by Brian McCormick
Over the last few weeks, a study from U.C. Davis on ACL injury prevention has made its way through the Internet with headlines like “Land on your toes, save your knees.”
However, the actual study’s conclusions differed from the headlines’ implications (“Alterations to movement mechanics can greatly reduce anterior cruciate ligament loading without reducing performance” by Casey A. Myers and David Hawkins in the Journal of Biomechanics). The reports circulating the Internet vary from incomplete to inaccurate, while the study suggests instructions that should be common teaching practice.
The study used 14 female college and high school girls basketball players with at least two years of basketball experience and no prior knee issues. Subjects were instructed to run at “game speed” and make a jump stop at a certain point.
The players executed multiple jump stops without any instructions. After a series of repetitions, the researchers instructed the players to use a specific technique to measure their intervention: “The intervention targeted: increasing the amplitude of the jump prior to landing, increasing the amount of knee flexion at landing, and striking the ground with the toes first, (Myers and Hawkins).”
The study found:
“Subjects increased their knee flexion angle an average of 5.3° and moved the center of pressure at contact an average of 6.6 cm closer to their toes. There was no change in shank angle relative to the vertical during landing...The subjects basically performed the intervention jump stops with greater bend at the knees and landed more on their toes” (Myers and Hawkins).
Here is the big issue with the headlines:
“Jump stops were performed with the toes striking the ground first during the intervention condition versus the majority of jump stops performed with the heels striking the ground first in the baseline condition” (Myers and Hawkins).
Based on my reading of the published study, I have one issue with the study and one issue with its reporting.
The study measured a controlled jump stop in a closed environment. Even if the players were instructed to go game speed, how many players go game speed in drills? Further, in similar drills where players run to a certain spot and jump stops, they slow down before executing the jump stop. Their stride length decreases and speed slows in order to make a more controlled jump stop.
Executing a jump stop in an open environment as a reaction to a stimulus (defender) is a more involved skill. An open-skill jump stop occurs at game speed and without anticipation or preparation. In some occasions, players prepare before executing the jump stop, thinking ahead about their move, but in most cases, the move is a reaction to a defender or situation.
Second, adding the ball and defenders change the skill execution. Executing the jump stop while catching a pass, dribbling or rebounding a ball differs from a planned jump stop.
Therefore, while the specific adaptations suggested by the study may reduce the sheer force on the knee, and may be valuable to incorporate, the findings provide only a starting point, as a coach or trainer would need to incorporate the same findings in open skills to enhance the efficacy of the instruction in a real world setting.
As for the reporting, the study does not advocate a “toe landing.” Instead, the study found that landing with a deeper knee flexion and initiating the landing with the toes lead to reduced force at the knee.
“While toe strikes that were accompanied by an increase in knee flexion angle at contact produced the largest decreases in peak tibial shear force (PTSF), some subjects were able to reduce PTSF without increasing their knee angle, (Myers and Hawkins).
Therefore, some subjects were able to reduce the force without deepening their knee bend; however, these subjects may have had a deeper knee bend than others at the outset or they may have run at less than full speed.
As for initiating the landing with the toes, what coach teaches players to initiate a landing with their heels? How does a player develop throughout high school and college with a heel-strike landing from a vertical jump?
When teaching jumping mechanics, I have seen two methods:
1. Land like a Ninja: Land softly; initiate the landing on your toes and the balls of your feet and sit back to a flat foot as your knee-bend increases, and you sit down by dropping your hips.
2. Dorsiflexion: Dorisflex your foot (toes up) and land on the balls of your feet. In this landing, there is less knee flexion. This landing takes advantage of the stretch-shortening cycle for repeat jumps. Even when landing with a dorsiflexed foot, the heel should not hit the ground and certainly should not initiate the contact.
In the article, a reporter interviewed U.C. Davis Women’s Basketball Coach Sandy Simpson:
“It almost always happens coming down from a rebound, catching a pass or on a jump-stop lay-up,” Simpson said. “It doesn’t have to be a big jump.”
