Muscle Action Spectrum
The term “muscle action spectrum” describes the different ways a muscle works, or performs an action. Particularly in the gym, we’re primarily familiar with the shortening action of muscles. The contraction of the muscles creates movement, helping to push a weight away from you or pull it toward you. But shortening is not all that muscles do, and becoming more familiar with the other aspects of muscular action can help you get far more out of your body.
Your muscles actually have three primary actions. Their official terms are eccentric, isometric, and concentric contractions. The eccentric contraction is when the muscles are producing force but the fibers are lengthening. An isometric contraction is when the muscle is producing force but the fibers are not changing in length. A concentric contraction is when the muscle is producing force and the fibers are shortening. At first glance it might seem like a relatively trivial thing, but the difference between them is huge.
The most common example of an eccentric contraction is when you’re preventing something from falling, slowly setting it down instead. This is a crucial aspect of muscular strength, because it is a necessary component in deceleration, alignment, and balance. It spares the joints during exercise, because it is the difference between a weight’s falling back to its start as opposed to being smoothly returned to that position. There are those who object to using the term “contraction” along with the word eccentric, because the nature of eccentric work is the lengthening of the muscle fibers. However, I think it’s appropriate to use the term, because the muscles are still producing force. For example, if you have a weight of 10 lbs. and you want to set it down carefully, you must counteract gravity. If your muscle produces exactly 10 lbs. of force, the weight will stand still. To set it down carefully you have to produce an amount of force that is less than the force of gravity, but is more than zero. So you’re still producing force in opposition to gravity, it just doesn’t exceed the force of gravity.
In order to fully use the eccentric action, a significant, controlled, deceleration must be taking place. One can’t realistically be said to be experiencing an eccentric action when the weight is simply falling. The slower the weight is falling, the more eccentric force you’re using to control and slow it, therefore the harder your muscles are working.
Making efficient use of eccentric action during your training also serves you with more immediate, tangible benefits. First, adding a slow and controlled eccentric action significantly increases muscles’ time under tension. Adding a mere 2 second eccentric component to a traditional concentrically-focused repetition (typically ~ 1 second) will triple the time under tension. If you used a very slow 4 second eccentric phase, the time under tension will be 5 times greater! This is a big boost for hypertrophy and muscular endurance. Second, eccentric actions will help prime the nervous system for more intense concentric contractions. Even a brief eccentric phase will allow the motor units to adapt to the weight being used. This leads to a greater number of motor units being primed and ready to be recruited to the primary action. Result: greater strength output. Finally, eccentric training can be used by more advanced trainees as a training tool. In a well trained athlete, eccentric strength actually exceeds concentric strength by as much as 30%. Because of this, a trainee can incorporate negative repetitions into their program to improve strength. A negative repetition is one where a load over 100% of the 1-rep maximum is used. The lifter slowly moves the weight eccentrically through the range of motion, then he and a partner both lift the weight back to the starting position. This technique can be very effective, but is also very taxing on the joints and soft tissues. For this reason, it’s recommended that negative repetitions only be used occasionally and intelligently.
In an isometric contraction, the muscle fibers are producing force but experiencing no effective change in length. Isometric action is one of the most important aspects of muscular contraction. Yet it is also the most overlooked when it comes to training. Since there is no change in muscle fiber length, isometric contractions are used to hold things still. The ability to hold various parts still is an absolute necessity for your body. That is how you hold yourself upright. But not only that, it provides stability for your joints and a necessary anchor from which to create movement. All muscles pull in both directions, pulling each end toward the center. If you wish to move you arm and only your arm, for example, then you need to anchor your torso and shoulder girdle so that they hold still while the arm moves. This is another example of how all muscles in your body work together. Most of the time you don’t realize it’s happening, but any time you use a muscle or muscle group to initiate movement, you’re also using several more to provide a foundation for that movement. Finally, isometric action also helps stabilize the joints and hold them together. Joints are designed to articulate in certain ways. Without the aid of supporting muscles, the alignment suffers and the joint is negatively affected.
Additionally, isometric contraction is great at recruiting high threshold muscle fibers. There is also the added benefit that isometric action can be utilized at a variety of segments of a lift. If you’re experiencing a strength plateau that you can’t seem to overcome, or if you have specific sticking points in a lift you’re struggling with; incorporate isometric training into your lifting. You’ll be amazed at how quickly you’ll achieve newfound levels of power.
The final type of muscle action is the one we’re most familiar with: concentric contraction. In a concentric contraction, the muscle fibers are producing force and are shortening their overall length. This is the action that produces movement (whereas eccentric reduces movement and isometric neutralizes movement). To return to the earlier example, when you’re holding a 10 lb. weight in your hand and you want to lift it up, you need to exert more than 10 lbs. of force to overcome the pull of gravity. Force above the 10 lb. mark will translate into speed. Strength and speed are tied to one another, so they can be used as means to enhance each other as well.
Understanding the full role of the muscle action spectrum can enhance anyone’s workouts. None of them occur without the others but often one or more of the components of the spectrum are neglected. This is unfortunate because all that accomplishes is diminishing the potential benefits the muscle can receive. Especially for people seeking to build muscle, neglecting the eccentric phase particularly hinders results. The eccentric phase is thought to be the primary phase that stimulates hypertrophy. At very least, maximizing time spent under eccentric load will maximize time under tension and total workload, both of which are undeniable factors in muscle growth. Regardless, utilizing the full ability of your muscles will change the way you work out and dramatically enhance your results.
Granted, this subject might be a little basic for some of you. But it never hurts to cover the basics.
Thanks so much for that, it'w well written and very clear.
Totally worth it.