Comparison of Selected Lateral Cutting Activities Used to Assess ACL Injury Risk

Transcription

1 Journal of Applied Biomechanics, 2009, 25, Human Kinetics, Inc. Comparison of Selected Lateral Cutting Activities Used to Assess ACL Injury Risk Kristian M. O Connor, Sarika K. Monteiro, and Ian A. Hoelker University of Wisconsin Milwaukee The purpose of this study was to compare the knee joint dynamics for males and females performing constrained cutting tasks to an unanticipated running and cutting maneuver. Sixteen male and 17 female recreational athletes were recruited to perform four cutting tasks; unanticipated run and cut (CUT), stride land and cut (SLC), far box-land and cut (FLC), and close box-land and cut (CLC). Three-dimensional knee joint kinematics and kinetics were recorded. Data were compared across gender and task with a 2 4 ANOVA (p <.05), and a factor analysis was performed to examine task relationships. There were significant group mean differences between the tasks and across genders. The factor analysis revealed high correlations between the three constrained tasks, but for variables typically associated with ACL injury risk there was a poor relationship to the CUT task. This was particularly true for the frontal plane variables. The constrained tasks were only moderately useful in predicting cutting mechanics. Keywords: anterior cruciate ligament, sidestep cutting, lower limb, gender Injuries to the anterior cruciate ligament (ACL) are alarmingly common for female athletes, in which they occur at a rate between two and seven times greater than for males (Arendt et al., 1999; de Loes et al., 2000). Many of these injuries occur in noncontact situations, particularly during changes in direction as happens during sidestep cutting maneuvers (Boden et al., 2000). The authors are with the Neuromechanics Laboratory, Department of Human Movement Sciences, University of Wisconsin Milwaukee, Milwaukee, WI. Given the prevalence of noncontact ACL injuries when performing this maneuver, the mechanics of the knee during a running and cutting maneuver and the potential for associated gender differences have received a great deal of attention. Appropriate neuromuscular control is required to avoid extreme joint positions, and the results of previous studies suggest that female athletes display knee joint mechanics during cutting that may increase the risk of injury (Malinzak et al., 2001; Pollard et al., 2004; Sigward & Powers, 2006). In particular, these studies have reported that females flex less (Malinzak et al., 2001; McLean et al., 2005b), abduct more (Malinzak et al., 2001; McLean et al., 2004), and experience a greater peak internal adduction moment at the knee (McLean et al., 2005a) during stance. These gender differences are also consistent with the findings of Hewett et al. (2005), who reported that subsequently injured females athletes exhibited less knee flexion and greater knee abduction during a two-leg drop jump (Hewett et al., 2005). In addition, increased ACL loading has been observed when internal rotation forces are applied to the tibia (Li et al., 1999; Markolf et al., 1995), and excessive rotation has been qualitatively identified as commonly occurring during noncontact ACL injuries (Boden et al., 2000). While not validated, it has been suggested that an unanticipated cutting maneuver may elicit a response best reflective of movement patterns during play (Besier et al., 2001a, 2003). These studies reported greater loading and muscle activity around the knee when an unanticipated cutting maneuver was employed. Aside from Pollard et al. (2004), most running and cutting studies have used anticipated tasks (Malinzak et al., 2001; McLean et al., 1999, 2004). There are several examples of more constrained tasks to explore knee dynamics. Hass et al. (2003, 2005) used single-leg box and stride landing tasks followed by a lateral cut and reported postpubescent mechanical changes that may relate to increased injury risk. Ford et al. (2005) also employed a lateral box landing maneuver that included an unanticipated response. Simpler landing and jumping protocols 9

