RELATIONSHIP BETWEEN LOWER LIMB MUSCLE ACTIVITY AND PLATFORM ACCELERATION DURING WHOLE-BODY VIBRATION EXERCISE KARIN LIENHARD, 1,2,3 JORDYN VIENNEAU, 3 SANDRO NIGG, 3 OLIVIER MESTE, 1 SERGE S. COLSON, 1,2 AND BENNO M. NIGG 3 1 CNRS, I3S, UMR 7271, University of Nice Sophia Antipolis, Nice, France; 2 LAMHESS, EA 6312, University of Nice Sophia Antipolis, Nice, France; and 3 Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada ABSTRACT Lienhard, K, Vienneau, J, Nigg, S, Meste, O, Colson, SS, and Nigg, BM. Relationship between lower limb muscle activity and platform acceleration during whole-body vibration exercise. J Strength Cond Res 29(10): 2844–2853, 2015—The pur- pose of this study was to identify the influence of different magnitudes and directions of the vibration platform accelera- tion on surface electromyography (sEMG) during whole-body vibration (WBV) exercises. Therefore, a WBV platform was used that delivers vertical vibrations by a side-alternating mode, horizontal vibrations by a circular mode, and vibrations in all 3 planes by a dual mode. Surface electromyography signals of selected lower limb muscles were measured in 30 individuals while they performed a static squat on a vibration platform. The WBV trials included 2 side-alternating trials (Side-L: 6 Hz, 2.5 mm; Side-H: 16 Hz, 4 mm), 2 circular trials (Circ-L: 14 Hz, 0.8 mm; Circ-H: 43 Hz, 0.8 mm), and 4 dual-mode trials that were the combinations of the single-mode trials (Side-L/Circ-L, Side-L/Circ-H, Side-H/Circ-L, Side-H/Circ-H). Furthermore, con- trol trials without vibration were assessed, and 3-dimensional platform acceleration was quantified during the vibration. Signif- icant increases in the root mean square of the sEMG (sEMG RMS ) compared with the control trial were found in most muscles for Side-L/Circ-H (+17 to +63%, p # 0.05), Side-H/Circ-L (+7 to +227%, p # 0.05), and Side-H/Circ-H (+21 to +207%, p , 0.01) and in the lower leg muscles for Side-H (+35 to +138%, p # 0.05). Furthermore, only the vertical platform acceleration showed a linear relationship (r = 0.970, p , 0.001) with the averaged sEMG RMS of the lower limb muscles. Significant in- creases in sEMG RMS were found with a vertical acceleration threshold of 18 m$s 22 and higher. The present results emphasize that WBV exercises should be performed on a platform that induces vertical accelerations of 18 m$s 22 and higher. KEY WORDS surface electromyography, muscle strength, frequency, amplitude, dual-mode platform INTRODUCTION W hole-body vibration (WBV) has been gaining significant interest as an exercise modality in athletic settings (6). The benefits of WBV ex- ercises include improved performance imme- diately after the exposure and after several weeks of training. More specifically, rate of force development (22) and peak force (27) of the lower limbs were increased to a higher extent after a WBV exercise than after the same exercise without vibration. Positive long-term effects of WBV training have also been found with increased jump height (21) and knee extensor strength (10). However, the effects of WBV training on muscle performance remain inconclusive, as other research groups have reported contradictory findings (9,39,13). This inconsistency may be related to the different vibration parameters and protocols used in these studies such as the frequency, amplitude, and platform type. Improvement in neuromuscular performance after WBV could be attributed to several mechanisms. Whole-body vibration is believed to elicit the tonic vibration reflex (34,38), that is, stretch reflex responses induced by changes in length of the muscle spindles because of rapid changes in the length of the muscle tendon units (7). In this context, WBV has been shown to increase corticospinal pathway excitability not only in upper limb muscles at frequencies above 80 Hz (44) but also more recently in lower limb muscles at 30 Hz (29). Another mechanism occurring during WBV could be muscle damping; increased muscle activity during the vibra- tion changes the natural frequency of the tissue to reduce potential adverse effects (47). As a matter of fact, numerous studies have found that the muscle activity of the lower limbs is greater during WBV than without vibration using surface electromyography (sEMG) recordings (3,7,16,23,25,37,40). Address correspondence to Karin Lienhard, karinlienhard83@gmail.com. 29(10)/2844–2853 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association 2844 Journal of Strength and Conditioning Research the TM Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.