100 Year Athlete Book Club: ROAR, Chapter 6: Core Strength, Stability, and Mobility

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If you ski hard this winter, what are your odds of blowing an ACL? How do you prevent that from happening? 

According to Stacy Sims, author of Roar, women are 3x to 8x more likely than men to tear a ligament, depending on their age and sport.  

Why? A lot of reasons:

• Hormones. Women produce hormones that make tissue more relaxed. In fact, a study found that before ovulation (roughly, days 1-14 of a 28-day cycle), women skiers suffer ACL injuries 2.4x more often than they do in the post-ovulation phase.  
• Hips. As women enter puberty, their hips grow wider in anticipation of childbirth, leading to a more knock-knee position. This puts more stress on the knee joints. 
• Size. On average, women are smaller than men, so their tissues are smaller too. Small ligaments require less force to rupture.
• Quad-dominant movement. If you overuse your quads and underuse your hips, hamstrings, and glutes—a more common pattern among women—the risk of ACL injury goes up. 

• Flat or high-arched feet. They change the ankle’s angle, putting more stress on the knees. The good news is that you can train foot and ankle strength to reduce that risk.
• Asymmetries: No one has a perfectly symmetrical body. However, major strength and mobility asymmetries between your two legs raises the risk of ACL injury. 
• Hypermobility: If you’re “double jointed,” your risk of injury goes up.
• High heels. Wearing them regularly increases the risk of ankle injuries, knee ligament tears, and low back pain. Wearing heels once a month for a special event is fine. Wearing them daily is no good if you care about longevity.

Academic studies comparing male v. female ACL injuries rates in alpine skiing are inconclusive. Some find no significant difference between the sexes. Some find that men are more likely to tear multiple ligaments than women, but women are more likely to tear the ACL alone. Other variables like skill level, terrain choices, and equipment selection have an effect as well.  

Whatever your risk factors, core strength, stability, and mobility are the key to preventing these injuries according to Sims.   

Your core (aka, “lumbo-pelvic-hip core complex” in Dr. Wetmore’s PhD classes) is everything between the tops of your shoulders and the bottom of your butt cheeks. It is not just the belly. That means bench press, pullups, and deadlifts are all core exercises. Stacy views the core muscles around the hips as the “steering wheel” for your legs. If you have a flimsy steering wheel, it can’t provide the stability and control your knees need. 

Building a strong core supports stability, and so does developing speed and power. If you can’t exert force quickly, you can’t stabilize the knee in dynamic situations. Think about bombing a groomer that unexpectedly turns to chop. Your body needs to respond quickly—meaning with speed and power—otherwise that terrain will buck you and potentially damage a knee.

If you remember anything from this, let it be the following: flexibility and mobility are NOT the same.

Flexibility is doing a forward fold from standing and passively putting your nose on your knees. As Sims puts it, “Flexibility is gathering the qualities of a rubber hose.”

Mobility is picking up one leg and lifting it straight up until your knee touches your nose. It’s about controlling the range of motion and developing strength throughout it. It gives your body options—and a margin for error—in situations that would cause most people a serious injury.

A lot of women are naturally flexible and don’t need any more flexibility. In fact, loosening the joints can increase the risk of ACL tears and other joint injuries. But most people lack mobility because they don’t know how to train it. If you do 100 Year Athlete or Kinstretch classes regularly, you’ve got that base covered (if not, check out our mobility videos on YouTube, or better yet, sign up for 100YA).

Bottom Line: To prevent ACL tears, train core strength, stability, speed + power, and mobility. That goes for men and women.