I have been fielding questions about whether one should train indoors and all the pros and cons of it. I even responded to an online forum question on the topic which also gave me a chance to read about what other people thought about indoor training. I will discuss indoor training in all three sports and give you some tips about what to watch out for.

 Swimming indoors- Swimming in a pool whether it is indoors or outdoors is generally similar. Many people try to swim outdoors as much as possible due to air quality issues that many indoor pools may have. But others prefer to save their skin from further sun damage by swimming under a roof. What I do recommend for pool swimmers is to make sure they get some open water swimming and learn to sight and navigate.

 Riding indoors- Indoor riding should be an option for any committed triathlete. The logistics of outdoor road riding in the winter (the lack of daylight, the cold, wet and snowy weather) can prevent many from being able to do any cycling unless it is inside. Having the option of riding indoors is essential in order to get all the training necessary to have a good showing on the bike at triathlons. The best option for indoor riding is to ride a trainer like the Computrainer where you can clip into your own bike. This way your body's position on the bike is the same whether you are indoors or outdoors. Here are some pros and cons to consider.

 Pros
 1.Convenience. You can ride anytime.
 2.Safety. In the age of texting it is good to know you will not get run over when riding the trainer.
 3.Performance comparisons. Since the wind is not a factor and temperature can be kept constant it is a great way to compare fitness and do fitness tests.
 4.Aerobic development. If your trainer is the kind you use your own bike and you do not have to balance you will find that the heart rate per given effort is lower. Not having to balance and being in a calm environment keeps your heart rate low. This allows your legs to work hard and develop. This is something that only aerobic training (low heart rate training) can bring.
 5.No coasting. For the most part coasting is not an option and because of this some coaches advise to cut one third of the time from your rides since you are really making time count. Just be careful to not lose endurance as endurance is all about time on the bike.
 6.Social. You can join a group class or invite a friend over to ride the trainer and all of a sudden the session is more fun and no one gets dropped.

 Cons
 1.Boring. Doing this on your own for hours will not just challenge your body but your mind. Get some friends or watch your favorite races on a TV to help.
 2.Not real conditions. Unless your race is indoors, an outside race has a lot more distractions that an athlete needs to train with to be well prepared for a race. Ride outside to learn how to deal with the wind, the hills, pot holes and objects on the road in addition to other riders.
 3.Dehydration. Generally speaking one will sweat a lot more riding indoors than outdoors. Take this into consideration.

 Running Indoors- The treadmill is another convenient way to get your run workouts in. If the weather or daylight is not cooperating or perhaps you have kids and leaving them at home alone is not an option you can just jump on the treadmill and get your run workout in.

 Pros
 1.Convenient. Get your shoes and shorts and hop on. You can place your water bottle on it. Some even come equipped with TV screens. It's easy to get a quick workout in.
 2.Controlled environment. You can set the pace and conditions to your wish. Set the temperature to 80 then run. Now you can have heat training for St. Croix while it's snowing outside.
 3.Easy does it. If you have extra pounds or are coming back from injury and need to take it easy for a while, the treadmill's soft surface is a great way to get started.

 Cons
 1.Boring. Compared to running outside on a nice trail, running indoors can be more difficult on the mind than the body. I know many people that cannot stand it.
 2.Safety. Many people use the treadmill to avoid icy roads or snow which can get you hurt outside. But I must caution that a fall on the treadmill is not going to be kind. You must stay focused when running on the treadmill.
 3.Too soft. One of the downfalls for many triathletes and particularly those training for Iron distance is the lack of strength and ability to take the pounding late in a race. This is even more important if you are larger than average. Part of the conditioning required comes from running on the same surface you will race on. For example, next year the Ironman Boulder marathon will take place almost entirely on cement. This is by far the toughest surface to run on for an extended period of time. Too much treadmill running will not have you ready for such a run course.
 4. Injuries. Many people advocate the treadmill for speed work as you set the pace and all you have to do is keep up. However, the treadmill does some of the work for you and you do not have to utilize your hamstrings as much to carry your center of gravity forward. It utilizes your muscles different than real running. I have had athletes hurt their hamstrings by trying to run speeds their body was not ready for. I would not advice to do any sort of maximal speed efforts on it.

 Training indoors is in a very important and viable alternative and almost necessary to be a successful triathlete. However, it would be very difficult to achieve your potential if done exclusively. Mix it up and consider the pros and cons based on your personal situation.