Written by Thomas Fahey, EdD
09 October 2006

Making Muscles Bigger and Stronger


People love films like "Star Wars," "Rocky," and "Rudy" because they show underdogs overcoming seemingly impossible odds. Rocky and Rudy succeeded through pure force of will, even though they appeared to have little chance. Luke Skywalker defeated an army of technologically advanced bad guys by getting in touch with "The Force." These films promote the idea that anyone can win if they develop a psychological edge. Their main message is "Feel, don't think!" Feelings are way more important than speed, power, a good right hook, eyesight, facts, reason, technology, common sense and computerized bombsights.

Most bodybuilding magazines keep this idea alive by displaying pictures of larger-than-life athletes with attitudes. A typical photo shows a cut behemoth grinding out a set of curls while wearing sunglasses. The photos imply that having a kick-ass, anti-establishment attitude is all it takes to achieve amazing size and strength. Attitude is certainly important in bodybuilding and other sports, but it is no substitute for physical ability, hard work, well-designed programs, hormones and high performance diets. Successful athletes know the elements necessary for success and approach them systematically. Those guys didn't get big and strong from wearing their baseball hats backwards; they got that way because of their physical abilities and by following challenging, well-designed, systematic programs.

A lot of people train hard, but few get impressively big and strong. Some people don't have the genetic makeup to build much strength. Others have potential but "spin their wheels" because they don't train effectively. (By definition, a person with potential hasn't accomplished anything yet). Knowledge is power! If you know how muscles get strong, it's easier to design a scientifically based training and nutrition program that will produce rapid and impressive gains. Don't just train hard; train smart!


How Muscles Get Strong

            Until recently, scientists didn't understand how muscles got bigger or stronger. We knew that muscles grew from regular weight training, provided you took in enough calories and got enough rest. We knew very little about the role of the nervous system in muscle activation, hypertrophy or breakdown. Some of our ideas about building muscle size and strength turned out to be wrong and our knowledge about the effects of drugs and supplements on muscle growth has been based as much on political correctness and wishful thinking as it has on systematic scientific study.

            Neuromuscular function, muscle structure, nutrition, hormones and skill determine muscle strength. Neglect even one of these factors and you won't increase strength as fast as you should. Consider each of these in your program and your strength will improve by leaps and bounds.


            Muscle Strength from Changes in Neuromuscular Function

Muscles get stronger by turning on more motor units during maximum lifts and decreasing the body's inhibitions against exerting maximum force. Neural changes occur in beginners and elite athletes. These changes occur only with intense training.

The motor unit controls movement and force output. It consists of a nerve and three to 1,000 muscle fibers. Motor units involved in precise movements (such as those controlling eye or finger movements) have fewer fibers, while those driving large powerful movements (e.g., hip extensors) have many fibers per unit.

Muscle physiologists classify human muscle fibers as Type I (slow-twitch; slow oxidative, SO); Type IIa (fast-twitch; fast oxidative glycolytic, FOG); and Type IIx (fast-twitch; fast glycolytic, FG).  Fibers are classified by their biochemical characteristics, strength, power, speed and endurance. A new way of describing muscle fibers is to identify the speed of their myosin (myosin heavy chain [MHC] isoform)- structures that generate force during muscle contraction.

The brain and spine turn on (recruit) one or more motor units to cause movement and they choose motor unit type (fiber type) according to the load and speed of contraction. Lifting heavy weights requires more motor units than lifting light weights. Intense or rapid movements and slow-twitch units are required for movements requiring less force. MD has published several articles on the Fiber-Blaster concept of training that uses these scientific principles to recruit and build all the fibers of the muscles. The basis for the program is to combine high resistance and high endurance sets to achieve maximum muscle fiber recruitment.

            Strength training increases the capacity to turn on more motor units, it speeds the rate of force development and turns off systems that protect the muscles from overload, such as Golgi tendon organs and muscle stretch receptors. Training can maximize the capacity of the brain and spine to turn on more motor units and prevent inhibition of contraction if you (1) include intense, low-volume training in your workouts; (2) accelerate the weight at the beginning of reps (without cheating); and (3) improve movement skills.

The research findings on neuromuscular adaptation are important for bodybuilders. Don't restrict your program to high-volume failure training that only emphasizes reps over weight. Include high-intensity lifts and accelerate the weight during the pushing phase of the lift. It's not enough to push muscles to failure doing high reps and high volume sets. You must also do high-quality overload sets, lifting heavy weights for one to five reps per set.

