Impact differences in ground reaction force and center of mass between the first and second landing phases of a drop vertical jump and their implications for injury risk assessment

Neurophysiology of ACL Injury

The neurophysiology of ACL injury extends beyond the mechanical rupture of the ligament to encompass profound alterations in the central and peripheral nervous systems, impacting sensorimotor integration and neuromuscular control. The ACL, densely populated with mechanoreceptors, plays a critical role in joint proprioception, dynamically regulating knee stability through complex neural circuits that connect to the spinal cord and brain. When disrupted by injury, these neural pathways contribute to delayed muscular activation, altered motor planning, and compromised joint stability. Such neuromechanical deficits increase the likelihood of reinjury and highlight the need for comprehensive neuroplastic rehabilitation. Neuroplastic therapy, employing tools like external focus strategies, stroboscopic glasses, smartboards, and virtual reality, aims to restore and enhance neural connectivity, sensory integration, and motor coordination. These advanced tools target distinct phases of motor learning, promoting automaticity and resilience in movement patterns. By integrating visual-cognitive, proprioceptive, and reflexive controls, this therapeutic approach not only accelerates recovery but also optimizes performance and reduces the risk of re-injury, representing a paradigm shift in ACL rehabilitation.

Kinetics During the Tuck Jump Assessment and Biomechanical Deficits in Female Athletes 12 Months After ACLR Surgery

BACKGROUND

Residual interlimb deficits after anterior cruciate ligament reconstruction (ACLR) can lead to functional maladaptation and increase the risk of reinjury. The tuck jump assessment (TJA) may offer a more effective evaluation of ACLR status as compared with traditional tasks owing to increased risk of altered landing mechanics, asymmetrical landing, and increased knee valgus attributed to the cyclical nature of the task. However, it remains unclear whether altered TJA kinetics resolve over time or persist through return-to-play phases of rehabilitation.

PURPOSE

To examine longitudinal kinetics, asymmetries, and functional performance deficits during TJA at 9 and 12 months after ACLR in female athletes at high risk of reinjury.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Female athletes (ACLR, n = 24; controls, n = 19; total, N = 43) performed a single trial of TJA on dual-force plates at 2 time points. The ACLR group (mean ± SD age, 16.8 ± 1.9 years) was tested at 9 and 12 months after surgery, and the control group (16.5 ± 3.6 years) was tested at similar time points. All athletes participated in similar sports and had comparable activity levels. Discrete time point analysis and statistical parametric mapping were used to identify deficits within each group.

RESULTS

At 9 months after surgery, the ACLR group exhibited significant interlimb differences in all kinetic variables (P < .05), which persisted at 12 months with only small reductions in magnitude. As compared with controls, the ACLR group demonstrated a persistent offloading strategy in the involved limb by exhibiting larger interlimb asymmetries for a range of kinetic variables and a greater vertical ground-reaction force in the uninvolved limb during most of the stance phase at both time points (P < .001). Distinct differences in functional performance of TJA were evident at both time points, characterized by lower peak vertical ground-reaction force, peak center of mass displacement, and relative vertical leg stiffness and longer ground contact times (P < .001).

CONCLUSION

This study revealed that young female athletes after ACLR exhibit persistent interlimb deficits and functional maladaptations up to 12 months after surgery. The TJA identified significant biomechanical impairments to both limbs, resulting in asymmetrical loading and altered movement strategies as compared with healthy controls. Despite some improvements, athletes with ACLR continued to demonstrate offloading to the uninvolved limb, indicating incomplete neuromuscular recovery.

Acquisition, Retention, and Transfer Effects of Landing Training to Increase Foot Progression Angle During Bilateral Drop Landings

Foot position during landing directly influences knee mechanics. Thus, the purpose of this study was to determine success in practicing, repeating, and transferring a desired foot progression angle (FPA) during landing, as well as changes in knee mechanics. Twenty females were randomly assigned to a control or verbal instruction group. On day 1, each group performed 40 drop landings. The verbal instruction group was instructed to "Land with 30 degrees of external rotation" before every trial. Feedback was provided on a terminal schedule in the form of knowledge of FPA error. On day 2, retention was assessed with 5 drop landings, while transfer was assessed during a 2-step stop-jump landing. Repeated-measures analyses of variance (2 × 4 [group × time]) were used to assess the influence of verbal instruction on knee mechanics. Participants who received verbal instruction exhibited increased FPA. They also demonstrated increased initial contact knee abduction during acquisition and retention. For all participants, initial contact knee flexion increased, while peak knee adduction moment decreased during acquisition. While the verbal instruction cue was effective in promoting an increase in FPA and reducing some ACL injury risk factors during practice and retention, this cue may only be effective to tasks similar to what was practiced.

Differences of simulated ankle dorsiflexion limitation on lower extremity biomechanics during long jump takeoff

The long jump is an athletic event that demands speed, power, force application, and balance, with each phase being critical to overall performance. However, previous research has neglected the limiting effect of the wedge pedals on ankle dorsiflexion range of motion. This cross-sectional study investigated biomechanical changes in the lower extremities during long jumps under varying degrees of ankle dorsiflexion. Thirty male Division II long jump athletes executed jumps under three conditions: no dorsiflexion, with 10° dorsiflexion restriction, and with 20° dorsiflexion restriction. A Vicon motion capture system with eight cameras and an AMTI force platform were used to collect biomechanical data simultaneously during the long jump. The angles, moments, and velocities of the ankle, hip, and knee joints during takeoff were simulated and calculated using a musculoskeletal model. Between-group variations were assessed using one-way repeated measures ANOVA, with statistical parametric mapping (SPM1D) applied for analysis. Results showed that as ankle restriction increased, vertical velocity gain increased: NW (3.34 ± 0.21 m/s), 10W (3.65 ± 0.14 m/s), and 20W (3.77 ± 0.12 m/s) (p < 0.001). Horizontal velocity loss was significantly higher only at 20W (p = 0.002). Peak extension angle, angular velocity, and power were highest at 10W for the knee and hip joints (p < 0.05). Joint forces at the ankle, knee, and hip were significantly affected by different pedal angles (p < 0.001). Athletes with a 10° ankle dorsiflexion limit showed increased vertical velocity with minimal horizontal velocity loss, potentially enhancing performance. This limit also increased muscle co-activation around the knee, possibly stabilizing it. Athletes should consider a 10° ankle dorsiflexion limit in training to improve performance and reduce injury risk.

Augmented Feedback Response Prediction by Peak Vertical Ground Reaction Force in Adolescent Female Athletes

Background and Purpose

Anterior cruciate ligament (ACL) tears often occur due to non-contact mechanisms in landing within females. Impact loading and aberrant landings may be addressed with augmented feedback training. The purpose of this study was to identify which female athletes most readily respond to a single session of augmented feedback to attenuate vGRF, by considering baseline peak vGFR and change in vGRF during training.

Design

Repeated Measures.

Methods

One hundred, forty-seven female athletes landed from 50 cm onto two force platforms with and without augmented feedback of vertical ground reaction force (vGRF), vGRF symmetry, and lower extremity position. Each performed six baseline trials and two sets of six training trials with cues. Following training, athletes completed six post-feedback trials (with no feedback) and six dual-task (transfer) trials where they randomly caught a basketball during landing. Peak vGRF was measured. Mean responses were reported for the sets of six trials. Participants were grouped based on their responses to training. Linear regression was used to indicate how well initial performance and response predicted the final response.

