We conclude our series on the anatomy and physiology of human muscle by looking at how exercise builds muscle, and armed with this understanding, you will be better able to evaluate the countless exercise routines that are available to determine which one works best for you.
In this newsletter, we conclude our series on the anatomy and physiology of human muscle by focusing on how to build muscle through exercise. We won’t be looking at specific exercise routines; you can get those from dozens of DVD’s, not to mention a bewildering assortment of exercise equipment, available all over the internet for a staggering range of prices…not to mention your local gym. Instead, we’re going to look at how exercise builds muscle–the different types of muscle fiber you have and how specific exercises develop specific fibers. Armed with an understanding of how to build muscle, you will be better able to evaluate the countless exercise routines that are available and determine which one works best for you.
Muscles grow through protein synthesis. That’s how we build muscle. Despite what supplement companies tell you, there is no magic formula that really changes this basic science. Once you understand how protein synthesis creates muscle growth, you can make use of that knowledge to achieve your goals, whether they are bodybuilding, athletics, or just basic fitness. You eat protein rich foods. You break those proteins down to their constituent amino acids during digestion. These amino acids are reassembled in your muscles cells to create the new protein used to build more muscle.
Specifically, exercise triggers the building of muscle by first breaking muscle fiber down in the form of small micro-tears that occur at the cellular level in those fibers (catabolic metabolism). Then it repairs those tears and makes them stronger (anabolic metabolism). When muscle experiences small micro-tears, your body responds by increasing blood flow to the damaged tissue. That increased blood flow brings with it the necessary components for repair through protein synthesis. The human body is designed to repair any part which is damaged, and in many cases it is designed to not only repair that part but to make it even stronger than before in order to prevent the damage from occurring again. And muscle is no exception. Each time you tear down your muscles through intensive exercise, your body repairs it and makes it stronger and larger than before. This “strengthening” beyond simple repair is an intelligent choice your body makes to prevent it from being damaged again as a result of performing a similar activity. In other words, your body senses that some activity has exposed an area too weak to protect itself so it rebuilds that area–ever stronger each time it’s damaged–until it is strong enough to resist further damage. Building muscle is simply a matter of exploiting that intelligent response. The bottom line is that muscle activity (i.e. regular exercise) is a prerequisite for meaningful muscle development.
However, exercise is only half the equation when it comes to how we build muscle. The other prerequisite, as we mentioned above, is protein synthesis.
Protein synthesis is the process by which individual cells construct proteins. It is related to the process by which cells replicate their genetic code. Enzymes in the cell’s nucleus begin the process of protein synthesis by unwinding the needed section of DNA, so that RNA can be made. The RNA forms as a copy of one side of the DNA strand, and is sent out of the nucleus and into the cytoplasm near the outer edge of the cell, where it combines with a ribosome to bring together the different amino acids that form proteins. This combination of messenger RNA and a ribosome serves as the cell’s work station for synthesizing protein.
The process of protein synthesis takes place in a multitude of RNA/ribosome factories located throughout the cell. A single cell, operating efficiently, can synthesize hundreds of proteins every second. Multiply that out to all the muscle cells affected when you exercise, and you can build muscle pretty rapidly by providing the right nutritional building blocks as we discussed when exploring the physiology of muscle tissue.
That said, the process is a bit more subtle than we have explained so far. As it turns out, you can control not only the amount of muscle you build, but also the type.
Types of Skeletal Muscle
Previously (again when examining the physiology of muscle tissue), we discussed the three different types of muscle tissue in your body: smooth, cardiac, and skeletal. Those you have no control over. Your heart, for example, is going to be made up of cardiac muscle tissue no matter how much you work out. It will never change to skeletal muscle tissue or smooth muscle tissue and vice versa. But skeletal muscle itself is comprised of three different types of muscle fiber: Type I, Type IIA, and Type IIB. Most skeletal muscle groups are made up of a combination of all three types of fiber, but the proportions of each vary based on the function of the muscle, genetics, and exercise. These three types of fiber primarily differ in how they process oxygen and/or sugar for energy, with that process determining the role each type of fiber plays. And when it comes to the development of these three types of fiber, you do have a lot of control over how they develop.
Type I Fibers: Slow Oxidative Fibers
These fatigue-resistant fibers are also known as slow-twitch fibers. They tend to generate ATP aerobically (using oxygen), which makes them very efficient. They are very resistant to fatigue and can go for a long period of time without rest. But like everything else in the human body, these advantages come with a trade off. Type I fibers split ATP slowly to power themselves and therefore contract slowly, which makes them not very good for fast movement or strength. But that’s not what they’re designed for. They are used for small ranges of motion that do not require rapid contractions, but they can hold their contraction for long periods of time. Type I fibers are found predominantly in postural muscles in the neck and back, but they are also great at helping athletes run marathons and bicycle for hours.
