Lateral ankle sprains are one of the most frequently incurred injuries during participation in sport (1). Alterations in movement mechanics of the lower extremity during functional tasks (e.g., single-leg drop landing or postural control) have been reported in patients with an acute, first-time lateral ankle sprain (2), with a 6-month post, first-time lateral ankle sprain (3,4), and with chronic ankle instability (CAI) (5–9). These altered lower extremity movement patterns have been proposed as a contributing factor to the development of CAI, which is characterized by the subject reporting of recurrent “giving way” of the ankle joint and a feeling of ankle joint instability (10).
Lower-extremity muscles provide dynamic joint stability for the ankle, knee, and hip joints during sport activities (11,12), which include landing (eccentric muscle action and energy absorption) and jumping (concentric muscle action and energy generation) (13). During landing, an impact ground reaction force occurs and is attenuated by eccentric muscle action of the plantarflexors and knee and hip extensors (13,14). Theoretically, an inability to attenuate this force and corresponding energy would result in increased energy transmitted to other anatomical structures (e.g., bones, ligaments, and/or connective tissues), which potentially increases joint contact stress (15) and risk for lower-extremity injuries (e.g., ligament sprains, articular cartilage damage, and/or menisci lesions) (13). During sport activities, the more energy absorbed by lower-extremity muscles during the eccentric phase of landing, the greater energy produced during the concentric phase of jumping, improving athletic performance (16). Thus, altered energetic patterns due to CAI during landing and jumping may influence injury risk and athletic performance during sport activities (17).
Joint stiffness is influenced by structures surrounding the joint, including the skin, muscles, ligaments, and/or joint capsule (18). Lower joint stiffness may be a risk factor of soft tissue injury (19). Altered joint stiffness has been reported in CAI patients during various functional activities (20,21). It is believed that because of sensorimotor deficits in the ankle (e.g., reduced eccentric/concentric plantarflexor strength) (22), CAI patients showed reduced ankle stiffness. It is obvious that because the lower extremity is connected via the kinetic chain, reduced ankle joint stiffness could result in an intralimb reweighting kinetic compensation from the distal to proximal joints (23).
Little is known about profiles of lower-extremity joint kinetics, energetics, and stiffness during landing and jumping in individuals with established CAI. Therefore, the primary aim of this study was to compare the lower-extremity joint kinetic and energetic patterns of individuals with established CAI with those of a noninjured control group across the entire ground contact phase of a landing and jumping task. We hypothesized that, relative to the control subjects, CAI patients would show (i) less internal plantarflexion moment, less internal knee extension moment, and more internal hip extension moment; (ii) less ankle and knee eccentric and concentric power, and more hip eccentric and concentric power; and (iii) less ankle and knee joint stiffness and more hip stiffness.
One hundred CAI patients (54 male, 46 female) and 100 able-bodied matched controls (54 male, 46 female) were recruited from a university population and participated in this study (Table 1). Participants were selected in accordance with endorsed inclusion criteria for CAI (24–26). Participants were classified using the Foot and Ankle Ability Measure (FAAM) (27) and the Modified Ankle Instability Instrument (MAII) (28). Inclusion criteria for the CAI group consisted of (i) at least two episodes of “giving way” in the past 6 months, (ii) a FAAM–Activities of Daily Living (ADL) score that was <90%, (iii) a FAAM-Sports score that was <80%, (iv) at least two “yes” answers on questions 4–8 of the MAII, (v) a history of at least two acute unilateral ankle sprains, (vi) no acute lower-extremity musculoskeletal injuries in the previous 3 months, and (vii) no lower-extremity surgery and/or fracture in their lifetime. The inclusion criteria for the control group consisted of (i) a score of 100% on the FAAM-ADL and FAAM-Sports, (ii) no “yes” answers on questions 4–8 of the MAII, (iii) no ankle sprain in their lifetime, (iv) no acute musculoskeletal injuries in lower extremity in the past 3 months, and (v) no lower-extremity surgery and/or fracture in their lifetime. Control subjects were matched to CAI patients for age (±5 yr), height (±5 cm), mass (±4.5 kg), and sex (Table 1). Control subjects’ involved leg was determined by matching involved ankle of corresponding CAI patients. Means and SD for self-reported ankle instability questionnaires are reported in Table 1. All participants were physically active, participating in weight-bearing activities with at least 30 min·d−1, 3 d·wk−1 in the 3 months before data collection. All procedures were approved by the appropriate institutional review board, and informed consent was provided by each participant before data collection.
