Differential influence of quadriceps rate of torque development on single- and double-leg landing mechanics in anterior cruciate ligament reconstructed and control females.

PURPOSE: The capacity to explosively contract quadriceps within the critical timeframe associated with anterior cruciate ligament (ACL) injury, quantified by the rate of torque development, is potentially essential for safe landing mechanics. This study aimed to investigate the influence of explosive quadriceps strength on ACL-related sagittal-plane landing mechanics in females with and without ACL reconstruction (ACLR). METHODS: Quadriceps explosive strength and landing mechanics were assessed in 19 ACLR and 19 control females during isometric contractions and double- and single-leg jump landings. A stepwise multiple linear regression model determined the variance in each of the landing biomechanics variables for the ACLR limb and nondominant limb of controls that could be explained by the group, rate of torque development and/or their interaction. If peak kinetic variables could be predicted by the rate of torque development or interaction, additional analyses were conducted, accounting for knee flexion as a covariate in the regression model. RESULTS: During single-leg landings, ACLR females exhibited greater knee flexion at initial contact than controls (p = 0.04). Greater quadriceps rate of torque development predicted higher peak posterior ground reaction force and anterior tibial shear force in both groups (p = 0.04). However, after controlling for knee flexion angle at those peak forces, quadriceps rate of torque development was not predictive. In double-leg landings, greater explosive quadriceps strength was associated with quicker attainment of peak knee extension moment and posterior ground reaction force in the ACLR limb (p = 0.03). CONCLUSION: Regardless of ACL injury status, females with greater explosive quadriceps strength adopted safer single-leg landings through increased knee flexion, potentially mitigating ACL loading despite encountering higher peak forces. During double-leg landings, a greater explosive quadriceps strength of the ACLR limb is associated with faster achievement of peak force upon landing. Incorporating explosive quadriceps strengthening into post-ACLR rehabilitation and injury prevention programmes may enhance landing mechanics for reducing primary and subsequent ACL injury risks. LEVEL OF EVIDENCE: Level II.

Deceleration Profiles Between the Penultimate and Final Steps of Planned and Reactive Side-Step Cutting.

CONTEXT: Noncontact anterior cruciate ligament injury often occurs during rapid deceleration and change-of-direction maneuvers. These activities require an athlete to generate braking forces to slow down the center of mass and change direction in a dynamic environment. During preplanned cutting, athletes can use the penultimate step for braking before changing direction, resulting in less braking demand during the final step. During reactive cutting, athletes use different preparatory movement strategies during the penultimate step when planning time is limited. However, possible differences in the deceleration profile between the penultimate and final steps of preplanned and reactive side-step cuts remain unknown. OBJECTIVE: To comprehensively evaluate deceleration during the penultimate and final steps of preplanned and reactive cutting. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-six women (age = 20.9 ± 1.7 years, height = 1.66 ± 0.07 m, mass = 62.4 ± 8.7 kg). INTERVENTION: Participants completed 90° side-step cutting maneuvers under preplanned and reactive conditions. MAIN OUTCOME MEASURE(S): Approach velocity, velocity at initial contact, and cutting angle were compared between conditions. Stance time, deceleration time, and biomechanical indicators of deceleration were assessed during the penultimate and final steps of preplanned and reactive 90° cuts. Separate repeated-measures analysis-of-variance models were used to assess the influence of step, condition, and their interaction on the biomechanical indicators of deceleration. RESULTS: Approach velocity (P = .69) and velocity at initial contact of the penultimate step (P = .33) did not differ between conditions. During reactive cutting, participants achieved a smaller cutting angle (P < .001). We identified a significant step-by-condition interaction for all biomechanical indicators of deceleration (P values < .05). CONCLUSIONS: A lack of planning time resulted in less penultimate step braking and greater final step braking during reactive cutting. As a result, participants exhibited a decreased cutting angle and longer stance time during the final step of reactive cutting. Improving an athlete's ability to respond to an external stimulus may facilitate a more effective penultimate step braking strategy that decreases the braking demand during the final step of reactive cutting.

Single-Legged Triple-Hop Propulsion Strategies in Females With and Those Without a History of Anterior Cruciate Ligament Reconstruction.