Type IIA Fibers: Fast Oxidative Fibers.
These “somewhat” fatigue-resistant fibers are also known as fast-twitch A fibers. Like Type I fibers, they generate ATP aerobically. But unlike Type I fibers, they split ATP rapidly and contract rapidly. This means that like Type I fibers, they can go for a long period of time. But unlike Type I fibers, they are not as fatigue-resistant and can’t go for hours. They are typical of sprinter’s muscles and are found in their strong calves and thighs.
Type IIB Fibers: Fast Glycolytic Fibers
These fatigable fibers are also known as fast twitch B fibers. They fatigue very quickly. Unlike the other types of fiber, these fibers generate ATP anaerobically (without oxygen). They get their energy from breaking down glycogen very quickly. They split ATP rapidly for energy to power themselves, but cannot maintain that for very long at all. In effect, they borrow energy that needs to be repaid later — when the ATP energy cycle can be rebuilt. They are typical of large muscles in the arms. They can generate a large amount of power, but will fairly quickly build up an oxygen debt. These are the muscles that bodybuilders use when doing power lifts. And you may only get 10 or 20 reps before exhausting Type II B fibers.
Mixing Muscle Types
As mentioned earlier, most muscle groups are actually mixtures of the Type I, IIA, and IIB muscle fibers. For example, large muscle groups of the legs need postural fibers (for standing), fast oxidative fibers for walking, and sprinting fibers for running. Thus the muscle groups in your legs contain all three types of fiber.
That said, muscles vary in the proportions of these types of fiber. The mix of the three types varies at birth according to genetic predisposition. Yes, that means that some people are born sprinters, for example, with a native ability to excel in certain physical activities. Top athletes tend to end up in sports that match their genetic makeup. Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who run marathons tend to have 80 percent slow twitch fibers.
But to some extent, that is changeable by implementing specific exercise patterns. For example, some people are born with leg muscles that naturally have a high proportion of Type IIA fibers geared for sprinting, but even a person without a natural gift for sprinting can switch the mix in their legs more to Type IIA with training. Or to look at it another way, because muscles of the shoulders and arms are used for short bursts rather than continuously, they tend to contain a higher proportion of Type IIB fibers. But if you were to take up a repetitive exercise such as long distance rowing, you would actually change the mix of these muscles to have a higher proportion of Type I fibers. Nevertheless, although you can change the mix, you cannot completely overcome the mix you are born with, but you can certainly make a difference. Given equal amounts of training, a person with the natural predisposition will have an advantage–in that one particular area. Then again, as professional athletes have shown over and over, there are many ways to overcome natural advantages such as better technique, more scientific training…and by using illegal performance enhancing drugs.
Before we start talking about the specifics of exercise, there’s one more concept we need to explore: the principles of muscle contraction.
Muscle contraction is an “all or none” phenomenon. A muscle fiber that is fired contracts throughout its whole length or not at all. It’s not like musclemen contract more than couch potatoes; they get their strength because they have more fibers to contract. Again, that said, there are a couple of qualifiers to this principle:
- First, muscle fibers get their contraction at their greatest stretch. Thus when we set muscle fibers up to contract when they are at a slight stretch, you will get a more powerful contraction.
- And the force of contraction depends on the number of stimulations that muscle receives per second, the length of the muscle prior to contraction, and the number of motor units stimulated.
As a side note, in pathological states, the brain may fire constantly, non-selectively, or inappropriately. In grand mal epileptic seizures, for example, the entire brain fires continuously and at once to all parts of the body; thus all muscles are contracting at once, which causes the person to have the typical epileptic seizure with its characteristic rigid postures. Spastic paralysis, on the other hand, is defined by opposing pairs of muscles firing at the same time–for example, where all of the muscles in the arm fire at once, causing the hand to bend down, because the adductor, biceps, and pronator muscles are stronger than their opposing muscles simultaneously pulling in the opposite direction.
Interestingly, seizures and spasms pull back the curtain and let us understand how muscle tone works. Muscle is not inherently hard, no matter how well developed it is. When a bodybuilder dies, their muscle tone instantly goes soft. What we think of as muscle tone actually comes from the continuous involuntary contractions of small numbers of motor units that give the muscle its firmness at rest. This is the primary reason that muscles burn calories even at rest, as they are constantly expending low levels of energy just to maintain tone. And the more muscle you have, and the better developed it is, the more calories you burn at rest.
