amount of time spent in warm-up (min)
English Text:
Amount of time spent in warm-up (minutes)
English Instructions:
If warm-up is completed, the time is always 2 minutes.
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2 2 463 463
. Missing 29 492

CVXWRPE - Warm-up rating of perceived exertion

Variable Name:
CVXWRPE
SAS Label:
Warm-up rating of perceived exertion
English Text:
Warm-up rating of perceived exertion (RPE)
English Instructions:
RPE is a scale of perceived exertion with a range of 6-20 with 6 being equivalent to a low level of effort and 20 being maximal exertion. The exam is stopped if the participant rates his/her effort greater than 17. (See CV Fitness Procedures Manual, Chapters 3.9.7 and 3.10.1)
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
6 to 20
Code or Value Value Description Count Cumulative Skip to Item
6 to 17 Range of Values 463 463
. Missing 29 492

CVDWHR - Warm-up heart rate (per min)

Variable Name:
CVDWHR
SAS Label:
Warm-up heart rate (per min)
English Text:
Warm-up heart rate (per minute)
English Instructions:
Heart rate is taken by the automated blood pressure/heart rate monitor and captured directly into the computer system. (See CV Fitness Procedures Manual, Sections 3.9.6 and 4.4.4)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
84 to 166 Range of Values 463 463
. Missing 29 492

CVDS1S - Stage 1 speed (mph)

Variable Name:
CVDS1S
SAS Label:
Stage 1 speed (mph)
English Text:
Stage 1 speed (miles per hour)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 3.7
Code or Value Value Description Count Cumulative Skip to Item
2.7 to 3.7 Range of Values 463 463
. Missing 29 492

CVDS1G - Stage 1 grade (% incline)

Variable Name:
CVDS1G
SAS Label:
Stage 1 grade (% incline)
English Text:
Stage 1 grade (% incline)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 14.5
Code or Value Value Description Count Cumulative Skip to Item
3 to 7 Range of Values 463 463
. Missing 29 492

CVDS1TIM - Amount of time spent in Stage 1 (min)

Variable Name:
CVDS1TIM
SAS Label:
Amount of time spent in Stage 1 (min)
English Text:
Amount of time spent in Stage 1 (minutes)
English Instructions:
If Stage 1 is completed, the time is always 3 minutes.
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.97 to 3 Range of Values 463 463
. Missing 29 492

CVXS1RPE - Stage 1 rating of perceived exertion

Variable Name:
CVXS1RPE
SAS Label:
Stage 1 rating of perceived exertion
English Text:
Stage 1 rating of perceived exertion (RPE)
English Instructions:
RPE is a scale of perceived exertion with a range of 6-20 with 6 being equivalent to a low level of effort and 20 being maximal exertion. The exam is stopped if the participant rates his/her effort greater than 17. (See CV Fitness Procedures Manual, Chapters 3.9.7 and 3.10.1)
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
6 to 20
Code or Value Value Description Count Cumulative Skip to Item
6 to 19 Range of Values 460 460
. Missing 32 492

CVDS1HR - Stage 1 heart rate (per min)

Variable Name:
CVDS1HR
SAS Label:
Stage 1 heart rate (per min)
English Text:
Stage 1 heart rate (per minute)
English Instructions:
Heart rate is taken by the automated blood pressure/heart rate monitor and captured directly into the computer system. In the event the heart rate is not captured automatically at the end of stage 1, the technician would manually enter the readings from the heart rate monitor. (See CV Fitness Procedures Manual, Sections 3.9.8 and 4.4.6)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
103 to 190 Range of Values 463 463
. Missing 29 492

CVDS2S - Stage 2 speed (mph)

Variable Name:
CVDS2S
SAS Label:
Stage 2 speed (mph)
English Text:
Stage 2 speed (miles per hour)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 3.7
Code or Value Value Description Count Cumulative Skip to Item
2.7 to 3.7 Range of Values 461 461
. Missing 31 492

CVDS2G - Stage 2 grade (% incline)

Variable Name:
CVDS2G
SAS Label:
Stage 2 grade (% incline)
English Text:
Stage 2 grade (% incline)
English Instructions:
See CV Fitness Procedures Manual, Appendix J for speed and grade table by protocol and stage
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
0 to 14.5
Code or Value Value Description Count Cumulative Skip to Item
7.5 to 12.5 Range of Values 461 461
. Missing 31 492

CVDS2TIM - Amount of time spent in Stage 2 (min)

Variable Name:
CVDS2TIM
SAS Label:
Amount of time spent in Stage 2 (min)
English Text:
Amount of time spent in Stage 2 (minutes)
English Instructions:
If Stage 2 is completed, the time is always 3 minutes.
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.8 to 3 Range of Values 461 461
. Missing 31 492

CVXS2RPE - Stage 2 rating of perceived exertion

Variable Name:
CVXS2RPE
SAS Label:
Stage 2 rating of perceived exertion
English Text:
Stage 2 rating of perceived exertion (RPE)
English Instructions:
RPE is a scale of perceived exertion with a range of 6-20 with 6 being equivalent to a low level of effort and 20 being maximal exertion. The exam is stopped if the participant rates his/her effort greater than 17 and confirms unable to continue the test. (See CV Fitness Procedures Manual, Chapters 3.9.7 and 3.10.1)
Target:
Both males and females 12 YEARS - 15 YEARS
Hard Edits:
6 to 20
Code or Value Value Description Count Cumulative Skip to Item
6 to 20 Range of Values 457 457
. Missing 35 492

CVDS2HR - Stage 2 heart rate (per min)

Variable Name:
CVDS2HR
SAS Label:
Stage 2 heart rate (per min)
English Text:
Stage 2 heart rate (per minute)
English Instructions:
Heart rate is taken by the automated blood pressure/heart rate monitor and captured directly into the computer system. In the event the heart rate is not captured automatically at the end of stage 2, the technician would manually enter the readings from the heart rate monitor. (See CV Fitness Procedures Manual, Sections 3.9.9 and 4.4.7)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 208 Range of Values 461 461
. Missing 31 492

CVDRTIM - Amount of time spent in recovery (min)

Variable Name:
CVDRTIM
SAS Label:
Amount of time spent in recovery (min)
English Text:
Amount of time spent in recovery (minutes)
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.08 to 3.3 Range of Values 463 463
. Missing 29 492

CVDR1HR - Heart rate after 1 minute recovery

Variable Name:
CVDR1HR
SAS Label:
Heart rate after 1 minute recovery
English Text:
Heart rate after 1 minute recovery
English Instructions:
Heart rate is taken by the automated blood pressure/heart rate monitor and captured directly into the computer system.
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
98 to 188 Range of Values 461 461
. Missing 31 492

CVDR2HR - Heart rate after 2 minutes recovery

Variable Name:
CVDR2HR
SAS Label:
Heart rate after 2 minutes recovery
English Text:
Heart rate after 2 minutes recovery
Target:
Both males and females 12 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
91 to 169 Range of Values 461 461
. Missing 31 492