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The Science Of Building Muscle

The science of building muscle: this groundbreaking article will help you get the most out of your workout by breaking down the critical components of each rep

Sets are competitions with yourself. They’re finite journeys taken again and again. Broken down into reps and stacked together to form workouts, they’re training’s fundamental unit of measurement. They’re like miniature lives, beginning with vigor, but debilitating with time and repetition, and always, eventually, ending. They’re regimented periods of joy and pain, and, at their best, they deliver an aching sense of accomplishment we’ll call “joyous pain.” They’re all that and more, and they’re the very essence of bodybuilding, so it’s remarkable that they’re seldom considered in depth.

What happens to your body during a set? Why do your muscles fail? What physiological factors dictate the very essence of bodybuilding? And, most important, what steps can you take to enhance your sets and eke out invaluable extra reps?

Here, in a step-by-step format, are the answers.

Prepare For Liftoff

It doesn’t matter what the exercise is. You slide plates on a bar, set a pin in a machine’s weight stack or pick the right dumbbells, and before you even begin the first set, your body is preparing itself for the onslaught that awaits. Your sympathetic nervous system releases norepinephrine, a.k.a. noradrenaline, from specialized nerve fibers that innervate your heart, thus boosting your heart rate. Your adrenal glands secrete epinephrine, a.k.a. adrenaline, along with some NE, which travels via your blood to your heart to ramp up the rate and force of its contractions. NE and EPI also increase the force of muscle contractions, resulting in greater strength. Your testosterone starts to rise. Secreted from your testicles into your bloodstream, it travels throughout your body to different tissues. It causes nerve signals to rush more rapidly to muscles, thus, like NE and EPI, increasing the force of muscle contractions.

Boost Tactic

The more you focus on the set before you even begin, the more NE, EPI and testosterone you will produce, allowing you to lift heavier weight and complete more reps. In addition, targeting the muscles you’ll work in the set by performing an isometric hold can increase strength. This is called postactivation potentiation, and it’s believed to work by ramping up the nervous system so it fires more rapidly during the set.

As an example of how to perform this hold before barbell curls, position a Smith machine bar at a height that replicates the curl’s halfway point (arms at 90 degrees). So it won’t move, load the bar with more weight than you can curl once. Then, as if doing a curl, pull up against the stationary bar (without unhooking it) as hard as you can for 20 seconds. Rest for two to three minutes, then do your set of barbell curls.

Start Of The Set

As you begin the first of a probable 10 reps, you have high energy and are pain free, and the weight feels relatively light. Your muscles must contract to move the weight. Contraction occurs in muscle fibers when specialized structural proteins called actin and myosin interact with each other. The motor nerves send a signal that causes sodium to enter muscle fibers and potassium to rush out. This process, known as depolarization, basically changes the electrical charge of the fibers and triggers the release of calcium into the cells, causing the myosin to attach to the actin so it can pull it in. This shortens the muscles and moves the weight. The farther the myosin pulls in the actin, the more the muscles contract.

During the first rep, your motor nerves call primarily on slow-twitch fibers.

These are much weaker than the bigger fast-twitch fibers, but since fast-twitch fibers fatigue rapidly, the body knows to save them for when a set gets tough. The slow-twitch fibers contract by pulling the actin in farther and farther until the weight is lifted as high as desired. As you lower the weight, the muscles resist it by allowing the actin to slide slowly back toward its original position.

Boost Tactic

Focus on the working muscles. Research shows that athletes who focus in that way during a set can recruit more muscle fibers.

The Midpoint

With each progressive rep, the weight becomes increasingly harder to lift. At the midpoint, you notice your strength and energy starting to wane and feel the first hints of pain. As the body exhausts slow-twitch muscle fibers, it recruits more of them and also starts to get help from fast-twitch fibers. Myosin requires energy to keep these fibers contracting rep after rep. This is supplied in the form of adenosine triphosphate, which is created in the muscle primarily by creatine phosphate. Creatine donates high-energy phosphate to form ATP, and ATP then passes it on to myosin to attach to actin and pull it in. During weight lifting, the muscles also make ATP by breaking down glucose in a chemical reaction known as glycolysis.

Many bodybuilders believe that each rep they perform brings more blood to working muscles, thus giving them a pump.

In fact, reps actually squeeze blood out of muscles. When a muscle contracts, it creates so much pressure on the tiny blood vessels that feed its fibers that it reduces blood flow to itself. Although muscle blood flow increases after a set, the pump you feel during a set is due to water. Each contraction produces more metabolic waste products, and sodium collects in the muscles. This buildup causes water from outside the cells, as well as water from the blood, to rush into muscle cells, as if filling a water balloon.

Boost Tactic:

To increase intermuscular creatine during exercise, ingest five grams of creatine within 30 minutes of your workout (along with 20 g of protein and 20-40 g of slow-digesting carbs). To augment blood flow to the muscles, take 3-5 g of arginine 30-60 minutes before the workout.

Enhanced blood flow means more water is delivered to the muscles between sets and then drawn into the muscles for a greater pump. Creatine, glutamine and taurine also draw water into muscles.

Near Failure

You start to falter on the seventh rep, struggling to move the weight up at your previous brisk pace. Your energy is quickly diminishing. A rapidly rising burning sensation floods your working muscles as you grind out the eighth rep. The immense power you felt just two reps ago is now gone. The ninth rep is harder still, but you gut it out, running through the stop signs. By the 10th rep, the lactic-acid-induced pain has your muscles blasting off nerve impulses like frantic 911 calls, demanding you halt the set. You seem to have virtually no strength or energy left, but you clench your eyes shut, trying your best to block out the pain and focus on your muscles. The weight slowly rises a 10th time.

