Barbara J. Hoogenboom, EdD, PT, SCS, ATC
Nancy E. Lomax, PT
After reading this chapter,
the athletic training student should be able to:
- Explain the principles of buoyancy and specific gravity and the role they have in the aquatic environment.
- Identify and describe the 3 major resistive forces at work in the aquatic environment.
- Apply the principles of buoyancy and resistive forces to exercise prescription and progression.
- Contrast the advantages and disadvantages of aquatic therapy in relation to traditional land-based exercise.
- Identify and describe techniques of aquatic therapy for the upper extremity, lower extremity, and trunk.
- Select and use various types of equipment for aquatic therapy.
- Incorporate functional work- and sport-specific movements and exercises performed in the aquatic environment into rehabilitation.
- Understand and describe the necessity for transition from the aquatic environment to the land environment.
In recent years, there has been widespread interest in aquatic therapy. It has rapidly become a popular rehabilitation technique for treatment of a variety of patient populations.76 This newfound interest has sparked numerous research efforts to evaluate the effectiveness of aquatic therapy as a therapeutic intervention. Current research shows aquatic therapy to be beneficial in the treatment of everything from orthopedic injuries to spinal cord damage, chronic pain, cerebral palsy, multiple sclerosis, and many other conditions, making it useful in a variety of settings.12,34,41,46,58,73 It is also gaining acceptance as a preventative maintenance tool to facilitate overall fitness, cross-training, and sport-specific skills for healthy athletes.27,38,43 General conditioning, strength, and a wide variety of movement skills can all be enhanced by aquatic therapy.23,51,57,69
The use of water as a part of healing techniques has been traced back through history to as early as 2400 BC, but it was not until the late 19th century that more traditional types of aquatic therapy came into existence.7 The development of the Hubbard style whirlpool tank in 1820 sparked the initiation of present-day therapeutic use of water by allowing aquatic therapy to be conducted in a highly controlled clinical setting.11 Loeman and Roen took this a step farther in 1824 and stimulated interest in use of an actual pool or what we now call aquatic therapy. Only recently, however, has water come into its own as a therapeutic exercise medium used for a wide variety of diagnoses and dysfunctions.49
Aquatic therapy is believed to be beneficial primarily because it decreases joint compression forces.59 The perception of weightlessness experienced in the water assists in decreasing joint pain and eliminating or drastically reducing the body’s protective muscular guarding and pain that can carry over into the patient’s daily functional activities.69,71 Although many patients perceive greater ease of movement in the aquatic environment compared to movement on land, the effects of land-based to aquatic-based exercise and the results are inconsistent. A study by Kim and Choi found that aquatic therapy in the rehabilitation of sports injuries improved pain, range of motion (ROM), muscle strength, balance, and performance, but the evidence regarding benefits of aquatic therapy compared to land-based physical therapy was inconclusive.36 Rhode and Berry demonstrated that plyometric exercises done both on land and in water can improve measures of athletic performance; however, neither appears to produce significantly better performance than the other.56 Similarly, Bayraktar et al looked at core stabilization exercises performed on land or in water with patients who had lumbar disc herniations and found no difference in benefits between the 2 environments.5 Shonewill et al recommend a combination of aquatic and land-based therapy for improving ROM and strength as well as for decreasing edema and pain.61 Barker et al suggest that aquatic exercise has only moderate beneficial effects on pain, physical function, and quality of life in adults with musculoskeletal conditions when compared with benefits achieved with land-based exercise.4 A study by Hall et al showed that aquatic therapy does not actually decrease pain more effectively than activities on land.29
The primary goal of aquatic therapy is to teach the patient how to use water as a modality for improving movement, strength, and fitness.2,69 Thus, along with other therapeutic modalities and interventions, aquatic therapy can become one link in the patient’s recovery chain.1
PHYSICAL PROPERTIES AND RESISTIVE FORCES
The athletic trainer must understand several physical properties of the water before designing an aquatic therapy program. Land exercise cannot always be converted to aquatic exercise because buoyancy rather than gravity is the major force governing movement.59 A thorough understanding of buoyancy, specific gravity, the resistive forces of the water, and their relationships must be the groundwork of any therapeutic aquatic program. The program must be individualized to the patient’s particular injury/condition and activity level if it is to be successful. Patients with chronic pain often demonstrate significant limitations in functional movement, in addition to musculoskeletal and cardiovascular conditioning. Submerging a patient in water at varying depths minimizes the compressive force of gravity. Consequently, patients undergoing water therapy are better able to practice movement patterns and engage in exercise that would not otherwise be able to tolerate on land.42
Buoyancy is one of the primary forces involved in aquatic therapy.59 All objects, on land or in the water, are subjected to the downward pull of the earth’s gravity. In the water, however, this force is counteracted to some degree by the upward buoyant force. According to Archimedes’ principle, any object submerged or floating in water is buoyed upward by a counterforce that helps support the submerged object against the downward pull of gravity. In other words, the buoyant force assists motion toward the water’s surface and resists motions away from the surface.30,61 Because of this buoyant force, a person entering the water experiences an apparent loss of weight.19 The weight loss experienced is nearly equal to the weight of the liquid that is displaced when the object enters the water (Figure 15-1).
