The effects of mid-flight whole-body and trunk rotation on landing mechanics: implications for anterior cruciate ligament injuries

Larger hip external rotation motion is associated with larger knee abduction and internal rotation motions during a drop vertical jump

Associations among hip motions, knee abduction and internal rotation motion during a drop vertical jump (DVJ), which increases the risk of anterior cruciate ligament injury, remain unclear. The purpose of this study was to examine associations among knee abduction, internal rotation and hip joint motions during a DVJ. Fifty-seven young female participants performed a DVJ from a 30-cm height. Hip and knee kinematics and kinetics were analysed using a three-dimensional motion analysis system and force plates. Multiple regression analysis showed that peak knee abduction angle was negatively associated with knee internal rotation and hip internal rotation excursions from initial contact (IC) to peak knee flexion, and positively associated with peak knee abduction moment (R2 = 0.465, P< 0.001). Peak knee internal rotation angle was negatively associated with the hip flexion excursion from IC to peak knee flexion and peak hip adduction moment (R2 = 0.194, P= 0.001). In addition, hip internal rotation excursion was negatively associated with knee abduction and internal rotation excursion from IC to 50 ms after IC. To avoid a large knee abduction and internal rotation motion during jump-landing training, it might be beneficial to provide landing instructions to avoid a large hip external rotation motion.

Exploring the relationship between core stability and vertical jump in recreationally active male college students based on a suite of novel core stability assessments

Various assessments have contributed to inconsistent findings regarding the correlation between core stability and vertical jumps. Therefore, this study aimed to re-examine this correlation based on novel core stability assessments. Twenty-one recreationally active male college students (age, 21.7 ± 2.1 years; stature, 174.9 ± 6.7 cm; body mass, 67.7 ± 7.8 kg; leg length, 88.9 ± 4.8 cm; arm length, 87.8 ± 4.0 cm) participated in this experiment. Core stability was divided into static and dynamic core stabilities, with the static core stability measured using the Eight-Level Prone Bridge and Five-Level Side Bridge tests and the dynamic core stability measured using the Y Balance Test (YBT). These tests comprehensively evaluate core stability as it is defined. Kinematic and kinetic data on vertical jumps were collected to provide process information beyond the outcome performance. Subsequently, these data were correlated with core stability for a deeper insight into the relationship between core stability and the process and outcome performance of vertical jumps. The main results revealed that the Eight-Level Prone Bridge demonstrated moderate to substantial correlations with Δ F y ‾ , Δ I y , Δ D l e f t k n e e z , and Δ D l e f t a n k l e y (-0.62 ≤ r ≤ 0.52); the Five-Level Side Bridge exhibited moderate correlations with Δ F x ‾ , Δ F y ‾ , Δ I x , Δ I y , Δ D l e f t k n e e z , and Δ D l e f t a n k l e y (-0.52 ≤ r ≤ 0.59); YBT displayed moderate correlations with F z ‾ , F l e f t z ‾ , Δ D l e f t a n k l e y , Δ D r i g h t a n k l e y , Δ D l e f t a n k l e z , Δ D r i g h t a n k l e z , NΔ T a n k l e y ‾ , and N T l e f t a n k l e z ‾ (-0.54 ≤ r ≤ 0.54) during the propulsive phase of vertical jumps. However, no significant correlations were observed between static/dynamic core stability and jumping height. Therefore, individuals with greater core stability should experience improved process performance (better movement quality), although this benefit is ineffective in translating into jumping height improvement due to impaired explosive features. Coaches may consider core stability in training to trigger an improved process performance of the vertical jump when the technique is the key issue to be solved, although future studies are required to verify this further.

Falling decreased anterior cruciate ligament loading variables during single-leg landings after mid-flight external trunk perturbation