How to Build Muscle — the Principles of Exercise
Concentric motion, or positive repetition, is what we normally think of when doing exercise. It is defined by the shortening of the muscle at work. It also could be defined as decreasing the angle between the two limbs in question. The act of curling a weight upward with your arms, for example, involves shortening the bicep and reducing the angle between the front side of the forearm and upper arm from 180 degrees to something less than 45. Doing a push up, on the other hand, involves shortening the tricep, which is pulling the arm straight from the back side, thus shortening the muscle and decreasing the angle of the forearm and upper arm from 315 degrees to 180 when viewed from the backside where the contraction is taking place.
Eccentric motion, or negative repetition, is the opposite of concentric motion — the muscle lengthens and the angle between the two limbs increases. Going back to our arm curl, lifting the weight up with your arm, as we’ve already discussed, is concentric motion. Slowly lowering it back down to the starting position while straining to control the weight is eccentric motion. So, big deal! Why is this distinction important when it comes to exercise? Well, as it turns out, and contrary to what might appear to be obvious, eccentric motion actually builds muscle faster than concentric motion. Eccentric motion damages muscle more than concentric motion. This is useful for weightlifters, because the point of exercise is to slightly damage muscle, which will receive added mass and strength when it is rebuilt. What this means is that the important part of lifting the weight is not the actual lift, but slowly lowering it back down. Another key point that we just mentioned is that muscle builds through a process of damage and repair. This is why weightlifters try to work out different parts of the body on consecutive days to give the muscles from the previous day’s workout an opportunity to rebuild before working them out again.
Isotonic VS Isometric Exercise
Isotonic literally means “the same tone, the same tension.” In isotonic exercise, then, tension is constant while the length of the muscle is contracting. If you are curling a 100 lb weight for example, you will be exerting the same 100 lb force with your biceps throughout the entire range of motion as your bicep contracts and shortens. Isometric contraction, on the other hand, is essentially the exact opposite. It keeps the length of the muscle the same throughout, while constantly changing the force. Imagine trying to lift a 5,000 lb weight. You strain against an immovable object. Since the object doesn’t move, the length of your muscles will remain unchanged. But the tension will steadily increase as you strain harder and harder.
So which is the better form of exercise? And the answer is: it depends on what you want. Isometric exercise can build bulk very quickly (thank you very much Charles Atlas1 Kelly Baggett. “The Charles Atlas Workout Revisited.” BodyBuilding.com Jun 14, 2004. (Accessed 5 Feb 2013. http://www.bodybuilding.com/fun/kelly4.htm ), but it’s not as good as isotonic at building strength.
And with that background in hand, let’s now turn to an exploration of exercise.
Factors to Consider When Exercising
We have previously explored how to do the different types of exercise in some detail, so there is no need to repeat that information at this time. Instead, I want to quickly look at exercise from several different points of view:
- Energy–exercise based on how your muscles are powered while working out.
- Gravity–it’s impact on your exercise outcomes.
Aerobic exercise involves regular, repeated, low-intensity movements. The key to aerobic exercise is that an oxygen rich body can meet its oxygen demands throughout the workout. In aerobic exercise, we can keep up with our oxygen consumption. Think conversational jogging in which you can talk comfortably while exercising.
Anaerobic exercise, on the other hand, involves routines in which oxygen is used up more quickly inside the working muscle` than the body is able to replenish it. As a result, muscle fibers have to derive their contractile energy from stored substrates, primarily in the form of glycogen (stored sugar). Anaerobic exercise is used by athletes in non-endurance sports to promote strength, speed, and power and by body builders to build muscle mass. Weight training is an example of such an activity. It is highly anabolic if done properly (in other words, it can build muscle rapidly) but also highly catabolic if done in excess. Or to put it another way, anaerobic exercise, such as weightlifting, builds mass by damaging muscle, which can, of course, lead to over-damage if done to excess.
When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, as in anaerobic exercise, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown–and thus energy production–to continue. The working muscle cells can continue this type of anaerobic energy production at high rates for only one to three minutes, during which time lactate can accumulate to high levels. Contrary to the popular misconception, lactic acid buildup is not responsible for the muscle soreness felt in the days following strenuous exercise. That’s most likely the result of muscle tissue breakdown. Rather, the production of lactate and other metabolites during extreme exertion results in the burning sensation often felt in active muscles.
