Professional versions of a zip-line are most typically used as an outdoor adventure activity. In contrast to "flying foxes" professional courses are usually operated at higher speeds, covering much longer distances and sometimes at considerable heights. The users are physically attached to the cable by a harness that attaches to a removable trolley. A helmet is required on almost all courses of any size.
Cables can be very high, starting at a height of over 9 m (30 ft), and traveling well over 460 m (1,510 ft). All zip-line cables have some degree of sag. The proper tensioning of a cable is important and allows the ability to tune the ride of a zip line.
Users of zip-lines must have means of stopping themselves. Typical mechanisms include:
• Friction created between the pulley against the cable.
• Thick purpose-built leather gloves.
• A mat or netting at the lower end of the incline.
• An arrester system composed of springs, pulleys, counterweights, bungee cord or other devices, which slows and then stops the trolley's motion.
• Gravity stop, exploiting the sag in the cable. The belly of the cable is always lower than the termination point. The amount of uphill on a zip line controls the speed at which the user arrives at the termination point.
Also, a user can be stopped with a hand brake at the end of the zip line, such as at The Canyons Zip Line in Florida.
Zip lines are a common way to return participants to the ground at the end of a ropes adventure course.
With proper knowledge and training on the part of the operators and good maintenance, zip lines are safe and easy to use.