A lateral ankle sprain is the most frequently occurring lower extremity injury among physically actives (22,39). It is estimated that approximately 74% of individuals with a previous history of an acute lateral ankle sprain experience residual symptoms, recurrent ankle sprain, and recurrent instability, significantly impairing ankle function (1). The condition associated with recurrent ankle sprain and residual symptoms is called chronic ankle instability (CAI) (21). Functional impairments associated with CAI have been related to posttraumatic osteoarthritis at the ankle joint (41). Although mounting studies have examined functional impairments associated with CAI, the underlying mechanisms of the alterations associated with CAI are not fully understood.
Several investigations have reported conflicting results regarding differences in biomechanical characteristics during a jump-landing task between participants with and without CAI (4,5,15,16). More specifically, Gribble and Robinson (16) observed less knee flexion angle at initial ground contact during a jump-landing task in participants with CAI, whereas Caulfield and Garrett (5) reported greater knee flexion angle during a drop-landing task compared with those without CAI. Brown et al. (4) reported differences in hip kinematics during a stop-jump task, but Gribble and Robinson (16) did not observed group differences in hip kinematics during a jump-landing task. Inconsistent results when comparing individuals with CAI to controls may be partially attributable to different jump-landing tasks.
Joint energetics has been suggested as a biomechanical factor contributing to developing and perpetuating injury (31). A kinetic energy event may be created by forces and moments of force resulting from ground impact during landing. This can increase sagittal-plane joint velocity of the hip, knee, and ankle, possibly leading to excessive, unintended lower extremity joint motion. The dissipation of the impact energy at each lower extremity joint is partially alleviated through eccentric extensor muscle actions, which contributes to stabilizing the body’s center of mass (COM) during landing (9,27). It has been proposed that the magnitude of energy dissipation during landing influences the internal and external force applied on a joint (43). Therefore, the inadequate energy attenuation capability of the lower extremity joints during landing may influence lower extremity injury risk by allowing increased stress placed on static stabilizers (9,26,43).
It has been accepted that the magnitude of energy dissipation can be mediated by adjusting lower extremity joint kinematics and kinetics, ground reaction force (GRF), and COM velocity throughout landing motion (9,27,43). DeVita and Skelly (9) observed that landing with smaller knee flexion angles reduced the dissipation of the kinetic energy by knee musculature. Moreover, Norcross et al. (31) identified a relationship between lower extremity energetics and biomechanical factors related to anterior cruciate ligament injury. Thus, identifying the capacity of each joint to dissipate impact energy may be important for prevention of lower extremity injury at specific joints.
Alterations in sagittal-plane biomechanical patterns have been shown in individuals with CAI during a jump-landing task compared with those without CAI (4,5,15,16). However, little research has examined the biomechanical characteristics of the lower extremity with energetic analysis in CAI population (12). The knowledge of joint energetics provides more comprehensive information regarding biomechanical characteristics during high-risk functional activities than joint kinematics or kinetics alone. Gage et al. (12) reported no differences in energy dissipation patterns between participants with and without CAI when performing a single-leg drop landing. However, the single-leg drop-landing task does not necessarily replicate the potential mechanism of injury and place a high demand on joints. As alterations in sagittal-plane biomechanical characteristics have been observed in CAI population during a vertical stop-jump task that is a more high-risk and common in sports such as basketball, soccer, and volleyball (4), the investigation of alterations in energy dissipation patterns during a vertical stop-jump task is needed in this population.
Understanding energy dissipation strategies in the lower extremity may assist in expanding our knowledge of functional impairments associated with CAI. Identifying an underlying relationship of the presence of CAI to joint energetics may help clinicians and research to develop and implement a more comprehensive intervention to modify alterations in the kinetic-chain relationship related to CAI. It is important to examine lower extremity energy dissipation strategies during a vertical stop jump to determine the potential effect of CAI on the biomechanical alterations. Therefore, the purpose of our study was to investigate sagittal-plane energy dissipation patterns of the lower extremity joints during a stop-jump task in individuals with CAI. On the basis of previous findings (3,4,16,28,40), we hypothesized that compared with healthy controls, participants with CAI would exhibit no difference in total energy dissipation in the lower extremity but would demonstrate alterations in contributions to energy dissipation from the hip, knee, and ankle joints during landing.
