Frederick C Hatfield PhD

International Sports Sciences Association, Santa Barbara, California 93101. Email: drsquat=AT=issaonline.com

Sportscience 3(1), sportsci.org/jour/9901/fch.html, 1999 (762 words)

Reviewed by: William J Kraemer PhD, Human Performance Laboratory, Ball State University, Muncie, Indiana 47306; Steven S Plisk, MS CSCS, Director of Sports Conditioning, Yale University, New Haven, Connecticut 06520

A new strength-training machine allows the user to instantly change resistance at any point in the exercise movement. The machine has the potential to improve strength by optimizing the time each targeted muscle spends under maximum stress. Whether it is more effective than other machines or free weights remains to be seen. Reprint · Help

KEYWORDS: gym equipment, strength training
Reviewers' Comments

Those of you who, like me, have spent nearly 50 years in the weight room will recall all manner of equipment that promised to revolutionize training. In my opinion only a small handful of innovative devices have been introduced, and most of those during the last two or three years. Whether they have improved the effectiveness of strength training is often hotly debated. The new machine I review here may be one of the good ones.

For years, strength-training machines were built with no special intent beyond making muscles bigger and stronger by allowing the user to work against resistance. Then a few of the more thoughtful athletes and trainers realized that the ability of a muscle to rapidly generate maximum force involves a time/rate dependency that their current training technology was unable to address adequately. An explosion of innovations ensued. Eventually four categories of device could be discerned (Hatfield et al., 1999):

constant-resistance--resistance does not increase or decrease during the course of exercise;
variable-resistance--devices that increase or decrease the resistance during a movement to match changes in joint leverage;
accommodating-resistance--devices designed to allow you to exert maximum resistance throughout the full range of movement by controlling the speed of movement;
static-resistance--devices that prevent movement altogether.
Most sport scientists agree that machines are generally inferior to the constant resistance provided by free weights. Nevertheless, derivative technologies continue to flood the marketplace. Recently, Scott Naidus has patented and produced a cam-operated selectorized (weight-stack) machine (Figure 1).

Figure 1: The new weights machine for providing dynamically controlled resistance.

The machine has an electric motor that drives two sprockets engaged by a cam designed to increase or decrease the angle of motion of a weighted lever arm. This innovation allows the user to adjust the resistance at any instant during a movement. The inventor uses the term dynamically controlled resistance (DCR) to describe the way the machine works (see his commercial site www.dcrtech.com). Naidus claims the following unique benefits for his machine:

The user can change either the positive or negative resistance instantly at any moment during a set or repetition.
If the user learns how to manipulate the resistance properly, s/he will be able to achieve a higher work load during each rep and set.
Casual fitness enthusiasts will therefore be able "…to work out twice as hard and be out of the gym in half the time."
Protocols can be fine tuned to make the training stress more closely match the user's sport-specific requirements.
Let's look at this technology from the standpoint of current gym practice. One training method in particular comes to mind: forced reps. An experienced and educated spotter can be helpful in ensuring that the lifter is working at the highest level of stress simply by adding to or taking away some of the weight in the lifter's hands. But such gifted spotters are rare. With the new machine, a lifter can alter the amount of resistance at any time, thereby accounting for momentary fatigue or a sticking point in a given movement. As usual, the chief drawback is the level of training wisdom of the lifter in knowing when to alter the resistance, and by how much.

In a personal communication to me, Naidus wrote:

I believe the features of my machines are excellent for permitting the exerciser to engage in different and unique routines in every workout, thereby serving to stimulate the muscles and impose upon them new patterns of workloads. This should ultimately result in constant adaptation, and better strength gains.
I do not disagree. This, from an old gym rat: it's certainly worth a try! Just don't throw away your dumbbells and barbells.

Hatfield FC, Kreis EJ, Hatfield II FC (1999). Sports conditioning: the complete guide. Santa Barbara, California: International Sports Sciences Association