CONTEXT: The single-legged triple hop is a commonly used functional task after anterior cruciate ligament reconstruction (ACLR). Recently, researchers have suggested that individuals may use a compensatory propulsion strategy to mask underlying quadriceps dysfunction and achieve symmetric hop performance. OBJECTIVE: To evaluate the performance and propulsion strategies used by females with and those without ACLR during a single-legged triple hop. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 38 females, 19 with ACLR (age = 19.21 ± 1.81 years, height = 1.64 ± 0.70 m, mass = 63.79 ± 7.59 kg) and 19 without ACLR (control group; age = 21.11 ± 3.28 years, height = 1.67 ± 0.73 m, mass = 67.28 ± 9.25 kg). MAIN OUTCOME MEASURE(S): Hop distance and limb symmetry index (LSI) were assessed during a single-legged triple hop for distance. Propulsion strategies were evaluated during the first and second hops of the single-legged triple hop. Separate 2-way analysis-of-variance models were used to examine the influence of ACLR, joint, and their interaction on mechanical joint work, moment impulse, and the relative joint contributions to total work and moment impulse in females with and those without a history of ACLR. RESULTS: Despite achieving a mean LSI of approximately 96%, the ACLR group produced less total work in the reconstructed than the uninvolved limb during single-legged triple-hop propulsion (first hop: t18 = -3.73, P = .002; second hop: t18 = -2.55, P = .02). During the first and second hops, the reconstructed knee generated 19.3% (t18 = -2.33, P = .03) and 27.3% (t18 = -4.47, P < .001) less work than the uninvolved knee. No differences were identified between the involved and uninvolved limbs of the ACLR group in moment impulse (first hop: t18 = -0.44, P = .67; second hop: t18 = -0.32; P = .76). Irrespective of limb or group, the ankle was the largest contributor to both work and moment during both the first and second hops (P < .001). CONCLUSIONS: Clinicians should exercise caution when using a single-legged triple hop as a surrogate for restored lower extremity function in females post-ACLR. This recommendation is driven by the compelling findings that knee-joint deficits persisted in the reconstructed limb despite an LSI of approximately 96% and, regardless of previous injury status, single-legged triple-hop propulsion was predominantly driven by the ankle.

Single-Legged Triple-Hop Propulsion Strategies in Females With and Those Without a History of Anterior Cruciate Ligament Reconstruction.

CONTEXT: The single-legged triple hop is a commonly used functional task after anterior cruciate ligament reconstruction (ACLR). Recently, researchers have suggested that individuals may use a compensatory propulsion strategy to mask underlying quadriceps dysfunction and achieve symmetric hop performance. OBJECTIVE: To evaluate the performance and propulsion strategies used by females with and those without ACLR during a single-legged triple hop. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 38 females, 19 with ACLR (age = 19.21 ± 1.81 years, height = 1.64 ± 0.70 m, mass = 63.79 ± 7.59 kg) and 19 without ACLR (control group; age = 21.11 ± 3.28 years, height = 1.67 ± 0.73 m, mass = 67.28 ± 9.25 kg). MAIN OUTCOME MEASURE(S): Hop distance and limb symmetry index (LSI) were assessed during a single-legged triple hop for distance. Propulsion strategies were evaluated during the first and second hops of the single-legged triple hop. Separate 2-way analysis-of-variance models were used to examine the influence of ACLR, joint, and their interaction on mechanical joint work, moment impulse, and the relative joint contributions to total work and moment impulse in females with and those without a history of ACLR. RESULTS: Despite achieving a mean LSI of approximately 96%, the ACLR group produced less total work in the reconstructed than the uninvolved limb during single-legged triple-hop propulsion (first hop: t18 = -3.73, P = .002; second hop: t18 = -2.55, P = .02). During the first and second hops, the reconstructed knee generated 19.3% (t18 = -2.33, P = .03) and 27.3% (t18 = -4.47, P < .001) less work than the uninvolved knee. No differences were identified between the involved and uninvolved limbs of the ACLR group in moment impulse (first hop: t18 = -0.44, P = .67; second hop: t18 = -0.32; P = .76). Irrespective of limb or group, the ankle was the largest contributor to both work and moment during both the first and second hops (P < .001). CONCLUSIONS: Clinicians should exercise caution when using a single-legged triple hop as a surrogate for restored lower extremity function in females post-ACLR. This recommendation is driven by the compelling findings that knee-joint deficits persisted in the reconstructed limb despite an LSI of approximately 96% and, regardless of previous injury status, single-legged triple-hop propulsion was predominantly driven by the ankle.

Biomechanical demands of exercises commonly performed by older adults in falls prevention programs.

BACKGROUND: Tailored, challenging and progressed exercise programs addressing risk factors are recommended for preventing falls in community-dwelling older adults. Knowing the biomechanical demands of exercises commonly performed in efficacious falls prevention programs provides evidence for exercise prescription. METHODS: Twenty-one non-sedentary older adults (10 men, 11 women, mean age 69 [SD 5] years) performed five standing exercises (hip abduction, side-step, squat, forward lunge, and side lunge). A biomechanical analysis of the dominant limb was performed to calculate peak joint angles and net joint moments at the ankle, knee and hip in multiple planes. Repeated-measures one-way analyses of variance followed by post-hoc comparisons were performed to identify differences in the calculated variables between exercises. FINDINGS: Peak hip abduction moments during hip abduction were greater than during the forward lunge and squat (P < 0.001). During the side-step, peak plantar flexion moments were greater than the squat and peak hip abduction moments were greater than the squat and forward lunge (P < 0.001). During the squat, peak hip flexion was greatest (P < 0.001) while peak plantar flexion (P < 0.001) and hip abduction moments (P ≤ 0.002) were less than all other exercises. During the forward lunge, peak hip extension moments (P < 0.001) were greatest. During the side lunge, peak knee extension moments were greater than all other exercises (P < 0.001). INTERPRETATION: These biomechanical data will allow clinicians to tailor exercises for falls prevention to efficiently challenge but not overload muscle groups and minimize exercise prescription redundancies.

