I see this shirt as what your typical crewman would wear while running laps in the ship gym.  Of course, there was an episode where they showed the ship gym (Episode 2, Charlie X, a great one IMO) but it was more a mat room where Kirk would practice his signature shoulder roll.  That over the top fighting style doesn't come without a lot of practice, I'm sure.  

I found an interesting article detailing some of the Starfleet Academy physical requirements.  I guess running would be recommended.  The best part of this article is their calling the Red Shirts the "best of the best".  I guess telling people their main job description is meat shield will not go a long way towards building moral.  Telling potential recruits that the best people go into it would be a way of keeping recruitment levels high.

My best friend has been playing the new Star Trek Online game and loves it.  He tells me he is pretty willing to let his Red Shirts step into the teeth of everything remotely dangerous.  He says if he could load them into photon torpedoes and fire them at enemy ships he would.

I have another friend that does these boot camp fitness programs, where they run around while guys yell at them like Harman from Full Metal Jacket.  Honestly, it has always seemed kind of a dumb idea.  What's the point of going through all that pain and suffering if you are not going to learn how to blow stuff up and kill people?  However, if they were to do one that was Starfleet Academy boot camp that including possible Starfleet weapons training, that might be kind of fun.  New idea out there for anyone who wants to run with it.