Women athletes who participate in pivoting and

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1 Effect of Functional Stabilization Training on Lower Limb Biomechanics in Women RODRIGO DE MARCHE BALDON 1, DANIEL FERREIRA MOREIRA LOBATO 1,LÍVIA PINHEIRO CARVALHO 1, PALOMA YAN LAM WUN 1, PAULO ROBERTO PEREIRA SANTIAGO 2, and FÁBIO VIADANNA SERRÃO 1 1 Department of Physical Therapy, São Carlos Federal University, São Carlos, BRAZIL; and 2 School of Physical Education and Sport at Ribeirão Preto, University of São Paulo, Ribeirão Preto, BRAZIL ABSTRACT BALDON, R. D. M., D. F. M. LOBATO, L. P. CARVALHO, P. Y. L. WUN, P. R. P. SANTIAGO, and F. V. SERRÃO. Effect of Functional Stabilization Training on Lower Limb Biomechanics in Women. Med. Sci. Sports Exerc., Vol. 44, No. 1, pp , Purpose: This study aimed to verify the effects of functional stabilization training on lower limb kinematics, functional performance, and eccentric hip and knee torques. Methods: Twenty-eight women were divided into a training group (TG; n = 14), which carried out the functional stabilization training during 8 wk, and a control group (CG; n = 14), which carried out no physical training. The kinematic assessment of the lower limb was performed during a single-leg squat, and the functional performance was evaluated by way of the single-leg triple hop and the timed 6-m single-leg hop tests. The eccentric hip abductor, adductor, lateral rotator, medial rotator, and the knee flexor and extensor torques were measured using an isokinetic dynamometer. Results: After 8 wk, the TG significantly reduced the values for knee abduction (from j6.86- to 1.49-), pelvis depression (from j to j7.86-) and femur adduction (from to 5.19-) as well as increasing the excursion of femur lateral rotation (from j0.55- to j3.67-). Similarly, the TG significantly increased the values of single-leg triple hop (from 3.52 to 3.92 m) and significantly decreased the values of timed 6-m single-leg hop tests (from 2.43 to 2.14 s). Finally, the TG significantly increased the eccentric hip abductor (from 1.31 to 1.45 NImIkg j1 ), hip lateral rotator (from0.75to0.91nimikg j1 ), hip medial rotator (from 1.45 to 1.66 NImIkg j1 ), knee flexor (from 1.43 to 1.55 NImIkg j1 ), and knee extensor (from 3.46 to 4.40 NImIkg j1 ) torques. Conclusions: Strengthening of the hip abductor and lateral rotator muscles associated with functional training improves dynamic lower limb alignment and increases the strength and functional performance. Key Words: CONTROLLED CLINICAL TRIAL, PREVENTION TRAINING, MOTION ANALYSIS, FUNCTIONAL PERFORMANCE, ISOKINETIC, KNEE Women athletes who participate in pivoting and jumping sports are two to six times more likely to suffer noncontact anterior cruciate ligament (ACL) injury than men athletes (2,29,42). In addition, the incidence rate of patellofemoral pain syndrome (PFPS) in women has been reported to be 2.2 times greater than in men (8). The greater incidence, associated with the growing number of women participating in sports during the last three decades, has led to an exponential increase in the number of these injuries (16). In an attempt to explain the disproportionate incidence of ACL injury and PFPS development in women, laboratory studies have evaluated gender differences in lower limb kinematics during functional Address for correspondence: Fábio Viadanna Serrão, Ph.D., Departamento de Fisioterapia, Universidade Federal de São Carlos, Rodovia Washington Luis, km 235, CEP: , São Carlos, SP, Brasil; fserrao@ufscar.br. Submitted for publication April Accepted for publication June /12/ /0 MEDICINE & SCIENCE IN SPORTS & EXERCISE Ò Copyright Ó 2012 by the American College of Sports Medicine DOI: /MSS.0b013e31822a51bb tasks. Several studies have shown greater knee abduction excursion in women during single-leg squat (43) and landing (13), and others have found greater hip adduction and medial rotation excursions in women during walking (19) and running (11). It is thought that the poor dynamic control of the knee and hip joints in the coronal and transverse planes observed in women may lead to ACL injury and PFPS development (38). The hip adduction movement has been correlated positively with the amount of knee abduction excursion during weight-bearing activities (13), and in vitro data suggest that knee abduction places an increased load on the ACL (27). Excessive hip adduction and knee abduction also increase the quadriceps angle (Q-angle) and, consequently, the lateral pressure on the patellofemoral joint (18). In addition, excessive hip medial rotation over the tibia fixed on the ground can result in increased lateral facet pressure because the patella is being forced against the lateral femoral condyle (22). Prospective studies have shown that both the knee abduction (31) and the hip medial rotation excursions (7) observed during landing tasks are two predictors of PFPS. The relationships established between lower limb mechanics and noncontact knee injuries in women athletes have led to the development of comprehensive prevention 135

2 programs (26,35). Recently, weakness of the hip abductor and lateral rotator muscles has been implicated in contributing to ACL injury and PFPS development (3,6,23). The hip abductor and lateral rotator muscles have an important role in controlling hip adduction (9), hip medial rotation (41), and knee abduction movements (20) during weight-bearing activities. Thus, it is plausible that a preventive program focused on the strengthening of these muscles might avoid excessive hip adduction, hip medial rotation and knee abduction movements, reducing the overload on the ACL and patellofemoral joint. Although it has been suggested that weakness of the hip abductor and lateral rotator muscles might be involved in both ACL injury and PFPS development, few studies have investigated the biomechanical effects of specific hip strengthening training in healthy women. Previous findings have suggested that an increase in hip abductor and lateral rotator strength alone seems to only partially influence