An anaerobic threshold workout means that you are pushing your heart rate to above 20 beats per minute less than your maximum heart rate. In other words, you are going close to race pace but for fewer and longer rest between distances swum. Most anaerobic threshold training is designed to help the shorter races of 200 on down to 50 meters. For this type of training, we recommend that you adopt the breathing patterns that you will use in each race, or as close as possible. In doing threshold 50’s , for example, you should take as few breaths as possible. For the hundreds, we recommend males breath every cycle (except off the turns) and for women, every cycle for two breaths, then hold for two cycles. In the 200, we feel both genders should breathe every cycle in free and 3 up one down in fly. For women training for the 100 fly, we recommend two up (breathing) and one down. The pain of accumulating lactate and the urge to breathe more is considerable on these sets, but you must be able to push through the pain. The reward is building an anaerobic system that buffers the acidity better and enables you to sustain the higher intensity effort for longer.