Mid-flight external upper-trunk perturbation is associated with increased anterior cruciate ligament (ACL) injury risk during landing. This study aimed to assess the effect of natural, soft, and falling landing techniques on knee mechanics and vertical ground reaction forces (VGRF) during single-leg landings with/without mid-flight medial-lateral external upper-trunk pushing perturbation. Twenty-eight participants performed single-leg landings using the three landing techniques with/without mid-flight pushing perturbation. The perturbation was created by a customized apparatus releasing a slam ball and pushing the participants near the peak jump height at the upper trunk. Perturbation resulted in significantly greater lateral trunk bending angles, knee flexion angles at initial contact, peak knee abduction angles, and peak knee adduction moments compared to no perturbation. The falling condition significantly demonstrated the greatest lateral trunk bending angles, knee flexion angles, and peak knee external rotation moments and the smallest peak knee abduction angles, peak VGRF, and peak knee extension moments compared to natural/soft landings regardless of perturbation conditions. Mid-flight external perturbation resulted in variables associated with greater ACL loading during single-leg landings. Falling demonstrated variables associated with smaller ACL loading, particularly for perturbation conditions. Incorporating falling techniques into jump-landing training programs may guide players to safely fall on the ground when perturbation occurs. Falling provides an alternative strategy to potentially decrease indirect contact ACL injury risk when the sports environment allows.

Biomechanical comparisons of back and front squats with a straight bar and four squats with a transformer bar

The purpose was to quantify trunk and lower extremity biomechanics among back and front squats with a straight bar and four squats with different anterior-posterior load placements imposed by a transformer bar. Ten males and eight females performed six squat conditions: back and front squats with a straight bar, back and front squats with a transformer bar, and squats with more posteriorly or anteriorly placed loads with a transformer bar. A constant load of 70% of the participant's one-repetition maximum in the straight-bar front squat was used. Kinematic and kinetic data were collected to quantify joint biomechanics at an estimated parallel squat position in the descending and ascending phases. Squats with more anteriorly placed load significantly decreased trunk flexion and pelvis anterior tilt angles with large effect sizes but increased low-back extension moments with medium to large effect sizes. Hip, knee, and ankle extension moments were generally similar among most conditions. Participants adjusted their trunk and pelvis to mediate the effects of load placements on low-back and lower extremity moments. While lower extremity loading was similar among different squats, the different trunk and pelvis angles and low-back moments should be taken into consideration for people with low-back impairment.

Kinematics, Kinetics and Muscle Activity Analysis during Single-leg Drop-jump Landing Followed by an Unanticipated Task: Focusing on Differences in Neurocognitive Function

Background

Lower neurocognitive function is a risk factor for anterior cruciate ligament (ACL) injury. However, the mechanism by which lower neurocognitive function increases the risk of ACL injury remains unclear.

Purpose

To clarify the effect of differences in neurocognitive function on landing mechanics during a single-leg drop-jump landing motion followed by an unanticipated task.

Study Design

Cross-sectional study.

Methods

Fifteen collegiate female athletes were recruited (20.1 ± 1.3 years, 166.6 ± 7.3 cm, 60.6 ± 6.9 kg) and were divided into two groups (the high-performance (HP) group and the lower-performance (LP) group) using the median Symbol Digit Modalities Test (SDMT) score. Three-dimensional motion analysis was employed for the analysis during the experimental task of a single-leg drop-jump followed by an unanticipated landing task from a 30-cm high box. Joint angular changes of the trunk, pelvis, hip, and knee were calculated within the interval from initial contact (IC) to 40ms. Knee and hip moments were calculated as the maximum values within the interval from IC to 40ms. Surface electromyography data from key muscles were analyzed 50ms before and after IC. Independent t-tests were used to compare the effects of different neurocognitive function on the measurement items. Statistical significance was set at p < 0.05.

Results

The SDMT score was significantly higher in HP group (HP: 77.9 ± 5.5; LP: 66.0 ± 3.4; p < 0.001). The LP group had a significantly greater trunk rotation angular change to the stance leg side (HP: 0.4 ± 0.8; LP: 1.2 ± 0.4; p = 0.020). There were no significant differences between the two groups in terms of joint moments, and muscle activities.

Conclusion

Differences in neurocognitive function by SDMT were found to be related to differences in motor strategies of the trunk in the horizontal plane. Although trunk motion in the sagittal and frontal planes during single-leg drop-jump landing increases the ACL injury risk by affecting knee joint motion, the effect of trunk motion in the horizontal plane remains unclear.

Level of Evidence

3© The Authors.

Effect of Whole Body Parameters on Knee Joint Biomechanics: Implications for ACL Injury Prevention During Single-Leg Landings

BACKGROUND

Previous studies have examined the effect of whole body (WB) parameters on anterior cruciate ligament (ACL) strain and loads, as well as knee joint kinetics and kinematics. However, articular cartilage damage occurs in relation to ACL failure, and the effect of WB parameters on ACL strain and articular cartilage biomechanics during dynamic tasks is unclear.

