The anterior cruciate ligament (ACL) is the tissue within the knee that connects the thighbone to the shinbone. Injuries of the ACL are common and often occur when you make sudden turning movements, land awkwardly from a jump or experience a direct hit or blow to the knee area.
According to Mark Miller, MD, division head for sports medicine at UVA Health System, women are more prone to ACL injury for a variety of reasons, including their tendency to take a knock-kneed stance during landings and the placement of the ligament within the knee. Decreased hamstring strength and limited range of motion in the hip and knee joints can also increase the risk for ACL injury.
The most powerful predictor of ACL injury, however, is previous injury, according to Joe Hart, PhD, director of the UVA Exercise and Sport Injury Laboratory (EASIL). “People with ACL reconstructions are at higher risk — compared to healthy people who have never been injured — for subsequent re-injuries and they are also at higher risk for injury to the healthy opposite limb.”
These patients have all of the risk factors they had prior to their initial injury – anatomic and/or neuromuscular deficiencies – in addition to new risks that come with ACL injury and recovery, such as asymmetry in leg strength and mechanics. For instance, the uninjured leg may have greater power or greater knee extension that can lead to imbalance or awkward landings.
At EASIL, experts in kinesiology have developed the Lower Extremity Assessment Program (LEAP), which involves careful evaluation of a patient’s strength, balance and jumping performance, to determine the optimal timing for a patient to return to a sport or athletic activities. Eventually, this same type of assessment may be used to evaluate healthy athletes and prevent injury. “We are just beginning to assess symmetry and strength profiles among different types of athletes so that we can determine which are more likely to get injured,” says Hart. “We assume that stronger is better, but not necessarily. It may be that you have to be strong in the right muscles.”
Although studies are still underway, there are steps you can take that have been shown to help protect the ACL and maintain knee health. “One of the best strategies for reducing ACL injury is jump training,” says Miller. “We like to teach athletes to land with their knees more flexed. Additionally, it is always beneficial to strengthen quadriceps muscles, so stationary cycling, leg presses and other exercises are very helpful.”
Exercises To Reduce Your Risk
Try the following exercises to strengthen your legs and stabilize your knees:
- Warm Up and Cool Down: Take a light jog across the room or field, then sprint from side to side, which will help prepare your body for turns and steps. Then, run backward to loosen up your calf muscles.
- Stretch: Take a few minutes to stretch out your calves and hamstrings: Stand with legs spread just beyond shoulder width and alternating leaning forward to each foot and holding for 15-20 seconds.
- Walking Lunges: Lunge forward with one leg, dropping your back knee to the ground. Be sure to keep your front knee over your ankle but not past your toes. Continue with your other leg. Repeat 15 to 20 times.
- Single Leg Heel Raises: With your arms to your sides or in front of you, bend your right knee, and then slowly lift your heel onto the toes of your left foot. Repeat about 20 times, then switch feet.
- Single Leg Hops: Stand on one leg and hop forward, landing softly on the same leg and bending at your knee. Hold your landing for a few seconds. Repeat for 20 hops on the same leg, and then switch legs.
- Vertical Jumps: Stand slightly forward with your feet shoulder distance apart and your arms and spine in a neutral position. With your knees slightly bent, push forward and straight up. Land softly with your knees directly over your feet. Repeat 15 to 20 times.
- Shuttle Run: Run forward and backward between markers for about a minute.
- Bounding Run: Perform single-leg high knee raises, alternating legs, for a minute.
If you’re concerned about your risk for ACL injury, consult with your doctor to find an exercise program that is best for you.