Exercise Analysis - Flyes

Bench presses might be the most popular resistance-training exercise for upper body, but there is another movement that is probably a close second. Dumbbell flyes are a basic exercise that many lifters employ to work the muscles of their chest. Unfortunately, there are some major flaws with this approach.

Execution-wise, dumbbell flyes are much like dumbbell bench presses. In both cases, you lie supine with dumbbells extended at arms’ length above your chest before starting the movement. And in both cases, you wind up back in this position when you are done. But in between, there is a major difference that has important implications for both safety and effectiveness. 

When you are performing flyes, you don’t bend your elbows like you do when you are bench pressing. Consequently, flyes involve movement at one joint only (the shoulder) and are considered an isolation exercise because the training effect will be exclusive to one specific muscle group (the chest). Bench presses are a compound exercise that involves the same motion at the shoulder as flyes, with movement also occurring at the elbow. As a result, your triceps (the three-headed muscle on the rear portion of your upper arm) are also active.

Muscles develop tension to create movement in a lever system where the opposition they encounter is a function of both the force opposing the movement and the perpendicular distance between the line of application of that force and the joint at which the movement occurs. This distance is known as the moment arm. During dumbbell flyes, the maximal opposition is encountered when your arms are extended directly out to your sides because the moment arm length is longest at this point. Unfortunately, this is also the position where your shoulder is most susceptible to injury, so maximal opposition through this segment of the movement range is not the best bet.

Due to changing leverage conditions, the effective resistance you are working against changes as you draw your arms up and together to perform a flye. Unfortunately, this alteration is also less than desirable. The moment arm shortens as you complete the movement because the line of pull of the force acting on the dumbbells (gravity) winds up closer to the joint. Therefore, effective resistance is progressively decreasing as you finish the repetition. The end result is that if you continue all the way until the dumbbells are touching above your chest, the load on your chest is negated and your target muscle gets a chance to rest between reps.

There is a way to alter the loading pattern on flyes to make the exercise more effective and less dangerous. In essence, instead of a force pulling your arms directly down, you need one pulling them out to the sides. This would shorten the moment arm when your chest is at end-range stretch (i.e., when your arms are directly out to your sides) and allow it to be maintained as you squeeze your hands up and together. Gravity can’t be altered, but you can change its direction by using a cable machine. In this case, gravity pulls the machine’s weight stack directly down, but the attached cable is wrapped around a pulley that changes the direction of that pull. Placing your body in an appropriate position with respect to the pulley ensures a suitable loading pattern.

To perform cable flyes, position a flat bench in the center of a cable crossover machine so that it is parallel to the weight stacks. Attach handles to the cables coming from the bottom pulleys and lie supine on the bench while holding the handles in your hands above your chest. The handles should be touching and your arms should be straight. From this position, lower your hands slowly out to your sides, terminating the movement when your arms are parallel to the floor. Do not pause at this point; instead, squeeze back up and together until the handles once again touch above your chest.

Much like dumbbell flyes, cable flyes can be modified according to the particular segment of the chest you wish to target. The muscle of your chest is multi-directional with a design similar to that of a peacock’s tail. From a broad origination on the collarbone, sternum and ribs, it converges to a small insertion point on the front portion of the upper arm. Consequently, when it develops tension and contracts to draw your arm toward the midline of your body, it can do so at a wide range of angles. Your chest can be worked by drawing your arms together from higher to lower angle, from lower to higher angle or directly across.

To work the different segments of your chest with cable flyes, all you have to do is change the angle of your body with respect to the line of pull of the cable. For example, to work upper chest, simply adjust the bench you are lying on so you are positioned at an incline. Similarly, lying on a decline bench would target the fibers that are angled downward. You could also opt to stand when performing this movement. Doing so and using the cables from the bottom pulleys would target upper chest, while changing to the upper pulleys will allow you to work the lower portion.  

This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.





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