Accuracy and Reliability of Grip Strength Measurements: A Comparative Device Analysis

Abstract

Background: Grip strength is widely used as a surrogate parameter for functional status. The current gold standard, the JAMAR^® Hydraulic Dynamometer (JAMAR^® Hydraulic), presents challenges for individuals with painful finger joints or low grip strength. Therefore, the objective of this observational study was to assess comparability across the JAMAR^® Smart, the Martin Vigorimeter and the gold standard. Additionally, the intrasubject and intersession reliability of all three devices were examined, which are essential for quality control before generating normative data. Methods: Forty healthy participants (aged 37.0 ± 11.3 years) were included, and a subset of 20 participants was randomly selected for retesting. Grip strength testing involved five attempts per measurement device. Results: Intrasubject reliability was excellent (ICC3,1: 0.91-0.97), and a strong correlation (ICC3,1: 0.90-0.98) was found between the first attempt and the best of five as well as between the best of two or three attempts and the best of five, demonstrating robust reliability across multiple measures. Intersession reliability was good to excellent (ICC3,1: 0.85-0.97) across all three devices, which was confirmed by Bland-Altman analysis. The PCC (r) revealed moderate to very strong agreement with the current gold standard JAMAR^® Hydraulic (r = 0.68-0.98), with increased differences between the Martin Vigorimeter and the JAMAR^® Hydraulic measurements, particularly at low and high values. Conclusions: The proposed devices are suitable for test-retest analysis with 2-3 attempts. Despite high correlations between all three devices, the diverging levels of agreement between the Martin Vigorimeter and the established gold standard warrant caution against using these devices interchangeably.

Keywords: hand strength; physical therapy; reproducibility of results; test-retest reliability; validation studies.

Figure A1

(a–f) Boxplots of attempts 1–5 for each device and both hands.

Figure 1

CONSORT flow diagram of the progression of study participants in groups A and B through the phases of the study. N = number of participants; MGS = maximum grip strength.

Figure 2

(a–c) JAMAR^® Hydraulic, JAMAR^® Smart, and Martin Vigorimeter.

Figure 3

(a–f) Bland-Altman plots of differences between session 1 and session 2 for both dominant (a–c) and nondominant (d–f) hands for all 3 devices (n = 20). The limits of agreement are represented as dotted lines (from −1.96 to +1.96 SD). LL = lower limits of agreement; UL = upper limits of agreement. Mean differences (MDs) are shown as solid black lines. • = outliers. (a) JAMAR^® Hydraulic, dominant (green dots); (b) JAMAR^® Smart, dominant (blue dots); (c) Martin Vigorimeter, dominant (yellow dots); (d) JAMAR^® Hydraulic (green dots), nondominant; (e) JAMAR^® Smart, nondominant (blue dots) and (f) Martin Vigorimeter, nondominant (yellow dots).

Figure 4

(a–d) Bland–Altman analyses of comparisons of the JAMAR^® Smart and Martin Vigorimeter to the gold standard JAMAR^® Hydraulic, assessing MGS in both the dominant (a,b) and nondominant (c,d) hands (n = 40). Mean differences (MDs) are shown as solid black lines, and the trendlines are presented as orange dotted lines. LL = lower limit of agreement; UL = upper limit of agreement (limits of agreement are represented as dashed black lines (from −1.96 to +1.96 SD)). (a) JAMAR^® Hydraulic vs. JAMAR^® Smart, dominant; (b) JAMAR^® Hydraulic vs. Martin Vigorimeter, dominant; (c) JAMAR^® Hydraulic vs. JAMAR^® Smart, nondominant and (d) JAMAR^® Hydraulic vs. Martin Vigorimeter, nondominant.