To examine the effect of endurance on the relationship between grip force and measures of functional capacity and disease activity, we performed a cross-sectional study at the University Department of Rheumatology, Physical medicine and Rehabilitation from January 2017 to August 2018. Functional capacity of the hand was measured by ABILHAND-RA questionnaire and disease activity was assessed by the Disease Activity Score (DAS-28-CRP). All participants underwent dynamometric measurements of maximal grip force and hand grip endurance during repeated gripping. We analyzed the data from 34 RA patients at the median (IQR) age of 57 (51–61), 31 (91%) of them women, and 44 healthy participants at the age of 55 (50–59), 39 (89%) of them women. The moderating effect of endurance on the correlation between maximum grip force and the ABILHAND-RA score was not significant in healthy participants (b = 0.000, 95% CI − 0.005–0.004, p = 0.862), but it was in RA patients (b = 0.003, 95% CI 0.000–0.005, p = 0.027). In RA patients, the effect of maximum grip force on the ABILHAND-RA score increased with the increase in hand grip endurance. In RA patients, the interaction between endurance and grip force significantly explained the 15% more variance of the disease activity than main effects of these two measures, age, gender and body mass index alone. Hand grip endurance during repeated gripping affects the correlation between maximum grip force and the ABILHAND-RA score in a pattern that differs in RA patients and in the healthy population. In RA patients, hand grip endurance significantly moderates the correlation between maximum grip force and the DAS-28-CRP.
Rheumatoid arthritis Functional performance Hand strength Endurance
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All authors were involved in the study design. Ines Doko and Simeon Grazio were local investigators. Žarko Bajić undertook the statistical analyses and the interpretation of the results and contributed significantly in writing the manuscript. Amir Dubravić is an author of the measuring algorithm and he wrote a significant part of the Method section of the manuscript. Merita Qorolli contributed in writing of the Introduction and Discussion parts of the manuscript. Simeon Grazio masterminded and contributed significantly in writing the manuscript and merited for critical revision of the manuscript. All authors participated in the preparation of the final version of the manuscript, read and approved the version to be submitted.
Compliance with ethical standards
Conflict of interest
Ines Doko, Žarko Bajić, Amir Dubravić and Merita Qorolli declare that they have no conflict of interest. Simeon Grazio is a member of the Editorial Board of Rheumatology Int.
All procedures performed were in accordance with ethical standards of the institutional research committee (protocol number EP–13030/11–8), and with the 1964 Helsinki Declaration and its later amendments.
Informed consent was obtained from all individual participants included in the study.
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