Anthropometric data, including subjects’ height, mass, shank length, and age, were recorded. Subjects dressed in standardized spandex clothing and athletic shoes provided by the researchers. Fifty-nine reflective markers were placed over specific anatomical landmarks, in a previously described arrangement (29). Subjects then walked for 5 min on a treadmill to warm up. Then, a single video frame was collected, with the subject standing, with feet shoulder width apart and arms abducted to 90°; all subsequent ankle, knee, and hip joint angles were reported, relative to this position. Next, two dynamic video trials were collected to calculate a right and left functional hip joint center (30). Subjects performed up to 10 practice trials of a landing and jumping task onto a force platform (OR6-6-1; AMTI, Watertown, MA; 2500 Hz) that was embedded in the laboratory floor. To perform the landing and jumping task, subjects stood 75–95 cm (standardized to 50% of the subject’s height), away from the center of the force plate, indicated by a plus sign marked with white tape as presented in Fig. 1A. The subjects performed a double-leg maximal vertical forward jump (Fig. 1B), a single-leg landing with the involved leg only (Fig. 1C), and an immediate side-cutting jump at 90° to the contralateral side (standardized to 65% ± 5% of the subject’s height; Fig. 1D, E). After practice trials, subjects performed 10 trials of the landing and jumping task. The first five trials were used to calculate a range of maximal vertical jump height. Ten high speed video cameras (VICON; Oxford Metrics Ltd., Oxford, United Kingdom; 250 Hz) were used to ensure that each jump height was maximum, which was defined as ±5% of the average maximum height of the reflective marker, placed on the posterior superior iliac spine, during the first five landing and jumping trials. The next five successful trials were used for data analysis. A trial was discarded and repeated when subjects missed a targeting location (a plus sign marked with white tape) on the center of the force plate or the maximal vertical jump height was outside the range of the maximal vertical jump height determined in the first five trials. There was a 1-min rest between the landing and jumping task.
All outcome variables were limited and normalized to 100% of the ground contact phase of landing and jumping, which was defined as the time the involved foot was in contact with the force plate. A 25-N vertical ground reaction force threshold was used to determine initial foot contact (0% of ground contact) and takeoff (100% of ground contact). Ground contact was divided into two phases: (i) landing (eccentric), which was from initial ground contact to peak dorsiflexion (which occurred approximately at average 50% of ground contact), knee flexion (which occurred approximately at average 50% of ground contact), and hip flexion (which occurred approximately at average 32% of ground contact), and (ii) jumping (concentric), which was from end of landing to takeoff (e.g., no ground contact). Average onset of a concentric jumping phase of ankle and knee joints was at 50% of ground contact. Unlike the ankle and knee joints, average onset of a concentric jumping phase of the hip joint was at 32% of ground contact. This was attributed to characteristics of our landing and jumping task that the hip initiated a direction change to the contralateral side earlier than the ankle and knee during landing and jumping (Fig. 1).
The three-dimensional (3D) trajectory for each reflective marker was measured using the aforementioned high-speed video cameras. 3D marker coordinates were identified using VICON Nexus and then exported to Visual 3D software (C-Motion, Germantown, MD), where they were filtered using a fourth-order low-pass Butterworth filter and a 10-Hz cutoff frequency; this frequency was determined via residual analysis (29). The force plate data were filtered using the fourth-order low-pass Butterworth filter at a frequency of 10 Hz (31). Next, a rigid link model (foot, shank, thigh, and pelvis segments) was created using the static calibration, and this model was assigned to all landing and jumping trials, to calculate ankle, knee, and hip joint kinematics (29). Ankle, knee, and hip joint angles were calculated using a Cardan rotation sequence (32). Sagittal-plane, net internal joint moments were calculated via the synchronized kinematic and ground reaction force data and anthropometric data using a standard inverse dynamics approach (33). Net internal joint moments were normalized to body mass for each subject. Joint power was calculated as the dot product of the net internal joint moment and joint angular velocity (13), and also normalized to body mass for each subject. Eccentric power was considered to be kinetic energy absorption, whereas concentric power was considered to be kinetic energy generation. Finally, sagittal-plane ankle, knee, and hip joint stiffness was calculated as the change in net internal moment divided by the angular displacement between initial ground contact and peak dorsiflexion, and knee and hip flexion, respectively, only during the landing phase (34).
