"The Neewa Adjustable Racing Harness is an H-style harness that provides uniform distribution of pressure through the entire body. It was designed to ensure unrestrained breathing as the airways stay free. This harness works well for all pulling activities, particularly dog sledding, canicross, skijoring, and bikejoring. The adjustable chest and back sections allow the harness to adapt perfectly for any breed or size of dog." Black Harness is a L Red Harness is a M The Blue has sold. Here is the website if you would like more information: https://www.neewadogs.com/collections/dog-harnesses/products/adjustable-racing-harness#