Hopping Task Research Articles

No evidence hip joint angle modulates intrinsically produced stretch reflex in human hopping

Motor output in activities such as walking and hopping is suggested to be mediated neurally by purported stretch reflex augmentation of muscle output. Reflex EMG activity during these tasks has been frequently investigated in the soleus muscle; with alterations in reflex amplitude being associated with changes in hip joint angle/phase of the gait cycle. Previous work has focussed on reflex activity induced by an artificial perturbation or by induction of H-reflexes. As such, it is currently unknown if stretch reflex activity induced intrinsically (as part of the task) is modulated by changes in hip joint angle. This study investigated whether hip joint angle modulated reflex EMG ‘burst’ activity during a hopping task performed on a custom-built partially reclined sleigh. Ten subjects participated; EMG and kinematic data (VICON motor capture system) was collected for each hop cycle. Participants completed 5 sets of 30s of self-paced hopping in (1) hip neutral and (2) hip 60° flexion conditions. There was no difference in EMG ‘burst’ activity or in sagittal plane kinematics (knee/ankle) in the hopping task between the two conditions. The results indicate that during a functional task such as hopping, changes in hip angle do not alter the stretch reflex-like activity associated with landing.

The Effect of a Novel Movement Strategy in Decreasing ACL Risk Factors in Female Adolescent Soccer Players

There is a need to investigate the effect of specific movement strategies in reducing biomechanical risk factors for anterior cruciate ligament injury in young female athletes. The purpose of this study was (a) to determine the feasibility of implementing a novel movement strategy (Core-PAC) into a team warm-up before soccer training based on subject compliance and integration of the Core-PAC into the warm-up and (b) to determine whether the Core-PAC would improve peak knee flexion angles and peak abduction moments at the knee during a side cut (SC) and an unanticipated side cut (USC) before kicking a soccer ball, and a side hop (SH) task after immediate instruction and after a 4-week training program. A convenience sample of ten 14- to 16-year-old female soccer players were instructed in the Core-PAC immediately after baseline testing and during a training program consisting of a 20-minute warm-up, 2 times per week. The Core-PAC was understood and accepted by the subjects and incorporated into their warm-up activities with good compliance. After the immediate instruction, there were significant increases in peak knee flexion angles of a mean 6.4° during the SC (p = 0.001), 3.5° during the USC (p = 0.007), and 5.8° during the SH (p < 0.001) tasks. Peak knee abduction moments decreased by a mean of 0.25 N·m·kg(-1) during the SC (p < 0.03), 0.17 N·m·kg(-1) during the USC (p = 0.05), and 0.27 N·m·kg(-1) during the SH (p = 0.04) tasks. After the 4-week training program, some individuals showed improvement. The results of this study suggest that the Core-PAC may be 1 method of modifying high-risk movements for ACL injury such as side cutting and single-leg landing.

The Interday Reliability of Ankle, Knee, Leg, and Vertical Musculoskeletal Stiffness During Hopping and Overground Running

A number of methods are used to measure lower extremity musculoskeletal stiffness, but there is a paucity of research examining the reliability of these techniques. Therefore, we investigated the reliability of vertical, leg, knee, and ankle stiffness during overground running and hopping in 20 active men. Participants were required to run on a 10 m overground runway at 3.83 m/s (actual; 3.35 ± 0.12 m/s) and to hop in place at 2.2 Hz (actual; 2.37 ± 0.03 Hz), and at a self-selected frequency (actual; 2.05 ± 0.12 Hz) and at 2.2 Hz (actual; 2.39 ± 0.04 Hz). Reliability was determined using the intraclass correlation coefficient, coefficient of variation, mean differences, and Cohen's effect sizes. There was good reliability for vertical stiffness, moderate reliability for leg stiffness, and poor reliability for knee and ankle stiffness during the running task. Similar results were observed during the 2.2 Hz hopping tasks, with good reliability displayed for vertical stiffness and poor reliability for ankle and knee stiffness. In conclusion, our results suggest that vertical stiffness is a reliable measure when running at 3.83 m/s and hopping at 2.2 Hz.

