Determining if an athlete, who has had Anterior Cruciate Ligament (ACL) surgery, is ready to return to sport is a difficult clinical decision, partially due to the lack of standardized evaluation protocols. Since there is a risk of re-injury post-surgery, medical teams need to be cautious. However, athletes who are perceived to be ready to return to sport do not necessarily do so. Some leave sport altogether while others return to a lower competition level. As psychological thoughts and emotions are relevant to athletes’ injury experiences, a psychological component, such as sport confidence, needs to be thoughtfully considered during the return to sport process. Our objectives were to develop the relationship between drop vertical jump (DVJ) performance and physical attributes in young healthy adults and to then apply this relationship to ACL participants. Another objective was to see if the relationship is improved by including confidence (determined from a survey). It was hypothesized that including confidence will predict the ACL participants’ DVJ performance more precisely. Thirty-five participants were in the control group with thirteen participants in the ACL group. All were recreationally active and all had the following anthropometric and performance measurements recorded: height, weight, calf and thigh girth, knee angle, leg dominance, percent body fat, skeletal muscle mass, anaerobic power, balance, and drop vertical jump height. The ACL group also completed a confidence survey. Regression analyses were performed. The results showed that anaerobic power and relative skeletal muscle mass were significant predictors of DVJ performance; however, DVJ performance could not be predicted precisely. The analysis was also carried out by gender. No significant predictors for male’s DVJ performance were found while the significant predictors for female’s DVJ performance were weight, power and knee extension angle. Once again, DVJ performance could not be precisely predicted. On the other hand, results showed that power could be more precisely predicted by body weight than could DVJ performance. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2009-08-19 16:08:52.13

Purpose: Young adolescent females are at the highest risk of sustaining an ACL injury, which may alter their movement and muscle activation patterns yet there is a lack sex- and age- specific guidelines for ACL injury management. The purpose of this study was to (1) evaluate the effects of limb dominance in a healthy uninjured population to serve as a baseline for the ACL-deficient cohort and (2) provide evidence of the neuromuscular patterns and biomechanical loading of uninjured and ACL-deficient knee joints in a female paediatric population. Methods: Eighteen active female adolescents with ACL rupture (ACLd) and 21 uninjured female adolescent controls matched for limb dominance (CON) participated in this study. Participants completed bilateral squats and drop vertical jumps (DVJ) while lower limb electromyography, kinetics and kinematics data were collected. Muscle synergies were extracted using a concatenated non-negative matrix factorization (CNMF) framework and compared between limbs, (CON dominant vs CON non-dominant and CON vs ACLd) across tasks and between limbs within tasks using intraclass correlation coefficients and statistical paramedic mapping. Results: ACLd participants took significantly longer to perform the squat relative to their uninjured peers. No significant differences were found for hip, knee and ankle peak joint flexion angles and moments between populations for the squat. Squat and DVJ muscle synergies were equivalent for dominant and non-dominant uninjured control limbs. ACL injured (ACL deficient and contralateral limbs) exhibited greater variability in DVJ synergy vectors than for the squat task. When comparing across tasks, scaling coefficients were consistently higher for the DVJ for all populations. Conclusion: Differences in lower limb kinematics, muscle activity and muscle activation patterns between dominant and non-dominant limbs indicate that limb symmetry, a clinical tool commonly used to assess rehabilitation and return to play may not provide relevant results. DVJ scaling factors were larger than those of the squat for all groups, likely due to the increased demand of that task. ACLd and CON participants completed squats and DVJ with similar lower limb joint angle patterns and muscle activity. ACL injured groups had fewer consistent vectors across tasks demonstrating greater variability in muscle activation patterns. This increased variability may be due to the ACL injury however, as injured participants were not studied pre- injury it cannot be confirmed.