PURPOSES

(1) To investigate the effect of WB parameters on ACL strain, as well as articular cartilage stress and contact force, during a single-leg cross drop (SLCD) and single-leg drop (SLD). (2) To identify WB parameters predictive of high ACL strain during these tasks.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Three-dimensional motion analysis data from 14 physically active men and women were recorded during an SLCD and SLD. OpenSim was used to obtain their kinematics, kinetics, and muscle forces for the WB model. Using these data in kinetically driven finite element simulations of the knee joint produced outputs of ACL strains and articular cartilage stresses and contact forces. Spearman correlation coefficients were used to assess relationships between WB parameters and ACL strain and cartilage biomechanics. Moreover, receiver operating characteristic curve analyses and multivariate binary logistic regressions were used to find the WB parameters that could discriminate high from low ACL strain trials.

RESULTS

Correlations showed that more lumbar rotation away from the stance limb at peak ACL strain had the strongest overall association (ρ = 0.877) with peak ACL strain. Higher knee anterior shear force (ρ = 0.895) and lower gluteus maximus muscle force (ρ = 0.89) at peak ACL strain demonstrated the strongest associations with peak articular cartilage stress or contact force in ≥1 of the analyzed tasks. The regression model that used muscle forces to predict high ACL strain trials during the dominant limb SLD yielded the highest accuracy (93.5%), sensitivity (0.881), and specificity (0.952) among all regression models.

CONCLUSION

WB parameters that were most consistently associated with and predictive of high ACL strain and poor articular cartilage biomechanics during the SLCD and SLD tasks included greater knee abduction angle at initial contact and higher anterior shear force at peak ACL strain, as well as lower gracilis, gluteus maximus, and medial gastrocnemius muscle forces.

CLINICAL RELEVANCE

Knowledge of which landing postures create a high risk for ACL or cartilage injury may help reduce injuries in athletes by avoiding those postures and practicing the tasks with reduced high-risk motions, as well as by strengthening the muscles that protect the knee during single-leg landings.

Subsequent Jumping Increases the Knee and Hip Abduction Moment, Trunk Lateral Tilt, and Trunk Rotation Motion During Single-Leg Landing in Female Individuals

Single-leg landings with or without subsequent jumping are frequently used to evaluate landing biomechanics. The purpose of this study was to investigate the effects of subsequent jumping on the external knee abduction moment and trunk and hip biomechanics during single-leg landing. Thirty young adult female participants performed a single-leg drop vertical jumping (SDVJ; landing with subsequent jumping) and single-leg drop landing (SDL; landing without subsequent jumping). Trunk, hip, and knee biomechanics were evaluated using a 3-dimensional motion analysis system. The peak knee abduction moment was significantly larger during SDVJ than during SDL (SDVJ 0.08 [0.10] N·m·kg-1·m-1, SDL 0.05 [0.10] N·m·kg-1·m-1, P = .002). The trunk lateral tilt and rotation angles toward the support-leg side and external hip abduction moment were significantly larger during SDVJ than during SDL (P < .05). The difference in the peak hip abduction moment between SDVJ and SDL predicted the difference in the peak knee abduction moment (P = .003, R2 = .252). Landing tasks with subsequent jumping would have advantages for evaluating trunk and hip control as well as knee abduction moment. In particular, evaluating hip abduction moment may be important because of its association with the knee abduction moment.

Relationship between the knee valgus moment and the hip abductor and adductor activity during single-leg landing

OBJECTIVES

To reveal the relationship between the knee valgus moment (KVM) and the hip abductor and adductor activity during single-leg landing.

DESIGN

A cross-sectional study.

SETTING

Laboratory-based, between April 2020 and May 2021.

PARTICIPANTS

Thirty female collegiate athletes.

MAIN OUTCOME MEASURES

KVM, hip adduction angle, hip internal rotation angle, knee valgus angle (KVA), gluteus medius muscle activity, adductor longus muscle activity, adductor longus to gluteus medius activity ratio (ADD/GMED), and vertical component of the ground reaction force (vGRF).

RESULTS

Stepwise multiple regression analysis was performed. KVM was significantly positively associated with KVA (β = 0.613, p < 0.001), vGRF (β = 0.367, p = 0.010), and ADD/GMED (β = 0.289, p = 0.038).

