Journal Logo

APPLIED SCIENCES

Movement Strategies among Groups of Chronic Ankle Instability, Coper, and Control

SON, S. JUN1; KIM, HYUNSOO2; SEELEY, MATTHEW K.1; HOPKINS, J. TY1

Author Information
Medicine & Science in Sports & Exercise: August 2017 - Volume 49 - Issue 8 - p 1649-1661
doi: 10.1249/MSS.0000000000001255

Abstract

Ankle sprains are the most common sport injury in basketball, volleyball, gymnastics, soccer, and football; sports involving a dynamic maneuver (31). A large majority of individuals (74%) have reported chronic residual symptoms after a single ankle sprain (1). In a 7-yr follow-up study, 32% of patients experienced chronic residual symptoms including pain, swelling and/or repeated ankle sprains, and 74% of the patients reported a feeling of functional impairments (38). More importantly, one of every three individuals who sustain a single ankle sprain suffers repeated episodes of ankle sprains (1,4,41). Despite a high recurrence rate, only 43% of ankle sprains are treated by health care providers (41). Research indicates that up to 78% of these patients go on to develop long-term joint degenerative diseases such as ankle osteoarthritis (30).

Chronic ankle instability (CAI) is defined by chronic residual symptoms including repeated episodes of ankle sprains, a feeling of giving way, joint instability, pain, swelling, and/or loss of function (1,25). Although mechanical ankle instability is related to changes in static structures (e.g., pathologic laxity, restricted arthrokinematics, etc.), functional ankle instability is associated with altered sensorimotor function (29). Risk of repeated ankle sprains is dependent on many factors, including reduced ankle musculature strength (33,52,54), restricted dorsiflexion angle (12,43,52), increased ankle anterior and inversion laxity (33), decreased reaction time of lower leg muscles (32,52), hip musculature dysfunction (3,24,33) altered postural control (33,54), and/or altered proprioception (54). It is theorized that one or any combination of these factors can result in altered movement strategies that potentially predispose the unstable ankle population to repeated ankle sprains. Recent prospective evidence supports this idea (20).

Some individuals with a history of ankle sprain injury are able to perform a highly demanding sports maneuver without complaint of chronic residual symptoms, these individuals are known as “ankle sprain copers” (50). Researchers suggest that copers may adopt favorable movement strategies to help avoid recurrent ankle sprains (50). Theoretically, altered movement strategies evolve from acute and/or subacute phases after ankle sprain injury depending on available constraints and movement demands as a postinjury adaptation (51). The capabilities of the sensorimotor system to deal with task demands may make some individuals prone to recurrent ankle sprains (51). Although most studies have used healthy controls as a comparison group to CAI patients, a few recent studies have used copers as a comparison group in CAI landing research (6–8,21). Comparing multiplanar landing/cutting movement strategies of copers with CAI patients will provide clues as to which joint position, net internal joint moment, and EMG activation strategies may contribute to CAI.

This study aimed to define movement strategies during the stance phase of a sports maneuver (e.g., a maximal vertical forward jump landing plus a quick side-cutting at 90° to the contralateral side) among groups of CAI, ankle sprain coper, and healthy control. Expected between-group differences in this study are based on previously collected data using the same jump landing/cutting task with a large sample size (n = 200) and previous CAI studies that have examined various uniplanar landing tasks including a drop jump (13), stop jump (40,47), side-cutting jump (39), or lateral hop jump (14). We hypothesized that relative to copers and/or controls, CAI patients will show altered movement strategies in a manner of more inversion and plantarflexion angle (e.g., greater susceptibility to lateral ankle sprains) (13,14,39,40), less knee and hip flexion angle (e.g., extended proximal joint positions) (47), and less knee and hip abduction angle (e.g., a more vertical position of the femur) during the entire stance phase of jump landing/cutting. These altered joint positions would coincide with reduced plantarflexion, eversion, knee extension, knee abduction, hip extension, and hip abduction moment. Moreover, deficits in neuromuscular firing have been reported in this injured population during landing (13,40) or simulated inversion sprain (3,32), which will lead to a reduction in EMG activation of seven lower extremity muscles including tibialis anterior (TA), peroneus longus (PL), medial gastrocnemius (MG), vastus lateralis (VL), medial hamstring (MH), gluteus medius (Gmed), and gluteus maximus (Gmax) in CAI patients relative to copers and/or controls.

METHODS

Research design

This research design was a controlled laboratory trial. Participants completed a single data collection session, which took place in a biomechanics laboratory. The independent variable was group (CAI, coper, control). The dependent variables were frontal and sagittal planes of lower extremity joint angle, net internal joint moment, and EMG activation of the seven muscles.

Sample size

We considered sample size, a priori (Version 3.1.5; G*Power, Kiel, Germany), from a previous study investigating movement variability during drop and stop jump landing tasks indicating that a total of 45 to 66 participants will be necessary to achieve an adequate power (80%) for ankle frontal- and sagittal-plane kinematics between CAI patients and copers (7). Considering alpha, beta, and Cohen’s d values of 0.05, 0.2, and 0.69, respectively, a feasible sample size of 66 participants was chosen.

Participants

A total of 66 physically active individuals, consisting of 22 CAI patients, 22 ankle sprain copers, and 22 healthy controls, were recruited from a university population with an age range of 18 to 35 yr. All participants in the three groups were matched for sex, height, weight, and leg dominance. Participants were identified using validated self-reported questionnaires such as the Functional Ankle Ability Measure-Activities of Daily Living (FAAM-ADL) (10), FAAM-Sports (10), and the Modified Ankle Instability Instrument (MAII) (17). Five (23%) of the 22 CAI patients had unilateral ankle sprains and the rest of 17 CAI patients had bilateral ankle sprains. Ten (45%) of the 22 copers had a single ankle sprain and the rest of 12 copers had unilateral ankle sprains. Group demographics are shown in Table 1.

T1-17
TABLE 1:
Participant demographics.