the lower limb alignment during dynamic activities (15,40). Moreover, only one study that investigated the effects of this intervention on functional performance was found (32). A physical training program aiming to prevent knee injuries and concomitantly assist in increasing functional performance might be better accepted by the coach and athletes, resulting in greater compliance with the training. During weight-bearing functional activities, stabilization of the pelvis and trunk by way of the lumbopelvic musculature, which is commonly known as core, is required to control movements of the distal segments (23). It is possible that a preventative program focused on hip strengthening associated with core training and functional exercises might positively influence the motor learning of the proper dynamic lower limb alignment. Thus, the purposes of this study were to verify the effects of preventative training, named here as functional stabilization training, on (a) lower limb kinematics during the single-leg squat, (b) functional performance of the single-leg triple hop (SLTH) and the timed 6-m single-leg hop (TH), and (c) eccentric hip and knee torques. We hypothesized that when compared with the control group (CG), the trained women would improve their lower limb alignment (decreased knee abduction, femur adduction, and medial rotation and pelvis depression), as well as improve their functional performance and increase the eccentric hip and knee torques of the trained muscles. METHODS Participants. Participants were recruited between August 2008 and April 2009 from the campus of the São Carlos Federal University. Twenty-eight young healthy women recreational athletes volunteered to participate in the experiment (Table 1). A recreational athlete was defined as anyone participating in aerobic or athletic activity at least three times per week. Anyone with current injury or previous surgery of the lower limb, or who experienced cardiovascular, pulmonary, neurological or systemic conditions that limited TABLE 1. Baseline demographic characteristics of the population studied (mean T SD). TG CG P Age (yr) T T Height (m) 1.64 T T Mass (kg) T T Body mass index T T Amount of physical activity per week (min) 205 T T her physical activity, was excluded from the study. All the experimental procedures and potential risks were explained fully to the participants before any testing, and all of them read and signed an informed consent form before the assessments. This study was approved by the São Carlos Federal University Ethics Committee for Research on Human Subjects. Design. This was a nonrandomized controlled pilot study carried out at the Laboratory of Intervention and Assessment in Orthopedics and Traumatology. The participants were divided equally into two groups: 1) a training group (TG; n = 14), which carried out the functional stabilization training; and 2) a CG (n = 14), which carried out no physical training. Because of logistic problems, randomization of the participants into the groups was not possible. This was because the sector reserved for training the participants was not available for the whole period necessary to conclude this experiment. Thus, the first 14 eligible participants were allocated to the TG and the training was initiated immediately, whereas the next 14 were allocated to the CG. Moreover, owing to the great time spent to train and evaluate the participants of the TG, it was not possible to evaluate the CG concurrently. The participants in the TG completed 8 wk of training as described below, whereas the participants in the CG were instructed to continue their daily life activities during this period. Before and after the 8-wk intervention period, the participants completed a series of tests that consisted of kinematic (primary outcomes), functional, and isokinetic (secondary outcomes) assessments. Immediately before the second evaluation, the participants of the CG were asked if they had engaged in any activities that might alter their physical status. There were no participants in the CG who had changed their daily life activities during this period. A single nonblinded experienced physical therapist carried out all the evaluations of the two groups for the dominant lower limb. For each participant, the dominant lower limb was determined by asking which leg she would use to kick a ball as far as possible. Kinematic assessment. Kinematic assessment of the participants was carried out during the single-leg squat. The trials were recorded using four digital cameras (Panasonic NV GS180; Matsushita Group, Osaka, Japan) adjusted to the acquisition frequency of 60 Hz, positioned so they could capture all the passive markers and located in front of (cameras 1 and 2) and posterolaterally (cameras 3 and 4) to the participants. The frontal cameras presented a 60- angle between them, whereas cameras 3 and 4 were angled 60- to 136 Official Journal of the American College of Sports Medicine

3 the participant (120- between them). For calibration, an object (1 m 1.8 m 0.8 m) was filmed in the area where the participants would perform the single-leg squat. This object had 24 control points with known absolute positions in relation to the Cartesian coordinate system. The global reference system was then defined with this calibrated object, in which the y axis was oriented upward, the x axis anteriorly, and the z axis to the right of the participants (45). In each evaluation, nine passive reflective markers (10 mm in diameter) were positioned at the following anatomical landmarks: both anterior superior iliac spines, first sacral vertebra, prominence of the greater trochanter, lateral and medial epicondyle of the femur, head of the fibula, lateral and medial malleolus. This marker distribution was necessary for the recording of the static standing position of the participants as well as to determine the lower limb alignment during the single-leg squat. The digitization procedure was carried out semiautomatically using the software Dvideow (Digital Video for Biomechanics for