Selectorized Machines Versus Free Weights

 

To provide an informed comparison of free weights and selectorized machines it is first necessary to have an explicit understanding of their purpose - both what it is and how it is best accomplished. The reason for the numerous misconceptions that exist surrounding the subject is that the majority of people claiming expertise and making authoritative statements on the issue lack this understanding, as well as understanding of related concepts such as motor learning and skill transfer, and basic mechanical physics.

It is important to note that there are currently over fifty companies manufacturing a wide variety of selectorized machines, and the overwhelming majority of these are incorrectly designed. This article is only concerned with properly designed machines.

The purpose of performing an exercise is to fatigue or inroad the strength levels of the involved muscular structures to a meaningful degree to stimulate a growth mechanism. Ideally, this should occur within some minimum time frame to avoid using any more of the body's limited metabolic resources than necessary, since those same resources are required for recovery and growth. There are a variety of factors which affect how efficiently an exercise accomplishes this. Some of these include how well the resistance is balanced to the users strength in different positions over the range of motion, whether the targeted musculature is loaded directly, and how well the exercise facilitates focus and concentration on the targeted musculature.

Variable Resistance

A person's usable strength changes from position to position during any movement due to the effects of friction, myofibril congestion, virtual cam effects resulting from the changes in tendon insertion angles and other factors, as well as changes in leverage resulting from the changing angles of the involved bones during multi-joint movements. If we graph these changes in usable strength over the full range of motion of any particular exercise, we have what is referred to as the strength curve for that exercise.

The resistance provided by free weights or machines can also vary over the range of motion of an exercise due to changes in leverage or torque. This change in resistance over the range of motion is what is referred to as the resistance curve for that exercise.

Ideally, this resistance should vary in proportion to the strength curve of the involved muscular structures, increasing in positions where they are stronger and decreasing in positions where they are weaker. This makes it possible to meaningfully load the muscles continuously throughout the exercise and achieve the desired level of inroad with little or no energy wasted. The less wasted during exercise, the more available to the body afterwards for recovery and growth.

In free weight exercises involving rotation around a single joint such as barbell curls, dumbbell lateral raises, and dumbbell chest flies, the resistance curve resulting from the change in torque over the range of motion matches a portion of a sinusoidal curve (see figure A below). This does not match the strength curve for most rotary movements, however, which require an exponential decrease in resistance towards the end of the range of motion (see figure B below). While some free weight exercises can be performed in a manner in which the resulting resistance curve more closely approximates the strength curve of the involved muscles, perfect congruence is difficult, if not impossible to accomplish.

Figure A - The resistance curve resulting from the strict performance of a barbell curl.

If the resistance provided by an exercise does not vary in proportion to the strength curve the amount of weight that can be used is limited to how much one is capable of handling in the position where the resistance is greatest. This is commonly known as the sticking point in free weight exercises. As a result, the involved muscular structures are only meaningfully loaded over a small portion of the range of motion of the exercise. During the rest of the exercise the relatively lower resistance allows the muscles a respite during which some motor units may recover more than if the muscles encountered meaningful resistance over the full range of motion. This reduces the rate of inroad resulting in less efficient growth stimulation.

In a properly designed machine a cam or system of levers varies the resistance over the full range of motion in proportion to the strength curve of the involved muscles, increasing it in positions where the muscles are stronger and decreasing it in positions where they are weaker. This provides continuously meaningful loading during the exercise, and inroads the muscles strength levels more efficiently. Less of the body's limited resources are wasted in the process of stimulating the muscles to grow, leaving more for recovery and growth.

The ideal resistance curve for nearly all single joint exercises as well as compound pulling exercises such as the bent-over barbell row, which require an exponential resistance decrease, can only be provided by a properly designed machine. In compound pushing movements, however, such as the squat and various presses, the relatively flat resistance curve provided by the near vertical movement of a barbell will provide a relatively balanced variation in resistance. Assuming that proper turnaround technique is used and lockout is avoided, these will load the muscles relatively efficiently.

Figure B - Comparison of arm flexion strength curve with the resistance curve of a strict barbell curl. Most compound pushing movements require a relatively flat resistance curve. Most compound pulling and rotary movements require an exponential resistance decrease over the last half of the movement.

The proper use of free weights can produce an incredible degree of improvement in muscular strength and size, but the same results can be achieved more safely and efficiently with the use of properly designed machines. Therefore the current popular bias against machines has no rational basis. Regardless of the tools used, results are ultimately more dependent upon the method of training.

Personalized Wellness Center seeks to set new standards in Personal Training, Physical Therapy, Nutrition Therapy, Massage Therapy and customer care. To this end, the Company utilizes proven methodology for producing client results while drastically reducing both the amount of time invested and the risk of injury.

PWC is a multidisciplinary facility that provides a unique wellness experience. We vertically integrated the health industry by combining the very best protocols in

• Physical Therapy

• Post Rehabilitation

• Strength Training

• Massage Therapy

• Nutrition Therapy

To learn more visit us at http://www.pwcworks.com

 

 

 

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