Subject exclusion criteria were based on a position statement of the International Ankle Consortium (26) including: (i) a history of previous surgery (e.g., bones, joint structures, and nerves), (ii) a history of a fracture in the lower extremity, (iii) a history of neurologic disorders, and (iv) acute injury to musculoskeletal structures of lower extremity joints in the past 3 months. Specific inclusion criteria for the CAI group were based on the position statement of the International Ankle Consortium (26) including: (i) a history of at least two repeated unilateral ankle sprains with the most recent ankle sprain that occurred more than 3 months prior, (ii) a score of <90% on the FAAM-ADL, (iii) a score of <80% on the FAAM-Sport, (iv) at least two “yes” answers on questions four to eight on the MAII, (v) no previous formal rehabilitation for the test ankle, and (vi) a history of physical activity at least 3 d·wk−1 for a total of 90 min in the past 3 months. Specific inclusion criteria for the coper group were based on the recent report for copers (50) including: (i) a history of at least one severe ankle sprain that occurred more than 12 months prior and required use of external ankle supports for at least 1 wk or immobilization and/or non–weight-bearing for at least 3 d, or both, (ii) a return to moderate levels of weight-bearing physical activity without repeated ankle injury in the past 12 months (iii) a score of 100% on the FAAM-ADL, (iv) a score of 100% on the FAAM-Sports, (v) no “yes” answer on questions four to eight on the MAII, (vi) no previous formal rehabilitation for the test ankle, and (vii) a history of physical activity at least 3 d·wk−1 for a total of 90 min in the past 3 months. Specific inclusion criteria for the control group include: (i) no history of ankle sprain injury in their lifetime, (ii) a score of 100% on the FAAM-ADL, (iii) a score of 100% on the FAAM-Sports, (iv) no “yes” answer on questions four to eight on the MAII, and (v) a history of physical activity at least 3 d·wk−1 for a total of 90 min in the past 3 months. All participants provided informed consent before their participation, and the study’s protocol was approved by the university’s institutional review board.

Motion analysis

Motion data were collected using 12 high-speed cameras (240 Hz; Vicon, Oxford, UK). An L-frame (Ergocal—14-mm markers; Vicon) and a calibration wand (240-mm wand to 14-mm markers, Vicon, Oxford, UK) were used for static and dynamic calibration within the capture space. Single and rigid cluster markers were placed on participant's anatomical landmarks bilaterally as described in a previous article (46). Ground reaction force data were collected using an in-ground force plate (1200 Hz; AMTI, Watertown, MA) in the biomechanics laboratory floor. For motion analysis, the entire ground contact time from initial contact to toe-off during jump landing/cutting was collected and analyzed.

EMG

EMG data were collected synchronously through the motion analysis software using wireless surface electrodes (1200 Hz; Delsys, Boston, MA). The electrodes were placed over the TA, PL, MG, VL, MH, Gmed, and Gmax. The electrodes were secured to the skin with a double-sided adhesives and stretch tape (Powerflex; Andover Healthcare Inc., Salisbury, MA). Skin preparation and electrode placement procedures were described in a previous article (28).

A maximal vertical forward jump landing/cutting task

Participants were instructed to “jump as high as they can,” “land on the force plate with the test leg only,” and “side-cut at 90° to the contralateral side as quickly as possible” in a maximal effort while facing forward during movement. Up to 10 practice trials of jump landing/cutting were allowed for each participant to reduce learning effects before actual data collection. Participants stood about 75 to 95 cm (standardized to 50% of participant’s height) away from a center of the force plate. Participants then performed a maximal double-leg vertical forward jump, landed on the force plate with the test leg only, and immediately transitioned to a side-cutting jump at 90° to the contralateral side to complete the task. Three target locations: the starting (standardized to 50% of participant’s height), the landing on the force plate (a circle with a diameter of 15 cm), and the side-cutting jump landing locations (standardized to 65% ± 5% of participant’s height) were marked to ensure consistency during the tasks. After practice trials, each participant performed 10 trials of jump landing/cutting. The mean of the first five trials were used to estimate a range of maximal vertical jump height by adding ±5% the average maximal vertical jump height. The next five successful trials were used for data analysis. A trial was discarded and repeated when participants missed any of the target locations 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 period between each trial to minimize fatigue effects.

Data processing

Details of data processing were described in previous articles (36,46). Spatial trajectories from 51 reflective markers were collected using Vicon Nexus software, and then were imported into Visual 3D (C-Motion, Germantown, MD). The trajectories data were smoothed using a fourth-order low-pass Butterworth filter; a cutoff frequency of 10 Hz was determined by residual analyses (34) for all jump landing/cutting trials. The smoothed marker coordinates were used to calculate 3D ankle, knee, and hip joint kinematics for the jump landing/cutting. A static model was created for each participant using previously described methods (23). 3D joint kinematics were calculated using a Cardan rotation sequence of flexion/extension, abduction/adduction, and internal/external rotation. 3D net internal joint moments using a standard inverse dynamic method were calculated from the synchronized joint kinematics, anthropometric data, and ground reaction force data (15). Force plate data were smoothed using the fourth-order low-pass Butterworth filter (10 Hz) with the trajectories data to overcome inaccuracies in assessment of the joint moments (5).

Reference EMG data were obtained during 3 s of an isometric double-leg squat position (e.g., 45° knee flexion and 30° hip flexion using a goniometer) before the jump landing/cutting task, and landing/cutting EMG data were collected across the entire stance phase. Both the reference and landing/cutting EMG data were imported into Visual 3D software and then smoothed using a root mean square algorithm (moving window = 125 ms). The smoothed landing/cutting EMG data were normalized to the smoothed reference EMG data (e.g., the mean of 3 s of an isometric double-leg squat position) using custom-written algorithms in MatLab. All EMG activation was reported as a percentage of this reference value, which provided us with the most stable and consistent value (36).

In describing jump landing/cutting movement strategies across the entire stance phase (e.g., initial contact to toe-off), we would like to provide details of movement phases. Zero percent of stance corresponds to initial contact, approximately 50% of stance corresponds to peak knee flexion, and 100% of stance corresponds to toe-off from the force plate. Due to time differences during jump landing/cutting between participants and trials, a time normalization process was performed using the landmark registration method (35,37). This method identified important locations (e.g., landmarks) of each individual’s curve before time normalization. Landmarks include the initial contact, maximum (e.g., peaks), minimum, valleys, and toe-off point. After defining landmarks, each landmark of the curve was aligned with other curves at similar time and then the entire curve was matched in time simultaneously (e.g., shrinking or elongating). Therefore, each curve is not just normalized by time, but aligned and matched with other curves’ landmarks. Approximately 0% to 50% of stance would indicate the landing phase as an energy absorption period corresponding to a sudden landing deceleration from a maximal vertical forward jump. Approximately 51% to 100% of stance would indicate the side-cutting phase as an energy propulsion period corresponding to a rapid side-cutting acceleration jump at 90° to the contralateral side.

The maximal vertical jump height was calculated via Vicon Nexus software using a sacral marker (e.g., posterior superior iliac spine) subtracting the height of the sacral marker during the static standing position from the maximal height of the sacral marker during jump landing/cutting.

Statistical analysis

An important feature of this study compared with others was the use of a relatively novel statistical approach: a functional data analysis (RStudio 1.0.136). This functional approach allowed comprehensive evaluation of statistical between-group differences (P < 0.05) and 95% confidence intervals to provide an estimate of effect size across the entire stance phase of jump landing/cutting. Using polynomial functions, this analysis used movement curves from copers or controls as a normal “function” for lower extremity kinematics, kinetics, and EMG activation compared with CAI patients. A function (polynomial curve) is generated for the dependent variables, from all of the trials observed during jump landing/cutting. When 95% confidence intervals do not cross zero, between-group differences were significant. In this study, we used a modified version of the functional data analysis and data processing is consisted of several steps including reparameterization using basis functions, landmark registration (35,37), and a B-spline basis with 19 basis functions to represent each curve in the dataset. Recently, a functional data analysis has more often used in biomechanics with slightly different data processing methods (48).

