SYNERGOS: A Multiple Muscle Activation Index

Abstract

The concept that multiple muscles are controlled together rather than independently provides a parsimonious explanation for efficiency of coordinated movement. The outcome of this control strategy is a state of 'multiple muscle coactivation' (MMC). The purpose of this paper is to introduce a novel analysis technique, titled SYNERGOS, to provide a quantitative index of MMC using surface electromyography (EMG) from multiple muscles as the input variables. To demonstrate the effectiveness of this approach, ten healthy young adults walked on a treadmill at successively increased speeds while EMG was collected from right rectus femoris, tibialis anterior, lateral gastrocnemius, soleus, vastus medialis, and biceps femoris. The initial step in the analysis technique was to use Recurrence Quantification Analysis to determine the changes in each dynamical state of muscle activity signal associated with increasing motor unit firing during increasing gait speed. The resulting data were then analyzed to obtain a single scalar value ranging from 0-100. This index includes the data from all muscles that reflects a combinatorial MMC index for each gait speed. Statistical testing indicated significant sensitivity of the technique to detect the changes in the mode of activity during the conducted protocol (i.e. walking vs. running conditions) (F (1,382.149) = 54.067, p <0.001). In addition, SYNERGOS was able to identify the changes in MMC over a range of minimal gait speed increases (F (1,382.537) = 75.85, p<0.001). The SYNERGOS technique has the potential to be used as a clinical tool to assess abnormalities in the neuromuscular system and monitor the effectiveness of treatments for these disorders.