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One reason your feet slip off foot holds
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By Don McGrath
From fort collins, CO
Feb 26, 2013

I was watching a climbing partner climb and slip off holds. After watching closely I noticed something subtle about his footwork. I think I know why and talk about it in this video.

www.masterrockclimber.com/rock-climbing-footwork-heel-toe/

I hope you get something from it.

Don


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By GLD
Feb 26, 2013

oh, I thought we were going to talk about my affinity for eating bbq while climbing again.


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By Dom
Administrator
From New Brunswick Canada
Feb 26, 2013
Moby dick 5.11-

Funny how ice climbing, you want to drop your heels to have the secondary points purchase the ice. Is your friend an ice climber by any chance?


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By Nate Reno
From Highlands Ranch, CO
Feb 26, 2013
Ellingwood Point Summit, Little Bear in the background.

One reason why *my* feet slip off holds, is because my footwork sucks! =)

I think your video perfectly describes why (for me) that slopey and smear type footholds are a lot harder to use and trust. You have to learn to judge that coefficient of friction force on various angle holds, as well as different rock types, or just the general smoothness of the hold on the same rock types, along with the direction of force you're able to apply with your foot, and this is what takes more time to learn and master.
With the flatter type footholds, its a much simpler situation and mostly just a matter of standing on the damn things with your foot in the right position as you point out.


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By Ian Stewart
Feb 26, 2013

It's an interesting video, but it does over simplify the problem a little since you seem to always be assuming that your center of gravity is directly over the point of contact and that no other holds are involved (if either of these weren't the case, F_1 would be less than your body weight).

Also, why do you state that F_N < F_1? That's not always true, and in some situations would actually be false. Consider a layback with your feet on a completely vertical/blank face: The friction of your shoes on the rock is the only force opposing gravity, and so if the coefficient of friction is less than 1 then the normal force (F_N) needs to be larger in magnitude than the gravitational force.

In general, however, I do think that a basic understanding of physics can really help understand climbing and this video could be certainly be useful to some people. If you know which values to increase (normal force, friction coefficient) and which to decrease (gravity), the rest is just figuring out how to get your body in the right position to make that happen.


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By slim
Administrator
Feb 26, 2013
tomato, tomotto, kill mike amato.

one of the really tough things (i think) is that in order to increase F_n on vertical to overhanging terrain, you will have to somehow pull more with your arms. the more you try to push your feet into the wall to get a better angle, the more it is going to push you outward. on jugs this is easy, but when you have poor handholds this gets really hard to do. the really hard part is determining the minimum amount that you need to pull with your arms, or the maximum amount or angle that you can push with your feet.

also, i think one thing that would really help (the guy in the video at least) is to make sure he watches his foot all the way until it is on the hold. a really common mistake is looking away from the foothold before landing your foot on the hold, and then the foot doesn't get set up correctly on the hold.


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By maineah
From Maine
Feb 26, 2013

does this 'heals up' idea apply to slab climbing? I usually find that I get more purchase on smears and technical small holds on slabs with my heal slightly dropped.


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By Jon Nelson
Administrator
Feb 26, 2013
Me

Nice idea for a discussion Don.

The video is great, but it might help next time to make the diagrams bigger and introduce the force arrows one-by-one.

As most of our weight is almost always on our feet, it makes sense to study footwork, including what makes a good foot placement and how to keep the foot from slipping off.

Other than keeping the heel high, I think that keeping the foot perfectly steady is a good goal.

It would be nice to hear other people's ideas about improving footwork.

For small edges, I often try to "crepe" my foot over the hold: I roll my foot onto the edge to try to get some compressive tension in the rubber and to get more rubber onto the hold. Imagine rolling the foot onto a thin flake as if you are trying to pry the flake off. Don't really know if or when it helps though. Obviously, you wouldn't want to do it on a loose flake.


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By Ian Stewart
Feb 26, 2013

maineah wrote:
does this 'heals up' idea apply to slab climbing? I usually find that I get more purchase on smears and technical small holds on slabs with my heal slightly dropped.


As I mentioned, the video oversimplifies the physics such that it's not really relevant in a lot of situations. Slab climbing is one of those.

What the video is actually comparing is a stance on a surface perpendicular to the force of gravity VS a stance that is angled. When the surface is perpendicular to gravity, zero friction is required so the coefficient of friction isn't important. When the surface is angled, there are horizontal forces at play that require friction to hold the foot on the hold.

With slab climbing, assuming the rock is featureless and the same angle everywhere, you don't have much choice in terms of the direction of the forces as you'll have the same angles pretty much any way you stand. In this case, what you want to do instead is increase the coefficient of friction. This can be done by increasing the contact area between your shoes and the rock, which is easily done by lowering your heel to allow more of your shoe to touch the rock.


