I bought this a little over 2 years ago, when I had what I now believe was a virus that caused arthritis-like joint pain, that was at least partially relieved by using braces/supports on effected joints. At the time, I was underweight (given that I'm a woman of average height -- 5'5", and barely 100 lbs), so there was no question about which size to buy. It fit, and it helped to stabilize my wrist, providing some relief. I pulled it out again about a week ago, after I sprained my wrist, and am still happy with it. Thanks to a medication I was on for several months, I have gained about 50 lbs in the last two years, and at 150 lbs, I'm now at the upper end of my healthy weight range. The small/medium still fits will, though (unsurprisingly) it's considerably tighter than it used to be. My wrist is now about 6.25", and my knuckles are about 7" at their widest point. The brace is snug enough to leave imprints from the seams on my wrist, but it's still comfortable, and I have not seen (or felt) any signs of restricted circulation to my fingers. I am wearing it as I type. When I first sprained my wrist, the doctor gave me a splint that covered my thumb and ended just below my elbow, which I could wear as much or as little as I wanted, since it was essentially just for my comfort. I'd brought this brace with me to the ER, and showed it to the nurse, who said it was a good alternative. For the first few days, I wore the thumb splint at night, and this brace during the day, since it allows for close to full use of my fingers (I'm wearing it as I type this, and can still touch-type at full speed; for nearly 20 years now, since I was in middle school, I've been able to type quickly enough that the rate limiting factor is knowing what letter I want next -- finding said letter is automatic and nearly instantaneous, and this brace does not interfere with this at all; it also has not interfered with writing, drawing, or coloring). I have not worn this brace overnight, since it feels a bit tight on my hand, and I worry about blood flow to my fingers at night, since it's tight find during the day, even though I know this is probably irrational (but I often wake up with one or the other arm numb just because it landed even slightly higher than my heart for a little while towards the end of the night, or I put my head on it while I slept, so I don't think it would take much to cut off blood flow to my hand while I sleep). I wore the splint the gave me at the ER for the first few nights, with this during the day, and since then, I've continued to wear this during the day, with nothing at night. It helps protect my wrist from the type of strain that is likely to make it feel worse, and it seems to help a lot, and is pretty comfortable. I came back to this page because I want to buy a second one of these so that I can wash one of them, and have another to wear while it dries.