A one-way ANOVA analysis was performed using JMP Pro 13 software (SAS Institute Inc., Cary, NC) to assess potential between-group differences for the maximal vertical jump height. The alpha level for all comparisons was set to 0.05.

RESULTS

Figure 1 shows sagittal-plane lower extremity kinematics. Relative to copers, CAI patients displayed up to (i) 5.6° less plantarflexion angle during 0% to 25% and 71% to 96% of stance, (ii) 6.3° more knee flexion angle during 5% to 98% of stance, and (iii) 5.6° more hip flexion angle during 3% to 100% of stance. Relative to controls, CAI patients displayed up to (i) 7.4° less plantarflexion angle during 0% to 24% and 83% to 100% of stance, and 2.5° less dorsiflexion angle during 34% to 69% of stance, (ii) 5.6° more knee flexion angle during 5% to 36% and 72% to 88% of stance, and (iii) 6.5° more hip flexion angle during 3% to 100% of stance. Relative to controls, copers displayed up to (i) 2.5° less dorsiflexion angle during 33% to 83% of stance and (ii) 3.3° less knee flexion angle during 37% to 91% of stance.

F1-17
FIGURE 1:
Sagittal-plane lower extremity kinematics across the entire stance phase (0%, initial contact; 100%, toe-off) during a jump landing/cutting task. When 95% confidence intervals (shaded gray area) do not cross zero, between-group differences were significant. Deg, degree; DF, dorsiflexion; PF, plantarflexion; Ext, extension; Flex, flexion.

Figure 2 shows frontal-plane lower extremity kinematics. Relative to copers, CAI patients displayed up to (i) 2.8° less inversion angle during 8% to 77% of stance and (ii) 6° less hip abduction angle during 0% to 100% of stance. Relative to controls, CAI patients displayed up to (i) 2.5° less inversion angle during 6% to 38% of stance, (ii) 2° more knee abduction angle during 0% to 7%, 18% to 42% and 84% to 97% of stance, and (iii) 2° less hip abduction during 10% to 20% of stance. Relative to controls, copers displayed up to (i) 3.5° more knee abduction angle during 4% to 64% of stance and (ii) 4.6° more hip abduction angle during 0% to 98% of stance.

F2-17
FIGURE 2:
Frontal-plane lower extremity kinematics across the entire stance phase (0%, initial contact; 100%, toe-off) during a jump landing/cutting task. When 95% confidence intervals (shaded gray area) do not cross zero, between-group differences were significant. Ev, eversion; Inv, inversion; Add, adduction; Abd, abduction.

Figure 3 shows sagittal-plane lower extremity kinetics. Relative to copers, CAI patients displayed up to (i) 0.15 N·m·kg−1 more plantarflexion moment during 6% to 11% and 83% to 94% of stance and 0.53 N·m·kg−1 less plantarflexion moment during 15% to 72% of stance, (ii) 0.62 N·m·kg−1 more knee extension moment during 9% to 22% and 73% to 91% of stance, and 0.55 N·m·kg−1 less knee extension moment during 27% to 60% of stance, and (iii) 0.7 N·m·kg−1 more hip extension moment during 9% to 20% and 33% to 89% of stance. Relative to controls, CAI patients displayed up to (i) 0.37 N·m·kg−1 more plantarflexion moment during 0% to 12% of stance and 0.54 N·m·kg−1 less plantarflexion moment during 16% to 82% of stance, (ii) 0.75 N·m·kg−1 more knee extension moment during 1% to 22% of stance and 0.82 N·m·kg−1 less knee extension moment during 26% to 74% of stance, and (iii) 0.25 N·m·kg−1 less hip extension moment during 0% to 8% and 23% to 27% of stance, and 0.78 N·m·kg−1 more hip extension moment during 8% to 18% and 32% to 100% of stance. Relative to controls, copers displayed up to (i) 0.22 N·m·kg−1 more plantarflexion during 0% to 12% of stance and 0.22 N·m·kg−1 less plantarflexion moment during 63% to 93% of stance, (ii) 0.18 N·m·kg−1 more extension moment during 0% to 11% of stance and 0.45 N·m·kg−1 less knee extension moment during 42% to 87% of stance, and (iii) 0.23 N·m·kg−1 less hip extension moment during 0% to 9% of stance.

F3-17
FIGURE 3:
Sagittal-plane lower extremity kinetics across the entire stance phase (0%, initial contact; 100%; toe-off) during a jump landing/cutting task. When 95% confidence intervals (shaded gray area) do not cross zero, between-group differences were significant.

Figure 4 shows frontal-plane lower extremity kinetics. Relative to copers, CAI patients displayed up to (i) 0.1 N·m·kg−1 less eversion moment during 8% to 70% of stance and (ii) 0.28 N·m·kg−1 more hip abduction moment during 6% to 19% and 53% to 85% of stance. Relative to controls, CAI patients displayed up to (i) 0.04 N·m·kg−1 more eversion moment during 0% to 7% and 89% to 97% of stance, (ii) 0.23 N·m·kg−1 more knee abduction moment during 3% to 9% and 53% to 90% of stance and 0.13 N·m·kg−1 less knee abduction moment during 31% to 37% of stance, and (iii) 0.34 N·m·kg−1 more hip abduction moment during 4% to 16% of stance and 0.15 N·m·kg−1 less hip abduction moment during 38% to 48% of stance. Relative to controls, copers displayed up to (i) 0.09 N·m·kg−1 more eversion moment during 0% to 35% of stance, (ii) 0.21 N·m·kg−1 more abduction during 2% to 12% and 63% to 89% of stance, and (iii) 0.1 N·m·kg−1 more hip abduction moment during 2% to 6% of stance and 0.25 N·m·kg−1 less hip abduction moment during 32% to 73% of stance.

F4-17
FIGURE 4:
Frontal-plane lower extremity kinetics across the entire stance phase (0%, initial contact; 100%, toe-off) during a jump landing/cutting task. When 95% confidence intervals (shaded gray area) do not cross zero, between-group differences were significant.