Purpose: Adolescents have significantly higher rates of diagnosed anterior cruciate ligament (ACL) injuries compared to adult cohorts. Approximately two-thirds of ACL injuries are non-contact scenarios that occur while performing “high-risk” maneuvers. Less than 50% of adolescents are able to return-to-activity, with females specifically having a lower activity level post-injury (Hewett, Di Stasi, & Myer, 2013; Schmale, Kweon, Larson, & Bompadre, 2014). Identifying the quantitative demand of a task used to assess return-to-activity will help establish its role in evaluating the knee stabilization strategies based on muscular coactivations and biomechanical outputs. Therefore, the aim of this study was to (1) assess the neuromuscular and biomechanical quantitative outputs of the lunge and drop-vertical jump (DVJ) in healthy adolescent male and females athletes and (2) to examine the muscular coactivation strategies of adolescent male and female athletes with and without an ACL injury. Methods: A total of 68 uninjured adolescent male and female athletes between the ages of 10 to-18 were used to identify the quantitative demand of the lunge and DVJ. Neuromuscular and biomechanical quantitative outputs included mean peak knee flexion (PKF), integrated knee excursion (iKEXC) in the sagittal and frontal planes, integrated knee joint power (iJP), and integrated electromyography (EMG) were used to assess the within (task) and between (sex) interactions. An additional 17 male and 37 female adolescents with an ACL injury were included to assess the impact of an ACL injury on the knee stabilization strategies (coactivations) used to maintain dynamic knee joint stability (frontal plane knee excursion). Ethics was approved by the University of Ottawa Research Ethics Board (uOttawa REB H09/17/10) (CHEO REB 17/74X). Results: Quantitative data for uninjured groups indicated that the lunge produced greater peak knee flexion, knee excursion, and quadriceps activation values than the DVJ. Conversely, the DVJ produced greater joint power, biceps femoris, gastrocnemii, and gluteus medius values. As for knee stabilization strategies, during the DVJ female ACL injured groups produced greater symmetry and higher muscular activations between anterior-posterior and medial-lateral muscular coactivations, which resulted in increased stability compared to uninjured female groups. Males with an ACL injury indicated similar knee stabilization strategies however decreased stability compared to males without an ACL injury. Conclusion: Results of this thesis identified differences in quantitative data between the lunge and DVJ, indicating differing demand requirements for each task. Results of the second study indicate that uninjured females use knee stabilization strategies that do not restrict their degrees of freedom through asymmetrical coactivations, while females with an ACL injury have increased coactivations in both anterior-posterior and medial-lateral muscle groups, resulting in increased dynamic knee joint stability as evidenced by reduced frontal plane knee excursion motion. Males, however, failed to show a difference between groups in dynamic knee stability, suggesting that those with an ACL injury compensated in a way to perform the DVJ efficiently and similarly to the uninjured group, while maintaining dynamic knee joint stability. In a clinical setting, these findings may help in understanding the direction of use of the lunge and DVJ tasks in a rehabilitation setting. As well as provide insight into the differing male and female adolescent knee stabilization strategies used to maintain dynamic knee joint stability during functional tasks.

INTRODUCTION: The prevalence of ACL injuries is increasing in previous years. One of the most common studied kinematic risk factors related to ACL injuries is a resultant weak, leg axis alignment known as the dynamic knee valgus angle presented during a vertical drop jump [8, 14, 15]. Hewett et. al. concluded that a knee valgus angle was a primary predictor of the mechanism that leads to an ACL rupture [8]. By increasing the excessive knee valgus angle during a two-legged DVJ, an athlete is in turn increasing the possibility of a high knee valgus moment, which can increase the anterior tibial translation as well as the load on the ACL several-fold and the chances for an ACL tear [4]. METHODS: In our study, ten collegiate female participants, including ballet and non-ballet athletes performed two-legged DVJs for 6 different flexor and extensor muscles while digital recordings of knee valgus angle were captured at initial contact and push off with simultaneous collection of EMG data. RESULTS: Results displayed statistical significance for the average valgus angle to estimated GRF ratio for the non-dominant leg at push-off between the ballet and non-ballet athletes (0.8 ± 0.43 vs. 1.8 ± 0.33 degrees/N, p < 0.05). In addition, we also found that the hip extensor activity significantly increased for the non-ballet group and that the lateral thigh CCI noticeably increased for the non-dominant leg for the non-ballet group, which could be indicative of the noticeable difference in the biceps femoris muscle activation for the non-ballet group when comparing sports type. In addition, statistically significant interactions between sports type and leg type for vastus medialis and gluteus maximus were produced. Observed results also indicated that there was an increase in overall variability for the dominant leg of the non-ballet athletes amongst all studied muscles and for the non-dominant leg for the ballet group specifically studying the gluteus maximus muscle activity. DISCUSSION: Relatively, the non-ballet group could be at a higher risk for increase in femoral adduction, hip adduction, and tibial external rotation, and overall predict a larger knee valgus moment; therefore, the non-ballet group could potentially be at a higher risk for an ACL injury than the ballet group. In addition, there is potential in continued research of neuromuscular differences between ballet and non-ballet athletes to further investigate the vastus medialis and the gluteus maximus muscle activations as well as to investigate the knee valgus moment values.

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