On the wall, there are numerous types of hand positions that a climber must utilize to send or complete a route. Of those grips, the crimp is an essential tool in the climber’s arsenal to hold onto small, narrow handholds. However, there are drawbacks to using a crimp grip, especially a full crimp, characterized by hyperextension of the distal phalanx (last joint in the fingers).
Vigouroux et al. (2005) investigated the differences between the full crimp and open hand grip (distal phalanx is flexed) and found that the full crimp exerted over 36 times more force compared to the open hand grip on the A2 pulley, a structure in the finger that helps keep the forearm flexor tendons gliding smoothly over our joints. A compromised pulley translates to finger injuries and the dreaded “pop” or pulley rupture heard around the climbing community.
In any case, climbers should avoid using a full crimp, but if you do decide to perform a full crimp to help send your project, place your thumb on top of your index finger. Research has shown that this “thumb lock” increases the force (around 17% more) you may generate without further damaging or straining your middle and ring finger (the two most frequently injured fingers in climbing) (Quaine et al., 2011). Keep climbing and stay safe.
Quaine et al. The thumb during the crimp grip.
Vigouroux et al. Estimation of finger muscle tendon tensions and pulley forces during specific sport-climbing grip techniques.