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By reboot
From Westminster, CO
Feb 26, 2013

Ian Stewart wrote:
As I mentioned, the video oversimplifies the physics such that it's not really relevant in a lot of situations.

The video oversimplifies climbing (that shouldn't surprise anyone). In friction slab you try to maintain your center-of-gravity right over your feet (your ass end up sticking out slightly) for the maximum amount of friction.

What slim is saying is on a slopping foothold, if your hand holds allow inward pull, then it becomes a delicate balance between the strain of pulling inward with your hands to shift your your center-of-gravity over your foothold, which increases friction and allow more weight to be taken off your hands in the downward direction. An extreme example of this is liebacking a crack.


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By Ian Stewart
Feb 26, 2013

reboot wrote:
What slim is saying is on a slopping foothold, if your hand holds allow inward pull, then it becomes a delicate balance between the strain of pulling inward with your hands to shift your your center-of-gravity over your foothold, which increases friction and allow more weight to be taken off your hands in the downward direction. An extreme example of this is liebacking a crack.


Getting your center of gravity over a hold does NOT increase friction. Increasing the coefficient of friction and/or increasing the NORMAL force, the force perpendicular to the surface, increases friction.

If you have a sloping foot hold, putting your center of gravity directly above the hold provides LESS friction than if you were to angle your body so your feet are pushing into the surface at a 90 degree angle.

Maximizing the friction on a purely slab climb would actually require your center of gravity to be BEHIND you such that you are pushing in 90 degrees to the wall. But since there's nothing for your hands to hold on to, the furthest you can lean back is having your center of gravity over your feet. A layback is an example where you DO have something to lean back on to get your center of gravity away from the wall to push in to it.


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By reboot
From Westminster, CO
Feb 26, 2013

Ian Stewart wrote:
Getting your center of gravity over a hold does NOT increase friction. Increasing the coefficient of friction and/or increasing the NORMAL force, the force perpendicular to the surface, increases friction. If you have a sloping foot hold, putting your center of gravity directly above the hold provides LESS friction than if you were to angle your body so your feet are pushing into the surface at a 90 degree angle. Maximizing the friction on a purely slab climb would actually require your center of gravity to be BEHIND you such that you are pushing in 90 degrees to the wall. But since there's nothing for your hands to hold on to, the furthest you can lean back is having your center of gravity over your feet.

I guess I wasn't clear when I said "over", it included going behind (outward) from the foot. And yes, perpendicular to the foothold provide the most amount of friction. But most of the time in climbing, creating the most amount of friction for your feet is secondary to reducing the overall pull force (measured at the muscles/tendons) required by your hands, and those 2 factors often conflict.


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By Don McGrath
From fort collins, CO
Feb 26, 2013

Glad to have spurned lots of discussion. Yes, the video only applies to a very specific situation. Got me thinking about making others that cover laybacks, slabs, stemming. Would that be interesting to this group?

I like thinking about this stuff!


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By Mark E Dixon
From Sprezzatura, Someday
Feb 26, 2013
At the BRC

I don't buy the "heel up" analysis.
In the first place, the climber in this video has bigger issues. He does have good hand strength and did a good job of brushing off the distraction of the rope at 1:14.
However, he usually initiates movements from his arms, and his legs are mostly just along for the ride.
He is careless and imprecise with his feet throughout, typically placing the ball of his foot on holds rather than his big toe.
He repeatedly skips footholds and hangs from his arms while "toe tapping" one foot up the wall, then placing his other foot on a higher hold. (see 1:30 and 1:36)
The final slip at 1:55 seems to me to be due to the fact he placed his foot without looking, and placed it onto the sloping right side of the hold. After the slip he managed to put his foot on the relatively pointy top of the hold.
It is clear that putting your foot on a sloper hold provides less f1 force than on top of a typical gym hold. However, going "heel up" on a sloper isn't going to increase the friction or the force!
I don't believe the heel up or down orientation had any influence on this climber's struggle, which seems to me to stem from his failure to use his legs to propel himself upwards (except at 1:12 and 1:19)
He's not alone, I too, have to frequently remind myself that climbing is a "rear wheel drive" sport.


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By SDY
Feb 26, 2013

Don McGrath wrote:
spurned


Doesn't mean what you think it does...


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By Don McGrath
From fort collins, CO
Feb 26, 2013

Love the discussion...


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By Don McGrath
From fort collins, CO
Feb 27, 2013

Ian, increasing the surface area with between your shoe and the rock on a slab, does not increase the frictional force.