Windows 32 bits, Campinas, Brazil) (12). In this process, when the markers were not identified automatically because of the markers approximation, the operator tracked them manually. This software uses the direct linear transformation method for three-dimensional representation (1). For the execution of the single-leg squat, the participants were instructed to stand with the contralateral lower limb off the floor and with their arms crossed in front of the thorax. The static standing trial was registered in this position and used to determine the lower limb anatomical position. This static measurement was used as the neutral alignment for each participant, with subsequent measurements referring to this position. The participants were asked to squat from this position to approximately 75- of knee flexion and then return to the starting position. An adjustable support was placed beside the participants at a height that represented the distance from the floor to the greater trochanter of the femur mark necessary to achieve the established knee flexion angle (43). The execution time of the single-leg squat was standardized at 2 T 0.3 s, controlled by a progressive digital stopwatch. Each participant completed three attempts for familiarization and five acceptable trials for the data analysis. If any of the evaluation requirements were not carried out, the attempt was invalidated and a new one performed. The lowest knee flexion angle accepted was 65-. The averages of the kinematic values obtained from five acceptable trials were used for the statistical analyses. After recording the three-dimensional coordinates for each marker, data were submitted to the software Matlab (Mathworks, Inc., Natick, MA) and analyzed using a low-pass fourth-order Butterworth filter with a 5-Hz cutoff frequency (44). Next, the local coordinate systems of the pelvis, femur, and leg were then defined, and algorithms were created to quantify the joint angles. The knee joint angles were calculated with the mathematical convention of Euler angles, using the coordinate system of the distal segment relative to the coordinate system of the proximal segment (14). Because the authors believe that isolated movements of the pelvis and femur are capable of altering the load on the ACL and patellofemoral joint, the movement excursions of these segments (femur and pelvis) were calculated relative to themselves. For this purpose, the local coordinate systems of the pelvis and femur were defined in the static standing trial, and the relative angles (in relation to its initial orientation) were calculated for the subsequent time instants. The kinematic variables studied were contralateral pelvis elevation/depression, femur adduction/abduction and medial/ lateral rotation, and knee adduction/abduction and medial/ lateral rotation. These variables represented the movement excursions that were calculated by subtraction of the values acquired when the knee was in maximum flexion, from that recorded in the static standing position. By convention, positive kinematic values represented contralateral pelvis elevation, femur adduction and medial rotation, and knee adduction, medial rotation, and extension excursions. The experimental error was verified using a specific test (9). This error was obtained through the values of accuracy and precision that was calculated according to the equations: p error : e ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi a 2 þ p 2 accuracy : a ¼ 1 n ~n jv dðiþj i¼1 precision : p ¼ sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 ~ n ðdðiþ d Þ 2 n 1 i¼1 with = modulus of a vector, v = real value adopted the distance between two landmarks obtained through direct measure, d(i) (i =1,I, n) = the number of measures done (number of lines of the matrix data), d = mean value of the n measures. Therefore, the smaller is the sum of accuracy and precision, the smaller was the experimental error. In this study, the experimental error was 2.8 mm, accuracy of 2.4 mm, and precision of 1.4 mm. Functional assessment. Functional evaluation was performed immediately after the kinematic evaluation. Before the functional assessment, each participant completed a 5-min submaximal warm-up on a treadmill (Explorer Proaction; BH Fitness, Vitoria-Gasteiz, Spain) at a speed of 1.66 mis j1, followed by self-stretching of the thigh muscles. Next, they were submitted to a familiarization process consisting of three attempts at each functional test conducted in a random order (draw) so that the influence of one test on the others was minimized. To measure the distance jumped in the SLTH, a standard tape measure was fixed to the ground, perpendicular to the starting line of the test, whereas a progressive digital stopwatch (Timex marathon, Timex Group USA, Inc., Middlebury, CT) was used to measure the execution time of the TH. Each participant began both tests standing on the dominant limb with the foot immediately behind the starting line. The arms were positioned behind the body to prevent any EFFECT OF FUNCTIONAL STABILIZATION TRAINING Medicine & Science in Sports & Exercise d 137

4 contribution by balancing during the activity (increasing the functional demand on the limb under consideration). To carry out the SLTH, the participants were instructed to execute three consecutive maximum jumps on the dominant limb and maintain their balance on the last landing for at least 2 s before placing the contra lateral limb on the ground. For the TH, the participants were instructed to complete the set distance (6 m) performing consecutive jumps on the dominant limb as quickly as possible and crossing the finishing line without slowing down at any point in the test. The participants had a 1-min rest period between attempts and a 3-min rest period between tests. The tests were repeated when the participants used their arms as a propulsion strategy or if there was a loss of balance during the test. Three valid attempts of each test were carried out. The longest distance achieved during the SLTH (m) and the shortest time achieved in the