General body tension causes us to breathe in a shallow way that also causes our heart rate and jittery feelings to increase. Proper deep breathing will slow our heart rate, increase calmness and ability to concentrate. Many activities such as athletic competition involve a warmup period. Purposeful physical activity decreases the excess energy that tends to creep out during delivery. If we don t release the energy in positive ways it will come out in ways like fidgeting, excessive shifting of weight, and general agitation.
Many professional speakers use physical activity to release stress right before a speech.
Once such activity which also uses abdominal breathing is called The Windmill .