Results

Four groups were identified, with 107 participants showing high baseline ground reaction forces and response to training. Only 23 participants (16.4%) did not respond to training. Baseline vGRF predicted post-feedback vGRF and transfer task vGRF (R2=0.508 and R2=0.400) across all participants. When change in vGRF was assessed following two blocks of augmented feedback training, prediction of responders improved with post-feedback vGRF and transfer vGRF (R2=0.911 and R2=0.761).

Conclusions

The combination of both baseline ground reaction force and response to initial training is more accurate than baseline measures alone in identifying those who respond to training. Assessing initial response to training may be necessary to more accurately identify individuals most likely to benefit from augmented feedback training and who may require further evaluation and training.

Level of Evidence

2b.

Differences in landing biomechanics in the presence of delayed onset muscle soreness following or not active recovery

OBJECTIVE

Delayed onset muscle soreness (DOMS) can reduce joint range of motion and strength, cause edema, and increase joint stiffness. Here we set out to determine whether quadriceps DOMS followed by an active recovery low-intensity exercise alters jump landing biomechanics.

METHODS

3D landing kinematics, kinetics, and DOMS were evaluated in 26 healthy adults (15 women) performing drop and vertical jump landings before and after a squat protocol to induce quadriceps DOMS. In the presence of DOMS, half of the participants (n = 13) performed a low-intensity exercise for active recovery (10-minute treadmill walking), while the other half (n = 13) did not. Descriptive statistics and generalized estimative equations were applied to determine the effects of DOMS and active recovery on landing kinematics and kinetics.

RESULTS

DOMS decreased knee and ankle flexion angles and increased knee and ankle frontal plane angles during vertical jumps. DOMS elicited a longer time to reach peak ground reaction force during drop jumps. Low-intensity exercise for active recovery reduced DOMS perception but did not alter the biomechanics of landing.

CONCLUSION

DOMS changes landing strategy. However, including a low-intensity exercise for active recovery before landing practice did not change the kinematics and kinetics of landing.

Racial differences in running and landing measures associated with injury risk vary by sex

It is unknown whether running and landing mechanics differ between racial groups despite injury disparities between African Americans (AA) and white Americans (WA). This study aimed to identify potential racial differences in running and landing mechanics and understand whether anthropometric, strength, and health status factors contribute to these differences. Venous blood samples, anthropometry, lower-extremity strength, and health status assessments were collected (n = 84, 18-30y). Three-dimensional motion capture and force plate data were recorded during 7 running and 7 drop vertical jump trials. Racial effects were determined, and regression models evaluated explanatory factors. AA females ran with longer stance times (p = 0.003) than WA females, while AA males ran with smaller loading rates (p = 0.046) and larger peak vertical ground reaction forces (p = 0.036) than WA males. Frontal plane knee range of motion during landing was greater in AA females (p = 0.033) than WA females; larger waist circumference and weaker knee extension strength accounted for this significance. Although outcome measures were associated with physiologic, anthropometric, and activity measures, their explanatory power for race was ambiguous, except for knee range of motion in females. Modifiable factors explaining racial effects during landing in females are potential intervention targets to reduce racial health disparities in running and landing injuries.

The acute effect of verbal instructions on performance and landing when dropping from different heights: the ground reaction force-time profile of drop vertical jumps in female volleyball athletes

Introduction

The drop vertical jump (DVJ) is extensively utilized for conditioning and evaluating physical performance, as well as reducing the likelihood of injury by enhancing joint stability through the coactivation of muscles acting on the joint. The execution of DVJ can be controlled by verbal instructions and evaluated by the vertical ground reaction force (vGRF)-time profile.

Methods

Our hypothesis was that varying verbal instructions could have an impact on the DVJ's parameter, thereby optimizing vertical performance and minimizing the impact during landing in young female volleyball players. Sixteen female volleyball players volunteered to participate in this study (age: 21.3 ± 2.6 years; stature: 1.66 ± 0.1 m; body mass: 62.0 ± 8.1 kg and BMI: 22.2 ± 1.8). They executed DVJs following verbal instructions ranging from "jump as high as possible" (1A), "jump as quickly as possible" (2A), "jump as high as possible and during the landing attempt to dampen the impact at ground contact" (1B), and "jump as high as quickly as possible and during the landing attempt to damp the impact at ground contact" (2B). The reactive strength index (RSI), vGRF (1st and 2nd peaks), and flight time (FT) were evaluated.

Results

The verbal instructions 1A improved the FT and the first peak of the vGRF (P < 0.05), whereas 2A the RSI (P < 0.05). On the contrary, "the damping" required in the 1B, and 2B verbal instruction reduced the 2nd peak of vGRF (P < 0.05), without altering the task required during the jump (P < 0.05).

Discussion

The instructions provided for the final landing (the second peak of vGRF) have the potential to enhance safety by reducing the peak of vGRF without affecting the performance required during the jump. When designing DVJ training, coaches or kinesiologists must consider the use of verbal instructions to induce specific adaptation over time.

Clinical relevance

The present study supports the use of specific verbal instructions to reduce impact forces in landing and injury risk.

Influences of fatigue and anticipation on female soccer players' biomechanical characteristics during 180° pivot turn: implication for risk and prevention of anterior cruciate ligament injury

Introduction

Athletes' capability to perform activities with body rotation could be weakened by fatigue accumulation. Making pivot turning in unanticipated scenarios after fatigue may greatly challenge athletes' ability to adapt rational motion strategies, elevating the risk of anterior cruciate ligament (ACL) injury. This study aimed to investigate the effects of fatigue and anticipation on biomechanical risk factors of ACL injury during 180° pivot turns in female soccer players.

Methods

Twenty-one female soccer players were selected as participants. The participants performed anticipated turning maneuver before the fatigue intervention. The participants sprinted along the runway, decelerated and planted their foot on the force plate, and then executed a 180° pivot turn. For unanticipated tests, the pivot turn was mixed with side/cross-cuts, which were indicated to the participant using a custom-designed light system. The tests were repeated by the participant after receiving a fatigue intervention. Lower-limb joint angles and moments were characterized. Peak ground reaction forces (GRFs) and GRF loading rates were determined. Two-way repeated measures analysis of variance was applied to examine the effects of fatigue and anticipation on the variables of interest.

