Test-retest reliability and concurrent validity of three different handgrip dynamometers (Jamar, Jamar Plus+ and Biodex) in healthy young adults.

Background: Handgrip strength (HGS) is a key indicator of upper limb function and overall health. While the Jamar dynamometer is considered the gold standard for HGS assessment, alternatives like the Jamar Plus+ and Biodex have emerged, though their reliability and agreement remain underexplored.

Aim: To evaluate the test-retest reliability and agreement of the Jamar, Jamar Plus+, and Biodex dynamometers in healthy young adults.

Methods: This exploratory cross-sectional study included 35 participants (22 females, 13 males; mean age 23.4 years). HGS was assessed using the three devices, following standardised protocols, with retest after 7 days. Reliability was analysed using the Intraclass Correlation Coefficient (ICC), Standard Error of Measurement (SEM), and Minimal Detectable Change (MDC). Agreement was examined through Bland-Altman plots and Limits of Agreement (LoA %).

Results: Jamar and Jamar Plus+ showed excellent reliability (ICC = 0.96-0.98) and strong agreement, with narrow LoA percentages and low measurement error, especially on the non-dominant hand. In contrast, comparisons involving the Biodex revealed wider LoA (up to ±73%) and higher SEM and MDC values, indicating lower agreement with handheld devices. These discrepancies are likely due to differences in measurement principles, hand positioning, and unit conversion. Male participants showed significantly higher grip strength across all instruments.

Conclusion: The Jamar and Jamar Plus+ can be used interchangeably. The Biodex may be considered when appropriate adjustments are made, though its agreement with handheld dynamometers is limited. These findings highlight the need for standardised protocols and further research to ensure consistent and reliable HGS assessment across devices.