Differences amongst landing types and implications for injury
Not all landings are created equal! What I mean by this statement is the following: during sport, athletes perform a variety of landing maneuvers that may have significant implications for injury risk. Landing is a fundamental movement pattern that every land-based athlete will be exposed to at some point in sport (and yes, walking and running are simply repetitive landings!). In response to environmental demands, an athlete may be required to perform a bilateral (double-limb) or unilateral (single-limb) landing maneuver, often in the close proximity of teammates and / or opponents. After completing the landing phase, an athlete typically performs sequential movements based on the situation presented (e.g., completing an additional jump for a rebound or a cutting maneuver to avoid a defender). In this post, I will discuss the phases of a landing maneuver, the biomechanical differences between bilateral and unilateral landings, as well as the influence of both preparatory and sequential movements on landing patterns. From the information presented, we can understand the external loads placed on an athlete as a function of task demand. This will allow us better understand injury risk during landing, as well as appropriate training methods to mitigate this risk.
Shown in Figure 1 is a nice representation of a typical landing profile from Dufek & Bates (1991). The first force peak (F1) corresponds to forefoot ground contact, while the second force peak (F2) signifies rearfoot ground contact. If an athlete were to initially contact the ground with the midfoot or (in very rare cases) the rearfoot, F1 would not be presented. An example of forefoot (Figure 2) and rearfoot (Figure 3) ground interaction from my thesis research is provided. It is believed that peak ACL strain (a mechanism for injury) occurs within the first 40 milliseconds after impact (Shin, Chaudhari, & Andriacchi, 2007), which roughly corresponds to the time when an athlete is experiencing maximum external landing forces (Figure 1). Another important area of interest is the kinematic (study of describing joint motion) patterns an athlete displays at initial ground contact. In a study of female jump-landing athletes (handball and basketball) who sustained a non-contact ACL injury, the mean knee flexion angle at ground contact was 23 degrees (Koga et al., 2010), which may be considered a “stiff” initial landing (more on this later). It should also be noted in the Koga et al. study that the researchers concluded “based on when the sudden changes in joint angular motion and the peak vertical ground-reaction force occurred, it is likely that the anterior cruciate ligament injury occurred approximately 40 milliseconds after IC (initial contact).” For those in a team setting without access to motion capture and force platform technology, a subjective time period of analysis would be from initial ground contact until maximum knee flexion, a period where lower extremity injury during landing is most likely to occur. From studying landing “signatures” in our athletes, we can gain potential insights into landing strategies and / or neuromuscular landing patterns that may expose one to injury.
Now that we have touched briefly on the time period of interest during the landing maneuver, let’s transition to some key biomechanical differences between a bilateral and unilateral landing. What must be taken into consideration is that during a unilateral landing task, one limb is responsible for attenuating landing forces that are often generated by both limbs during the jump phase. As you may guess, unilateral landings present a much greater injury risk, especially when performed in crowded environmental conditions. One can view the recent injuries to Gordon Hayward and Jeremy Lin for examples of the significant loads being placed on these athletes during single-limb landings in contested areas. Single-limb landings are very common amongst aerial athletes (volleyball and basketball to name a few). A study of jump-landing technique in female volleyball players indicated that approximately 45% of offensive landings were completed on one limb (Tillman, Hass, Brunt, & Bennett, 2004).
Compared to bilateral maneuvers, unilateral landings have been associated with quite a few factors that are associated with an increased risk of injury to the lower extremity. These include: decreased knee flexion angle, increased knee valgus, higher vertical and lateral GRFs, and muscular activation patterns (quadriceps dominant) that increase stress on the ACL. In examining the mechanical differences between landing type, peak knee flexion of 16 males and 16 females performing unilateral landings was 72.2 degrees (Pappas, Hagins, Sheikhzadeh, Nordin, & Rose, 2007), indicating a “stiff” landing. Compared to a “soft” landing (defined as greater than 90 degrees of knee flexion), stiff landings may increase injury risk by placing additional stress on skeletal and ligamentous structures (Devita & Skelly, 1992). Let’s take a brief look at the principle of impulse and momentum to understand the mechanics behind stiff and soft landings:
[F∆t = m∆(vf – vi)]
Momentum will remain constant regardless of landing type because mass, m, and initial velocity, vi, are unchanged for both conditions when landing from the same height. Final velocity, vf, is zero at the end of each landing. Since momentum is constant, impulse must also be equal for both conditions; however, one can manipulate force and time (impulse) by altering landing technique. A soft landing, due to increased flexion of various lower extremity joints, increases the amount of time over which energy is absorbed by the musculature upon impact. In an examination of landing stiffness, Devita & Skelly (1992) determined the lower extremity musculature absorbed 19% more energy in a soft landing compared to a stiff landing. Energy not absorbed by the musculature is placed on the surrounding body structures (e.g. ligaments and cartilage), potentially increasing injury risk to these areas.