Relationship between knee kinetics during jumping tasks and knee articular cartilage MRI T1rho and T2 relaxation times

BackgroundArticular cartilage of young healthy individuals is dynamic and responsive to loading behaviors. The purpose of this study was to evaluate the relationship of cartilage T1ρ and T2 relaxation times with loading kinetics during jumping tasks in healthy young individuals. MethodsFourteen healthy subjects underwent: 1) motion analysis while performing a unilateral hopping task and bilateral drop jumping task; and 2) quantitative imaging using a 3 Tesla MRI for T1ρ and T2 relaxation time analysis. Three dimensional net joint moments and angular impulse was calculated using standard inverse dynamics equations. Average T1ρ and T2 relaxation times and medial-lateral ratios for each were calculated. Multiple regression was used to identify predictors of cartilage relaxation times. FindingsAverage knee flexion moment during hopping was observed to best predict overall T1ρ (R2=.185) and T2 (R2=.154) values. Peak knee adduction moment during a drop jump was the best predictor of the T1ρ medial-lateral ratio (R2=.220). The T2 medial-lateral ratio was best predicted by average internal rotation moment during the drop jump (R2=.174). InterpretationThese data suggest that loads across the knee may affect the biochemistry of the cartilage. In young healthy individuals, higher flexion moments were associated with decreased T1ρ and T2 values, suggesting a potentially beneficial effect. The medial-to-lateral ratio of T1ρ and T2 times appears to be related to the frontal and transverse plane joint mechanics. These data offer promising findings of potentially modifiable parameters associated with cartilage composition.

Utilization of modified NFL combine testing to identify functional deficits in athletes following ACL reconstruction.

Case control. To use modified NFL Combine testing methodology to test for functional deficits in athletes following anterior cruciate ligament (ACL) reconstruction following return to sport. There is a need to develop objective, performance-based, on-field assessment methods designed to identify potential lower extremity performance deficits and related impairments in this population. Eighteen patients (mean ± SD age, 16.9 ± 2.1 years; height, 170.0 ± 8.7 cm; body mass, 71.9 ± 21.8 kg) who returned to their sport within a year following ACL reconstruction (95% CI: 7.8 to 11.9 months from surgery) participated (ACLR group). These individuals were asked to bring 1 or 2 teammates to serve as control participants, who were matched for sex, sport, and age (n = 20; mean ± SD age, 16.9 ± 1.1 years; height, 169.7 ± 8.4 cm; body mass, 70.1 ± 20.7 kg). Functional performance was tested using the broad jump, vertical jump, modified long shuttle, modified pro shuttle, modified agility T-test, timed hop, triple hop, single hop, and crossover hop tests. A 1-way multivariate analysis of variance (MANOVA) was used to evaluate group differences for dependent performance variables. The functional performance measurements of skills requiring bilateral involvement of both lower extremities showed no group differences between the ACLR and control groups (P>.05). An overall group difference (P = .006) was observed for the combined limb symmetry index (LSI) measures. However, the modified double-limb performance tasks (long shuttle, modified agility T-test, and pro shuttle) were not, independently, sufficiently sensitive to detect limb deficits in individuals with ACL reconstruction. Conversely, the LSI on the distance measures of the single-limb performance tasks all provided moderate to large effect sizes to differentiate between the ACLR and control groups, as the individuals who had ACL reconstruction demonstrated involved limb deficits on all measures (P<.05). Finally, the LSI for the timed hop test was not different between groups (P>.05). These findings indicate that, while unilateral deficits are present in individuals following ACL reconstruction, they may not be evident during bipedal performance or during modified versions of double-limb performance activities. Isolation of the involved limb with unilateral hopping tasks should be used to identify deficits in performance.

BIBuilder: Exhaustive Searching for De Novo Ligands.