TH (s) were used for the statistical analyses. A prior test retest reliability of both tests was assessed by the evaluator. Twelve participants were tested on two occasions, which were separated by 1 wk. Intraclass correlation coefficients (ICC; 3,1) and SEM were 0.92 (0.15 m) for the SLTH and 0.86 (0.09 s) for the TH. Isokinetic assessment. The evaluations of the eccentric hip and knee torques were carried out using an isokinetic dynamometer (Biodex Multi-Joint System 2; Biodex Medical System, Inc., Shirley, NY) from 48 to 96 h after the functional assessment. An eccentric evaluation was chosen because the primary muscles focused during the training (hip abductor and lateral rotator muscles) must act eccentrically to control excessive femur adduction and medial rotation during the strike of the heel on the ground during functional weight-bearing activities (10). Thus, an eccentric strength evaluation of these muscles might be more closely related to the lower limb kinematics and functional capacity of the participants. The dynamometer was calibrated at the start of every day of testing. Before testing, each participant completed a warm-up procedure similar to that described above plus stretching of the hip muscles. All the isokinetic assessments were performed using a protocol similar to that used in a previous study (36) and conducted in a random order (draw). Specifically, eccentric hip abductor and adductor torques were tested with the participants in a side lying position. The dominant limb was positioned parallel to the ground in neutral hip flexion/extension and medial/lateral rotation. The contralateral hip and knee were flexed and fixed with straps. Stabilization of the trunk was carried out using a single belt proximal to the iliac crest. The mechanical rotation axis of the dynamometer was aligned with a point representing the intersection of two lines. One line was directed inferiorly from the posterior superior iliac spine toward the knee and the other one was posteriorly and medially directed from the greater trochanter of the femur toward the midline of the body. The lever arm of the dynamometer was laterally attached to the thigh under test, 5 cm above the base of the patella. The participants were instructed to not bend their knees during the test. The range of motion of the test was from 0- (neutral) to 30- of hip abduction. For the eccentric test of the hip medial and lateral rotator muscles, the participants were placed in the sitting position with their knees and hips flexed at 90- and with the hip of the limb under test placed at 10- of medial rotation. The rotational axis of the dynamometer was then aligned with the center of the patella (long axis of the femur) and the lever arm attached 5 cm above the lateral malleolus using straps. Four belts were used to stabilize the trunk and limb under test: two crossing the trunk, one around the pelvis, and one on the distal thigh. The range of motion of this test was from 10- of hip medial rotation to 20- of hip lateral rotation. The angular speed in both hip evaluations was 30-Is j1. Although it is known that the femur moves at higher velocities during jump landing tasks (20), a lower test speed was chosen to increase the isokinetic phase of the test. Because of the small range of motion during the eccentric tests of the hip muscles, high isokinetic testing speeds might decrease the time of the isokinetic phase and, consequently, underestimate the torque production capacity. The eccentric knee extensor and flexor torques were tested with the participants in the sitting position, with the knees and hips flexed at 90- and in neutral hip adduction/ abduction and medial/lateral rotation. The rotational axis of the dynamometer was aligned to the lateral epicondyle of the femur and the lever arm attached 5 cm above the lateral malleolus using straps. Stabilization of the participants was identical with that described above. The range of motion of the test was from 90- to 20- of knee flexion (0- full extension) and the angular speed of the test was 60-Is j1. For the familiarization procedure, the participants performed one series of five submaximal and one series of two maximal reciprocal eccentric contractions, with a 1-min interval between series. After a further 1-min interval, the participants performed two series of five maximal repetitions with a 3-min rest period between the series. Oral encouragement was provided to stimulate the participants to produce the maximum torque. To correct for the influence of gravity on the torque data acquired, the limb was weighed before each test according to the instructions found in the manual of the dynamometer, and thus, the results of the test were automatically corrected by the data acquisition software. In the statistical analyses, we used the isokinetic peak torque normalized according to body mass (NImIkg j1 ), which could be from either the first or the second series. A previous test retest reliability of eccentric hip and knee torque measurements was assessed by the evaluator. Nine participants were tested on two occasions, which were separated by 1 wk. ICCs (3,1) and SEM were 0.97 (0.07 NImIkg j1 ) for hip abduction, 0.78 (0.16 NImIkg j1 ) for hip adduction, 0.87 (0.07 NImIkg j1 ) for hip lateral rotation, 0.92 (0.11 NImIkg j1 ) for hip medial rotation, 0.92 (0.14 NImIkg j1 ) for knee extension, and 0.81 (0.07 NImIkg j1 ) for knee flexion. 138 Official Journal of the American College of Sports Medicine

