Visceral fat affects organ function. Visceral fat develops when the body’s natural reservoir of fat underneath the skin (subcutaneous fat) “is completely overfilled, so you get spillage of fat both into and around organs, where fat is not usually found,” Dr. Srikanthan explains. Fat cells secrete a number of hormones, and when those hormones move into abdominal blood vessels, they affect the normal functioning of the organs in the abdominal region, including digestive organs and organs such as the pancreas that play a role in glucose metabolism.

“Normally, there would be a two-way signaling process between subcutaneous fat and fat stores in the pancreas to help regulate insulin secretion. But when you have fat living in very close proximity to the pancreas and other organs, it changes the normal signals that govern body metabolism,” Dr. Srikanthan observes. “This results in changes in insulin response and metabolism that, in turn, can cause problems such as altered levels of growth hormones in various organs. In the end, these changes can result in cancer,” she says.

In addition, the presence of visceral fat in various organs can cause inflammation, which further interferes with normal cell and organ functioning.

How much is too much? At what point does subcutaneous fat spill over into organs and become visceral fat? There are no easy answers, Dr. Srikanthan acknowledges. “Different people appear to respond differently to the same amount of abdominal fat, depending in part on genes, ethnicity, and gender.” she says. “Before we can relate quantification of fat to risk, we need a better understanding of the metabolic effects of a specific amount of fat in different population groups.”

Further complicating the picture is the fact that only between 20 percent to 30 percent of obese individuals have insulin resistance as a result of their weight. That means there is a group of people that could be considered “healthy obese,” she says, as well as normal-weight individuals who may be at risk because they’re not physically fit.

The bottom line, regardless of your weight, is to “maximize your fitness level,” Dr. Srikanthan stresses. But because overweight and obesity contribute to a range of health problems, including conditions such as osteoarthritis, which is not related to glucose metabolism, it still makes sense to aim to attain a normal weight while staying as fit as possible, she concludes.

WHAT YOU CAN DO

To avoid visceral fat accumulation:

* Do aerobic and strengthening exercises regularly to become as fit as possible.

* Don’t assume you have nothing to worry about if you’re normal weight; if you’re not fit, you could still be accumulating visceral fat.

* Make efforts to lose weight, if you are overweight, for overall health, while exercising to boost your aerobic capacity and build muscle mass.

The concept of plyometrics is actually incorporated in many functional or sporting activities that involve the stretch-shorten type of muscle action. A vital part of the accelerated rehabilitation programs is the use of plyometrics for performance enhancement. Because of the large forces involved, plyometrics are most appropriately used in a periodization rehabilitation program during the final phases of rehabilitation, as well as for sport-specific conditioning of highly trained athletes. The concepts of specificity of rehabilitation and specific adaptation to imposed demands require that plyometrics should form the power foundation for the athlete.

The actual term plyometrics was first coined by Wilt in 1975.1 The word “plyometrics” is derived from the Greek word plythein or plyo, which means “to increase.” The term metric derives from the Greek and means “to measure.” Consequently, the purpose of plyometrics may be thought of as “to increase the measurement.”

The stretch-shorten cycle

Plyometrics is a form of resistance training that involves the quick stretching then contracting of muscle from an eccentric muscle action to a concentric muscle action. This stretch-shortening cycle may be divided into three phases: the eccentric prestretch phase, the amortization phase, and the concentric shortening phase.

The eccentric prestretch phase has been described as the preparatory, facilitation, readiness, setting, preloading, potentiation, counterforce, and countermovement phase. The eccentric prestretch phase of a plyometric activity stimulates the muscle receptors and prepares the muscle for loading. This stimulation of the muscle receptors is often referred to as the neurophysiological-biomechanical response. Several investigators have shown that an eccentric muscle action immediately preceding a concentric muscle action increases the concentric force production.2-4 The prestretch phase depends on three stretch factors: the magnitude, rate, and duration of the stretch. Changing any of these factors will have a significant effect on the amount of energy that is stored by the eccentrically acting muscles.1

The amortization phase is also known as the electromechanical delay phase of plyometrics. This is the time delay between the eccentric prestretch of the muscle and the concentric shortening, or from negative to positive work. During this time delay, the muscle overcomes the negative work of the eccentric prestretch to generate force production and accelerate muscle contraction and elastic recoil in the direction of the plyometric movement. The shorter the amortization time, the more effective and powerful the plyometric movement, because the stored energy is used efficiently in the transition.2 Also, the shorter the amortization phase, the greater the work output, for the same reason. During a longer amortization phase, the stored energy is wasted as heat, the stretch reflex is not activated, and the resultant concentric contraction is not as effective. Shortening the amortization phase is one of the key goals of plyometric training.1

The concentric shortening phase is described as the performance, power, facilitated, or enhancement phase of plyometrics. All these terms describe the final phase of the plyometric movement and are descriptive of what actually happens during plyometric activity. This third component of the stretch-shorten cycle includes the biomechanical responses that utilize the elastic properties of the prestretched muscles.1

The eccentric prestretch, amortization, and concentric shortening phases are blended in plyometric training to enhance muscles’ performance. The careful planning (periodization programs) and execution of the actual plyometric drills to be described later are what make these exercises so effective for performance enhancement.

Plyometric exercises have several different effects on the person training. Some of these effects can be described as physiological, biomechanical, or neurophysiological. When combined, these effects create a cascade response that results in performance enhancement.