These four exercises should help athletes avoid damaging their anterior cruciate ligaments
As Sports Injury Bulletin readers are well aware, one of the most devastating injuries you can sustain as an athlete is a tear or rupture of an anterior cruciate ligament (ACL), the key strap of connective tissue which stabilises the knee joint and connects the back of the femur (thigh bone) with the front of the tibia (shin bone). The word 'cruciate' in this important ligament's name means cross-shaped or marked with a cross, a seemingly odd designation for a straight strap of connective tissue which is roughly the size of one's little finger. However, within the knee joint, especially when the tibia is rotated in an internal direction (counterclockwise for the right knee, clockwise for the left knee), the anterior cruciate ligament (ACL) runs over the front of - and is roughly perpendicular to - the posterior cruciate ligament (PCL), creating a 'cross' of connective-tissue cords within the knee. An easy way to picture this is to cross your index finger under your middle finger; the middle finger represents the ACL and the index finger is the posterior cruciate.
The cruciates provide support for the knees and guide rotational movements at the knee joint. Basically, the ACL prevents hyperextension of the knee, limits excessive forward movement of the tibia during knee flexion, and controls internal rotation of the tibia. It's possible that the ACL also controls external rotation of the tibia, especially since it tends to be wrapped around the inside of the lateral femoral condyle (the bony projection at the outside bottom of your femur).
How injuries can happen
The possible scenarios for injury are varied. For example, someone might collide with you as you are running along, slamming into your leg near the knee while the foot of that leg is planted on the ground. The sudden movement of the tibia which results can tear the ACL surprisingly easily. Alternatively, you might step on someone else's foot while running (or while landing after jumping during a basketball game), causing your knee to hyperextend and rip the ACL out of its moorings. Or, you might simply attempt to come to a sudden stop, often while twisting your leg at the knee, to get out of the way of another athlete. The extreme knee flexion and torquing which result can easily damage the ACL.
If an ACL is seriously harmed during activity, you'll often hear a 'pop' when the injury occurs, and swelling will occur almost immediately. In addition, the knee itself will tend to be quite unstable, usually giving way during weight-bearing.
What the Australian researchers found
Which factors increase your risk of sustaining a serious ACL injury during your sporting activity? To find this out, exercise scientists carried out a prospective cohort study with Australian footballers involving 100,820 'player-match exposures' between the years 1992 and 1999 (a player-match exposure is simply one player competing in one competition). During this time period, there were 63 surgically proven non-contact ACL injuries (Orchard, J. et al., 'Intrinsic and Extrinsic Risk Factors for Anterior Cruciate Ligament Injury in Australian Footballers,' American Journal of Sports Medicine, Vol. 29(2), pp. 196-200, 2001).
As you might expect, the strongest risk factors for a serious ACL injury were either a history of anterior-cruciate-ligament reconstruction in the previous 12 months before injury - or any time before the previous 12 months. If an athlete had undergone ACL reconstruction in the previous 12 months, his risk of severe ACL damage was roughly 11 times greater, compared with reconstruction-free athletes. If the reconstructive surgery had been undertaken before the previous 12 months, the risk was over four times as great. It's clear from these findings that knees with repaired ACLs tend to remain unstable for prolonged periods of time, risking further damage to the 'restored' ACLs.
Why is this the case? One might argue that individuals with relatively little strength in their knee areas are no doubt prone to ACL injury. Surgical reconstruction of the knee does not strengthen the knee; it merely puts the ACL (or a substitute for the ACL) back into position within the knee. If the entire knee area is not strengthened, the individual remains at high risk, especially if the new ACL structure is weaker than the old one.
However, in a very interesting twist in the findings, the increased risk of injury in the first 12 months after reconstruction was associated with the reconstructed knee, but after 12 months there was an even distribution of new injuries between the reconstructed knee and contralateral knee. This suggests that after 12 months, the reconstructed knee becomes as strong as the uninjured knee, but the individual remains at higher risk for ACL problems, probably because of basic, underlying functional weakness in the knee joints.