CONCLUSIONS

Increased KVA, vGRF, and ADD/GMED were the independent factors that contributed to increased KVM during single-leg landing, and only ADD/GMED was found among the muscle activity values. The relative muscle activity of the gluteus medius and adductor longus, rather than those of the gluteus medius or adductor longus alone, may be useful in preventing anterior cruciate ligament injury during single-leg landing.

Diagnostics Using the Change-of-Direction and Acceleration Test (CODAT) of the Biomechanical Patterns Associated with Knee Injury in Female Futsal Players: A Cross-Sectional Analytical Study

The primary aim of this study was to identify kinematic differences at initial contact between female futsal players with and without previous knee injury, using a functional motor pattern test. The secondary aim was to determine kinematic differences between the dominant and non-dominant limb in the whole group, using the same test. A cross-sectional study was performed in 16 female futsal players allocated into two groups: eight females with a previous knee injury, i.e., affected by the valgus collapse mechanism without surgical intervention, and eight with no previous injury. The evaluation protocol included the change-of-direction and acceleration test (CODAT). One registration was made for each lower limb, i.e., the dominant (the preferred kicking limb) and non-dominant limb. A 3D motion capture system (Qualisys AB, Göteborg, Sweden) was used to analyze the kinematics. The Cohen's d effect sizes between the groups demonstrated a strong effect size towards more physiological positions in the non-injured group in the following kinematics in the dominant limb: hip adduction (Cohen's d = 0.82), hip internal rotation (Cohen's d = 0.88), and ipsilateral pelvis rotation (Cohen's d = 1.06). The t-test for the dominant and non-dominant limb in the whole group showed the following differences in knee valgus: dominant limb (9.02 ± 7.31 degrees) and non-dominant limb (1.27 ± 9.05 degrees) (p = 0.049). Conclusions: The players with no previous history of knee injury had a more physiological position for avoiding the valgus collapse mechanism in the hip adduction and internal rotation, and in the pelvis rotation in the dominant limb. All the players showed more knee valgus in the dominant limb, which is the limb at greater risk of injury.

Pelvic Rotation Is Associated With Asymmetry in the Knee Extensor Moment During Double-Leg Squatting After Anterior Cruciate Ligament Reconstruction

Asymmetry in knee extensor moment during double-leg squatting was observed after anterior cruciate ligament reconstruction, even after the completion of the rehabilitation program for return to sports. The purpose of this study was to clarify the association between asymmetry in the knee extensor moment and pelvic rotation angle during double-leg squatting after anterior cruciate ligament reconstruction. Twenty-four participants performed double-leg squatting. Kinetics and kinematics during squatting were analyzed using a 3-dimensional motion analysis system with 2 force plates. The limb symmetry index of knee extensor moment was predicted by the pelvic rotation angle (R2 = .376, P = .001). In addition, the pelvic rotation and the limb symmetry index of the vertical ground reaction force independently explained the limb symmetry index of the knee extensor moment (R2 = .635, P < .001, β of pelvic rotation = -0.489, β of vertical ground reaction force = 0.524). Pelvic rotation toward the involved limb was associated with a smaller knee extensor moment in the involved limb than in the uninvolved limb. The assessment of pelvic rotation would be useful for partially predicting asymmetry in the knee extensor moment during double-leg squatting. Minimizing pelvic rotation may improve the asymmetry in the knee extensor moment during double-leg squatting after anterior cruciate ligament reconstruction.

Loading mechanisms of the anterior cruciate ligament

This review identifies the three-dimensional knee loads that have the highest risk of injuring the anterior cruciate ligament (ACL) in the athlete. It is the combination of the muscular resistance to a large knee flexion moment, an external reaction force generating knee compression, an internal tibial torque, and a knee abduction moment during a single-leg athletic manoeuvre such as landing from a jump, abruptly changing direction, or rapidly decelerating that results in the greatest ACL loads. While there is consensus that an anterior tibial shear force is the primary ACL loading mechanism, controversy exists regarding the secondary order of importance of transverse-plane and frontal-plane loading in ACL injury scenarios. Large knee compression forces combined with a posteriorly and inferiorly sloped tibial plateau, especially the lateral plateau-an important ACL injury risk factor-causes anterior tibial translation and internal tibial rotation, which increases ACL loading. Furthermore, while the ACL can fail under a single supramaximal loading cycle, recent evidence shows that it can also fail following repeated submaximal loading cycles due to microdamage accumulating in the ligament with each cycle. This challenges the existing dogma that non-contact ACL injuries are predominantly due to a single manoeuvre that catastrophically overloads the ACL.

