NHANES National Youth Fitness Survey

NNYFS 2012 Data Documentation, Codebook, and Frequencies

Muscle Strength - Grip Test (Y_MGX)

Data File: Y_MGX.xpt

First Published: September , 2013

Last Revised: NA

Locator Record

Title: Muscle Strength - Grip Test (Y_MGX )
Contact Number: 1-866-441-NCHS
Years of Content: 2012
First Published: September , 2013
Revised: NA
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject: NNYFS muscle strength/grip test component measured the isometric grip strength for participants aged 6 to 15 years, using a handgrip dynamometer
Record Source: NNYFS 2012
Survey Methodology: NNYFS 2012 is a stratified multistage probability sample of the non-institutionalized population aged 3 to 15 years in the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

The muscle strength/grip test component measured the isometric grip strength using a handgrip dynamometer. The goals of this component were to provide: 1) nationally representative data on muscle strength; 2) prevalence estimates of children with poor muscle strength; and 3) data to study the association between muscle strength and other health conditions and risk factors, such as obesity, physical activity and dietary patterns.

Eligible Sample

Participants aged 6-15 years, who did not meet any of the exclusion criteria, were eligible for this component.

Participants were excluded from this component if a doctor had ever said they should not participate in sports or other activities because of a health condition or do only sports or other physical activities recommended by a doctor. Participants were excluded if they were unable to hold the dynamometer with both hands (e.g., missing both arms, both hands, or thumbs on both hands, or paralyzed in both hands). Participants who were able to grip the dynamometer with one hand still performed the component. Participants who had surgery on either hand or wrist in the last three months were not tested on that particular hand.

Protocol and Procedure

In this component, muscle strength was measured through a grip test using a handgrip dynamometer. A trained examiner explained and demonstrated the protocol to the participant. The examiner then adjusted the grip size of the dynamometer to the participant’s hand size and asked the participant to squeeze the dynamometer for a practice trial. The practice trial was to determine if the procedure was understood by the participant and the grip size properly adjusted.

After the practice, the participant was asked to use one of the hands to squeeze the dynamometer as hard as possible, exhaling while squeezing to avoid build-up of intra-thoracic pressure. The test was then repeated for the other hand.  Each hand was tested three times, alternating hands between trials with a 60-second rest between measurements on the same hand.

The grip test was performed in the standing position unless the participant was physically limited. In this NNYFS sample, less than 0.2% of the participants were tested in a seated position.

The participant was randomly assigned to start the test with his/her dominant or non-dominant hand. The practice trial was usually proformed with the opposite hand that was assigned to be tested first, unless the participant was physically limited and only had one hand that was eligible for the test.

Detailed descriptions of the protocol are provided in the NNYFS Muscle Strength/Grip Test Procedure Manual available on the NNYFS website at: http://www.cdc.gov/nchs/nnyfs/manuals.htm.

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.

 Grip test status code (MGDEXSTS):

This derived variable indicates the following for each participant:

1 = Completed test on both hands - the participant performed the test on both hands.

2 = Completed test on only one hand - due to physical limitations, the participant only performed test on one of the hands.

3 = Did not perform test - Grip test did not take place due to various reasons (such as no time, arrived late/left early, refusal, illness, emergency, or equipment failure).

Combined grip strength (MGDCGSZ):

The combined grip strength was calculated as the sum of the largest reading from each hand, and expressed in kilogram. This variable was not calculated for participants who only performed the test on one hand.

Analytic Notes

The NNYFS examination sample weights should be used to analyze the muscle strength/grip test data. Please refer to the NNYFS Analytic Guidelines for details on the use of sample weights and other analytic issues.

References

N/A.

Codebook and Frequencies