Nineteen participants with self-reported unilateral CAI and 19 participants with no previous history of ankle sprain were recruited from the university community and volunteered for the study. The age and the anthropometrical characteristics of the CAI and the control groups are found in Table 1. Inclusion criteria for the CAI group consisted of 1) having a previous history of at least one acute unilateral ankle sprain, which caused swelling, pain, and temporary loss of function, but no significant injury to the ankle in the previous 3 months; 2) reporting a history of at least two repeated episodes of “giving way” in the previous 6 months; 3) reporting no previous history of any musculoskeletal and neurovascular injury in the lower extremity other than the ankle in the previous 2 yr; 4) reporting no previous history of low back pain in the previous 6 months; and 5) no previous fractures or surgery in the lower extremity.
To determine additional inclusion criteria, participants completed questionnaires related to ankle instability: the Foot and Ankle Disability Index (FADI) including the FADI Sports Subscale and the Ankle Instability Instrument (AII). The FADI and the AII have been reliable and valid in assessing functional limitations in those with CAI (10,20). To be classified into the CAI group, the participant was required to self-report functional disability on a score of ≤90% on the FADI and ≤80% on the FADI Sport Subscale (16) as well as a score of at least three on the AII (18).
The inclusion criteria for the control group consisted of 1) no previous history of any self-reported musculoskeletal and neurovascular injuries and disorders in the lower extremity, 2) no history of low back pain in the previous 6 months, 3) no history of surgery in the lower extremity, 4) a score of 100% on both the FADI and Sports Subscale, and 5) answering “no” to the question, “Do you have a history of ankle sprain?” on the AII. Inclusion criteria for both groups included that participants were physically active, which was defined as an individual engaging in at least 20 min of vigorous activity three or more days per week and that participants were free of self-reported balance or vestibular disorders. Participants in the control group were matched by sex, age, height, mass, and limb dominance to those in the CAI group. Limb dominance was defined as the preferred limb to kick a ball.
The group mean values for the FADI, FADI Sport, and AII are shown in Table 1. All participants read and signed the informed consent forms approved by the institutional review board of the University of Toledo at the beginning of testing.
An electromagnetic tracking system (Ascension Technology Corp, Burlington, VT) synchronized with a nonconductive force plate (model 4060NC; Bertec Inc., Columbus, OH) via the MotionMonitor software (Innovative Sports Training, Inc., Chicago, IL) was used. Electromagnetic sensors were placed over the sacrum, lateral midthigh, lateral midshank, and dorsal surface of the foot of the testing leg and were secured to the skin using a double-sided tape, a nonadhesive elastic tape, and a white adhesive tape. A fifth sensor was attached to a plastic stylus and used for digitizing the body segments in the software.
Participants reported to the Motion Analysis Laboratory for one testing session. At the beginning of the session, the assessment of maximum vertical jump height (Vertmax) was conducted to designate a target of 50% of Vertmax for the participants during the vertical stop-jump task (16).
Participants performed a vertical stop-jump task, as described in previous literature (38) and modified for this study. Participants stood on a line that was set up at a distance away from the center of the force plate equal to the participant’s height (Fig. 1A) and took a step forward with the testing limb to a line measured as 50% of the participant’s height from the center of the force plate (Fig. 1B). They took off on a testing limb immediately after the testing foot made contact with the ground on the line (Fig. 1C) reached up to touch a marker indicated as 50% of Vertmax on the Vertec, landed with both feet at the same time (only the testing limb in the middle of the force plate) (Fig. 1D), and then performed a maximum two-legged vertical jump as reaching up to touch an marker indicated for Vertmax on the Vertec (Fig. 1E). They landed in approximately the same position after the maximum vertical jump. The tasks of the stop-jump were first explained by the investigator. Participants were allowed to practice this task until comfortable. No instructions about jumping techniques were provided to participants to minimize a bias effect on the participants’ natural performances of the task. After practicing, participants performed five testing trials on the testing leg, with approximately 60 s of rest between trials to prevent fatigue. Trials were discarded and repeated if the participant made contact with the nontesting leg on the force plate or failed to reach up to touch the targets on the Vertec.
