Hayley M. Ericksen

Contributions of neural excitability and voluntary activation to quadriceps muscle strength following anterior cruciate ligament reconstruction.

BACKGROUND Persistent quadriceps weakness is common following anterior cruciate ligament reconstruction (ACLr). Alterations in spinal-reflexive excitability, corticospinal excitability and voluntary activation have been hypothesized as underlying mechanisms contributing to quadriceps weakness. The aim of this study was to evaluate the predictive capabilities of spinal-reflexive excitability, corticospinal excitability and voluntary activation on quadriceps strength in healthy and ACLr participants. METHODS Quadriceps strength was measured using maximal voluntary isometric contractions (MVIC). Voluntary activation was quantified via the central activation ratio (CAR). Corticospinal and spinal-reflexive excitability were measured using active motor thresholds (AMT) and Hoffmann reflexes normalized to maximal muscle responses (H:M), respectively. ACLr individuals were also split into high and low strength subsets based on MVIC. RESULTS CAR was the only significant predictor in the healthy group. In the ACLr group, CAR and H:M significantly predicted 47% of the variance in MVIC. ACLr individuals in the high strength subset demonstrated significantly higher CAR and H:M than those in the low strength subset. CONCLUSION Increased quadriceps voluntary activation, spinal-reflexive excitability and corticospinal excitability relates to increased quadriceps strength in participants following ACLr. CLINICAL RELEVANCE Rehabilitation strategies used to target neural alterations may be beneficial for the restoration of muscle strength following ACLr.

Sex differences, hormone fluctuations, ankle stability, and dynamic postural control

CONTEXT Hormonal fluctuation as a risk factor in anterior cruciate ligament injury has been investigated with conflicting results. However, the influence of hormone fluctuations on ankle laxity and function has not been thoroughly examined. OBJECTIVE To examine the potential hormone contributions to ankle laxity and dynamic postural control during the preovulatory and postovulatory phases of the menstrual cycle using an ankle arthrometer and the Star Excursion Balance Test in healthy women. The cohort group consisted of male control participants. DESIGN Cohort study. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty healthy women (age = 23.8 ± 6.50 years, height = 163.88 ± 8.28 cm, mass = 63.08 ± 12.38 kg) and 20 healthy men (age = 23.90 ± 4.15 years, height = 177.07 ± 7.60 cm, mass = 80.57 ± 12.20 kg). INTERVENTION(S) Ankle stability was assessed with anterior-posterior and inversion-eversion loading. Dynamic postural control was assessed with the posteromedial reaching distance of the Star Excursion Balance Test. MAIN OUTCOME MEASURE(S) Female participants used ovulation kits for 3 months to determine the time of ovulation; during their preovulatory and postovulatory phases, they were tested in the laboratory with an ankle arthrometer and the Star Excursion Balance Test. Male participants were tested on similar dates as controls. For each dependent variable, a time by side by sex repeated-measures analysis of variance was performed. Statistical significance was set a priori at P < .05. RESULTS For anterior-posterior laxity, a side main effect was noted (F₁,₃₈ = 10.93, P = .002). For inversion-eversion laxity, a sex main effect was seen (F₁,₃₈ = 10.75, P = .002). For the posteromedial reaching task, a sex main effect was demonstrated (F₁,₃₈ = 8.72, P = .005). No influences of time on the dependent variables were evident. CONCLUSIONS Although women presented with more ankle inversion-eversion laxity and less dynamic postural control, hormonal fluctuations during the menstrual cycle (preovulatory compared with postovulatory) did not affect ankle laxity or dynamic postural control, 2 factors that are associated with ankle instability.

