Exercise Analysis - Machines vs. Free Weights
If you’ve read previous installments of this column, you’ve probably noticed that I’ve assumed a nonpartisan stance with regard to the machines-versus-free-weight issue that is frequently debated. This was by design because each form of training has its strengths, so including both ensures that you’ll capitalize on benefits that might be exclusive to one modality. However, it’s also important to realize there are instances when one option is clearly inferior. A recent investigation in the Journal of Sports Sciences exemplifies this point.
Before explaining the study, I’ll review two distinctly different interpretations of the stimulus overload that resistance training should involve and the modality that is best suited for its application. Many trainers suggest that free weights provide greater benefit because they must be controlled through all spatial dimensions. The need to perform in this manner certainly makes this form of training more comparable to everyday physical activity, so it’s understandable why this benefit is frequently heralded. But before you swear off machines and opt exclusively for the iron, pay heed to the alternative view. If you want to specifically strengthen one weak area of your body, machines are the way to go.
Isolating one muscle group is a difficult proposition because when faced with a challenge, the nervous system recruits the population of muscle fibers that is best suited to get the job done. Unfortunately, there is no way to voluntarily turn off this neural outflow to certain areas in order to force other ones to bear the brunt of the effort. In addition, it’s a sure bet that the fibers that are activated will be those that are more capable. Consequently, when many muscles are involved during free weight lifting, it’s difficult to make a weak area take center stage.
To exemplify how challenging it is to isolate with free weights, consider an exerciser trying to target the muscles of the front thigh (quadriceps) with barbell squats. Squats involve motion at both the hip and knee, so the quadriceps are definitely active players. However, when a bar is held behind the neck, it’s impossible to maintain a posture that would allow these muscles to be used exclusively. Instead, it’s necessary to lean forward, thereby situating the load further from the hip and closer to the knee. This reduces quadriceps involvement and if your hip extensors are already predominant, you can rest assured the rich will only get richer.
Free weight advocates would suggest that a modification of barbell squats can force the front thigh muscles to contribute their fair share. If you hold the barbell in front of the neck, an upright posture that keeps the load situated over the hip can be maintained as you descend. With the load positioned further from the knee, the quadriceps are more loaded throughout. However, maintaining a resistive load is only one requirement that must be fulfilled to ensure adequate muscular stimulation. The muscle must also encounter an adequate amount of opposition. Unfortunately, holding enough weight in the front squat to satisfactorily satisfy this requirement is very difficult.
To isolate the quadriceps with no limitations that prevent maximal stimulation, a single-joint exercise with motion at the knee exclusively can be employed. There is a free weight maneuver that allows for this movement (an old-school favorite called sissy squats), but much like front squats, providing sufficient opposition is challenging. On the other hand, sitting on a leg extension machine and extending your legs against the opposition offered by the machine’s weight stack (transferred to your limb through the machine’s movement arm) is as simple as can be. This is a classic example of a circumstance where machines are superior, at least if the machine is built right for the user. And that brings us back to the study.
Researchers at Loughborough University in the U.K. recently examined whether the resistance provided by knee extension machines effectively matches the changing capacity of the quadriceps muscle as subjects perform leg extensions. These machines are constructed with cams that are strategically shaped in an attempt to mirror the strength curve of the muscle being targeted. For example, if the capacity for a muscle to create movement has been shown to be less at a specific joint angle, the shape of the cam should ensure that the resistive load is lessened during this portion of the movement. Unfortunately, the eight different machines that were evaluated by these researchers failed to live up to this claim.
To sum it up, machine training has unique advantages, so long as the machine is constructed appropriately for the particular user. The cam shape must be suitable for the exerciser’s specific strength curve, not the nebulous generic one that is typically referenced. And sufficient adjustability must be present to accommodate different limb lengths and ranges of motion. The take-home message is that an exerciser is responsible for more than simply using a machine without thought. Instead, attention must be devoted to the “feel” of the movement; specifically, whether the muscle group being targeted is receiving adequate stimulation. If something associated with the construction of the machine is preventing this from occurring, movements utilizing free weights or cables (which often provide a best-of-both-worlds alternative) should be considered.
This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.