Strength is important for bodybuilders. The goal of bodybuilding is to increase muscle size and shape and minimize body fat. Muscle grows in response to tension. Stronger muscles have the capacity to get even larger because they create more tension. Bodybuilders should build neuromuscular capacity as well as muscle size.


            Muscle Strength from Changes in Muscle Structure

            Muscles get stronger by increasing in size (cross-sectional area) and density. Bodybuilding increases the size of fast- and slow-twitch fibers. High- intensity exercise (more weight) builds more fast-twitch fibers, while high- volume exercise (more reps) builds more slow-twitch fibers. Curiously, weight training slows down myosin- the structures that cause muscle contraction. The change is similar to that of resting and submaximal exercise heart rate: The system becomes more efficient by producing more force with less effort.

            Bodybuilding boosts muscle density by increasing the fiber angle (pennation angle). This accounts for percent changes in strength being greater than changes in cross-sectional area of muscle. This is particularly good news for women, who are interested in improving strength without building bulk. Increasing pennation angle allows muscles to increase in strength without getting too big.

As with changes in neuromuscular activation, high muscle tension during training is essential for changes in muscle structure. Optimize tension in your workout by using cycles (periodization). Intense workouts increase muscle size. You must be adequately rested to train intensely. If you kill yourself every time you go into the weight room, you will never recover enough to train hard. Quality of the training stimulus is the key to maximizing protein synthesis in muscle. Design your program so you set yourself up for intense workouts.


            Muscle Strength from Changes in the Genes

            Weight training increases the number of nuclei in muscle cells. The nuclei contain the genes that contain cellular information for making new proteins. More nuclei mean a greater capacity to make new protein. Training also increases chemicals in the nuclei, such as MyoD and myogenin that cause the cells to make more muscle proteins.

During hypertrophy, the muscle cells create satellite cells- muscle cells consisting of just a nucleus. Muscle growth factors can cause the satellite cells to combine with muscle cells that were stressed or damaged during training and assist in cell repair and adaptation. Satellite cell formation is important because it maintains a balance between the number of cell nuclei and cell mass. Occasionally, several satellite cells can join and form new muscle cells- a process called hyperplasia. Most muscle physiologists believe that hyperplasia is not significant for increasing muscle size with training. Weight training increases the rate at which the cells line up amino acids to make new protein, a process called RNA transcription and translation.


Muscle Strength from Changes in Hormones, Growth Factors

Hormones increase muscle size and strength by speeding protein synthesis, slowing protein breakdown, increasing the supply of amino acids to make new protein and providing fuels to drive the process. The four most important hormones affecting protein synthesis in muscle are testosterone, growth hormone, insulin-like growth factor and insulin. Each of these hormones influences either muscle cell nuclei or their messengers to speed the production of muscle proteins.

Insulin stimulates the nucleus to increase protein synthesis and also speeds the movement of amino acids into the muscle cells. Most amino acids enter muscle cells via a process called the sodium pump. Insulin speeds the action of the sodium pump, which increases the rate at which amino acids enter the cell. This is critical for muscle growth- the more amino acids transported into the muscle cell, the greater the rate of muscle hypertrophy and strength.

Testosterone increases strength and lean body mass, and decreases fat mass. The changes depend on blood levels of the hormone (natural or supplements). Training increases the number of testosterone receptors in muscle cells, which makes testosterone even more effective for protein synthesis. High-dose testosterone supplementation (greater than 400 milligrams per week) increases IGF-1- an important muscle growth factor. Growth hormone- an extremely anabolic hormone- works mainly by increasing IGF-1 levels. It's also a potent fat mobilizer, which explains its popularity with bodybuilders.

Training does not lead to continuous gains in muscle size. Muscle size increases for a while, then levels off and sometimes regresses. One reason for this is protein turnover- the constant buildup and breakdown of structural proteins. Some hormones and anti-growth factors cause protein breakdown or prevent satellite cell formation. The most important of these are the corticosteroids, produced by the adrenal glands. They increase after a hard workout or during periods of overtraining.

Overtraining increases catabolic hormones and decreases anabolic hormones. Gains in muscle size are impossible in a catabolic state. If you provide the optimal training environment for the muscles (i.e., good muscle tension during training and ideal concentrations of anabolic hormones and amino acids), your muscles will grow. You are in an anabolic or growing phase. If rest, training and nutritional considerations are not optimal, then training gains will be less, or you may actually lose ground. The goal of the training program should be to stay anabolic and avoid catabolic periods.