For example, a 100-lb individual, when almost completely submerged, displaces a volume of water that weighs nearly 95 lb; therefore, that person feels as though he or she weighs less than 5 lb. This sensation occurs because, when partially submerged, the individual only bears the weight of the part of the body that is above the water. With immersion to the level of the seventh cervical vertebra, both males and females only bear about 6% to 10% of their total body weight (TBW).59 The percentages increase to 25% to 31% TBW for females and 30% to 37% TBW for males at the xiphisternal level, and to 40% to 51% TBW for females and 50% to 56% TBW for males at the anterosuperior iliac spine level31 (Table 15-1). The percentages differ slightly for males and females because of the differences in their centers of gravity. Males carry a higher percentage of their weight in the upper body, whereas females carry a higher percentage of their weight in the lower body. The center of gravity on land corresponds with a center of buoyancy in the water.49 Variations of build and body type only minimally effect weightbearing values. As a result of the decreased percentage of weight-bearing offered by the buoyant force, each joint that is below the water is decompressed or unweighted. This allows ambulation and vigorous exercise to be performed with little impact and drastically reduced friction between joint articular surfaces.
Progressing the activity from walking to running in the aquatic environment does not change the forces on the joints; however, minimal changes in the joint forces occur as the speed of running is increased. Fontana et al24 report a 34% to 38% decrease in force while running at hip level of water and a 44% to 47% decrease force with running at chest level, compared to running on land. The relative decrease in weightbearing forces during aquatic activities needs to be considered when dealing with athletes with injuries and restrictions of weight-bearing, and may allow early running for those with such conditions and limitations.
Through careful use of Archimedes’ principle, a gradual increase in the percentage of weightbearing can be undertaken. Initially, the patient would begin nonweightbearing exercises in the deep end of the pool. A wet vest or similar buoyancy device might be used to help the patient remain afloat for the desired exercises. This and other commercial equipment available for the use in the aquatic environment will be discussed in the upcoming section, “Facilities and Equipment.”
Clinical Decision-Making Exercise 15-1
A 35-year-old male sustained a right rotator cuff tear while playing softball. Three weeks ago, he had a surgical repair of a tear of less than 2 cm and has now been referred for rehabilitation. He is active and plays softball, golf, and tennis. At what point could he begin to participate in an aquatic program during his rehabilitation?
Buoyancy is partially dependent on body weight. However, the weight of different parts of the body is not constant. Therefore, the buoyant values of different body parts will vary. Buoyant values can be determined by several factors. The ratio of bone weight to muscle weight, the amount and distribution of fat, and the depth and expansion of the chest all play a role. Together, these factors determine the specific gravity of the individual body part. On average, humans have a specific gravity slightly less than that of water. Any object with a specific gravity less than that of water will float. An object with a specific gravity greater than that of water will sink. However, as with buoyant values, the specific gravity of all body parts is not uniform. Therefore, even with a total body specific gravity of less than the specific gravity of water, the individual might not float horizontally in the water. Additionally, the lungs, when filled with air, can further decrease the specific gravity of the chest area. This allows the head and chest to float higher in the water than the heavier, denser extremities. Many athletes tend to have a low percentage of body fat (specific gravity greater than water) and, therefore, can be thought of as “sinkers.” Consequently, compensation with floatation devices at the extremities and trunk might be necessary for some athletes.6,61
Water has 12 times the resistance of air.64 Therefore, when an object moves in the water, the several resistive forces that are at work must be considered. Forces must be considered for both their potential benefits and their precautions. These forces include the cohesive force, bow force, and drag force.
There is a slight but easily overcome cohesive force that runs in a parallel direction to the water surface. This resistance is formed by the water molecules loosely binding together, creating a surface tension. Surface tension can be seen in still water because the water remains motionless with the cohesive force intact unless disturbed.