Results

Compared to the anticipated conditions, the approach speed was significantly lower in the unanticipated tests (P < 0.0001). Lower-limb kinematics showed varied angular patterns across conditions: greater hip joint variations in flexion, abduction, and internal rotation during unanticipated turns; consistent knee joint flexion and ankle plantarflexion with dorsiflexion observed mid-turn. Significant interactions (P = 0.023 to P = 0.035) between fatigue and anticipation influenced hip joint angles. Anticipation effects were notable at initial contact and peak ground reaction force, increasing hip, knee, and ankle joint angles (P < 0.0001 to P = 0.012). Participants showed consistent ground reaction force (GRF) patterns during pivot turns across fatigue and anticipation conditions, with the first peak occurring approximately 10% into the turn period. Significant interaction effects (P = 0.016) between fatigue and anticipation were observed for knee flex/extension moments at the first peak vertical GRF. Anticipation significantly increased first peak vertical (P < 0.0001), anteroposterior (P < 0.0001), and mediolateral (P < 0.0001) GRFs. Fatigue increased first peak vertical (P = 0.022), anteroposterior (P = 0.018), and mediolateral (P = 0.019) GRFs. Post-fatigue, participants exhibited reduced first peak GRFs and loading rates compared to pre-fatigue conditions, with higher rates observed in unanticipated turns (vertical GRF: P = 0.030; anteroposterior GRF: P < 0.0001).

Conclusion

Female soccer players' lower-limb Biomechanical characterization could be greatly affected by the change of anticipatory scenarios. With the associated increase of GRF, the risk of their ACL injury might be elevated. Fatigue affected female soccer players' abilities on movement performances, but the interaction of these two factors could potentially weaken their knee's functions during pivot turns. Cognitive training on unanticipated tasks may be important for rehabilitation training after ACL injury.

Differences in Lower-Extremity Joint Coordination During Two Landing Phases of a Drop Jump Task

The aim of the present study was to compare the differences in joint coordination patterns and variability in the lower extremity between the first and second landing phases of the drop jump. Eighteen resistance-trained men (age: 22.8 ± 1.8 years) performed drop jumps from a height of 0.40 m. An eight-camera motion capture system was utilized to record kinematic trajectories. Modified vector coding technique and circular statistics were used to determine the coordination pattern and variability of the following joint couples during the first and second landings: hip frontal-knee frontal (HfKf), hip sagittal-knee frontal (HsKf), hip sagittal-knee sagittal (HsKs), knee frontal-ankle frontal (KfAf), knee sagittal-ankle frontal (KsAf), and knee sagittal-ankle sagittal (KsAs). Statistical differences in the distribution frequencies of coupling angles and variability between the dominant and nondominant limbs across the two landing phases were compared using two-way repeated analysis of variance and Wilcoxon rank-sum tests. During the second landing phase, the proportion of HsKs, KfAf, and KsAs showing in-phase coordination was reduced but the proportion of KfAf and KsAs showing proximal joint (knee) coordination was increased (p < .05). Significant differences in bilateral asymmetry were observed only for the HfKf and KfAf patients (p < .05). HsKs, KfAf, and KsAf varied considerably during the second landing phase (p < .05). Joint coordination patterns during the second landing phase of the drop jump differed considerably from those during the first landing phase, thereby increasing the risk of knee and ankle injuries.

New Insights Optimize Landing Strategies to Reduce Lower Limb Injury Risk

Single-leg landing (SL) is often associated with a high injury risk, especially anterior cruciate ligament (ACL) injuries and lateral ankle sprain. This work investigates the relationship between ankle motion patterns (ankle initial contact angle [AICA] and ankle range of motion [AROM]) and the lower limb injury risk during SL, and proposes an optimized landing strategy that can reduce the injury risk. To more realistically revert and simulate the ACL injury mechanics, we developed a knee musculoskeletal model that reverts the ACL ligament to a nonlinear short-term viscoelastic mechanical mechanism (strain rate-dependent) generated by the dense connective tissue as a function of strain. Sixty healthy male subjects were recruited to collect biomechanics data during SL. The correlation analysis was conducted to explore the relationship between AICA, AROM, and peak vertical ground reaction force (PVGRF), joint total energy dissipation (TED), peak ankle knee hip sagittal moment, peak ankle inversion angle (PAIA), and peak ACL force (PAF). AICA exhibits a negative correlation with PVGRF (r = -0.591) and PAF (r = -0.554), and a positive correlation with TED (r = 0.490) and PAIA (r = 0.502). AROM exhibits a positive correlation with TED (r = 0.687) and PAIA (r = 0.600). The results suggested that the appropriate increases in AICA (30° to 40°) and AROM (50° to 70°) may reduce the lower limb injury risk. This study has the potential to offer novel perspectives on the optimized application of landing strategies, thus giving the crucial theoretical basis for decreasing injury risk.

Effect of unpredictable timing on the hip, knee, and ankle kinematics and center of mass during deceleration tasks

BACKGROUND

Unpredictable stopping or deceleration tasks are crucial to prevent ACL injury. The purpose of this study was to reveal differences and relationships in kinematics during different deceleration tasks with and without anticipation.

METHODS

Twenty-four collegiate athletes were recruited. Three commercial video cameras were used to capture frontal and sagittal lower-extremity kinematics. Participants were instructed to perform three deceleration tasks: 1) anticipated stopping and running backward at a point indicated previously (SRB-P); 2) anticipated stopping and running backward in front of a badminton net (SRB-N); and 3) unanticipated stopping and running backward upon random flashing of a light (SRB-U). Differences and relationships between hip, knee, and ankle kinematics at stopping (SS) and deceleration steps (DS) and the height of the great trochanter (HGT) at SS were analyzed.

RESULTS

For all tasks, the knee flexion angle was less than 25° at SS. There were no significant differences in hip, knee, and ankle kinematics between tasks. HGT during SRB-U was higher than that in the other tasks at DS. Hip flexion angle at SS and DS was significantly correlated with HGT at SS. During SRB_P and SRB_N, only knee flexion angle at DS was significantly correlated with HGT at SS.

CONCLUSIONS

The deceleration task in this study, SRB, causes a low knee-flexion angle at SS. The COM remained higher during unanticipated stopping, which is related only to hip flexion angle during the task. Knee flexion movement does not contribute to lowering COM during an unpredictable deceleration task.

The Effects of Pointe Shoes on Ballet Dancers' Biomechanics, Muscle Activity, Movement and Symptoms: A Scoping Review

Introduction: Dancing en pointe requires ballet dancers to stand on the tips of their toes while wearing a structured pointe shoe. Understanding the effect of pointe shoes on ballet dancers' biomechanics, function, symptoms and skin health is essential to guide shoe development and ultimately improve dancer performance. Therefore, the purpose of this scoping review was to map the evidence and identify knowledge gaps related to the effect of wearing pointe shoes on professional and recreational ballet dancers. Method: A scoping review was conducted by searching 6 electronic databases and the International Association for Dance Medicine and Science Bibliography. Results: Thirty-five studies were grouped into 5 categories: pointe shoe factors (eg, toe box and shank, pointe shoe status; 9 studies), shoe types (eg, flat shoes vs demi pointe vs pointe; 10 studies), ballet movements (11 studies), symptoms (5 studies), and intrinsic dancer factors (eg, foot type/toe length; 7 studies). Studies were published between 1979 and 2023, with 72% (n = 23) published between 2006 and 2020. Most (86%) of the studies were cross-sectional. Most studies explored biomechanical outcomes and the most common data collection device was force plates (19 studies). Overall, there was an insufficient volume of evidence for specific research aims. Significant gaps in knowledge exist regarding functional and performance-based outcomes, injury outcomes including exploration of factors such as shoe age/usage, and pointe shoe treatment factors. Conclusions: Currently the field of research suffers from threats to ecological validity, with many study methods not reflecting ballet-specific demands or environments. The impact of pointe shoes on ballet dancers is a developing research area, and this scoping review can help guide future research decisions. Studies need to target the knowledge gaps and employ rigorous ecologically valid study designs and ensure that findings inform shoe design and dancer education to minimize injury and maximize comfort and performance.

