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Background: Current return-to-sport screening paradigms after anterior cruciate ligament (ACL) injury are inadequate as they fail to reflect cognitive-motor sports demands. This pilot study aimed to evaluate dual-task ability in individuals with ACL reconstruction (ACLR) using a novel dual-task test paradigm. Specifically, we compared (1) cognitive and motor performance between individuals with ACLR and controls, (2) hop test performance between the injured and non-injured legs within the ACLR group, and (3) performance across test-retest sessions.

Materials and Methods: Twenty sports active individuals (10 ACLR, 10 controls) performed the dual-task paradigm twice within a week, comprising a cognitive test, a dual-task drop-vertical hop test, and an upper-body hand-tapping test. All tests incorporated a visuospatial working-memory task (cognitive performance), with the latter two additionally engaging attention, decision-making, and inhibitory control (motor performance). Between-group, between-leg, and test-retest differences were analyzed using independent and paired t-tests with Cohen’s d effect sizes (ESs). Test–retest reliability was examined using intraclass correlation coefficient (ICC), along with the within-person standard deviation and minimal detectable change.

Results: No significant differences were observed between ACLR and controls at the first test session (p = 0.09 − 0.34; ESs = 0.19–0.62 [very small–medium]), although ACLR mean performances were 3.8%–14.1% lower. At retest, ACLR performed significantly worse than CTRL for most outcomes (p = 0.01 − 0.03; ESs = 0.91–1.17 [large]) and showed smaller improvements for a hop test outcome (p = 0.04; ES = 0.97 [large]). No differences were found between ACLR legs, both groups improved across test sessions, and test–retest reliability was excellent for ACLR (ICCs = 0.74–0.97) and ranged from poor to excellent in CTRL (ICCs = 0.19–0.86).

Conclusions: This pilot study demonstrates the feasibility and preliminary reliability of the dual-task paradigm, particularly within the ACLR group. Poorer cognitive, hop, and upper-body test performances and smaller test–retest improvements for the ACLR group suggest persistent dual-task deficits following injury, supporting the paradigm’s utility for ecologically valid ACL rehabilitation and return-to-sport assessment.

Background: Subjective patient-reported outcome measures (PROMs) and physical performance tests are important tools for assessing rehabilitation after anterior cruciate ligament reconstruction (ACLR). However, the associations and interrelationships between PROMs and dual-task jump performance, and sex-specific differences among patients with ACLR remain unclear.

Hypothesis: Associations exist between PROMs and dual-task jump performance, and do not differ between men and women with ACLR.

Study Design: Controlled laboratory study.

Level of Evidence: Level 3.

Methods: A total of 44 sports-active people with ACLR (50% men; mean [SD] 25.4 [16.0] months postsurgery) completed the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF), the Anterior Cruciate Ligament-Return to Sport after Injury (ACL-RSI) scale, and a dual-task drop vertical jump test. The test incorporated cognitive challenges targeting short-term memory, attention, fast decision-making, and inhibitory control. Dual-task performance was quantified as the percentage of correctly completed memory and motor trials. Associations were analyzed using partial correlations, controlling for time post-ACLR.

Results: Across all participants, no significant correlations were observed between dual-task performance and ACL-RSI or IKDC-SKF scores (r = 0.02-0.14; P = 0.37-0.92). Women demonstrated positive correlations (r = 0.39-0.40; P = 0.07-0.08) with both PROMs, suggesting a potential association, although shallow linear slopes, whereas men showed negative, nonsignificant correlations (r = -0.10 to -0.36; P = 0.11-0.65). A high and significant correlation was found between ACL-RSI and IKDC-SKF scores among women (r = 0.76; P < 0.01) but not men (r = 0.36; P = 0.11).

Conclusion: After ACLR, ACL-RSI and IKDC-SKF scores were not significantly associated with dual-task jump performance. However, women showed greater consistency between the 2 PROMs than men.

Anterior cruciate ligament (ACL) tears are prevalent career-ending sports injuries. A barrier to successful return to activity is fear of re-injury. Evaluating psychological readiness is however limited to insufficient self-reported assessments. We developed machine learning models using biomechanical data from standardized rebound side hops (SRSH) to objectively classify fear levels post-ACL reconstruction (ACLR) and identify key biomechanical variables. Sixty individuals with ACLR and 47 controls performed up to 10 side hops per leg. Kinematic and kinetic data were collected using motion capture and force platforms. ACLR participants were classified (Tampa Scale for Kinesiophobia-17) as HIGH-FEAR (n = 32) or LOW-FEAR (n = 28). Analyses involved 1D convolutional neural networks (1D CNN) and logistic regression. Integrated gradients identified influential movement variables. The 1-D CNN distinguished HIGH-FEAR versus LOW-FEAR ACLR individuals in agreement with Tampa Scale scores, achieving a mean accuracy of 75.6% (F₁ Score = 0.76, Matthews Correlation Coefficient = 0.52), which was 8.6% better than logistic regression. Influential variables included trunk tilt, hip flexion/extension, and ankle supination/pronation. Machine learning from biomechanics can identify movement linked to fear of re-injury post-ACLR, potentially informing personalised rehabilitation to mitigate fear and enhance recovery.