Surprisingly enough, the Australian research revealed another factor associated with ACL problems: weather conditions! Environmental conditions which produced dry playing fields (for example, high rates of water evaporation in the month before a match or low rainfall in the year before a match) significantly raised the likelihood of ACL damage during play. Spiked water evaporation increased the risk by over two and one-half times, while low rainfall caused ACL injuries to swell by roughly threefold!
Why would dry fields make it more likely that athletes would tear their ACLs to shred? Remember that one potential cause of serious ACL injury is sudden stopping, and sudden stops are much easier to carry out on firm, dry terrain than on wet, slippery surfaces. Athletes may reach higher speeds on dry fields and decelerate more suddenly on firm surfaces, compared with slimy grounds. In addition, athletes tend to run with slightly greater knee flexion on hard surfaces, which can put added stress on the ACLs.
So what can be done to protect yourself from a spell of ACL hell? You can't control your teammates and competitors; no matter what you do, they may still ram into your tibia at high speed and transform one of your ACLs into an imitation of a well-used mop head. However, what you CAN control is the strength of your knees - and the ACLs within them. Although the following exercises aren't a foolproof guarantee against ACL problems, they mimic injury-producing movements (in a controlled and strengthening - but not threatening - manner), improve knee strength in a functional way, and represent a great way to minimise the overall risk of ACL injury. Each exercise is accompanied by a description of why it is helpful.
The Six-Way Lunge with Arm Drop
To carry out this exercise, begin by standing with your feet parallel and hip-width apart. Your arms should be bent at the elbows so that your hands are directly in front of your shoulders. Then, take a long step forward with your right foot, as if you were doing a lunge, and lean your upper body forward approximately 45 degrees at the waist as you do so. Drop your hands on either side of your right knee as your right foot makes contact with the ground. Quickly extend your right knee (eg, straighten your right leg) and return your body to the initial, full-standing position. Repeat with your left leg.
Then, from the starting position (feet shoulder-width apart and pointing straight ahead, hands up in front of shoulders), step directly to your right with your right foot into a lateral-lunge position. Your upper body should also face to the right, and it should lean forward over your right leg at approximately 45 degrees from the vertical position. Again, drop your hands on either side of your right knee as your right foot makes contact with the ground (your left foot should remain pointing straight ahead). Quickly extend your right knee and return your body to the starting position. Repeat the same motion with your left leg moving to the left.
Finally, from the starting position, twist your body around at the hips and step diagonally and to the rear with your right foot into a backward-lateral-lunge position. Your upper body should face to the right-rear at about 'four o'clock' position, and it should be inclined over your right leg at approximately 45 degrees from the vertical. Again, drop your hands on either side of your right knee as your right foot makes contact with the ground (your left foot should remain pointing straight ahead). Quickly extend your right knee and return your body to the starting position. Then, repeat the overall motion with your left leg, moving it to the left-rear ('eight o'clock') position.
Repeat this entire sequence (forward right leg, forward left leg, right-side right leg, left-side left leg, back-and-right right leg, back-and-left left leg) three times for a total of 18 repetitions of stepping. Rest for 30 to 60 seconds, carry out the 18 reps again, rest for 30 to 60 seconds, and perform the 18 reps one last time, for a total of three sets. Progressively toughen the exercise over a period of four to six weeks by increasing the resistance held in your hands (small dumbbells weighing up to ten pounds) and the speed of the exercise.
The benefits of this exercise
Why does the six-way lunge help prevent ACL problems? The six-way lunge stretches and strengthens the hamstring muscles on the back of the thigh in all three planes of motion (sagittal, frontal, and transverse). Strong and flexible hamstring muscles give the ACL an assist in its job of controlling the knee joint and preventing the tibia from moving excessively during knee flexion.
