from: Full Squats for Strength and Development
Squats and Systemic Growth
You may be wondering, "Just exactly how do squats promote growth throughout the body?" To begin with, the squat involves multiple joints and muscles which in turn increase the level at which the nervous system must coordinate movement in conjunction with the lifter's muscle-skeletal system. In the squat there are numerous muscles of the body working simultaneously to provide the stability and mobility needed for this exercise. It has been estimated that there are up to 200 muscles involved in the squat.
The hormonal or endocrine system combined with the nervous system makes up what is known as "neuroendocrinology". This term describes the relationship of chemical substances that have both neural and hormonal functions. The endocrine glands are stimulated to release hormones by a chemical signal received by the receptors on the gland or by neural stimulation, which is what occurs during weight training. Ever wonder why you feel particularly upbeat and euphoric after a hard workout, even if you are physically drained? Its because of the increased presence of hormones in your body, hormones that also influence our moods. This is similar to the runners high experienced by long distance runners.
The increase in anabolic hormone levels observed after a hard workout can increase hormonal interactions with various cellular mechanisms and enhance the development of muscle protein contractile units. On neural stimulation from an alpha motor neuron to initiate a muscle action, various signals (electrical, chemical, and hormonal) are sent from the brain and from activated muscles to a number of endocrine glands. Hormones are secreted during and after the workout in response to the physiological stress of resistance exercise. This simply means that the nervous, muscle-skeletal, and hormonal systems are responsible for the effects promoted by exercises like the squat.
There are various hormones, which produce this effect, and the one that most people are familiar with is testosterone. It's been demonstrated that testosterone serum concentrations can increase with exercises such as the squat.
Squats can increase growth throughout the entire body because they use numerous muscles and this means they stimulate more muscle fibers than say an exercise such as a leg extension or a leg press. The greater the fiber recruitment, the greater the process for potential growth and development in the muscle. Only muscle fibers that are recruited by resistance training are subject to adaptation and the more muscles used in an exercise like the squat the more the muscle fibers are stimulated.
Keith Wassung