5 Training protocol. The intervention began after 5 d of baseline isokinetic assessment. The participants of the TG carried out the training protocol three times per week for approximately 8 wk, each session being at least 48 h after the previous one. The average duration of each session was 80 min, and all sessions were supervised by two nonblinded experienced physical therapists, who were involved in this research. One of them was the same one who carried out all the evaluations. No more than two participants were supervised by each physical therapist per session. Participants in the TG were required to take part in at least 19 (80%) of the 24 sessions for inclusion in the data analysis. The functional stabilization training was based on exercises used in previous clinical trials (28,34,36), and the protocol was divided into three phases as indicated by Mascal et al. (28): 1) non weight-bearing exercises, 2) weight-bearing exercises, and 3) functional training. In all phases and for most of the exercises, the initial loads were based on the one repetition maximum (1RM) for each exercise. The exercises were progressed when the participant could perform a whole specific exercise while maintaining a neutral spinal position and without the presence of local muscle pain 48 h after the previous training session. Exercise progression was done by increasing the resistance ( kg for free-weight exercises and one resistance level for elastic band exercises) or time (5 10 s for transversus abdominus and multifidus muscle training). The main objectives of the first training phase (1 2 wk) were to enhance motor control and endurance of the transversus abdominus, multifidus, hip abductor, and lateral rotator muscles. The participants were taught how to achieve isometric cocontraction of the transversus abdominus and multifidus muscles, independent of the global muscles (large and superficial muscles of the trunk that do not have direct attachment to the vertebrae and cross multiple segments, acting mainly to generate torque of the spine) (4), using the motor relearning approach for lumbopelvic stabilization proposed by Richardson et al. (39). These exercises were carried out in different postures (quadruped, prone, sitting, and standing) using a Swiss ball and unstable platforms (Fig. 1). The participants carried out two sets of 15 repetitions, with 10-s isometric muscle cocontraction for quadruped and prone postures, and 10 repetitions with 10-s isometric muscle cocontraction for sitting and standing postures. Opened kinetic chain exercises for the hip abductor and lateral rotator muscles were also performed (Fig. 1). The participants were taught the importance of controlling pelvic motion throughout the hip strengthening exercises, by cocontraction of the transversus abdominus and multifidus muscles. Moreover, because the authors believed it would be necessary for the participants to have high levels of knee extensor and flexor strength to perform the next phases of the protocol, specific exercises for these muscle groups were also included. For the hip exercises, the participants attempted FIGURE 1 Non weight-bearing exercises (A D) and core training carried out during phase 1 with the spine and pelvis maintained in a neutral position (E F). A. Hip abduction/lateral rotation/extension in a side-lying position. B. Hip extension/lateral rotation with knee flexed in a prone position. C. Hip lateral rotation/abduction/extension in a quadruped position. D. Hip abduction/lateral rotation with slight knee and hip flexion. E. Single-leg stance on unstable platform. F. Seated Swiss ball. EFFECT OF FUNCTIONAL STABILIZATION TRAINING Medicine & Science in Sports & Exercise d 139

6 to carry out two sets of 20 repetitions, with 5-s isometric muscle contraction and 90-s rest periods between series. The isometric phase was carried out to emphasize the coordinated action of the lumbopelvic stabilizers. The initial resistance level for the free-weight exercises was 25% of 1RM. For the elastic exercises, Thera-Band Ò Exercise Bands (Hygenic Corporation, Akron, OH) were used, which show increased resistance according to their colors (tan, yellow, red, green, blue, black, silver, and gold). In the current study, only five different colors were used (red, green, blue, black, and silver). After determining the greatest resistance level during the 1RM test, the women were instructed to perform the exercises during this phase with two resistance levels lower than that determined during the 1RM test. For the knee exercises, the participants also performed two sets of 20 repetitions with 90-s rest periods between series. However, the initial level of resistance was 50% of 1RM because the isometric phase was not carried out. The main objective of the second phase (3 5 wk) was to increase the strength of the hip abductor and lateral rotator muscles as well as thatofthekneeflexorandextensor muscles. Lateral and prone knee bridges were added, and the exercises with the unstable platform and Swiss ball were advanced (Fig. 2). The unstable platform exercise was carried out in single-leg stance with external perturbation of a medicine ball, and the Swiss ball exercise was carried out as in the first phase but with the limb support on an unstable platform. All the opened kinetic chain exercises carried out during the first phase were maintained, with the exception of the hip abduction/lateral rotation with slight knee and hip flexion. Moreover, closed kinetic chain exercises were inserted into the program, and the participants were introduced to the concept of neutral lower extremity alignment (Fig. 2). This involved alignment of the lower extremity, such that the anterior superior iliac spine (ASIS) and knee remained positioned over the second toe, with the hip positioned with approximately 10- of external rotation. In this phase and in the following one, the participants attempted to carry out three sets of 12 repetitions, with 120-s rest periods between series. The initial resistance level for the free-weight exercises was 70% of 1RM and one resistance level lower than that determined during the 1RM test for the elastic band exercises. Finally, the main objective of the third phase (6 8 wk) was the learning of the proper lower limb alignment FIGURE 2 Core training (A and B) and weight-bearing exercises (C F) carried out during phase 2. A. Lateral knee bridge. B. Prone knee bridge. C. Upper extremity extension with elastic resistance performed in a single-leg stance. D. Relative hip lateral rotation by way of trunk medial rotation with elastic resistance. E. Pelvic drop exercise. F. Single-leg stance on unstable platform associated with ball throwing. 140 Official Journal of the American College of Sports Medicine

