Training for The Normal Force

How can you train to gain The Normal Force?

There are a lot of ways to increase The Normal Force, like compression and stemming etc. But these are special moves for special circumstances. On a "blank" face you cannot simply use compression to stick to the wall, this requires an orientation of holds to enable to to find a direction to create compression. There are however some general considerations that will increase the normal force and there are things you can do to exploit this in your training.

In general you know to "stick close to the wall" and on a slab you might not want to... rather stick your butt out to center the weight above the feet. In all circumstances, this is about creating a force into the rock and you have muscles that you can use to create even more of this pressure than what gravity alone gives you. Use your core muscles to tighten and press your feet into the rock with your abdomen. The limit of how great a force you can create is down to your core strength... and a few other factors.

Think of how you can stand an a blank vertical wall if you grab a jug and place your feet directly on the blank wall. You can stay there, but only if you apply some pressure on your feet. The required push into the wall on your feet results in an equal pull on your hands on the jug. The same thing applies at any angle and with any size hold and with any type of grip. Standing on the same blank wall, fully extended, hanging on small crimps... is equally possible. This does however require a lot more core tension to create the required normal force to not slip.

The core is the core, is the core...

Core strength is of course essential, but core strength is not core strength. Your core is made up of a gazillion muscles or so and not everyone of these are involved in creating this specific tension. Doing a lot of traditional crunches will enable you to do... a lot of crunches. A crunch targets your ability to curl you upper body inwards, fighting gravity. Thinking about how you use your abdominal muscles during a smear (as described above), do you recognise the motion or tension from a crunch here?

The required core tension is initialized low in the thigh, then hip muscles, on to the abdomen and upward. It would then be reasonable to train these specific muscles, mimicking this load as closely as possible in your training. Crunches are the exact opposite and does not follow trough down to your legs at all. To gain more control ver The Normal Force you should include or even focus on exercises that include the legs and puts load in the correct area and direction.

Some exercises that are worth considering are: leg raises (hanging or lying), leg lowering (single or double), reverse crunch, suspension crunches, the plank, the spiderman plank crunch, etc. To get a more complete range of engagement you could even combine exercises like double leg lowering with reverse crunch.

The core is the core, but is there more...

So what if you do have the best set of core muscles ever... are you all set? Taking a step back to the "illustration" of The Normal Force by hanging on a jug with both feet placed on the blank wall... you still need to be able to hang on the jug. Pressing harder and harder with your legs... the thing that popps is likely to be your hands, not your feet. This becomes more and more likely as your body gets more extended and the holds get smaller. The point is that you will always need grip strengt or contact strength to keep from popping the hands off the holds.

Finger strength and contact strength is already a well known and prioritized area of climbing training and should remain so, even in the context of climbing technique. You can use it to "hang on", but it helps to know how and why... and the finer details about what "hanging on" actually means.

May The Normal Force Be With You!

The Science Of Friction... Skin vs Rubber

Friction between fingers and rock

Having dug into the science of friction that applies to rubber (on rock) there is still the question of how friction works for the skin on our fingers. The rubber on the shoes are only half of the equation, we slip just as much in our gripping of the rock as we do in our step.

There is not much industrial use for this information and the funding of research and studies into the subject is equally absent. I will however offer an abstraction based on the science of rubber friction.

Comparing skin to rubber

The qualities of rubber that are relevant for the different components of the friction between rubber and rock is the rubber surface:

• the atoms on the contact surface that come into contact with the rock
• the plasticity of rubber making the surface bend into shape by the shape of the rock surface
• the ability of the rubber to compress
• the fact that the surface is rough
• the fact that it gets worn by the contact with the rock.

Now... as far as I can tell... skin, or more precisely skin on the finger with all its underlying layers of tissue, display very similar characteristics:

• It has a rough surface
• It adapts in shape, filling gaps and small divots etc in the rock when loaded
• On a microscopic level it also compresses when loaded
• It definitely gets worn when we climb.