Functional analyses of variance (FANOVA) were used to evaluate between-group (CAI and control) differences for net internal joint moment and power throughout ground contact (P < 0.05). This approach facilitated the comparison of the moments and powers, represented as polynomial functions, rather than discrete values (35). Furthermore, this approach allowed us to detect between-group differences for joint moment and power at any point in time during ground contact. We plotted our estimates of pairwise comparison functions between the CAI and control groups, as well as 95% confidence interval (CI) bands to determine significant differences. Differences were considered to be significant if an estimate of effect size (95% CI) did not overlap zero (36). These FANOVA analyses were performed using the FDA package in R (version 2.15.1). Independent t-tests were performed (P < 0.05), using JMP Pro 13 software (SAS Institute Inc., Cary, NC), to assess between-group differences (CAI and control) for ankle, knee, and hip joint stiffness only during the landing phase.
There were no significant between-group differences in participants’ demographics (Table 1). Maximum jump height did not significantly differ between the CAI (0.34 ± 0.12 m; 95% CI, 0.33–0.35) and control (0.35 ± 0.12 m; 95% CI, 0.34–0.36) groups (P = 0.28). Between-group differences for net internal joint moment, power, and stiffness were not due to the maximum jump height.
There were numerous between-group differences for sagittal-plane net internal joint moment (Fig. 2). During landing, plantarflexion moment was up to 0.06 N·m·kg−1 greater for the CAI group during 5%–8% of ground contact and 0.13 N·m·kg−1 less during 16%–50% of ground contact. During jumping, plantarflexion moment was up to 0.10 N·m·kg−1 less for the CAI group between 51% and 75% but up to 0.05 N·m·kg−1 greater between 84% and 95% of ground contact (Fig. 2A, B; P < 0.05). During landing, the CAI group demonstrated up to 0.2 N·m·kg−1 less knee extension moment between 21% and 50% of ground contact. During jumping, knee extension moment was up to 0.14 N·m·kg−1 less between 51% and 63% of ground contact for the CAI group, but 0.07 N·m·kg−1 greater between 80% and 91% of ground contact (Fig. 2C, D; P < 0.05). During landing, the CAI group exhibited up to 0.2 and 0.18 N·m·kg−1 greater hip extension moment between 8% and 20%, and between 27% and 32% of stance, respectively. During jumping, hip extension moment was up to 16% 0.16 N·m·kg−1 greater for the CAI group between 33% and 86% of ground contact (Fig. 2E, F; P < 0.05).
Figure 3 shows the between-group differences for ankle, knee, and hip joint power across the ground contact of the landing and jumping task. During landing, the CAI group produced up to 0.82 W·kg−1 less eccentric ankle power between 10% and 45% of ground contact (P < 0.05). During jumping, the CAI group produced up to 0.74 W·kg−1 less concentric ankle power between 60% and 84% (Fig. 3A, B; P < 0.05). During landing, at the knee, the CAI group produced up to 1.61 W·kg−1 less eccentric power between 18% and 32% of ground contact (P < 0.05). During jumping, the CAI group produced up to 0.76 W·kg−1 less concentric knee joint power between 50% and 70% of ground contact, but 0.61 W·kg−1 greater concentric power between 80% and 90% of ground contact (Fig. 3C, D; P < 0.05). During landing, the CAI group produced up to 1.06 W·kg−1 greater eccentric hip joint power between 8% and 15% of ground contact, but about 0.79 W·kg−1 less eccentric hip joint power between 22% and 25% of ground contact. During jumping, the CAI group produced 0.47 W·kg−1 less concentric hip joint power during 33%–40% of ground contact, but approximately 0.55 and 0.17 W·kg−1 greater concentric hip joint power between 60% and 90%, and 95% and 100% of ground contact, respectively (Fig. 3E, F; P < 0.05).
Ankle and knee joint stiffness during the landing phase differed between the CAI and control group. The CAI group exhibited 0.004 N·m·kg−1·°−1 less ankle stiffness (CAI: 0.051 N·m·kg−1·°−1 vs control: 0.055 N·m·kg−1·°−1) and 0.006 N·m·kg−1·°−1 less knee stiffness than the control group (CAI: 0.052 N·m·kg−1·°−1 vs control: 0.058 N·m·kg−1·°−1; Table 2). Conversely, the CAI group exhibited 0.008 N·m·kg−1·°−1 more hip joint stiffness than the control group (CAI: 0.100 N·m·kg−1·°−1 vs control: 0.092 N·m·kg−1·°−1; Table 2).
