Lifting Heavy = Good

Matt M has two tickets to the gun show in rippedville

In crossfit, we lift heavy things, often.  We do this because it’s a good thing to do.  It is worth asking the question: why?  Well, we get stronger as a direct result of lifting heavy things.  Generally we attribute this effect to increasing muscle size and as a result adding ability to produce force.  This is true, but the story is much juicier than that.  Adding muscle mass will increase strength, but this isn’t the only way we can get stronger.  Our bodies can actually get better at the skill of recruiting our muscles.  The skill of using our body is controlled by our nervous system.  To understand how our nervous system adapts to exercise I’m going to need to detour and first describe how our nerves (and in turn, our brains) control our muscles.

Soft lighting for a hard lifter like Amanda

Our brains control our bodies by sending electrical signals through our nervous system.  These electrical signals reach their destination where a nerve interacts with that body part to cause an action.  The nerves that control our muscles are called motor neurons. The motor neuron is something like an on/ off switch.  When the motor neuron fires, every muscle fiber it controls is stimulated to contract.  This runs a little contrary to our experience because our muscles aren’t either off or on, they are capable of producing a wide range of forces.  It would be pretty inconvenient if we couldn’t control how much force our muscles produced.  You could imagine trying to walk if every time you took a step you got the same kind of muscle contraction that you used for a 1 RM deadlift.  (Maybe something like this is happening when I try to “dance”.  It might explain the sudden loss of coordination, the spastic movements…) Fortunately, we have very fine control over how much force we can produce because of the way that motor neurons are structured and recruited.

And now for our next trick, Jon will bend a solid metal bar with his bare hands. Oh and he'll also do a 500+ lbs deadlift.

Each motor neuron enervates somewhere between 10- 1000 muscle fibers.  The muscle fibers collectively enervated by 1 nerve are called a “motor unit” and they will all collectively either be at rest or contracting fully.  There are many motor neurons in each muscle.  Each motor unit is composed entirely of 1 type of muscle fiber (i.e. either all fast twitch or all slow twitch).  Some motor neurons are very sensitive, and will fire easily, while others take stronger signals from the brain to be recruited.  When a muscle is only producing a small amount of force, only a small number of motor units are active, so a light force is produced.  This is useful for things like writing, walking, lifting a PVC pipe, etc.  When the brain is sending a very strong signal to recruit muscle, more of the motor units will fire, until close to 100% of the muscle fibers are contracting, producing maximal force.  This is useful for things like sprinting, 1 RM lifts, etc.  The number of motor units recruited help to control amount of force produced.  The other half of the equation is how fast the motor neurons are asked to fire, and the brain controls this.

Jean getting stronger every day.

Read this article from NPR on seniors and strength training: Seniors can still bulk up on muscle by pressing iron

The brain controls which motor neurons fire, and thus how much force is produced, by the way that it sends electrical signals out.  A weak signal to contract will look like a twitch.  One short burst is sent out which recruits only the most sensitive motor units, which briefly contract and then relax.  To send a stronger signal out the brain must start with that same little twitch, then quickly follow it with another twitch.  This makes for a second muscle contraction that builds on the first small initial contraction.  The brain can control how much force is produced by how frequently it sends the electrical impulses.  If the rate of firing is fast enough, the muscle will have no chance to relax in between twitches and effectively the muscle is constantly contracting.  As the strength of the signal builds, more motor units are recruited, and the newly recruited motor units add the force of their contraction to muscle.  This is the way we can produce the force along a continuum, allowing us to pick up a pencil and pick up a barbell, using the exact same muscles.

Merideth, all smiles all day every day.

Our muscles strive to be efficient (read: lazy).  They only want to produce the minimum amount of force required to do what you are asking them to do.  When you ask your muscle to work, all the motor units don’t fire at the same time, the most sensitive fire first, and then more and more motor units are recruited until enough muscle fibers are firing to do the job   As might be expected the motor units that are most likely to fire first are the weakest.  The first units to fire are usually slow twitch fibers, which tend to produce less force than fast twitch fibers.  They are also usually smaller motor units, closer to the 10 fibers, than the 1000. As the stimulus to contract builds, larger and stronger motor units are recruited.  The last motor units to be recruited contain large numbers of powerful fast twitch fibers.  What this means is that we have to place enough of a demand on our muscles that we require all of our motor units to fire if we want to strengthen our whole muscle.

Bryce loves to cop a feel on Moffett when he's most defenseless. Straight pervin' on some heavy back squats.

At this point you’re probably wondering when I’m going to bring this back around to heavy weight and why we need to lift it. Only the heaviest weights, in the 1-5 repetition max range, will force you to recruit those last, most powerful motor units.  Lighter weights, even done in large volumes, simply don’t demand enough of your muscle to make these fibers contract.  Heavy weight doesn’t just stimulate your muscle to adapt; it stimulates your nervous system to adapt.  It is this nervous system adaptation that is the sexy part of lifting heavy things.  It turns out that when we lift heavy things, we get stronger. (Horay! Science proves the obvious, again!)  However, only maybe 1/3 of the increases in strength can be attributed to an increase in muscle mass.  That leaves the other 2/3 to improvements in the nervous system leading to increased functional ability.  When we lift heavy, we get better at the skill of recruiting our muscles.  This is especially true of beginning athletes. When most people walk into our door for the first time they have little experience with the kinds of lifting that they will be asked to do.  After a couple months most find that they have made incredible gains in strength incredibly quickly.  Muscle mass alone can’t possibly explain such fast improvements in strength because it increases at a much slower rate.  As we adapt to lifting heavy things, our nervous system gets better at recruiting more motor units, faster.  In plainer language, that means our muscles switch on faster.  We get stronger because we have improved the skill of using our muscles.

Announcements

Classes Canceled this weekend due the CrossFit Endurance Cert:

Friday 6PM
Saturday 9AM
Sunday 10AM

This Friday night from 6:30 to 8PM there we will be hosting the CrossFit Endurance War Tour. It’s a free Q&A about endurance training and CrossFit. It’s totally free and there will also be free beer. Anyone is invited to come and we hope to see you all there!

Endurance Cert - We will be hosting our first certification this weekend. The Endurance cert will be Saturday & Sunday from 9AM till about 5PM. Our updated class schedule will be posted tomorrow. You can register for the cert at the button on the side of our blog.

If you ever wondered what a cert was like, come by and be a fly on the wall to check it out. We also need a couple of volunteers throughout the day. Email Forrest if you are interested in helping out.

Workout of the Day 2/25/2011

A. 500M Row x 2

B. 6-5-4-3-2-1
Deadlift (275/185)
Muscle Ups (Bar or Ring)
Triple Unders

*Before everyone gets crazy, this is an advanced workout. Here is how you will scale:

Muscle ups > 3 pull-ups 3 Ring dips (use band assisted if necessary)
Triple Under > Reverse Double Under > Double Unders > Tuck Jumps
Deadlifts = Scale weight accordingly. LISTEN TO YOUR COACHES. If your posterior is rounding, they will take the weight down…down…down.
Row = You’re pretty much screwed.

This guy does triple under crossovers…with his shirt off. Hot AND dangerous: