Galley Proof 4/11/2016; 9:02 File: ies–1-ies646.tex; BOKCTP/xhs p. 1 Isokinetics and Exercise Science -1 (2016) 1–8 1 DOI 10.3233/IES-160646 IOS Press Adaptation mechanisms of the knee extensors contractile properties in response to short-term stretch-shortening exercise training János Négyesi a,b,∗ , Márk Váczi c , Olivér Mátyás Magyar b , Milan Pantovic d , József Tihanyi a and Levente Rácz e a Department of Biomechanics, Kinesiology and Informatics, University of Physical Education, Budapest, Hungary b Fájdalom Ambulancia, Budapest, Hungary c Institute of Sport Sciences and Physical Education, University of Pécs, Pécs, Hungary d Faculty of Sport and Physical Education, University of Novi Sad, Novi Sad, Serbia e Research Institute of Sport Science, University of Physical Education, Budapest, Hungary Received 15 April 2016 Accepted 30 September 2016 Abstract. BACKGROUND: The effects of stretch-shortening cycle (SSC) training are well-described in the literature but the mechanism of how it changes the characteristics of the SSC moment-time curve and contraction velocity is unknown. OBJECTIVE: The purpose of the present study was to investigate the adaptation mechanisms of the knee extensor contractile properties in response to a short-term unilateral SSC exercise training. METHODS: Twenty-four subjects (22.9 ± 2.4 years) were randomised to an experimental or control group. A custom-built dynamometer was used to test the mechanical properties of the quadriceps muscle. Each subject participated in the pre-, and post-test session. Subjects in the experimental group participated in nine training sessions and performed maximal voluntary stretch-shortening cycle contractions on the dynamometer. Changes in the knee extensor contractile properties were measured from an SSC curve. RESULTS: Multivariate analysis of variance (MANOVA) revealed a significant multivariate effect for the measured variables in relation to group assignment. SSC exercise training significantly changed concentric moment (MCC, F1,22 = 96.2, p = 0.000), and contraction velocity (F1,22 = 125.6, p = 0.000) resulting in a 29.6% improvement in concentric peak angular velocity (ω). Stepwise multiple regression analysis showed that ω was significantly predicted only by MCC (r = 0.751, p = 0.005). CONCLUSIONS: Short-term unilateral SSC exercise training modifies the characteristics of the SSC moment-time curve and contraction velocity through the mechanical adaptation of the knee extensor contractile properties. Keywords: Plyometric exercises, dynamometer, stretch-load 1. Introduction 1 The stretch-shortening cycle (SSC) is a complex 2 ∗ Corresponding author: János Négyesi, Department of Biome- chanics, Kinesiology and Informatics, University of Physical Educa- tion, Alkotás 44, 1123 Budapest, Hungary. Tel.: +36 30 522 6227; E-mail: j.negyesi88@gmail.com. muscle contraction in which the active stretch (ec- 3 centric contraction) of a muscle is followed by an 4 immediate shortening (concentric contraction) of the 5 same muscle. In exercise training, SSCs were used for 6 decades by individuals of various ages and training sta- 7 tus. In many sports, athletes perform maximum effort 8 jumps, sprints, and activities that involve rapid mus- 9 cle stretches. Following these stretches, the muscle is 10 ISSN 0959-3020/16/$35.00 c  2016 – IOS Press and the authors. All rights reserved uncorrected proof version