The routine at circuit training health clubs is quick and simple, allowing each woman to progress at her own pace. The ladies exercise in a circle, each at a station. They spend 30 or 45 seconds at each station, either working a hydraulic resistance machine or doing aerobics. The entire routine takes just 30 minutes.

Sufficient anecdotal evidence exists to prove that circuit training can help women achieve fast weight loss. But how about the training technology behind the workout? Does the equipment in this type of gym provide true weight loss exercise, or is it just another fad?

To completely understand fitness and exercise equipment it's important to comprehend the four different technologies of that equipment:

1) Constant Resistance Devices

2) Variable Resistance Devices

3) Static Resistance Devices

4) Accommodating Resistance Devices

Constant Resistance Devices:

"The term constant resistance means that a weight (resistance) does not increase or decrease during the course of exercise" (source: International Sports Sciences Association; 2001). The amount of resistance encountered by the user remains unchanged from the beginning of the exercise movement to the end.

Examples of training or weight lifting with constant resistance devices would be lifting a barbell, dumbbell, or using a cabled weight stack. Weight training in this manner has some inherent disadvantages. First of all, constant resistance weight lifting exercise does not correct for changes in the musculoskeletal leverage that occurs during an exercise movement. Secondly, this method does not account for reduced effort that comes with fatigue.

When following a weight lifting routine with constant resistance devices, the user experiences changes in leverage during the joint movement. For example, when doing dumbbell curls the amount of muscular force required is much greater at the bottom of the movement (when the dumbbells are at waist level) than it is at the top of the movement (when the dumbbells are near the chin). As the dumbbells approach the top of the movement, leverage improves and the user doesn't have to work as hard.

Therefore, the user doesn't gain as much benefit during the 'easy' portion of the movement. Muscles need stress to gain strength and endurance, so with the relatively diminished stress of constant resistance devices some of the benefit is gone.

Some experts argue that constant resistance exercise is more natural than any other weight lifting program because leverage imbalances match the actual day-to-day movement of the body.

Variable Resistance Devices:

"When you hoist a weight by pulling on a cable that goes over the top of a pulley and is attached to a weight, you're engaged in constant resistance training" (source: International Sports Sciences Association; 2001). Some exercise equipment manufacturers have experimented with pulleys that aren't round or don't have the hole in the exact middle of the pulley, resulting in different levels of resistance felt during different points in the exercise movement.

Unlike constant resistance devices, variable resistance fitness equipment does not match the natural way the human body works. Some exercise scientists view this as a disadvantage, as it may cause disturbance in the brain centers that interpret force and movement patterns.

The advantage of variable resistance fitness equipment is that it amplifies the level of stress placed on the muscles by forcing them to work equally hard throughout the full range of motion. Critics respond that since everyone is different is size, stature and strength it is virtually impossible to match everybody's leverage with machine leverage.

Static Resistance Devices:

"Contracting your muscles without movement is called static contraction. The term isometric exercise was coined to describe this form of stress" (source: International Sports Sciences Association; 2001).

The public, searching for a new weight loss tip in the 1950's and early 1960's, adopted isometric exercise as their new weight lifting workout. Unfortunately, scientists eventually proved what many weight watchers had already learned: isometrically contracting a muscle results in that muscle only gaining strength in that position. To gain strength throughout the entire range of movement, the user would have to isometrically contract their muscles throughout every conceivable angle in the entire range!

Today, very few people consider using static resistance devices as part of their weight loss system for the simple reason that isometric exercise is the least effective of the four training technologies.

Accommodating Resistance Devices:

"Like variable resistance devices, accommodating resistance machinery is designed to allow you to exert maximum resistance throughout the full range of movement in each of your exercises. In doing so, you are able to maximize the amount of exercise stress your muscles receive" (source: International Sports Sciences Association; 2001).

Accommodating resistance exercise equipment somewhat controls the resistance that is encountered, thereby allowing the user to exert maximum force throughout the entire range of motion and throughout the entire exercise.

This is the type of gym equipment used at circuit training fitness centers. Again, the primary benefit is that the user can exert maximum force in any position, which allows for a full and complete workout. As an example, consider dumbbell curls. Traditional dumbbell curls result in decreased leverage at the top of the movement. Circuit training exercise equipment, on the other hand, applies even and consistent force throughout the entire range of motion. In other words, circuit training equipment places the muscle under constant tension for more time than alternative training technologies.

"Tension (resistance that is stressful enough to cause muscles to adapt), together with sufficient time over which it is applied, go hand-in-hand to produce superior gains" (source: International Sports Sciences Association; 2001).

Another advantage of accommodating resistance exercise equipment is that the relatively controlled speed of the movement drastically reduces the opportunity for injury. As ballistic movement is virtually impossible on this type of equipment, injury from overextended joints, pulled muscles and uncontrolled movements is also highly unlikely.

Conclusion:

It's easy to see that the training technology behind circuit training is solid. Circuit training exercise equipment utilizes accomodating resistance to deliver consistent results.