Reliability and criterion validity of a low-cost handgrip dynamometer: The Camry

BackgroundHandgrip strength has been related with multiple health outcomes, including all-cause mortality and morbidity. Handgrip testing is a highly valid and reliable method, included in evidence-based fitness test batteries from preschool to older ages. Previously, Jamar and TKK dynamometers have shown good reliability and validity against known weights. However, the cost of these dynamometers is the major limitation for implementing handgrip strength testing in certain countries and settings, as well as at large scale. Recently, a ten times cheaper model (Camry Dynamometer) has been used in fitness surveillance systems, though its reliability and validity, compared to known weights and other well-validated dynamometers, remains unknown. Therefore, the aims of the current study were to test to examine test-retest reliability, inter-model reliability (comparing a Camry dynamometer with 3000 uses versus a new Camry dynamometer), and inter-instrument reliability (Camry versus TKK dynamometer) of Camry dynamometer, using calibrated known weights. MethodsA digital TKK 5401 dynamometer and two Camry EH101, a new and an "old" (3000 uses), dynamometers were used. Intra-instrument and inter-instrument reliability, and criterion related validity were assessed comparing the measures of the dynamometers with calibrated weights using the Bland and Altmans method. ResultsIntra-instrument (retest minus test) reliability was very high (systematic error for test-retest reliability: New Camry = 0.01{+/-}0.49kg; Old Camry = -0.10{+/-}0.49kg; TKK = 0.14{+/-}0.77kg). The comparison between instruments showed small mean differences between Camry dynamometers and TKK (New Camry VS TKK: 0.84{+/-}0.79kg; Old Camry VS TKK: 0.88 {+/-}0.85kg). The systematic error between New and Old Camry dynamometers was 0.03{+/-}0.57kg. Criterion-related validity showed smaller magnitude systematic errors in the Camry than TKK instruments (New Camry: -0.21{+/-}0.35kg; Old Camry: -0.18{+/-}0.79kg; TKK: -1.07{+/-}0.75kg). ConclusionsOur results support that Camry dynamometer has an excellent reliability and validity and is therefore a more affordable alternative for handgrip strength assessment. Our results also indicate a good durability of these devices, and that calibration is not necessary, even after several thousands of uses.