2 10 O Connor, Monteiro, and Hoelker have also been used by several for use in large-scale data collections and postfatigue assessments (Augustsson et al., 2006; Chappell et al., 2005; Fagenbaum & Darling, 2003; Hewett et al., 2005; McLean et al., 2007) The constrained tasks are advantageous because they can be collected more quickly. Tasks originating from a box or a single stride are easier to experimentally control and avoid issues with accurate speed control and foot placement. Given the prevalence of injuries during cutting, tasks with lateral movement may provide more direct insight into injury risk than studies that used single-plane landing and jumping tasks. It is unknown, however, whether the knee dynamics observed by Hass et al. (2003, 2005) can be directly related to those of the more demanding running and cutting task. For example, the greater horizontal velocity of the center of mass for a running and cutting maneuver will likely cause substantially greater loading and potentially lead to qualitatively different dynamic patterns. Therefore, the question remains as to whether a constrained task can yield critical information about an individual s knee mechanics during a running and cutting maneuver, which may better approximate dynamics during play. McLean et al. (2005b) examined the possible utility of a constrained land and cut task in understanding knee dynamics during play. They compared the lower extremity mechanics of an anticipated cut with those of a jumpland and a shuttle run. While peak knee abduction differed between genders, there was a high correlation between peak knee abduction across tasks. Since it has been previously demonstrated that an unanticipated cutting maneuver resulted in different joint mechanics and muscle activation patterns (Besier et al., 2001a, 2003), the results of McLean et al. (2005b) do not necessarily demonstrate that these tasks can be used to approximate knee dynamics associated with the inherent randomness of game play. Given the wide variety of protocols currently employed in the study of knee mechanics and their relationship to ACL injury risk, there is a need to understand how the nature of the experimental protocol affects the conclusions reached. Ideally, a constrained task will produce kinematic and kinetic patterns that, while likely different in magnitude, are at least correlated to less constrained tasks such as running and cutting. To explore this relationship, the purpose of this study was to compare the knee joint kinematics and kinetics for individuals performing side cutting maneuvers starting from three static positions to an unanticipated running and cutting maneuver. It was hypothesized that the magnitudes of kinematic and kinetic parameters for constrained tasks would differ from an unanticipated cutting maneuver (CUT), but that the constrained task parameters would correlate highly with the CUT task. It was also hypothesized that a constrained task that included both a vertical and horizontal impact velocity (far land and cut FLC) would best correlate to the CUT task and that gender would not affect the degree of correlation between tasks. Methods Sixteen recreationally active (defined as physically active for 30 min at least 3 days per week) males (22.7 ± 2.7 years, 86.1 ± 13.5 kg, 1.81 ± 0.08 m) and 17 recreationally active females (20.9 ± 1.5 years, 62.9 ± 5.9 kg, 1.68 ± 0.06 m) volunteered to participate in this study. A power analysis was performed based on pilot data to detect a between-subject 2 frontal plane difference with an alpha of.05 and 80% power. The clinical significance of this kinematic threshold was supported by the results of Withrow et al. (2006). Thirty total subjects (15 of each gender) were sufficient to detect this difference, and additional subjects were collected to account for possible dropouts. A background questionnaire to screen for health status and an informed consent form were read and signed by all volunteers before the beginning of the study. The protocol was approved by the university institutional review board. Volunteers were accepted in the study if they had not suffered a knee injury requiring surgery and have been free of any other injury within the previous six months that could interfere with normal movements. Subjects were also asked how many years they competed (if any) in competitive team sports. Males participated 11.4 ± 3.4 years, and females participated 6.4 ± 4.0 years. To track lower extremity kinematics, twenty-five light-reflecting skin markers were placed on the participants (Figure 1). Markers used exclusively for the standing calibration trial (calibration markers) included the left and right iliac crests and greater trochanters, and stance leg lateral and medial femoral epicondyles, lateral and medial malleoli, and first and fifth metatarsal heads. Additional tracking markers were placed on the left and right antero-superior iliac spines, the sacrum, two four-marker plates attached to elastic Velcro straps on the thigh and shank segments, and a marker triad secured on the heel counter of the shoe. The