Neural Excitability Alterations After Anterior Cruciate Ligament Reconstruction

CONTEXT Neuromuscular dysfunction is common after anterior cruciate ligament reconstruction (ACL-R). However, little is known about quadriceps spinal-reflex and descending corticomotor excitability after ACL-R. Understanding the effects of ACL-R on spinal-reflex and corticomotor excitability will help elucidate the origins of neuromuscular dysfunction. OBJECTIVE To determine whether spinal-reflex excitability and corticomotor excitability differed between the injured and uninjured limbs of patients with unilateral ACL-R and between these limbs and the matched limbs of healthy participants. DESIGN Case-control study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 28 patients with unilateral ACL-R (9 men, 19 women; age = 21.28 ± 3.79 years, height = 170.95 ± 10.04 cm, mass = 73.18 ± 18.02 kg, time after surgery = 48.10 ± 36.17 months) and 29 participants serving as healthy controls (9 men, 20 women; age = 21.55 ± 2.70 years, height = 170.59 ± 8.93 cm, mass = 71.89 ± 12.70 kg) volunteered. MAIN OUTCOME MEASURE(S) Active motor thresholds (AMTs) were collected from the vastus medialis (VM) using transcranial magnetic stimulation. We evaluated VM spinal reflexes using the Hoffmann reflex normalized to maximal muscle responses (H : M ratio). Voluntary quadriceps activation was measured with the superimposed-burst technique and calculated using the central activation ratio (CAR). We also evaluated whether ACL-R patients with high or low voluntary activation had different outcomes. RESULTS The AMT was higher in the injured than in the uninjured limb in the ACL-R group (t27 = 3.32, P = .003) and in the matched limb of the control group (t55 = 2.05, P = .04). The H : M ratio was bilaterally higher in the ACL-R than the control group (F1,55 = 5.17, P = .03). The quadriceps CAR was bilaterally lower in the ACL-R compared with the control group (F1,55 = 10.5, P = .002). The ACL-R group with low voluntary activation (CAR < 0.95) had higher AMT than the control group (P = .02), whereas the ACL-R group with high voluntary activation (CAR ≥ 0.95) demonstrated higher H : M ratios than the control group (P = .05). CONCLUSIONS The higher VM AMT in the injured limbs of ACL-R patients suggested that corticomotor deficits were present after surgery. Higher bilateral H : M ratios in ACL-R patients may be a strategy to reflexively increase excitability to maintain voluntary activation.

Different Modes of Feedback and Peak Vertical Ground Reaction Force During Jump Landing: A Systematic Review

CONTEXT Excessive ground reaction force when landing from a jump may result in lower extremity injuries. It is important to better understand how feedback can influence ground reaction force (GRF) and potentially reduce injury risk. OBJECTIVE To determine the effect of expert-provided (EP), self-analysis (SA), and combination EP and SA (combo) feedback on reducing peak vertical GRF during a jump-landing task. DATA SOURCES We searched the Web of Science database on July 1, 2011; using the search terms ground reaction force, landing biomechanics, and feedback elicited 731 initial hits. STUDY SELECTION Of the 731 initial hits, our final analysis included 7 studies that incorporated 32 separate data comparisons. DATA EXTRACTION Standardized effect sizes and 95% confidence intervals (CIs) were calculated between pretest and posttest scores for each feedback condition. DATA SYNTHESIS We found a homogeneous beneficial effect for combo feedback, indicating a reduction in GRF with no CIs crossing zero. We also found a homogeneous beneficial effect for EP feedback, but the CIs from 4 of the 10 data comparisons crossed zero. The SA feedback showed strong, definitive effects when the intervention included a videotape SA, with no CIs crossing zero. CONCLUSIONS Of the 7 studies reviewed, combo feedback seemed to produce the greatest decrease in peak vertical GRF during a jump-landing task.

Immediate effects of real-time feedback on jump-landing kinematics.

STUDY DESIGN Randomized controlled trial. OBJECTIVE To determine if the addition of real-time feedback (RTF) to postresponse feedback (PRF) improves jump-landing kinematics compared to PRF alone and a no-feedback control group. BACKGROUND Injury-prevention programs to reduce risk of anterior cruciate ligament injury have shown promising results in altering jump-landing biomechanics. Real-time feedback provided during the task may allow participants to more easily understand and execute new movement strategies compared to PRF provided after the task is completed. METHODS Thirty-six healthy females were randomized to 1 of 3 groups: RTF plus PRF, PRF, or control. Sagittal plane moments and angles at the knee and hip, frontal plane angles at the knee, and vertical ground reaction forces during a jump-landing task were quantified at baseline and postintervention. The RTF plus PRF and PRF groups received a PowerPoint presentation containing the goals of correct landing technique. In addition to the PowerPoint presentation, the RTF plus PRF group was provided real-time visualization of their frontal plane knee angle. Participants in the control group performed the jump-landing task without feedback. RESULTS Posttraining, the RTF plus PRF and PRF groups demonstrated similar improvements in hip and knee flexion and decreased vertical ground reaction forces compared to the control group. There were no changes in frontal plane knee kinematics between groups posttraining. CONCLUSION The addition of RTF to PRF did not result in significant changes in jump-landing kinematics compared to PRF alone. LEVEL OF EVIDENCE Prevention, level 5.

Jump-landing biomechanics following a 4-week real-time feedback intervention and retention.