A second force is the bow force, or the force that is generated at the front of the object during movement. When the object moves, the bow force causes an increase in the water pressure at the front of the object and a decrease in the water pressure at the rear of the object. This pressure change causes a movement of water from the high-pressure area at the front to the low-pressure area behind the object. As the water enters the low-pressure area, it swirls in to the low-pressure zone and forms eddies, or small whirlpool turbulences.18 These eddies impede flow by creating a backward force, or drag force (Figure 15-2).
This third force, the fluid drag force, is very important in aquatic therapy. The bow force on an object (and, therefore, also the drag force) can be controlled by changing the shape of the object or the speed of its movement (Figure 15-3).
Frictional resistance can be decreased by making the object more streamlined. This change minimizes the surface area at the front of the object. Less surface area causes less bow force and less of a change in pressure between the front and rear of the object, resulting in less drag force. In a streamlined flow, the resistance is proportional to the velocity of the object. When working with a patient with generalized weakness, consideration of the aquatic environment is necessary. Increased activity occurring around the patient and turbulence of the water can make walking a challenging activity (Figure 15-4).
On the other hand, if the object is not streamlined, a turbulent situation (also referred to as pressure or form drag) exists. In a turbulent situation, drag is a function of the velocity squared. Thus, by increasing the speed of movement 2 times, the resistance the object must overcome is increased 4 times.19 This provides a method to increase resistance progressively during aquatic rehabilitation. Considerable turbulence can be generated when the speed of movement is increased, causing muscles to work harder to keep the movement going. Another method to increase resistance is to change directions of movement, creating increased drag. Finally, by simply changing the shape of a limb through the addition of rehabilitation equipment that increases surface area, the athletic trainer can modify the patient’s workout intensity to match strength increases (Figure 15-5).
Drag force must also be considered when portions of a limb or joint must be protected after injury or surgery. For example, when working with a patient with an acutely injured medial collateral or anterior cruciate ligament of the knee, resistance must not be placed distal to the knee because of the increased torque that occurs caused by drag forces.
It has been suggested that inadequate resistance in aquatic exercise limits the effectiveness in increasing muscle strength in patients with musculoskeletal conditions. To better understand the potential therapeutic benefit of aquatic strengthening exercise, assessing resistance and applying greater levels of resistance should be considered.32 However, quantification of resistive forces that occur during aquatic exercise is a challenge. Pöyhönen et al55 examined knee flexion and extension in the aquatic environment using an anatomic model in barefoot and hydroboot-wearing conditions. They found that the highest drag forces and drag coefficients occurred during early extension from a flexed position (150 to 140 degrees of flexion) while wearing the hydroboot (making the foot less streamlined), and that faster velocity was associated with higher drag forces.55
Once therapy has progressed, the patient could be moved to neck-deep water to begin light weightbearing exercises. Gradual increases in the percentage of weightbearing are accomplished by systematically moving the patient to shallower water. Even when in waist-deep water, both male and female patients are only bearing about 50% of their TBW. By placing a sinkable bench or chair in the shallow water, step-ups can be initiated under partial weight-bearing conditions long before the patient is capable of performing the same exercise when full weightbearing on land. Thus, the advantages of diminished weightbearing exercises are coupled with the proprioceptive benefits of closed kinetic chain exercise, making aquatic therapy an excellent functional rehabilitation activity.
|Indications for Use||Illustration of Benefits|
Assist in edema control, decrease pain, increase mobility as edema decreases
Earlier initiation of rehabilitation, controlled active movements
Strength progression from assisted to resisted to functional; gradual increase in exercise intensity
Decreased balance, proprioception, coordination
Earlier return to function in supported, forgiving environment, slower movements
Can partially or completely unweight the lower extremities; regulate weightbearing progressions
Cardiovascular deconditioning or potential deconditioning because of inability to train
Gradual increase of exercise intensity, alternative training environment for lower weightbearing
Slower movements, easier assessment, and modification of gait
Difficulty or pain with land interventions
Increased support, decreased weightbearing, assistance as a result of buoyancy, more relaxed environment
ADVANTAGES AND BENEFITS OF AQUATIC REHABILITATION
The addition of an aquatic therapy program can offer many advantages to a patient’s therapy26,61 (Table 15-2). The buoyancy of the water allows active exercise while providing a sense of security and causing little discomfort.65 Using a combination of the water’s buoyancy, resistance, and warmth, the patient can typically achieve more in the aquatic environment than is possible on land.40 Early in the rehabilitation process, aquatic therapy is useful in restoring ROM and flexibility. As normal function is restored, resistance training and sport-specific activities can be added.