Indirect contact matters: Mid-flight external trunk perturbation increased unilateral anterior cruciate ligament loading variables during jump-landings

BACKGROUND

To determine the effect of unanticipated mid-flight medial-lateral external perturbation of the upper or lower trunk on anterior cruciate ligament (ACL) loading variables during jump-landings.

METHODS

Thirty-two participants performed double-leg vertical jump-landings while bilateral kinematics and kinetics were collected under 6 conditions (upper or lower trunk perturbation locations; no, left, or right perturbation directions). Two customized catapult apparatuses were created to apply pushing perturbation to participants near the maximal jump height.

RESULTS

The ball contacted participants near the center of mass for the lower-trunk conditions and approximately 23 cm above the center of mass for the upper-trunk conditions. Under upper-trunk perturbation, the contralateral leg demonstrated significantly smaller knee flexion angles at initial contact and greater peak knee abduction angles, peak vertical ground reaction forces, peak knee extension moments, and peak knee adduction moments compared to other legs among all conditions. Under lower-trunk perturbation, the contralateral leg showed significantly smaller knee flexion angles at initial contact and increased peak vertical ground reaction forces and peak knee extension moments compared to legs in the no-perturbation conditions.

CONCLUSION

Mid-flight external trunk pushing perturbation increased ACL loading variables for the leg contralateral to the perturbation. The upper-trunk perturbation resulted in greater changes in ACL loading variables compared to the lower-trunk perturbation, likely due to trunk and ipsilateral leg rotation and more laterally located center of mass relative to the contralateral leg. These findings may help us understand the mechanisms of indirect-contact ACL injuries and develop jump-landing training strategies under mid-flight trunk perturbation to better prevent ACL injury.

Sex difference in frontal plane hip moment in response to lateral trunk obliquity during single-leg landing

BACKGROUND

Lateral trunk obliquity during landing is a characteristic of anterior cruciate ligament (ACL) injuries in female athletes and affects their knee and hip kinetics and kinematics. However, it is unclear whether these effects differ between females and males. The purpose of this study was to compare the effects of lateral trunk obliquity on knee and hip kinetics and kinematics in females and males during single-leg landing.

METHODS

Eighteen female (aged 22.1 ± 1.5 years) and 18 male participants (aged 21.8 ± 1.1 years) performed single-leg landings under two conditions: (1) without any instructions about trunk position (natural) and (2) with leaning their trunks laterally 15° from the vertical line (trunk obliquity). The kinetics and kinematics of their hip and knee were analyzed using a three-dimensional motion analysis with a force plate. Two-way repeated-measures ANOVA (sex × trunk obliquity) and Bonferroni pairwise comparisons were conducted.

RESULTS

The trunk obliquity angle at initial contact was significantly greater in the trunk-obliquity landing condition than in the natural landing condition (natural 4.0 ± 2.2°, trunk-obliquity 15.1 ± 3.6°, P < 0.001) with no sex difference (95% CI - 1.2 to 2.2°, P = 0.555). The peak knee abduction moment was significantly larger in the trunk-obliquity landing condition than in the natural landing condition (trunk-obliquity, 0.09 ± 0.07 Nm/kg/m; natural, 0.04 ± 0.06 Nm/kg/m; P < 0.001), though there was no sex or interaction effect. A significant interaction between sex and landing condition was found for the peak hip abduction moment (P = 0.021). Males showed a significantly larger peak hip abduction moment in the trunk-obliquity landing condition than in the natural landing condition (95% CI 0.05 to 0.13 Nm/kg/m, P < 0.001), while females showed no difference in the peak hip abduction moment between the two landing conditions (95% CI - 0.02 to 0.06 Nm/kg/m, P = 0.355).

CONCLUSIONS

The knee abduction moment increased with a laterally inclined trunk for both female and male participants, while the hip abduction moment increased in males but not in females. It may be beneficial for females to focus on frontal plane hip joint control under lateral trunk-obliquity conditions during single-leg landing.