calibration markers were removed after standing calibration trial completion. Participants wore standard laboratory footwear (Saucony Jazz, Lexington, MA). Marker trajectories were collected at 200 Hz with a seven-camera Motion Analysis Eagle System (Santa Rosa, CA, USA), and ground reaction forces were collected synchronously at 1000 Hz with an AMTI OR6 5 force plate (Watertown, MA, USA). Running speed was monitored through two gates 2.5 m apart positioned along the runway just before the athlete reached the force plate. There were two sessions for this study. During the first session, subjects practiced the required tasks until they could comfortably complete the four tasks. Subject also completed three maximum two-leg countermovement jumps on the force plate to calculate jump height. During this session, subjects practiced the four tasks: an unanticipated running and cutting maneuver, and three discrete single-leg landing tasks incorporating an immediate 90 lateral cut (Figure 2). All tasks were performed on the subject s dominant leg, which was determined from the subject s preferred jumping leg. This resulted

3 Comparison of Cutting Mechanics 11 Figure 1 Frontal and sagittal plane views of the locations of retro-reflective markers. Markers on the right and left ASIS and PSIS, and marker plates on thigh, leg, and foot remained for dynamic trials, whereas the rest were removed after the standing calibration trial. in 29 right limb and four left limb dominant subjects. For the unanticipated cutting maneuver (CUT), subjects approached the force plate at m/s and were presented with a visual stimulus to either continue running straight ahead, stop quickly, or side cut 45. The speed is similar to the range ( m/s) used by McLean et al. (2004), and the cutting angle and visual stimulus were based on the protocol used by Pollard et al. (2004). The cutting angle was guided by a 1-m wide runway oriented 45 from the line of progression (restricting movement between ~35 and 55 ), and trials were deemed successful if the subject was able to remain on the runway. The visual stimulus was triggered by the first timing gate that was ~3 m before reaching the force plate. The stride-land and cut maneuver (SLC) required subjects to leap from the nondominant to the dominant leg from level ground (Figure 2a). Subjects initiated the task from as far as possible from the force plate while still being able to complete the task, which was based on the task used by Hass et al. (2003). The subjects also performed a far-land and cut (FLC) maneuver, which was initiated from a box height equal to their maximum countermovement jump height at a distance equal to three times the box height away from the force plate (Figure 2b). The close-land and cut (CLC) maneuver was initiated from the same box height used for the FLC with the box placed a distance to the center of the force plate equivalent to the box height (Figure 2c). The testing session was scheduled within one week of the practice session. Following a 5-min jogging warm-up, markers were placed on the participants, and a 2-s calibration trial was collected. Each participant then completed five trials of each cutting task. These trials were considered valid only if the stance foot was entirely on the force plate. For logistical reasons, the CUT was performed first, but the order of the three static landing tasks was subsequently randomized. These four tasks were part of a larger data collection protocol where several single- and two-leg landing and jumping activities were recorded during a session that lasted ~90 min (data not presented here). The CUT task was performed at the beginning of the protocol to minimize effects of mental fatigue, allowing greater success in responding to the visual stimulus. Custom-made software calculated countermovement jump height from the ground reaction force (GRF) curve (Luhtanen & Komi, 1978). The highest jump height was used to set the landing height for the FLC

4 12 Figure 2 (a c) Initial position for the three constrained land and cut tasks: (a) stride land and cut (SLC), (b) far land and cut (FLC), and (c) close land and cut (CLC)

