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Deep Water Running for Prevention and Rehabilitation of Running Injuries
Acknowledgments
David Brennan, MEd, for sharing his vast expertise in DWR and use of his sample workouts and RPE scale.
Lew Thorne, president and founder of AquaJogger, for his counsel and supplying us with images.
Introduction
Deep water running (DWR) is a form of cardiovascular exercise that is useful for the injured and noninjured athlete. It is an important cross-training tool for runners, as it closely matches the intensity, duration, range of motion and muscle recruitment patterns of land running (LR). In DWR, the participant wears a flotation belt and is immersed in water to the level of the shoulders. The athlete simulates running; however, no contact with the bottom of the pool is made. This allows for a similar range of motion and muscle recruitment pattern to LR without repeated impact with the ground and consequent joint and soft-tissue loading (see Fig. 13.1 ). DWR is demonstrated to achieve a similar metabolic response to LR and is therefore an effective method to maintain cardiovascular fitness while healing from an overuse injury. It can be used as a supplement to LR and to aid in recovery after strenuous exercise. In addition, it has been shown to increase cardiovascular fitness in the untrained individual. While similar in many ways to LR, there are idiosyncrasies to DWR and aquatic fitness that should be understood by both clinician and athlete. This chapter will discuss these differences, the literature demonstrating the utility of DWR, and its practical application.
Physics of Water
Water has many physical properties that make it a unique medium for exercise. While there are numerous forces interacting when underwater, a complete discussion of fluid dynamics is beyond the scope of this text. Those most pertinent to DWR are discussed below.
Viscosity
Water is much more viscous than air. The higher viscosity has large implications for aquatic exercise because it creates resistance to movement as a logarithmic function to velocity. As there is no contact with the ground during DWR, it is an open-chain exercise. DWR relies on water's viscosity for muscle loading while avoiding the potentially deleterious ground reaction forces of LR. During LR, there are greater resistive forces during stance phase as the leg propels the body forward against gravity, and less resistive forces during swing phase as the leg travels through air. In contrast, during DWR there is similar resistance throughout the whole gait cycle, which is largely responsible for the slower cadence that is observed during DWR.
Buoyancy
Buoyancy is the upward force of a fluid on an immersed object and is equal to the weight of the displaced fluid. The effects of buoyancy during DWR depend on the body composition of the runner. Specific gravity is the ratio of the mass of an object compared to that of water. Objects with a specific gravity less than 1 will float on water due to buoyant forces. The specific gravity of bone is 1.5–2.0, muscle 1.0, and fat 0.8. Thus, a well-trained athlete with high lean body mass tends to have a relatively higher specific gravity. For this reason, a flotation device should be worn to allow the focus to be on proper running technique rather than on staying afloat, which can lead to less ideal mechanics, thus losing sport specificity for the runner. The center of buoyancy is the point through which a buoyant force acts. In a submerged human, this is at the level of the chest cavity.
Hydrostatic Pressure
Hydrostatic pressure is the evenly distributed pressure exerted by fluid on an immersed object. This pressure is the result of the gravitational force on the water above the object. Consequently, the pressure exerted increases proportionally to the water depth. Hydrostatic pressure is responsible for numerous physiologic alterations in the cardiopulmonary system during DWR. Pressure on the peripheral and mesenteric vasculature causes a large increase in central blood volume, which dramatically alters stroke volume and cardiac output. The hydrostatic pressure also decreases pulmonary compliance and increases the work of inspiration by 60%.
Thermodynamics
Specific heat is defined as the amount of energy needed to raise the temperature of 1 kg of mass by 1°Kelvin. The specific heat of water is much higher than that of air. Water is also an effective thermal conductor. Because of this, heat dissipates from the body 26 times faster while in cold water than while in air. It is therefore important to keep the pool water at an appropriate temperature for exercise. “Thermoneutral” water during exercise has been defined as 29–33°C (84.2–91.4°F). During more strenuous DWR, the thermoneutral temperature is lower, and thus the water should be cooler. The ideal temperature is varied in the literature, with a commonly recommended range of 26–28°C (78.8–82.4°F).
Physiologic Changes to the Body Submerged in Water
There are a myriad of changes to the body's normal physiology during DWR compared with LR which are essential to understand when prescribing or overseeing DWR.
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