A certain degree of physical tension is necessary for all the actions that performers do onstage: in physical theatre, actors selectively tense certain muscle groups to create movements with different qualities. In musicals, muscles around the ribcage and back work to provide breath support to the voice.
However, tension can also interfere with the body and voice, preventing performers from using their instruments healthily.
Frederick Matthias Alexander—creator of the Alexander technique—studied the effects of physical tension on the voice and body. While participating in amateur drama performances in the early 20th century, Alexander often suffered from hoarseness and shortness of breath. When advice from doctors and elocution teachers did not resolve his issues, he embarked on a years-long study observing his own speaking habits by using a mirror. Using his observations, Alexander developed the Alexander technique as we know it today, and he was able to performance onstage once again.
The Alexander technique consists of various postural exercises to align the head, neck and body, ensuring that “bad” tension does not affect voice production. (A common exercise is to rest in the semi-supine position.) Practiced over time, the Alexander technique encourages performers to build useful tension into their muscle memory. Performers are able to access this useful tension with no conscious exertion.
Alexander, however, also insisted that his technique was mental in addition to physical. By encouraging his students to perform deliberate and mindful actions, he taught them to be self-aware of damaging habits.
The Alexander technique is now used widely in drama and music conservatories in the Western world, and has influenced other practitioners such as Kristin Linklater. For those interested in learning more about managing tension in relation to the voice and body, they can look at:
Guided Lessons for Students of the Alexander Technique by Nancy Dawley, Vivien Schapera, et al.
The Alexander Technique for Musicians by Judith Kleinman and Peter Buckoke
Freeing the Natural Voice by Kristin Linklater