The One-Leg Squat with Lateral Hops
To carry out this exercise, stand with your left foot forward and your right foot back, with your feet about one shin-length apart (your feet should be hip-width apart from side to side). Place the toes of your right foot on a step or block which is about six to eight inches high. Most of your body weight should be directed through the heel of your left foot.
Bend your left leg and lower your body until the left knee reaches an angle of about 90 degrees between the thigh and lower part of the leg. Then, hop upward and laterally, so that your left foot lands about six to eight inches to the left of your take-off point. Upon landing, immediately descend into another squat and again hop upward, but this time hop back to your original take-off point (six to eight inches back to the right). Finally, hop to the right a distance of about six to eight inches, descend into another squat, and then hop back to the starting, straight-ahead position. Be sure to maintain upright posture with your upper body as you do this, and hold your hands at your sides throughout the squatting and hopping movement. Complete a total of 12 lateral hops (to the left and to the right) with your left leg before switching over and doing the same thing with your right leg. Perform a total of three sets with each leg, with 30 to 60 seconds of rest in between.
Make certain that you perform these one-leg squats with lateral hops only on soft soil, an aerobics floor, a wooden gym floor, a grassy surface, a rubberised track, or some other resilient surface which offers some give. Hopping repeatedly on concrete or asphalt may increase the risk of overuse injuries to the lower part of your leg.
The benefits of this exercise
Why are the one-leg squats with hops important? Sudden changes in direction while running and jumping can cause injury to the ACL due to the increased stress placed on the knee. Lateral hopping movements help prepare the ACL and muscles around the knee for these sudden (and often unpredictable) movements in the frontal (side-to-side) plane. Even if you're not very worried about your ACLs, this is a great exercise!
Start by running at half-speed straight ahead for about five metres. At the five-metre mark, cut quickly to your left for several strides by pushing off your right foot and moving in a left-forward (diagonal) direction. Then cut back toward the right for several strides by pushing off your left foot and moving in a right-forward (diagonal) direction. Repeat this sequence for a total of eight to ten cuts (four to five to the right and four to five to the left). Perform three to five sets of this exercise with a break of 30 to 45 seconds between each run.
Gradually increase the intensity of your zig-zag runs over a period of four to six weeks by running faster and also by changing the number of strides between direction changes (vary the number of strides between one and five). If you like to participate in sports that require running backwards (eg, football, rugby, and basketball), complete some of the sets in a backwards direction.
The benefits of this exercise
Zig-zag runs help develop the balance and body control required to move in multiple directions at various speeds. These runs require the knee joints to move through a number of different angles and directions, thus mimicking movements which can lead to ACL injury in unprepared athletes.
The High-Bench Step-Up
Yes, this old stand-by for runners is great for warding off ACL difficulties. Begin from a standing position on top of a bench which is approximately knee high, with your body weight on your left foot and your weight shifted toward your left heel. The right foot should be free and held slightly behind the body. Then, lower your body in a controlled manner until the heel of the right foot touches the ground, but support all of your weight on your left foot. Return to the starting position by driving down with the left heel (the one that's on the bench, not the one that hits the floor) and straightening your left leg. Repeat for a total of of 10 to 12 repetitions, and then switch over to the right leg. Maintain absolutely upright body posture with your trunk throughout the entire movement, with your hands held at your sides (with or without dumbbells).
The benefits of this exercise
Make this exercise progressively more difficult over time by increasing the resistance (up to 20-pound dumbells may be used) and by increasing the height of the step (up to mid-thigh height). Increasing the height of the step increases the involvement of the hamstring muscles on the back of the thigh; these are the muscles which function in tandem with the ACL to stabilise the knee joint. Strong yet flexible and coordinated hamstrings help minimise the risk of ACL injury.
Overall, these exercises - if carried out a couple of times a week - should help keep your ACLs away from serious injury. If you are involved in a sport with a relatively high risk of ACL damage, the exercises should be part of your regular strength training.