Electromyography
This chapter will cover the methods commonly used to asses muscle activity and function. This includes the techniques used to record electomyographic (EMG) singals, the best pracites for obtaining good-quality EMG singnals, and methods fot the analysis and interpretaion of the EMG recording.
6. EMG amplitude interpetation
6.2. EMG Amplitude During Concentric and Eccentric (Anisometric) Muscle Contractions
Muscle length remains more or less constant during isometric contractions, whereas it shortens during concentric contractions, and it lengthens during eccentric contractions. Concentric contractions are generally weaker and require greater muscle activation than isometric and eccentric contractions for a particular load. ( If a surface EMG signal is recorded from the biceps i brachii muscle when flexing (concentric) and extending (eccentric) the arm at the elbow while holding a fixed load, the raw and EMG patterns in picture Con vs ECC EMG bellow are generated. The highest muscle activity is bserved during the concentric phase and the lowest are during the eccentric movement.
It should be noted that the difference in EMG amplitude during dynamic eccentric and. concentric contractions may be affected by several factors, including changes in the length of the muslce fibres. THe relative movment between the surface sensors on the skin and the shifting muscles fibres underneath laso cause changes in the amplitude of the EMG. Thus, the use if MEG amplitude as in indication of muscle activity during anisometric concractions souhld be conisedered with caution.