June 2010

Eric I still don't know the exact role of the CNS in weight lifting. “Priming the CNS" and "CNS recovery" are things I say, but I don't really know how they work. So, what is the role of the CNS in weight lifting?

-Bryce

Bryce, the CNS (the central nervous system, i.e. the brain, spinal cord and the nerves which control voluntary movement) is one of the first things that adapts to weight lifting and it is widely misunderstood. The development of strength is caused by structural and neural adaptations in the body. Structural adaptations include increased size of muscle fibers, increased cross sectional area of muscles and also increased bone and connective tissue strength. On the other hand, neural adaptations include a host of other changes in the body.

These adaptations occur along the entire CNS. They occur centrally in the motor cortex of the brain, in the spinal cord, within the motor unit, at the neuromuscular junction, and within the reflexive systems of the muscle (Golgi tendon organs and muscle spindles). 

When a muscle contracts to lift a weight, it does so by receiving a series of contraction signals. The frequency (among other things) of these contraction signals determines the force of contraction. The more frequent the contraction signal, the stronger the contraction. This is called rate coding. Strength training, especially in the lower rep ranges, increases rate coding, which in turn increases contraction force and thus strength.

Low rep strength training also increases your ability to recruit as many muscle fibers as possible, especially the fast twitch fibers with the highest strength capacity. The more experienced a lifter is with lifting heavier weights, the closer to 100% recruitment that lifter gets. In the vast majority of studies, it has been proven that fibers are recruited according to the “size principle”. It states that muscle fibers are recruited in order of size on an as needed basis according to the demands of the resistive force. This means that slow twitch fibers are recruited first and the largest of the fast twitch fibers are recruited last. Therefore, heavy weight lifting recruits all muscle fibers (and will induce hypertrophy in all muscle fibers), including the smaller oxidative fibers. In some studies, using dynamic and ballistic movements, athletes have shown that they can preferentially recruit fast twitch fibers before slow twitch fibers in order to increase the rate of maximal force development.

Heavy lifting also causes conversion of type IIx muscle fibers to type IIa muscle fibers. Although still fast twitch in nature and sometimes misunderstood as fibers with the greatest capacity for strength, recent research reveals type IIx fibers as essentially fibers "in waiting". This means that they are “reservoir-like” fibers that adapt when trained. They are more present in sedentary folks than in weight lifters. When trained with lower rep heavy weight lifting, they convert to type IIa fibers and are more easily recruited and contribute more force. Intuitively, fiber type adaptations may seem like a "structural" adaptation, but fiber type has been revealed to be controlled by the nerve that innervates that muscle fiber. If you surgically take the nerves that innervate type I fibers and connect them to type II fibers, those fibers become type I.

Another factor of neural adaptation is simply motor learning. As you learn a movement your body figures out the best recruitment pattern, i.e. which muscles to recruit, in what order and at what magnitude. This creates stability and smoothness in a movement. The less "smooth" a movement is the more your body has to correct the movement pattern to maintain balance, the right angle, form etc. To make these corrections you have to fire the opposing muscle groups to essentially correct the original miscalculation. This is like turning the wheel of a car to steer back into your lane if you drift. This of course creates increased time under tension, range of motion, antagonist contraction and metabolic energy expenditure and for all those reasons, limits maximal strength. It can also put you into a position or angle that hampers your leverages and limits your maximal strength in that lift.

Lastly, improved neural efficiency reduces antagonist inhibition and increases reflex potentiation. This one is not as well researched, but in essence, when lifting (especially in beginners) the opposing muscle groups and mechanisms within the muscle (Golgi tendon organs) actually act against what you are trying to do in small amounts. This is thought to be a safety mechanism when doing heavy, unfamiliar movements. As you become better at the movement, the antagonist muscle groups and the reflexive mechanisms inhibit your strength less and allow you to exert more of your potential strength.

To sum up, the functional neural adaptations to strength training include:

·         Increased rate of muscle contraction signaling

·         Greater recruitment of fast twitch muscle fibers

·         Fiber type shift towards anaerobic power production

·         Improved coordination

·         Reduced neural inhibition and increased reflex potentiation.

So powerful are these CNS adaptations that they can be seen systemically, affecting the whole body. In studies where weight trainers only trained one limb, they found that strength was also increased in the untrained limb, showing evidence of the powerful centralized adaptations to weight training.

This is all fine and dandy, but many bodybuilders think that getting stronger through neurological means is a waste of time. Hell, nobody cares how strong bodybuilders are, it only matters how strong they look! So, by this logic they focus on training methods that produce strength through muscle growth, not by neurological means. This makes sense on paper; however it’s simply not how the body works.

Sorry guys, only works that way with drugs.

In actuality, the vast majority of the initial gains one makes in strength on any type of weight training program are always neurological in nature. In fact, it seems that neural adaptations are in many ways permissive to gains in muscle size. Meaning, that not only do they work together to produce strength gains, but in many ways they are interdependent. After the initial neurological gains in strength are made, only then do the muscle fibers increase in size and contribute to strength. After hypertrophy occurs, neuromuscular activity decreases when lifting those same loads. If further size is to be gained it’s quite likely that further neural adaptations must occur before additional size is added. Remember, the body is conservative! Its job is to survive and creating muscle tissue is metabolically expensive, so if it can get the job done with improved wiring instead of added muscle tissue, you better believe it will!

So instead of focusing on pump-training and avoiding heavy lifting like the plague, bodybuilders would be better served incorporating progressive heavy training in order to expedite the process of neurological adaptation, so that they can get on with what they really care about: muscle growth!

Obviously if strength is your goal, heavy lifting will be an intrinsic part of your program and I hope that bodybuilders reading this now realize that it should be a part of their routines too. Remember, without injecting hormones into our bodies, it is necessary to get stronger in order to get bigger. In the world of professional natural bodybuilding, the biggest invariably tend to be very strong.  We just recently interviewed the WNBF Heavyweight World Champion Martin Daniels and it was no surprise that he has squatted over 600lbs raw below parallel!

IFPA World Champion Doug Miller deadlifts 585 for 3 reps:

Like anything, heavy lifting has its limitations and cannot be done every time you hit the gym. The immune system, the endocrine system, and the neurological system each respond in harmony to a training stimulus. When one is heavily taxed, it taxes the rest. So, to lift heavy weights to near exhaustion, it takes a lot of output of the CNS. This also causes disturbances (that are interrelated with the adaptations themselves) in the endocrine (hormonal) system and the immune system.

If taken too far, recovery is hampered and the whole system cannot function at 100%. When lifting heavier weights, if you’re not at your best, you aren’t lifting the weight. Therefore you have to balance your training so that the disturbance to the immune, endocrine and neural system is only so much that you can recover from it for the next block of training. Programming your training to meet this demand depends on individual training level, recovery abilities, nutritional status, supplementation, sleep schedule and many other factors. If done properly you can gain continuously, with little risk of injury or overtraining and you will consistently add quality muscle to your physique.

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