The water offers a therapeutic environment which brings unique fluid and thermal properties to the therapeutic table. Before choosing to work in water, however, the therapist should be able to construct a case for aquatic-based physiotherapy based on the known effects of immersion.
Why? Participating in aquatic therapy can often require a greater time and resource commitment than does traditional therapy. Patients must purchase or obtain a bathing suit, travel to a location with a pool, dress, undress and shower in order to participate — and all of these factors can serve as barriers to patient care.
Although it is certainly possible to construct an argument for aquatic intervention based on an understanding of the physical properties of immersion alone, it helps to examine the literature which helps make the case.
Consistent physical exercise is an effective intervention for the management of musculoskeletal disorder. However, load-bearing during physical exercise may lead to an exacerbation of pain and protective muscle spasm in patients with musculoskeletal disorders. Pain alone may be a compelling reason to select the aquatic environment for a treatment environment.
When the therapist stops to consider the massive ramifications of pain — ranging from hormonal stressors to impaired sleep to constipation — the savvy therapist may choose the aquatic environment on the basis of pain alone. Post-surgical and post-fracture patients often make excellent candidates for aquatic therapy because of their reduced weight-bearing tolerances.
Proper positioning in water produces less spinal and lower extremity loading than the identical positioning on land. Exercise in water produces less joint and neural loading than the identical exercise performed on land permitting the graded and reproducible application of weight bearing.
Archimedes’ principle states: ‘when a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of fluid displaced.’
This upthrust, or buoyancy, counterbalances gravity and supports the body, resulting in an apparent reduction in weight bearing through the spine and lower extremities.
Although the human body is mostly water, the body’s density is slightly less than that of water and averages a speciﬁc gravity of 0.974, with men averaging higher density than women. Lean body mass, which includes bone, muscle, connective tissue, and organs, has a typical density near 1.1, whereas fat mass, which includes both essential body fat plus fat in excess of essential needs, has a density of about 0.9. Highly ﬁt and muscular men tend toward speciﬁc gravities greater than one, whereas an unﬁt or obese man might be considerably less.
So what? Well, all that means is that the patient displaces a volume of water weighing slightly more than the body, forcing the body upward. This effect can be used to create a perfect environment for working with patients with weight-bearing restrictions, such as those with musculoskeletal complaints.
The scientific literature also supports the concept that weight bearing may be systematically reduced by increasing the amount of the body submerged. A classic study by Harrison and Bulstrode with a near-cultish following measured static weight bearing in a pool using a population of healthy adults. What did they find?
Immersion to C-7 (neck) levels reduced weight bearing to between 6-10% of actual total body weight. Immersion to the xiphisternum reduced weight bearing to 25%-37% of actual total body weight. Immersion to the level of the anterior superior iliac spine (ASIS) reduced weight bearing to 40%-56% of actual total body weight.
Since that study from the 1980’s has been published, therapists everywhere have used those numbers to stake a claim that the pool is a reduced weight-bearing environment. For generations, physios have been using these standards – 50% at the hips; 25% at the nipple line, 10% at the C7 junction) to determine how much weight-bearing and load is occurring underwater.
But this may be grossly oversimplified. Patients on weight-bearing restrictions (and their physios!) may not realize how much load can be produced in water. Often, in the pool, pain signals can be reduced or absent; thus patients may overdo exercise or move into excessive weight bearing without knowing it.
In 2015, a team of researchers performed a study to determine if such anatomical landmarks could be used to predict weight-bearing in water. Luckily, the “rule of thumb” proved its worth; the anatomical tests that therapists have been using to determine weight-bearing seem to hold water (so to speak). The percentage of weight-bearing seen by these researchers was 6-7% at the neck, 23.9% at the nipple, and 51.4% at the navel. Whew. Lucked out on that one.
But wait. Physios are not off the hook yet. What if joint load in water can occur because of movement in addition to weight?
Kutzner (2017) examined the question of how much hip and knee joint load would be experienced by patients during immersion. The results were startling. They found that while it is true that immersion produces less joint load, that is not the whole picture. Drag forces had to be considered and such drag could actually produce MORE joint loading than simple weight bearing. Patients who were positioned wearing fins in non-weight bearing positions and cued to move rapidly produced joint forces 3x the person’s body weight.
What about deep water movements?
Therapists have long experimented with creating even greater traction effects than those present with waist or chest-deep immersion alone. Clinicians routinely position patients in deep water — either hanging or aqua-running — in an ‘unloaded’ position. Some clinicians have experimented with gaining extra traction by applying external weights at the waist (with a diver’s weight belt) or ankles.
One ‘unloading’ method used in hospitals and health resort sanitaria in Hungary for more than fifty years is getting re-examined by researchers. It looks like something out of a medieval (torture) textbook, but patients line up for treatment. Kurutz and Bender published a comprehensive examination of the effects of this technique, known as Weightbath Hydrotraction Treatment (WHT).
They found that WHT (see photos; WHT is essentially a cervical suspension of the human body in water) resulted in approximately 25 N stretching load in the cervical spine and about 11 N in the lumbar spine. By applying extra weights, the above tensile forces along the spinal column was increased. WHT for discopathy showed significant improvement of clinical parameters, which was still evident three months later, as demonstrated by using a controlled pilot study.
A just-published Journal of Aquatic Physical Therapy article examined 26 research articles which studied the effectiveness of aquatic vertical traction for patients with low back pain and sciatica (a population which traditionally seeks decreased compression of the spine and lower extremities). They found a mixed bag. While at least 2 studies seemed to point to benefit, they were not rigorous and needed to be reproduced.
Aquatic physiotherapy is becoming increasingly popular as a studied treatment intervention — especially for the pre and post-arthroplasty, fibromyalgia, arthritis and back and leg pain populations. It is merely good evidence-based practice to remain up-to-date on such studies.