Back to the science

Looking back at how this friction breaks down for rubber on rock:

FT = FA + FHS + FHb + FC

where:

FT = The total frictional slip resistance
FA = Friction from adhesion
FHS = Friction from surface deformation (microhysteresis)
FHb = Friction from surface bulk deformation (macrohysteresis)
FC = Friction from rubber wear

F_A - Adhesion

Adhesion is the force between two surfaces that exists on the molecular level, between molecules and atoms of the two surfaces. This is undeniably a factor for skin on rock, the atoms are bound to come into contact and thus to be bonds between atoms of the different materials.

F_HS - Microhysteresis

Microscopic asperities in the surface of the finger interlocks with microscopic asperities in the rock surface (or climbing hold surface). This is also likely to be a factor for skin as the skin surface is not a smooth surface.

F_Hb - Macrohysteresis

The tissue/skin on the finger will flex somewhat around the protuberances of the rock, causing a larger contact area between the two surfaces. The added adhesion this creates has to be a significant part of this friction contribution just as it is for rubber on rock.

F_C - Wear

The skin on your fingers gets worn, tearing off microscopic pieces of skin from your fingers takes force. This force contributes to the total friction force experienced.

Conclusions

The similarities between rubber and the skin on your fingers are undeniable. This makes for a plausible comparison of the mechanics of friction for rubber on rock to the mechanics of friction for skin on rock.

We also instinctively know that there is a lot of differences, shoes stick a lot better than fingers. This however does not mean that the mechanics are not similar, but it points to the fact that rubber at least have a much stronger adhesion (to rock) than skin does.

There are also factors that apply to skin that don't apply to rubber, our skin breathes and perspires. This causes a film of moisture between the surfaces that influences the mechanics. The effect of moisture on rubber friction is well documented and studied and it is likely that this applies similarly to skin on rock.

However well this comparison gets or how detailed the different factors are broken down, the overall conclusion is that as a climber you have to address friction in the same way for your fingers as you do for your feet (shoes). You may not want to prolong contact time as perspiration may become a problem, but otherwise it all applies and you have to be vigilant when it comes to observing and addressing The Normal Force.

How well do you find this reasoning to match your experience with skin friction?

May The Normal Force Be With You!

The popularity of climbing technique

Technique vs Power

I wanted to find out how much focus there is on climbing technique, compared to power. The focus on power in climbing is enormous, but most climbers talk about technique every now and then. I figured the use of search terms on Google would be a relatively good way to measure the focus on the two aspects.

The choice of words to research will of course influence this picture enormously, but here is one perspective that is representative. It is interesting to see that a general term as "climbing technique" performs so badly compared to a very specific climbing strength term like "campus training". You could throw in a lot of different other power centric terms, like "hangboard", "crimp strength" etc, the picture is the same. They all point in the same direction: Power is far more on everyone's mind than technique, and it is getting worse by the minute. A decade ago the gap was very small, now the focus is turned all the way over on power. Combining the focus of all power terms and comparing it to the same for technique, it may be as bad as technique getting only 10% of the focus that power gets.

My ultimate goal is to raise climbing technique back to equilibrium, both in terms of attention and the resulting impact on the level of performance in climbing.

Branding and marketing

The brand I chose for this effort is not entirely random. There is a huge need to market climbing technique, make climbers more aware, create attention, engage and provide some results in the community with regards to technique. I have yet to meet a climber that don't care about climbing technique, but there are very few that make this a focus area and really explore this for gains.

I chose to brand this marketing, wrap it up and sell the concept as plainly as possible. I still think it will be a hard sell.

May The Normal Force Be With You!

The Science Of Friction... Breaking down the Normal Force

What is the Normal Force

If you apply force to a surface, provided you are not able to make the object (rock) move, it will push back with an equal force. Forces can be broken down into smaller components that make up the total force. In order to identify the Normal Force, you have to do this in a way that focuses on the angle of the force in relation to the surface. The Normal Force will always be perpendicular to the surface that you apply the force to. So you have to break the force down with regards to this particular force component.

