After describing the forces at work on hand and footholds as well as the function of kinetic chains we can now see how these features are at work in body tension.
You will remember that the contact force and the friction force are proportional, as the contact force increases so does the friction force. In situations where the angle of the hold surface is not perpendicular to the line of force our hand or foot applies to it, the friction force plays a greater role in maintaining hold contact. So the question is how do we increase the contact force thus affecting the necessary increase of the friction force? We might say that we that we grip the holds harder. The problem with this answer is that we grasp handholds using isometric muscular contractions. In isometric contractions the contraction is equal to the force it is resisting. So on a crimper, sloper, jug, gaston, pocket, etc a more forceful contraction will not increase the contact force on the hold, it would only mean that the hand would be prepared to resist a greater force. The only exception to this is pinches. The opposition between the thumb and fingers will increase the contact force, resulting in a greater friction.
Other than in the case of pinches, if gripping the holds harder will not increase the forces, how are greater forces generated?
In the case of the hands we use the rest of the kinetic chain to pull the hands into the holds with greater force. This is easiest to see in the example of side pulls. When using a side pull elbow flexion and adduction of the shoulder will increase the force at work on the handhold.
In situations when the arm is straight, it’s more likely that pushing away from the hold with a foot will increase the forces. This action is common when doing laybacks. It’s also very common on steep face climbs to see a heel hook on one side of the body, used to increase the contact force on the hand hold on the other side of the body.
The situation is similar when considering footholds. It’s the joints of the legs that are used to increase the contact force. It’s plantar flexion of the ankle, extension of the knee and extension of the hip that tend to contribute to increasing the forces at work on footholds when the body is facing the rock.1 If the body is turned to the side, then the action of the hip joint favors adduction, but the actions of the knee and ankle will be the same since neither of these joints is capable of adduction.
These are just a few of many possible examples; the important point here is that large segments of the closed kinetic chain contribute to increasing the forces at work on foot and handholds.
So here is where we can articulate what body tension actually is. As stated in the last post Climbing consists largely of closed kinetic chain movements. The main purpose of which is to move/ position the COG through space and to facilitate a hand or foot reaching a new hold. However, there are situations in which the closed kinetic chain is also engaged in the task of increasing the contact force on hand and footholds, for the purpose of affecting a proportional increase in the friction force. It’s the application of closed kinetic chains to both these tasks at the same time that is responsible for body tension.
It’s probably the case that using the kinetic chain to increase the forces at work on holds is going to be enough to create the sensation of body tension. But I am interested in the ways the two different uses of the kinetic chain conflict with one another. Thus, the farther the COG needs to move in space, the more difficult it can be to maintain a sufficient friction force on the holds, especially the footholds. The corollary is that the more effort required to maintain adequate friction on the holds, the more difficult it will be to perform certain movements of the COG.
There are a lot of details that need to be noted. For example, just the movement of the COG in space is going to increase the contact force on some holds. A basic mechanical principle is that the closer the COG moves to a point of contact with a supporting surface, the greater the force applied at that point. Thus the forces at work on any point of contact during a move are dynamic. Sometimes they work in our favor but often they do not.
In addition, some configurations of kinetic chains are more common than others. For example, it’s often the case that the chain we are most interested in runs between the hand remaining in contact with its hold and a foot or both feet. It’s the movement of the COG away from the footholds that’s instrumental in pulling the feet off the rock. It’s the climber’s job to increase the forces working on the footholds during the course of a move that is naturally reducing those forces.
The main source of the sensation of body tension is most likely the need to apply the close kinetic chain to the task of increasing the contact force on footholds and handholds. The greater the effort necessary for this task, the more difficult it will be to move the COG through space. The conflict between the goal of moving the COG in space, and the necessity of increasing forces on the holds, which gives body tension moves their character and makes them so difficult.
This might all seem very abstract, so in the next post or two I will use photos and videos to show how these ideas apply to actual moves. I think the first video I want to present an analysis of is of Dave Graham on his V15 problem called The Island. You can see it here:
Create your own analysis and we can compare notes. Also, if anyone is still reading this post at this point; if you have good body tension video or stills feel free to send them along and I’ll try to present analysis of them.
1. I think it’s likely that the trunk through extension, and shoulders through flexion can also participate in this action in some cases.