Figure 5 shows EMG activation of seven muscles in the lower extremity. Relative to copers, CAI patients displayed up to (i) 3% less TA activation during 41% to 100% of stance, (ii) 14% less PL activation during 0% to 3% and 20% to 97% of stance, (iii) 48% less MG activation during 27% to 65% of stance, (iv) 1.5% less VL activation during 0% to 4% and 39% to 65% of stance, (v) 16% less Gmed activation during 0% to 2% and 35% to 74% of stance, and (vi) 15% less Gmax activation during 0% to 3% and 28% to 72% of stance. Relative to controls, CAI patients displayed up to (i) 3.5% less TA activation during 36% to 100% of stance, (ii) 24% less PL activation during 0% to 66% of stance, (iii) 80% less MG activation during 23% to 65% of stance, (iv) 2% more VL activation during 2% to 21% of stance and 1% less VL activation during 44% to 60% of stance, (v) 13% more Gmed activation during 3% to 14% of stance and 8% less Gmed activation during 35% to 45% of stance, and (vi) 24% less Gmax activation during 24% to 71% of stance. Either no (e.g., TA) or very small EMG activation differences (e.g., PL, MG, VL, MH, Gmed, and Gmax) were observed in all seven muscles between copers and controls.

F5-17
FIGURE 5:
Lower-extremity EMG activation of seven muscles across the entire stance phase (0%, initial contact; 100%, toe-off) during a jump landing/cutting task. When 95% confidence intervals (shaded gray area) do not cross zero, between-group differences were significant. Amp, amplitude; Ref, reference.

Lastly, no between-group differences in the maximum vertical jump height were observed (P = 0.45). The mean maximum vertical jump height was 42.21 cm (95% confidence intervals; 40.00–44.41 cm), 43.99 cm (41.78–46.19 cm), 42.27 cm (40.07–44.48 cm) for the CAI, coper, and control groups, respectively.

DISCUSSION

The purpose of this study was to identify movement strategies during a demanding sports maneuver among groups of CAI, ankle sprain coper, and healthy control by using a robust functional statistical analysis approach, which provides an estimate of effect size (95% confidence intervals) across the entire stance phase of jump landing/cutting between groups. The important finding of this study was that CAI patients displayed a seemingly safe (up to 5.6°–7.4° less plantarflexion and 2.5°–2.8° less inversion angle; Figs. 1 and 2), soft (up to 5.6°–6.3° more knee flexion and 5.6° to 6.5° more hip flexion angle; Fig. 1), and vertical (up to 2°–6° less hip abduction angle; Fig. 2) joint positions during the initial contact to midlanding phase (0%–25% of stance) when compared with copers and/or controls. These joint positions coincided with up to 0.53 to 0.54 N·m·kg−1 less plantarflexion, 0.1 N·m·kg−1 less eversion, 0.62 to 0.75 N·m·kg−1 more knee extension, 0.7 to 0.78 N·m·kg−1 more hip extension, and 0.28 to 0.34 N·m·kg−1 more hip abduction moments during the similar 0% to 25% stance phase (Figs. 3 and 4) compared with copers and/or controls. Furthermore, after the initial 25% of stance, CAI patients displayed up to 6.3° more knee and 6.5° more hip flexion; these positions coincided with up to 0.82 N·m·kg−1 less knee extension and 0.51 N·m·kg−1 more hip extension moments compared with copers and/or controls (Fig. 3). Importantly, up to 2.5° less dorsiflexion angle was observed in both CAI patients and copers relative to controls during the midlanding absorption to mid–side-cutting propulsion phase when the ankle and knee reached its peak range of motion (e.g., 34%–69% of stance for CAI patients, 32% to 87% of stance for copers; Fig. 1). Relative to copers and/or controls, CAI patients revealed up to 3.5% less TA, 24% less PL, 80% less MG, and 16% less Gmed EMG activation during the midlanding to mid–side-cutting phase (25%–75% of stance), which could be due to altered kinematics that were in less muscular demanding positions with the observed reductions in joint moments (Fig. 5). Moreover, up to 1.5% less VL EMG activation during 39% to 65% of stance is likely associated with up to 0.82 N·m·kg−1 less knee extension moment during 26% to 74% of stance, while 24% less Gmax EMG activation during 24% to 71% of stance is conflicting with the observed 0.78 N·m·kg−1 more hip extension moment during 32% to 100% of stance in addition to up to 6.5° more hip flexion angle during 3% to 100% of stance in CAI patients relative to copers and/or controls. All significant differences between CAI patients and copers or controls, respectively for lower extremity kinematics, kinetics, and EMG activation are shown in the supplemental digital content (see Figure, Supplemental Digital Content 1, Significant differences of all measures [sagittal- and frontal-plane lower extremity kinematics, kinetics, and muscle activation], https://links.lww.com/MSS/A911).

A dynamic, multiplanar, maximal vertical forward jump landing/cutting task

Although previous landing studies have identified altered movement strategies during various landing tasks among groups of CAI, coper, and/or control, a research gap exists in the current literature because the studied landing tasks including a drop jump (7,11,13,21), stop jump (7,8,40), vertical jump (6), or lateral hop jump (14), may be oversimplified and uniplanar without direction changes compared with sports activities. This provides limited generalization to an active CAI population. Because of the fact that 75% of all reported ankle sprains occur during landing and side-cutting movement (41), we used a more dynamic, multiplanar, sport-specific task, which contains a component of maximal vertical forward jump, a single-leg sudden deceleration during high impact landing, and immediately followed by a rapid side-cutting acceleration jump at 90° to the contralateral side. This highly demanding sports maneuver simulates movement that often occurs during sports activities and further mimics a typical ankle sprain injury mechanism (41).

Less plantarflexion angle from the initial contact to midlanding phase

Relative to copers and controls, CAI patients revealed a relatively stable landing strategy at the ankle joint, which includes up to 5.6° to 7.4° less plantarflexion angle from initial contact to 25% of stance (Fig. 1). When a rotational force is applied, a more plantarflexed foot position can be more vulnerable to lateral ankle sprain injury as a result of a loose-packed position and its moment of inertia (2). It is important to note that less plantarflexion angle may be due to a voluntary self-defense mechanism used by CAI patients to avoid what they may perceive as an unstable position (11,42), which coincided with 0.53 to 0.54 N·m·kg−1 less plantarflexion moment relative to copers and controls, respectively (Fig. 3). However, less plantarflexion angle at the initial highest impact period may reduce the ability to absorb the impact effectively via eccentrically controlled plantarflexors (53). These results suggest that although CAI patients may have advantages of the relatively stable foot position (up to 5.6°–7.4° less plantarflexion) against lateral ankle sprain injury, this foot position would lose mechanical advantages at impact absorption via plantarflexors. It might be concluded that CAI patients may rely more on the inert characteristics of the bones, ligaments, and connective tissues than muscles to absorb the impact, which potentially increase stress on the tibiotalar (talocrural) articular cartilage surface (27).

