Table 1.

Examples of sEMG applications in assessment and treatment, see Chapter 10 in Criswell (4).

Assessment
Assess level of muscle activation:	sEMG evaluation:
• Unwanted muscle activation during rest	• Evidence of MU activity in baseline sEMG recording
• Relative activation of different muscles across the range of motiona	• Variation in sEMG amplitude across the range of motiona, b
• Presence of unwanted muscle activation/inhibition during muscle contractions	• Excessive/insufficient muscle activation (higher/lower than expected sEMG amplitude) relative to the task or in relation to other synergistsb, c
• Inappropriate muscle co-activation during bilateral movements	• Differences in sEMG activity between homologous muscles on the involved and uninvolved sides during bilateral movementsb, c
Assess timing of muscle activation:	sEMG evaluation:
• Altered recruitment/derecruitment of muscles during eccentric and concentric phases of movement • Inappropriate timing of agonist/antagonist muscle activation during joint stabilization	• Delayed muscle onset during movement • Premature muscle onset during movement • Muscle active for an excessive (or insufficient) time period during movement
Assess muscle fatigue:	sEMG evaluation:
• Indirect estimate of changes in muscle fiber conduction velocity (MFCV) associated with peripheral fatigue	• Rate of decline of the mean/median frequency of the sEMG signal (see section Surface EMG Spectral Features (Frequency Domain)) during a fatiguing contraction and subsequent recovery (normalized to baseline value)
• “Global” estimate of MFCV	• Estimated from the delay between sEMG signals from spatially displaced electrodes
• Changes in muscle activation (motor unit firing rate/recruitment) to compensate for reduced force generating capacity	• Increase in sEMG amplitude with respect to baseline value
Treatment
Objective:	Use of sEMG:
• Uptraining muscle(s) (i.e., increase sEMG amplitude)	• sEMG activity can be provided as feedback to the patient as an aid to increase awareness of their level of muscle activation • Begin with training an isolated muscle, recording also from other muscles to ensure they are not inappropriately recruited to the contraction • Threshold level can be set a for sEMG activation and patient encouraged to exceed this threshold • Threshold can be gradually increased to encourage patients to increase the strength of the muscle contraction
	• A threshold could also be used in endurance training, where the subject must maintain a target level of muscle activation
• Relaxation or down-training muscles (i.e., reduce sEMG amplitude)	• Record from muscles that are chronically hyperactive to promote relaxation • Threshold can set be for muscle activation and encourage patient to relax the muscle to keep below this threshold • This threshold can be gradually lowered over time to increase relaxation ability

^aResources are available showing the normal template for muscle activations during different movements, for example the atlas in Part III of CRAM's provides a “benchmark” for the relative activation of certain muscles during static load conditions (e.g., during normal shoulder abduction, there should be a balanced activation of the upper and lower trapezius).

^bCaution should be exercised when interpreting sEMG amplitude due to intersubject and intrasubject variability associated with factors such as electrode contact, electrode placement, anatomical factors, temperature etc. which can influence the signal amplitude.

^cNormalization of sEMG amplitude with respect to a reference value is usually recommended, see Besomi et al. (22). However, sEMG signals between homologous muscle groups can be approximately compared (e.g., between left and right upper trapezius).