People frequently write or talk about the physiological differences between muscle fibers (fast versus slow twitch, oxidative capacity, etc.), but this information is generally not very useful to the typical health and fitness enthusiast. Some understanding of how your muscles work is certainly important, but most people don’t need to know all the physiology in depth. Instead, I believe that understanding the basic functional differences between muscles provides more practical information than you would get from learning a lot about muscle physiology.
Looking at the functional differences between muscles, you can certainly dig deep and examine how all the muscles work at each joint, but in the end, muscles generally fall into two different functional categories: prime movers and stabilizers. Prime movers are the muscles that actively create movement, while stabilizers provide balance and support to your body.
Core muscles are usually the largest muscles in the body and include muscle groups such as the quads and hamstrings (upper thigh), pectorals (chest), lats (back), biceps and triceps (arms), etc. They connect to your bones (via tendons) and create movement around a joint. For example, the biceps connects the upper arm to the lower arm (forearm), crossing the elbow joint, and when the biceps contracts, it brings the forearm closer to the upper arm. Since the contraction of the biceps creates this movement, it is considered a prime mover.
Stabilizers, as the name implies, have more to do with stabilizing your body than creating movement. The stabilizers are smaller muscles and in many cases are not even visible because they are so small or so deep below the superficial muscles. These muscles help keep bones, joints, and muscles in proper alignment both during movement and while standing.
Stabilizing muscles are also essential for maintaining good posture throughout life. For example, the stabilizer muscles in your middle 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 the chest and front shoulder muscles become proportionally too strong or tight, the 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 of the shoulders will progress and your posture will worsen over time, leading to further problems.
Both prime movers and stabilizers play valuable roles in your body and any complete training program will include exercises or workouts to improve both types of muscles. It is also important to note that since the prime movers and stabilizers have different functions and muscular demands, they must be trained differently. Unfortunately, many people try to train stabilizers as if they were prime movers, and possibly an increasing number of people don’t realize that stabilizers need to be trained at all.
This is really not surprising, because most people in the fitness industry and the media still focus on using exercise to improve the way your body looks and rarely spend time explaining how training can improve the way you look. your body works. It’s a common assumption that training will always improve the way your body works, but this is only partially true. A well-balanced program will improve how your body functions, but many programs are unbalanced or ignore important aspects that actually lead to physical dysfunction.
Improving stabilizer muscles is an example of something that is often left out of the average training program. Since stabilizers are so small, training them usually doesn’t cause any dramatic changes in your body’s appearance, so they don’t get much attention and are often completely ignored. It’s very tempting to train just the prime movers, because they’re responsible for most of your calorie burn and physical change. While most of your training time can be spent on the main movers, at least some stabilization training should also be included.
When doing resistance training (lifting weights, using exercise bands, etc.), your prime movers are usually trained by performing sets of exercises where each set typically contains between 3 and 15 repetitions, depending on your goals of training. In general, lower reps and higher weight result in more strength gains, while higher reps and lower weight result in more local muscular endurance. However, in both cases, the muscles are trained for a certain number of repetitions, usually until they are fatigued, and then there is a period of rest so that they can recover for the next set.
This type of training is effective, because the prime movers generally only work for shorter periods (with the exception of long duration events), but the stabilizers often have to contract for hours every day. The difference is that the stabilizing muscles are designed to produce small, sustained contractions for prolonged stabilization as opposed to the brief, strong contractions of the prime movers. As a result, it is not necessary to train the stabilizer muscles to produce a greater amount of force for a short period of time.
The good news is that you can train your stabilizer and prime mover muscles at the same time, depending on the exercises you use. For example, the use of machines to work the leg muscles (leg press, leg extension, etc.) provides little benefit to leg stabilizers, but exercises performed standing in a split position (one leg straight) forward and one leg back), on one leg, or on balance devices (Bosu, inflated discs, etc.) will challenge the stabilizer muscles along with the prime movers.
One thing to keep in mind is that when you do exercises that challenge your stabilizers, your prime movers won’t be challenged as much, because you won’t be able to use as much weight and perform as many reps as when the stabilizers aren’t used. This is because the energy that would be used to contract the prime movers is spent on stabilization and motion control. Also, its stabilizers can fail before its prime movers, if the exercise stabilization demand is high enough.
However, for most people, the benefits of including stabilization training far outweigh the negatives of having slightly less improvement in the main motors. Unfortunately, there isn’t much incentive for people to include stabilization exercises, because they often don’t realize the importance of the stabilizer muscles, at least not until they start experiencing problems associated with stabilizer malfunction. Also, these problems usually don’t start to occur until middle or late life and are often considered normal parts of aging, rather than preventable or reversible muscle and joint problems.
For example, let’s go back to my earlier example of a person who has rounded shoulders. It is common for older people to have forward rounded shoulders along with excessive curvature in the upper back and spine. In most cases, this is not a normal part of aging and is actually caused by a combination of poor muscle stabilizing function, lack of flexibility, general lack of muscle use, and the postural changes that result from these problems.
When people strive to stay active, maintain their flexibility, and practice good posture throughout their lives, rounding of the shoulders and other postural changes can usually be avoided. Fortunately, if you haven’t done everything you should have done when you were younger, there is still hope. A comprehensive training program, including stabilization training that focuses on problem areas, can go a long way toward reversing and preventing many of the muscle, bone, and joint problems typically associated with aging.