The applied force breaks down into two components, one that is parallel to the surface and one perpendicular to the surface. The parallel component is the one that may cause you to slip and the perpendicular is ultimately the one that prevents you from slipping. You should make every effort to ensure that you apply pressure that feeds the perpendicular component and that contribute as little as possible in the parallel direction. In non theoretical terms, putting your hand on a table top it is less likely to slip when pressing down on the table than when you press along the surface of the table top.

Perpendicular and angles, this spells trigonometry

If it has been a while, remember to think straight angles, squares. It's only if you need actual values for the forces and angles that you need to bring in sin and cosine to do calculations. When we climb, we really don't care how many newtons this and that force is, we only care for the direction we optimally should apply the pressure and in what scenario should we expect to start slipping.

Uneven surfaces

What then, when the surface is not even. It may be curved, it may have any shape or form. How can you break down the Normal Force for a surface like that? You have to think of the entire surface like many small sections of flat surfaces, and for each of these break down the forces in play and find the direction of its Normal Force. The combined Normal Force for the surface will be the sum of the Normal Force for each section.

This again gives you good information about how to handle the surface. Of all the sections, which gives the best use of the Normal Force in terms of creating friction, and which gives lousy contribution to the friction? Bearing in mind the direction that you might slip and what direction you care most about not slipping. You should try to use all the surface fractions that contribute well and avoid using those that don't. This way you can manipulate the combined Normal Force and thus the friction.

Applying more than one force

Just as with an uneven surface, there are other complexities to consider. Gravity is not the only force in play, you generate a series of forces with your muscles and these are not always aligned. The result is that more often than not, there are forces pulling in different directions and friction countering them in equally many opposite directions. Will friction win, and thus you... or will any of the forces overcome its respective opposing friction force? The resulting analysis is the same, break down each one separately and find the answer, but... keep in mind that one force may break down into a force component that contributes to another of the forces you consider and thus be the very thing that tips the scale and makes you slip.

To sum it up...

Analysis and consideration of how, when and why you slip and fail may not be a 5 second break between attempts. It may require careful consideration and many sleepless nights. My point is though, that this time is well spent, what else are you going to with that brain capacity? I'm not suggesting that you stop pushing the boundaries of your physical strength, I'm only suggesting that you also use your mind for analysis, rather than just counting pull-ups.

May The Normal Force Be With You!

The Science Of Friction... Factors for rubber

How to make every possible effort to push the limits!

The factor that influences the friction of your climbing shoes on rock the most, is by far the Normal Force. You should spend time analyzing it and always having this in mind as you place and load your feet. In my next post I will focus on breaking down the Normal Force into something comprehendible, but now I will dig deep into the minute details of the other factors.

If you are climbing at the very limits of what is physically possible, every sliver of contribution will actually be important. Knowing what these factor are will be essential, and knowing what can be done about them is what separates you from the rest.

The factors that influence friction

Besides the main contribution from the Normal Force, there are the factors that influence the coefficient of static friction.

Humidity

It should come as no surprise that humidity is a factor. This is a factor that all climbers have battled. Rain just shatters all your (outdoor) climbing plans, it does not even have to be raining on the day of your climb to ruin it. Moisture takes time to dry. Even rain elsewhere, or no rain at all... just humidity in the air or lack of air circulation to transport away moisture could be enough to prevent the friction from being optimal. The actual (negative) contribution of humidity on friction is dependant on several factors, like the surface of the rock in question. Some rock seems to be just as good to climb regardless of air humidity, while others are useless with even slightly humid air.

The Bleausards of Fontainebleau have fine tuned this aspect to a level where they routinely whack the holds with a cloth to remove as much moisture as possible before getting on the rock. I am not talking about wet holds, they whack the seemingly dry rock when humidity in the air causes issues with friction.

How significant is this factor?
I have found no scientific studies on rubber friction on rock with regards to the effect of humidity, nor any similar studies that I could extrapolate from. I might pursue this later, please advise me (comment) if you stumble across any relevant studies.

I will however suggest that the impact of humidity on the friction of your shoes on the rock is far less than the impact it has on the friction between your fingers and the rock.