Lower-extremity kinematics and kinetics differ based on drop vertical jump variation: An assessment of methodology for a return-to-play protocol using motion analysis

BACKGROUND

The drop vertical jump (DVJ) is commonly used in return-to-play evaluations to assess movement quality and risk during a dynamic task. However, across biomechanics literature, a multitude of DVJ variations have been used, influencing the generalizability and potential interpretation of the reported findings.

RESEARCH QUESTION

The purpose of this study was to identify differences in lower extremity kinematics and kinetics between DVJ variations that differ based on horizontal jump distance, verbal instructions, and the use of a jump target.

METHODS

A single-group repeated measures design was used in a laboratory setting. Twenty participants were tested, and three-dimensional angles and moments of the pelvis, hip, knee, and ankle were computed. Wilcoxon signed rank tests were performed to determine differences between DVJ variations.

RESULTS

Reduced knee flexion at initial contact and greater knee extensor moments across the descent phase were observed with increased horizontal jump distance. Additionally, both verbal instructions and a jump target influenced movement strategies at the pelvis, hip, and knee. Ground reaction forces were found to be similar across conditions and jump height following the first landing increased with a target.

SIGNIFICANCE

Although subtle, the biomechanical differences observed between task variations emphasize the importance of standardizing motion analysis protocols for research and clinical decision-making. Given the findings of the current study, the authors recommend using the Half Height variation in patients treated for a knee injury as it will likely be the most indicative of movement quality.

Athletes with a History of ACL Reconstruction Exhibit Greater Inter-Limb Asymmetry in Impact Forces During the First Landing of a Drop Vertical Jump Compared to the Second Landing

The primary objective of this study was to examine the degree of inter-limb asymmetry in impact force magnitudes and rates during the first and second landings of a drop vertical jump in adolescent athletes with a history of anterior cruciate ligament (ACL) reconstruction. We also compared the degree of asymmetry exhibited by the athletes who had undergone ACL reconstruction to a group of uninjured athletes. This study included 14 athletes who had undergone ACL reconstruction and 28 uninjured athletes, matched for age, sex, and sport. All athletes completed a double-leg drop vertical jump task. Peak vertical ground reaction forces (vGRFs) and loading rates were examined for both limbs during the first and second landings of the drop vertical jump. For the athletes who had undergone ACL reconstruction, peak vGRFs were 11.9% greater for the uninvolved limb vs. the involved limb during the first landing; however, peak vGRFs were only 2.4% greater for the uninvolved limb (vs. the involved limb) during the second landing. The athletes who had undergone ACL reconstruction exhibited greater asymmetry in peak vGRFs for the first landing compared to the uninjured athletes; however, there was no difference between the groups (ACL reconstruction, uninjured) for the second landing.

Knee joint biomechanics and cartilage damage prediction during landing: A hybrid MD-FE-musculoskeletal modeling

Understanding the mechanics behind knee joint injuries and providing appropriate treatment is crucial for improving physical function, quality of life, and employability. In this study, we used a hybrid molecular dynamics-finite element-musculoskeletal model to determine the level of loads the knee can withstand when landing from different heights (20, 40, 60 cm), including the height at which cartilage damage occurs. The model was driven by kinematics-kinetics data of asymptomatic subjects at the peak loading instance of drop landing. Our analysis revealed that as landing height increased, the forces on the knee joint also increased, particularly in the vastus muscles and medial gastrocnemius. The patellar tendon experienced more stress than other ligaments, and the medial plateau supported most of the tibial cartilage contact forces and stresses. The load was mostly transmitted through cartilage-cartilage interaction and increased with landing height. The critical height of 126 cm, at which cartilage damage was initiated, was determined by extrapolating the collected data using an iterative approach. Damage initiation and propagation were mainly located in the superficial layers of the tibiofemoral and patellofemoral cartilage. Finally, this study provides valuable insights into the mechanisms of landing-associated cartilage damage and could help limit joint injuries and improve training programs.

Can a knee sleeve influence ground reaction forces and knee joint power during a step-down hop in participants following anterior cruciate ligament reconstruction? A secondary analysis

PURPOSE

Elastic knee sleeves are often worn following anterior cruciate ligament (ACL) reconstruction. The study aimed to define immediate and 6-week effects of wearing a knee sleeve on ground reaction forces (GRF) and knee joint power during a step-down hop task.

METHODS

Using a cross-over design, we estimated GRF and knee kinematics and kinetics during a step-down hop for 30 participants following ACL reconstruction (median 16 months post-surgery) with and without wearing a knee sleeve. In a subsequent randomised clinical trial, participants in the 'Sleeve Group' (n = 9) wore the sleeve for 6 weeks at least 1 hour daily, while a 'Control Group' (n = 9) did not wear the sleeve. We compared the following outcomes using statistical parametric mapping (SPM): (1) GRF and knee joint power trajectories between three conditions at baseline (uninjured side, unsleeved injured and sleeved injured side); (2) GRF and knee joint power trajectories within-participant changes from baseline to follow-up between groups. We also compared discrete peak GRFs and power, rate of (vertical) force development, and mean knee joint power in the first 5% of stance phase.

RESULTS

SPM showed no differences for GRF for the (unsleeved) injured compared to the uninjured sides; when wearing the sleeve, injured side mean power in the first 5% of stance increased significantly from a concentric to an eccentric power. Discrete variables showed lower peak anterior (propulsive) GRF, mean power in the first 5% of stance, peak eccentric and concentric power for the injured compared to the uninjured sides. After six weeks, a directional change for vertical GRF differed showed slightly decreased forces for the Control Group and increased forces for the Sleeve Group.

CONCLUSION

Wearing a knee sleeve on the anterior cruciate ligament injured knee improved knee power during the first 5% of stance during the step-down hop. No consistent changes were observed for ground reaction forces for SPM and discrete variable analyses. Wearing the knee sleeve at least one hour daily for 6-weeks lead to a directional change of increased vertical GRF for the Sleeve Group at follow-up.

TRIAL REGISTRATION

The trial was prospectively registered with the Australia New Zealand Clinical Trials Registry No: ACTRN12618001083280, 28/06/2018. https: //anzctr.org.au/Trial/Registration/TrialReview.aspx?id=375347&isClinicalTrial=False.