The de novo design program BIBuilder has been developed for structure-based as well as ligand-based design. Incremental growth allows for the de novo design of novel molecules with putative bioactivity. In addition, linking between existing fragments enables scaffold hopping tasks. A RECAP-based retrosynthetic fragment connection protocol yields ligands that are synthesizable. An exhaustive fragment search protocol assures that known ligands are always found if all necessary fragments exist in the database of building blocks. To make an exhaustive search possible, a strategy of connecting tens of thousands of unique fragments with only three growth or linking steps is adopted resulting in the generation of up to 10(16) possible compounds with up to 10(21) conformations. Ligands are scored by shape and pharmacophore matches that can be individually weighted. Final hits are evaluated through customizable scoring functions. Estrogen receptor, COX-2, renin, and NNRTI examples illustrate the performance of BIBuilder in different tasks such as structure-based or ligand-based growing and linking. Not only are known ligands reproduced in all test cases but a number of interesting alternative scaffolds and ligands have been found.

Landing Mechanics During Side Hopping and Crossover Hopping Maneuvers in Noninjured Women and Women With Anterior Cruciate Ligament Reconstruction

To compare, landing mechanics and electromyographic activity of the lower extremities during side hopping and crossover hopping maneuvers, in noninjured women and women with anterior cruciate ligament (ACL) reconstruction. A case-control study. A 3-dimensional motion analysis laboratory. Twenty-eight young women (range, 21-35 years) (15 control subjects and 13 subjects with ACL reconstruction). All participants performed a side-to-side hopping task that consisted of hopping single-legged 10 times consecutively from side to side across 2 lines marked 30 cm apart on 2 individual force plates. The task was designated as a side hopping when the hop was to the opposite side of the stance leg and as crossover hopping when the hop was toward the side of the stance leg. Peak hip-/knee-joint angles; peak knee extension/abduction joint moments; electromyographic studies of the gluteus maximus, gluteus medius, rectus femoris, and hamstring muscles; and quadriceps/hamstring co-contraction ratio were compared between the groups by means of 2 × 2 multivariate analysis of variance tests (group × maneuver). Noninjured women and women with ACL reconstruction exhibited similar hip- and knee-joint angles during both types of hopping. Hip-joint angles were greater during the crossover hopping in both groups, and knee-joint angles did not differ between the groups or hops. Knee-joint moments demonstrated a significant group × maneuver interaction. Greater knee extension and valgus moments were noted in the control group during crossover hopping, and greater knee abduction moments were noted in the ACL group during side hopping. Electromyographic data revealed no statistically significantly differences between the groups. Women with ACL reconstruction exhibited the restoration of functional biomechanical movements such as hip-/knee-joint angles and lower extremity neuromuscular activation during side-to-side athletic tasks. However, not all biomechanical strategies are restored years after surgery, and women who have undergone a procedure such as ACL reconstruction may continue to exhibit knee-joint abduction moments that increase the risk of additional knee injury.

Analogy between Juggling and Hopping: Active Object Manipulation Approach

Dynamic manipulation of an active object is introduced as a general model of hopping and juggling tasks. In this setting, juggling and hopping are two extreme cases of this general model. Behavioral resemblance of these two tasks is afterwards extended to a detailed mathematical analogy between them. Then the analogy is exploited to develop a unified and abstract planning framework for juggling and hopping. To this end, dynamic manipulation of an active object is decomposed into three distinct phases and two transitions: Carry I, Free flight and Carry II phases. These phases are analogous to Lift off, Free flight and Touch down in hopping. In the next step, a mathematical model for each phase is developed. It is shown that dynamic grasp (in Carry phases of juggling) and foot stability (in Support phases of hopping) conditions share similar sets of dynamic equations. Accordingly, Lift off/Release and Touch down/Catch conditions in hopping/juggling are derived. It is shown that analogous strategies can be developed for Lift off and Release. The analogy is held for Touch down and Catch conditions as well. It is discussed that in the planning framework the initial and the goal configurations of the three phases are set in a model-based and forward manner. To do so, Touch down/Landing time, Free flight duration and robot/object maneuvers during Free flight are used as free parameters for planning in order to ensure foot stability in hopping and dynamic grasp in juggling along with other constraints.

