An ExoTi 50 between its two evolutionary predecessors, an internal frame pack on the left and an external frame pack on the right. Image credit: Edwin Durning @old_man_grom
Evolving over millions of years, human locomotion has become a highly efficient process. However, carrying a backpack requires us to deviate from our natural upright walking posture. The more we, as backpackers, can maintain our natural upright posture while walking, the more comfortable and less strenuous backpacking is to our body. Below, I will demonstrate the principles behind our ExoTi backpack series and their specific features that allow us to maintain a comfortable, natural posture while hiking without having to overcompensate for the load we are carrying.
The Act of Falling Forward
From a biomechanical perspective, walking (or in our case hiking) is the repeated act of falling forward and using our legs in a pendulum fashion to perpetuate this motion. To begin walking, we must change our center of gravity (by stepping outward) and allow our body to fall forward. Our bodies do this naturally without our having to think about it whenever we attempt to walk.
Carrying a loaded backpack changes our center of gravity. In order to fall forward then, we need to adjust our center of gravity to compensate for the weight on our back. We do this by pivoting at the hips and bending our upper body (back, shoulders and head) forward to counterbalance the weight in our backpack.
In the photo below, notice the angle at which I am required to bend forward at the hips in order to compensate for the backpack’s load.
Notice how much my body bends forward to compensate carrying a load while walking as opposed to walking upright without a load.
Increased Comfort
Backpacks that require us to bend forward excessively or put added stress on the upper body and vertebrae are not comfortable. In general, there are two things we can do to minimize the discomfort of carrying weight on our backs:
- At weight bearing points, maximize the effectiveness and comfort of distributing weight evenly.
- Decrease the angle at which we need to bend forward to compensate for the weight on our backs.
Weight bearing point comfort
There are two major weight bearing points on backpacks, the shoulder straps and hip belt.
Anatomically, requiring the vertebrae and soft disc tissue of your spinal column to support a load or the majority of a load via the shoulder straps is inefficient and uncomfortable, especially as the load or mileage increases. Instead, to improve comfort while carrying a backpack, backpackers should aim for approximately 80% of the weight on their hips and 20% on their shoulders. Twenty pounds carried on the shoulders is a lot different than twenty pounds on the hips. Packs that fail to adequately get most of the weight off the shoulders and onto the hips are increasingly uncomfortable compared to the opposite.
From my experience, most hip belts (particularly those on ultralight backpacks), apart from insufficiently transferring the weight to the hips, disregard the shape and anatomy of the lumbar region. The result are packs that slide off the lumbar region (i.e. sag) which decreases load transferability. Packs that sag not only are less effective at transferring weight to the hips, they are also, in my opinion, incredibly annoying.
Without a solid structure that fits the natural curvature of the lower back, there is no way to sufficiently prevent sagging or increase load transfer. Specific to the Vargo line of ExoTi backpacks, the titanium lumbar plate is a critical part of the pack’s frame to prevent sagging and precisely transfer the load’s weight onto the lumbar region. The additional leverage gained also helps maintain an upright walking posture compared to packs without this feature.
The ExoTi’s Lumbar Support Plate ensures that the load’s weight is transferred directly to the lumbar region while preventing sagging (an inefficiency).
Frame vs No Frame
However, in order to do this, the lumbar plate cannot act alone. The frame of our ExoTi system connects two rigid vertical bars to the lumbar support plate. These bars hold the load in the attached bag and directly transfer the weight down to the lumbar area. Without these connected rigid bars there is no effective way to transfer the weight in the pack to your hips. Of course frameless packs are lighter in weight but do so at the expense of load transferability to the lumbar region. In short, as pack frame rigidity is reduced or eliminated, load transferability directly decreases as well.
ExoTi Frame vs. a pack without a frame. Which has better load transfer?
Decreasing the angle at which we need to bend forward
The less we need to compensate for the weight on our back and the more we stand or walk in a natural upright position, the more comfortable and efficient the walking experience becomes. This being the case, and for the sake of visualization, I will use the bottom of the ExoTi frame as a fulcrum to demonstrate the effects of loading a pack in the ideal configuration (with the load’s center of gravity higher and closer to the body) and the least desirable configuration (with the load’s center of gravity lower and away from the body).
High versus Low Center of Gravity as it relates to falling forward
In the photos below I am demonstrating the tipping point (i.e. the point at which the frame is balanced and will not fall forward or backward) of the frame with a weight approximately 6 inches away from the frame. In the first photo on the left, the tipping point is approximately 25 degrees. When moving the same weight to a higher part of the frame the tipping point is reduced to approximately 14 degrees. Therefore, the higher a load’s center of gravity is, the less we need to bend forward to compensate.
The angle at which one has to bend forward to compensate for carrying a load drops 11 degrees (i.e. more upright) when the load’s center of gravity is moved from a low to a high position.
Distance from your body
Now that we have established that higher center of gravity is better, the next consideration is a load’s distance from your body. As I have already demonstrated, the tipping point of the weight at a higher point is 14 degrees. By bringing the weight even closer to the frame (approximately 1 inch) the tipping point is reduced to only 4 degrees! That is 21 less degrees an upper body needs to bend forward in order to compensate for a load that is low and away from the body.
The angle at which one has to bend forward to compensate for carrying a load drops an additional 10 degrees (i.e. even more upright) when the load’s center of gravity is moved closer to the body.
Additional ExoTi Features
In addition to the rigid, lightweight titanium frame and lumbar support plate, the ExoTi series backpacks all have Load Lifting Compression Straps. The straps extend from the bottom of the pack and connect to the top reinforcement angle brackets. They are designed to lift the load in your pack and compress the contents up and closer to your body. Together these features keep the load higher and closer to your body in the ideal configuration shown above while maximizing load transfer from the top of the pack precisely to the lumbar region.
The ExoTi’s Load Lifting Compression Strap System pulls the load up and in for a more upright carry.
Conclusion
What I’ve outlined above explains the thought process behind the design and benefits of the Vargo ExoTi backpack series and why they excel at keeping you upright while walking and their overall carrying comfort compared to packs that don’t incorporate these design points. Again, the three main points are:
- The hip belt and Lumbar Support Plate design holds the weight in the preferred lumbar region of your body, prevents sagging (i.e. inefficient load transfer), and promotes even weight distribution throughout the mid-section for increased comfort.
- The necessity of a rigid structure to more efficiently transfer the load’s center of gravity from a higher point on your back to your lumbar region.
- The benefit of the Load Lifting Compression Straps in bringing the load’s center of gravity higher and closer to your body for a more upright walking posture.
In short, the ExoTi’s rigid frame gets the load higher, its Load Lifting Compression Straps pull the load up and in, and the lumbar support plate keeps the load from sagging downward. Working together, these features help you to carry your load as comfortably and efficiently as possible.
The difference between a standard backpack and the ExoTi (both images captured while walking).
Of course there is no substitute for actually taking our backpack out and giving it a try. I believe that proof is in the experience and I sincerely hope that you are willing to try our ExoTi series backpacks and see for yourself!
Thank you.
Brian Vargo