Ankle/Wrist Weights
The above link is to a post I made a while back on these forums about using weights for training. Specifically I talked about ankle and wrist weights along with the advantages and disadvantages. Also I talked about the use of weighted clothing, such as the weight vests that are out there.
Recently I came upon a local in door pool. I have been using it to train for my 2nd Dan test. However I have not been using it in the same way that you might be thinking. In this little post I will talk about all the various ways that you can use pools to benefit your training.
The most obvious training activity you can do in a pool is swiming laps. Swiming laps is very low impact, so it saves your joints. In addition it will also burn a lot of calories per hour in comparison to running. Finally swiming will also build some some very impressive muscular endurance. However generally this will require good swiming technique. If you already know how to swim, that's great. If not you will have to devert time from martial arts training for swim training (a useful skill, but not what we are after).
Another training technique is breath training. Basically you want to see how far you can swim underwater or how long you can stay underwater. This will teach you to take deeper breaths as well as slowly expand your overall lung capasity. Finally swiming underwater will also get your body used to stresses such as lack of oxygen and eye irritation (if you open your eyes underwater. The obvious danger here is drowning. So if you plan on swiming underwater make sure the pool is free of large floatation devices. They are very easy to get trapped under and life guards might not be able to see you and save you in time.
The last obvious training method is diving. In this case last is least. Mostly you will be focused on how to dive as opposed to martial arts training. Although, you will learn a bit about coordination and balance. Generally I would advise against diving as martial arts training.
In all of the above, athletes tend to shave all the hair from their bodies. I don't recommend that martial artists do this specifically for swiming as our main goal by training in water is to increase the resistance against our muscles, not setting new world records. Shaving is counter productive.