A Framework for Automatic Generation of a Contact State Graph for Robotic Assembly

Dynamic manipulation of an active object is introduced as a general model of hopping and juggling tasks. In this setting, juggling and hopping are two extreme cases of this general model. Behavioral resemblance of these two tasks is afterwards extended to a detailed mathematical analogy between them. Then the analogy is exploited to develop a unified and abstract planning framework for juggling and hopping. To this end, dynamic manipulation of an active object is decomposed into three distinct phases and two transitions: Carry I, Free flight and Carry II phases. These phases are analogous to Lift off, Free flight and Touch down in hopping. In the next step, a mathematical model for each phase is developed. It is shown that dynamic grasp (in Carry phases of juggling) and foot stability (in Support phases of hopping) conditions share similar sets of dynamic equations. Accordingly, Lift off/Release and Touch down/Catch conditions in hopping/juggling are derived. It is shown that analogous strategies can be developed for Lift off and Release. The analogy is held for Touch down and Catch conditions as well. It is discussed that in the planning framework the initial and the goal configurations of the three phases are set in a model-based and forward manner. To do so, Touch down/Landing time, Free flight duration and robot/object maneuvers during Free flight are used as free parameters for planning in order to ensure foot stability in hopping and dynamic grasp in juggling along with other constraints.

Pelvic Kinematic Method for Determining Vertical Jump Height

Sacral marker and pelvis reconstruction methods have been proposed to approximate total body center of mass during relatively low intensity gait and hopping tasks, but not during a maximum effort vertical jumping task. In this study, center of mass displacement was calculated using the pelvic kinematic method and compared with center of mass displacement using the ground-reaction force-impulse method, in experienced athletes (n = 13) performing restricted countermovement vertical jumps. Maximal vertical jumps were performed in a biomechanics laboratory, with data collected using an 8-camera motion analysis system and two force platforms. The pelvis center of mass was reconstructed from retro-reflective markers placed on the pelvis. Jump height was determined from the peak height of the pelvis center of mass minus the standing height. Strong linear relationships were observed between the pelvic kinematic and impulse methods (R² = .86; p < .01). The pelvic kinematic method underestimated jump height versus the impulse method, however, the difference was small (CV = 4.34%). This investigation demonstrates concurrent validity for the pelvic kinematic method to determine vertical jump height.

Patellar Tendinopathy Alters the Distribution of Lower Extremity Net Joint Moments during Hopping

The purpose of the current investigation was to test the hypothesis that subjects with patellar tendinopathy would demonstrate altered sagittal plane joint moment contributions during hopping tasks. Fourteen subjects (7 patellar tendinopathy, 7 controls) participated. Sagittal net joint moments of the lower extremity, total support moment, and joint contributions to the total support moment were calculated while subjects hopped continuously at a self-selected frequency and at 1.67 Hz. Significant differences were observed for contributions to the total support moment (p=.022). When averaged across hopping frequencies, subjects with patellar tendinopathy demonstrated greater hip contribution (p=.030) and lesser knee contribution (p=.006) compared with the control subjects. Shifting the workload away from the knee and toward the hip may result in a detrimental increase in hip demand and potentially harmful long-term effects on the articular cartilage of the hip.

