Triathletes tend to be extraordinarily fit, and many amateur athletes choose triathlon specifically for its fitness benefits. Because all three events are endurance sports, nearly all of triathlon training is cardiovascular exercise. In addition, since triathletes must train for three different disciplines, they tend to have more balanced whole-body muscular development than pure cyclists or runners, whose training emphasizes only a subset of their musculature.
Specialization of swimming, cycling and running in triathlon
Each element of the triathlon is a little different from those sports if encountered alone. While amateur triathletes who also compete in individual swimming, cycling or running races generally apply the same techniques and philosophy to triathlon, seasoned triathletes and professionals have specialized techniques for each discipline that improve their race as a whole.
Triathletes will use their legs less vigorously and more carefully than other swimmers, husbanding their energy for the cycle and run to follow. Many triathletes use altered swim strokes to compensate for turbulent, aerated water and to conserve energy for a long swim. In addition, the majority of triathlons involve open-water (outdoor) swim stages, rather than pools with lane markers. As a result, triathletes in the swim stage must jockey for position, and can gain some advantage by drafting, following a competitor closely to swim in their slipstream. Triathletes will often use "dolphin kicking" and diving to make headway outward against waves and body surfing to use a wave's energy for a bit of speed at the end of the swim stage. Also, open-water swims necessitate "sighting", raising the head to look for landmarks or buoys which mark the course. A modified stroke allows the triathlete to lift the head above water to sight without interrupting the swim or wasting energy.
Because open water swim areas are often cold, specialized triathlon wetsuits have been developed. In addition to warmth, wetsuits add buoyancy and smoothness, both of which increase swimming speed. Wetsuits are only legal in sanctioned events with a water temperature equal to or below 78° Fahrenheit (25.5° Celsius). Some events allow wetsuits regardless of water temperature, and sometimes they are required. Or, in a single event, wetsuits may be allowed for "age groupers" but not for professionals, as the temperature rules differ slightly between the two groups.
Triathlon cycling, with the exception of Olympic triathlon and ITU World Cup races, is very different from most professional bicycle racing because it does not allow drafting, and so racers do not cluster in a peloton. It more closely resembles individual time trial racing. Triathlon bicycles are generally optimized for aerodynamics, having special handlebars called "aero-bars" or "tri-bars", aerodynamic wheels or other components. Triathlon bikes use a specialized geometry including a steep seat-tube angle both to improve aerodynamics and spare muscle groups needed for running (see also Triathlon equipment). 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. It is believed, though, that the primary benefit to spinning in a triathlon is the strain of the effort being placed disproportionately on the slow twitch muscle fibers, preventing the athlete from accumulating an oxygen debt before the run.
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 very profound; first-time triathletes are often astonished at the bizarre 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 or "bricks": back-to-back workouts involving two disciplines, most commonly cycling and running. (The term "brick" has multiple claims of origination/derivation. Among those is the derivation from a partial anagram of Bike-Run. Also, it is simply a descriptive term of how your legs feel for the first part of the run. Another is given credit to Mark Sisson and Scott Zagarino (1988) who associated the term brick to the idea of "Just another brick in the wall"... as noted in a song by the group "Pink Floyd". Another association of this term has been claimed to originate from a New Zealand athlete by the name of Matt Brick.)