"I think the problem ive run into is my files contain the same variable names..."
That is not a problem at all, actually that is very good news.
"...so i cant load them form different .mat files at the same time..."
Yes, you can. In fact, having the exactly the same names in each file makes your code simpler and much more robust.
"...so i think i either need to rename all of the variables in the file from say altitude to user1_altitude..."
Ugh, do NOT do that.
Forcing meta-data (e.g. user IDs) into variable names is a sign that you are doing something wrong.
Numbering variables like that is also a sign that you are doing something wrong. Trying to access lots of numbered variables is one way that beginners force themselves into writing slow, complex, buggy code:
You did not give much information about your filenames, etc. but something like this should get you started:
P = 'absolute or relative path to where the files are saved';
S = dir(fullfile(P,'*.mat'));
F = fullfile(P,S(k).name);
All of the file data is stored in the structure array T, which you can easily access using indexing and fieldnames:
For example, the second file:
"alternatively could i combine 2 users data so i can directly compare each persons performance"
Of course, you can trivially concatenate the any of the imported data into numeric matrices, just as you request:
You can also loop over the fieldnames to process them all:
Your approach (numbering all of the variables) would make these tasks slower and much more complex.