The purpose of this study was to assess lower-extremity joint kinetics and energetic patterns across the ground contact phase of a landing and jumping task between the CAI and control groups. The primary findings of this study were that patients with CAI absorbed less kinetic energy at the ankle and knee, and compensated for this by absorbing more kinetic energy at the hip joint during the eccentric phase of landing (Fig. 3). Like energetic patterns, CAI patients tended to decrease plantarflexion and knee flexion moment with less ankle and knee joint stiffness and increased hip extensor moment with greater hip joint stiffness during landing (Fig. 2). Both the CAI and control groups demonstrated relatively similar joint moment and power patterns during the concentric phase of jumping (Figs. 2 and 3). Overall, the CAI patients seemed to alter lower-extremity kinetic patterns, redistributing mechanical work and energy absorption, from the distal (ankle and knee) to proximal joint (hip) during landing and jumping. Therefore, the results supported our hypotheses that CAI patients altered lower-extremity joint kinetics and energetic patterns across various portions of the ground contact phase during landing and jumping.
The gastrocnemius–soleus muscle complex plays an important role in providing dynamic ankle joint stability and dissipating ground reaction force via eccentric muscle action during jump landing (13). When eccentric plantarflexor strength is deficient and does not provide necessary plantarflexor moment and ankle joint stiffness on high-impact landing during functional activities, plantarflexors would likely produce less eccentric ankle joint power and be unable to effectively dissipate ground reaction force during landing. This may result in increased joint contact stress and strain on the static, inert structures of the ankle joint (e.g., bones, ligaments, and other soft tissues) (18). In addition, from a motor control perspective, CAI patients may develop altered motor programming in the cortex after initial or repeated lateral ankle sprain(s) (37). For example, when plantarflexor function (e.g., strength and activation) in CAI patients is reduced, as a global/central motor control adaptation through the supraspinal pathways, altered motor programming, reweighting the load from the unstable or weakened distal ankle to proximal hip joint, may be developed and adapted as observed in the current and previous data (3,9). If this newly adapted motor programming is persisted over the long term, compromised motor programming could be permanent in CAI patients and reduced ankle joint function (e.g., less plantarflexor moment, ankle joint power, and stiffness) during landing could be consequences. As such, strength training in a short period time (4–8 wk) may not be enough to recreate and adapt an appropriate motor control program. Therefore, our observed changes of an intralimb reweighting pattern suggest that a global/central adaptation through the supraspinal pathways may play a role in observed altered energy absorption during landing. The current finding of decreased eccentric ankle joint power during landing might be, at least partially, related to the observed deficit in plantarflexor moment and ankle joint stiffness. In contrast, a previous report indicated that CAI patients increased eccentric ankle joint power during a double-leg stop jump task (17). These conflicting results could be due to the difference in task (e.g., double-leg stop jump task vs our single-leg landing and jumping task). Our task involved maximum vertical forward jump landing on a single leg and side cutting at 90° to the contralateral side (Fig. 1), which may be more demanding and representative of certain sport activities, relative to previous uniplanar tasks such as double-leg landing and/or single-leg drop landing as uniplanar motion without direction changes (17).
CAI may influence not only ankle plantarflexor but also knee extensor strength (38). Previously reported deficits in knee extensor strength (38) are consistent with the current findings of reduced knee joint kinetics (e.g., less knee extension moment and eccentric power) during landing. Decreased joint torque production may be attributed to a reduction in neural drive (39). It has been suggested that the sensorimotor deficits at the ankle affect neural drive to the knee (38). This may be evidence of reorganization of the central nervous system integration with CAI patients that could result in altered knee joint neuromuscular control. Previous studies have demonstrated that the presence of CAI influences sensorimotor control at both the spinal (40) and supraspinal levels (41). Patients with CAI demonstrated increased motor neuron pool excitability (40) and preparatory muscle activation (4) of the quadriceps muscles compared with the controls. These observed central changes in sensorimotor function at the knee joint in patients with CAI during a landing task may indicate alteration in feedforward neuromuscular control in an effort to compensate for knee extensor deficits. Knee extensors are important in attenuating impact force, via eccentric action, during landing (42). Reduced knee extension moment in patients with CAI could have contributed to the observed reduction in knee joint stiffness throughout the landing phase (19). Furthermore, previous research also demonstrated that eccentric capabilities of the knee extensors were decreased, as the demands of a jump landing task were increased (14). Because our task (maximum single-leg jump landing and cutting) was relatively more challenging and demanding compared with previously studied double-leg stop jump (17,21) and single-leg drop landing (16), it required a higher muscular demand on the knee extensors.
