When mountain biking or bmxing, the knees and elbows are the parts of the body that bear the brunt of the force and are the first or second to hit the ground in a fall. You therefore want to give your elbows and knees optimum protection when mountain biking or bmxing. Nothing is as irritating as having to apply force to your legs with bruised knees or holding your handlebars with bruised elbows. Demon supplies mtb elbow pads in all shapes and sizes, with or without D3O, with hardshell or soft padding.