Abstract
ObjectivesThe purpose of the study was to establish regression equations that could be used to predict muscle thickness and pennation angle at different intensities from electromyography (EMG) based measures of muscle activation during isometric contractions.DesignCross-sectional study.MethodsSimultaneous ultrasonography and EMG were used to measure pennation angle, muscle thickness and muscle activity of the rectus femoris and vastus lateralis muscles, respectively, during graded isometric knee extension contractions performed on a Cybex dynamometer. Data form fifteen male soccer players were collected in increments of approximately 25% intensity of the maximum voluntary contraction (MVC) ranging from rest to MVC.ResultsThere was a significant correlation (P < 0.05) between ultrasound predictors and EMG measures for the muscle thickness of rectus femoris with an R2 value of 0.68. There was no significant correlation (P > 0.05) between ultrasound pennation angle for the vastus lateralis predictors for EMG muscle activity with an R2 value of 0.40.ConclusionsThe regression equations can be used to characterise muscle thickness more accurately and to determine how it changes with contraction intensity, this provides improved estimates of muscle force when using musculoskeletal models.
Highlights
The most commonly used approach for the assessment of skeletal muscle is EMG and can provide the biochemical and electrophysiological features of the of the muscle (Brody et al 1991; Cifrek et al 2009)
The regression equations can be used to characterise muscle thickness more accurately and to determine how it changes with contraction intensity, this provides improved estimates of muscle force when using musculoskeletal models
An increase in muscle force leads to an increase in muscle thickness for the rectus femoris and pennation angle for the vastus lateralis with the largest difference recorded from rest to maximum voluntary contraction (MVC) (100%)
Summary
The most commonly used approach for the assessment of skeletal muscle is EMG and can provide the biochemical and electrophysiological features of the of the muscle (Brody et al 1991; Cifrek et al 2009). Many studies have reported the relationship between the surface EMG (sEMG) and muscle force, length and muscle fibre conduction velocity (McGinnis 2005; Merletti and Lo Conte 1997; Lieber 2002). The ultrasound image has been widely used to assess human muscles referred to as sonomyography (Shi et al 2007). This has been used to measure the changes in muscle thickness Zheng et al 2006; Brancaccio et al 2008; Legerlotz et al 2010), muscle fibre pennation angle (Rutherford and Jones 1992; Lieber and Friden 2000; Klimstra et al 2007), muscle fascicle length (Fukunaga et al 1997a, and muscle size (Fukunaga et al 1997b; Reeves et al 2004) during static and dynamic conditions. Muscle is generally less echogenic than subcutaneous fat or tendons
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