BMXing is the activity of riding a BMX — that strong, low bicycle people use for jumps and tricks. The word is BMX with -ing on the end, the same pattern as swim and swimming. So BMXing is not another kind of bike; the bike is a BMX, and BMXing is the riding, the sport, the jumping. You might hear he is BMXing this afternoon, in casual talk among younger people and riders. It can also name the hobby in general: BMXing is hard on your knees. Though the idea is the same world as the bicycle, the -ing tells you someone is doing it, not that they own a thing called a BMXing.

玩 BMX；騎小輪車