Explosive Quadriceps Strength Symmetry and Landing Mechanics Limb Symmetry After Anterior Cruciate Ligament Reconstruction in Females.

CONTEXT: Emerging evidence suggests that a lower quadriceps rate of torque development (RTD) after anterior cruciate ligament (ACL) reconstruction (ACLR) may be associated with altered landing mechanics. However, the influence of quadriceps RTD magnitude and limb symmetry on landing mechanics limb symmetry remains unknown. OBJECTIVE: To assess the influence of quadriceps RTD magnitude and limb symmetry on limb symmetry in sagittal-plane landing mechanics during functional landing tasks in females with or without ACLR. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 19 females with ACLR (age = 19.21 ± 1.81 years, height = 164.12 ± 6.97 cm, mass = 63.79 ± 7.59 kg, time after surgery = 20.05 ± 9.50 months) and 19 females serving as controls (age = 21.11 ± 3.28 years, height = 167.26 ± 7.26 cm, mass = 67.28 ± 9.25 kg). MAIN OUTCOME MEASURE(S): Landing mechanics were assessed during a double-legged (DL) jump-landing task, a single-legged jump-landing task, and a side-cutting task. Quadriceps RTD was collected during isometric muscle contractions. Separate stepwise multiple linear regression models were used to determine the variance in limb symmetry in the sagittal-plane knee moment at initial contact, peak vertical ground reaction force, and loading rate that could be explained by quadriceps RTD magnitude or limb symmetry, group (ACLR or control), and their interaction. RESULTS: In the ACLR group, greater limb symmetry in quadriceps RTD was associated with greater symmetry in sagittal-plane knee moment at initial contact during the DL task (P = .004). Peak vertical ground reaction force and loading rate could not be predicted by quadriceps RTD magnitude or limb symmetry, group, or their interaction during any task. CONCLUSIONS: Developing greater symmetry but not magnitude in quadriceps RTD likely enabled more symmetric sagittal-plane knee landing mechanics during the DL task in the ACLR group and thus may reduce the risk of a second ACL injury. Such a protective effect was not found during the single-legged or side-cutting tasks, which may indicate that these tasks do not allow for the compensatory landing mechanism of shifting load to the uninvolved limb that was possible during the DL task.

A Majority of Anterior Cruciate Ligament Injuries Can Be Prevented by Injury Prevention Programs: A Systematic Review of Randomized Controlled Trials and Cluster-Randomized Controlled Trials With Meta-analysis.

BACKGROUND: Anterior cruciate ligament (ACL) injury prevention programs (IPPs) are generally accepted as being valuable for reducing injury risk. However, significant methodological limitations of previous meta-analyses raise questions about the efficacy of these programs and the extent to which meeting current best-practice ACL IPP recommendations influences the protective effect of these programs. PURPOSE: To (1) estimate the protective effect of ACL IPPs while controlling for common methodological limitations of previous meta-analyses and (2) systematically categorize IPP components and factors related to IPP delivery to assess the validity of current best-practice IPP recommendations. STUDY DESIGN: Systematic review with meta-analysis. METHODS: A systematic search of 5 electronic scientific databases was conducted to identify studies testing the efficacy of ACL IPPs. Studies were included if (1) the intervention aimed to prevent ACL injury, (2) the incidence rate (IR) or other outcome data that made it possible to calculate the IR for both the intervention and control groups were reported, and (3) the study design was a prospective randomized controlled trial (RCT) or cluster-RCT. RESULTS: Of the 2219 studies screened, 8 studies were included in the quantitative synthesis, and their analysis revealed a significant reduction in ACL IR when athletes received IPPs (IR ratio = 0.47; 95% CI, 0.30-0.73; P < .001). The majority of included IPPs tended to meet minimum best-practice recommendations and incorporated plyometric, strengthening, and agility exercises along with feedback on proper landing technique. However, the specific exercises included in each IPP and key factors related to IPP delivery were highly variable. CONCLUSION: Despite limiting the analysis to only high-quality studies and controlling for time at risk and potential clustering effects, the study showed that ACL IPPs had a significant protective effect and reduced injury rates by 53%. However, significant variability in the specific exercises and the manner of program delivery suggests that ACL IPPs may be able to be designed within an overarching best-practice framework. This may allow practitioners the flexibility to develop IPPs that meet the specific characteristics of the target population and potentially increase the likelihood that these programs will be widely adopted and implemented.