Influence of Fatigue and Anticipation on Knee Kinematics and Kinetics during a Jump-cut Maneuver

BACKGROUND AND PURPOSE: Injuries to the anterior cruciate ligament (ACL) are common among athletes, particularly females. This research aims to reconcile the anticipated and unanticipated movement pattern of jumping and cutting with fatigue for both genders. The research will compare lower extremity biomechanics of a jump-cut after a sports specific fatigue protocol, intending to examine movement patterns which may predispose the subject to ACL injury. METHODS: Twenty healthy subjects were studied (24.9±3.3yrs), including 10 females. A 3D electromagnetic system measured knee kinematics and kinetics during jump-cut tasks. The jump-cut task included anticipated (A) and unanticipated (UA) trials to both directions. For the UA trials, the subject was unaware of the cutting direction until initiation of the task. The fatigue protocol consisted of jumping, sprinting, step-ups, and agility. Subjects completed the jump-cut task again in a fatigued state. A repeated measures ANOVA was used to analyze peak and mean angles, moments and ground reaction forces (GRF), with post-hoc Tukey tests for significant findings between factors (gender, pre/post-fatigue, A/UA). RESULTS: Significant main effects were found for gender and IR/ER and ADD/ABD peak and/or mean angles, and ADD/ABD moments; pre and post-fatigue and IR/ER, EXT/FLEX, and ADD/ABD peak and/or mean angles, and ADD/ABD moments; A/UA conditions and IR/ER and ADD/ABD peak and/or mean angles. Significant interactions existed for gender and A/UA for EXT moment and for pre/post-fatigue and A/UA for EXT moment, IR moment and IR/ER angles. CONCLUSION: Subjects demonstrated significant changes in knee kinematics and kinetics. Fatigue and A/UA states influenced knee movement patterns in variable ways, which may indicate an attempt to safely land and cut. Additionally, females demonstrated biomechanics that may increase their risk for ACL injury relative to males. Gender, fatigue, and A/UA conditions had an impact on one another and should be considered when designing sports training programs to reduce risky movement patterns

3D Knee Kinematics and Kinetics With Visual Disruption in Subjects With ACL Reconstruction

BACKGROUND AND PURPOSE: The anterior cruciate ligament (ACL) is a commonly ruptured ligament among male and female athletes. Women are at a higher risk of ACL injuries compared to men. The leading cause of female ACL injuries has been identified as non-contact mechanisms. Several risk factors for injury among females that have been theorized include: quadriceps/hamstring activation pattern and force production, greater dynamic knee valgus, hormonal influenced laxity and anatomical gender variation. The purpose of this research was to analyze three dimensional (3D) kinetic and kinematic dynamic landing patterns at the knee between ACL reconstructed and healthy females and any interaction effects of visual disruption. METHODS: Seventeen healthy female subjects (25.3± 6 y) and 17 female subjects with an ACL reconstruction (26.5± 6.3 y) were studied. A 3D electromagnetic system measured knee position during a cutting maneuver from an athletic stance position. Anatomic boney landmarks on the occiput, sacrum, femur and tibia were digitized for capture. Subjects began on a force plate and were instructed to catch a ball and cut immediately left or right as indicated by a specific tone, which was randomized (40 trials). Vision was randomly disrupted via shutter glasses for either one second at the beginning of the cutting maneuver or was left intact for the duration of the movement. A two-way repeated measures ANOVA analyzed the differences between healthy and ACL reconstructed subjects and intact vision versus disrupted vision. RESULTS: The results indicate significant differences exist between subjects with ACL reconstruction and healthy subjects for flexion, adduction, and external rotation knee angles and extension, abduction, and internal rotation moments. Significant interactions of group and vision conditions also exist for flexion, adduction, and external rotation knee angles. Vision alone displayed no significant differences for all subjects. CONCLUSION: Years later, subjects with ACL reconstructions continue to display different knee kinematics and kinetics that could increase their risk for re-injury or injury of other leg. Furthermore, visual disturbances have significant effects on ACL reconstructed knee angles and moments when landing compared to healthy subjects. These results support continued movement related rehabilitation with visual disturbances for ACL reconstructed patients

