Journal of Science and Medicine in Sport 16 (2013) 477–481 Contents lists available at SciVerse ScienceDirect Journal of Science and Medicine in Sport journal homepage: www.elsevier.com/locate/jsams Original research Whole-body vibration training improves flexibility, strength profile of knee flexors, and hamstrings-to-quadriceps strength ratio in females Konstantina Karatrantou a , Vassilis Gerodimos a,∗ , Konstantina Dipla b , Andreas Zafeiridis b a Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece b Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Greece article info Article history: Received 10 July 2012 Received in revised form 7 November 2012 Accepted 16 November 2012 Keywords: Vibration exercise Isokinetic torque Eccentric muscle contraction Isometric torque Reciprocal muscles Knee injury abstract Objectives: Short-term whole-body vibration training (WBVT) has emerged as an exercise method for improving neuromuscular performance and has been proposed for injury prevention and rehabilita- tion. This study investigated the effects of a short-term (≤2 months) WBVT program using a side-to-side vibration on: (i) strength profile of knee extensors (KE) and flexors (KF), (ii) “functional” hamstrings-to- quadriceps ratio (ECC KF /CON KE ), (iii) flexibility and (iv) vertical jumping performance (VJ). Furthermore, we explored the retention of performance gains 21 days following WBVT. Design: Randomized-controlled trial. Methods: Twenty-six moderately active females (20.40 ± 0.27 years) were assigned to a vibration (VG) or a control group (CG). The short-term WBVT program consisted of sixteen-sessions on a side-to-side vibration platform (frequency: 25 Hz, amplitude: 6 mm, 2 sets × 5 min). Isokinetic and isometric peak torque of KE and KF, ECC KF /CON KE , flexibility, and VJ were measured pre, 2 days post, and 21 days following the cessation of WBVT. Results: Post-training values of flexibility, isokinetic and isometric peak torques of KF and ECC KF /CON KE ratio were higher than pre-training values in VG (p < 0.05); however, they remained unchanged in CG. Post-training values were greater in VG vs. CG (p < 0.05). Twenty-one days following WBVT, post-training values were no longer significantly different than pre-training values. The short-term WBVT program had no effect on strength profile of KE and on VJ. Conclusions: A short-term side-to-side WBVT program improved flexibility, the strength profile of knee flexors, and the “functional” hamstrings-to-quadriceps ratio in moderately active females. Coaches and clinical practitioners should consider this type of training as an effective exercise mode for improving the strength asymmetry of reciprocal muscles at the knee joint. © 2012 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. 1. Introduction Whole-body vibration (WBV) is an alternative mode of exer- cise training that has been used in sport and rehabilitation for improving neuromuscular performance. 1 Long-term (>2 months) WBV-training may increase muscular strength, power and jump- ing ability, with greater improvements observed in untrained and elderly individuals. 2 Recently, short-term WBV-training has been proposed as an exercise method for injury prevention and rehabilitation. 3–5 Research has now been focusing on the efficacy of a short-term WBVT program to improve attributes of neuromus- cular performance and flexibility. Short-term WBV studies (up to 24 sessions or 2 months) have been shown to either increase 3,6–9 or to have no-effect 6,10 on strength of knee extensors (KE) and verti- cal jumping performance (VJ). The few studies that examined the ∗ Corresponding author. E-mail address: bgerom@pe.uth.gr (V. Gerodimos). effects of a short-term WBVT program consisting solely of WBV on strength of knee flexors (KF) 6,10 and on flexibility 3,11,12 have also reported inconsistent findings. All the aforementioned studies (except for one 7 ), have uti- lized platforms that vibrate simultaneously in vertical direction. However, the effects of WBV are influenced by the method that the vibration is transmitted to the body (vertical simultaneous vs. side-to-side alternating movement). 1,13 Platforms producing side-to-side alternating vibration may induce a different degree of muscle stretch and tissue vibration on leg muscles that could lead to different neuromuscular responses compared with platforms using vertical simultaneous movement. 13 Therefore, it is of inter- est to examine the short-term (≤2 months) effect of WBV on the flexibility and strength profile of lower limbs with a platform that produces side-to-side alternating vibration. The few studies that examined the effects of a short-term (≤2 months) side-to-side alternating WBVT program on neuromuscu- lar performance have focused on VJ and strength of KE. The authors reported either a marginal increase 14 or no change 15,16 in VJ with 1440-2440/$ – see front matter © 2012 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsams.2012.11.888