Fatigue Effects on Knee Joint Stability During Two Jump Tasks in Women

Dynamic knee joint stability may be affected by the onset of metabolic fatigue during sports participation that could increase the risk for knee injury. The purpose of this investigation was to determine the effects of metabolic fatigue on knee muscle activation, peak knee joint angles, and peak knee internal moments in young women during 2 jumping tasks. Fifteen women (mean age: 24.6 +/- 2.6 years) participated in one nonfatigued session and one fatigued session. During both sessions, peak knee landing flexion and valgus joint angles, peak knee extension and varus/valgus internal moments, electromyographic (EMG) muscle activity of the quadriceps and hamstrings, and quadriceps/hamstring EMG cocontraction ratio were measured. The tasks consisted of a single-legged drop jump from a 40-cm box and a 20-cm, up-down, repeated hop task. The fatigued session included a Wingate anaerobic protocol followed by performance of the 2 tasks. Although participants exhibited greater knee injury-predisposing factors during the fatigued session, such as lesser knee flexion joint angles, greater knee valgus joint angles, and greater varus/valgus internal joint moments for both tasks, only knee flexion during the up-down task was statistically significant (p = 0.028). Metabolic fatigue may perhaps predispose young women to knee injuries by impairing dynamic knee joint stability. Training strength-endurance components and the ability to maintain control of body movements in either rested or fatigued situations might help reduce injuries in young women athletes.

Abnormal landing strategies after ACL reconstruction

The objective was to analyze muscle activity and movement patterns during landing of a single leg hop for distance after anterior cruciate ligament (ACL) reconstruction. Nine (six males, three females) ACL-reconstructed patients 6 months after surgery and 11 (eight males, three females) healthy control subjects performed the hop task. Electromyographic signals from lower limb muscles were analyzed to determine onset time before landing. Biomechanical data were collected using an Optotrak Motion Analysis System and force plate. Matlab was used to calculate kinetics and joint kinematics. Side-to-side differences in ACL-reconstructed patients and healthy subjects as well as differences between the patients and control group were analyzed. In ACL-reconstructed limbs, significantly earlier onset times were found for all muscles, except vastus medialis, compared with the uninvolved side. The involved limbs had significantly reduced knee flexion during the take-off and increased plantarflexion at initial contact. The knee extension moment was significantly lower in the involved limb. In the control group, significantly earlier onset times were found for the semitendinosus, vastus lateralis and medial gastrocnemius of the non-dominant side compared with the dominant side. Muscle onset times are earlier and movement patterns are altered in the involved limb 6 months after ACL reconstruction.

The Effects Of Growth And Maturation On Leg Stiffness And Reactive Strength Index In Youths Aged 7 - 18 Years

Stretch-shortening cycle (SSC) function, recognized as fundamental for effective plyometrics and sprinting, can be estimated from measures of leg stiffness and reactive strength index (RSI). Whilst published data for these measures exist for adult populations, limited data is available within paediatric populations. Given the significance of SSC to explosive ability, it is deemed necessary to identify potential sensitive periods of growth and development which may produce accelerated adaptations. (i) determine differences in leg stiffness and RSI between chronological- and maturity-divided groups of schoolchildren (2nd-11 th Grade) and (ii) investigate whether age- or maturity-related factors were dominant contributors to RSI and leg stiffness performance. Two hundred and fifty high school-aged boys performed four maximal hopping trials and a single trial of sub-maximal hopping (2.5Hz). RSI was calculated from the maximal hopping task, whilst leg stiffness was calculated from the sub-maximal test. Additionally, four trials of both squat- (SJ) and countermovement-jumps (CMJ) were performed, representing concentric strength and slow SSC respectively, with the mean of the best two jump heights being used for analysis. One-way ANOVA's revealed significant increases in leg stiffness between grades 3-5 and 7-10; and between grades 4-6 and 7-10 for RSI. When grouped according to estimated maturity, significant differences were found for both leg stiffness and RSI between-3 years pre-PHV (mean −2.97 yr) and PHV(mean −0.05 yr), and between PHV and + 3 years post PHV (mean 2.99 yr). Multiple stepwise regression analysis revealed that body mass (R2 change = 0.62), RSI (R2 change = 0.02) and maturity status (R2 change = 0.02) produced the greatest explained variance for leg stiffness (R2 = 0.66; p < 0.001). When leg stiffness was normalised to body mass, height (R2 change = 0.28), RSI (R2 change = 0.09) and maturity (R2 change = 0.03) produced the greatest explained variance (R2 = 0.40; p < 0.001). For RSI, SJ (R2 change = 0.54), stiffness (R2 change = 0.03), body mass (R2 change = 0.02), CMJ (R2 change = 0.01) and age (R2 change = 0.01) produced the largest explained variance (R2 = 0.61; p < 0.02). Statistics for both tolerance (> 0.1) and VIF (< 10) suggested minimal risk of multicolinearity for both models. The greatest variance in leg stiffness and RSI can be explained by maturational factors (body mass and concentric strength respectively). Therefore the windows of accelerated adaptation should be expressed in relation to the onset of PHV as opposed to chronological age. Three years pre- and post-PHV should be considered as suitable windows in which to maximise SSC adaptation. Periods of accelerated adaptation have been suggested to reflect a time when a system(s) is most sensitive to manipulation, therefore SSC-type training may be most beneficial during the identified maturity related periods of accelerated adaptation. Within these identified periods training emphasis should be placed on concentric strength expression for RSI development. Whilst body mass was identified as the main contributor to leg stiffness, owing to the limited amount of explained variance for relative leg stiffness alternative biomechanical, neuromuscular or motor control variables should be considered in future research.