Influence of Fatigue on Jump and Land Movement Patterns

BACKGROUND AND PURPOSE: Injuries to the anterior cruciate ligament (ACL) are common among both male and female athletes. Both the female gender and fatigue have been demonstrated to increase injury rates. This research aims to reconcile the movement pattern and fatigue protocol with what is seen in sport, while including both men and women to see differences between knee biomechanics. The research will compare the lower extremity biomechanics of a jump-land (double and single leg) between healthy men and women after a sports specific fatigue protocol. Ultimately, this research is intended to examine movement patterns which may predispose the subject to ACL injury. METHODS: Twenty healthy subjects were studied (26.3 ± 3.5 years old), 10 of which were female. A 3D electromagnetic system measured knee kinematics and kinetics during 3 jumping tasks. The subjects completed 4 sets of 3 different, randomized jumps (bilateral to bilateral, bilateral to single-leg right, and bilateral to single-leg left) on force plates. The subjects completed a fatigue protocol consisting of jumping, sprinting, step-ups, and an agility ladder and were immediately re-assessed by completing the 3 different jumps. A paired t-test was used to analyze pre and post fatigue and a one-way ANOVA was used for analyzing gender comparisons for each variable. RESULTS: Significant differences were found between pre-fatigue and post-fatigue internal rotation and adduction knee angles for all 3 landings; other angles and knee moments were significantly different dependent on type of landing. When comparing gender for each variable, internal adduction moments and ground reaction forces were significantly different for all landings. Knee angles were also significantly different dependent on type of landing and dependent variable. Finally, females demonstrated greater biomechanical changes in landing mechanics post-fatigue than males. CONCLUSION: The results support previous literature that fatigue and gender have an impact on jump and land movement patterns at the knee. The differences in knee angles and moments from the current study, as seen by internal adduction moments and ground reaction forces, demonstrate that fatigue and the female gender are risk factors for ACL injury. This may support the current pattern of greater ACL injuries in female athletes, especially when doing a jump-land movement

Muscle Excitation of the Lower Extremity During a Single Leg Rotational Squat in Individuals With and Without a Previous Hamstrings Strain Injury

The hamstrings muscles work with quadriceps and gluteal muscles to stabilize the hip and knee during multidirectional movements. The purpose of this study was to determine muscle excitation patterns of the lower extremity during a single leg rotational squat (SLRS) in individuals with and without a previous hamstrings injury. Twenty physically active individuals between 19-23 years old participated in the study, ten with previous injury and ten without. The Hamstring Outcome Score was used to assess participants’ perceived physical abilities (Hamstring=89.37+7.2%, Control=96.75+2.83%; p=0.011). Participants completed five trials of a SLRS moving through four phases to a 72bpm metronome and reaching to maximum excursion. Wireless electromyography (EMG) was collected on the hamstrings, quadriceps, and gluteal muscles. Mean EMG of each muscle was normalized and reported as %EMG. Between group differences were assessed using one-way ANOVAs for each muscle by phase. Limb differences for the hamstring group were assessed using paired samples t-tests. Significance was set at p\u3c0.05. No statistically significant differences were observed between groups (P\u3e0.05). A statistical difference was observed within group for the biceps femoris during the down phase (P=0.023). The results suggest that individuals with a previous injury perceive a physical deficit, but muscle excitation patterns are similar to their healthy counterpart when performing a SLRS that requires strength and stability. Individuals with previous injury exhibit greater muscle excitation in the biceps femoris of the previously injured limb when moving into a squat position compared to the non-injured leg

Comparison of neuromuscular control strategies between collegiate female dancers and athletes