A healthy exercise routine done for general health mixes aerobic and anaerobic exercise in the same activity by varying the intensity. Interval training is an example of effectively mixing both types. This is very beneficial.
When it comes to exercise, gravity is both friend and foe–depending on need. Exercises involving gravity are beneficial for the bones and bone density. This includes upright sports such as tennis, basketball, weight training, and rebounding. Since these types of exercise stress the bones, they are very useful for building bone density. This is worth keeping in mind as you get older and the natural lowering of bone density starts becoming an issue.
On the other hand, gravity negating exercises such as swimming and rowing allow people with joint and bone problems to exercise without undue stress. These types of exercise are great for the heart and lungs, but don’t really help the bones. Ultimately, you want to do some of both.
As we mentioned earlier, muscle is more metabolically active than fat. Muscle uses energy even while resting to maintain its tone. Thus, muscle at rest burns more calories than fat at rest. The amount of calories that a pound of muscle burns each day may be open to debate, but the fact that it burns calories is not. Thus adding muscle mass helps control weight.
Contrary to old beliefs, regular exercise builds muscle mass and improves health even in the very elderly. Exercise fundamentally changes every system and function in your body. The older you get, the more important that is — and the more pronounced the benefits. For athletes, exercise can bring your athletic performance to the next level, a not insignificant benefit. But for a person in their 80’s, exercise can literally increase muscle strength by as much as 175% in a matter of just a few weeks.2 Diane Dahm, Jay Smith. “Older doesn’t have to mean weaker.” I. (Accesed 30 Jan 2013.) http://healthletter.mayoclinic.com/editorial/editorial.cfm/i/444/t/Older%20doesn’t%20have%20to%20mean%20weaker That equates to a profound improvement in quality of life. In fact, people who start a good exercise program in their 80’s also improve their balance, find climbing stairs to be easier, and can rise out of a chair without pushing off with their hands. The bottom line is that it doesn’t matter how old you are, with exercise, you can build muscle mass and strength. You can regain balance and postural tone. You can transform your life.
Your muscles are equipped with a feedback system of proprioceptors called muscle spindles. This feedback system is highly important for a sense of body position and for maintaining posture and motor control. The stretch reflex, or myotatic reflex as it is more technically referred to, is a neural mechanism that automatically responds to sudden changes in muscle length (stretching) by attempting to resist that change in length. For instance, if you stand for a long period of time, your extensor muscles, which are being used to maintain your position, will relax and thus lengthen. This causes your body to lean to one side or other, the proprioceptors in your leg muscles notice this sudden lengthening and cause the muscles to contract and thus return the body to its correct positioning without conscious involvement.
Why is this important? Because we need to keep this automatic reflex in mind when stretching our muscles. If we move quickly, say bouncing up and down while trying to touch our toes, we will automatically trigger the reflex and cause our muscles to contract — thus counteracting the very essence of the stretch we are trying to achieve. On the other hand, if we relax, move slowly and breathe into the stretch, we bypass this automatic reflex and give our muscles a chance to relax and stretch to their maximum length.
When stretching, we may encounter another problem: adhesions. Since muscle builds through the process of micro-tearing and rebuilding, there is a strong possibility that small amounts of scar tissue may form — and the more intense the workout, the more likely you will leave behind small amounts of scar tissue in your muscles. This scar tissue can cause muscle fibers to bind together and may even cause the fascia covering of the different muscle groups to bind together, making it difficult for them to smoothly slide over each other.
In normal situations, these adhesions are unlikely to be noticed, let alone cause you any problems. But when you try and stretch muscles to their max, the adhesions can be painful and prevent your muscles from achieving full stretch. Given time, you can work through adhesions–breaking them up, if you will–through dedicated programs such as Yoga or Feldenkrais.3 http://www.feldenkrais.com Even Pilates, if you can find an original pure form of it, can be helpful in this regard. On the other hand, you can use deep muscle body work such as BioSync4 http://www.biosync.com or even Active Release Technique5 http://www.activerelease.com to achieve the same result far more quickly.
Muscle knots, technically known as myofascial trigger points, are a primary source of muscle aches and pains. They are most often found in the large muscles of your legs and butt and in your back–anywhere from the base of your spine to the top of your neck–and across your shoulders. You can think of a knot as a small patch of super-contracted and irritated muscle tissue. It can range from mildly painful to excruciating, and it can cause anything from mild stiffness to a total lock up of your entire back.