The Effect of Two Types of Foot Orthoses on the Knee Valgus Angle Within Single-Leg Landing: Implications for ACL Damage Hazard Decrease

Background: Non-contact anterior cruciate ligament (ACL) injuries commonly occur when athletes land in high risk positions such as knee valgus. The impact of foot orthoses during exercises that recreate a non-contact ACL harm system (i.e., landing) in any case will be obscured. Objectives: The purpose of the current study research was to evaluate the effect of two foot orthoses (semi-hard foot orthoses and hard foot orthoses) on knee valgus angle during single-leg drop landing. Methods: Twenty male leisure volleyball gamers performed landing in one-leg step from 30 cm height in 3 conditions (without foot orthoses, mid-hard foot orthoses, and hard foot orthoses). A motion capture system was used to measure lower extremity kinematics. Two risk factors of ACL injury, maximum knee valgus angle (KVA), and maximum knee flexion was measured. ANOVA was used for statistical analysis (P < 0.05). Results: With mid-hard foot, orthoses provide the maximum level of knee flexion and the minimum level of knee valgus during single-leg drop landing. Conclusions: It may be concluded showed that foot orthoses affect knee kinematics. More knee flexion and less knee valgus brought about by mid-hard foot orthoses can reduce injuries of the anterior cruciate ligament (ACL).

Effects of auxetic shoe on lumbar spine kinematics and kinetics during gait and drop vertical jump by a combined in vivo and modeling investigation

The present study examined the effects of auxetic shoes on the biomechanics of the spine, as compared to barefoot and conventional shoe conditions, during gait and drop vertical jump (DVJ) activities using a combined in vivo and musculoskeletal modeling approach. Motion and force-plate data as well as electromyographic (EMG) activities of select trunk muscles of 11 individuals were collected during foregoing activities. In DVJ activity, two main phases of first landing (FL) and second landing (SL) were studied. In the FL phase of DVJ noticeable alternations were observed when auxetic shoes were used. That is, compared to the conventional footwear condition, smaller EMG activities in extensor muscles (by ~ 16-29%, p < 0.001), smaller anterior-posterior (AP) distance between the center of pressure of ground reaction force and heel (by ~ 19%, p = 0.002), generally larger maximal hip, knee, and ankle flexion angles (p < 0.005) and finally smaller maximal L5-S1 compression force and maximal external moment (by ~ 12 and 8%, respectively, p < 0.001) were obtained by wearing auxetic shoes. Our results, therefore, indicate that using auxetic shoes can reduce load on the lumbar spine during high-demanding activities such as vertical jump and thus may decrease the musculoskeletal risk of injuries during these activities.

Effects of a soccer-specific vertical jump on lower extremity landing kinematics

Anterior cruciate ligament (ACL) injury frequently occurs in female soccer athletes during deceleration movements such as landings. In soccer, landings mostly occur following jumping headers. Little research has been done to determine the mechanics that follow and how they compare to standard drop vertical jumps (DVJ). The purpose of this study was to analyze differences in kinematics between the DVJ and the soccer-specific vertical jump (SSVJ) in female soccer athletes to better assess the sport-specific risk for ACL injury. A secondary aim was to compare second landings (L2) to first landings (L1). Eight female recreational soccer athletes performed DVJs and SSVJs initiated from a 31 ​cm height. Motion capture was performed during landings and data were analyzed using repeated-measures ANOVA. SSVJs produced less peak hip flexion (p ​= ​0.03) and less peak knee flexion (p ​= ​0.002) than DVJs. SSVJs also demonstrated increased ankle plantarflexion at initial contact (IC) than DVJs (p ​= ​0.005). L2s produced less peak hip (p ​= ​0.007) and knee flexion (p ​= ​0.002) than L1s. SSVJs and L2s displayed a more erect landing posture than the DVJs and L1s at the hip and knee, a known ACL risk factor. The significant results between jump styles show that the SSVJ displays mechanics that are different from the DVJ. The SSVJ may be a better sport-specific screening tool for ACL injury mechanisms than the DVJ in soccer athletes as it has a more direct translation to the sport.

Peak Loads Associated With High-Impact Physical Activities in Children

Physical activities involving impact loading are important for improving bone strength and mineral density in children. There is little research quantifying impact loads associated with various high-impact activities.

PURPOSE

Examine the magnitude of peak ground reaction forces (pGRF) across different jumping activities in children.

METHODS

Eight children between 8 and 12 years (9.63 [1.49] y; 1.42 [0.08] m; 33.69 [4.81] kg), performed 5 trials of a broad jump, countermovement jump, jumping jack, leap jump, and drop jump on a force plate. The pGRF were determined during the landing phase of each activity and expressed in units of body weight (BW). A repeated-measures analysis of variance was employed to assess differences in pGRF across activities.

RESULTS

Drop jump exhibited the greatest pGRF (3.09 [0.46] BW) in comparison with the vertical jumping jack (2.56 [0.21] BW; P < .001) and countermovement jump (2.45 [0.22] BW; P = .001), as well as the horizontal broad jump (2.25 [0.2] BW; P = .003), and leap jump (2.01 [0.1] BW; P = .002).

CONCLUSION

Peak loads between 2 and 3.1 BW were exhibited across each jump activity, which is moderate compared with magnitudes in most jump interventions seeking to improve bone health. All conditions except drop jump exhibited loading <3 BW, suggesting these activities may not produce sufficient loads to improve bone outcomes.

Application of Polynomial Regression Model for Joint Stiffness

Quasi-stiffness (joint stiffness) is often used to characterize leg properties during athletic and other activities and has been reported by a single slope of angle-moment curve. However, the joint angle-moment relationship of some relationship are not effectively represented by a simple linear regression model. Thus, the purpose of this analysis was to investigate the benefits of utilizing a 2nd order polynomial regression (quadratic) model as compared to the linear model when calculating lower extremity joint stiffness incorporating subdivided eccentric phases. Thirty healthy and active college students performed 15 drop jumps from a 30-cm platform. The eccentric phase was identified as the time from initial foot contact (IC) to the lowest vertical position of the center of mass and subdivided into the loading and attenuation phases, separated by the peak vertical ground reaction force. Lower extremity joint stiffnesses (hip, knee, and ankle) for the loading and attenuation phases were calculated using a linear and quadratic model. Multiple 2 by 2 repeated measures ANOVAs were performed. In the post-hoc analyses, the quadratic model had greater goodness-of-fit (r 2 and RMSE) than the linear model (p < .05) for all joints. The quadratic model revealed differences between the loading and attenuation phases for both hip (p = .001) and knee stiffness (p < .001). These results suggest that the quadratic model is more representative of the angle-moment relationship while subdividing the eccentric phase of a drop jump into the loading and attenuation phases.

The Effect of Repetitive Drop Jumps among Different Heights on Bilateral Asymmetry of Countermovement Jumps

Background: The study explored the influence of repeated drop jumps (DJs) from different drop heights on the lower extremity bilateral asymmetry and muscle activation of countermovement jumps (CMJs). Methods: Eighteen male athletes performed 200 drop jumps (DJs200) from three drop jump height (DJH30, 40 and 50 cm). The CMJs were performed before the first DJ and after the 50th, 100th, 150th and 200th DJs, recording them as pre-CMJ, CMJs50, CMJs100, CMJs150 and CMJs200. One-way repeated measures ANOVA was used to compare differences among the three drop heights at pre-CMJ, CMJs50, CMJs100, CMJs150 and CMJs200, respectively. Results: The peak ground reaction forces (PGRF) of CMJs100, CMJs150 and CMJs200 at DJH50 were greater than at DJH30 and DJH40 (all p < 0.05). The muscle activation during CMJs50 at DJH50 was greater than at DJH30 and DJH40 (all p < 0.05). The muscle activation during CMJs100, CMJs150 and CMJs200 at DJH50 was smaller than at DJH40 and DJH30 (all p < 0.05). The PGRF had no significant difference among the three different drop heights during CMJs50 (p > 0.05). Conclusions: The DJs50 at DJH50 had no effect on the bilateral asymmetry and increased muscle activation of CMJs. The excessive DJs100 at DJH50 increased bilateral asymmetry and decreased CMJ muscle activation during CMJs.