Another point of emphasis during single-leg landings is the potential influence of altered trunk / hip position during the landing maneuver. Figure 4 is from Powers (2010), examining the effect of hip mechanics on injury risk at the knee. What you’ll notice is the pelvic lean over the landing limb, quite similar to a compensated Trendelenburg pattern well-known throughout the gait community. Laterally displacing the body’s center of mass over the landing limb will in turn shift the external ground reaction force lateral to the joint centers of the landing limb. At the knee, this can create a valgus moment, a definite risk factor for ACL injury (although this is one of a few factors that contribute to knee injury). From a practitioner’s standpoint, single-limb landing training is of great importance for injury management (notice I don’t say “prevention”, it’s impossible to completely prevent injury in sport…there’s too many variables beyond our control). My suggestion would be to expose your athletes to wide variety of single-limb landing conditions, because sport requires a variety of movement demands. This leads me to my last talking point in regards to landing…the prior and / or subsequent movement and their potential effects on injury.
It is very rare in sport to perform an isolated landing. The environmental demands call for movement prior to- and post-landing. Now Harjiv is definitely the expert in this domain, but I’ve picked up quite a few knowledge nuggets from our talks. Injury doesn’t necessarily occur from the landing itself, it can occur due to the intent for creating subsequent movement! And I have evidence to substantiate this claim. In a paper that is currently under peer-review from our research group at Ball State, we examined unilateral landings as a function of different tasks pre- and post-landing. Specifically, we had individuals perform unilateral drop landings, drop jumps, and countermovement jumps. We found that the countermovement jump was more protective in terms of lower extremity rotation at the hip and the knee, which we attributed to pre-activation of the musculature during the initial downward motion (although this is speculative, as we did not collection muscular activity data). We also found that drop-jump landings were suggestive of increased injury risk, as individuals had to transition quickly from a relatively static state (starting from a pre-determined box height) to a dynamic one in order to complete the secondary jumping task. And therein lays the key to injury analysis. It was the intent of the individual to maximally perform a subsequent jump after landing, and from our analysis, individuals may have sacrificed joint landing stability for jumping performance. This paper should be available for public viewing in the near future.
Well folks, this wraps up my first post on The Rebel Movement blog. I hope you enjoyed the content. Please feel free to reach out to me, I’m very receptive to continued conversations, as I feel this is the best way to expand our knowledge base.
Email – Jason.Avedesian@unlv.edu
Twitter – @JasonAvedesian
Devita, P., & Skelly, W. A. (1992). Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Medicine and Science in Sports and Exercise, 24(1), 108–115. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1548984
Dufek, J. S., & Bates, B. T. (1991). Biomechanical Factors Associated with Injury During Landing in Jump Sports. Sports Medicine, 12(5), 326–337. https://doi.org/10.2165/00007256-199112050-00005
Koga, H., Nakamae, A., Shima, Y., Iwasa, J., Myklebust, G., Engebretsen, L., … Krosshaug, T. (2010). Mechanisms for Noncontact Anterior Cruciate Ligament Injuries. The American Journal of Sports Medicine, 38(11), 2218–2225. https://doi.org/10.1177/0363546510373570
Pappas, E., Hagins, M., Sheikhzadeh, A., Nordin, M., & Rose, D. (2007). Biomechanical Differences Between Unilateral and Bilateral Landings From a Jump: Gender Differences. Clinical Journal of Sport Medicine, 17(4), 263–268. https://doi.org/10.1097/JSM.0b013e31811f415b
Powers, C. M. (2010). The Influence of Abnormal Hip Mechanics on Knee Injury: A Biomechanical Perspective. Journal of Orthopaedic & Sports Physical Therapy, 40(2), 42–51. https://doi.org/10.2519/jospt.2010.3337
Shin, C. S., Chaudhari, A. M., & Andriacchi, T. P. (2007). The influence of deceleration forces on ACL strain during single-leg landing: A simulation study. Journal of Biomechanics, 40(5), 1145–1152. https://doi.org/10.1016/j.jbiomech.2006.05.004
Tillman, M. D., Hass, C. J., Brunt, D., & Bennett, G. R. (2004). Jumping and Landing Techniques in Elite Women’s Volleyball. Journal of Sports Science & Medicine, 3(1), 30–36. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/24497818