**Author details**

#### Mark Halaki

Computational Intelligence in Electromyography Analysis – 186 A Perspective on Current Applications and Future Challenges

activity recorded during the submaximal isometric contraction is then used to normalize the

The main limitation of using submaximal isometric contractions is that comparisons of activity levels between muscles and individuals are not valid because, once again, the reference value used in this method is not relative to the maximum capacity of the muscle. Lifting an absolute load of say 1 kg mass might require 10% of the maximum muscle capacity in a strong individual compared to say 40% of the maximum muscle capacity in another person who is not as strong. It is not possible to estimate maximum muscle activity from a relative submaximal contraction by linear extrapolation because the torque/EMG relationship is nonlinear [96]. Additionally, the lengths of muscle moment arms in individuals vary and since the EMG signal is related to the force produced by the muscle and not the torque produced by the limb, the force required by the muscle to produce a given torque would be different between individuals. Another limitation is that the motor strategy may not be the same between individuals or between sides within the same individual [95] during the reference submaximal contraction. This is not a problem during maximal contractions as heightened central drive engages all possible muscle resources to achieve the maximum force possible. Therefore, using submaximal isometric contractions as the reference for normalizing EMG

data is reliable but doesn't allow valid comparisons between muscles or individuals.

This method of normalizing EMG signals involves external stimulation of α-motor neurons. When a peripheral motor nerve is stimulated at a point proximal to a muscle it activates the muscle to contract. This signal is called the M-wave and can be recorded using EMG electrodes placed on/in that muscle. To obtain maximum activation in the muscle and produce a maximum M-wave (M-max), the amplitude of stimulation is increased until the peak to peak amplitude of the M-wave does not increase further. To ensure maximum simulation, the amplitude of the stimulation is increased by an additional 30%. The amplitude of the M-max is then used to normalize EMG signals from the same muscle during the tasks of interest [97]. Currently, this normalization method is problematic as the repeatability of the M-max is questionable. It seems to be less reliable as the background contraction level increases [98], decreases with time [99], and is dependent on muscle length [100-102] and the task performed [98, 102]. If these factors that affect the M-max values could be controlled resulting in more reliable measurements, this method to normalize EMG data has the potential to facilitate

In summary, only the normalization method that uses MVICs as the reference level can be validly used to compare muscle activity levels and activation patterns between muscles, tasks and individuals, provided that maximum neural activation is achieved in all muscles and individuals tested. The use of peak or mean activation levels obtained during the task under investigation as the reference EMG level can be used to compare patterns of muscle activation

**3.4. Peak to peak amplitude of the maximum M-wave (M-max)** 

comparisons between muscle, between tasks and between individuals.

**4. Summary** 

EMG in the same muscle while performing the task under investigation.

*Discipline of Exercise and Sport Science, Faculty of Health Science, The University of Sydney, Sydney, Australia* 

#### Karen Ginn

*Discipline of Biomedical Sciences, Sydney Medical School, The University of Sydney, Sydney, Australia* 
