Physiology is the study of biological systems of living things, the integration of which is necessary in order to sustain a state of homeostasis, or the stability of the internal environment of an organism. Physiology recognizes that the integrated processes that take place between the cardiovascular, respiratory and urinary systems, for example, is what enables the body to regulate fluid volume, internal temperature, pH levels and blood pressure.

Traditionally, physiology is divided between two disciplines — plant physiology and human physiology. However, the basic principles of physiology as a whole remain constant, regardless of the subject. In fact, it is generally accepted that what physiology can learn about the cellular functioning of microorganisms can be extrapolated to human physiology.

Applied physiology goes beyond the study of biological systems and steps into practice. In fact, it involves the application of the knowledge of physiological properties to restore stability. Applied physiology differs from clinical practice, however, although many fields in the life sciences are closely related. For example, anatomy involves the study of muscle, organs and connective tissue in terms of form and structure, while applied physiology is more concerned with the purpose and function of these systems and how they relate to the rest of the organism. As a result of this approach, applied physiology has paved the way for several new veins of scientific disciplines to emerge, such as paleobiology, biochemistry and pharmacology.

Applied physiology also seeks to understand how certain factors may alter or hinder system functioning by monitoring how each system interacts with the other. This is generally accomplished by observing chemical or electrical feedback. For instance, we know from the study of neurology that the nervous system plays a key role in controlling muscle movement. Applied physiology principles address how the nervous system functions to control muscle movement at the cellular level. It does this by employing the appropriate technique to monitor intracellular chemical changes or responses to controlled stimuli. This muscle monitoring may be in the form of observing its reaction to electrical impulses delivered mechanically, or by the response to the presence of protein or other substance within muscle cells. In addition, many researchers believe in the value of regular muscle testing to gain additional biofeedback about the overall health status of an individual, as measured by muscle strength or weakness.

While the basics of physiology date back to the forefathers of medicine in ancient Greece, applied physiology is still a relative newcomer to the biomedical arena. However, it is growing steadily in application and consistently diversifying into other branches of medicine. Researchers hope that future advances in applied physiology will lead to improving the quality of life for those who experience limited range of motion due to age-related disorders, degenerative diseases, neurological conditions, and even spinal cord injuries.