In middle and older-aged adults, handgrip strength predicts all-cause and disease-specific mortality, including mortality related to cardiovascular disease, chronic obstructive pulmonary disease, and cancer [1–7]. Furthermore, among older adults in particular, decreased handgrip strength is associated with greater risk of frailty, and loss of physical function, mobility, lean mass, and overall muscular strength and power [8–14]. Handgrip strength is generally recognized as a surrogate measure of whole-body strength and can be used clinically to assess for age-related deterioration in function and health status associated with frailty [3, 8, 14].
Frailty and loss of function and health are also associated with sarcopenia, a geriatric syndrome characterized by loss of muscle and strength [15]. Globally, the prevalence of sarcopenia among adults aged 60 years and over is estimated to be at least 10% [16]. Sarcopenia not only predicts mortality among community-dwelling and acutely ill older adults [17–19], but is also related to functional decline, loss of independence, and hospitalization [20–22]. Exercise interventions can successfully prevent and reverse muscle loss and functional decline [23, 24], but clinical assessment is needed to identify older adults who are at risk [16].
Muscle strength is a biomarker for sarcopenia [25], and handgrip strength measured with dynamometry has been recommended for diagnostic purposes [26, 27]. However, although absolute and precise gender-specific cut points for normal handgrip strength have been identified, these cut points do not consider potential differences between measurement devices. Currently, there is no universally agreed-upon device or procedure for clinical measurement [26, 27]. In fact, a systematic review of handgrip measurement protocols found incomplete reporting of both the procedures and the devices used [28]. The Jamar hydraulic dynamometer is widely used, but multiple other devices are available for clinical and research purposes [29]. Recent systematic reviews of handgrip strength named at least 10 different devices used for measurement [4, 6, 30]. Among these, the Jamar hydraulic dynamometer and Smedley spring dynamometer were the most frequently identified [4, 6, 30].
There are similarities and differences between the two dynamometers. Both devices weigh approximately 0.66 kg and provide force measurements up to 90 kg. However, the Jamar hydraulic dynamometer displays force using an analog dial with 2-kilogram increments, so smaller more discrete measurements must be interpreted by the operator. By comparison, the Smedley uses a digital display that provides force measurements to the nearest 0.l kg, so operator interpretation is eliminated. Also, both have adjustable handles, to modify grip size, although the Jamar has a concave grip while the Smedley grip is straight. Finally, the Jamar is metal, so the surface temperature can be cooler to touch than the Smedley, which is plastic.
The differences in these two devices may influence the validity and reliability of measurement. To date, we can find only one study comparing the Jamar and Smedley dynamometers in older adults [31]. Although measurements obtained by the two devices were similar, they were statistically different and influenced by gender and age. Specifically, differences were greater in women compared to men, and in older compared to younger participants [31]. Moreover, only a single trial was used for comparison, so reliability over time could not be evaluated. Therefore, to assess validity and reliability, we compared sequential grip strength measurements in older adults over a two-day period using a Jamar hydraulic (Patterson Medical, USA) versus a Smedley spring (Takei Scientific Instruments, Japan) handgrip dynamometer. Our secondary aim was to evaluate the effect of gender and age on agreement between devices.