Machine Learning-Based Estimation of Ground Reaction Forces and Knee Joint Kinetics from Inertial Sensors While Performing a Vertical Drop Jump

Nowadays, the use of wearable inertial-based systems together with machine learning methods opens new pathways to assess athletes' performance. In this paper, we developed a neural network-based approach for the estimation of the Ground Reaction Forces (GRFs) and the three-dimensional knee joint moments during the first landing phase of the Vertical Drop Jump. Data were simultaneously recorded from three commercial inertial units and an optoelectronic system during the execution of 112 jumps performed by 11 healthy participants. Data were processed and sorted to obtain a time-matched dataset, and a non-linear autoregressive with external input neural network was implemented in Matlab. The network was trained through a train-test split technique, and performance was evaluated in terms of Root Mean Square Error (RMSE). The network was able to estimate the time course of GRFs and joint moments with a mean RMSE of 0.02 N/kg and 0.04 N·m/kg, respectively. Despite the comparatively restricted data set and slight boundary errors, the results supported the use of the developed method to estimate joint kinetics, opening a new perspective for the development of an in-field analysis method.

Drop Landing Biomechanics in Individuals With and Without a Concussion History

Research has identified an increased risk of lower extremity injury postconcussion, which may be due to aberrant biomechanics during dynamic tasks. The purpose of this study was to compare the drop landing biomechanics between individuals with and without a concussion history. Twenty-five individuals with and 25 without a concussion history were matched on age (±3 y), sex, and body mass index (±1 kg/m2). Three-dimensional landing biomechanics were recorded to obtain dependent variables (peak vertical ground reaction force, loading rate, knee flexion angle and external moment, knee abduction angle and external moment, and knee flexion and abduction angle at ground contact). A 1-way multivariate analysis of variance compared outcomes between groups. There was no difference in drop landing biomechanics between individuals with and without a concussion history (F10,39 = 0.460, P = .877, Wilk Λ= .918). There was an effect of time since concussion on knee flexion characteristics. Time since most recent concussion explained a significant amount of variation in both peak (ΔR2 = .177, β = -0.305, ΔP = .046) and initial ground contact (ΔR2 = .292, β = -0.204, ΔP = .008) knee flexion angle after covarying for sex and body mass index. Therefore, time since concussion should be considered when evaluating biomechanical patterns.

Optimization-based subject-specific planar human vertical jumping prediction: Effect of elbow flexion and weighted vest

Jumping strategies differ considerably depending on athletes' physical activity demands. In general, the jumping motion is desired to have excellent performance and low injury risk. Both of these outcomes can be achieved by modifying athletes' jumping and landing mechanics. This paper presents a consecutive study on the optimization-based subject-specific planar human vertical jumping to test different loading conditions (weighted vest) during jumping with or without elbow flexion during the arm-swing based on the validated prediction model in the first part of this study. The sagittal plane skeletal model simulates the weighting, unweighting, breaking, propulsion phases and considers four loading conditions: 0%, 5%, 10%, and 15% body weight. Results show that the maximum ground reaction forces, the body center of mass position, and velocities at the take-off instant are different for different loading conditions and with/without elbow flexion. The optimization formulation is solved using MATLAB^® with 35 design variables with 197 nonlinear constraints for a five-segment body model and 42 design variables with 227 nonlinear constraints for a six-segment body model. Both models are computationally efficient, and they can predict ground reaction forces, the body center of mass position, and velocity. This work is novel in the sense that presents a simulation model capable of considering different external loading conditions and the effect of elbow flexion during arm swing.

Altered trunk and lower extremity movement coordination after neuromuscular training with and without external focus instruction: a randomized controlled trial

Background

This study sought to determine the effects of a 6-week neuromuscular training (NMT) and NMT plus external focus (NMT plus EF) programs on trunk and lower extremity inter-segmental movement coordination in active individuals at risk of injury.

Methods

Forty-six active male athletes (controls = 15, NMT = 16, NMT plus EF = 15) participated (age = 23.26 ± 2.31 years) in this controlled, laboratory study. Three-dimensional kinematics were collected during a drop vertical jump (DVJ). A continuous relative phase (CRP) analysis quantified inter-segmental coordination of the: (1) thigh (flexion/extension)—shank (flexion/extension), (2) thigh (abduction/adduction)—shank (flexion/extension), (3) thigh (abduction/adduction)—trunk (flexion/extension), and (4) trunk (flexion/extension)—pelvis (posterior tilt/anterior tilt). Analysis of covariance compared biomechanical data between groups.

Results

After 6 weeks, inter-segmental coordination patterns were significantly different between the NMT and NMT plus EF groups (p < 0.05). No significant differences were observed in CRP for trunk-pelvis coupling comparing between NMT and NMT plus EF groups (p = 0.134), while significant differences were observed CRP angle of the thigh-shank, thigh-trunk couplings (p < 0.05).

Conclusions

Trunk and lower extremity movement coordination were more in-phase during DVJ in the NMT plus EF compared to NMT in active individuals at risk of anterior cruciate ligament injury.

Trial registration: The protocol was prospectively registered at UMIN_RCT website with ID number: UMIN000035050, Date of provisional registration 2018/11/27.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-021-00326-9.

Analysis of Foot-Ankle-Leg Injuries in Various Under-Foot Impact Loading Environments with a Human Active Lower Limb (HALL) Model

Lower limb injuries caused by under-foot impacts often appear in sport landing, automobile collision, and anti-vehicular landmine blasts. The purpose of the present study was to evaluate a foot-ankle-leg model of the Human Active Lower Limb (HALL) model, and used it to investigate lower leg injury responses in different under-foot loading environments to provide a theoretical basis for the design of physical dummies adapted to multiple loading conditions. The model was first validated in allowable rotation loading conditions, like dorsiflexion, inversion/eversion, and external rotation. Then, its sensitivity to loading rates and initial postures was further verified through experimental data concerning both biomechanical stiffness and injury locations. Finally, the model was used to investigate the biomechanical responses of the foot-ankle-leg region in different under-foot loading conditions covering the loading rate from sport landing to blast impact. The results showed that from -15&#176; plantarflexion to 30&#176; dorsiflexion, the neutral posture always showed the largest tolerance, and more than 1.5 times tolerance gap was achieved between neutral posture and dorsiflexion 30&#176;. Under-foot impacts from 2 m/s to 14 m/s, the peak tibia force increased at least 1.9 times in all postures. Thus, we consider that it is necessary to include initial posture and loading rate factors in the definition of the foot-ankle-leg injury tolerance for under-foot impact loading.