5 Comparison of Cutting Mechanics 13 and CLC maneuvers. Data reduction was implemented with Visual3D (v3.89, C-Motion, Inc. Rockville, MD). The raw three-dimensional coordinate data of all markers were filtered using a fourth-order, zero lag, recursive Butterworth filter with a cutoff frequency of 12 Hz. This was consistent with the 10- to 15-Hz range that has been used by previous studies for analyzing cutting maneuvers (Besier et al., 2001b; Malinzak et al., 2001). Righthanded Cartesian local coordinate systems (LCS) for the pelvis, thigh, shank, and foot segments of the support leg were defined to describe position and orientation of each segment. Three-dimensional knee angles were calculated using a joint coordinate system approach (Grood & Suntay, 1983), and all joint angles were reported relative to the standing calibration position. Joint centers were given by the midpoint between the medial and lateral calibration markers for the knee and ankle joints (Grood & Suntay, 1983; Wu et al., 2002). Body segment parameters were estimated from Dempster (1955), and joint kinetics were calculated using a Newton Euler approach (Bresler & Frankel, 1950). Internal knee joint moments were reported in the tibia reference frame. The beginning and end of the support phase of cutting were determined by the instant when the vertical GRF exceeded and fell below 20 N, respectively. Processed data were time normalized to 101 data points. For presentation purposes, the 101 data points were scaled by the average stance time for that task and gender. To assess the relationship of the knee mechanics between the four tasks, the touchdown (TD) angles and range of motion (ROM) of the knee were reported in all three planes, as well as the internal peak extension, adduction, and internal rotation moments during stance. The ROM values were calculated from touchdown to the peak flexion, abduction, and internal rotation angles during stance. Touchdown angles and ROM were chosen to be consistent with the reporting of Hass et al. (2003; 2005). Joint moments were normalized to body mass and height. A 2 4 ANOVA (gender task) was performed for each of the dependent variables. Gender was a between-subjects factor and task was a within-subjects factor. Initially, years of playing experience was included as a covariate, but no influence was found for any variable. Therefore the previously described ANOVA design was used. Significant findings were subsequently examined with a Tukey s post hoc analysis. The significance level was set at p<.05. To determine whether performance was correlated between tasks, a factor analysis was performed on each dependent variable. This approach was chosen because a factor analysis was able to provide a more coherent view of relationships between tasks than would a collection of pairwise correlation coefficients (six correlations for four tasks). Factors were extracted using a principal components analysis (Jackson, 2003). Factors with eigenvalues greater than 1 were retained (Kaiser, 1960), and a varimax rotation was employed. To assess whether these relationships between tasks were gender specific, the factor analyses were performed on each gender separately. A total of 18 separate factor analyses were conducted (9 dependent variables for each gender). The ANOVA and factor analysis were performed with SPSS (v13.0, Chicago, IL). ANOVA Results Results Kinematics. There were no significant gender task interactions for any of the kinematic variables, nor were there differences between the box landing tasks (FLC and CLC; Figure 3 and Table 1). There was a significant task main effect for the sagittal TD angle (p <.001), with the greatest flexion at TD occurring for the SLC and least occurring for the FLC (Figure 3 and Table 1). There were gender (p =.010) and task (p <.001) main effects for sagittal ROM. Females flexed significantly less when averaged across all tasks, and the least flexion occurred for the CUT. Significantly greater flexion occurred during the box landing tasks. In the frontal plane, only the TD angle differed between tasks (p <.001). The knee was significantly more adducted at contact for the SLC as compared with the CLC and FLC tasks, and the knee was abducted at contact for the CUT (significantly different from other tasks). However, there were no gender or task effects for the frontal plane range of motion. Transverse plane TD angle differed across tasks (p =.047). The knee was significantly less externally rotated at contact for the CUT task. There were also significant gender (p =.022) and task (p =.019) main effects for the transverse ROM. There was less internal rotation during stance for the CUT task and for males when averaged across all tasks. Kinetics. There was a significant gender task interaction (p =.014) for the peak internal extension moment (Table 2). Post hoc analysis of the simple main effects within each task indicated the male peak extension moment was greater for the CLC task. In the frontal plane and transverse planes, there were no interactions or gender main