by Bruce E. Becker, MD, MS
Many effects have been observed anecdotally throughout centuries of aquatic environment use for health maintenance and restoration but they are difficult to study.
Predominant among these are the relaxation effect of water immersion and the effect that water immersion has on pain perception.
Skin sensory nerve endings are stimulated. Both animal and human studies suggest that sensory overflow may be the mechanism by which pain is less well perceived when the affected body part is immersed in water[187,188].
Pain modulation is consequently affected with a rise in pain threshold, which increases with temperature and water turbulence, producing the proposed therapeutic effect of agitated whirlpool immersion [189,190].
Numerous studies of pain in persons with fibromyalgia have shown statistically significant improvement in pain and function [119,120,122,127,129].
A 1998 study of postoperative pain found warm water immersion treatments to reduce pain and possibly promote wound healing .
Studies have shown that aquatic exercise reduces anxiety scores and increases perceived well-being, equal to or superior to the effects noted with land exercise activity [190,191].
Heart rate variability can be analyzed to assess the impact of respiration and autonomic nervous system activity. During relaxation states, heart rate variability demonstrates an autonomic bias toward vagal or parasympathetic nervous system control, whereas during stressed states, sympathetic nervous system influence predominates and heart rate variability decreases [192,193].
The heart rate variability pattern seen during immersion is that of vagal or parasympathetic control, indicating perhaps an inherent bias toward the relaxation state .
In work done in the author’s laboratory studying heart rate variability, peripheral circulation and core temperature during cool, neutral, and warm water immersion in both younger (ages 18-30) and older (ages 40-65) subjects , the authors found a dramatic decrease in sympathetic nervous system activity during warm water immersion, but less so during neutral immersion and an increase in sympathetic bias during cool water immersion.
During warm water immersion, the authors also found a significant increase in sympathovagal balance, the interplay between the two components of the autonomic nervous system. Both groups of subjects responded similarly, although the older group had a more muted response.
During the same study, the authors found consistent decreases in diastolic blood pressures and dramatically increased distal circulation.
Aquatic therapy techniques for pain management may include Watsu, an aquatic technique derived from Shiatsu massage and Bad Ragaz, a floating technique focusing on carefully controlled movement and breathing, and gently progressive strengthening combined with aerobic exercise.