Conversely, current findings suggest that CAI patients seemed to increase reliance on the hip during landing relative to the controls, which was likely necessary because of the decreased ankle plantarflexor and knee extensor moments. As such, the current CAI patients may use an intralimb reweighting strategy; for example, CAI patients increased up to 30% (1.06 W·kg−1) eccentric hip joint power between 8% and 15% of ground contact (Fig. 3E, F) by increasing up to 25% (0.2 N·m·kg−1) hip extensor moment between 8% and 20% of ground contact (Fig. 2E, F) during the initial landing phase. This increased hip moment likely contributed to the observed 8% (0.008 N·m·kg−1·°−1) increase in hip joint stiffness (Table 2) for the present CAI patients. These findings are congruent to previous reports that patients with a first-time lateral ankle sprain use a hip-dominant strategy during a single-leg postural control task (43) at 2 wk after injury. This altered strategy persisted for up to 6 months after injury (3). Other research has also observed this hip-dominant strategy during single-leg drop landing (9) in CAI patients at 6 months after initial ankle injury. Patients with CAI demonstrated increased postural sway and loss of sensorimotor function due to deafferentation and peripheral nerve injury at the ankle (44). As a result, the central nervous system decreased latency of hip muscle activation via a centrally mediated feedforward mechanism (45). It has been speculated that altered lower-extremity movement pattern (a shift from an ankle to a hip strategy) indicated an attempt to compensate for the partially deafferented ankle joint to maintain postural control (46). It is important to note that patients with an acute lateral ankle sprain would not be able to adequately attenuate impact forces through the injured ankle; conversely, the hip joint would be used as a compensation (2). Because the fact that hip musculature has greater muscle volume and strength compared with the ankle, the hip joint can account for absorbing more kinetic energy when a mechanical demand of landing is increased (42). In this study, patients with CAI demonstrated a distal-to-proximal redistribution strategy during high-impact landing.
We observed similar patterns during the concentric phase of the movement task, for example, the kinetic energy generating phase of the task (jumping). During jumping, CAI patients produced less concentric ankle and knee joint power, and more concentric hip joint power (Fig. 3A–D) relative to the control group (Fig. 3E, F). Interestingly, our findings demonstrated that the entire energetic patterns are likely related between the eccentric and concentric powers. Specifically, the observed reduced eccentric power at the ankle and knee during landing is likely associated with reduced concentric ankle and knee joint power during jumping, whereas observed higher eccentric hip joint power during landing gives rise to higher hip concentric power during jumping. Our findings are consistent with those associated with the stretch–shortening cycle (47). As such, sport activities such as landing, cutting, and jumping involve stretch–shortening cycle, which is characterized by eccentric muscle action immediately followed by concentric muscle action (48). Increased eccentric joint power and elastic energy stored during the eccentric phase of landing resulted in greater concentric joint power with the release of more elastic energy during the concentric phase of jumping (47). In the current study, more elastic energy absorbed in hip musculature during landing may contribute to greater power generation at the hip during jumping. Observed increased concentric power at the hip might be an altered energetic pattern to compensate for decreased concentric power at the ankle and knee in the current study.
This study is novel and important for at least three reasons. First, this is the first study to analyze lower-extremity kinetic and energetic patterns during the entire ground contact phase of a novel demanding jump task, rather than only considering mechanical characteristics at certain, discrete time points. Previous studies used a traditional statistical analysis such as ANOVA (42) or t-test (9,17) to analyze movement biomechanics. However, considering mechanical characteristics at certain, discrete time points may provide limited insight into how movement biomechanics are changed across entire ground contact of the movement task. As such, we accomplished this by using a robust statistical analysis, called FANOVA, which has not often been applied in sport science research. In clinical settings, the FANOVA findings, comparing the data of the whole movement cycle, are relatively easy to understand for clinicians and allow them to better understand about kinetic and energetic patterns. Thus, our findings regarding kinetic and energetic patterns of lower-extremity joints in patients with CAI provide useful insights for clinicians in developing rehabilitation and strengthening and conditioning programs for the CAI patients. Second, compared with previously studied tasks such as double-leg drop jump landing and single-leg stop jump landing, and single-leg drop landing (16,17,21), our landing task (e.g., the single-leg landing and jumping to the side) may be more representative of certain sports movements, because of components of sudden deceleration at landing and rapid acceleration at jumping along with required direction changes (cutting). Third, relative to previous studies regarding CAI movement biomechanics (17,20,38), our large sample size (100 CAI patients and 100 matched controls) may provide a strong statistical power for findings fo lower-extremity joint stiffness, kinetic, and energetic patterns in this patient population during functional movement.