Sex Disparity in Bilateral Asymmetry of Impact Forces during Height-Adjusted Drop Jumps

Side-to-side asymmetry of lower extremities may influence the risk of injury associated with drop jump. Moreover, drop heights using relative height across individuals based on respective jumping abilities could better explain lower-extremity loading impact for different genders. The purpose of the current study was to evaluate the sex differences of impact forces and asymmetry during the landing phase of drop-jump tasks using drop heights, set according to participants’ maximum jumping height. Ten male and ten female athletes performed drop-jump tasks on two force plates, and ground reaction force data were collected. Both feet needed to land entirely on the dedicated force plates as simultaneously as possible. Ground reaction forces and asymmetry between legs were calculated for jumps from 100%, 130%, and 160% of each participant’s maximum jumping height. Females landed with greater asymmetry at time of contact initiation and time of peak impact force and had more asymmetrical peak impact force than males. Greater values and shorter time after ground contact of peak impact force were found when the drop height increased to 160% of maximum jumping ability as compared to 100% and 130%. Females exhibited greater asymmetry than males during drop jumps from relative heights, which may relate to the higher risk of anterior cruciate ligament injury among females. Greater sex disparity was evident in impact force asymmetry than in the magnitude of peak impact force; therefore, it may be a more appropriate field-screening test for risk of anterior cruciate ligament injury.

Mechanics of cadaveric anterior cruciate ligament reconstructions during simulated jump landing tasks: Lessons learned from a pilot investigation

BACKGROUND

Around half of anterior cruciate ligament (ACL) injuries are treated through reconstruction, but the literature lacks mechanical investigation of reconstructions in a dynamic athletic task and rupture environment. The current objective was to ascertain the feasibility of investigating ACL reconstructions in a rupture environment during simulated landing tasks in a validated mechanical impact simulator.

METHODS

Four cadaveric lower extremities were subjected to simulated landing in a mechanical impact simulator. External joint loads that mimicked magnitudes recorded from an in vivo population were applied to each joint in a stepwise manner. Simulations were repeated until ACL failure was achieved. Repeated measures design was used to test each specimen in the native ACL and hamstrings, quadriceps, and patellar tendon reconstructed states.

FINDINGS

ACL injuries were generated in 100% of specimens. Graft substance damage occurred in 58% of ACLRs, and in 75% of bone tendon bone grafts. Bone tendon bone and quadriceps grafts survived greater simulated loading than hamstrings grafts, but smaller simulated loading than the native ACL. Median peak strain prior to failure was 20.3% (11.6, 24.5) for the native ACL and 17.4% (9.5, 23.3) across all graft types.

INTERPRETATION

The simulator was a viable construct for mechanical examination of ACLR grafts in rupture environments. Post-surgery, ACL reconstruction complexes are weaker than the native ACL when subjected to equivalent loading. Bone tendon bone grafts most closely resembled the native ligament and provided the most consistently relevant rupture results. This model advocated reconstruction graft capacity to sustain forces generated from immediate gait and weightbearing during rehabilitation from an ACL injury.

Kinematic and Neuromuscular Measures of Intensity During Plyometric Jumps

Andrade, DC, Manzo, O, Beltrán, AR, Álvarez, C, Del Rio, R, Toledo, C, Moran, J, and Ramirez-Campillo, R. Kinematic and neuromuscular measures of intensity during plyometric jumps. J Strength Cond Res 34(12): 3395-3402, 2020-The aim of this study was to assess jumping performance and neuromuscular activity in lower limb muscles after drop jumps (DJs) from different drop heights (intensity) and during continuous jumping (fatigue), using markers such as reactive strength, jump height, mechanical power and surface electromyography (sEMG). The eccentric (EC) and concentric (CON) sEMG from the medial gastrocnemius (MG), biceps femoris (BF), and rectus (R) muscles were assessed during all tests. In a cross-sectional, randomized study, 11 volleyball players (age 24.4 ± 3.2 years) completed 20-90-cm (DJ20 to DJ90) DJs and a 60-second continuous jump test. A 1-way analysis of variance test was used for comparisons, with Sidak post hoc. The α level was <0.05. Reactive strength was greater for DJ40 compared with DJ90 (p ≤ 0.05; effect size (ES): 1.27). In addition, jump height was greater for DJ40 and DJ60 compared with DJ20 (p ≤ 0.05; ES: 1.26 and 1.27, respectively). No clear pattern of neuromuscular activity appeared during DJ20 to DJ90: some muscles showed greater, lower, or no change with increasing heights for both agonist and antagonist muscles, as well as for EC and CON activity. Mechanical power, but not reactive strength, was reduced in the 60-second jump test (p ≤ 0.05; ES: 3.46). No changes were observed in sEMG for any muscle during the EC phase nor for the R muscle during the CON phase of the 60-second jump test. However, for both MG and BF, CON sEMG was reduced during the 60-second jump test (p ≤ 0.05; ES: 5.10 and 4.61, respectively). In conclusion, jumping performance and neuromuscular markers are sensitive to DJ height (intensity), although not in a clear dose-response fashion. In addition, markers such as mechanical power and sEMG are, especially sensitive to the effects of continuous jumping (fatigue). Therefore, increasing the drop height during DJ does not ensure a greater training intensity and a combination of different drop heights may be required to elicit adaptations.

Overuse-Related Injuries of the Musculoskeletal System: Systematic Review and Quantitative Synthesis of Injuries, Locations, Risk Factors and Assessment Techniques

Overuse-related musculoskeletal injuries mostly affect athletes, especially if involved in preseason conditioning, and military populations; they may also occur, however, when pathological or biological conditions render the musculoskeletal system inadequate to cope with a mechanical load, even if moderate. Within the MOVIDA (Motor function and Vitamin D: toolkit for risk Assessment and prediction) Project, funded by the Italian Ministry of Defence, a systematic review of the literature was conducted to support the development of a transportable toolkit (instrumentation, protocols and reference/risk thresholds) to help characterize the risk of overuse-related musculoskeletal injury. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach was used to analyze Review papers indexed in PubMed and published in the period 2010 to 2020. The search focused on stress (overuse) fracture or injuries, and muscle fatigue in the lower limbs in association with functional (biomechanical) or biological biomarkers. A total of 225 Review papers were retrieved: 115 were found eligible for full text analysis and led to another 141 research papers derived from a second-level search. A total of 183 papers were finally chosen for analysis: 74 were classified as introductory to the topics, 109 were analyzed in depth. Qualitative and, wherever possible, quantitative syntheses were carried out with respect to the literature review process and quality, injury epidemiology (type and location of injuries, and investigated populations), risk factors, assessment techniques and assessment protocols.

Short and long versions of a 12-week netball specific neuromuscular warm-up improves landing technique in youth netballers

OBJECTIVE

To investigate the efficacy of two 'NetballSmart', netball specific warm-ups in improving landing technique measures in New Zealand secondary school netball players.

DESIGN

Multi-site cluster experimental trial.

PARTICIPANTS

77 youth participants, mean ± SD age = 15.8 ± 0.9 were recruited from secondary school netball teams.

SETTING

12 teams from 6 schools performed either the NetballSmart Dynamic Warm-up (NSDW) (n = 37); or Power warm-up (PWU) (n = 40), three times a week for 12 weeks. All players within a school (2 teams) were assigned the same warm-up, avoiding treatment contamination.