Restricted dorsiflexion angle from the midlanding to mid side-cutting phase in both CAI and coper groups

While we observed up to 7.4° less plantarflexion angle from the initial contact to midlanding phase (0%–25% of stance), CAI patients displayed up to 2.5° less dorsiflexion angle than controls during the side-cutting phase. This side-cutting phase corresponds to the period from a rapid landing deceleration to a side-cutting acceleration maneuver when the ankle and knee reached its peak range of motion (e.g., peak dorsiflexion and peak knee flexion). Importantly, our finding is consistent with previous studies, reporting that restricted dorsiflexion angle is common in CAI patients (9,22). Further, restricted dorsiflexion range of motion has been identified as a strong predictor for the risk of ankle sprain injury (12,52). Pope et al. (43) reported that restricted dorsiflexion range of motion resulted in ankle sprain injury five times more likely. It is believed that inversion ankle sprain injury results in increased anterior translation, internal rotation, and superior translation of the talus which potentially prevents a tibiotalar (talocrural) joint from reaching its full dorsiflexion (e.g., osteokinematics restriction) (9). Noteworthy, however, up to 2.5° less dorsiflexion angle was also observed in copers during the similar midlanding to terminal side-cutting phase (33%–83% of stance) compared with controls (Fig. 1). Together, these results of restricted dorsiflexion angle from both CAI and coper groups provide very important clinical implications. For example, in this study, the average number of ankle sprains in the CAI group were 4.1 ± 2.8, whereas the coper group was 2.0 ± 1.1. To be qualified as a coper in this study, participants had at least one severe ankle sprain that required use of external ankle supports for at least 1 wk, or immobilization and/or non–weight-bearing for at least 3 d or both (50). Our data suggest that restricted dorsiflexion angle could be present during dynamic movement in individuals who have successfully (e.g., copers) and unsuccessfully (e.g., CAI patients) dealt with ankle sprain injury. Restricted dorsiflexion range of motion may not be the defining factor associated with the chronic nature of ankle instability. Other deficits, in combination with restricted dorsiflexion range of motion, likely increase the risk for CAI (12,52). Because we selected copers who have never received formal treatment, this restricted dorsiflexion angle could be simply due to a lack of focus on regaining full dorsiflexion range of motion after ankle sprain injury. Because a more dorsiflexed position of the foot is considered as a stable close-packed position when the ankle is fully loaded, our results suggest that the restricted dorsiflexion range of motion during the landing/cutting phase could predispose this injured population to a more vulnerable joint position to recurrent ankle sprains, thereby potentially increasing the risk of ankle sprain injury (12,43,52). Clinicians should focus on restoring full dorsiflexion range of motion after ankle sprain injury through manual therapy (e.g., ankle joint mobilization).

Increased knee and hip flexion angle during most of the landing/cutting phase

The current results revealed interesting sagittal-plane kinematic movement strategies. CAI patients exhibited altered landing strategies by increasing up to 5.6° to 6.3° more knee flexion and 5.5° to 6.5° more hip flexion angle across most of the stance phase of landing/cutting (3%–100% of stance) compared with copers and controls. Increased knee and hip flexion angle can assist in absorbing or dissipating the impact effectively by eccentrically controlled knee and hip extensors over the longer period because the proximal limbs have better anatomical advantages including longer muscle fibers, greater muscle volume and strength than the ankle (55). As DeVita and Skelly (16) reported, the knee and hip joints play a key role in a “soft” landing whereas the ankle and knee joints are more involved in a “stiff” landing. Our data suggest that CAI patients appeared to attenuate the impact by using the proximal joints that were in more flexed positions, which may be due to observed restricted dorsiflexion range of motion in a manner of compensatory movement strategies in sagittal-plane kinematics. Furthermore, the observed jump landing/cutting movement strategies of greater knee and hip flexion angle are supported by the finding of Zhang et al. (56) that as the jump height and loading are increased, the lower extremity angle appeared to be more flexed. Since our movement task is highly demanding and challenging relative to other uniplanar landing tasks (6–8,11,13,14,21,40), CAI patients may try to land safely with more flexed positions of the knee and hip, and protect the unstable ankle against the high impact landing. Although each of CAI landing studies have examined slightly different landing tasks which may lead to different findings, increased hip flexion angle might be a common landing strategy used by CAI patients. Specifically, increased hip flexion angle from prelanding to postlanding has been reported in patients with acute ankle sprain injury within 2 wk (18), with first-time ankle sprain injury after 6 months (19), with mechanical ankle instability (8), and with CAI (39) when compared with controls. It is possible that since the unstable ankle joint may not adequately support the high impact on landing, a greater compensation at the hip joint may be necessary to achieve overall body equilibrium to safely control the jump landing/cutting task in this study. Our findings indicate that CAI patients may adapt altered movement strategy in a manner of redistributing the impact from the unstable distal joint (e.g., ankle) to more stable proximal joints (e.g., knee and hip) due to mechanical advantages of the proximal joints (e.g., longer muscle fibers, greater muscle volume and strength) (56). However, further research is necessary to determine whether this altered movement strategy in sagittal-plane lower extremity kinematics helps CAI patients reduce the risk of recurrent ankle sprain injury, or what other consequences may stem from this strategy.

Sagittal-plane joint moment movement strategies

The result of this study demonstrated unique sagittal-plane moment strategies. From the initial contact to early landing phase (0%–20% of stance), CAI patients exhibited up to 0.15 to 0.37 N·m·kg−1 more plantarflexion, 0.62 to 0.75 N·m·kg−1 more knee extension, and 0.7 to 0.78 N·m·kg−1 more hip extension moments compared with copers and controls, which might be an attempt to control the high impact landing task eccentrically (Fig. 3). However, after the early landing phase (0%–20% of stance), CAI patients displayed up to 0.53 to 0.54 N·m·kg−1 less plantarflexion and 0.55 to 0.82 N·m·kg−1 less knee extension moment while maintaining 0.7 to 0.78 N·m·kg−1 more hip extension moment during the midlanding to mid–side-cutting phase (25%–75% of stance; Fig. 3) when compared with copers and controls. Although the observed reduction in plantarflexion moment and MG EMG activation are likely associated with up to 2.5° less dorsiflexion angle in CAI patients relative to copers and controls, reduced both knee extension moment and VL EMG activation were in conflict with the observed increased knee flexion angle during the midlanding to mid–side-cutting phase (25%–65% of stance). It is possible that up to 0.55 to 0.82 N·m·kg−1 less knee extension moment and 1% to 1.5% less VL EMG activation as opposed to 5.6° to 6.3° more knee flexion angle might be indicative of abnormal neural activation of knee extensors in CAI patients or they may not use knee extensors primarily to control the jump landing/cutting task, both of which potentially increase compensation to the other ankle and hip joints.