Following an injury, the aquatic experience provides a medium where early motions can be performed in a supportive environment. The slow-motion effect of moving through water provides extra time to control movement, which allows the patient to experience multiple movement errors without severe consequences.51,62 This is especially helpful in lower extremity injuries where balance and proprioception are impaired. Geigle et al demonstrated a positive relationship between use of a supplemental aquatic therapy program and unilateral tests of balance when treating athletes with inversion ankle sprains.26 The increased amount of time to react and correct movement errors, combined with a medium in which the fear of falling is removed, assists the patient’s ability to regain proprioception and neuromuscular control. For the patient population with a diagnosis of rheumatoid and/or osteoarthritis with lower extremity involvement, about 80% demonstrate balance difficulties and higher risk for falls.20,21 A study performed by Suomi and Koceja67 demonstrated that aquatic exercise helped decrease total sway area and medial/lateral sway in both full vision and no vision conditions, which placed them in lower risk for falls. In all ages, the fear of falling can limit people from progressing to their highest level of function.
Turbulence functions as a destabilizer and as a tactile sensory stimulus. The stimulation from the turbulence generated during movement provides feedback and perturbation challenge that aids in the return of proprioception and balance.
There is also an often overlooked benefit of edema reduction that occurs as a consequence of hydrostatic pressure. Edema reduction could benefit the patient by assisting in pain reduction and allowing for an increase in ROM.
By understanding buoyancy and using its principles, the aquatic environment can provide a gradual transition from nonweightbearing to full weightbearing land exercises.59 This gradual increase in percentage of weightbearing helps provide a gradual return to smooth, coordinated, and low-pain or pain-free movements. By using the buoyancy force to decrease the forces of body weight and joint compressive forces, locomotor activities can begin much earlier following an injury to the lower extremity than on land. This provides an enormous advantage to the athletic population. The ability to work out hard without fear of reinjury provides a psychological boost to the athlete. This helps keep motivation high and can help speed the athlete’s return to normal function.40 Psychologically, aquatic therapy increases confidence because the patient experiences increased success at locomotor, stretching, or strengthening activities while in the water. Tension and anxiety are decreased, and the patient’s morale increases, as does postexercise vigor.18,19,49
Clinical Decision-Making Exercise 15-2
A collegiate football player sustained a severe anterior cruciate/medial collateral ligament and medial meniscus injury to the right knee. The injury to the medial meniscus was so severe that it was deemed nonrepairable, and the surgeon determined that a staged surgery (anterior cruciate ligament reconstruction first, later a meniscal allograft) would best serve the athlete. The medial collateral ligament is allowed to heal without surgical intervention. Despite well-designed and well-executed rehabilitation after the anterior cruciate ligament reconstruction, it is likely that after the meniscal transplant, a clinical “regression” in strength, ROM, and function will occur due to postoperative restrictions.
What rehabilitation techniques can the athletic trainer use to maximize the rehabilitation after the meniscal allograft during the requisite nonweightbearing and partial weightbearing phases?
Muscular strengthening and reeducation can also be accomplished through aquatic therapy.52,69 Progressive resistance exercises can be increased in extremely small increments by using combinations of different resistive forces. The intensity of exercise can be controlled by manipulating the flow of the water (turbulence), the body’s position, or through the addition of exercise equipment. This allows individuals with minimal muscle contraction capabilities to do work and see improvement. The aquatic environment can also provide a challenging resistive workout to an athlete nearing full recovery.69 Additionally, water serves as an accommodating resistance medium. This allows the muscles to be maximally stressed through the full ROM available. One drawback to this, however, is that strength gains depend largely on the effort exerted by the patient, which is not easily quantified.
In another study, Pöyhönen et al54 studied the biomechanical and hydrodynamic characteristics of the therapeutic exercise of knee flexion and extension using kinematic and electromyographic analyses in flowing and still water. They found that the flowing properties of water modified the agonist/antagonist neuromuscular function of the quadriceps and hamstrings in terms of early reduction of quadriceps activity and concurrent increased activation of the hamstrings. They also found that flowing water (turbulence) causes additional resistance when moving the limb opposite the flow. They concluded that when prescribing aquatic exercise, the turbulence of the water must be considered in terms of both resistance and alterations of neuromuscular recruitment of muscles.
