This file provides data from the muscle strength/grip test component for the combined samples from NHANES 2012 and the NHANES National Youth Fitness Survey (NNYFS).
The muscle strength/grip test component measured 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.
This dataset can only be accessed through the NCHS Research Data Center (RDC). Instructions for requesting use of these data are available at the RDC website (http://www.cdc.gov/rdc/).
NNYFS and NHANES 2012 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 they should only do 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, 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 his/her 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 NHANES 2012 and NNYFS combined 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 performed with the opposite hand that was assigned to be tested first, unless the participant was physically limited and/or had only had one hand that was eligible for the test.
Detailed descriptions of the protocol are provided in the Muscle Strength/Grip Test Procedure Manual available on the NHANES (http://www.cdc.gov/nchs/data/nhanes/nhanes_11_12/Muscle_Strength_Proc_Manual.pdf) and NNYFS websites (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.
The analysis of the combined NHANES and NNYFS muscle strength/grip test data must be conducted using the appropriate survey design variables, sample weights, and the basic demographic variables. Please refer to the NNYFS Analytic Guidelines for further details on the use of sample weights and other analytic issues