During the final reps, your body starts calling on more fast-twitch muscle fibers, which exhaust quickly, accounting for your feeling of boundless strength and energy dissipating so rapidly from one rep to the next. The heavier the weight and the more reps you perform, the harder it is for the myosin and actin to extend under the force of the weight, and, in some muscle fibers, the actin literally rips away from the myosin, like Velcro being torn apart. This damages the muscle fibers at the molecular level.

Glycolysis not only provides ATP, but it also creates lactic acid–traditionally seen as the great villain in gyms everywhere, for it was the one metabolic byproduct that seemed to be responsible for ending the set. Lactic acid is the reason your muscles burn during and after a grueling workout. It creates an acidic environment, and it may indeed halt your set. It does, however, have a good side: it seems to trigger growth hormone release. As lactic acid levels rise, so does your GH response. Lactic acid is also a substrate that can be used for fuel. New research suggests lactic acid may even help muscles contract more forcefully.

Boost Tactic

As you approach failure, you need to focus intensely on the task and fight through the pain. Research shows that taking 200 milligrams of caffeine before workouts blunts muscle pain during exercise. One study even found that caffeine reduces pain more effectively than aspirin.


After your final rep–when you cannot, no matter how hard you try, grind out one more–the fibers have become fatigued and can no longer contract. The myosin and actin slowly struggle to extend and return the weight back to the starting position, and some fibers may have ripped apart.

New research suggests that a set may end for a reason other than lactic acid buildup. As was mentioned, when muscles receive signals to contract, sodium is moved into the cells while potassium flows out. As you perform more reps (and more sets during your workout), sodium levels start to build up in muscles, while potassium levels continually decline.

Sodium/potassium pumps help offset these changes by moving electrolytes back in and out of the cells, but during intense exercise, the pumps can’t keep up with the large changes in electrolyte concentrations. The result is a decline in the amount of force muscles can produce, which leads to fatigue and, ultimately, failure.

Boost Tactic

Take 600-1,000 mg of N-acetylcysteine before workouts to delay fatigue by enhancing sodium/potassium pumps. Pushing a set beyond failure via techniques like forced reps and drop sets ensures the recruitment of as many muscle fibers as possible, allowing for more muscle growth.


After your set, the acidic environment caused by lactic acid is buffered mainly by bicarbonate, thus rapidly diminishing or eliminating pain before your next one. Simultaneously, fat is burned to produce ATP, which donates a phosphate to creatine and restores creatine phosphate levels, giving you quick energy for another set. The spike in lactic acid levels at the end of your set signals your body to release GH, which enhances fat burning and initiates muscle regeneration and growth. Likewise, testosterone levels have risen during the set, which will further aid the process of muscle regeneration and muscle building.

Cellular damage has also caused the muscle to flood with proteins which further break down the damaged structures.

This starts an inflammatory cascade of white blood cells that serve numerous functions, such as the removal of broken-down muscle tissue so that new and stronger tissue can be built up in its place. That process takes a few days to complete; 24 to 48 hours after your workout, if you suffered enough damage, you will likely feel the effects of calcium and prostaglandins, which build up in the muscle fibers, sensitizing nerve cells that signal your brain and thus providing the lingering ache known as delayed onset muscle soreness.

Boost Tactic

Postworkout, consume 40 g of whey protein and 60-100 g of fast-digesting carbs to enhance muscle recovery and blunt DOMS. Taking 5-10 g of glutamine can help increase GH levels. A massage may speed recovery, as can low-intensity activities (such as walking, cycling and swimming).

The Next Set

A minute or two after your set, you’re ready to do it all over again. You grab the barbell, the dumbbells or the handle once more. You focus entirely on the targeted muscles. The inevitable pain is like a false fire alarm, extreme heat that never sparks a flame, so you vow not to let it distract you.

You know every set has to end, but you feel limitless strength and energy once again. Hope springs eternal, and the life of a set is born anew as you lower the weight, launching the first rep of the next set.

Author: Greg Merritt, Jim Stoppani
COPYRIGHT 2010 Weider Publications
COPYRIGHT 2010 Gale Group

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  1. rudy t, says:

    wow. very cool article.
    a bit wordy, but it’s a good read. the “boost tactics” were especially cool.

  2. Shando says:

    Aweseom article – will read it agian and again

  3. Jonas says:

    Cool! Thanks! I like the end ;D

  4. jelet says:

    very nice article. good info

  5. Cueto says:

    thanks for your take

  6. Igor says:

    Awesome article, I like the idea of focusing on the set before you begin.

  7. Lindsey says:

    As a research biochemist, the science part was on par for the molecular level and enlightening on how it relates to health.

  8. Rob S says:

    Awesome article, I wish I found this website earlier.

    As far as pain being the reason for having to end a rep/set I don’t encounter it. Yea I’ll get the pain in my hands when holding onto a bar too long, usually only bicep/back workouts, but the larger muscle group never has pain. The contraction stops for me just because it does. I’ve heard it said by a lot of people but it’s so unfamiliar.
    Guess I have to add more poundage.

  9. Max HB says:

    Great article, science was bang on, heaps of stuff learned in this

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