Association of Quadriceps and Hamstrings Cocontraction Patterns With Knee Joint Loading

Sex differences in neuromuscular control of the lower extremity have been identified as a potential cause for the greater incidence of anterior cruciate ligament (ACL) injuries in female athletes compared with male athletes. Women tend to land in greater knee valgus with higher abduction loads than men. Because knee abduction loads increase ACL strain, the inability to minimize these loads may lead to ACL failure. To investigate the activation patterns of the quadriceps and hamstrings muscles with respect to the peak knee abduction moment. Cross-sectional study. Neuromuscular research laboratory. Twenty-one recreationally active adults (11 women, 10 men). Volunteers performed 3 trials of a 100-cm forward hop. During the hop task, we recorded surface electromyographic data from the medial and lateral hamstrings and quadriceps and recorded lower extremity kinematics and kinetics. Lateral and medial quadriceps-to-hamstrings (QratioH) cocontraction indices, the ratio of medial-to-lateral QratioH cocontraction, normalized root mean square electromyographic data for medial and lateral quadriceps and hamstrings, and peak knee abduction moment were calculated and used in data analyses. Overall cocontraction was lower in women than in men, whereas activation was lower in the medial than in the lateral musculature in both sexes (P < .05). The medial QratioH cocontraction index (R(2) = 0.792) accounted for a significant portion of the variance in the peak knee abduction moment in women (P = .001). Women demonstrated less activation in the vastus medialis than in the vastus lateralis (P = .49) and less activation in the medial hamstrings than in the lateral hamstrings (P = .01). Medial-to-lateral QratioH cocontraction appears to be unbalanced in women, which may limit their ability to resist abduction loads. Because higher abduction loads increase strain on the ACL, restoring medial-to-lateral QratioH cocontraction balance in women may help reduce ACL injury risk.

Effectiveness Of Aquatic Therapy Versus Land Therapy In Athletes With Lower Extremity Injuries