While moments at the ankle and knee were decreased, up to 0.7 to 0.78 N·m·kg−1 more hip extension moment was observed across most of the landing/cutting phase (8%–100% of stance) in CAI patients relative to copers and/or controls. This finding suggests a compensatory load redistribution strategy from the unstable distal (e.g., ankle) to proximal (e.g., hip) joints, indicating that the hip joint in the sagittal plane may play an important role in controlling the jump landing/cutting task. However, the observed 15% to 24% less Gmax EMG activation during the similar phase (24%–72% of stance) may indicate abnormal neural activation of hip extensors in CAI patients compared with copers and/or controls (Fig. 5). Our finding is consistent with a previous study (21) showing that relative to copers, CAI patients displayed up to 0.2 N·m·kg−1 more hip extension moment during 136 to 156 ms postlanding, and 5° more hip flexion angle from 148 ms prelanding to 4 ms postlanding during a single-leg drop landing task. The authors concluded that the hip joint may play a key role in attenuating impact loads and preventing the lower limb from collapsing, however it remains still unclear whether this altered hip strategy increases risk of ankle injury in this study’s data. Our data suggest that CAI patients may rely more on the hip in the sagittal plane to resist lower extremity landing moments as the hip joint has greater musculature supports (e.g., Gmax) than the unstable ankle joint (55). Further research is needed to examine whether this hip dominant strategy (e.g., greater hip flexion angle and hip extension moment) is associated with the risk of ankle sprain injury during jump landing/cutting.

Less inversion angle during most of the landing/cutting phase

Several studies have investigated frontal-plane ankle kinematics during various landing tasks because a majority of ankle sprains often occur during lateral movement (29,41). However, findings of individual studies are inconclusive as to which foot position in the frontal plane increases risk of recurrent ankle sprain injury. Previous studies reported increased inversion angle in CAI patients across various phases from prelanding to postlanding during different landing tasks including a side-cutting jump at 45° (39), drop jump (13,19), lateral hop jump (14), and stop jump (40), whereas some studies demonstrated no ankle kinematic differences during single-leg vertical jump landing in CAI patients compared with the coper group (21) or coper and control groups (6). Our findings are contrary to the results of previous studies, as CAI patients had up to 2.5° to 2.8° less inversion angle during most of the stance phase (9%–77% of stance) than copers and controls (6%–38% of stance). Although our results are in conflict with previous studies, more maximum eversion angle has been reported in patients with mechanical ankle instability during drop jump landing compared with copers (7). Indeed, many factors may play a role in the disparity between findings. First, the nature of the movement should be considered. The highly demanding task that participants completed in this study used a maximal vertical jump, immediately transitioning to a side-cutting jump. The high loads, demand for stiffness, and relative risk to the participants may result in a voluntary movement strategy, which participants might have perceived, would be most protective. Further, it should be considered that movement strategies are likely individualized given the available constraints (51), and the participants observed in this study tended to show a strategy of less inversion. This could account for the diverse findings reported in the literature. Finally, it should be noted that our data were analyzed as a curve (e.g., polynomial function) across the entire stance phase using a functional data analysis approach as opposed to a discrete time point(s) such as initial contact or peak, which would not allow for the entire evaluation of the movement.

When it comes to frontal-plane ankle moment and PL EMG activation, CAI patients displayed up to 0.1 N·m·kg−1 less eversion moment during 8% to 70% of stance and 14% less PL EMG activation during 20% to 97% of stance relative to copers. The reduced eversion moment and PL EMG activation might be due to the 2.8° less inverted position of the foot where a more vertical tibia position in the frontal plane would reduce the external torque at the ankle, thereby decreasing the muscular demands on the evertors to eccentrically control the inversion motion while the foot is firmly fixed to the ground during stance. Future research is needed to determine whether the less inverted foot position along with the reduced moment and EMG activation may be successful at avoiding repeated ankle sprain injury and what the consequences might be.

Frontal-plane hip angle and moment movement strategies

Although previous CAI studies (8,21,39) have shown altered sagittal-plane hip movement strategies, changes in frontal-plane hip biomechanics were relatively small. However, the findings of this study exhibited obvious alterations in frontal-plane hip movement strategies as CAI patients displayed up to 6° less hip abduction angle (e.g., a more vertical position of the femur) across the entire stance phase (0%–100% of stance), which coincided with 0.28 N·m·kg−1 more hip abduction moment during 6% to 19% and 53% to 85% of stance compared with copers. CAI patients also showed 2° less hip abduction angle during early landing (10%–20% of stance) relative to controls. These results indicate that CAI patients adopted a more vertical position of the femur in the frontal plane, allowing them to maintain their center of mass closer to the center of pressure. When this finding is combined with up to 2.5° to 2.8° less inversion angle in this study relative to copers and/or controls, CAI patients utilized what they may have perceived as a safe frontal-plane landing strategy in an attempt to achieve a stable vertical position in the lower extremity. However, it is important to note that as the lower limbs are connected via kinetic and kinematic chains, altered frontal-plane hip movement strategies affect the position of the foot (45), and thus the observed 8% to 16% less Gmed EMG activation may decrease frontal-plane hip stability, thereby changing the position of the foot during jump landing/cutting (Fig. 5). Further, as Beckman et al. (3) reported that neuromuscular firing patterns at the ankle and hip were simultaneously altered after ankle sprain injury, and Friel et al. (24) also reported Gmed weakness in CAI patients, CAI patients may tend to place the hip into a less muscular demanding position in the frontal plane due to existing hip abductor dysfunction.

Clinical Implications

This study demonstrated that CAI patients displayed altered movement strategies, specifically lower extremity kinematics, kinetics, and EMG activation across various portions of jump landing/cutting compared with copers and/or controls. It is important to note that both CAI patients and copers who have a history of ankle sprain injury exhibited up to 2.5° restricted dorsiflexion range of motion during the midlanding to mid–side-cutting phase. Because restricted ankle dorsiflexion range of motion makes ankle sprains five times more likely (43), clinicians should focus on restoring full dorsiflexion range of motion using open chain posterior talar glide, talocrural joint mobilization with movement (e.g., weight-bearing lunge) (49), and/or calf stretching (44) after ankle sprain injury to reduce risk of ankle reinjury. Moreover, as the lower extremity is connected as kinetic and kinematic chains, clinicians should recognize that a single ankle joint problem would alter entire lower extremity biomechanics during functional movement. As such, the clinicians should consider a movement quality based, multijoint rehabilitation program for this injured population. Further, as a majority of ankle sprains occur during landing and side-cutting (41), appropriate joint positions and posture adjustment before high impact landing are critical in reducing risk of ankle sprains. Because changes in feedforward (proactive) control mechanisms have been observed during the prelanding and initial landing phase in CAI patients (11,13,14,40), interventions should consider feedforward modulation during the flight phase of landing. For example, preactivation of lower extremity musculature would help the body attenuate high impact landing effectively, and preactivation of peroneus longus, brevis, and TA would place the foot into more stable positions (less inversion and plantarflexion) against potential lateral ankle sprain injury before landing.

