Climbing Hands: How We Evolve When We Push Ourselves in Pursuit of Pump

As an injury biomechanist I spend my days reading reports about deeply broken people, but my favorites are the climbers. Falls can cause gory injuries, but the minor reports are more fascinating to me because the true art of the sport reveals itself in the subtle traumas: the pulls on minor ligaments in the fingers, the elbow sprains caused by extreme dynos. The hands and forearms of climbers take more abuse than perhaps those of any other athletes in the world. Even as a gym rat, someone who’s down on the “dilettante” end of the spectrum, I can’t count the number of times I have lovingly wrapped an H of tape around a finger to assist a sorry tendon, either a buddy’s or my own.

The opening scene of the movie Free Solo causes an audience-wide gasp when the camera pivots slowly around the edge of a vertiginous granite slab. However, the real secret to superhuman climbing power is actually revealed in the next, less dramatic scene, when Alex Honnold is shown curling his atypically large fingers around a microphone that in contrast looks comically small. This trait, the overgrowth of tissue, is called hypertrophy, and it is not unique to Honnold. It is also not genetic. Hypertrophic hands and forearms are common to every professional and serious climber, but climbers are not born this way; they have made themselves become this way.

Through use, and sometimes abuse, people force their bodies to grow and evolve into the proper shapes for the activities they perform. For climbers, the most obvious changes are in the hands and forearms. The muscles that cause the fingers to flex do grow in response to activity, but so do bones, ligaments, and tendons, all of which scramble to generate more cells and therefore more strength after each brutal workout session. And with the increasing popularization of recreational climbing and its accompanying growth in the professional and Olympic worlds, scientists are finally starting to invest the time required to figure out exactly how we force our bodies to evolve when we power through just one more route in pursuit of pump.

One major difference is in the collagen, which does more than plump lips. The long, twisting spirals of this specialized protein act as biological springs, holding together the various structures of pretty much every part of our bodies. Long ropes of collagen form the muscles and tendons that keep our hands from literally pulling apart under stress, and the bones themselves are cells living within collagen cages. As we age, it is the degradation of collagen that causes our skin to wrinkle, our lips to flatten, and our bones to become more fragile.

Like muscles, collagen can be developed, to a degree. Repeated practice tugs on the bones, ligaments, and tendons. In response the body slowly builds them stronger by adding more cells and collagen, and overuse leads to the telltale sport-specific injuries of the same structures. The collagen petrified from our bones will remain long after we are dead, and unusual heft in the fingers and forearms will permanently differentiate the skeletons of those who dangled their bodies from seemingly impossible credit card crimps. The bones of the crew of the Civil War submarine HL Hunley soaked in oceanic salt water for over 130 years, yet they could still tell stories to the examining forensic specialists about the back-breaking types of physical labor like shoveling coal that their owners had forced them to do during life.

Recent scientific research examining climbers has led to an epiphany: we can force our collagen to grow somewhat, but it’s really the adaptation of blood vessels that leads to true prowess. In the book The Impossible Climb, Honnold laments his own lack of tendon strength—relative to the insane standards of professional climbers—but author Mark Synnott inadvertently hits on the real biological factor that makes all climbers more able to scale walls than otherwise fit athletes from other sports: forearm endurance. In the human body, endurance comes from vasculature.

Climbers give the muscles of each forearm just the briefest reprieve when they move that hand between holds. During this pause, measured at an average of two seconds long, blood has the chance to rush in and resupply the fatigued muscles. The more blood and therefore the more oxygen the muscles can receive in two seconds, the longer they can work overall without reaching exhaustion. Elite climbers have been shown to have vasculature in their forearms that can dilate and pump more blood over less time than athletes from other sports.

The post-climb pump is blood, rushing in to resupply tired tissue, until finally the vessels give up and the climber’s fingers curl into helpless shapes from fatigue. But regardless of innate genetics or talent, every climber can force themselves to adapt to the utmost of their own limits, the limits where blood fills their forearms faster and more efficiently than for any other sport. Injuries come when we try to force our bodies to evolve literal superpowers, but within limitations our ridiculous goals become achievable because our bodies can take the forms we demand of them.

Rachel Lance is a biomedical engineer and professor at Duke University who specializes in patterns of injury and trauma, and she is especially fascinated by blast and ballistic events. Her first book, In the Waves, is available now, wherever books are sold.