If you are just getting started in your triathlon training, or if you have been doing it for a while and not sure how to make some noteworthy improvements, it could be very useful to break down the individual disciplines and understand more deeply how they are different when you do them in a triathlon, than when you do them on their own.
So, swimming in a triathlon is different from other types of swimming in a few key ways:
1. Open water. Most triathlons take place in open water, though not all do (many super-sprint and sprint races might take place in swimming pools). When you swim in open water, you may have to wear a wetsuit if the temperature is between 12 and 22 degrees C (between 54 and 72 degrees F). Lower than that, and most event organisers will cancel the event because it is too cold; higher than that, and they will not let you wear a wetsuit because it is too warm, but will still have the swim without westsuits.
Wearing a wetsuit changes the way you swim, in some good ways and some not-so-good ways. Wetsuits can give you more buoyancy and more streamlining, and most people find that they swim a little faster and a little more effortlessly. Wetsuits can also create more tension in the neck, shoulders and chest areas, make you feel a little heavy in the arms, and just feel uncomfortable. So, it is important to learn how to put on your wetsuit to create less tightness in the upper body, and get lots of practice in your wetsuit before your race.
2. Swimming straight. When swimming in open water, you have no lane ropes on either side or black line at the bottom of the pool to keep you swimming in a straight line. Swimming 750m to 1500m in open water can easily become 800m-1800m if you don't swim in a straight line. So, what can you do?
Keeping yourself straight in the water is fundamentally about balanced and straight swimming technique - keeping the body in a straight line, extending long and straight from your fingertips to your toes, rotating and extending evenly on both sides, pulling your hands evenly and in a straight line under your body. So, there is a lot you can do when practising in a swimming pool to make sure that, when you get out in open water, you swim straight.
Another thing you can do to make sure you are swimming straight in open water is called sighting. Sighting is when you look up in front of you and see where you are going (usually best to just lift your eyes above the water and not your whole head, in what is sometimes called the "crocodile eyes" technique). Sighting should be done as little as possible, because it will disturb your rhythm and your body position in the water, but can be a good fail-safe measure to ensure that you are, indeed, still heading in a straight line towards your destination.
Most races will have a buoy that you are swimming towards, but you probably want to find a larger, fixed object (a tree, a house, a telephone pole, etc) behind the buoy to aim for. A buoy can be hard to see from a distance or, if it is not a very large buoy, can be obscured by the other swimmers in front of you (sometimes the buoy might even be the same bright color as some of the swim caps people are wearing in front of you).
3. Beginning of the race. Swimming is almost always the first of the three sections of a triathlon. This means that you do not want to finish the swim section absolutely, totally spent from delivering a maximal, exhausting effort. You certainly want to deliver a strong effort, feeling like you have put in a strong effort for your race, but you need to be able to recover pretty quickly, jump on your bike and carry on for a whole lot more activity. So, when you swim in a triathlon you probably want to be more focused on pacing, efficiency, and aerobic endurance than if you were just swimming the same distance on its own.
Cycling in a triathlon has some key differences from a cycling-only event, much like the swimming issues discussed above, in rules, equipment and metabolic focus:
1. No drafting. Most age-group entrants in triathlons will have no-drafting rules (as opposed to elite, junior and youth triathletes in sprint and Olympic distance races, who are allowed to draft off each other), while most road cycling races (other than time trials) rely very heavily on drafting. For those of you who don't know what drafting is, it is the practice of a cyclist to ride very close behind another cyclist, so that the front cyclist blocks some of the wind resistance and saves the rear cyclist a noticeable amount of energy (reportedly, as much as 40% less effort for the rider at the back). The International Triathlon Union stipulates that, in draft-illegal events, you must maintain a distance of at least 10 meters (33 feet) between you and the cyclist in front of you. If you decide you want to pass the cyclist in front of you, you can enter this "draft zone" and pass the other cyclist in less than 20 seconds, as long as you maintain a distance of at least 3 meters (10 feet) sideways between you and the other cyclist. If you are caught by one of the marshalls in a race breaking any of these rules, you can be given a warning, a time penalty, or a disqualification. It is quite important to read the rules of each race, from the race organiser, before you start your race.
2. Time Trial bikes. In a draft-illegal race, the (arguable) upside is that you get to ride an insanely cool-looking Time Trial (or TT) bike. These bikes are specifically designed to be ridden as fast and aerodynamically as possible for a time trial (which is usually not as long as the bike sections of middle-distance and long-distance triathlons, by the way), where racers are staggered by their start times and not allowed to draft. As you can probably see above, the handlebars are set up very differently from a normal road racing bike, with the brakes and the gears also set up very differently. As such, it is probably a good idea to make sure you are first very comfortable and confident on a road racing bike before going out and buying a TT bike, and then make sure you give yourself plenty of time to get comfortable and confident with this new set-up. Plus, they are usually more expensive than road racing bikes.
3. Aero bars. Rather than going out and buying a whole, new TT bike, you could just opt to attach aero bars to the handlebars on your current road bike. Aero bars will still deliver some of the aerodynamic benefits that you would get from changing the placement of your hands and arms at the front of the bike, without the radical change in set-up, and the expense, of a TT bike. As you can see from the photo below, using aero bars (on the left) puts you in a very different position than you would normally have when riding comfortably on your road bike (on the right). Again, make sure you are first very comfortable on your road bike before putting aero bars on it, and then make sure you give yourself lots of time to get used to using the aero bars before you race with them.
4. Middle of the race. The other unique thing about cycling in a triathlon is that it is usually the middle of the three sections. Therefore, part of what you are doing at the beginning of the bike section is recovering from the efforts you put in on the swim, getting refueled, catching your breath and then building through the rest of the ride. Towards the end, you have to think about your transition to the run, get ready for the next section. Again, you don't want to finish the bike section totally exhausted from a maximal effort. So, cycling for a triathlete is often more about efficient riding, effective fueling, and finishing strong, but still having enough left in your legs for a strong run.
Well, at least the run section of a triathlon is typically at the end, so you don't need to finish the run with any other race efforts waiting for you afterwards. You can finish the run totally exhausted and spent when you cross the finish line, so in that regard it is more like doing a run on its own.
However, the fact that the run usually follows on from the bike means that you have to contend with the muscular strains and sudden adaptations that you might expect from such a change-over. Cycling typically engages the glutes, hips and thighs more, while running typically engages the hamstrings and calves more. As the blood rushes from one area to the other, it can create a strange rush of blood that many triathletes call "jelly legs."
On the plus side, the fact that the run comes after quite a lot of other activity means that you should be well warmed-up by the time you get to the run, arguably better warmed-up than if you were just doing a run on its own. Many triathletes (myself included) find that they actually have their best run results for distances up to half-marathon when done at the end of a triathlon. Of course, many triathletes (especially very experienced runners) find that they can't quite run as fast at the end of a triathlon as they would in a stand-alone running race.