The crimp grip: when is it used and why
This grip type is effective – and as such often used – when dealing with small holds, as defined by those less than one and a half phalanx deep, according to Schweizer & Hudek (2011), or 30 mm according to Amca, Vigouroux, Aritan, & Berton (2012b). There are several possible reasons for this, among them:
a) Increased contact surface between the hold and the distal phalanx, which improves friction (Schöffl et al, 2009; Amca, Vigouroux, Aritan, & Berton, 2012), as long as the cross section of the hold is flat or incut.
b) It takes advantage of the passive moment of ligaments and tendons (connective tissue) at the DIP due to hyperextension, that could represent up to ¼ of the total external moment (moment is the amount of force applied at a certain distance of a pivot point) measured at the fingertip (Vigouroux, Quaine, Labarre-Vila, & Moutet, 2006); in other words, part of the load is born by passive structures rather than our muscles.
c) It allows the little finger to participate in the grip. The slope grip is a three-finger grip for most hands; when the extra force of a fourth finger is required, the other three are crimped enabling the shorter finger to reach the edge if the hold has a depth of less than 40 mm.
d) The torque generated at the PIP is greater, because flexing it increases the arm length (*see note); unsurprisingly, the 90-110º angle is the most efficient (Moor, Nagy, Snedeker, & Schweizer, 2009, Schweizer, 2001). Such biomechanical advantage arises because the muscle contraction forces the tendon farther from the rotation axis; this so called tendon excursion can suppose a 0,5 to 1 mm displacement according to Klauser et al., (2002) and (An, Takahashi, Harrigan, & Chao, 1984; Neumann, 2007) thanks to the ability of the pulley that routes it to slightly give. The arm or virtual lever also gets longer with warming up (Schweizer,
2001; figure 3). (*) Muscle moment arm is the shortest distance between the force across a joint and its center of rotation (Zajac, 1992).
e) The friction between pulley and tendon sheath brings about “energy savings”. During an isometric or eccentric crimping maximal effort the friction at the A2 pulley is up to 9% of the total force generated on the PIP (Schweizer, 2001; Schweizer, Frank, Ochsner, & Jacob, 2003 and Quaine & Vigouroux, 2004).
This means that, In theory, friction will bear almost 9% of our body weight, leaving the remaining 91% to our muscles and tendons. It can be seen as our flexor muscles “saving 9% force”, or activating our muscles at 100% and being able to grab smaller holds than would be possible if this “rubbing” did not enter the equation.
Summing up, friction between structures is helpful when the goal is to grab smaller holds but, as you can imagine, there’s a catch: it is a key factor in finger injuries as well, which brings us to the next point.
Another advantage of crimping is that it allows the hand to apply force on a wide range of holds (added paragraph on April 6 2016 thanks to comment from Will Anglin on my facebook page), partly because the wrist adopts an ideal prehensile posture: slight extension and ulnar deviation (Kapandji, 2006), partly because this, in turn, broadens our repertoire of body positions. Varying the angle of the fingers, shifting the carpal bones (that work together like two rows of marbles), and changing the wrist flexion or deviation allows us to grip sidepulls and gastons. It also lets us extend our wrists while raising our elbows chicken-wing style, to compensate for the fatigue-induced finger extension that is compromising our contact with the hold… good luck trying that with an open hand.
How it is associated to injuries
It has been observed that crimping is the grip type most frequently tied to pulley (because of friction), cartilage (due to compression) and tendon (over-elongation or torsion) injuries. Under a maximal isometric or eccentric contraction, a pulley can get torn when the tension produced by muscle and tendon is transmitted to the sheath and in turn to the pulley. To put it in context, the A2 pulley bears almost three times the force that the fingertip is eventually applying on the hold (Schweizer, 2001; Vigouroux et al., 2006). This is the downside of a mechanism that is responsible for the aforementioned tendon excursion (Schweizer et al., 2003).
It has been observed that under the kind of contractions mentioned above the tendon fibers change shape and direction, precisely with the aim of promoting friction against the pulley. This is an important biomechanical function similar to the one that allows some birds and bats to hang upside down without muscle effort even during sleep (Walbeehm & McGrouther, 1995), but it is especially dangerous when the load goes up abruptly in a maximal effort. Some examples:
a) we are already performing a maximal effort and our foot pops (maximal eccentric contraction).
b) the contraction is quick, and we have not allowed our fingers to “settle” correctly on the hold, with the added risk of damaging the tendon’s cell matrix.
c) insufficient warming-up. Under cold conditions these tissues are less elastic; a pulley that is prepared for the effort will dissipate some of the energy by stretching slightly, but if it has no give it can instead tear under the same load.
Don’t panic yet. The fact that this grip type is frequently associated to those injuries does not mean you must not train it. The opposite is true.
We are going to need it while climbing hard sections anyway, and if we do not train it neither our tendons and pulleys (Benjamin & Ralphs, 1998; Kongsgaard et al., 2007; Couppé et al., 2008) nor our cartilages (Schöffl, Hochholzer, & Imhoff, 2004) will have had the chance of undergoing the necessary adaptations in girth, elasticity load-bearing and resistance to compression, making them more prone to injury. In fact, it can be argued that this is why the pulleys of an experienced elite climber have a higher breaking point than those of recreational level ones (Schweizer, 2001; Klauser, Bodner, Frauscher, Gabl, & Nedden, 1999), not to talk about the kind of pulleys than can be submitted by researchers to stress tests: those of cadaveric fingers (Hume, Hutchinson, Jaeger, & Hunter, 1991; Marco et al., 1998, Schöffl et al., 2009).
It is worth mentioning the relationship between crimping and injury among children and young adults. According to Schweizer (2012) and Morrison & Schöffl (2007), crimping should be avoided in this population. The growth plate at the base of the medial phalanx, that is just at the point were higher crimping forces are generated, does not close until the age of 17 to 19 and is two to five times weaker than the surrounding tissue (figure 5, 6). This makes it prone to injury; it can fracture, and the finger’s growth can be impaired or the joint end up seriously deformed (Hochholzer & Schöffl, 2005; Morrison & Schöffl, 2007) (figure 7). These authors’ recommendation for kids that report pain at the PIP is to avoid the crimp-grip until it does not hurt anymore, and to seek professional medical advice, including x-ray controls.
Summing up, the crimp grip is a really effective way of holding to small holds, and very likely to be used in the more intense sections of a route. At the same time, it is the most related to finger injuries. Instead of avoiding it, this should allow us to reflect on a couple of ideas:
- What we don’t train, we don’t improve.
- Since we are going to need it, why not train it under safe conditions; the key for injury-free progression is individualization and an adequate evolution of the load.
Lastly, when choosing one type of grip or other, there are more factors to take into account than its biomechanical advantage or the hold’s size (which have more of a theoretical nature); we need to look at the hold’s texture and orientation, and even at the conditions of our skin or the weather. But we are venturing in a topic that involves other ways of gripping a hold, and these we will save for the next occasion…
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