Relative Validity and Reliability of Isometric Lower Extremity Strength Assessment in Older Adults by Using a Handheld Dynamometer.

BACKGROUND

Handheld dynamometry (HHD) is a practical alternative to traditional testing of lower extremity strength. However, its reliability and validity across different populations and settings are not clear.

HYPOTHESIS

We hypothesize that HHD is a valid and reliable device to assess lower extremity strength in a population of older adults.

STUDY DESIGN

Cross-sectional/cohort.

LEVEL OF EVIDENCE

Level 3.

METHODS

This study included 258 older adults (≥65 years). Isometric knee extension and flexion force were measured by 1 examiner, using an HHD (n = 222), including 3 repetitions to calculate within-day intrarater reliability. These measurements were repeated by the examiner in a subgroup (n = 23) to analyze intrarater reliability over a test-retest period of on average 8 weeks. In addition, HHD force measures were performed by a second examiner (n = 29) to analyze interrater reliability. In another subgroup (n = 77), isometric knee extension and flexion torque were measured by 1 examiner using both the HHD and Biodex System 4 to assess relative validity.

RESULTS

HHD and Biodex measurements were highly correlated and showed excellent concurrent validity. HHD systematically overestimated torque as compared with Biodex by 8 N·m on average. Same-day intrarater intraclass correlation coefficients (ICCs) ranged from 0.97 to 0.98. Interrater reliability ICCs ranged from 0.83 to 0.95.

CONCLUSION

HHD represents a reliable and valid alternative to Biodex to rank individuals on leg strength, or to assess within-person changes in leg strength over time, because of the high validity and reliability. The HHD is less suited for absolute strength assessment because of significant systematic overestimations.

CLINICAL RELEVANCE

Clinicians are encouraged to use HHD to rank older adults on leg strength, or to assess within-person changes in leg strength over time, but not to compare readings with cut-offs or normative values.