those governed by USA Triathlon and the World Triathlon Corporation, drafting is not allowed, and thus the cycling portion more closely resembles individual time trial racing. In other races, such as those in the World Triathlon Series and World Triathlon Cup racing, drafting and the formation of pelotons are legal. This places an emphasis on running performance as several athletes will enter the bike to run transition at the same time due to drafting. Triathlon bicycles are generally optimized for aerodynamics, having special handlebars called aero-bars or tri-bars, aerodynamic wheels, and other components. Triathlon bikes use a specialized geometry, including a steep seat-tube angle both to improve aerodynamics and to spare muscle groups needed for running. At the end of the bike segment, triathletes also often cycle with a higher cadence (revolutions per minute), which serves in part to keep the muscles loose and flexible for running. Running The primary distinguishing feature of running in a triathlon is that it occurs after the athlete has already been exercising in two other disciplines for an extended period of time, so many muscles are already tired. The effect of switching from cycling to running can be profound; first-time triathletes are often astonished at their muscle weakness, which may be caused by lactate accumulation and the bizarre, sometimes painful sensation in their thighs a few hundred yards into the run, and discover that they run at a much slower pace than they are accustomed to in training. Triathletes train for this phenomenon through transition workouts known as "bricks": back-to-back workouts involving two disciplines, most commonly cycling and running. Transition The change over from sport to sport takes place in a designated transition area. The transition provides a staging area where bicycles, running shoes, hydration and other gear is set up ready to be used during the course of the event. The first transition, known as T1, is between the swim-to-bike segments of the race. The second transition, T2, is between the bike-to-run segments. Most events have one common transition area for both T1 and T2, while some point to point events have two separate transition areas. The time spent in transition is a timed segment and contributes towards the overall finishing time of the event. Races can hinge on transition skills, either by gaining or losing time in transition itself, or because of time penalties taken for faulty changeovers. As such, transition is