Data collection and reduction
Kinematics data were collected at a sampling rate of 100 Hz, whereas force plate data were sampled at 1000 Hz. Kinematic and kinetic data were filtered by the MotionMonitor software with a low-pass, third-order Butterworth filter set at a cutoff frequency of 20 Hz. The lower extremity model was generated by digitizing the ankle, knee, and hip joint centers. The representations of the ankle, knee, and hip joints were created by using the proximal segment as the reference frame in the software setup. The ankle joint center was defined as the midpoint between the digitized medial and lateral malleoli, and the knee joint center was defined as the midpoint between the digitized medial and lateral femoral condyles. The Davis et al. (8) method in the software was used to estimate the hip joint center. The segment axis systems of the foot, shank, thigh, and sacrum were established with a right-hand coordinate system, with the x-axis designated as flexion/extension, the y-axis as abduction/adduction, and the z-axis as internal/external rotation.
Lower extremity joint energy dissipations were calculated for the ankle, knee, and hip in the sagittal plane during four periods immediately after initial contact (IC) with the force plate (the point at which the vertical GRF exceed 10 N). The time intervals of 50 and 100 ms after IC were chosen to quantify energy dissipation patterns because it has been demonstrated that a lateral ankle sprain occurs within this time interval (29). In addition, we selected the 150- and 200-ms period after IC because Kristianslund et al. (25) reported that the high deflections likely caused the injury in the period between 130 and 180 ms. First, joint moments at the ankle, knee, and hip were calculated from force plate, lower extremity kinematic, and anthropometric data using an inverse dynamic procedure (13). Next, lower extremity joint power was calculated for the ankle, knee, and hip during each interval by multiplying joint angular velocities and net internal joint moments for each trial. Negative mechanical joint work was then calculated by integrating the negative portion of the joint power curve during each interval, indicating that the extensor muscles dissipated mechanical energy (27,31). Absolute energy dissipation values were normalized to product of body mass (N) and height (m). Lastly, total energy dissipation during each interval was calculated by summing the normalized ankle, knee, and hip joint energy dissipation values (31). Because of the nature of lower extremity kinetic-chain relationship, we focused on individual joint contribution to total lower extremity energy dissipation (relative ankle, knee, and hip energy dissipation) and reported it as the percentage of energy dissipation by each joint over the total energy dissipation of all three joints: ankle, knee, and hip. Although the stop-jump task consisted of double-leg landing, we quantified energy dissipation patterns only from the testing limb. Therefore, we assumed that the testing and nontesting limbs were equally contributing to the energy dissipation and generation during the stop-jump task.
Control participants were matched to CAI participants by demographic information (age, height, body mass, and limb dominance), and the limbs of the control participants were matched with that CAI participant for statistical comparison. For example, if the CAI participant had a right involved ankle, then the right limb of the matched control participant was designated as the comparison limb for the statistical analysis. Demographic variables and self-reported measures were compared between groups using independent sample t-test.
For all biomechanical variables (absolute total energy dissipation value as well as relative ankle, knee, and hip energy dissipation values), mean and SD values were calculated from the five test trials and used for statistical analysis. Independent t-tests were used to compare each dependent variable between the CAI and the control groups. Cohen’s d effect sizes using the pooled SD values were calculated along with 95% confidence intervals (CI) to determine the magnitude of difference in dependent variables between groups. The strength of effect sizes was interpreted as weak (d < 0.4), moderate (0.40 ≤ d < 0.8), and strong (d ≥ 0.8) (7).
The level of significance was set a priori at P < 0.05 using the Statistical Package for the Social Sciences for Windows (version 17.0; SPSS Inc., Chicago, IL) for all statistical analyses.
There were no statistically significant differences in age, height, or mass between groups. The CAI group scored significantly lower on the FADI and FADI sport instruments and higher on the AII, verifying the presence of the targeted pathology (Table 1).