Limitations of the Study

We acknowledge two limitations in this study. First, there were very small mean differences in VL and TA EMG activation, whereas other muscles revealed up to 80% differences, especially in the MG. Because we used an isometric squat position as a reference position for EMG normalization, the TA and VL muscles were most activated in this position. Conversely, muscles not as active during the isometric squat reference position provided little to the normalization process, inflating relative differences. It is possible that our EMG normalization process created a scaling issue as it related to relative differences. Although mean differences were small in this study in particular muscles (e.g., the TA and VL), and the reader should consider the magnitude, we believe this could be due to our EMG normalizing process, which had an effect on the scaling. Second, altered feedforward control mechanism during the flight phase of landing has observed in this injured population (11,13,14,40) and prelanding biomechanics (preactivation of lower extremity musculature and joint positions) could be likely associated with altered load, stiffness, and/or positions of lower extremity joints at initial contact during landing. However, we did not analyze prelanding data in this article so we acknowledge this as a limitation.

CONCLUSIONS

In conclusion, the results of this study confirm altered movement strategies during a sports maneuver in CAI patients relative to copers and/or controls. CAI patients adopted landing positions of less inversion, less plantarflexion, more knee flexion, more hip flexion, and less hip abduction angle during the initial contact to midlanding phase (0%–25% of stance) compared with copers and controls. After the initial 25% of stance of landing, compared with controls both CAI patients and copers exhibited up to 2.5° less dorsiflexion angle during the midlanding to mid side-cutting phase when the ankle and knee reached its peak range of motion, and were fully loaded. Together, relative to copers and/or controls, overall landing strategies used by CAI patients may be an attempt to avoid self-perceived dangerous positions at the ankle and to have more flexed positions of the knee and hip along with a more vertical position of the femur in the frontal plane as a self-defense mechanism. Sagittal joint positions appeared to increase the external torque on the knee and hip extensors. Frontal joint positions seemed to reduce the muscular demands on evertor and hip abductor muscles along with observed reduced PL and Gmed activation, which may be indicative of sensorimotor deficiencies in these muscle groups in CAI patients. The observed reductions in TA, PL, MG, and Gmed EMG activation could be due to altered kinematics that were in less muscular demanding positions, while the observed reductions in VL and Gmax EMG activation may be indicative of abnormal neural activation as opposed to more muscular demanding positions of knee and hip flexion.

This study was supported by a doctoral student grant from the National Athletic Trainers’ Association (NATA) Research & Education Foundation (15DGP011). The authors declare no conflict of interest. The results of this study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