Temperature

Just as with humidity, heat is a known enemy of friction. Professional climbers migrate the globe in structured patterns, chasing the winter for cold, crisp conditions. The effect of temperature on friction is significant, but can be ignored if you are only looking for an enjoyable climb. If you aim to tick your list or break new ground, you need to keep an eye on the thermometer and the forecasts.

How significant is this factor?
Studies have proven a link between temperature and rubber friction and it effects adhesion, microhysteresis and macrohysteresis (see my previous post on these contributors to the total friction). The only data I found were from aircraft tire testing and extrapolated from that data the effect is about 0.24% per degree Celsius. This is not good enough to be used for anything scientific, but it is good enough to give an indication of temperatures effect on friction for your rubber shoes on the rock.

I will again, however suggest that the impact of temperature on the friction of your shoes on the rock is far less than the impact it has on the friction between your fingers and the rock.

Pressure / Area

Pressure and area are two sides of the same thing. The pressure per square inch on the rubber sole is dependant of the actual force applied and the surface area of the contact surface. Applying more force will not result in an equally increase in friction. As you apply more and more force, the friction gain will decrease.

Note that applying more pressure is always good for the friction as long as the majority of the extra force is a contribution to the Normal Force.

The practical value of this is that smearing is better for friction than edging and that distributing your weight on both feet gives better friction than standing on one foot.

How significant is this factor?

There are studies that expose this factor, but they are performed with "hard rubber" and "soft rubber" etc. These indicate that this factor can be as large as 10 to 30%, or even higher. These however may not apply that well as they do not cover the entire range of force that a human body will produce by its weight and it is not targeted at the custom designed, sticky climbing shoe rubber. To get a better indication further studies has to be carried out. I might venture into this in later posts.

We should also assume that climbing shoe brands put a lot of effort into tuning the rubber blend to achieve characteristics that perform well within the range of force produced by the human body.

Oxidation

As described in the previous post about rubber friction, the adhesion part of the friction is highly dependant on the availability of atoms and molecules to bind with atoms and molecules on the contact surface. Oxygen in the air will bind with any surface and reduce this availability to a minimum. 

Does this imply that friction is better at high altitude where the air is thinner? Not likely, as oxygen is plentiful, it might effect the time it takes for a surface to be "saturated", fully oxidized, but I would suggest that this is insignificant.

How significant is this factor?

You would definitely experience a totally different friction if you were climbing in an oxygen free environment, but that is not really an option. Within the practical aspect of climbing, rubbing your shoes down to get fresh rubber exposed before stepping on the rock will give you some effect of this, but only slightly.

I have found no studies on rubber for this to give an indication on the significance, but it is enough to have climbers identify this by themselves without scientific studies. So if the very limit is your playground, you should definitely start to rub your shoes with your palm before attempts when you chase your projects.

Contact Time

As with oxidation this factor is about adhesion, the bonding of atoms and molecules between the contact surfaces. This bonding is dependant on the availability of atoms and molecules to bond with, but this bonding actually improves with time. As time passes, the atoms and molecules adapts to the intermolecular forces and more and more bonds are formed. If you push the limits of what will not slip, climbing slower, allowing those feet to settle in and the rubber to stay in place a little longer will actually help.

How significant is this factor?

Scientific studies have detected and quantified this effect in the testing of tribometers. I have not found any actual data from these studies, but it is of significant size when it comes to determining the coefficient of friction with these instruments. I guess most climbers will not need to adopt a conscious habit of considering this factor, but again, if you are pushing the boundaries you should consider every possible aspect.

The Normal Force

The Normal Force is not the focus of this post, but it is the single most important factor of friction. You should pay attention to all factors, but if you miss out on the Normal Force all the other efforts are in vain. My next post will take friction back to the basics and focus entirely on the Normal Force.

May The Normal Force Be With You!

References

Robert Horigan Smith, Analyzing Friction in the Design of Rubber Products and Their Paired Surfaces, CRC Press 2008, ISBN: 0-8493-8136-3