Influence of sidestepping expertise and core stability on knee joint loading during change of direction

The aims of this study were twofold: first, to compare core stability and knee joint loading between sidestepping experts and nonexperts; secondly, to determine core predictors of knee joint loading. Thirteen handball male players (experts) and 14 karatekas (nonexperts) performed six unanticipated 45° sidestepping manoeuvers, while trunk and pelvis 3D kinematics as well as ground reaction forces were measured, and peak knee abduction moment (PKAM) was determined. Student t-tests enabled a comparison of both groups and a linear mixed model approach was used to identify PKAM predictors. Sidestepping experts demonstrated significantly lower pelvis rotation towards the new movement direction at the initial contact than nonexperts (4.9° vs. 10.8°) and higher PKAM (0.539 vs. 0.321 Nm/kg-bwt). Trunk medial lean, trunk axial rotation and pelvis anterior tilt at the initial contact predicted PKAM, while trunk axial rotation, pelvis medial lean and posterior ground reaction force predicted PKAM during the weight acceptance phase. Despite higher PKAM, handball players might not be at a higher risk of anterior cruciate ligament injury as the knee joint loading remained at a relatively low level during this sidestepping task. Core stability, in its three dimensions, is a key determinant of knee joint loading.

A systematic video analysis of 21 anterior cruciate ligament injuries in elite netball players during games

This systematic video analysis of 21 anterior cruciate ligament (ACL) injuries sustained by elite-level netball players during televised games, describes the situation, movement pattern and player behaviour, providing insight regarding the injury mechanism. Seventeen of the ACL injuries occurred from jump-landing actions and only two from cutting manoeuvres. A common scenario was identified for 11 players. In this scenario, players were decelerating rapidly after jumping to receive a high pass, utilising a double-footed landing with a wide base of support (WBOS). Deceleration appeared to be applied predominantly via the injured leg with the knee extended and foot planted. Often the players appeared unbalanced on landing leaning too far back. ACL injury risk was possibly exacerbated by the players head turning away from the injured side. A further compressive knee moment may have been placed on the lateral aspect of the knee by bringing the ball from a high position to a low position at the estimated time of injury. Players may benefit from landing technique training programmes that encourage shoulder-width foot landings, with ≥30° knee flexion, a small amount of plantar-flexion and good balance. Incorporating challenges to players balance and ability to cope with perturbations may also be beneficial. Training programmes should include instruction on securing the ball in a stable above pelvis-level position after receiving a pass and bringing their whole body around during landing into the direction of their next pass, rather than simply turning their head to look.

Trunk and lower extremity long-axis rotation exercise improves forward single leg jump landing neuromuscular control

BACKGROUND

Anterior cruciate ligament (ACL) injuries often involve sudden single leg loading with directional changes. Trunk and lower extremity (LE) load transfer and muscle power are directly coupled during these movements. The effect of trunk and LE long-axis rotation training on forward single leg drop jump landing and stabilization (FSLDJLS) was studied.

METHODS

Using block randomization (gender), 36 (18 men, 18 women) subjects were assigned to experimental (nine, 20 min exercise sessions) and control groups with equal subject number. Ground reaction force (1000 Hz), kinematic (60 Hz) and LE EMG (1000 Hz) data were synchronously collected. Statistical analysis compared pre- and post-test neuromuscular control mean change differences (MCD), and hip flexion-LE peak EMG % maximum volitional isometric contraction (%MVIC) (expressed as decimal equivalents), mean change difference (MCD) relationships.

RESULTS

The experimental group had greater landing knee flexion (3.5 ± 3.6° vs. -0.4 ± 3.3°, p = .002) MCD, greater dynamic LE stiffness after landing (0.09 ± 0.14 vs. -0.11 ± 0.14, p = .001) MCD, and increased gluteus maximus (GMAX) (0.20 ± 0.39%MVIC vs. -0.23 ± 0.46%MVIC, p = .006) and gluteus medius (GMED) EMG amplitude (0.22 ± 0.31 vs. -0.07 ± 0.36%MVIC, p = .018) MCD. This group also had decreased GMAX (-166.5 ± 403.6 ms vs. 89.3 ± 196 ms, p = .025), GMED (-75.9 ± 126.8 ms vs. 131.2 ± 207.1 ms, p = .002) and vastus lateralis (-109.1 ± 365 ms vs. 205.5 vs. 510 ms, p = .04) activation duration MCD. More experimental group subjects had increased landing knee flexion MCD (15/18 vs. 8/18, p = .015), increased dynamic LE stiffness MCD (15/18 vs. 2/18, p < .0001) and increased GMAX (15/18 vs. 7/18, p = .006) and GMED (17/18 vs. 10/18, p = .007) EMG amplitude MCD, and reduced GMAX (12/18 vs. 6/18, p = .046), GMED (11/18 vs. 5/18, p = .044), rectus femoris (12/18 vs. 6/18, p = .046), and vastus lateralis (13/18 vs. 7/18, p = .044) EMG activation duration MCD. Only the experimental group displayed significant relationships between landing and peak hip flexion and peak LE EMG amplitude MCD.

