Singular muscle men including one remarkable example (8)
I believe the answer is:
specimen
'remarkable example' is the definition.
'specimen' can be an answer for 'example' (specimen is a kind of example). I'm not certain of the 'remarkable' bit.
'singular muscle men including one' is the wordplay.
'singular muscle' becomes 'spec' (I can't justify this - if you can you should give a lot more credence to this answer).
'including' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'spec'+'men'='specmen'
'specmen' enclosing 'i' is 'SPECIMEN'.
Can you help me to learn more?
(Other definitions for specimen that I've seen before include "Example regarded as typical of its class" , "Sample to be studied" , "Exemplar" , "Example of type" , "Typical example - sample" .)