There are several limitations to this study. We only presented sagittal-plane, lower-extremity joint kinetic and energetic patterns, which is insufficient to fully describe the complexity of our landing and jumping maneuver. Using current methods, however, it is difficult to accurately quantify the present metrics (lower-extremity joint moment, power, and stiffness) in the frontal and transverse planes of motion, because of low signal-to-noise ratios (less frontal- and transverse-plane motion). Second, the lack of joint muscle activation data makes some of the present statements difficult to confirm, as do the lack of trunk kinematics and kinetics. Our landing and jumping task requires trunk musculature to stabilize the trunk against a posterior ground reaction force during initial landing. Like the altered hip joint mechanics we observed, altered trunk flexion might be a compensatory strategy that CAI patients use during landing and jumping. Lastly, a research design comparing individuals with a history of a lateral ankle sprain who have no residual symptoms or deficiencies (ankle sprain copers) against those who have developed CAI would be useful.
The current findings relating to altered landing kinetic and energetic patterns in CAI patients provide useful insights for clinicians in developing rehabilitation protocols for patients with CAI. Previous studies revealed that CAI leads to a neuromuscular adaptation of the knee and hip (8,9,38). The current results reinforce existing body of literature showing intralimb reweighting kinetic and energetic patterns from the distal to proximal joints in patients with CAI. Restoring neuromuscular function is a key point of the rehabilitation process, and our findings may help clinicians develop better neuromuscular training protocols for patients with CAI. A traditional rehabilitation approach to CAI patients has been focused on the injured ankle joint. However, the present findings suggest that a single joint injury seems to alter the entire lower-extremity movement biomechanics via alterations in spinal and supraspinal pathways, and clinicians should emphasize entire lower-extremity joints when developing rehabilitation programs for CAI patients. Our findings suggest that the presence of CAI reorganized lower-extremity energetic patterns during landing. Altered motor programming is influenced by the global/central neuromuscular control adaptation through the supraspinal pathways. The interventions should focus on reorganizing or recreating new motor programming to alter existing adapted motor control. Furthermore, repetition may be a key factor in reorganizing a motor programing in the cortex as well as the duration of the interventions. Movement-related functional rehabilitation is also important because the early stage of rehabilitation is not functional as a static position or not movement-related such as a theraband strengthening training, joint mobilization, electrotherapy, and so on. To create new motor programing in the cortex, the rehabilitation should challenge the sensorimotor system to adapt and achieve a certain task goal from the predicted to unpredicted sequence.
Ankle joint instability is a risk factor for the development of ankle joint degenerative disease. Some have speculated that CAI might be early onset of posttraumatic osteoarthritis (49). It has been suggested that some level of joint stiffness is required for optimal joint stability and minimizing soft tissue injury (19). Lower ankle stiffness may be related to less dynamic stabilization during landing, which may contribute to recurrent ankle sprains during functional tasks. Several studies report that the changes in the landing techniques could alter the amount of joint stiffness (13,19,42), decreasing the joint loads. Eccentric muscle actions of lower extremity play an important role in absorbing joint loads during landing (13,14). Altered eccentric joint power might be a potential risk factor for osteoarthritis (50). Regarding posttraumatic osteoarthritis progression, altered joint loads could be a factor for developing articular cartilage degeneration (51). Altered joint stiffness and eccentric power may affect the risk of injury. Clinicians should take these into consideration for rehabilitation program.
Landing and jumping biomechanics differed between the CAI and control groups during our novel multiplanar landing and jumping task. CAI patients used a landing strategy that relied more on the hip than on the ankle and knee. The present findings indicate that, for CAI patients, the hip likely plays a critical role in both energy absorption and generation during sport-related, multiplanar landing and jumping. Observed reductions in ankle and knee joint moments in the CAI group may increase joint contact stress on the inert structures (e.g., the bones, ligaments, cartilage, and connective tissues) at the ankle and knee. Observed reduced plantarflexion and knee extension moments during landing may suggest that the involved muscles may not adequately absorb impact force through the plantarflexor and knee extensor, and it is believed that unabsorbed force during landing could be transmitted to the inert structures, which may result in increased shear and/or compressive force on the structures. This could increase risk for noncontractile, soft tissue injuries. In the present study, increased energy generation by the hip may be an effort to compensate for decreased ankle and knee joint power.
The authors declare no conflict of interest and no funding.
The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation, and the results of the present study do not constitute endorsement by the American College of Sports Medicine.
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