CONCLUSION

Increased dynamic LE stiffness, increased hip muscle EMG amplitude and decreased hip and knee muscle activation duration MCD in the experimental group suggests improved LE neuromuscular control.

Test-retest reliability of entire time-series data from hip, knee and ankle kinematics and kinetics during one-leg hops for distance: Analyses using integrated pointwise indices

Motion capture systems enable in-depth interpretations of human movements based on data from three-dimensional joint angles and moments. Such analyses carry important bearings for evaluation of movement control during for instance hop landings among sports-active individuals from a performance perspective but also in rehabilitation. Recent statistical development allows analysis of entire time-series of angle and moment during hops using functional data analysis, but the reliability of such multifaceted data is not established. We used integrated pointwise indices (intra-class correlation, ICC; standard error of measurement, SEM) to establish the test-retest reliability of three-dimensional hip, knee and ankle angle and moment curves during landings of one-leg hop for distance (OLHD) in 23 asymptomatic individuals aged 18-28. We contrasted these findings to reliability of discrete variables extracted at specific events (initial contact, peak value). We extended the calculations of ICC and SEM to handle unbalanced situations (varying number of repetitions) to include all available data. Hip and knee angle curves proved reliable with stable ICC curves throughout the landing, with integrated ICCs ≥ 0.71 for all planes except for knee internal/external rotation (ICC = 0.57). Hip and knee moment curves and ankle angle and moments were less reliable and less stable, particularly in the first ~ 10-25% of the landing (integrated ICCs 0.44-0.57). Curve data were generally not in agreement with the results for discrete event data, thus advocating analysis of curve data which contains more information. To conclude, hip and knee angle curve data during OLHD landings can reliably be evaluated, while moment curves necessitate careful consideration.

The non-sagittal knee moment vector identifies 'at risk' individuals that the knee abduction moment alone does not

Multi-planar forces and moments are known to injure the anterior cruciate ligament (ACL). In ACL injury risk studies, however, the uni-planar frontal plane external knee abduction moment is frequently studied in isolation. This study aimed to determine if the frontal plane knee moment (KM-Y) could classify all individuals crossing a risk threshold compared to those classified by a multi-planar non-sagittal knee moment vector (KM-YZ). Recreationally active females completed three sports tasks-drop vertical jumps, single-leg drop vertical jumps and planned sidesteps. Peak knee abduction moments and peak non-sagittal resultant knee moments were obtained for each task, and a risk threshold of the sample mean plus 1.6 standard deviations was used for classification. A sensitivity analysis of the threshold from 1-2 standard deviations was also conducted. KM-Y did not identify all participants who crossed the risk threshold as the non-sagittal moment identified unique individuals. This result was consistent across tasks and threshold sensitivities. Analysing the peak uni-planar knee abduction moment alone is therefore likely overly reductionist, as this study demonstrates that a KM-YZ threshold identifies 'at risk' individuals that a KM-Y threshold does not. Multi-planar moment metrics such as KM-YZ may help facilitate the development of screening protocols across multiple tasks.

