Biology of Sport, Vol. 28 No3, 2011 199 Effects of neuromuscular responses during whole body vibration exercise with different knee angles Reprint request to: Gusi Narcis Addres: Faculty of Sports Sciences, University of Extremadura 10071 Caceres, Spain Tel. number: (+34) 671166089 Fax number: (+34) 927 257461 E-mail address: ngusi@unex.es Accepted for publication 09.08.2011 INTRODUCTION Whole body vibration is based on oscillating waves causing mechanical stimulation that increases the effect of the gravitational load on the skeleton, joints and neuromuscular system [3]. The mechanism responsible for the vibration benefts is not entirely clear. However, it is fair to say that WBV stimulates the sensory receptors localized in muscle or tendon activating mainly the muscle spindles [22]. The activation of these muscles facilitates the activation of α-motoneurons via α-afferent and α-efferent pathways [21], leading to tonic vibration refex (TVR) [7] increasing the motor unit activation [18]. Currently, there are many vibration platforms on the market and they basically differ in terms of their frequency range, amplitude and type of vibration stimulation. The effects of using WBV with separate types of platforms on training [14], osteoporosis [9], muscle strength [26], equilibrium and falls [6], etc. have been studied. However, the fndings are not unanimous as benefts were not present in all the studies [5,27]. The diversity of results may be due to the fact that the optimal dose for improving each value remains unknown, as does the most effcient posture for each training session and the specifc population [1]. Furthermore, many unanswered questions EFFECTS OF NEUROMUSCULAR RESPONSES DURING WHOLE BODY VIBRATION EXERCISE WITH DIFFERENT KNEE ANGLES AUTHORS: Gusi N. 1 , Parraca J.A. 1 , Adsuar J.C. 1 , Olivares P.R. 1 , Tomas-Carus P. 2,3 1 Faculty of Sports Sciences, University of Extremadura, Caceres, Spain 2 Department of Sport and Health, University of evora, Evora, Portugal 3 Health Sciences and Technologies Research Center, University of Evora, Evora, Portugal ABSTRACT: The purpose of this study was to compare the effects of whole body vibration (WBV) exercise using different knee angles on three-dimensional acceleration received in the lumbar region and neuromuscular activation of 8 muscles that were selected in order to determine their implications for rehabilitation. Thirty physically active women (mean ± SD; 21.7 ± 1.67 years) were randomized in three groups. The frst group performed on the platform with 15, 45 and 90º knee fexions, the second group with 45, 90, 15º, and the third group with 90, 15, 45º. The WBV frequency was 12.6 Hz. The acceleration was recorded by a tri-axial accelerometer (Biopac) attached on the skin at L3 level and the electromyography (EMG) was recorded by surface active electrodes (Biopac) on the extensors and fexors of the knee and lower trunk. The lateral acceleration was 3 times greater (p< 0.05) at the vertical line in 3 angles of fexion, and the vertical line was 2 times greater (p< 0.05). Maximum accelerations: lateral (11-13 g) and vertical line (6-7 g) had increased when reducing the knee-fexion angles. In conclusion, WBV using the Galileo platform transmits more lateral neuromuscular and mechanical stimuli than vertical stimuli. A smaller degree of knee fexion transmits a greater mechanical stimulus, and a higher fexion of the knees implies an increase of muscular activity in the vastus internus muscle. These fndings open the possibility of different applications. KEY WORDS: vibration, electromyography, posture, rehabilitation concerning aspects of great relevance in WBV training remain: 1) oscillation frequency; 2) amplitude of movement; 3) exposure time; 4) resting time; and 5) body posture, whereby the joint fexion angle is of key importance [1]. Most prevalent in professional and scientifc settings are vertical and tilting vibration platforms. Only a few studies describe the infuence of the degree of knee fexion on a vertical vibratory platform, which significantly modulates the transmissibility of mechanical stimuli through the body [23]. However, too little is known about the subject of tilting platforms. The purpose of this study was to provide researchers and rehabilitation professionals with information concerning the implication of varying the degree of knee fexion, when exposed to WBV on a tilting platform at frequencies below 12.6 Hz. Particularly, the neuromuscular response of eight selected muscles and the three- dimensional acceleration at the lumbar level (L3) were studied so as to expand our knowledge of the most suitable dose response. We hypothesized that changes in the degree of knee fexion on a tilting vibration platform affect or modulate the mechanical and neuromuscular stimuli. Original Paper Biol. Sport 2011;28:199-205 DOI: 10.5604/959286