Ff=Fn*u=m*g*u ...no A
When you increase the contact surface area, all it does is spread the force Fn over a larger area, decreasing the force per unit area, but the total Fn force stays the same. Therefore Ff stays the same.

In reality, it often does help to increase the surface area of your shoe on the slab. I think this is because a) it's a more relaxing position and b) the surface is not totally uniform and you may catch a crystal or rougher spot, which increases the frictional force.

Just clarifying this. Maybe I'll make a short video about how this works in the case of a slab.

Don


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By maineah
From Maine
Feb 27, 2013

Don McGrath wrote:
Maybe I'll make a short video about how this works in the case of a slab. Don


That would be cool


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By rgold
From Poughkeepsie, NY
Feb 27, 2013
The traverse out to the Yellow Ridge on the Dogstick Ridge link-up.  Photo by Myriam Bouchard

If you want to make the point that dropping your heel too much might make your foot slip off a sloping hold, best to leave it at that. The pseudo-science adds nothing to it.

The mechanics of how the hold is weighted is far more complicated than the diagrams suggest. For openers, body weight force acts through the leg bones and the foot creates a lever arm, requiring torque analysis, which is complicated by the fact that the ankle joint is not rigid and foot muscles are capable of generating torque by themselves.

The foot can be and usually is rotated to various positions and is only occasionally used with the toe directly in as illustrated.

As others have suggested, a more critical aspect is the location of the climber's center of gravity relative to the hold, something that is entirely missing from the discussion.

Finally, the naive use of the coefficient of friction formula is probably inappropriate to the situation of getting rubber to stick to rock or plastic. That formula is not a physical principle so much as an empirical approximation that works best when the two surfaces in contact are, for example, highly polished metals. Once the macro-structure of the surfaces in contact becomes significant, the standard coefficient of friction formulation becomes invalid. There are entire PhD dissertations on what happens in such cases, but something every climber with even a little experience knows experientially is that the area of surface contact does matter and it is not just a question of the normal force.

Finally, encouraging climbers to keep their heels up is going to be highly counterproductive most of the time, as it forces the climber to climb in a continually high state of tension and thereby contributes to the premature burning of physical resources. The trick is to learn how much you can relax without slipping, and of course the devil is in the details.

As for the climber in the video, I'd say his foot slips because it was carelessly placed, not because of anything related to his heel angle. It also appears that, because of the location of his center of gravity off to the side, the foot is only partially weighted and so slips off for lack of enough force to generate the required friction (here used in the experiential sense and not in the high-school physics sense).


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By NorCalNomad
From San Francisco
Feb 27, 2013

lol and now it's not there


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By Ian Stewart
Feb 27, 2013

Don McGrath wrote:
Ian, increasing the surface area with between your shoe and the rock on a slab, does not increase the frictional force. Ff=Fn*u=m*g*u ...no A When you increase the contact surface area, all it does is spread the force Fn over a larger area, decreasing the force per unit area, but the total Fn force stays the same. Therefore Ff stays the same. In reality, it often does help to increase the surface area of your shoe on the slab. I think this is because a) it's a more relaxing position and b) the surface is not totally uniform and you may catch a crystal or rougher spot, which increases the frictional force. Just clarifying this. Maybe I'll make a short video about how this works in the case of a slab. Don


You're right. It's been a while since I took physics and I oversimplified things, too.

I'm pretty sure all of these equations must assume that the bodies are completely rigid; that is, they don't deform at all. With the rubber on climbing shoes, that is not the case. In reality the rubber on a shoe deforms a LOT. Because of this, your (b) point is partly correct in that increasing the contact area increases the shoe's ability to deform around the rock and provide more traction. This doesn't change the coefficient of friction itself, but all those deformities mean that there will be many other forces acting on the shoe than just that of friction (eg. there will be many small "normal" forces in many different directions, not just one). So instead of thinking as slab as one featureless surface, you should instead think of it as many many many small holds (that you can't see) that the rubber can deform around...you're not standing on one slab, you're standing on thousands of mini holds.


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By slim
Administrator
Feb 27, 2013
tomato, tomotto, kill mike amato.

not necessarily - sometimes increasing surface area is better in terms of higher probability of being in contact with a 'rough' spot. sometimes a smaller surface area is better for increasing interlocking and increasing required shear to break this interlocking.


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By reboot
From Westminster, CO
Feb 27, 2013

slim wrote:
not necessarily - sometimes increasing surface area is better in terms of higher probability of being in contact with a 'rough' spot. sometimes a smaller surface area is better for increasing interlocking and increasing required shear to break this interlocking.

By extension, with rubber, friction is not proportional to normal force either. How many times have you discovered that if you don't weigh the foot enough, it'll slip off?


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