Best way to store EMG data on an SD card for easy use in MATLAB


I am using electrodes on a persons cheek to collect EMG data for muscle spasms. I am trying to figure out what data type and extension file would be the best to use for collecting then transferring the data to MATLAB. I want to take data points every 2ms at least.
Currently, I have the integer value from analogRead being converted into a string and then written to a .txt file on the SD card. I believe there is a better way to do this, one that is more efficient and might be easier to work with MATLAB. What extension should I use? Normally I would use a .dat file, but I dont see anyone doing that with a SD card (at least the examples I have seen).

Any suggestions on what data type I should store the voltage values in and what extension I should use is much appreciated.

Using readtable in MATLAB, extensions .txt or .csv would be a quick and easy way to import string-based tables created by delimiting columns with a comma and rows with a newline.

Alternatively, you don't have to convert the values to a string. If you write binary data then the file could be much smaller and easily indexed, but its not "human readable" and a little more work to get it into a table in MATLAB.