Physics of Infantry Gear/Kit: IcePlate® Rotational Force Advantages

Always give more than you take.

Put six water bottles in your backpack, then see how quickly you can turn. Find out how elite special operators can move using less energy with IcePlate®, boosting endurance.

A great attitude to acquire in life and an even greater attitude to use in product design.  

The design of the IcePlate® epitomizes this philosophy.  1" in width, the size of a medium SAPI plate, worn close to the body.  These features allow you to carry 50 fluid ounces of water in the most efficient way on the market.

Introduction

By the time I reached the 5th grade, my family had moved six times.  From an early age, I learned the art of moving boxes (Boxes that arguably should not have been moved by a four, six, eight, and ten year old).  The lesson was simple though.  Lift a heavy box far away from your body = super hard.  Lift a heavy box close to your body = manageable.  Imagine now, that you are in the same situation.  You need to move a box full of kitchen dishes to a moving truck.  Do you stand 3 feet from the box and try to lift?  No - you get close to the box and try to get under it before lifting.

This lesson has been reinforced through years of hiking and backpacking.  Carrying a pack on your back is much easier than carrying it with your arms.  Carry the pack on your back with a chest strap, even easier.  Tighten the shoulder straps, easier still.  The conclusion is simple: you can carry more weight the closer that weight is to your body. What though, is the science behind this well understood concept?

In this article we'll answer the following questions:

• What is the history of the Armed Forces as thought leaders in load carrying efficiency?
• What is our Center of Gravity?  How does Center of Gravity relate to rotational force or Torque?  
• How does the Torque created by the IcePlate® differ from a traditional Hydration Bladder?
• What implications does this difference have on exertion and performance?

Every object has a Center of Gravity.  The Center of Gravity (or center of mass) of any object is a theoretical concept.  It can best be understood by imagining the point at which you could balance a given object on your finger [5].  Because Center of Gravity is defined as "the average location in a 3-dimensional space, of a person's mass," your center of gravity can actually be outside of your body depending on your state of motion.  

Generally speaking though, the Center of Gravity for an upright human is in front of your sacrum (approximately hip level), although this differs depending on gender and body type. [6]  

Gravity acts on a person as a straight line through their Center of Gravity. As long as your Center sits over your Base of Support (or the area beneath an object or person that includes every point of contact that the object makes with the supporting surface [12]), you are stable.  The minute your Center shifts (and thus the force of Gravity is applied away from your Base), your body destabilizes. 

Torque is an often feared physics concept, but the definition is fairly simple.  Torque is any twisting force that causes something to rotate. Any force applied to an object at a point away from the point of rotation will produce a torque [7].  Let's think of the simple example of a lever. Levers are stabilized on one side (the stabilized end is the point of rotation). When you apply a force (pushing motion) to the lever, you rotate it in that particular direction.  Torque can act on people too. Anytime you wear something on your back, that weight is causing a torque. Imagine a small child putting a large pack on. The weight of the pack would rotate them (causing them to fall backwards). 

Torque can be calculated using a simple equation (equations! equations!) and the sum total of all Torques determines the direction of rotation.  

Torque = Force x Distance

Think again about our example of the lever.  When you push the lever very close to it's stationary axis, you have to push a lot harder to get it to rotate compared to pushing it further away from the axis.  This is also the science behind loosening bolts with a ratchet.

Another important equation we will need for this study is Weight.  Weight is a force and is calculated using Mass and Gravity.

Weight = Mass x Acceleration

In this case the Acceleration caused by Gravity close to the earth is 9.8 m/s^2.  We will need this value later.

What does this have to do with carrying weight close to your body?  Let's look at two highly simplified examples to acquire a clear understanding of this concept - the Qore Performance IcePlate® versus a traditional Hydration Bladder.  We will assume an upright human (with a typical Center of Gravity) is carrying these weights on their back. 

To calculate the Torque caused by the Weight of the IcePlate®, we need to calculate the distance between the IcePlate® and the theoretical human's Center of Gravity (using the straight line through the middle of a human's body as our point of reference).  Let's assume a 4 inch distance between this line and the center of the IcePlate®.  The IcePlate® is 1" in width. So, the distance between the human's Center and the IcePlate's® Center is 4.5 inches. 4.5 inches = 0.11 meters.

The IcePlate® (fully filled) in the Safety Sleeve is roughly 4 pounds.  4 pounds = 1.81 kg.

Now we can calculate the Weight in Newtons of the IcePlate®.

Weight = Mass x Acceleration, so:

Weight (IcePlate®) = 1.81 kg x 9.8 m/s^2 = 17.7 N

As such:

Torque (IcePlate®) = Force x Distance = 17.7 N x 0.11 m 

Torque (IcePlate®) = 1.95 Nm

Case #2: Traditional Hydration Bladder

Now let's look at the Torque created by a traditional Hydration Bladder.  These Bladders do not have the same rigid design as the IcePlate®, so they bulge outward, moving the Center of Gravity of the Bladder outward.  Let's use a highly simplistic example to demonstrate the difference in torque this creates. Let's assume this Hydration Bladder is identical in Weight and water-holding capacity to the IcePlate.  In this case Weight (Hydration Bladder) = 17.7 N.  The metric that will change in this scenario is the Distance variable in our Torque equation (D2 > D1 in hand drawing above). Let's assume the Hydration Bladder's Center moves out 1 inch (0.03 m) compared to the IcePlate.  Our Torque equation changes:

Torque (Hydration Bladder) = 17.7 N x 0.14 m

Torque (Hydration Bladder) = 2.48 Nm

Perhaps this difference in Torque doesn't mean much to you.  I mean, 1.95 Nm is a small number and so is 2.48. The implications are actually profound though, because your body has to compensate for this Torque to keep from being pulled in that direction.  "Postural Sway" is "the amount of torque and tension placed on the spine by a heavy load." Carrying weight closer to the body will reduce the amount of sway and stress placed on the spinal muscles. [10]  Our lower back muscles, in particular, feel the brunt of this strain. "When a load is held away from the body, the stress on the lower back increases substantially. The maximum weight you can lift safely is reduced dramatically the further away from the body that the load is handled." [11]

Anecdotally, this muscular stress accumulates over time the longer you carry the load.  For people whose jobs, enjoyment, or lives depend on staying hydrated, the reduced strain produced by the IcePlate® versus the traditional Hydration Bladder has important implications in terms of health and stamina.  

Make the change.  See the difference.

How has switching from a traditional Hydration Bladder to the Qore Performance IcePlate® improved your load carrying experience?  Has your level of back strain reduced? We'd love to hear more!