The effects of skinfold thicknesses and innervation zone on the mechanomyographic signal during cycle ergometry Jorge M. Zuniga a,⇑ , Terry J. Housh a , Clayton L. Camic a , C. Russell Hendrix b , Haley C. Bergstrom a , Richard J. Schmidt a , Glen O. Johnson a a Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, Lincoln, NE 68583, USA b College of Science and Health, Department of Exercise and Sport Science, University of Wisconsin-La Crosse, 1725 State St. La Crosse, WI 54601, USA article info Article history: Received 23 December 2010 Received in revised form 22 April 2011 Accepted 25 May 2011 Keywords: Innervation zone Accelerometer placement Pedaling exercise MMG abstract The purpose of this study was to examine the effects of skinfold (SF) thicknesses at four locations on the vastus lateralis (VL) muscle and the placement of accelerometers relative to the innervation zone (IZ) on the mechanomyographic (MMG) amplitude and mean power frequency (MPF) responses during incre- mental cycle ergometry. Twenty adults (age ± SD = 23.8 ± 3.0 years) participated in the investigation. The MMG signals were detected during incremental cycle ergometry using four accelerometers placed on the right VL. Prior to the cycle ergometer test, SF thicknesses were measured. Simple linear regression analyses and one-way repeated measures analyses of variance (ANOVAs) were performed. The present study found that only 10% of the regression analyses and mean comparisons were significant (p < 0.05). Furthermore, the accelerometer placed at the most proximal site (Prox 2) had significantly greater MMG amplitude and MMG MPF than accelerometers placed at more distal sites (Prox 1, Over IZ, and Dist). There were no significant differences, however, in SF thickness between accelerometer placement sites. In addition, the IZ had no effect on MMG amplitude and little effect on MMG MPF values. The results of the present study indicated that the SF thickness values and IZ did not affect the MMG signal. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The mechanomyographic (MMG) signal records and quantifies the low-frequency lateral oscillations of contracting skeletal muscle fibers (Barry, 1987; Orizio et al., 1989a,b) and represents the mechanical counterpart of motor unit activity as measured by electromyography (EMG) (Gordon and Holbourn, 1948; Petit- jean and Maton, 1995). It has been suggested (Barry and Cole, 1988; Orizio, 1993) that the lateral oscillations are the result of: (a) the gross lateral movement of the muscle as it moves toward or away from its line of pull during contraction or relaxation; (b) smaller subsequent lateral oscillations generated at the resonant frequency of the muscle; and (c) dimensional changes of the active muscle fibers. The mechanical properties of the muscle captured in the MMG signal can be used to examine various aspects of muscle function during cycle ergometry. For example, previous studies have used the MMG signal to provide information regarding motor-unit activation strategies (Perry et al., 2001a,b), characterize fatigue in the quadriceps femoris muscles (Housh et al., 2000; Shinohara et al., 1997; Stout et al., 1997), and control external prostheses (Silva et al., 2003, 2004). Jorgensen (1976) found that when using an accelerometer to measure the lateral oscillations of activated muscle fibers ‘‘The magnitude of the mechanical vibrations is determined by the net force acting upon the tissue between the muscle and the skin sur- face and the mechanical properties of this layer of tissue.’’ (p. 159). In addition, it has been shown that the amplitude and frequency contents of the MMG signal can be affected by the location of the accelerometer over the muscle, in part, due to differences in the thickness of the subcutaneous fat layer along the muscle (Cescon et al., 2004; Orizio, 1993). Recently, Jaskolska et al. (2004) sug- gested that during isometric muscle actions, the subcutaneous fat layer as reflected by skinfold (SF) thicknesses act as a low pass fil- ter to the MMG signal. It is unclear, however, if SF thicknesses are related to the amplitude or mean power frequency (MPF) of the MMG signal from the vastus lateralis (VL) muscle during a dynamic activity, such as cycle ergometry. In addition to the characteristics of the tissue layer over a muscle, the location of the innervation zone (IZ) with respect to the recording accelerometer may affect the MMG signal (Made- leine et al., 2006; Maton et al., 1990). Previous studies, however, 1050-6411/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jelekin.2011.05.009 ⇑ Corresponding author. Address: Department of Nutrition and Health Sciences, 110 Ruth Leverton Hall, University of Nebraska-Lincoln, Lincoln, NE 68583-0806, USA. Tel.: +1 402 472 2690; fax: +1 402 472 0522. E-mail address: jzuniga2@unlserve.unl.edu (J.M. Zuniga). Journal of Electromyography and Kinesiology 21 (2011) 789–794 Contents lists available at ScienceDirect Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin