2 Different Types of Muscles: What They Are and Why They Are Important - a Functional Approach

People frequently write or talk about physiological differences between muscle fibers (fast twitch vs. slow twitch, etc.), but this information is not very useful to most health and fitness enthusiasts. Some understanding of how your muscles work is important, but you probably don't need to know the in-depth physiology. Instead, you can gain more practical information by understanding the basic functional differences between muscles.

You can go into great depth and examine how various muscles function at every joint, but in the end, muscles basically fall into two functional categories: prime movers and stabilizers. Prime movers are muscles that actively create movement, while stabilizers provide balance and support.

Prime movers are typically larger muscles and include muscle groups such as the quads and hamstrings (upper thigh), pecs (chest), lats (back), biceps and triceps (arms), etc. They connect to your bones (by tendons) and create movement around a joint.

For example, your bicep connects your upper arm to your lower arm (forearm), crossing the elbow joint, and when the bicep contracts it brings your forearm closer to your upper arm. Since the bicep contraction creates this movement, it is a prime mover.

Stabilizers have more to do with stabilizing your body than actually creating movement. They are smaller muscles and in many cases they are not really visible, because they are either too small or hidden under surface muscles. Stabilizer muscles help keep your bones, joints, and muscles correctly aligned both during movement and while stationary. They are also essential for maintaining good posture throughout your life.

For instance, stabilizer muscles in your mid and upper back work to keep your shoulders back and in line with the rest of your body. If those muscles become too weak or your chest and front shoulder muscles become too strong or tight, your shoulders will begin to round forward. If the stabilizer muscles are not strengthened to the point where they can reverse this change, then the rounding will progress and posture will decline.

Prime movers and stabilizers both play valuable roles and any well-rounded training program should include exercises to improve both types of muscles. It is important to note that prime movers and stabilizers have different functions and muscular demands, so they should be trained differently. Unfortunately, a lot of people try to train stabilizers as if they are prime movers and other people don't realize stabilizers need to be trained at all.

This is not surprising, since most people in the fitness industry and the media focus on exercise as a way to improve how your body looks and rarely spend time explaining how training improves the way your body functions. It is a common assumption that training always improves the way your body functions, but this is only partially true. A well-balanced program will improve function, but many programs are imbalanced or ignore important aspects and actually cause dysfunction.

Stabilizer muscle training is often left out of the average exercise program. Since stabilizers are so small, training them usually does not cause a dramatic change in how your body looks, so they don't get much attention and are often completely ignored. It is tempting to only train prime movers, because they are responsible for the most calorie burning and physical change, but at least some stabilization training is needed for a healthy body.

Prime movers are typically trained by performing sets of exercises containing between 3 and 15 reps, depending your training goals. In general, lower reps and higher weight result in more strength gains, while higher reps and lower weight results in more local muscular endurance. However, in both cases, the muscles are trained for a certain number of reps, followed by a period of rest so they can recover for the next set.

This type of training is effective, because prime movers usually only work for shorter durations (with the exception of long endurance events), but stabilizers often have to contract for hours every day. The difference is stabilizer muscles are designed to produce small and sustained contractions opposed to the strong and brief contractions of prime movers. As a result, stabilizer muscles do not need to be trained to produce large amounts of force.

The good news is you can train stabilizer and prime mover muscles at the same time, if you use certain exercises. For example, using machines to work your leg muscles (leg press, leg extension, etc.) provides little benefit to your leg stabilizers, but exercises performed standing in a split stance (one leg forward and one leg back), on one leg, or on balance devices (Bosu, inflated discs, etc.) challenge both stabilizer muscles and prime movers.

One thing to note is that when performing exercises that challenge your stabilizers, your prime movers will not be challenged as much, because you will not be able to use as much weight or perform as many reps as when your stabilizers are not used. This is because energy that would be used to contract your prime movers is spent on stabilization and control of the movement. and stabilizers may give out before prime movers during difficult exercises.

However, for most people, the benefits of including stabilization training far outweigh the disadvantage of having a little less improvement in the prime movers. Unfortunately, there is not much incentive for people to include stabilization exercises, because they often don't realize how important stabilizer muscles are, at least not until after they start experiencing problems associated with poor stabilizer function.

Another reason is because stabilizer related problems typically do not start to occur until the mid to late stages of life and they are frequently thought of as normal parts of aging, instead of preventable or reversible muscle and joint problems.

For instance, when thinking about shoulder posture, it's common for elderly individuals to have forward rounding shoulders along with excessive curvature in their upper spine and back. In most cases, this is not a normal part of aging and it is caused by a combination poor stabilizer muscle function, lack of flexibility, general lack of muscle strength, and the postural changes that result from these issues.

When people stay active, maintain their flexibility, and practice good posture throughout their life, the rounding of the shoulders and other postural changes are avoided or at least minimized. Fortunately, a well-rounded training program, including stabilization training focusing on your problem areas, can go a long way in reversing and preventing many of the problems typically associated with aging.

Source:
14 years of experience and education in health and fitness