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 dear. 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 (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.

Automated summary

This study demonstrates that handheld dynamometry (HHD) is a reliable and valid alternative to traditional testing for assessing lower extremity strength in older adults. HHD measurements showed a high correlation and excellent concurrent validity with Biodex measurements. However, HHD systematically overestimated torque.