7 during functional activities. The participants performed functional activities such as forward lunge, single-leg squat, and anterior stair descent (Fig. 3). Additional elastic resistance around the knee of the support limb was applied by the therapist to encourage hip abduction and lateral rotation. During the exercises, the participants received frequent and simultaneous oral feedback regarding the proper lower limb alignment. All the opened and closed chain exercises carried out in the second phase were maintained. The core training was advanced with lateral and prone bridges without knee supports and kneeling on the Swiss ball (Fig. 3). Statistical analyses. All the statistical analyses were applied using the Statistica software (version 7.0; StatSoft, Inc., Tulsa, OK). Descriptive values (means, SDs) were first obtained for each variable, and the data were analyzed with respect to their statistical distribution and variance homogeneity using the Shapiro Wilk W and Levene tests, respectively. The Student s t-tests for independent samples were used to verify differences in the baseline demographic characteristics of the groups. The contralateral pelvis elevation/depression, femur adduction/abduction and medial/lateral rotation, knee adduction/abduction, medial/lateral rotation and extension/flexion excursions, SLTH distance and TH time, eccentric hip abductor, hip adductor, hip lateral rotator, hip medial rotator, knee flexor, and knee extensor peak torques were considered to be dependent variables. The time and the group were treated as independent variables: the time being considered as a repeated measurement with two levels (baseline and after 8 wk) and the group as an independent factor, which also had two levels (TG and CG). The effects of training on the dependent variables were evaluated by a two-way (group time) ANOVA with a mixed-model design for each dependent variable. When significant differences were found, a pairwise comparison was carried out using the Tukey post hoc test. A preset > level of 0.05 was used for all the statistical tests. RESULTS All 24 participants successfully completed the training protocol and were included in the data analyses. No statistically significant differences were observed between the TG and CG for age, height, mass, body mass index, or amount of physical activity per week (P for all comparisons) (Table 1). All the participants in the intervention group FIGURE 3 Core training (A C) and functional exercises (D F) carried out during phase 3. A. Lateral bridge. B. Prone bridge. C. Kneeling on Swiss ball. D. Forward lunge with knee valgus traction. E. Single-leg squat on step with knee valgus traction. F. Anterior stair descent with knee valgus traction. EFFECT OF FUNCTIONAL STABILIZATION TRAINING Medicine & Science in Sports & Exercise d 141

8 TABLE 2. Knee, femur, and pelvic kinematics for single-leg squat (mean T SD). Knee extension (+)/ flexion (j) Knee medial (+)/ lateral (j) rotation Knee adduction (+)/ abduction (j) Pelvis elevation (+)/ depression (j) Femur adduction (+)/ abduction (j) Femur medial (+)/ lateral (j) rotation Time TG CG Baseline j75.90 T 5.80 j79.57 T wk j76.51 T 6.73 j79.64 T 6.11 Baseline T T wk T T 7.70 Baseline j6.86 T 5.20 j8.20 T wk 1.49 T 3.56 b j9.36 T 6.21 Baseline j10.21 T 3.80 j12.00 T wk j7.86 T 4.51 a j12.22 T 6.14 Baseline 7.08 T T wk 5.19 T 3.38 a 5.92 T 4.92 Baseline j0.55 T T wk j3.67 T 4.01 b 2.93 T 5.56 a Significantly different with respect to the TG at baseline. b Significantly different with respect to the TG at baseline and the CG at baseline and after 8wk. complied with the training session requirement of taking part in at least 19 of the total of 24 sessions, with an overall attendance of 87%. Kinematic measurements. The kinematic results are reported in Table 2. No significant group time interactions were shown for the knee flexion/extension and (P = 0.81) and medial/lateral rotation (P = 0.63) excursions. However, statistically significant group time interactions were verified for the knee adduction/abduction (P G 0.001), pelvis elevation/ depression (P = 0.02), femur adduction/abduction (P = 0.04), and femur medial/lateral rotation (P = 0.03) excursions. Moreover, some main effects were observed. The knee abduction excursion decreased in the second evaluation (P G 0.001), whereas knee abduction excursion was greater in the CG (P = 0.003) and the femur lateral rotation excursion was greater in TG (P = 0.001), respectively. No other main effects were verified for the kinematic variables. Postintervention knee abduction excursion in the TG was significantly lower than both preintervention TG (P G 0.001) and CG (P G 0.001) and CG after intervention (P = 0.002). In fact, after intervention, the participants in the TG changed their knee movement patterns from abduction to adduction. Moreover, postintervention pelvis depression (P = 0.02) and femur adduction (P = 0.02) excursions in the TG were significantly lower than the preintervention TG but not in the CG before and after intervention (P ). Finally, postintervention femur lateral rotation excursion in the TG was significantly greater than both TG (P = 0.02) and CG (P = 0.001) before intervention and CG (P = 0.01) after intervention. For all the kinematic variables, no significant differences were observed between the TG and CG at baseline (P ) or between the CG at baseline and after 8 wk (P ). Functional measurements. The functional performance results are reported in Table 3. Statistically significant group time interactions were verified for the SLTH distance (P G 0.001) and TH time (P = 0.001). Moreover, it was verified that the SLTH distance increased (P G 0.001) and TH time decreased in the second evaluation (P G 0.001). No main effects for group were observed in either of the functional tests (P ). Postintervention SLTH distance in the TG was significantly greater than the preintervention TG (P G 0.001) but not