Reliability and Concurrent Validity of a Low-Cost Handgrip Dynamometer: The Camry.

Abstract

Importance: Handgrip testing is highly valid and reliable, but the high cost of dynamometers limits their use in some settings. A more affordable option, the Camry dynamometer, has recently been used in fitness surveillance; however, its reliability and validity compared with known weights and well-validated models remain unknown.

Objective: To investigate test-retest reliability, intermodel reliability (new vs. old Camry), and interinstrument reliability (Camry vs. TKK dynamometer) and concurrent validity of the Camry dynamometer by using calibrated known weights.

Design: Comparison study with a digital TKK 5401 dynamometer and two Camry EH101 dynamometers (new and old, with more than 3,000 uses).

Outcomes and measures: Intrainstrument and interinstrument reliability and concurrent validity were assessed to compare measures of the dynamometers with calibrated weights using the Bland-Altman method.

Results: Intrainstrument (retest minus test) reliability was very high (systematic error for test-retest reliability): new Camry, M = 0.01 kg (SD = 0.49); old Camry, M = -0.10 kg (SD = 0.49); TKK, M = 0.14 kg (SD = 0.76). Comparison showed small mean differences between Camry dynamometers and TKK (new Camry vs. TKK, M = 0.84 kg, SD = 0.79; old Camry vs. TKK, M = 0.88 kg, SD = 0.85). The mean systematic error between the new and old Camry dynamometers was 0.03 kg (SD = 0.57). Concurrent validity showed smaller magnitude systematic errors in the Camry than TKK: new Camry, M = -0.21 kg (SD = 0.35); old Camry, -0.18 kg (SD = 0.79); TKK, M = -1.07 kg (SD = 0.75).

Conclusions and relevance: The Camry dynamometer is highly reliable and valid and is a more affordable alternative for handgrip strength assessment. Plain-Language Summary: Handgrip strength is an important measure of health and is linked to outcomes such as overall mortality and illness. Testing handgrip strength is useful for health and fitness-related professionals, including occupational therapists, to track rehabilitation progress. However, the cost of the dynamometers limits their use in some places or large-scale studies. Recently, a cheaper alternative, the Camry dynamometer, has been used, but its accuracy compared with known weights or other validated devices has not been confirmed. This study tested the reliability and accuracy of two Camry dynamometers (a new and an old device) versus the TKK dynamometer and known weights. Results showed that the Camry dynamometer is highly reliable, valid, and durable and remains accurate even after many uses. The findings could make handgrip strength testing more accessible in health care and fitness evaluations.