Aquatic therapy is one of the many options for the rehabilitation of lower extremity injuries in athletes. However, the literature comparing the effects of aquatic and land therapy combined in athletes is scarce. PURPOSE: The purpose of this investigation was to determine if a combined aquatic and land therapy program was more effective than land therapy alone in improving lower extremity power and agility of injured athletes. It was hypothesized that athletes participating from the combined program would exhibit greater power and agility measures than those in the land program after four weeks. METHODS: Nine athletes were randomly assigned to land (n=5) and the combined (n=4) therapy rehabilitation programs. Physical therapy prescription was individualized to meet specific needs of the athlete and their injury. Treatment was offered three times per week for approximately 60 - 75 minutes each day. The follow-up measures were at four weeks after the beginning of therapy and included assessment of power, hopping and running agility. A maximal vertical jump was used to measure lower extremity power and jumping performance. Dynamic stability during hopping and pivoting activities was measured by using a figure eight hop task. A zigzag run task was used to measure running agility. Symmetry indexes between the noninjured and injured limb were calculated for the vertical jump and figure-eight tasks. Mann-Whitney U-test was used to compare differences between groups after the intervention for each of the variables. RESULTS: Statistically significant differences were found for both vertical jump measures (p<.03), with the group receiving the combined therapy exhibiting better outcomes at four weeks compared to the land therapy group. No statistically significant differences for the figure eight and zigzag run results were found. CONCLUSIONS: Aquatic therapy combined with land therapy helped improve lower extremity power and symmetry between both legs in young athletes after four week intervention. However, the results showed no differences in running, cutting, pivoting and agility for those elite athletes participating in either intervention. Perhaps the demands of these tasks or small sample size could have affected the results. Nevertheless, studies with bigger sample size are needed before conclusions can be drawn.

Neuromuscular Control During Sidestepping and Cross- Over Maneuvers Among Noninjured Women and Women With ACL Reconstruction

Dynamic joint stability is an essential requirement for the prevention of knee injuries during pivoting and cutting maneuvers especially after ACL reconstruction. PURPOSE: To compare electromyographic (EMG) activity and quadriceps/ hamstrings EMG co-contraction ratio in noninjured women and women with ACL reconstruction during a sidestepping and cross-over maneuver. METHODS: Twenty seven young women (noninjured = 15, ACL = 12) participated in this investigation. Each participant performed a repetitive side-to-side hop task after a warm-up protocol. The side-side hop task comprised of hoping single-legged ten consecutive times from side to side of two lines marked 30-cm apart in two individual force plates. Participants performed two trials of this task. The task was divided as a side step when the hop was to the opposite side of the landing leg and as a cross-over when the hop was towards the side of the landing leg. Each participant had four self adhesive Ag/AgCl pre-amplified electrodes on the skin over the gluteus maximus/medius, rectus femoris, medial hamstring and lateral hamstring muscles on the dominant leg for the noninjured women and in the reconstructed leg for the women with ACL reconstruction. The maximum muscle activity during the specific trial during the ground contact phase was used as a dynamic normalization procedure. EMG data was time synchronized to two force plates at a frequency of 1 kHz. The raw EMG signal was filtered, rectified, and then normalized. The quadriceps/hamstrings co-contraction ratio was calculated as the ratio between the EMG of the less active muscle divided by the more active muscle multiplied by a 100. Separate 2 x 2 factorial MANOVAs (group x maneuver) with repeated measures for the maneuver factor were performed with follow-up ANOVAs when necessary. RESULTS: No statistically significant differences were found for the interaction and main effects (p > .05). CONCLUSIONS: Women with ACL reconstruction exhibited similar neuromuscular recruitment strategies that allowed them to perform both maneuvers comparable to noninjured women. It appears that the selected lower extremity muscles perform similarly during sidestepping and crossover maneuvers in ACL reconstructed and healthy women. Supported by NIH grants G12RR03051, 1P20RR11126 and NSCA Foundation.

Landing Mechanics between Noninjured Women and Women with Anterior Cruciate Ligament Reconstruction during 2 Jump Tasks

