Source: record emgdb/emg_myopathy
val has 1 row (signal) and 110336 columns (samples/signal)
Duration:     0:27
Sampling frequency: 4000 Hz  Sampling interval: 0.00025 sec
Row	Signal	Gain	Base	Units
1	EMG	10000	0	mv

To convert from raw units to the physical units shown
above, call the 'rdmat.m' function from the wfdb-matlab
toolbox: https://physionet.org/physiotools/matlab/wfdb-app-matlab/