effects. There was a significant task effect (p <.001) for the peak internal adduction moment. All tasks significantly differed from one another, with the CUT exhibiting a peak adduction moment ~3 times the magnitude of the others tasks. In the transverse plane, the peak internal rotation moment was significantly different between tasks (p <.001), with the greatest moment occurring for the CUT, which was twice the magnitude of the other tasks. Factor Analysis Results Kinematics. For each of the factor analyses performed (kinematics and kinetics), a maximum of two principal components were extracted, with a single principal component (PC) representing a majority of the variables (Tables 3 and 4). Extraction of a single PC indicates that

6 14 O Connor, Monteiro, and Hoelker Figure 3 Group mean male (black) and female (gray) stance phase knee joint angles and moments. Time is scaled to the average stance time within each gender and task. all tasks were correlated highly with one another, whereas extraction of two PCs indicates that there are two distinct groupings of related tasks. Based on the factor analysis, sagittal TD angle and ROM for the CUT were not related to the other three tasks because the three constrained tasks grouped together but the CUT was entirely captured by a separate principal component (Table 3). In the frontal plane, TD angle was highly related between all tasks. However, frontal ROM was weakly related, particularly for females, for whom the CUT loaded heavily on Principal Component 2 (PC2). Examination of the pairwise relationships illustrates the complex relationship between the tasks for each gender for this variable (Figure 4). Transverse plane kinematics were generally highly related between the four tasks. Kinetics. The kinetics factor analyses indicated a strong relationship between all tasks for the peak extension moment (Table 4). The frontal plane relationships were more complex, particularly for females. Whereas the peak adduction moments were highly correlated across tasks for males, the CUT and SLC tasks were weakly related to the moments observed during the two box landing tasks (FLC and CLC) for females. Although a single PC was extracted for females, the variance explained by that PC was relatively low (62%) and the weighting of the CUT and SLC tasks were moderate (~0.70). Examination of the pairwise correlations illustrates that the males and females responded differently to the tasks (Figure 5). In the transverse plane, the relationship between tasks was also weaker for females. There were two principal components extracted with the CUT loading heavily on PC1, the SLC loaded heavily on PC2, and the two box landing tasks exhibiting moderate relationships to each. Discussion The purpose of this study was to examine the relationship between the dynamics of constrained cutting tasks with those of an unanticipated running and cutting

7 Comparison of Cutting Mechanics 15 Table 1 Group Mean (± SD) Kinematic Variables for Each Gender Across All Tasks Sagittal Frontal Transverse TD ( )* ROM ( )* TD ( )* ROM ( ) TD ( )* ROM ( )* CUT Male 14.2 (7.4) 41.2 (6.1) 1.1 (2.2) 6.2 (2.3) 1.5 (5.5) 12.5 (4.6) Female 18.5 (5.7) 34.6 (5.7) 1.6 (2.4) 6.3 (3.1) 1.1 (4.1) 13.9 (4.3) Mean 16.4 (6.8) a 37.8 (6.7) a 1.4 (2.3) a 6.3 (2.7) 1.3 (4.8) a 13.2 (4.4) a SLC Male 18.0 (6.6) 44.5 (7.0) 1.4 (2.6) 5.8 (2.1) 0.6 (5.5) 13.9 (3.3) Female 22.6 (5.4) 41.4 (6.4) 0.5 (3.1) 7.7 (3.2) 2.1 (7.5) 16.5 (5.0) Mean 20.4 (6.4) b 42.9 (6.7) b 0.9 (2.9) b 6.8 (2.8) 1.4 (6.6) b 15.2 (4.4) b FLC Male 13.3 (7.1) 51.4 (7.7) 0.0 (2.0) 5.8 (2.7) 0.4 (5.0) 13.5 (3.0) Female 15.8 (4.9) 46.7 (5.2) 0.5 (2.3) 7.2 (3.3) 2.1 (5.6) 16.5 (3.7) Mean 14.6 (6.1) c 49.0 (6.9) c 0.2 (2.1) c 6.6 (3.3) 0.9 (5.4) b 15.0 (3.6) b CLC Male 13.1 (7.4) 51.4 (7.0) 0.1 (1.7) 5.9 (3.1) 0.3 (5.3) 14.0 (2.8) Female 17.1 (5.6) 48.8 (3.9) 0.5 (2.0) 7.2 (3.4) 2.2 (5.7) 17.3 (4.6) Mean 15.2 (6.8) a,c 50.0 (5.7) c 0.2 (1.9) c 6.5 (3.1) 1.0 (5.6) b 15.7 (4.2) b Mean Male 14.7 (7.2) 47.1 (8.1) 0.1 (2.3) 5.9 (2.5) 0.4 (5.3) 13.5 (3.5) Female 18.5 (5.9) 42.9 (7.6) 0.5 (2.6) 7.1 (3.2) 1.3 (5.9) 16.0 (4.5) Note. Positive angles represent knee extension, adduction, and internal rotation. *Indicates significant task main effect (p < 0.05). Like letters are not different from one another. Indicates significant gender main effect (p < 0.05). maneuver for males and females. The knee joint kinematics observed were comparable to previous cutting studies in terms of overall patterns and magnitudes (McLean et al., 1999, 2004; Pollard et al., 2004; Sigward & Powers, 2006), and the close (CLC) and stride (SLC) landing