Optimal Nutrition Helps Muscles Get Stronger

            Amino acids are the building blocks of proteins. Also, the amino acids released during protein breakdown are used for fuel and help maintain blood sugar. Optimal amino acid transport into muscle cells to make new proteins requires an adequate concentration of amino acids in the blood and muscles. Usually, this is not a problem because most athletes take in enough protein in their diets to supply the muscles with plenty of amino acids. However, during times of heavy training, extensive soft tissue injury, or overtraining, amino acid concentration- particularly essential amino acids (those the body can't produce)- may not be adequate.

Energy intake is also important. If you do not take in enough calories, your body will break down its structural proteins for energy. Don't diet when trying to increase muscle size. Low energy intake compromises protein turnover and favors protein breakdown and inhibits protein synthesis.

Creatine monohydrate supplements can also help muscles energize protein synthesis and increase muscle size and strength. It doesn't seem to affect translation (interpreting information from DNA), but it may increase satellite cell formation or speed the rate at which amino acids enter the cells and are organized into new proteins. Effective doses (in the long run) are three to six grams per day. This supplement safely increases strength and muscle size and improves performance in about 80 percent of people.

Amino acid availability can promote muscle protein synthesis. Consume a drink or meal (energy bar) containing carbohydrates and proteins about 30 minutes before weight training and immediately after. The protein and carb intake doesn't have to be excessive- about 15 grams of protein and 35-100 grams of carbs before and after exercise.  This practice promotes protein synthesis.

Don't eat too much protein in your diet. Bodybuilders need approximately 1.5 grams of protein per kilogram of bodyweight. Taking in more than that increases enzymes that break down proteins. Excessive protein intake may slow recovery and promote muscle breakdown after exercise. Most athletes follow the philosophy that you can't consume too much protein. New studies suggest that eating excessive protein is a waste of money and may be counterproductive.


            Cover the Bases in Your Program

            Increasing muscle strength and hypertrophy involves changes in muscle structure, neuromuscular activation and gene activity. The process requires optimal hormone and nutritional environments. Each factor is vital for making optimal gains. Don't forget any of them.



Aagaard, P. Making muscles "stronger": Exercise, nutrition, drugs. Musculskel Neuron Interact, 4: 165-174, 2004.

Adams G. R., D. C. Cheng, F. Haddad, and K. M. Baldwin. Skeletal muscle hypertrophy in response to isometric, lengthening, and shortening training bouts of equivalent duration. J Appl Physiol, 96: 1613-1618, 2004.

Brooks G.A., Fahey T.D., Baldwin K. Exercise Physiology: Human Bioenergetics and Its Applications. New York: McGraw Hill, 2005. 4th edition.

Cameron-Smith D.  Exercise and skeletal muscle gene expression. Clin Exp Pharmacol Physiol, 29: 209-213, 2002.

Fahey, T.D. Weight Training Basics. New York: McGraw Hill, 2005.

Glass D. J. Molecular mechanisms modulating muscle mass. Trends Mol Med, 9: 344-350, 2003.

Glass D. J. Signaling pathways that mediate skeletal muscle hypertrophy and atrophy. Nat Cell Biol, 5: 87-90, 2003.

Goldberg Y., G. Taimor, H. M. Piper and K. D. Schluter. Intracellular signaling leads to the hypertrophic effect of neuropeptide y. Am J Physiol, 275: C1207-1215, 1998.

Herbst K. L. and S. Bhasin. Testosterone action on skeletal muscle. Curr Opin Clin Nutr Metab Care, 7: 271-277, 2004.

Higbie E. J., K. J. Cureton, G. L. Warren, 3rd and B. M. Prior. Effects of concentric and eccentric training on muscle strength, cross- sectional area, and neural activation. J Appl Physiol, 81: 2173-2181, 1996.

Inoue K., S. Yamasaki, T. Fushiki, Y. Okada and E. Sugimoto. Androgen receptor antagonist suppresses exercise-induced hypertrophy of skeletal muscle. Eur J Appl Physiol Occup Physiol, 69: 88-91, 1994.

Joyner, M.J. Skeletal muscle hypertrophy. Exer Sport Sci, Rev. pp. 127-128, 2004.

Rennie M. J., H. Wackerhage, E. E. Spangenburg and F. W. Booth. Control of the size of the human muscle mass. Annu Rev Physiol, 66: 799-828, 2004.