BACKGROUND Poor neuromuscular control can increase the risk of anterior cruciate ligament (ACL) injury. Landing with decreased knee and hip flexion may increase the risk of lower extremity injury. Feedback interventions have demonstrated changes in jump-landing biomechanics. Traditional feedback (TF), provided after task completion, includes critical factors to focus on during jump-landing. Real-time feedback (RTF), provided while completing the task, may be superior for improving jump-landing biomechanics. This investigation evaluated the effect of RTF+TF compared to TF and a control group in changing lower extremity jump-landing biomechanics following a 4-week feedback intervention and a 1-week no feedback retention. METHODS Participants completed 12 feedback sessions over 4 weeks. At each session, participants performed 6 sets of 6 jumps off a 30 cm box. Participants were provided TF or RTF+TF following each set of jumps. Participants were tested at baseline, immediately following the 4-week intervention and following a 1-week retention. The control group was tested at two time points 4 weeks apart. FINDINGS Acquisition analysis: RTF+TF and TF groups demonstrated greater change in peak hip flexion angles and peak knee flexion angles compared to the control group following the intervention. TF and RTF+TF groups demonstrated a greater decrease in peak vertical ground reaction force compared to the control group. No significant differences were observed between groups in the retention analysis. INTERPRETATION This study provides evidence of acquisition of biomechanical changes following a 4-week feedback intervention. Future research should further investigate the retention of biomechanical changes, the optimal length of feedback interventions and transfer of learned biomechanics to similar athletic tasks.

Evaluation of Agreement between Participant and Expert on Jump-landing Characteristics During a 4-week Intervention

CONTEXT Feedback is an important factor in interventions designed to reduce anterior cruciate ligament injury risk. Self-analysis feedback requires participants to self-critique their jump-landing mechanics; however, it is unknown if individuals can effectively self-analyze their own biomechanics and if this self-analysis agrees with observed biomechanical changes by an expert. OBJECTIVE To determine agreement between an expert and participants on biomechanical errors committed during 3 of 12 sessions, which were part of an intervention to change jump-landing biomechanics in healthy females. DESIGN Descriptive analysis. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Healthy recreationally active females with no history of lower-extremity fracture or surgery. INTERVENTIONS Participants completed a 4-week, 12-session feedback intervention. Each intervention session lasted approximately 15 minutes and included asking participants to perform 6 sets of 6 jumps off a 30-cm-high box placed 50% of their height away from the target landing area. Participants performed self-analysis feedback and received expert feedback on 7 different jump-landing criteria following each set of jumps. MAIN OUTCOME MEASURES Data were coded, and agreement between the expert and the participant was assessed using Cohens unweighted kappa for sessions 1, 6, and 12. RESULTS There was agreement between the expert and participants for 0/7 criteria for session 1, 3/7 criteria for session 6, and 4/7 criteria for session 12. CONCLUSIONS Participants demonstrated some agreement with the expert when evaluating their jump-landing biomechanics. Self-analysis feedback may not replace what an expert can provide; both types of feedback may be better used in conjunction to produce significant biomechanical changes. Changes made by the participant may not translate into biomechanical changes during a real-life game or practice situation. Future research should continue to investigate effective interventions to reduce injury risk.

No Biomechanical Changes Observed with the Addition of Video Feedback to an ACL Prevention Program in Female Collegiate Athletes

Poor landing biomechanics could put an athlete at risk of anterior cruciate ligament (ACL) injury. ACL intervention programs aim to reduce injury risk by improving strength, flexibility and neuromuscular control. Video feedback interventions have shown success in improving jump-landing biomechanics in a laboratory setting; however, ACL injury prevention programs have yet to incorporate video feedback interventions. Aim: Examine if the addition of video feedback to a modified Sportsmetrics© ACL injury prevention program would produce biomechanical changes in collegiate female soccer athletes during landing. Methods: Hip and knee biomechanics were collected during landing pre- and post-intervention. Participants were allocated into feedback or control groups. All participants completed a 9 week modified Sportsmetrics© ACL intervention program. The feedback group received individualized feedback on their performance of the squat jump task once a week for 6 weeks. Results: No significant differences were observed between groups for any knee or hip biomechanical variables. Discussion: The task chosen for feedback, caliber of athletes,surface on which the athletes completed the jump-landing task and participant’s lack of previous experience with feedback may have contributed to the lack of statistical significance. Conclusion: Six video feedback sessions may not be enough exposure to produce biomechanical changes. Additionally, feedback should be provided on tasks prone to biomechanical errors (e.g., single leg landing) in order to receive the most benefit from the feedback intervention. Future research should continue to investigate adding formalized feedback to ACL intervention programs in an effort to decrease injury risk.