I run a long distance and have recently developed a severe "runner's knee" on both sides of my knees. I already have Osgood-Schlatter disease on my left knee which I also fractured (and has healed) last year, so realized that I'd need a good knee support if I run more than 10 miles.I have tried THREE (3) knee support braces/compression sleeves including "PowerLix Compression Knee Sleeve" for that purpose, and wanted to list them for comparison.(1) Breg "FreeRunner". Formerly prescribed for the fracture and designed for an athlete/runner to help with their rehab. It did a great job staying in place during my 13-mile run. But it did NOT completely keep my knee pain-free as it normally would with stairs and biking. I started to feel the same discomfort --> disturbing pain around 10 miles. The brace is bulky so occasionally rubbed against the other thigh - which is a big NO-NO.(2) PowerLix Compression Knee Sleeve (this product): This is a BRACE that is in a form of a compression sleeve. It holds my kneecap in place, protects my Osgood-Schlatter bump (bone protrusion), prevents abnormal gait due to the uneven pulls by the thigh muscles, keeps the optimal temperature inside, allows FULL range of motion. I can flex my knee all the way. It is nice and tight but never uncomfortable.I wore this on my problem left knee and ran a full marathon race this past weekend. It stayed on without ever sliding/rolling down or chafing for the entire 26.2 miles and I did not have to worry or think about it. Most importantly - Absolutely NO PAIN during and post race. I was SO amazed.(3). Physix Gear Knee Support Brace: this is more of a firm compression knee sleeve than a brace. It did also an amazing job in protecting my right knee which was suffering runner's knee. It fits like your favorite compression knee-high sock with no limit in movement and is definitely a more comfortable wear than PowerLix Compression Knee Sleeve (#2). But the anti-slip grips of this knee sleeve at the top is tighter than PowerLix's and may feel a bit too tight. It is however never uncomfortable and the sleeve stayed on without rolling or chafing for the entire 26.2 miles. It kept my right knee totally PAIN-FREE during and post race.[OVERALL]Both "PowerLix Compression Knee Sleeve" (this product) & "Physix Gear Knee Support Brace" did an amazing job and are highly recommended for long-distance runners. They stabilize the knee joint and prevent pain/inflammation by right support and compression but never restrict the movement or stop the blood flow - even for hours!*Sizing: I took the measurements 4 & 5 inches above the top of the BENT KNEE in a sitting position. They fell between 15.3 -15.7 inch. So according to the sizing chart provided by the company, I got a MEDIUM for "PowerLix Compression Knee Sleeve" and a SMALL for "Physix Gear Knee Support Brace". They fit perfectly.*Length: According to the product specification, "PowerLix Compression Knee Sleeve" is a bit longer than "Physix Gear Knee Support Brace". But due to the very firm fabric of PoweLix and very stretchy fabric of Physix, Physix knee sleeve ends up slightly taller than PoweLix when I wore them.*Color: Grey/Black for PowerLix (this product) is almost entirely black (see photo - upper right). It doesn't look like the product photo on this webpage and thought I got a wrong product! Not sure about Blue which I didn't get.I hope they both last long!!! Thank you for reading my long review :-)-------------- UPDATE 12/18/2023 -----------------I'm still using POWERLIX Leg Sleeve (this product) and have run 7 marathons and hundreds of runs with them since the first purchase in 2018. Nothing wrong with running with knee braces although some sports experts may preach that you need to train your own muscles and correct your form and such. You've got your personal reasons for needing special support for your knees, and these sleeves do the job. I replace the sleeves every year and am on #5 :)