His comment suggests one misunderstanding of the mechanics of the injury and points out the flaw with the study that I mentioned above: the ball makes the game jump stop different from the jump stops in the study.
As for the misconception, many coaches who have eliminated the jump stop for fear of ACL injuries have encouraged stops with a smaller vertical component. However, the study’s intervention encouraged the players to jump higher. As Simpson says, and the study suggests, the vertical component does not necessarily influence the incidence rate of injuries, and, in fact, a greater amplitude may decrease injuries (possibly by creating a more straight-down landing, which may help to control the sheer force on the ACL caused by controlling the anterior movement of the tibia).
I have never witnessed an ACL tear on a jump stop. Instead, I have seen injuries on cuts and stops when moving forward. I know two players who tore their ACLs when landing from a rebound, but there was some contact in each case.
It is not the same sport, but I saw some pictures recently of a Division I outside hitter; we assume that OHs land on two feet at the same time, but that never happened. Further, the player did not land with a balanced body, as with a basic, closed-skill jump stop. If we watched slow-motion footage of players landing from rebounds, I imagine that we would find that oftentimes players land one foot at a time and in off-balanced positions. Therefore, to reduce ACL injuries in these instances, we need to practice these landings starting in closed environments and moving to open skill executions.
“Hawkins recommends warm-ups that exercise the knee and focusing on landing on the toes and balls of the feet. The study does not definitively prove that these techniques will reduce ACL injuries, Hawkins said: that would require a full clinical trial and follow-up. But the anecdotal evidence suggests that high tibial shear forces are associated with blown knees,” (from the article, not the actual study).
These exercises should be part of a dynamic warm-up. Jumping, skipping, and running with proper technique should be taught early in the season and emphasized at the beginning of practice to prepare the players for the open skills during practice sessions and games.
“Simpson said that the team had tried implementing some changes during last year's preseason, but had found it difficult to continue the focus once the full regular season began.”
This is the attitude that I do not understand. Coaches have time to run 20 out-of-bounds plays and practice every possible scenario, but not to ensure the safety of their players? I have heard this excuse for years. However, what helps your team more, an extra OB play or having your entire team healthy for a full season?
I have watched college practices; there is plenty of wasted time to incorporate exercises to reduce the potential of injuries. This is like when I worked the Cal Women’s Basketball Camp and sat with the athletic trainer as she pointed to girl after girl who was at-risk for ACL tears; I asked why she did not do a session to teach the girls or at least make them aware. She said that the coaches said that there was not time. We had this conversation while watching the girls play “Land-Sea-Air,” the ultimate camp time-waster.
Even better, the study found that when using the intervention technique, subjects jumped higher after the jump stop than they did with their old technique. Not only would teaching the improved technique potentially lead to fewer injuries, but it could also improve performance! It is a win-win situation, yet one ignored by many coaches and trainers. This is not a matter of adding resistance training sessions or incorporating plyometrics. The intervention effectively suggested that teaching a more effective jump stop - a fundamental basketball skill - would lead to decreased risk of an ACL tear. It isn’t a matter of adding anything, but improving the typical instruction to create a more effective jump stop.
From a skill development perspective, coaches can start with the closed skill used in the drill. Emphasize the higher amplitude on the jump, the toe-to-heel landing and the deeper knee flexion. Next, move to more involved skills. Execute the jump stop with a ball in one’s hands. Then, jump stop while dribbling; then jump stop on the catch; then, land with the ball from a rebound. Finally, move toward the open-skill application by having players jump stop as a reaction to a verbal or visual stimulus (for youth players, Red Light-Green Light works well).
Eliminating ACL injuries is likely impossible. However, incorporating better technique instruction into normal footwork and jump stop drills as well as incorporating proper landing technique into dynamic warm-up drills may reduce injuries and improve performance, which ultimately leads to a better team performance and more wins.