It’s been estimated that some 90% of all the activity affecting our central nervous system is related to gravity. Moshe Feldenkrais concluded that, “the bulk of stimuli arriving at the nervous system is from muscular activity constantly affected by gravity.” All our perceptions and sensations take place against this background of muscular activity, and that gravity therefore decreases our sensitivity to and awareness of the external and internal reality. If gravity-related tension reduces our sensitivity and awareness then it seems obvious that reduction of that tension should be beneficial. The floatation tank has this effect: Because of the Epsom salts-saturated water, the human body is completely supported, bobbing on the surface. Feet, legs, hands, arms, spine, head are all supported independently, rather than resting on top of or in a tension relation with one another. What floating affects, in John Lilly’s words, is “the peripheral countergravity stimulation exerted by the force of the accelerated mass, (i.e., the weight of the body). Floating in water, one distributes this countergravity pressure over the maximum possible area and hence attenuates this source of stimulation to the minimum possible value while still on this planet.” By lowering the gravitational muscular tension, then, we enable ourselves to perceive or detect much smaller sensations, that is, to intensify our sensations. Because our bone-muscle system is not constantly straining against gravity, and every muscle can relax more totally than is possible under any other circumstances, we can become intensely aware of knots and hot spots of chronic muscular tension and skeletal strain.
The release from gravity also allows the blood to circulate more freely and completely, reaching parts of the body that may be unhealthy because of cardiovascular constriction, and in the process allowing the heart to operate more efficiently with less effort. Another result is a drop in blood pressure. The pulse rate slows. By relieving gravitational pressure on joints, tendons, ligaments, bones, and muscles, the tank alleviates temporarily the chronic pain of such ailments as bursitis, arthritis, tendonitis, and traumatic or structural pains from bruises, sprains, broken bones, and muscle strain.