Mean and SD values for all relative energy dissipation values are found in Table 2. Figure 2 represents the percentage of total energy dissipation for each joint relative to summed ankle, knee, and hip energy dissipation. A statistically significant group difference was found in the percentage of knee (t 36 = −2.128, P = 0.040) and ankle (t 36 = 2.185, P = 0.035) energy dissipation of the total energy dissipation during the 100 ms immediately after IC. The effect size was moderate for relative knee and ankle energy dissipation during the 100 ms interval, with 95% CI that did not cross zero (Fig. 3). These results indicated that the CAI group demonstrated significantly less knee and higher ankle joint contribution to total lower extremity energy dissipation during the 100 ms immediately after IC compared with the control group.
Group differences in relative energy dissipation values at the ankle and knee joints during the 50-, 150-, and 200-ms intervals were not statistically significant (Table 2). However, the group difference in relative energy dissipation in the knee approached significance during the 150-ms interval after IC (t 36 = −1.946, P = 0.059), and we found a moderate effect size (d = −0.63). There was no statistically significant difference for relative energy dissipations between the CAI and the control groups at the hip joint during any of the time intervals (Table 2). The effect sizes were small or moderate for these relative energy dissipation values with 95% CI that crossed zero (Fig. 2).
Differences in absolute total energy dissipation between the CAI and the control groups were not statistically significant during any of the time intervals (Table 3). All effect sizes were small for these absolute vales with 95% CI that crossed zero (Table 3).
The purpose of our study was to investigate the influences of CAI on energy dissipation patterns at the ankle, knee, and hip during a stop-jump task. The main findings of our study were that CAI participants exhibited higher ankle and lower knee joint contributions to total energy dissipation in the lower extremity compared with control participants during the 100 ms immediately after IC.
Numerous factors have been identified as contributing to CAI (23,37), but biomechanical characteristics of CAI during functional activities perhaps need more attention. Individual joints of the lower extremity work together and influence each other during functional activities. These governing musculature works synergistically to produce an internal force, dissipate an external force, and provide dynamic joint stabilization throughout the kinetic chain. Previous investigations (9,26) suggested that greater capability of energy dissipation during functional tasks would be beneficial as the lower extremity joints can provide adequate shock absorption while reducing the stresses on the surrounding static joint stabilizers due to the wide anatomical joint range of motion. Thus, the investigation of energy dissipation patterns during landing in a sports-related functional task may provide insight into the contributing factors of recurrent ankle sprains.
We found significant differences in ankle and knee relative energy dissipation patterns during part of the studied time intervals, but no significant group differences in absolute total energy dissipation values during any of time intervals. Compared with the control group, the greater amount of energy was dissipated at the ankle with the landing in the CAI group. Participants with CAI also demonstrated less knee joint contribution to total energy dissipation compared with control participants. These findings suggest that the presence of CAI may alter the kinetic-chain relationship in the lower extremity. The distal-to-proximal linkage provides an efficient and effective system to transfer force up the kinetic chain (32). If altered kinetic-chain relationship in the lower extremity during movement exists, it may be associated with the recurrent nature of CAI. The demonstrated energy dissipation pattern at the ankle may be an effort to increase landing stiffness and reduce stress on static stabilizers at the unstable ankle by maximizing the contribution of the plantarflexors. Suppressed gamma and alpha motoneuron activations and decreased corticospinal excitability in the muscles surrounding the ankle have been observed in individuals with CAI (28,35). These inhibitions may make the muscle spindles less sensitive and lead to a decrease in muscle–tendon stiffness through lack of activation or torn in these muscles (30). Altered feedback and feed-forward neuromuscular control may be driving the altered knee and ankle joint contributions to energy dissipation, possibly making participants with CAI perform stiff landing to compensate decreased muscle–tendon stiffness after ground impact. As landing stiffness increases, the relative contribution of the ankle to energy dissipation increases while those of the knee and hip to energy dissipation decreases (9,36). It has been described that the presence of CAI is creating interplay between peripheral neural afferent and centrally mediated alteration in sensorimotor control that appears as a manifestation of lower extremity movement patterns (15,19). However, placing greater demands on the ankle joint to dissipate energy with limited ability to transfer force up the kinetic chain could induce rapid fatigability during repetitive movements of the task, which may be related to the development of CAI. We acknowledge that the retrospective design does not permit a causal link to be established between CAI and the identified alterations in energetics. Therefore, it remains unknown whether altered kinetic chain relationship observed in this current study is helpful to protect the ankle or predisposes individuals with CAI to their self-reported pathology. Clearly, prospective studies are needed to fully address these questions. It may also be interesting in future study to explore long-term sensorimotor consequences after an initial lateral ankle sprain.
