An exercise program is a well-accepted component of a healthy lifestyle and can be tailored to provide you with benefits such improved cardiovascular, respiratory, metabolic and musculoskeletal fitness. Many beginning exercisers fail to realize that a good, hard workout is only part of a well-balanced exercise program and that ensuring you have proper and adequate rest is equally important. A common phrase used by exercise scientists and personal trainers that addresses this is, “Exercise breaks you down — rest builds you up.”
The scientific basis for this phrase lies in a physiological principle known as the “General Adaptation Syndrome” which describes how the body responds to stress. Physical stress can come in many forms such as extremes of temperature, exposure to ultraviolet radiation, and hard physical work. The General Adaptation Sydrome teaches us that when stress becomes severe enough or is applied frequently enough to begin to damage parts of the body, your body will respond by releasing hormones that stimulate the development of the system being stressed in order to try and prevent further damage.
When exposed to high enough levels of potentially damaging ultraviolet radiation from the sun, your body will increase the production of melanin pigments, darkening your skin and preventing further radiation from reaching the UV-sensitive cells at the base of your skin. We see this response as tanning. When you subject your hands to the constant trauma and friction of chopping wood with an axe, your body will respond by increasing the thickness of your skin at the precise points where the stress is most severe in order to better protect the structures lying under your skin. The result of this response is the development of calluses. Similarly, stressing your muscles, tendons, ligaments and bones with the stress of weight lifting exercises will triger the growth of larger and stronger muscles, stronger tendons and ligaments, and bones with increased density and strength. Aerobic exercise will lead to a greater respiratory capacity and stronger, larger heart.
While all of these improvements are triggered by hard exercise wich impacts the body as a stress, they do not occur during the time of your exercise workout. Rather, the growth and development of these various body systems and structures takes place during rest. Rest, in this regard, is considered to be the days you take off from training as well as the period during which you sleep. Training too intensively every day without giving your body time to rest and recover will interfere with your physical development and improvement. The damage will simply accumulate and result in overtraining injuries.
Getting adequate sleep is equally important because it is during Stage 4 of your sleep cycle that your pituitary gland releases growth hormone which stimulates your physical development. Failing to get adequate sleep while in training, and that means 8-9 hours each night, will also interefere with your physical development.