Great article by arena coaches
The most familiar and popular swim aids include a swim snorkel and short fins. Both give you greater power and ease of movement through the water.
Fins are used to increase your forward trust and the power of your leg kick, but they also help you recover and can be used for aerobic workouts.
A swim snorkel is mainly used for technical drills but is also extremely useful for breathing and body stability purposes.
Controlling your posture is extremely important for improving your technique and the first step is to be able to control your body position without struggling with your breathing. You could try working on the technical side of your training with the help of a swim snorkel, so you can concentrate on performing your drills more effectively.
Here is an example of a workout using fins.
After warming up as usual and then swimming a little harder with the aid of a snorkel, put on your fins and swim about one hundred metres with backstroke legs to “loosen up” your ankles.
Here is the workout:
8×25 butterfly legs on your back, 15 secs recovery.
10×50 freestyle with fins, 15 secs recovery.
12×25 medley with fins (obviously not breaststroke!)
200 backstroke with fins
200 breaststroke (without fins!) to get the feel back in your legs and feet more quickly