Elbows are tricky because height and arm size don’t always line up. If you have longer, thinner arms, you may need a medium circumference but large length, depending on where you like things to sit. Or large circumference and medium length.
I’m 6’2”, and historically wear a medium, because it’s what best fist the circumference of my forearm. Currently in a medium original Reebok 10k.
The past few years, when I try things on, I’ve felt better in a large (for Tacks, Vapors, Supremes, and Warriors), as I feel like I need the extra volume around my elbow. Even though my pads are old and I’m 8-10 years older than when I bought them, I don’t think my arms have really changed. To me, it feels like the space your elbow sits into is shallower on recent elbow.
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Total aside.... I feel like elbow pads are the most annoying, least sexy thing to buy. They are hard to size and boring to try on, and if you do it right, don’t notice them at all when you get new ones. You can visually see new pants and gloves and helmet, and they let other players know you are awesome. New sticks allow you to rip shots and make buttery toedrags. New skates change your whole game up and down the ice. New elbow pads...immediately go in the background.