tasks were similar to those reported by Hass et al. (2003, 2005). While similar in pattern, peak knee joint moments in the frontal plane differed somewhat from previous studies (Besier et al., 2001a; McLean et al., 2005a; Pollard et al., 2004; Sigward & Powers, 2006), but this is likely due to two factors: the reference system in which moments are reported (Schache et al., 2007) and the effects of anticipation (Besier et al., 2001a). The rationale for this study was to determine whether a simplified and constrained task could be used to represent an individual s knee joint mechanics during an unanticipated running and cutting maneuver (CUT). Although group mean kinematics and kinetics differed between tasks, the correlational results were mixed, indicating that the constrained tasks were only moderately related to the CUT task. Frontal plane dynamics are considered a key determinant of injury risk (Hewett et al., 2005), but the relationship between the CUT and the other three tasks was poor, especially for females. A primary goal of the current study was to determine the relationship of knee joint mechanics between tasks. The current kinematic results are similar to those of McLean et al. (2005b), who compared touchdown and peak joint angles for three cutting tasks: run and cut (sidestep), jump-land, and shuttle run. In comparing the current results to ROM values extracted from McLean et al. (2005b) who reported TD and peak angles, there is strong agreement in the observed trends. The current study reported significant task differences in ROM between the CUT and CLC tasks in the sagittal and transverse planes. There was ~12 greater knee flexion and ~2.5 greater internal rotation for the CLC task as compared with the CUT. McLean et al. (2005b) report ~6 greater flexion and ~3 greater internal rotation for their jump-land task compared with their sidestep maneuver (similar to the current CLC and CUT tasks). Interestingly, the mean frontal plane ranges of motion did not differ between any of the tasks in the current study, which is also consistent with the results of McLean et al. (2005b). This last result would suggest that the constrained tasks can represent running and cutting frontal plane behavior, but the factor analysis contradicts this conclusion. The factor analyses demonstrated that the relationships between the CUT and the three landing tasks were mixed. The CUT sagittal plane touchdown angle and range of motion were generally unrelated to the SLC, FLC, and CLC, which were more strongly related to each other. In the frontal plane, the touchdown angle was highly correlated between all tasks. However, abduction range of motion for the CUT was only weakly

8 16 O Connor, Monteiro, and Hoelker Table 2 Group Mean (± SD) Peak Moments for Each Gender Across All Tasks Extension Adduction* Internal Rot.* (Nm kg 1 m 1 ) (Nm kg 1 m 1 ) (Nm kg 1 m 1 ) CUT Male 1.33 (0.24) 0.98 (0.39) 0.29 (0.08) Female 1.31 (0.23) 1.05 (0.26) 0.30 (0.07) Mean 1.32 (0.23) 1.01 (0.32) a 0.29 (0.08) a SLC Male 1.22 (0.23) 0.43 (0.19) 0.15 (0.05) Female 1.23 (0.24) 0.46 (0.17) 0.17 (0.04) Mean 1.22 (0.23) 0.44 (0.18) b 0.16 (0.05) b FLC Male 1.23 (0.22) 0.31 (0.14) 0.11 (0.05) Female 1.20 (0.30) 0.33 (0.15) 0.13 (0.06) Mean 1.22 (0.26) 0.32 (0.14) c 0.12 (0.06) c CLC Male 1.30 (0.22) 0.39 (0.16) 0.13 (0.05) Female 1.18 (0.30) 0.36 (0.15) 0.14 (0.06) Mean 1.23 (0.27) 0.38 (0.16) d 0.13 (0.05) d Mean Male 1.27 (0.23) 0.53 (0.35) 0.17 (0.09) Female 1.23 (0.27) 0.54 (0.35) 0.18 (0.09) Note. Positive values represent knee extension, adduction, and internal rotation moments. CUT = unanticipated run and cut, SLC = stride land and cut, FLC = far box-land and cut, and CLC = close box-land and cut. Indicates significant gender task interaction (p <.05). Task-specific gender difference noted. *Indicates significant task main effect (p < 0.05). Like letters are not different from one another. ver elicits different mechanical responses (Besier et al., 2001a). The jump-stop unanticipated cut (JSUC) task introduced by Ford et al. (2005) may be a task that bridges this gap, and comparison of an unanticipated running and cutting maneuver to their protocol would provide interesting insight into the role of anticipation on lower extremity dynamics. Another possible explanation may be that McLean et al. (2005b) used highly trained subjects, and perhaps these subjects had greater experience with these tasks, and were therefore more consistent across tasks. Sigward and Powers (2006) reported differences in the cutting knee kinetics between experience levels of female soccer players; however, they