The bow is the 'granddaddy' of Alexander Lowen's bioenergetic exercises
Instructions: Stand with feet slightly wider than shoulder width apart, perhaps 18 inches. Keep the outside edges of the feet going straight forward (which will point the toes inward somewhat). Make a loose fist with both hands and reach arms around to push into the small of the back. Bend both knees deeply but keep heels on the floor. Arch backward so that shoulders go back and pelvis goes forward. The shoulders should end up directly above the heels Keep weight on the balls of the feet. Try to pull the shoulders and elbow back to open up the chest.
The idea and ideal behind this exercise is to assume a smooth curve or 'bow' The goal however, is not to 'perform' a shape. The goal is to induce tremors or vibration, which may not happen for a considerable time. The position is never really comfortable for anyone. Remember to breathe into the belly. Try to hold the position for at least a minute. It is necessary to endure some discomfort because the difficulty of the position is what is tiring the muscles and leading to loosening. Much discomfort should be avoided because pain will just tighten muscles. Follow up with the forward bend.
Rationale: This is a 'stress' position. Part of the way it works is 1) it will not be comfortable at all until the muscles tighten and 2) as some of the unnecessarily engaged muscles fatigue, it is possible that a person will sink into the position better. The exercise also increases breathing, opens the chest. And it obviously challenges a tight pelvis, especially one which is 'cocked back' (Lowen's term, referencing the bottom of the pelvis) or said differently, tipped anteriorly (mainstream physical therapy, referencing the top of the pelvis)
Source:Alexander Lowen's Bioenergetic exercises