SEMG
Surface EMG recordings provide information about aggregate motor unit activity in superficial muscle.The advantage of SEMG is its convenience and good overall correlation to generated muscle force. 

In an SEMG recording, a bipolar electrode is placed on the skin surface overlying a muscle of interest. As the muscle contracts, myoelectric activity is revealed as a complex waveform with an amplitude range of about 0-10 mV. 

Intramuscular
Alternatively, intramuscular EMG techniques may be used where increased signal specificity is required. Intramuscular EMG recordings provide high spatial selectivity allowing for individual superficial or deep muscle groups to be recorded from. This requires the use of fine needle electrodes placed within the muscle of interest. 

Because the current source is highly localized with respect to the electrode tip, i.e. only involving a few muscle fascicles, the recorded EMG waveform will appear less complex and is therefore better suited to studies relating motor unit firing rates to generated muscle force. Multiple recording sites may be used within the same muscle group. Like SEMG, recordings using needle electrodes also have amplitudes within the 0 to 10 mV range, although due to being closer to the current source amplitudes will predictably be more toward the higher end of this range.