significantly greater than in the CG before and after intervention (P ). In addition, postintervention TH time in the TG was significantly lower than the preintervention TG (P G 0.001) but not significantly lower than in the CG before and after intervention (P ). The improvement in functional performance in both tests was approximately 12% in the TG. No significant difference was observed between the TG and CG at baseline in either functional test (P ) or between the CG at baseline and after 8 wk (P ). Isokinetic measurements. The isokinetic results are reported in Table 3. No significant group time interaction was shown for the eccentric hip adductor peak torque (P = 0.056). However, statistically significant group time interactions were found for the eccentric hip abductor (P G 0.001), hip lateral rotator (P = 0.005), hip medial rotator (P G 0.001), knee flexor (P G 0.001), and knee extensor (P G 0.001) peak torques. Moreover, some main effects were observed. The eccentric hip lateral rotator (P G 0.001) and knee extensor (P G 0.001) peak torques increased in the second evaluation, whereas the eccentric knee extensor peak torque was greater in the TG (P = 0.008). No other main effects were verified for the isokinetic variables (P ). Postintervention eccentric knee extensor torque in the TG was significantly greater than both preintervention TG (P G 0.001) and CG (P = 0.001) and CG after the intervention (P = 0.02). Moreover, postintervention eccentric hip abductor (P = 0.02), hip medial rotator (P = 0.003), hip lateral rotator (P G 0.001), and knee flexor (P = 0.01) peak torques in the TG were significantly greater than the preintervention TG but not significantly greater than in the CG before and after intervention (P ). Finally, the eccentric knee flexor torque in the CG after 8 wk was significantly lower than the CG at baseline (P = 0.04). The improvements in the eccentric hip abductor, hip lateral rotator, and hip TABLE 3. Functional performance and eccentric knee and hip torques (mean T SD) a. Time TG CG SLTH Baseline 3.52 T T wk 3.92 T 0.43 b 3.59 T 0.58 TH Baseline 2.43 T T wk 2.14 T 0.21 c 2.23 T 0.24 Eccentric hip abductor torque Baseline 1.31 T T wk 1.45 T 0.19 b 1.25 T 0.27 Eccentric hip adductor torque Baseline 2.04 T T wk 2.06 T T 0.24 Eccentric hip lateral rotator torque Baseline 0.75 T T wk 0.91 T 0.11 b 0.86 T 0.16 Eccentric hip medial rotator torque Baseline 1.45 T T wk 1.66 T 0.28 b 1.38 T 0.18 Eccentric knee flexor torque Baseline 1.43 T T wk 1.55 T 0.20 b 1.33 T 0.16 d Eccentric knee extensor torque Baseline 3.46 T T wk 4.01 T 0.54 e 3.20 T 0.46 a Distance in meters, time in seconds, and torque in newton metersiper kilogram. b Significantly greater with respect to the TG at baseline. c Significantly lower with respect to the TG at baseline. d Significantly lower with respect to the CG at baseline. e Significantly greater with respect to the TG at baseline and the CG at baseline and after 8 wk. 142 Official Journal of the American College of Sports Medicine

9 medial rotator peak torques in the TG were 11%, 21%, and 14%, respectively. In addition, the improvements in the eccentric knee flexor and extensor peak torques in the TG were 8% and 16%, respectively, whereas the impairment of the eccentric knee flexor torque in the CG was 8%. No significant differences were observed for any of the isokinetic tests between the TG and CG at baseline (P ) or between the CG at baseline and after 8 wk (P ), with the exception of the reduction in the eccentric knee flexor torque. DISCUSSION Some authors have recently discussed the importance of including specific training of the hip abductor and lateral rotator muscles in knee injury prevention programs (29,40) because it has been suggested that weakness of these muscles might impair lower limb control and favor noncontact ACL injuries and PFPS development (37). Thus, the aims of this study were to determine the effects of a training program emphasizing hip and core strengthening, associated with functional exercises on lower limb kinematics, functional performance, and eccentric hip and knee torques. The results of this study supported the original hypothesis that only women who carried out the function stabilization training program exhibited changes in lower limb kinematics for the knee (decreased knee abduction), femur (decreased femur adduction and increased lateral rotation), and pelvis (decreased pelvis depression). Moreover, only trained women showed increases in functional performance and eccentric hip and knee torques. To the best of the authors knowledge, no study has previously verified the effects of functional stabilization training on the eccentric action of the hip and knee muscles in healthy women. As expected, in this study, only trained women displayed increases in the eccentric hip abductor and lateral rotator torques, as well as in the knee flexor and extensor torques after 8 wk of intervention. Other studies have also shown increases in hip and knee strength after training in healthy women. Snyder et al. (40) observed increases in isometric hip abductor and lateral rotator strength after 6 wk of closed-chain exercises, and Herman et al. (15) showed increases in isometric hip abductor and extensor strength as well as in knee flexor and extensor strength after 9 wk of opened chain exercises. In a pilot study, Myer et al. (30) verified an increase in concentric hip abductor torque after 10 wk of neuromuscular training focused on trunk control and hip strengthening. Data from the current study supplied evidence that training protocols carried out from 6 to 10 wk and focused on hip strengthening associated with core training and functional exercises are efficient in increasing hip and knee strength in women. During weight-bearing activities, the hip abductor and lateral rotator muscles assist in maintaining the pelvis level and act eccentrically controlling excessive femur adduction and medial rotation (9) as well as knee abduction excursions (20). Moreover, cocontraction of the knee flexor and extensor muscles may