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The aim of our study was to test grip strength and assess the effects of various degrees of standardization on repeatability and level of peak force. Sixteen healthy persons and eight subjects with an impaired hand function have been tested using a strain-gauge dynamometer. We compared four measurement protocols: (A) the subject is free to assume a comfortable arm position; (B) the subject is also free to assume a comfortable arm position but in addition a challenging stimulus to exceed a previous maximal effort, is given; (C) the arm was held in a predescribed and partly fixated position, as recommended by the American Society of Hand Therapists; (D) the position of the dynamometer is standardized using two reference points both on the hand and on the dynamometer. We found high test-retest reliabilities for each measurement protocol without any significant difference. There were, however, significant differences in strength level. With measurements according to protocol B the highest peak values were noted. Since the measurement protocol B combined good reliability with realistic peak forces, this procedure seems most suitable for grip strength measurements.
Spijkerman et al. (2020) studied this question.