Hi mate, sorry for the late answer.. I didn't noticed you asked me this question.
Well please remember that there is a BIG difference between Movie like Gladiator and reality
Anyway, the Muscle Cuirass was wear for Parade reason. Expecially the Metal Muscle Cuirass. Probably at war the Musclar Cuirass used was made in Leather, and had much more simple design.
Anyway the Metal Muscle Cuirass was designed for Emperors and VERY HIGH rank officers (like Generals).
Anyway it's almost sure Lorica Muscolata was not used often in battle, because the movement was very reduced by this kind of armour.
The most common armour used in battle was Lorica Hamata (Chain Mail) and Lorica Segmentata (the one we used with Valerius)
The "General" helms you have seen in the movies, once again there is a lot of "fantasy" there
The helm much more similar to Quintus in Gladiator is this one:
It is a General (or high rank officer) PARADE helm.
And as you can see it's very different to the one we can see in the movie.
Today you can see this very rare helm at Nuremberg Germanisches Nationalmuseum.