Participants
Our participants came from an existing longitudinal population-based community cohort study, the West China Health and Aging Trends Study (WCHAT), and the criteria for inclusion in the cohorts were people aged over 50 years. The initial intent of the WCHAT cohort was to establish a sample biobank in relation to the risk and prognosis of frailty, sarcopenia, and other geriatric syndromes. Our study aimed to evaluate the reliability and validity of the CAMRY dynamometer, and all participants performed handgrip strength measurements by two dynamometers simultaneously. Participants underwent sarcopenia and frailty screening in this research. Since the purpose of this study did not include screening for sarcopenia and frailty, we did not report it specifically.
To further explore the relationship between the two dynamometers used by different populations, we recruited both ethnic minorities who lived in the Tibetan Qiang Autonomous Prefecture in Sichuan Province and Han Chinese who lived in Chengdu in Sichuan Province. Tibetan Qiang Autonomous Prefecture in Sichuan Province is a plateau region at an altitude of 2000 m above sea level. People living there are Qiang, Tibetan and Yi ethnic minorities. The inclusion criteria of this study were as follows: (a) regular medical check-ups and good activity capacity; (b) compliance, defined as being serious about completing the study. Participants with fractures, trauma, deformities, acute exacerbation of joint diseases, rheumatoid disease, and gout, neuromuscular disease or other acute conditions affecting the grip strength test were excluded from this study. Individuals with unstable chronic disease or other conditions that may affect the hand functional examination were also excluded.
Finally, 1064 older adults aged 50–90 years, including 686 minorities and 378 Han Chinese, were enrolled from July to September 2021. The study was performed in accordance with the Declaration of Helsinki and approved by the Institutional Review Boards of West China Hospital, Sichuan University; the approval number is 2021(96). Written informed consent was obtained from all participants (the participants who were unable to write by providing a thumb print and the authorization letter were also signed by the legal guardians).
Grip strength measurements and procedures
First, two professional researchers explained how to use the two dynamometers and inquired about hand dominance. Dominance is defined as carrying out well-learned skills such as writing, holding chopsticks and throwing a ball. Generally, dominance is right-handed for the majority of people. Three grip strength tests were performed with two dynamometers for each hand, with a 10-min gap between the two devices. The test order of the two dynamometers was randomized in a 1:1 ratio, and randomization was carried out according to an Excel random number table. The second handle position has been assumed to be the most reliable position because it can help to maximize grip strength [5]. Both the Jamar dynamometer and CAMRY handgrip dynamometer were set in the second-handle position. Standard testing procedures of the Jamar hydraulic dynamometer are listed as follows: the subjects were seated in a comfortable chair without arm support, with the elbow in 90° flexion; the upper arm and lateral thorax were separated to ensure accuracy. This position is also recommended as a standardized grip strength testing guideline by the American Society of Hand Therapists (ASHT). Measurement of the CAMRY dynamometer was performed with the elbow fully extended in the standing position. In this research, grip strength testing was performed on two devices using a standardized testing protocol. Subjects were asked to squeeze the handle with maximal effort for at least 5 s and were given verbal encouragement. A break of at least 15-s was taken between the two tests to prevent fatigue effects. Both hands were tested three times with maximal effort, and average HGS values were mainly recorded and analysed. HGS values were measured in kilograms, and a kilogram was equal to 2.2046 pounds. The maximum value measured by the CAMRY dynamometer is 90 kg, and the limitation of accuracy is 0.1 kg. All participants strictly carried out HGS testing procedures under the supervision and instruction of two specialized researchers. A standard operation procedure (SOP) was developed in this study, and data were deposited into the unified database platform. Five research staff checked the data and treated missing values according to age and sex.
Other anthropometric measurements
The elements of anthropometry include height, weight, mid-upper arm circumference (MUAC), calf circumference (CC), waist circumference, hip circumference, blood pressure and pulse. Height and weight in this study were measured by the Tsinghua Tongfang height and weight tester. Participants were asked to remove shoes and heavy clothing before the height and weight measurements. Height and weight were measured twice, and the average of two measurements was taken for analysis. The MUAC was measured at the middle point of the upper arm on the dominant side. The midpoint of the acromion and olecranon was marked when the subject was in a stand position; subsequently, the researcher wrapped the measuring tape at the marked midpoint. CC measurement was performed with the subjects in a seated position. The knee and ankle bent at 90°, and a specialized researcher used tape located at the maximum horizontal distance around the calf of the right leg. Waist circumference and hip circumference were measured with the subjects in a standing position. A trained observer measured the waist circumference of the subject at the umbilicus level after deep expiration. Hip circumference was measured with a tape measure at the largest circle level of the hip while standing. Blood pressure and pulse were measured after a 5-min rest period in a seated position using an electronic sphygmomanometer.
Statistical analysis
Data analysis was performed with IBM SPSS (version 21.0), and the average grip strength value of six times was selected for further analysis. Study population baseline characteristics are presented as the mean ± standard deviation (SD). The reliability and measurement bias of the CAMRY dynamometer were assessed to determine accuracy and agreement with the Jamar device.
Relative reliability was assessed using the intraclass correlation coefficient (ICC). ICC was performed based on a single measurement, absolute agreement, and two-way random-effects model. Generally, ICC is considered good for 0.75–0.90 and excellent for 0.91–1.00 [9]. Absolute reliability includes the standard error of measurement (SEM) and minimal detectable change (MDC). SEM and MDC were calculated with the following formulas:
SEM = SD × \(\sqrt{1-\mathrm{ICC}}\); MDC = 1.96 × \(\sqrt{2}\)×SEM; SEM% = (SEM/mean) × 100% [10]; MDC% = (MDC/mean) × 100% [11] (SD: standard deviation of the difference; mean: average grip strength values of two dynamometers). Moreover, Spearman correlation and simple linear regression were also performed to assess correlations between the two devices. We considered Spearman correlation coefficients larger than 0.80 to be excellent.
The overall difference between the two dynamometers was determined through systematic bias and measurement error. Paired t tests and Bland–Altman analyses were performed to quantify the measurement bias of both dynamometers [12]. Systematic bias was expressed as the mean difference between two methods by Bland–Altman plots. The 95% limits of agreement (LOA) were defined as bias ± 1.96 SD, and SD was the standard deviation of the difference [13]. p < 0.05 indicated statistical significance.