Fear of re-injury after anterior cruciate ligament (ACL) rupture often hinders return-to-sport and has been linked to movement patterns associated with increased injury risk. Identifying fearful individuals is thus critical. Self-reported questionnaires are commonly used but may be affected by underreporting in sporting and clinical contexts. We aimed to classify individuals with ACL reconstruction (ACLR) into HIGH-FEAR and LOW-FEAR groups, using machine learning (ML) models trained on unimodal or multimodal time-series movement data from side hop landings. Seventy-two participants (median: 13.0 months post-ACLR; interquartile range: 15.8 months) were dichotomized into HIGH-FEAR/LOW-FEAR groups using a single item (statement 9) from the Tampa Scale for Kinesiophobia. Participants performed one-leg standardized rebound side hops while kinematics and kinetics were recorded using 3D motion capture and force plates, respectively, and electromyography (EMG) was registered from flexor and extensor thigh muscles. We extracted time-series features from each modality and ten ML algorithms were trained and evaluated using leave-one-participant-out and grouped 3-fold cross-validation. Integrating kinematic/kinetic and EMG data improved classification accuracy compared to single modality datasets. The extreme gradient boosting model achieved the highest accuracy for fused data (86%) using the top 40 ranked features, including trunk tilt, pelvic obliquity, knee rotation, and flexor and extensor muscle activations. Kinematic/kinetic data alone achieved 83% accuracy per participant, while EMG data alone yielded 85%. This study demonstrates the potential of integrating different movement-related data to enhance the accuracy of ML models in classifying fear of re-injury post-ACLR, supporting identification of patterns associated with fear and guiding treatment.

Anterior cruciate ligament (ACL) reinjury rates among athletes remain very high despite screening protocols designed to assess readiness for return to sport. To better identify biomechanical risk factors for ACL injury, combining neurocognitive challenges and high-impact tasks would more closely resemble sporting demands. We investigated the influence of secondary cognitive tasks on landing mechanics during bilateral drop vertical jumps (DVJs) among athletes following ACL reconstruction and whether sex affected these results. We also assessed whether adding secondary cognitive tasks to DVJs influenced loading asymmetries. Forty individuals (20 males) performed three DVJ conditions: (1) without secondary cognitive tasks (DVJ), (2) with secondary cognitive tasks targeting fast decision-making and inhibitory control of the motor action (DVJmot), and (3) with secondary cognitive tasks targeting fast decision-making, inhibitory control, attention, and short-term memory (DVJcogmot). We collected movement mechanics time-series data during the first 100 ms of landing using a motion capture system and force plates and compared outcomes between the three DVJs using functional t-tests. Secondary cognitive tasks altered trunk, hip, knee, and ankle landing mechanics (adjusted p-values < 0.05), representing more upright and stiffer landings. Loading asymmetries were increased by unloading the injured limb (adjusted p-values < 0.05). We found no differences between DVJmot and DVJcogmot or between males and females. Adding secondary cognitive tasks to DVJs better identifies landing mechanics associated with an increased ACL injury risk and inadequate rehabilitation. Future research should focus on optimizing the challenge point of the cognitive and motor tasks and how to best integrate them in RTS testing.

Background: Chaotic sporting environments require the performance of concurrent cognitive and motor tasks. A reduced capacity for either or both of the tasks when performed concurrently is known as cognitive-motor interference (CMi) and is believed to increase the injury risk. A greater susceptibility to CMi after a rupture of the anterior cruciate ligament (ACL) has been suggested to be caused by central nervous system adaptations, thus possibly contributing to high secondary ACL injury rates.

Purpose: To investigate whether patients after ACL reconstruction (ACLR) demonstrate greater CMi than noninjured controls when adding secondary cognitive tasks to the drop vertical jump (DVJ) and explore the potential influence of sex on CMi.

Study Design: Controlled laboratory study.

Methods: A total of 40 (50% male) sports-active patients who had undergone ACLR (mean, 24.9 ± 16.1 months after surgery) and 40 (50% male) sports-active noninjured controls performed DVJs with and without secondary cognitive tasks targeting short-term memory, attention, fast decision-making, and inhibitory control. Outcomes included a letter position recall task and 3 motor variables: (1) correct action (landing or landing with a subsequent vertical jump), (2) relative jump height (relative between DVJs), and (3) relative peak vertical ground-reaction force (relative between DVJs). Participants also completed isolated cognitive tests (CANTAB) included as covariates in multivariate analysis.

