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.
Participants aged 6 years and older, who did not meet any of the exclusion criteria, were eligible for this component.
Participants were excluded from this component 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 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 2011-2012, among those who were tested, less than 0.2% of the participants younger than 20 years old were tested in a seated position. Therefore information on testing position was not released for participants younger than 20 years due to disclosure concern. Researchers who are interested can access this information through the NCHS Research Data Center. Information on testing position for participants 20 years and older is included in the present dataset.
Prior conditions may affect a person’s grip strength; therefore, we collected data on whether the participant has ever had surgery on his/her hands or wrists for arthritis or carpal tunnel syndrome. In 2011-2012, among those who were tested, less than 0.1% of the participants younger than 20 years old reported ever had hand/wrist surgery for arthritis or carpal tunnel syndrome. Due to potential disclosure risk, this prior surgery information is only released for participants 20 years and over in the present dataset. Information on younger participants is only available through the Research Data Center.
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 NHANES Muscle Strength/Grip Test Procedure Manual available on the NHANES website.
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 NHANES examination sample weights should be used to analyze the muscle strength/grip test data. Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.