reported no differences in joint kinematics. In addition, McLean et al. (1999) reported a correlation between intertrial variability and experience, but no differences in mean movement patterns with experience. While the use of less skilled participants and the difference in competitive experience between genders in the current study may be viewed as a limitation and could relate to some differences between studies, the effects are not clear cut. Experience was not a significant covariate for any of the dependent variables, indicating that in the current study this was not a factor in explaining the observed gender differences. Based on the variability findings of McLean et al. (1999), the different levels of experience could account for the weaker task relationship of frontal plane range of motion for females, and it would be beneficial to examrelated to the other tasks for males and unrelated for females. Based on this analysis, it appears that the constrained tasks are not useful predictors of frontal plane motion, even though the group mean data were the same between tasks. While there were significant task mean differences in the transverse plane, the relationship between all tasks was relatively strong. Overall, these observations are functionally important, because the SLC and CLC tasks have been used previously to explore knee injury risk factors (Hass et al., 2003; Hass et al., 2005). These tasks appear useful in characterizing certain functional aspects in the transverse plane, but the sagittal and frontal plane CUT kinematics were poorly related to any of the other tasks. The poor relationship between the CUT and other tasks is contradictory to the findings of McLean et al. (2005b), who reported a high degree of correlation between the peak abduction angle of a planned side cut and a jump-land task. Their jump-land task was somewhat similar to the current SLC, FLC, and CLC tasks. It involved a running jump onto one leg followed by a lateral jump. The poor relationship in the current study between the CUT and other tasks is also observable in Figure 5, which indicates high correlations between SLC, FLC, and CLC, but low correlations of those tasks to the CUT. The discrepancy between the studies may be due to the effects of anticipation. The current study used an unanticipated cutting maneuver, and it has been previously demonstrated that an unanticipated maneu-

9 Comparison of Cutting Mechanics 17 Table 3 Factor Analyses for Each Kinematic Variable Separated By Gender Sagittal TD Angle Males Females PC1 PC2 PC1 PC2 CUT SLC FLC CLC Variance Explained 56% 26% 41% 39% Sagittal ROM CUT SLC FLC CLC Variance Explained 57% 29% 61% 25% Frontal TD Angle CUT SLC FLC CLC Variance Explained 87% 87% Frontal ROM CUT SLC FLC CLC Variance Explained 66% 62% 29% Transverse TD Angle CUT SLC FLC CLC Variance Explained 75% 79% Transverse ROM CUT SLC FLC CLC Variance Explained 62% 79% Note. PC1 and PC2 correspond to the first two principal components. Values represent the weighting ( 1 to 1) of each factor. Variance Explained = (Eigenvalue / Total) 100%. CUT = unanticipated run and cut, SLC = stride land and cut, FLC = far box-land and cut, and CLC = close box-land and cut. ine the task relationships in a group of more experience female athletes. Whereas some of the kinematic variables demonstrated moderate-to-poor relationships between tasks, the kinetic data were more strongly related between the four tasks. In the sagittal plane, there were no significant differences between tasks within gender, although the peak extension moment was greater for the males for

10 18 O Connor, Monteiro, and Hoelker Figure 4 Frontal plane range of motion compared between tasks. Solid diamonds represent males and open squares represent females. Trend lines are shown with r 2 values reported for males (+) and females (o). plane. For males, there was a relatively strong relationship of peak adduction moment between all tasks, but for females the SLC correlated more highly with the CUT than the box land tasks. Whereas for males all of the constrained tasks could reasonably predict running and cutting frontal plane kinetics, for females the SLC was the only task that provided a moderate predictive ability. The reason for the gender difference in correlations is unclear, but may be due to differences in athletic experience between genders. McLean et al. (2005b) reported significant correlations between frontal plane touchdown angle and peak adduction moment (expressed as internal moment to be consistent with current study) with r 2 =.21 for males and r 2 =.35 for females. In the