REFERENCES

1. Anandacoomarasamy A, Barnsley L. Long term outcomes of inversion ankle injuries. Br J Sports Med. 2005;39(3):14.
2. Barrett J, Bilisko T. The role of shoes in the prevention of ankle sprains. Sports Med. 1995;20(4):277–80.
3. Beckman SM, Buchanan TS. Ankle inversion injury and hypermobility: effect on hip and ankle muscle electromyography onset latency. Arch Phys Med Rehabil. 1995;76(12):1138–43.
4. Beynnon B, Murphy D, Alosa D. Predictive factors for lateral ankle sprains: a literature review. J Athl Train. 2002;37(4):376–80.
5. Bisseling RW, Hof AL. Handling of impact forces in inverse dynamics. J Biomech. 2006;39(13):2438–44.
6. Brown C, Bowser B, Simpson KJ. Movement variability during single leg jump landings in individuals with and without chronic ankle instability. Clin Biomech (Bristol, Avon). 2012;27(1):52–63.
7. Brown C, Padua D, Marshall SW, Guskiewicz K. Individuals with mechanical ankle instability exhibit different motion patterns than those with functional ankle instability and ankle sprain copers. Clin Biomech (Bristol, Avon). 2008;23(6):822–31.
8. Brown CN, Padua DA, Marshall SW, Guskiewicz KM. Hip kinematics during a stop-jump task in patients with chronic ankle instability. J Athl Train. 2011;46(5):461–7.
9. Caputo AM, Lee JY, Spritzer CE, et al. In vivo kinematics of the tibiotalar joint after lateral ankle instability. Am J Sports Med. 2009;37(11):2241–8.
10. Carcia CR, Martin RL, Drouin JM. Validity of the Foot and Ankle Ability Measure in athletes with chronic ankle instability. J Athl Train. 2008;43(2):179–83.
11. Caulfield BM, Garrett M. Functional instability of the ankle: differences in patterns of ankle and knee movement prior to and post landing in a single leg jump. Int J Sports Med. 2002;23(1):64–8.
12. de Noronha M, Refshauge KM, Herbert RD, Kilbreath SL, Hertel J. Do voluntary strength, proprioception, range of motion, or postural sway predict occurrence of lateral ankle sprain? Br J Sports Med. 2006;40(10):824–8 discussion 8.
13. Delahunt E, Monaghan K, Caulfield B. Changes in lower limb kinematics, kinetics, and muscle activity in subjects with functional instability of the ankle joint during a single leg drop jump. J Orthop Res. 2006;24(10):1991–2000.
14. Delahunt E, Monaghan K, Caulfield B. Ankle function during hopping in subjects with functional instability of the ankle joint. Scand J Med Sci Sports. 2007;17(6):641–8.
15. Dempster WT. Space Requirements of the Seated Operator, Geometrical, Kinematic, and Mechanical Aspects of the Body with Special Reference to the Limbs. Wright-Patterson Air Force Base, OH: WADC Technical Report (TR-55-159); 1955.
16. Devita P, Skelly WA. Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Med Sci Sports Exerc. 1992;24(1):108–15.
17. Docherty CL, Gansneder BM, Arnold BL, Hurwitz SR. Development and reliability of the ankle instability instrument. J Athl Train. 2006;41(2):154–8.
18. Doherty C, Bleakley C, Hertel J, Caulfield B, Ryan J, Delahunt E. Single-leg drop landing motor control strategies following acute ankle sprain injury. Scand J Med Sci Sports. 2015;25(4):525–33.
19. Doherty C, Bleakley C, Hertel J, Caulfield B, Ryan J, Delahunt E. Single-leg drop landing movement strategies 6 months following first-time acute lateral ankle sprain injury. Scand J Med Sci Sports. 2015;25(6):806–17.
20. Doherty C, Bleakley C, Hertel J, Caulfield B, Ryan J, Delahunt E. Recovery from a first-time lateral ankle sprain and the predictors of chronic ankle instability: a prospective cohort analysis. Am J Sports Med. 2016;44(4):995–1003.
21. Doherty C, Bleakley C, Hertel J, Caulfield B, Ryan J, Delahunt E. Single-leg drop landing movement strategies in participants with chronic ankle instability compared with lateral ankle sprain 'copers'. Knee Surg Sports Traumatol Arthrosc. 2016;24(4):1049–59.
22. Drewes LK, McKeon PO, Kerrigan DC, Hertel J. Dorsiflexion deficit during jogging with chronic ankle instability. J Sci Med Sport. 2009;12(6):685–7.
23. Ford KR, Shapiro R, Myer GD, Van Den Bogert AJ, Hewett TE. Longitudinal sex differences during landing in knee abduction in young athletes. Med Sci Sports Exerc. 2010;42(10):1923–31.
24. Friel K, McLean N, Myers C, Caceres M. Ipsilateral hip abductor weakness after inversion ankle sprain. J Athl Train. 2006;41(1):74–8.
25. Gerber JP, Williams GN, Scoville CR, Arciero RA, Taylor DC. Persistent disability associated with ankle sprains: a prospective examination of an athletic population. Foot Ankle Int. 1998;19(10):653–60.
26. Gribble PA, Delahunt E, Bleakley C, et al. Selection criteria for patients with chronic ankle instability in controlled research: a position statement of the International Ankle Consortium. Br J Sports Med. 2014;48(13):1014–8 bjsports-2013-093175.
27. Grodzinsky AJ, Levenston ME, Jin M, Frank EH. Cartilage tissue remodeling in response to mechanical forces. Annu Rev Biomed Eng. 2000;2:691–713.
28. Hermens HJ, Freriks B, Disselhorst-Klug C, Rau G. Development of recommendations for SEMG sensors and sensor placement procedures. J Electromyogr Kinesiol. 2000;10(5):361–74.
29. Hertel J. Functional anatomy, pathomechanics, and pathophysiology of lateral ankle instability. J Athl Train. 2002;37(4):364–75.
30. Hintermann B, Boss A, Schäfer D. Arthroscopic findings in patients with chronic ankle instability. Am J Sports Med. 2002;30(3):402–9.
31. Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for 15 sports: summary and recommendations for injury prevention initiatives. J Athl Train. 2007;42(2):311–9.
32. Hopkins JT, Brown TN, Christensen L, Palmieri-Smith RM. Deficits in peroneal latency and electromechanical delay in patients with functional ankle instability. J Orthop Res. 2009;27(12):1541–6.
33. Hubbard TJ, Kramer LC, Denegar CR, Hertel J. Contributing factors to chronic ankle instability. Foot Ankle Int. 2007;28(3):343–54.
34. Jackson KM. Fitting of mathematical functions to biomechanical data. IEEE Trans Biomed Eng. 1979;26(2):122–4.
35. James GM. Curve alignment by moments. Ann Appl Stat. 2007;1(2):480–501.
36. Kim H, Son S, Seeley MK, Hopkins JT. Functional fatigue alters lower-extremity neuromechanics during a forward-side jump. Int J Sports Med. 2015;36(14):1192–200.
37. Kneip A, Gasser T. Statistical tools to analyze data representing a sample of curves. Ann Statist. 1992;20(3):1266–305.
38. Konradsen L, Bech L, Ehrenbjerg M, Nickelsen T. Seven years follow-up after ankle inversion trauma. Scand J Med Sci Sports. 2002;12(3):129–35.
39. Koshino Y, Ishida T, Yamanaka M, et al. Kinematics and muscle activities of the lower limb during a side-cutting task in subjects with chronic ankle instability. Knee Surg Sports Traumatol Arthrosc. 2016;24(4):1071–80.
40. Lin CF, Chen CY, Lin CW. Dynamic ankle control in athletes with ankle instability during sports maneuvers. Am J Sports Med. 2011;39(9):2007–15.
41. McKay GD, Goldie PA, Payne WR, Oakes BW. Ankle injuries in basketball: injury rate and risk factors. Br J Sports Med. 2001;35(2):103–8.
42. Pope M, Chinn L, Mullineaux D, McKeon PO, Drewes L, Hertel J. Spatial postural control alterations with chronic ankle instability. Gait Posture. 2011;34(2):154–8.
43. Pope R, Herbert R, Kirwan J. Effects of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in Army recruits. Aust J Physiother. 1998;44(3):165–72.
44. Radford JA, Burns J, Buchbinder R, Landorf KB, Cook C. Does stretching increase ankle dorsiflexion range of motion? A systematic review. Br J Sports Med. 2006;40(10):870–5.
45. Sadeghi H, Sadeghi S, Prince F, Allard P, Labelle H, Vaughan CL. Functional roles of ankle and hip sagittal muscle moments in able-bodied gait. Clin Biomech (Bristol, Avon). 2001;16(8): 688–95.
46. Son SJ, Kim H, Seeley MK, Hopkins JT. Efficacy of sensory transcutaneous electrical nerve stimulation on perceived pain and gait patterns in individuals with experimental knee pain. Arch Phys Med Rehabil. 2017;98(1):25–35.
47. Terada M, Pietrosimone B, Gribble PA. Individuals with chronic ankle instability exhibit altered landing knee kinematics: potential link with the mechanism of loading for the anterior cruciate ligament. Clin Biomech (Bristol, Avon). 2014;29(10):1125–30.
48. Ullah S, Finch CF. Applications of functional data analysis: a systematic review. BMC Med Res Methodol. 2013;13:43.
49. Vicenzino B, Branjerdporn M, Teys P, Jordan K. Initial changes in posterior talar glide and dorsiflexion of the ankle after mobilization with movement in individuals with recurrent ankle sprain. J Orthop Sports Phys Ther. 2006;36(7):464–71.
50. Wikstrom EA, Brown CN. Minimum reporting standards for copers in chronic ankle instability research. Sports Med. 2014;44(2):251–68.
51. Wikstrom EA, Hubbard-Turner T, McKeon PO. Understanding and treating lateral ankle sprains and their consequences: a constraints-based approach. Sports Med. 2013;43(6):385–93.
52. Willems TM, Witvrouw E, Delbaere K, Mahieu N, De Bourdeaudhuij I, De Clercq D. Intrinsic risk factors for inversion ankle sprains in male subjects: a prospective study. Am J Sports Med. 2005;33(3):415–23.
53. Winters JM, Woo SL eds. Multiple muscle systems: biomechanics and movement organization. New York, NY: Springer Science & Business Media; 2012. pp. 568–77.
54. Witchalls J, Blanch P, Waddington G, Adams R. Intrinsic functional deficits associated with increased risk of ankle injuries: a systematic review with meta-analysis. Br J Sports Med. 2012;46(7):515–23.
55. Yamaguchi G, Sawa A, Moran D, Fessler M, Winters J. A survey of human musculotendon actuator parameters. In: Multiple muscle systems: Biomechanics and movement orgarnization. New York, NY: Springer Science & Business Media; 1990:717–73.
56. Zhang SN, Bates BT, Dufek JS. Contributions of lower extremity joints to energy dissipation during landings. Med Sci Sports Exerc. 2000;32(4):812–9.
Keywords:

MOVEMENT PATTERN; JUMP LANDING; FUNCTIONAL MOVEMENT; LOWER EXTREMITY; KINEMATICS; KINETICS; ELECTROMYOGRAPHY

Supplemental Digital Content

© 2017 American College of Sports Medicine