Results: Multivariate analysis of variance revealed that the ACLR group had greater CMi than the control group (P < .001), as manifested by more incorrect answers for the cognitive letter recall task (mean difference [MD], –13.3% [95% CI, –20.8% to –5.9%]; P < .001), more incorrect motor actions (MD, –7.5% [95% CI, −12.4% to –2.6%]; P = .003), and a reduced relative jump height (MD, –4.5% [95% CI, –7.9% to –1.2%]; P = .010). No difference in relative peak vertical ground-reaction force was found (MD, 2.8% [95% CI, –7.7% to 13.3%]; P = .59). Isolated cognitive outcomes did not affect these results, and there were no significant differences between male and female participants.

Conclusion: Patients after ACLR showed greater CMi than noninjured controls, which was unrelated to isolated cognitive outcomes, thus indicating aberrant neurocognitive function.

Clinical Relevance: Clinicians should consider cognitive and dual-task training and screening during ACL rehabilitation to better prepare patients for chaotic and uncontrolled sporting environments in which dual tasking is prevalent. Such interventions may help to reduce the risk of secondary ACL injuries.

Background: Athletes with anterior cruciate ligament reconstruction (ACLR) have high rates of secondary injury. Insufficient return-to-sport screening may be due to standard functional tests not resembling chaotic sporting environments where injuries occur. Neurocognitive deficits among individuals with ACLR indicate that cognitive challenges during screening tests may better reveal atypical movement mechanics.

Hypothesis: Adding secondary cognitive tasks to drop vertical jumps (DVJs) would increase between-group differences in landing mechanics and jump height compared with the standard DVJ.

Study Design: Controlled laboratory study.

Methods: Forty sports-active individuals 24.9 ± 16.1 months after unilateral ACLR and 40 uninjured controls (both groups 50% female) performed DVJs; downward- or upward-pointing arrows indicated whether to drop only or complete the vertical jump. Conditions were (1) black arrow presented before drop and (2) black or red arrow presented during drop (red arrow pointing in opposite direction of requested motor action) together with a memory task involving letter recalling. Jump height and biomechanical time-series data from an 8-camera motion capture system and 2 force plates during the first 100 ms of landing were compared between groups using conventional and functional t tests, respectively.

Results: For the standard DVJ, the ACLR group had significantly less hip power and more hip abduction moment for the injured leg and uninjured leg, respectively, compared with controls. For the DVJ with secondary cognitive tasks, the ACLR group again showed significantly less hip power and more hip abduction moment but also less knee power, knee flexion moment, ankle power, and ankle dorsiflexion moment and lower jump height than controls.

Conclusion: The addition of secondary cognitive tasks during DVJs elicited further significant differences in landing mechanics and jump performance among athletes with ACLR compared with uninjured athletes than were found for the standard DVJ. The aberrant biomechanical outcomes for the ACLR group indicate an incomplete rehabilitation.

Clinical Relevance: The greater between-group differences in landing mechanics and jump height when adding secondary cognitive tasks to a DVJ indicate a need to provide neurocognitive challenges in rehabilitation and return-to-sport screening as a first step toward improved rehabilitation outcomes and more ecologically valid testing.

Investigations of kinetic asymmetries during bilateral squats following anterior cruciate ligament reconstruction (ACLR) are limited to mainly cross-sectional studies and discrete value data extracted at specific knee angles. We assessed loading asymmetries during squats longitudinally throughout rehabilitation using curve analysis and compared patient-reported outcome measures (PROMs) between those with and without asymmetry. Bodyweight squats were performed by 24 individuals (13 females) post-ACLR on three occasions: (1) Early 2.9 (1.1) months; (2) Mid 8.8 (3.1) months; (3) at Return to Sport (RTS) 13.1 (3.6) months; and 29 asymptomatic controls (22 females) once. Time-normalized between-leg asymmetry curves of sagittal plane hip, knee, and ankle moments and vertical ground reaction forces were compared using functional data analysis methods. Individual asymmetrical loading for ACLR was classified when exceeding the 95% confidence interval of controls during ≥50% of the squat. At Early, ACLR had greater asymmetry than controls for knee (15%–100% eccentric phase; 0%–100% concentric) and ankle flexion moments (56%–65% concentric). At Mid, ACLR had greater asymmetry for knee (41%–72% eccentric) and ankle flexion moments (56%–69% concentric). No between-group differences were found at RTS. From Early to RTS, ACLR reduced asymmetry for hip (21%–46% eccentric), knee (27%–58% concentric), and ankle flexion moments (21%–57% eccentric). At Early, 11/24 underloaded their ACLR knee and 1 overloaded compared with controls. At RTS, 4 underloaded and 6 overloaded. No differences in PROMs were found based on loading asymmetry. Beyond the early phase of rehabilitation from ACLR, individual-level analyses are required to reveal differing loading strategies during bilateral squats.