Although energy dissipation strategies of the lower extremity during functional tasks have been previously studied to compare landing height, landing technique, and sex (9,27,36,42,43), there is only one study that investigated the effect of CAI on lower extremity energetics during a single-leg drop landing; therefore, the comparison of our data to previous studies is limited.
Gage et al. (12) assessed lower extremity energy dissipation patterns during a single-leg drop landing and reported no difference in any of lower extremity joints between the CAI and the control groups. When relative energy dissipation values in our study are compared with their data, there appear to be differences in the relative energy dissipation of lower extremity joints. In their results, the knee joint was the largest contributor to the total energy dissipation from IC until the mechanical power curve become positive, and the least joint contribution to it was the hip joint. In our data, the largest relative joint contribution to the total energy dissipation during the 100-ms interval immediately after IC was the ankle joint in both of groups (Table 2). Our data indicated that the ankle plantarflexors may be primarily responsible for dissipating the kinetic energy during all intervals of the stop-jump task in the CAI and the control groups, followed by hip and knee extensors. These differences in the largest relative joint contribution to the total energy dissipation between our data and their results may be attributable to differences in the jump-landing protocol. Previous investigation (42) reported that the lower extremity energy dissipation patterns are different between landing techniques. In the investigation of Gage et al. (12), the jump-landing task was performed with participants’ dominant leg from a platform 35 cm in height and created a steady base of support as quickly as possible after making contact with ground during a single-leg landing. Their results may be because with a smaller base of support during a single-leg drop landing, it is a matter of stabilizing the COM quickly. Although Gage et al. (12) did not report any of kinetic and kinematic characteristics of the proximal segments of the body segments, Caulfield and Garrett (5) reported increases in knee flexion and ankle dorsiflexion in participants with CAI during a drop-landing task. It is possible that greater knee flexion at impact may influence capability of dissipating and controlling the GRF to assist in keeping the body’s COM lower and within the smaller base of support available during a single-leg landing. A location of the COM is one of elements that lead to improvement in postural stability. In addition, several authors (3,15,16) have demonstrated that individuals with CAI have a diminished level of dynamic postural stability and altered knee kinematics during a single-leg landing in other more dynamic tasks, suggesting that an altered movement pattern of the knee associated with CAI may influence the location of COM, possibly contributing to altered dynamic postural stability. Further study should quantify the position and movement of the COM and biomechanical characteristics of the more proximal segments of the body during functional tasks as well as the level of relationship between lower extremity energy dissipation patterns and the position of the COM in individuals with CAI.
In contrast, we used a modified stop-jump task intended to provide a more functional simulation of jumping and landing during physical activity and sports participation rather than dropping down from a box. It has been reported that participants with CAI demonstrated less knee flexion angle after IC during a vertical stop-jump task compared with those without CAI (40). With an extended knee at landing, knee extensor muscles are in a less advantageous position to dissipate the experienced external loading after ground impact and store elastic energy. A previous investigation reported the strong association between energy dissipation capability and knee flexion angle (31). In addition, the knee extensors are critical for energy attenuation capability (34), and a decreased force production of knee extensors leads to earlier activation of the ankle plantarflexors that may provide synergistic and compensatory dynamic knee stabilization by increasing joint stiffness (33). Deficits in force production of the knee extensors have been shown in individuals with CAI (17). Therefore, it is possible that decreased strength of the knee extensor coupled with altered knee kinematics leads to diminished capability of energy attenuation at the knee after ground impact during the stop-jump task in CAI population, which may result in placing greater demands on the ankle joint to store elastic energy as preparation to generate force for the final double-leg vertical jump immediately after the landing. However, the stop-jump task consisted of double-leg landing, and we did not bilaterally quantify energy dissipation patterns in the lower extremity at the same time. It is possible that the uninvolved limb was attenuating more force during the landing. We are unaware how the nontesting leg influenced total energy dissipation patterns in the testing leg. Therefore, future investigation should consider the effect of interlimb or intralimb coordination on biomechanical characteristics during a double-leg landing task.