It can be initiated by a single vertebrae being slightly out of alignment and thus impinging on a nerve controlling a nearby muscle. Or it can be caused by a muscle on one side of your body tightening up because of an injury, which causes a corresponding muscle on the other side of your body to tighten up even more in a misguided attempt to overcompensate. And if that’s all that was involved with muscle knots, they would be fairly easy to deal with — correct the imbalance or go to a chiropractor and have your vertebrae put back in alignment (both good things by the way). But there’s another factor involved.
It’s what I referred to in my report on pain as the Snowball Effect. An injury such as a muscle knot triggers the release of the bio-chemicals of pain at the source of the injury, which produce more pain, which trigger the release of even more bio-chemicals of pain, which yet again increase the level of pain — continually ratcheting up the level of pain until the process itself is self-generating. That means even if you get rid of the original cause of the pain, the pain will persist…until you break the cycle. And in fact, a 2008 study identified 11 such bio-chemicals of pain that continually bathe the original knot in a toxic soup of self-generating pain.
To get rid of the pain, you not only have to remove the original trigger, you also have to break the snowball effect in order to decrease those bio-chemicals of pain and allow the muscle knot to release. A deep tissue oil can help in this regard, as can body work, or hydrotherapy (alternating hot and cold water treatments to stimulate circulation and the removal of toxic waste in the muscle tissue).
Exercise has a profound effect on muscle growth, which can occur only when muscle protein synthesis (anabolic activity) exceeds muscle protein breakdown (catabolic activity).6 Tipton KD, Wolfe RR. “Exercise, protein metabolism, and muscle growth.” Int J Sport Nutr Exerc Metab. 2001 Mar;11(1):109-32. http://www.ncbi.nlm.nih.gov/pubmed?term=11255140 And it is here that proper nutrient intake plays a key role. The response of muscle protein synthesis to the breakdown of muscle tissue resulting from exercise lasts for 24-48 hours–or even up to 72 hours in the case of strenuous exercise. Key nutrients required in order to maintain a favorable balance of muscle synthesis over breakdown include:
- Amino acids (proteins) to maximize the stimulation of muscle protein synthesis.
- Hormones such as testosterone and HGH have important roles as regulators of muscle protein synthesis.
- Carbohydrates deliver glycogen to synthesizing muscle which arrests the catabolic process and kick-starts the muscle building process.
- For more on the nutrients required for building muscle, check out the Physiology of Muscles.
Note: since the degradation of muscle due to strenuous exercise does not peak until two to three days after the exercise that affected the muscle is over, it is important to continue the ingestion of protein and other key nutrients during that timeframe. The maintenance of sound dietary practices is essential to the body’s ability to respond on an ongoing basis to the demand for muscle protein synthesis.
For more on the advantages and disadvantages of different types of protein, check out our series on protein.
When it comes to the ideal exercise routine, it all depends on what you want to achieve. If you play football, you need one kind of body. If you’re a sprinter, you need another kind. If you just want to have a healthy cardiovascular system and avoid aches and pains as you age, then you need another.
In all cases, though, the difference in exercise is merely a matter of emphasis, not exclusivity. That means that even if your emphasis is on bodybuilding, you still need to do cardio work and stretching. And even if you want to be a sprinter, you also need flexibility (to avoid injury) and strength (to burst out of the starting blocks). The difference is that you’re emphasizing one type of muscle tissue over another–not exclusively developing one type over the others. The bottom line is that unless you’re using steroids to win a world championship and don’t care about anything else, you need to do it all:
- Cardio/aerobic/interval training
- Strength training
- Weight bearing exercise
- Resistance breathing
In our next newsletter, we will begin looking at the levers that our muscles act on: the skeletal system.
References [ + ]
|1.||↑||Kelly Baggett. “The Charles Atlas Workout Revisited.” BodyBuilding.com Jun 14, 2004. (Accessed 5 Feb 2013. http://www.bodybuilding.com/fun/kelly4.htm|
|2.||↑||Diane Dahm, Jay Smith. “Older doesn’t have to mean weaker.” I. (Accesed 30 Jan 2013.) http://healthletter.mayoclinic.com/editorial/editorial.cfm/i/444/t/Older%20doesn’t%20have%20to%20mean%20weaker|
|6.||↑||Tipton KD, Wolfe RR. “Exercise, protein metabolism, and muscle growth.” Int J Sport Nutr Exerc Metab. 2001 Mar;11(1):109-32. http://www.ncbi.nlm.nih.gov/pubmed?term=11255140|