The influence of decision making and divided attention on lower limb biomechanics associated with anterior cruciate ligament injury: a narrative review

Cognitive loads have been shown to influence anterior cruciate ligament (ACL) injury risk. Two main sources of cognitive loads that athletes experience are decision making and dividing attention between multiple tasks. The aim of this paper was to review previous studies examining the effects of decision making and divided attention on lower limb biomechanics during landing and cutting. Previous research has shown decision making to significantly influence a number of biomechanical variables associated with increased risk of ACL injury, such as reduced knee flexion at initial contact, increased knee valgus angles, increased knee extension moment and increased knee valgus moment in decision-making tasks compared to pre-planned tasks. Furthermore, dividing attention between multiple tasks has been shown to result in reduced knee flexion at initial contact, increased vertical ground reaction force, and reduced stability during landing/cutting. The changes in lower limb biomechanics observed as a result of both decision making and dividing attention are likely due to a reduced ability to anticipate ground contact and implement protective movement patterns associated with reduced ACL loading. Collectively, these findings emphasise the need for tasks that incorporate decision making and divided attention when investigating ACL injury mechanisms and developing ACL injury risk screening assessments.

Trunk motion and anterior cruciate ligament injuries: a narrative review of injury videos and controlled jump-landing and cutting tasks

The aims of this narrative review were to summarise trunk motion and external trunk perturbation observed in anterior cruciate ligament (ACL) injury videos and to review the association between trunk motion and ACL loading variables in controlled jump-landing and cutting tasks in non-injured populations. Video analyses have shown limited trunk flexion and increased trunk lateral bending towards the injured leg are associated with increased risk of ACL injuries, while trunk axial rotation away from the injured leg is more frequent than rotation towards the injured leg. Contact with the trunk before and at the time of the injury is common and might increase the risk of ACL injury. Controlled jump-landing and cutting studies have shown that limited trunk flexion and increased trunk lateral bending are associated with increased ACL loading. However, the findings of trunk axial rotation are not consistent with most video analyses. Mid-flight external trunk perturbation could increase ACL loading variables for one leg and is consistent with the videos of trunk-contact ACL injuries. These findings may help understand the role of trunk motion on primary ACL injury mechanisms and improve ACL injury screening tasks and ACL injury prevention strategies with the consideration of trunk motion.

Side-hops challenge knee control in the frontal and transversal plane more than hops for distance or height among ACL-reconstructed individuals

We compared knee landing mechanics with presumed relation to risk of anterior cruciate ligament (ACL) injury among three single-leg hop tests and between legs in individuals with unilateral ACL reconstruction. Thirty-four participants (>10 months' post-surgery, 23 females) performed the standardised rebound side hop (SRSH), maximal hop for distance (OLHD) and maximal vertical hop (OLVH). We calculated the following knee outcomes from motion capture and force plate data: finite helical axis inclination angles (approximates knee robustness), frontal and transversal plane angles at initial contact, peak angles of abduction and internal rotation during landing, and peak external moments of flexion, abduction and internal rotation during landing. Repeated-measures MANOVA analysis ('sex' as covariate) confirmed that SRSH induced greater angles and moments, particularly in the frontal plane, compared to OLHD and OLVH. There was between-leg asymmetry for peak knee flexion moment for males during OLHD and OLVH, and for females during SRSH. Our results advocate the SRSH over OLHD and OLVH for assessment of knee landing control to screen for movement patterns potentially related to ACL injury risk. However, clear differences in both knee kinematics and kinetics between OLHD and SRSH motivate the use of both tests to evaluate different aspects of landing control.

Falling as a strategy to decrease knee loading during landings: Implications for ACL injury prevention

Anterior cruciate ligament (ACL) injuries often occur when individuals land primarily on a single leg. Falling has been proposed as a potential strategy to decrease knee loading during landings. The purpose of this study was to compare impact forces, knee angles, and knee moments during natural landings, soft landings, and landings followed by falling after forward and vertical jumps, each under single or double-leg conditions. Sixteen male and sixteen female participants (age: 22.0 ± 2.9 years) completed each landing condition while kinematics and ground reaction forces were collected. In the natural landing condition, participants landed as they would in a sport setting. In the soft landing condition, participants landed as softly as possible with increased knee and hip flexion. In the falling condition, participants landed softly and then fell forward or backward onto a mat after forward and vertical jumps, respectively. The falling condition demonstrated the greatest initial and peak knee flexion angles, the least peak vertical ground reaction forces, and the least peak knee extension and adduction moments compared to the natural landing and soft landing conditions. The soft landing condition resulted in similar changes in landing mechanics compared to the natural landing, but the effect was limited for single-leg landings compared to double-leg landings. When the sports environment allows, falling appears to be a potential strategy to decrease knee loading when individuals must land on a single leg with sub-optimal body postures. Future studies are needed to develop progressive training of effective and safe falling techniques.