High risk neuromuscular control strategies during landing and cutting maneuvers are thought to be a major contributing factor to the 6 times greater risk of ACL injury in female athletes compared to male athletes. However, female dancers who have similar fitness capabilities and perform many of the same cutting and landing tasks as female athletes are less likely to display high risk neuromuscular strategies, have similar neuromuscular control strategies as male dancers, and are 3- 5 times less likely to suffer an ACL injury compared to female athletes. While multiple theories have been proposed to explain this protection in female dancers, preliminary research suggests female dancers may adopt a more protective neuromuscular control strategies as a result of their training practices. Therefore, the primary objective of this study was to comprehensively compare neuromuscular control strategies in collegiate female dancers and collegiate female field athletes to determine if female dancers demonstrate more protective neuromuscular control patterns during functional tasks as characterized by 1) decreased vertical ground reaction forces (vGRF), 2) quicker stabilization of the anterior-posterior and medial-lateral ground reaction force, 3) smaller distance between center of mass (COM) and location of center of pressure (COP), 4) decreased knee valgus, 5) increased ankle plantar flexion, 6) decreased knee extensor moment, and 7) quicker muscular activation. Forty collegiate females, 20 dancers (age= 20.4 ± 1.9 yrs, height= 164.8 ± 6.1 cm, weight= 63.5 ± 8.8kg, experience= 14.3 ± 3.9 yrs) and 20 athletes (age= 19.4± .9 yrs, height= 169.3 ± 7.1 cm, weight= 69.8 ± 13.0 kg, experience= 12.2 ± 2.9 yrs) matched on year of experience were measured for postural control during a dynamic forward hop stabilization task; hip, knee and ankle joint neuromechanics during a planned double leg drop landing; and reflex response characteristics during an unplanned lower extremity perturbation. Results revealed no significant differences between female athletes and dancers on muscle reflex time following a functional perturbation or in their time to stabilization during the dynamic balance test. During the drop jump landing, dancers versus athletes landed with lower vGRF [F (3, 33) = 3.44, p = .03, ES = .24], position their COM more anteriorly [F (1,38) = 4.8, p=.03], moved through a greater sagittal plane ROM [F (3, 36) = 4.6, p=.008] primarily driven by greater ankle joint excursion, and move through equal frontal plane motion at the hip and knee [F (2, 37) = 1.6 p=.23, Partial Eta Squared ( )=.08]. The greater sagittal plane excursions values were largely a product of a more extended posture at ground contact and did not result in larger peak values. These findings suggest that dancers and athletes may have similar abilities to respond to postural perturbations, but that female dancers may demonstrate some elements of more protective neuromuscular control strategies during planned movements as a result of their training practices. Investigation of dance training may assist in the development of more protective strategies in dancers and inform our future prevention efforts in female athletics

Effect of Frontal Plane Foot Position on Lower Extremity Muscle Activation and Limb Positioning in a Single Leg Squat

Purpose/Background: Foot positioning during a single leg landing may affect the muscles above the ankle joint and promote positions of increased vulnerability to ACL injury. The purpose of the study was to analyze muscle activity of six muscles in the lower extremity during completion of a single leg squat on the subject’s dominant leg with the subtalar joint in 5 different positions. Methods: Seventeen healthy males and females (ages 18‐30) performed five single leg squats in five foot positions: neutral, five degrees and ten degrees of declination, and five degrees and ten degrees of inclination. Electromyography data was collected from electrodes placed over each muscle. The declination mimicked pronation while the inclination mimicked supination of the foot/subtalar joint. Results: The ten degree angle of pronation had the highest % MVC in four of the six muscles including anterior tibialis, lateral gastrocnemius, gluteus maximus and gluteus medius. With the high variability and large standard deviations, we are unable to make certain of our results. On average, the gluteus maximus muscle had the highest % MVC for all foot positions while the anterior tibialis had the lowest % MVC at 60.22. Lateral gastrocnemius, biceps femoris and gluteus maximus were the three muscles showing statistically significance using Friendman’s. Friedman’s was chosen as our study violated assumptions which prevented us from running a parametric test. Conclusions: Pronation caused the highest % MVC which makes us suspect that the distal joint of the ankle can impact the degree of muscle activation above that joint. This also could be a position of vulnerability as it causes the muscles to contract more which could be secondary to instability, malalignment, or some other factor. More research is needed to study the effect of pronation as our study had several limitations