YOUR MUSCLES' STRENGTH BUILDING PROCESSES

Is there a physiological difference between getting bigger muscles and getting stronger muscles? How does it happen? More important, if you knew the answers to these two questions, would your knowledge aid you in improving the efficiency of your powerlifting workouts?
"Who cares, Dr. Squat! Just gimme a barbell, let me lift it, and to hell with all this science!" is the pragmatic response I get from powerlifters who are into lifting for lifting's sake. That's ok. But, since you've gotten this far along in reading this article -- and since you've come to know what to expect of my articles -- I'm certain that you've already learned the answer to the third question posed in paragraph one.
In a word, yes.
Let's have a look at some of the important structural elements comprising a muscle cell. Then you'll be able to more clearly visualize how you -- the ultimate architect -- can build more muscular strength (without inducing unnecessary size increases) by manipulating the stresses you inflict upon your body during intense training.

Your muscles' structure and function

Inside every muscle cell there are thick filaments (myosin) and thin filaments (actin). They are the contractile elements you your cells. They are the proverbial "bottom line" when it comes to explaining where strength comes from. They are the proteins which, when called upon to contract, cause the processes of force output. It's an amazing process, and understanding it holds the key to maximum powerlifting success.
Energy released during the breakdown of ATP molecules (adenosine triphosphate) causes the thick filaments to slide across the thin filaments. How do we get the ATP to break down? An enzyme called myosin ATPase is secreted from the tiny hairlike structures (called "cross-bridges") of the thick filaments, and interacts with the ATP molecules, causing them to split. This interaction liberates energy for contraction.
Now, let's back up for a moment. Remember that you have red (slow twitch) and white (fast twitch) muscle fibers. They're so-named because of their color, inherent contraction speed and level of resistance to fatigue. Scientists call the slow twitch (fatigue-resistant) fibers Type I fibers, and the fast twitch, fibers Type II fibers. The fast twitch fibers are the ones that have the greatest capacity for both hypertrophy and force output, and are divided into two specific groups: Type IIa fibers (which are both fast-twitch and highly fatigue-resistant) and Type IIb fibers (fast-twitch but have a very low resistance to fatigue).
Each one of these fiber types contract in the manner described above. However, the tiny hairlike cross-bridges located on the three different fibers' myosin myofilaments secrete their own unique form of ATPase. Importantly, whether a muscle cell becomes a Type I, Type IIa or Type IIb fiber is largely determined by the specific form of ATPase the "heads" of the myosin filaments' cross-bridges secrete.


MUSCLE FIBER TYPES AND THEIR FUNCTIONS


FIBER TYPE FUNCTION & TRAINING ADVICE
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Type I Slow twitch, oxidative (highly fatigue-resistant), little capacity for exercise-induced hypertrophy or high force output (however, hypertrophy pronounced with anabolic steroid use), high resistance to exercise-induced structural damage

Training Tips:

Responds best to high repetition training with lighter weights and slow, continuous tension movements; however, powerlifters are warned to steer clear of this type of training, as it will ultimately "rob" you of greater gains in strength
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Type IIa Fast twitch, highly fatigue-resistant, high capacity for exercise-induced hypertrophy, moderate resistance to exercise-induced structural damage, moderate-to-high capacity for force output

Training Tips:

Responds best to medium rep training with moderate weight and fast concentric movements but slow, deliberate eccentric movements; acceptable as a training technique during off-season and early pre-competition cycle only (i.e., during "foundation" training period when limit strength of all muscle groups is being established)
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Type IIb Fast twitch, low oxidative capacity (highly susceptible to fatigue), great capacity for exercise-induced hypertrophy, great susceptibility to exercise-induced damage (especially from negative movements), high force output capacity

Training Tips:

Responds best to explosive training with heavier weights, addition of a deliberate eccentric phase induces hypertrophy process, but little advantage is gained in the arena of force output; powerlifters advised to engage in explosive training with a decided DE-EMPHASIS of the eccentric (negative) portion of the movement during the early phase of precontest preparation
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Eccentric Training and Powerlifters