Background Women with anterior cruciate ligament reconstruction have different neuromuscular strategies than noninjured women during functional tasks after ligament reconstruction and rehabilitation. Hypothesis Landing from a jump creates high loads on the knee creating dynamic instability in women with anterior cruciate ligament reconstruction, whereas noninjured women have stable knee landing mechanics. Study Design Controlled laboratory study. Methods Fifteen noninjured women and 13 women with anterior cruciate ligament reconstruction performed 5 trials of a single-legged 40-cm drop jump and 2 trials of a 20-cm up-down hop task. Multivariate analyses of variance were used to compare hip and knee joint kinematics, knee joint moments, ground-reaction forces, and electromyographic findings between the dominant leg in noninjured women and reconstructed leg in women with anterior cruciate ligament reconstruction. Results No statistically significant differences between groups were found for peak hip and knee joint angles for the drop jump task. Statistically significant differences in neuromuscular activity (P = .001) and anterior-posterior knee shear forces (P < .001) were seen in women with anterior cruciate ligament reconstruction compared with noninjured women in the drop jump task. However, no statistically significant differences (P > .05) between groups were found for either peak hip and knee joint angles, peak joint kinetics, or electromyographic findings during the up-down hop task. Conclusion Women with anterior cruciate ligament reconstruction have neuromuscular strategies that allow them to land from a jump similar to healthy women, but they exhibit joint moments that could predispose them to future injury if they participate in sports that require jumping and landing.

Landing Mechanics Between Non-injured Women and Women with ACL Reconstruction During a 40-cm Drop Jump

Women with ACL reconstruction present with neuromuscular deficits that could predispose them to further injuries during sports participation. PURPOSE: To compare landing mechanics during a 40-cm drop jump and a 20-cm up-down hop tasks between ACL reconstructed and non-injured women. METHODS: Fourteen women with ACL reconstruction (25.4 ± 3.1) and fifteen non-injured women (24.6 ± 2.6) participated in this study. Each participant had 12 retro-reflective markers attached over bony prominences on one lower extremity and surface EMG electrodes in the gluteus maximus, quadriceps, and hamstrings. Each participant performed five drop jump task trials and 2 trials of the up-down hop task after a warm-up protocol. The drop jump consisted of standing on a 40-cm platform and performing a maximal vertical jump after landing onto a force plate. The up-down consisted of jumping single-legged ten times up-to and down-from a 20-cm step. Peak kinematics, kinetics, normalized rectified electromyography measures and quadriceps/hamstrings co-contraction ratio were analyzed after normality assumptions and outliers screening procedures. Multivariate analyses of variance, with follow-up ANOVA's, were used for analyses. RESULTS: During the drop jump, no statistically significant differences between groups were found for peak hip and knee joint angles. However, significant differences between groups were found for kinetic and EMG variables. Follow-up ANOVA's on kinetic and EMG variables showed lower peak anterior-posterior shear forces, greater joint moments, greater quadriceps/hamstrings co-contraction ratios, greater gluteus maximus EMG and greater rectus femoris EMG in the group with ACL reconstruction. During the up-down, no statistically significant differences were found for any of the variables measured. CONCLUSIONS: Landing mechanics were similar between healthy, non-injured women and women more than one year after ACL reconstruction. During the drop jump, electromyographic measures suggested neuromuscular compensation strategies in women with ACL reconstruction that could explain the similarities in landing kinematics. However, differences for kinetic measures suggested differences in landing strategies that could predispose women with ACL reconstruction to further injury.

Ankle function during hopping in subjects with functional instability of the ankle joint

A common mechanism of inversion injury involves a lateral movement producing a hypersupination of the ankle joint. To date, no study has investigated patterns of muscle activity, three-dimensional (3D) joint kinematics and kinetics simultaneously in a group of subjects with functional instability (FI) compared with a non-injured control group during a lateral hopping test. Twenty-six subjects with the subjective complaint of FI of the ankle joint and 24 non-injured healthy control subjects volunteered to participate in the study. We measured 3D lower limb kinematics, kinetics and surface electromyography (EMG) of the rectus femoris, tibialis anterior, peroneus longus and soleus muscle in all subjects during a lateral hop task for the period 200 ms pre- and post-initial contact (IC). FI subjects were observed to have a less-everted position of the ankle joint during the time period from 45 ms pre-IC to 95 ms post-IC (P<0.05). FI subjects were also found to have an increase in pre- and post-IC rectus femoris, tibialis anterior and solues EMG activity. The results suggest that subjects with FI exhibit changes in ankle joint movement and neuromuscular control that could predispose to further injury.