BACKGROUND: Muscle response in older adults is believed to decrease with maximal muscle strength, although it has not been adequately assessed; further, the relationship between frailty and muscle response remains unexamined. OBJECTIVES: This study aimed to develop a practical method for measuring muscle response using grip strength in older adults and to clarify the relationship between frailty and grip strength response. DESIGN, SETTING, AND PARTICIPANTS: We performed a cross-sectional, clinical, observational study. A total of 248 patients (94 men and 154 women, mean age: 78.2 years) who visited the outpatient unit in the Integrated Healthy Aging Clinic of our Hospital for the first time were enrolled. MEASUREMENTS: Using a grip strength measuring device originally developed by us, we measured grip strength response indices, such as reaction time, time constant, rate of force development (response speed), and maximum grip strength. Grip strength response indices were compared among three groups (robust, pre-frail, and frail) according to the Fried and Kihon checklist assessments for frailty. RESULTS: Based on Fried's assessment, marked differences were found between groups not only in maximal grip strength but also in response time and response speed. Based on the Kihon checklist assessment, there was no significant difference in response time; however, a considerable difference in response speed for the left hand was observed. Moreover, according to the Kihon checklist assessment, some cases showed differences in muscle response although not in maximal muscle strength. CONCLUSIONS: The response speed of grip strength was suggested to decrease with frailty. The results suggest that measurement of grip strength response in both hands is useful to examine the relationship between frailty and grip strength response.
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