Resistance and Viscosity
What are Resistance and Viscosity, and How Do They Affect Water Exercise?
Resistance actually occurs between the molecules of a liquid, effecting how a liquid flows. Viscosity can be thought of as a measure of a fluid’s resistance to flow. Liquids of high viscosity, such as syrup, flow slowly.
Liquids of a low viscosity flow fast, such as mercury. Water is 790 times more viscous, and provides twelve times the resistance than the air normal exercise is performed in. The density of water is approximately 1,000 times greater than air.
Resistance can Make Your Muscles Work Harder without Stressing Your Joints
Viscosity allows for a variety of ways to create resistance in hydrotherapy exercises that will not overload muscles or joints involved. As your body moves through the water, you drag along with you the water molecules that not only cling to your body, but are also trying to stick to each other.
During aquatic therapy, if the surface area of a body part is increased by a piece of equipment such as a flotation device, even more force is required to move the amount of water in front of it.
Resistance can Speed Your Progress while Preventing Injury
If you increase the speed of a hydrotherapy exercise, the force required to perform the exercise is also increased. A good way to measure your progress with hydrotherapy is to see how many repetitions of an exercise you can perform in one minute.
The more repetitions you can do the greater the force that is overcome by the muscle. This, in turn, means that the muscle is getting stronger. As the muscle tires, it will naturally slow down, which automatically decreases the amount of force to be overcome. This is a unique way in which aquatic therapy helps to prevent injury during exercise.
Viscosity Means all of Your Muscle Groups will Get a Good Workout
Viscosity creates an equal amount of resistance in all planes of motion. When performing an exercise on land to strengthen muscles of the knee, gravity allows you to strengthen only one muscle group at a time. Either you strengthen the muscles that extend the knee with an exercise such as the knee extension machine, or you can strengthen the muscles that flex the knee, as with a hamstring curl machine.
In the water exercise, because of the greater viscosity, you can work both of these muscles groups at the same time, with the same amount of resistance, using a single exercise. This can help to create a better balance between the muscle groups so that one group does not overcome its opposing group.
With Aquatic Therapy, Viscosity is Your Best Friend
The properties of viscosity and drag resistance that work so well in a training environment, are a swimmer’s biggest enemy. Swimmers attempt to move as fast as they can through the water, with the least resistance possible. Every effort is made to streamline the body and its movement.
The goal of aquatics exercise is just the opposite. To increase the intensity of the water exercise, you want to make every effort to increase surface space and use non-efficient physical movements. That means using a lot of space and moving a lot of water.
The benefits of using resistance and viscosity to enhance the benefits of exercise are numerous:
- Equal resistance in all planes of motion, so that several muscle groups can be worked simultaneously.
- The intensity of the workout can be greatly altered by changing shape, size, and, or speed of the moving body parts. You will enhance your progress exponentially by increasing speed while maintaining surface area and range of motion.
- Every movement performed under the water will encounter resistance. This means that your body will meet resistance in every direction of movement.
- Resistance dampens the speed of motion and the end point of each movement thus preventing or diminishing the occurrence of jerky movements and the risk of injury. You will execute movements slowly, yet with precision and grace.
- The energy you will expend in water is equal to or greater than on land because more stabilizer muscles are used during water exercise, especially when performed while suspended in deep water.
- The force and energy required to move through water develops bone and muscle strength as well as cardiovascular and muscular endurance.
- Aquatic Therapy – Scientific Foundations and Clinical Rehabilitation Applications, Clinical Review by Bruce E. Becker, MD, MS