Strength gains through aquatic exercise are facilitated by the increased energy needs of the body when working in an aquatic environment. Studies show that aquatic exercise requires higher energy expenditure than the same exercise performed on land.14,18,19,69 The patient has to perform the activity as well as maintain a level of buoyancy while overcoming the resistive forces of the water. For example, the energy cost for water running is 4 times greater than the energy cost for running the same distance on land.18,19,22
A simulated run in either shallow or deep water assisted by a tether or floatation devices can be an effective means of alternate fitness training (cross-training) for the injured athlete. The purpose of aquatic running is to reproduce the posture of running and use the same muscle groups in the aquatic environment as would be used on land. However, it should be noted that there are differences while being in the unloaded environment and resistance of the water with aqua running changes the relative contributions of the involved muscle groups.75 It should be noted that a study of shallow-water running (xiphoid level) and deep-water running (using an aqua jogger), at the same rate of perceived exertion, found a significant difference of 10 beats/min in heart rate, with shallow-water running demonstrating a greater heart rate. The authors of that study point out that aquatic rehabilitation professionals should not prescribe shallow-water working heart rates from heart rate values obtained during deep-water exercise.57
Hydrostatic pressure assists in cardiac performance by promoting venous return, thus the heart does not have to beat as fast to maintain cardiac output. Deep-water running at submaximal and maximal speeds demonstrates lower heart rates than shallow-water running. The greater the temperature of the water, the higher the heart rate in response.75 All patients should be instructed in how to accurately monitor their heart rate while exercising in water, whether deep or shallow.14
Not only does the patient benefit from early intervention, but aquatic exercise also helps prevent cardiorespiratory deconditioning through alterations in cardiovascular dynamics as a result of hydrostatic forces.10,33,68 The heart actually functions more efficiently in the water than on land. Hydrostatic pressure enhances venous return, leading to a greater stroke volume and a reduction in the heart rate needed to maintain cardiac output.70 The corresponding decrease in ventilatory rate and increase in central blood volume can allow the injured athlete to maintain a near-normal maximal aerobic capacity with aquatic exercise.26,71
For the patient who has comorbidities, there is a study that examined the cardiovascular response during aquatic interventions in patients with osteoarthritis. The authors found that the systolic and diastolic blood pressure increased with entering and exiting the aquatic environment secondary to the rapid changes in hydrostatic pressure.3
For the athlete or the geriatric patient with compensations, consideration must be paid to monitoring responses. Because of the hydrostatic effects on heart efficiency, it has been suggested that an environment-specific exercise prescription is necessary.38,47,67,74 Some research suggests the use of perceived exertion as an acceptable method for controlling exercise intensity. Other research suggests the use of target heart rate values as with land exercise, but compensates for the hydrostatic changes by setting the target range 10% lower than what would be expected for land exercise64,69 (Figure 15-6). Regardless of the method used, the keys to successful use of aquatic therapy are supervision and monitoring of the patient during activity and good communication between patient and athletic trainer.
Untreated infectious disease (patient has a fever/temperature)
Open wounds or unhealed surgical incisions
Contagious skin diseases
Serious cardiac conditions
Seizure disorders (uncontrolled)
Excessive fear of water
Allergy to pool chemicals
Vital capacity of 1 L
Uncontrolled high or low blood pressure
Uncontrolled bowel or bladder incontinence
Menstruation without internal protection
Clinical Decision-Making Exercise 15-3
A high school cross-country runner sustained a small, second-metatarsal stress reaction/fracture during the short 3-month season in response to increased volume and intensity of training. She has been cleared by her physician to finish out the remaining 3 weeks of the competitive season but is only allowed to run in meets. What might the athletic trainer suggest for alternate training to allow her to maintain aerobic function and enable her to compete?
DISADVANTAGES OF AQUATIC REHABILITATION
As with any therapeutic intervention, aquatic therapy has its disadvantages. The cost of building and maintaining a rehabilitation pool, if there is no access to an existing facility, can be very high. Also, qualified pool attendants must be present, and the athletic trainer involved in the treatment must be trained in aquatic safety and therapy procedures.16 An athlete who requires high levels of stabilization will be more challenging to work with because stabilization in water is considerably more difficult than on land. Thermoregulation issues exist for the patient who exercises in an aquatic environment. Because the patient cannot always choose the temperature of the pool, the effects of water temperature must be noted for cool, warm, or hot pool temperatures. Water temperatures that are higher than body temperature cause an increase in core body temperature greater than that in a land environment as a result of differences in thermoregulation. Water temperatures that are lower than body temperature decrease core body temperature and cause shivering in athletes faster and to a greater degree than in the general population because of their low body fat.14 Another disadvantage of aquatic exercise used for cross-training is that training in water does not allow athletes to improve or maintain their tolerance to heat while on land.
Recently healed wound or incision, incisions covered by moisture-proof barrier
Altered peripheral sensation
Respiratory dysfunction (asthma)
Seizure disorders controlled with medications
Fear of water