An earlier finding of the presence of less knee flexion angle in the CAI group (15,16,40), combined with our current finding of altered capability of kinetic energy dissipation at the knee joint, provides insight regarding future proximal joint injury mechanisms. A more extended knee position as well as decreased knee contributions to total energy dissipation may create injurious positions to the knee. Previous work (42) suggested that the presence of decreased knee flexion angle during landing can lead to inadequate energy attenuation capability of the knee, resulting in the knee joint would receive large compressive impact forces (26), which can cause cartilage lesions and osteoarthritis (6) as well as increase the risk for ACL injury (31). Although there is limited information, it has been suggested that there may be a potential association between the history of ankle sprain and the risk of knee injury (2,24). Kramer et al. (24) identified that 52% of patients with ACL injury had a previous history of ankle sprain and there were common factors that predicted both the ACL-injured and ankle-sprained groups, suggesting that individuals with ACL injury history were more likely to have suffered previous ankle sprain. Anterior tibial shear force, which has been considered as a biomechanical factor associated with ACL injury (31,38), has been shown to be significantly related with knee flexion angle (38,40). Therefore, the proposed landing strategy associated with CAI, including a more extended knee position as well as a decreased knee joint contribution to energy dissipation, may provide rationale for future research regarding an association between CAI and future proximal joint injury.
In addition to diminished relative knee energy dissipation, placing greater demands on the plantarflexors to dissipate the kinetic energy may be associated with an increase in a risk for future knee injury. Fleming et al. (11) have reported that greater gastrocnemius contraction results in significant increases in ACL strain when the knee is more extended position. Further, soleus muscle inhibition was previously demonstrated in individuals with CAI (3,28). This suggests that the gastrocnemius muscle may have responsibility to dissipate the kinetic energy at the ankle in the CAI participants. It has been suggested that a landing pattern with greater ankle energy dissipation during the first 100 ms of landing may increase a risk of ACL injury by resulting in greater gastrocnemius muscular force that could contribute to increase ACL load (31). The CAI group demonstrated the greatest amount of energy dissipated at the ankle during the 100 ms of landing. Conversely, the control group initially dissipated more energy at the ankle with landing, and the ankle joint contribution to the total energy dissipations was then reduced by transferring up the kinetic chain. Therefore, our findings indicate that participants with CAI dissipating relatively greater amounts of their energy dissipation at the ankle during the 100 ms after IC may be at increased risk of an ACL injury.
With only 19 participants in each group, there was a potential for a statistical error. Although an a priori sample size calculation was not conducted, in this study, post hoc power analyses showed that we had strong observed power to detect group differences (observed powers = 0.87–0.99). However, all of our nonsignificant findings were associated with low to moderate statistical power (observed powers = 0.09–0.64). We performed a post hoc sample size calculation based on the difference in mean and SD values of our completed results. From these calculations, we would have needed 1315 participants per group to achieve a level of power of 0.80 for the dependent variables, which was not significantly different between groups. We believe that it would be difficult and unrealistic to recruit such numbers of participants. Furthermore, the addition of the Cohen’s d effect size analysis with a calculation of 95% CI strengthens our results by emphasizing the magnitude of difference between groups. Some of the nonsignificant differences were associated with small effect sizes, indicating that these relationships are not likely clinical difference. In cases of moderate effect sizes with the 95% CI that crossed zero, it is possible that these relationships may be strengthened with an expanded sample size.
