Here's my shirt before I did any re-vamping.
Here's the after!
Here's what you'll need:
Rotary cutter and mat (scissors will work too)
Sewing essentials (machine, thread, etc.)
I simply marked with a marker where I wanted my arm holes to be. It doesn't matter what kind of marker you use here, because you will be cutting it off.
Next, I folded the shirt hot dog style, making sure it was lining up exactly with both sides. You could cut one at a time, but folding it over ensure the cuts are identical.
Cut on the inside of you dashes and save the sleeves.
Next, cut the neck line wherever you like it to be. I pulled to front layer up to line it up with the back, but you can cut it however you want! You could mark it out when you mark the sleeves too.
From the saved sleeve, cut a section out from the middle (this will be what hold the back so it is scrunched). I cut mine longer than needed and after sewing trimmed it off. Cut another part off so it lays out flat, without being folded.
Wrap it around the back part of shirt and pin. If your material isn't the same color on both sides make sure it's inside out when pinning it.
Sew up the little section, ensuring not to get the actual shirt in the seam. Flip the "scrunchie" right side out and trim excess fabric if needed. I went over it a couple times to make sure it stays sewn through washing.
There ya have it! A nice loose workout shirt!