current study, this angle was highly correlated between all tasks for both genders; therefore, this does not explain the observed gender difference. When combined with the kinematic findings, it appears that the constrained tasks were generally more poorly related to CUT frontal plane mechanics for females. The goal of the current study was to determine whether relatively simple tasks could be used to reprethe close box landing task (CLC). This was expected because the female subjects dropped from a lower height on average and would therefore have lower velocities at impact. Studies of landing mechanics between genders must choose between equating absolute (same drop height) or relative (scaled by jump height) task demands. It was decided to equate relative difficulty of the landing tasks in the current study, to avoid creating an unnatural landing condition for one of the groups that could skew the task relationships. Group mean joint moments were greater for the running and cutting maneuver (CUT) in the frontal and transverse planes for both genders. It is clear from these results that the task demands on the out-of-plane knee rotations are considerably greater for CUT than for the constrained tasks. Given the greater velocity at impact this was not unexpected, but the critical question was whether the peak loads correlated across the tasks. The frontal plane loads, in particular, have been shown to correlate with injury risk (Hewett et al., 2005). In the current study, the correlational relationship between tasks differed for each gender in the frontal

11 Comparison of Cutting Mechanics 19 Table 4 Factor Analyses for Each Peak Moment Separated by Gender Extension Moment Adduction Moment Males Females PC1 PC2 PC1 PC2 CUT SLC FLC CLC Variance Explained 84% 91% CUT SLC FLC CLC Variance Explained 75% 62% Int. Rot. Moment CUT SLC FLC CLC Variance Explained 71% 47% 38% Note. PC1 and PC2 correspond to the first two principal components. Values represent the weighting ( 1 to 1) of each factor. Variance Explained = (Eigenvalue / Total) 100%. CUT = unanticipated run and cut, SLC = stride land and cut, FLC = far box-land and cut, and CLC = close box-land and cut. sent knee joint dynamics observed during a more challenging and potentially more realistic task. There were significant differences in group mean data between genders and tasks that were consistent with previous reports. More importantly, however, some of the differences between tasks were not simply a matter of scale but rather due to characteristically different dynamics when performing an unanticipated running and cutting maneuver when compared with the three constrained tasks. The results of this study also suggest that constrained tasks may not be adequately representative of cutting dynamics within a realistic sports environment. Even though these results would indicate limitations in utilizing these tasks to approximate more dynamic maneuvers, there is other evidence indicating that a simple task has predictive value of injury risk (Hewett et al., 2005). Perhaps other tasks exist that can better relate to an individual s mechanics during activities associated with traumatic knee injuries. Acknowledgments The authors would like to thank the University of Wisconsin Milwaukee Graduate School Research Committee for its financial support of this project. We would also like to thank Joshua Weinhandl, Richard Deklotz, and Carl Johnson for their invaluable assistance. References Arendt, E.A., Agel, J., & Dick, R. (1999). Anterior cruciate ligament injury patterns among collegiate men and women. Journal of Athletic Training, 34, Augustsson, J., Thomee, R., Linden, C., Folkesson, M., Tranberg, R., & Karlsson, J. (2006). Single-leg hop testing following fatiguing exercise: reliability and biomechanical analysis. Scandinavian Journal of Medicine & Science in Sports, 16, Besier, T.F., Lloyd, D.G., & Ackland, T.R. (2003). Muscle activation strategies at the knee during running and cutting maneuvers. Medicine and Science in Sports and Exercise, 35, Besier, T.F., Lloyd, D.G., Ackland, T.R., & Cochrane, J.L. (2001a). Anticipatory effects on knee joint loading during running and cutting maneuvers. Medicine and Science in Sports and Exercise, 33, Besier, T.F., Lloyd, D.G., Cochrane, J.L., & Ackland, T.R. (2001b). External loading of the knee joint during running and cutting maneuvers. Medicine and Science in Sports and Exercise, 33, Boden, B.P., Dean, G.S., Feagin, J.A., & Garrett, W.E. (2000). Mechanisms of anterior cruciate ligament injury. Orthopedics, 23,

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