With our introduction of the new A.T.V. (Advanced Training Visualizer), we need to better explain the differences between ISOMETRIC and ISOTONIC muscle building exercises.
The following is an excerpt from a longer article written about the P.E.T.E. by our good friend and dealer in Japan, Taijiro Takeura. Original article is here.
Generally speaking, there are two methods for training your muscles: isotonic exercises and isometric exercises.
Isotonic training (a.k.a. dynamic training) involves repeating a fixed set of movements while placing strains on a particular muscle, for example by using weights. In isometric training (a.k.a. static training), on the other hand, you strengthen a particular muscle by exerting a fixed amount of force over a certain period of time.
Both training methods have their advantages and shortcomings.
Isotonic training is very effective at training large muscles and easy to understand. It's also easy for the trainee to notice its effects. At most gyms that cater to the general public, muscle training is based on isotonic training methods. Its drawback, however, is that you can injure yourself if you choose the wrong parameters-- for example, by lifting weights that are too heavy for you, or by training for too long a time.
Isometric training is based on the theory that you can most effectively train your muscles by exerting about 60-70% of your maximum strength and holding still for about ten seconds. The most widely known isometric exercise, perhaps, is to press your palms together in front of your chest and hold still. Your muscles will always be working within their limits, so you can't injure yourself this way. You can also use isometric training to strengthen smaller muscles which may be difficult to train isotonically. On the other hand, the effects of isometric training are never as spectacular as those of isotonic training, which leads some people to overwork themselves; it can also be difficult to maintain your motivation when the results are difficult to see. In order to effectively train yourself using isometric methods, you do need a certain amount of knowledge. Isometric training can be seen in some of the more advanced gyms, especially those that cater to professional athletes.
Now let's see how all of this relates to brass playing.
Practicing on your instrument, including routines (such as long tones and scales) and etudes, consists of articulating various notes repeatedly, where the force of the air varies according to the height of the note, volume, etc. This can be thought of as a type of isotonic training. By going through the routines and etudes (which hopefully has been chosen to match your level of expertise) in a consistent manner, you can expect to significantly improve your playing. The visible improvement will give you great satisfaction. On the other hand, if you become impatient and tackle advanced materials too early, you can cause your muscles to degrade; caution is required.
Practicing using the P.E.T.E. is a type of isometric training; you exert a certain amount of force and hold still for a certain amount of time. It's possible to isolate and strengthen just those muscles that work in the way (explained above) that is unique to the embouchure. You can also strengthen the muscles that surround and support the embouchure. There isn't much chance of injuring your muscles, because you should be able to keep the strain on your muscles within bounds; you should, however, still be watchful. You should also note that isometric training using the P.E.T.E. can't improve all aspects of brass playing. You still have to use your instrument to practice the techniques that involve the air stream.