6.2.2012 Coach Dan’s Friday Focus

Good Morning CFTP Members,

Fridays seem to come faster and faster. One more week and one more month down. I want to congratulate everyone on their progress this past month. It has been quite amazing. especially for those of you consistently coming. I can’t emphasize enough the importance of coming consistently in order to reach our goals. Missing a week at a time will retard your progression toward your goals. I understand that sometimes life gets in the way. Do your best to get in here as consistently as possible so you don’t have to suffer the pain of starting over.

This week I would like to talk about rowing. From the beginning I have said that the rower must be set at 10, trying to level the playing field, to later find out that the setting does not effect the distance. It is a damper setting like we used to have on those old bikes. For the stronger people a 10 setting could be appropriate because they can maintain that force for a long distance. For those who struggle with rowing, like myself, or just aren’t quite as proficient a lower setting may be appropriate. The key is to find the setting that works best for you for the distance we are doing that day. So when you warm up on the rower be sure to try out some different settings to see which one makes you the most proficent. I got this article off of www.crossfitsouthbay.com’s website. They explain what the body does to the rower and more specifically how the damper setting works.

I know it is long and has some math but it is very interesting. Thank you CrossFit South Bay.

“Today we’re going to break down the rower (also known to some as the portal to hell) and explain the damper setting and how it works. To do this we’ll break the system of rowing into two parts: #1 – You, #2 – The machine. If you just want the conclusion scroll down, important parts are in bold!

Lets define a couple of physics terms:
Mass, Velocity, Acceleration, Force, Work, Power, and Kinetic Energy. Open this link up if you want the definitions in equations (math? I thought we were working out!).

Whew that’s done! But how do these apply to us on the rower? When we extend our legs, hips, and pull with our back and arms, we are generating a force. This force is transferred to the handle, through the chain, and to the machine. By generating this force we cause the mass of the flywheel (that whizzing thing in the machine) to accelerate. Or in other words an increase in the flywheel’s velocity (rate of spinning). The harder and faster we pull, the bigger increase in the velocity of the flywheel we will make. Now we’re going to translate these physics terms into a spinning object (which is basically adding the radius of the spinning object into the equation). Againthis link will open up the PDF with equations :)

Ok now we’ll translate what the body does to the rower.
Lets go back to the force we generate:  f copy
And starts substituting in for how this translates to the flywheel. With Some substitutions we get . f-2
Simplify and Torque becomes equal to the moment of inertia (the rotating mass of the flywheel times the angular acceleration). t-1 copy
Point 1: The force we generate becomes torque and speeds up the flywheel.
Well now lets look back at that equation for power. p-1
Point 2: The more torque (force we apply) or the faster the flywheel spins (angular velocity) the more power we generate.
3750~Blow-Your-Mind-PostersWHOA did I just blow your mind? No not really, makes sense right. But there is two factors of this equation, the force applied, and the speed of the flywheel. If you halve one and double the other, you end up at the same power (keep this in mind for the damper setting).

But what does it all mean batman?

BatmanAccent2We’re almost there hang tight! This is the answer to the question of “What do I put the damper at?” Lets look at the kinetic energy of the flywheel, and the power it dissipates (loses) due to the air it moves.

p-4
Substitute in the equation for kinetic energy and p-5

Point 3: The last piece of the puzzle is the mass of air the flywheel moves is in direct relation to its angular velocity, multiplied by the time it is spinning, multiplied by the “drag factor”(z) – or the damper setting!
m-air

Put these together and viola! The power becomes

p-6

Point 4: When you change the damper setting (z) you alter the relationship between power and flywheel speed. The damper setting has nothing to do with how much power you can generate. It only determines how fast you can spin the flywheel with the same power.

The power dissipated by the machine must be equal to the power put into the machine (Law of Conservation of Energy). This means that the power we put into the rower is not dependent on the damper setting! It is directly related to the cube of the velocity of the flywheel, and the amount of drag we set it at. The power we put in correlates directly to speed, but we now have two ways to generate the power.

Point 5: The Concept 2 rower is constantly measuring only 1 thing: the velocity of the spinning flywheel. From that it can find how quickly it slows down and can calculate the “drag factor” (z). It knows the resistance of the mechanical systems (y). From there it knows the power, and in another derivation of exactly the same factors; the Concept 2 calculates speed of the rower (in meters per second).

As we come forward on the rower in the recovery phase, the flywheel slows down, and the difference between the maximum and minimum speeds of the flywheel is the difference in power of the flywheel, and therefore the amount of power we put into the machine, and therefore the speed and distance we traveled on the rower.

Point 6: The Concept 2 constantly takes measurements, and measures the change in velocity of the flywheel during the deceleration (forward movement or recovery) of the flywheel to find power input, which is directly related to distance.

Conclusion:

  • The body generates power (force per time) which we transfer into the rower.
  • It is the goal in Crossfit to increase our power output (more force in less time).
  • We can transfer that power to the machine via one stroke in a given time. If we halve the time it takes us to do one stroke, we only have to generate half the force to meet the same power.
  • The higher the damper setting; the slower maximum speed of the flywheel, and the faster it will decelerate. The lower the damper setting; the higher the maximum speed of the flywheel, and the slower it will decelerate.
  • The rower measures power based only on the design of the flywheel’s inertia factor (y), the drag due to air (z), and the angular speed of the flywheel (w).
  • The fastest way to row is dependent on how much force your body can generate, and how long it can sustain that force output. If your capable of high force (ex: a 300 lb dead lift) you might row faster at a higher damper setting, if your capable of half that force (ex: a 150 lb dead lift) you will probably row faster at a lower damper setting.
  • When taking a strategy of the fastest times, you must also take into account how fast your muscles fatigue. A higher force output by your muscles will generally mean faster fatigue.
  • Play around with different settings to find what feels easiest for you to row your max power.

Now you can argue with Forrest when he tells you to row at 10 and give him scientific evidence of why you may or may not be able to row faster at 5, or possibly even lower!”

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