One of the most common types of restraints on roller coasters today, OTSRs are typically made of plastic and fold down over the rider's shoulders, pinning them to the seat at their lap. This allows for very little movement and almost no airtime, yet OTSRs are generally fairly comfortable and theoretically they minimize headbanging, a common and unpopular aspect of many coasters. OTSRs are common on rides made by Bolliger & Mabillard and Intamin but have been used by many manufacturers of inverted rides. A stand-up OTSR attaches directly to the saddle while a sit-down OTSR attaches to the seat with a standard seat belt.

Source: http://www.coasterforce.com/restraints.htm