In this current investigation, only sagittal-plane energy dissipation patterns of the lower extremity joints were examined during a vertical stop jump. Previous studies (25,29) have reported that a lateral ankle ligamentous injury results from a motion combining internal rotation and inversion on the ankle joint. Lastly, the altered frontal and transverse plane kinematics of the proximal lower extremity joints has been associated with the presence of CAI (4). However, no previous investigations have examined frontal or transverse plane energy dissipation strategies in individuals with CAI. Before the potential multifactorial problems associated with CAI injury can be understood, further investigation is needed, including additional quantification of frontal- and transverse-plane kinetics and kinematics during functional activities. In addition, we are unaware of any published work demonstrating the normal range of measurement error in energetics during this task, especially in CAI patients. Although this and other similar landing tasks have been used commonly to illustrate differences related to CAI, this area of research may benefit from further exploration of the minimum detectable changes of these energetic differences for improved study replication.
The modified stop-jump task consisted of rapid acceleration and deceleration. Although every effort was made to secure the kinematic sensors using normal protocols, it is always possible that rapid acceleration and deceleration may induce measurement errors in assessing the true joint motions. Further, we did not record the maximum jumping height and the 50% of Vertmax. Lower extremity energetics has been associated with jump heights (42,43). Although we normalized jumping height among participants using 50% of Vertmax, we acknowledge that variability in the landing height could have affected the results of energy dissipation patterns during landing. Further research is necessary to determine whether effects of CAI on energy dissipation patterns in the lower extremity are observed consistently across various jump heights and other dynamic tasks.
The method of quantifying energy dissipation, which we performed in this study, has been used previously (27,31,36). However, it is important to acknowledge that the specific contributions of dynamic and static joint stabilizers to energy dissipation cannot be differentiated from our data.
Finally, it should be noted that we did not classify CAI specifically to mechanical or functional instability because CAI is a multifactorial problem (21). Differences in motion patterns during landing tasks have been identified between mechanical and functional instability groups (4). Therefore, future research should examine how the landing strategies might be influenced by specific mechanical and functional (or perceived) deficiencies.
Our findings may prompt clinicians and researchers to develop a better understating of potential kinetic alterations in the entire lower extremity associated with CAI as well as the potential for the screening and prevention of possible future injury in individuals with CAI.
Our data suggest that it is important for clinicians 1) to consider the influence of CAI on global function during ankle rehabilitation and 2) to evaluate the entire kinetic chain relationship between joints across the lower extremity and not just in isolation during a jump-landing task. In addition, our findings of altered contributions of the knee and ankle to energy dissipation may have important clinical implications. Specifically, there may be an association between CAI and future proximal joint injury as less energy dissipation at the knee joint after ground impact increases compressive impact force at the knee joint and to stress capsuloligamentous structures, and greater ankle energy dissipation during landing may be possibly associated with an increase in risk for ACL injury. It has been demonstrated previously that individual joint contributions to energy dissipation can be modified by changing lower extremity kinematics and kinetics during landing (9,27,42,43) as well as with an application of a moderately restrictive boot brace (14). Improving jump-landing strategies, such as an increase in knee flexion before and during landing, may be addressed for clinical intervention of CAI. For future investigations, it will be beneficial to determine whether those modifications could reduce CAI and future musculoskeletal injuries at the proximal joints in those with CAI.
In our study, we observed altered energy dissipation patterns at the knee and ankle during a stop-jump task in the CAI group. Specifically, the CAI group demonstrated significantly greater ankle and less knee joints contributions to the total energy dissipation during the 100-ms interval after IC compared with the control group. Although the intent of our current study was to examine lower extremity energy dissipation patterns, it will be important for clinicians and researchers to understand how energy dissipation patterns in the entire lower extremity are influenced by the presence of CAI. These findings may provide insight into kinetic alterations that may be associated with CAI as well as the potential for proximal joint injury in individuals with CAI. Future research should consider this information as it may be used to develop more effective interventions to target these potentially modifiable energy dissipation patterns in those with CAI as well as to determine whether the modifications could reduce CAI and minimize the future knee injury.
This study was supported by the National Athletic Trainers’ Association Research and Education Foundation (Dallas, TX) through its Osternig Master’s Grant Program. All data were collected at the University of Toledo.
No conflicts of interest were associated with the authors and the results of this research.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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