improve knee stabilization and, consequently, reduce knee abduction movements (25). Thus, it was expected that the strengthening of these muscles might improve lower limb control in the coronal and transverse planes during dynamic activities. The results of the present study showed that the functional stabilization training produced changes in the lower limb kinematics such as decreases in knee abduction and femur adduction and increases in femur lateral rotation. These changes have been associated with reductions in overload on the ACL and patellofemoral joint (38). Although the intervention period was short (8 wk), it was sufficient to cause significant lower limb changes that might contribute to preventing rupture of the ACL and the development of PFPS. The nonexistence of core training and functional exercises with movement pattern correction strategies may have been associated with the absence of significant lower limb kinematic alterations in the literature (15). During landing activities, Herman et al. (15) did not show any strength effects on lower extremity kinematics and kinetics in women after 9 wk of strengthening of the gluteus maximus and medius, hamstring, and quadriceps muscles. These authors concluded that strength training was not sufficient to alter lower limb biomechanics and may not be effective in preventing knee injuries when used alone. The training protocol carried out by the women in the present study was not focused only on strength gains. Indeed, the protocol consisted of a series of closed-chain, core training, and functional exercises, with feedback concerning the dynamic lower limb alignment. The women were introduced to the concept of neutral lower limb alignment as from the third week of intervention, and the exercises were constantly monitored by the physical therapists. Recently, studies have shown positive effects of motor learning strategy instruction in modifying lower limb kinematics, probably by way of changes in neuromuscular patterns. Kato et al. (21) showed that women had better lower limb control in the coronal and transverse planes after only 2 wk of training, emphasizing the neutral position of the lower limbs in dynamic activities. Moreover, beneficial biomechanical effects such as decreases in knee abduction (33), hip adduction (33), and medial rotation excursions (37), as well as increases in gluteus medius EMG activity (24), have been shown in healthy women after the completion of comprehensive neuromuscular training, including plyometric exercises and oral feedback concerning lower limb alignment and control. Thus, although we believe that the increase in hip and knee strength may be an important factor responsible for altering lower limb kinematics, changes in the neuromuscular patterns should not be ruled out and should be considered in future investigations. Another important finding was the increase in functional performance that only occurred in the TG during both the SLTH and TH tests. Some studies have shown improvement in performance after training that emphasized plyometric exercises (17,34). On the other hand, only one study was found that verified the effects of dynamic stabilization EFFECT OF FUNCTIONAL STABILIZATION TRAINING Medicine & Science in Sports & Exercise d 143

10 training on functional performance in healthy women. Myer et al. (32) compared the effects of plyometric versus dynamic stabilization and balance training, on performance in the vertical jump. Improvement in performance was shown in both groups after 7 wk of intervention. Bobbert and van Zandwijk (5) reported that hip muscles activation significantly affects the ability of the quadriceps and hamstring muscles to generate force or resist the forces experienced by the entire leg during jumping. These authors also showed that an increase in hip joint moment, earlier and faster than the other lower limb joint moments, was the only way of promoting an upward forward acceleration of the mass center, necessary for better jumping performance. Thus, it is possible that the functional stabilization training optimized the lower limb propulsion force in the sagittal plane, resulting in better performance. Future studies should investigate the biomechanical factors responsible for improving functional performance after training. The authors recognize there were some limitations in this study. First, the women were not randomized into the groups. Although this could cause bias in the study, we believe the effect was minimized because the women in each group were not chosen by the authors. Moreover, no differences were observed between the groups for the baseline values for any of the variables studied. Second, the evaluator was not blinded to group allocation. Although we are aware that this represents an important concern with respect to bias, it is not always practical or possible to have blinded physical therapists in studies with the current design. Moreover, we believe that the evaluator was less likely to affect the results because all evaluations carried out in this study were objective. Third, because the TG and CG were not studied concurrently this could also induce bias. However, we believe that this error was minimized because of the great experience of the evaluator and the great ICCs of the tests carried out. Fourthly, because the data were only collected at the beginning and end of the training protocol, the long-term effects could not be determined. Finally, the sample used in this study consisted only of healthy women recreational athletes. Future studies should investigate the biomechanical effects of functional stabilization training in healthy elite woman athletes and patients with PFPS. CONCLUSIONS The results of this study provide evidence that functional stabilization training focused on hip abductor and lateral rotator strengthening, core training, and functional exercises with motor learning strategy instruction induce positive changes in lower limb kinematics and functional performance. 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