Abstract
The extensor digitorum communis muscle plays an important role in hand dexterity during object manipulations. This multi-tendinous muscle is believed to be controlled through separate motoneuron pools, thereby forming different compartments that control individual digits. However, due to the complex anatomical variations across individuals and the flexibility of neural control strategies, the spatial activation patterns of the extensor digitorum communis compartments during individual finger extension have not been fully tracked under different task conditions. The objective of this study was to quantify the global spatial activation patterns of the extensor digitorum communis using high-density (7 × 9) surface electromyogram (EMG) recordings. The muscle activation map (based on the root mean square of the EMG) was constructed when subjects performed individual four finger extensions at the metacarpophalangeal joint, at different effort levels and under different finger constraints (static and dynamic). Our results revealed distinct activation patterns during individual finger extensions, especially between index and middle finger extensions, although the activation between ring and little finger extensions showed strong covariance. The activation map was relatively consistent at different muscle contraction levels and for different finger constraint conditions. We also found that distinct activation patterns were more discernible in the proximal–distal direction than in the radial–ulnar direction. The global spatial activation map utilizing surface grid EMG of the extensor digitorum communis muscle provides information for localizing individual compartments of the extensor muscle during finger extensions. This is of potential value for identifying more selective control input for assistive devices. Such information can also provide a basis for understanding hand impairment in individuals with neural disorders.
Highlights
The convergent and divergent spinal neuronal networks and the multi-tendinous extrinsic finger muscles afford the dexterous control of human finger movement
The muscle activation level was significantly higher during high effort finger extension than during low effort conditions [F(1, 9) = 34.91, p = 0.001]
The post hoc analysis showed that the root mean square (RMS) was higher in four-finger task compared with all the individual finger tasks (p < 0.05), and that the RMS in little finger extension was lower than the RMS in index and ring finger extension tasks (p < 0.05)
Summary
The convergent and divergent spinal neuronal networks and the multi-tendinous extrinsic finger muscles afford the dexterous control of human finger movement. Schieber and Santello, 2004), especially in populations with neurological disorders (Lang and Schieber, 2003; Lee et al, 2013) These coupled finger movements can arise from mechanical coupling and/or from non-selective neural control. The divergent projections of cortical neurons to multiple motoneuron pools across compartments result in synchronized activation of motoneurons innervating multiple compartments of the finger muscles (Zatsiorsky et al, 2000; Keen and Fuglevand, 2004a,b). These complex anatomical structures and neural control strategies impose challenges for quantifying the extensor muscle spatial activation patterns under different task requirements
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