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Injury Prevention Strategies: Four tips for strong knees

Your knees bear your body weight day in and day out, whether it’s walking around the office or climbing the mountains in Afghanistan. The anterior cruciate ligament—or ACL—is often the center of attention, and for good reason. It’s a major ligament of the knee, and an injury to it can put you on profile for six months or even more. Injuring it also can increase your risk for chronic problems such as arthritis later on in life.

There are certain risk factors that you cannot control—such as gender, hormones, and being flat-footed—that increase the risk of tearing your ACL. But some things are in your control, such as starting an ACL injury prevention program. These aren’t well suited for everyone, so be sure to check first with a qualified healthcare professional who can give you individual advice before you start.

Current evidence shows that an ACL injury prevention program should include balance training, plyometrics, and strength/stability exercises. You also can start to pay close attention to your landing technique when jumping down from a height.

The following strategies won’t completely eliminate your chances of tearing your ACL, but they can make it less likely.

Issue #1: Landing

In the military, “landing” can range from jumping off the back of a vehicle to a paratrooper jumping out of a plane and contacting the ground. Regardless of what type of landing you are doing, whether landing on solid ground after jumping up into the air or from a height, the way you land is important. First, pay attention to how you land. Landing with your knees buckled to the inside can increase the risk of injury to the ACL. Women tend to land with more stress on the inside of the knee (think “knock kneed”) and men tend to land with their toes pointed out; both of these have been linked to an increased risk of ACL injury. Since this is such a complicated issue with some of the details varying based on gender, it’s best to consult with an expert on landing techniques, but a couple of key points are:

  • Avoid landing with your knees in a knock-kneed position. This is called a “valgus stress,” and it increases your risk of injury.
  • Maintain some bend in your knees to help absorb the force instead of landing with your knees in a straight, locked position.
  • Land on both feet instead of just one, if possible. This helps to distribute the weight of your body.

Issue #2: Balance

Balance wobble boards can help you improve your “proprioception”—the ability to know where your body is in space. If you are just starting this type of exercise, begin from a seated position and then progress to a standing position as your balance improves. (This progression is essential: Trying to do standing exercises on a wobble board before you are ready can result in injury to your ankles as well as potential falls.) The time needed to perform these exercises varies greatly, so it’s impossible to provide specific guidelines; it will depend on your specific balance capabilities. You can gradually increase the amount of time you train as your balance improves. Start from a seated position, perform smooth and coordinated movements for 30 seconds, and if this seems easy, increase your time and the amount of weight you apply.

Issue #3: Explosive leg power

Lower-extremity plyometrics can help greatly with balance and explosive power, but be sure to follow these safety tips from the American Council on Exercise. The goal of these exercises is to lengthen and shorten the muscles quickly. There are hundreds of plyometric exercises, but box jumps and depth jumps are two good examples. Check with your fitness specialist for how to perform these exercises correctly and which ones are right for your current fitness level.

Issue #4: Strength and stability

Improving your core strength as you stand on one leg (“single-leg core strength”) is an important part of ACL prevention. An exercise that can help to increase stability on your legs is to jump onto flat ground, land on one leg, and hold that position for a few seconds. Start with just 10 repetitions and increase the number as you improve. Improving your general leg strength also can help. HPRC has more information on strength training you can use.