Provocation of delayed-onset muscle soreness in the human jaw-closing muscles Kemal S. Tu ¨ rker a,b,c, *, Michail Koutris d , N. Ceren Su ¨ mer c , E. Sibel Atıs ¸ c , Ian R. Linke e , Frank Lobbezoo d , Machiel Naeije d a Ege University, Center for Brain Research, Bornova, Izmir, Turkey b Ege University, Faculty of Medicine, Department of Physiology, Bornova, Izmir, Turkey c Ege University, Faculty of Medicine, Department of Biophysics, Bornova, Izmir, Turkey d Department of Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA, Research Institute MOVE, University of Amsterdam and VU University Amsterdam, The Netherlands e University of Adelaide, Department of Electrical Engineering, Adelaide 5000, Australia 1. Introduction Human jaw muscles are of vital importance for the biological and social well-being of humans. They act as a group of jaw closers or jaw openers and are important for functions like chewing, talking, drinking, and smiling, which are essential for the human race. 1 Jaw-closing muscles are considered to differ in several aspects from muscles in other parts of the human body. Human jaw-closing muscles contain large, homogeneous archives of oral biology 55 (2010) 621–626 article info Article history: Accepted 29 May 2010 Keywords: Eccentric exercises Delayed-onset muscle soreness (DOMS) Human jaw-closing muscles Jaw-muscle fatigue Jaw-muscle pain Visual analogue scale (VAS) Maximum mouth opening Maximum voluntary bite force abstract Eccentric contractions of jaw-closing muscles are difficult to perform. This may explain why fatigue-inducing experiments performed so far suggest the jaw-closing muscles to be fatigue resistant. Aim of this study was to construct an apparatus that can impose intense eccentric contractions to the jaw-closing muscles, and to test the hypothesis that eccentric contractions can provoke symptoms of delayed-onset muscle soreness (DOMS) in these muscles. The provocation apparatus consists of two tungsten arms connected by a hinge axis on one end. Participants bite with their anterior teeth on biting plates located on the other end. Each time the experimenter gradually releases the compression force of the apparatus’ rubber tubings, the mouth is forced open and the jaw-closing muscles perform an eccentric contraction. Six male participants performed eccentric contractions of their jaw-closing muscles in six sets of exercises, each lasting 5 min, and with 1 min of rest in between. Each set consisted of 60 open-close movements. Before and after the exercises, and after 24 h, 48 h, and 1 week, feelings of fatigue and pain, the maximum mouth opening without pain, muscles’ tenderness to palpation and the maximum voluntary bite force were recorded. After 24 h and 48 h, the levels of fatigue and pain were elevated, the maximum mouth opening without pain was smaller, and five of the participants reported tenderness to palpation. The maximum voluntary bite force was also smaller after 24 h. These findings indicate that this novel apparatus is successful in inducing DOMS in the jaw-closing muscles. # 2010 Elsevier Ltd. All rights reserved. * Corresponding author at: Marie Curie Chair of the European Union, Center for Brain Research, Department of Physiology, Faculty of Medicine, Ege University, Frome Road, Bornova, Izmir, Turkey. Tel.: +90 2323901810; fax: +90 2323432653. E-mail addresses: turker.77@gmail.com, kemal.turker@adelaide.edu.au (K.S. Tu ¨ rker). available at www.sciencedirect.com journal homepage: http://www.elsevier.com/locate/aob 0003–9969/$ – see front matter # 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.archoralbio.2010.05.015