For explosive athletes -- particularly you serious powerlifters out there -- whose sport-related skills are primarily dependent on the ATP/CP pathways of muscle energetics, avoidance of excessive eccentric training (especially with your assistance exercises) during the initial period of precompetition preparation is usually advised. This is because microtrauma to the thick and thin myofibers invariably accompanies such "forced elongation" of the myofilaments.
However, for the purpose of inducing hypertrophy -- an overriding requirement of the sport of bodybuilding -- the eccentric phase is of critical importance in the later reps of a (say) 8-10 rep set.
"Whoa! Do you mean that bodybuilders have to purposely inflict damage to my muscle cells in order to get them to grow bigger?"
Yep. But powerlifters (who get their increased muscle size almost exclusively from myofibrillar proliferation) should strive to avoid this size increase technique.
"Why?"
Dr. Scott Connelly, some 12 or 15 years ago, provided an erudite explanation of the hypertrophy process in the then-newly launched controversial magazine, Muscle Media 2000. He elaborated on the process of doing several reps in order to exhaust the ATP regeneration process so that the muscle would cease to contract.
At that point, said he, "...stretching a myofiber in this [fatigued] condition as would occur on the subsequent eccentric phase of the next rep would be predicted to 'tear' the sarcomere [the actin/myosin filaments] at its weakest link...
"This would be expected in Type IIb fibers with the least total oxidative capacity..."
Dr. Connelly went on to explain a relatively new concept in weight training science, which involves a muscle cell's "switching" to a different form of ATPase (the enzyme that breaks ATP down in order to liberate energy for muscle contraction). According to his theory, "...the replacement of Type IIb ATPase with the Type IIa variety..." is caused by heavy use of exhausting eccentric training.
This, in turn, increases your muscles' population of Type IIa fibers at the expense of Type IIb fibers. The theory, of course, is that by inflicting such exhausting stress on your muscles, they "adapt" to the increased energy, tensile strength (protection from destruction) and repair needs by switching to the ATPase isomer form that Type IIa fibers possess. Reducing the population of the more injury-prone Type IIb fibers isn't necessarily advantageous for powerlifters, though it may be good for middle distance runners.
The steps through which this entire process progresses are 1) damage (microtrauma primarily stemming from eccentric contraction), 2) inflammation, 3) repair (protein turnover and elimination of destroyed tissue), and 4) tissue remodelling (adaptive growth).

The Hypertrophy Process

The most interesting element of Dr. Connelly's theory is that, upon damaging the cells' membranes through eccentric contraction while the cell is in a "fatigued" state, certain protein growth factors are liberated in the interstitial spaces surrounding the injured cell. Called FGF (Fibroblast Growth Factor -- "fibroblasts are newly-forming cells), IGF-I (Insulin-like Growth Factor type one) and IGF-II (Insulin-like Growth factor type two).
These growth factors are known to 1) stimulate the development of non-contractile satellite cells, and 2) cause the conversion of satellite cells to become part of the neighboring contractile cell in order to give it greater protection from stress. This, Connelly reasons, is what causes hypertrophy of the contractile cell.
This is a revolutionary concept, folks! But remember this, and remember it well! It ONLY applies to our brothers and sisters in the bodybuilding world! Powerlifters are not interested in getting bigger muscles in this fashion. Powerlifters are ONLY interested in getting STRONGER muscles within a given weight division.
Of course, if you're underweight for your division, you have to get bigger muscles. But it's done through high tension exercises (sans excessive eccentric contraction) which stimulate myofibrillar proliferation. Bodybuilders and powerlifters alike have come to call this form of muscular growth "density." Fusion of contractile and satellite cells will not give the hypertrophied cell greater contractile force capabilities.
Trouble is, if this process were to continue for any length of time, pretty soon all of your Type IIb fibers would be gone -- converted to Type IIa fibers. This is not good news for bodybuilders OR powerlifters! Theoretically, when that happens to bodybuilders, further hypertrophy would be impossible. This situation may well be what all of us have for many years called "plateauing." And, for powerlifters, the conversion of desirable Type IIb fibers to less desirable Type IIa fibers robs us of the explosive strength we need to excel as powerlifters.
This is the most compelling rationale for applying PERIODIZATION to your carefully integrated training program. It's reasonable to speculate that carefully alternating both your training intensity and the application of eccentric movements, two very important things will happen: 1) you can limit the amount of (unwanted) conversion of Type IIb to Type IIa fibers, and 2) (for bodybuilders) you'll continue to develop more satellite cells (whose ultimate destiny is to become part of the contractile cell), thereby allowing hypertrophy to continue.
Now, I realize that this is pretty complicated stuff for the average powerlifter to relate to. It's also a relatively new concept, which means that it's untested in the "trenches." But, if new records are ever to be established in the drug-free environment our sport has (almost unanimoulsy) adopted, you're going to have to get a grip on it.
In future articles for MD, I will fully elaborate on precise training strategies -- "cook book" techniques -- for you to experiment with. I, for one, welcome such new science with open arms.

But the final embrace will only come after a bit of foreplay.