MAIN OUTCOME MEASURES

A series of unilateral and bilateral drop vertical jumps on to a portable force plate were completed by all participants. Measures included peak vertical ground reaction force (GRF) for single-leg and bilateral landings; frontal plane projection angle (FPPA) for right and left single-leg landings and Landing error scoring system (LESS) for bilateral landings. Paired t-tests were used to assess mean differences pre and post the warm-up. Generalised linear mixed effects models were developed to evaluate the effects between the NSDW and PWU groups.

RESULTS

Significant improvements were found in all the landing technique outcome measures for both warm-up groups (ES Range- GRF = -0.6 to -1.1; FPPA = 0.8 to 1.2; LESS = -1.6 to-3.2; p < 0.05). Results of mixed effects models revealed that there was only a significantly greater improvement in LESS for the PWU group (β = -0.30, p = 0.001).

CONCLUSION

Results show both warm-ups can improve landing technique measures in youth secondary school netball players. It is recommended that coaches should consider implementing one of the two warm-ups in their netball programmes. Their choice of warm-up will likely be dependent on their environment and time demands.

The Immediate Effects of Expert and Dyad External Focus Feedback on Drop Landing Biomechanics in Female Athletes: An Instrumented Field Study

BACKGROUND

Anterior Cruciate Ligament (ACL) injury prevention interventions have used trained experts to ensure quality feedback. Dyad (peer) feedback may be a more cost-effective method to deliver feedback to athletes.

PURPOSE

To determine the immediate effects of dyad versus expert feedback on drop landing kinematics and kinetics in female athletes.

STUDY DESIGN

Cohort study.

SETTING

College gymnasium.

METHODS

Two teams (one female basketball and one female volleyball), from a local college, were team randomized to dyad feedback (volleyball team) or expert feedback (basketball team) (13 expert, 19±0.87years, 1.7±0.09m, 68.04±7.21kg) (10 dyad 19.4±1.07years, 1.73±0.08m, 72.18±11.23kg). Participants completed drop vertical jumps at two different time points (pre- and post-feedback). Knee flexion and abduction displacement were assessed with Inertial Measurement Units (IMUs) and vertical ground reaction force (vGRF) was assessed with a force plate during the landing phase of the drop vertical jump and compared across groups and condition (pre- and post-feedback) with a repeated measures ANCOVA a priori α <0.02 was set for multiple tests conducted.

RESULTS

There were no significant differences between groups for flexion displacement. There was a significant change pre- to post- (decrease 4.65˚ p=0.01) in abduction displacement, with no group effect. There was a significant interaction of group by condition (p=0.01) for vGRF with no difference between groups before feedback (p>0.05). Between groups there was a decrease of vGRF in the expert group (difference 0.45 N*bw-1, p=0.01) at post-feedback relative to dyad. Within the expert group there was a significant difference between pre- and post-feedback (difference 0.72 N*bw-1, p=0.01), while the dyad group did not change pre- to post-feedback (difference 0.18 N*bw-1, p=0.67).

CONCLUSION

Movement screening experts giving real-time feedback were successful in improving key injury-risk kinematics and kinetics in female athletes, while dyad feedback only improved kinematics, indicating that expert feedback may be needed to ensure changes in kinematics and kinetics.

LEVEL OF EVIDENCE

2.

Single-Leg Landings Following a Volleyball Spike May Increase the Risk of Anterior Cruciate Ligament Injury More Than Landing on Both-Legs

Volleyball players often land on a single leg following a spike shot due to a shift in the center of gravity and loss of balance. Landing on a single leg following a spike may increase the probability of non-contact anterior cruciate ligament (ACL) injuries. The purpose of this study was to compare and analyze the kinematics and kinetics differences during the landing phase of volleyball players using a single leg (SL) and double-leg landing (DL) following a spike shot. The data for vertical ground reaction forces (VGRF) and sagittal plane were collected. SPM analysis revealed that SL depicted a smaller knee flexion angle (about 13.8°) and hip flexion angle (about 10.8°) during the whole landing phase, a greater knee and hip power during the 16.83–20.45% (p = 0.006) and 13.01–16.26% (p = 0.008) landing phase, a greater ankle plantarflexion angle and moment during the 0–41.07% (p < 0.001) and 2.76–79.45% (p < 0.001) landing phase, a greater VGRF during the 5.87–8.25% (p = 0.029), 19.75–24.14% (p = 0.003) landing phase when compared to DL. Most of these differences fall within the time range of ACL injury (30–50 milliseconds after landing). To reduce non-contact ACL injuries, a landing strategy of consciously increasing the hip and knee flexion, and plantarflexion of the ankle should be considered by volleyball players.

Prospective Frontal Plane Angles Used to Predict ACL Strain and Identify Those at High Risk for Sports-Related ACL Injury

Background:

Knee abduction moment during landing has been associated with anterior cruciate ligament (ACL) injury. However, accurately capturing this measurement is expensive and technically rigorous. Less complex variables that lend themselves to easier clinical integration are desirable.

Purpose:

To corroborate in vitro cadaveric simulation and in vivo knee abduction angles from landing tasks to allow for estimation of ACL strain in live participants during a landing task.

Study Design:

Descriptive laboratory study.

Methods:

A total of 205 female high school athletes previously underwent prospective 3-dimensional motion analysis and subsequent injury tracking. Differences in knee abduction angle between those who went on to develop ACL injury and healthy controls were assessed using Student t tests and receiver operating characteristic analysis. A total of 11 cadaveric specimens underwent mechanical impact simulation while instrumented to record ACL strain and knee abduction angle. Pearson correlation coefficients were calculated between these variables. The resultant linear regression model was used to estimate ACL strain in the 205 high school athletes based on their knee abduction angles.

Results:

Knee abduction angle was greater for athletes who went on to develop injury than for healthy controls (P < .01). Knee abduction angle at initial contact predicted ACL injury status with 78% sensitivity and 83% specificity, with a threshold of 4.6° of knee abduction. ACL strain was significantly correlated with knee abduction angle during cadaveric simulation (P < .01). Subsequent estimates of peak ACL strain in the high school athletes were greater for those who went on to injury (7.7-8.1% ± 1.5%) than for healthy controls (4.1-4.5% ± 3.6%) (P < .01).

Conclusion:

Knee abduction angle exhibited comparable reliability with knee abduction moment for ACL injury risk identification. Cadaveric simulation data can be extrapolated to estimate in vivo ACL strain. Athletes who went on to ACL injury exhibited greater knee abduction and greater ACL strain than did healthy controls during landing.

Clinical Relevance:

These important associations between the in vivo and cadaveric environments allow clinicians to estimate peak ACL strain from observed knee abduction angles. Neuromuscular control of knee abduction angle during dynamic tasks is imperative for knee joint health. The present associations are an important step toward the establishment of a minimal clinically important difference value for ACL strain during landing.

Change of Direction Performance Is Influenced by Asymmetries in Jumping Ability and Hip and Trunk Strength in Elite Basketball Players

Change of direction (COD) ability is essential for sport performance in high level team sports such as basketball, however, the influence of asymmetries on COD ability is relatively unknown. Forty-three junior and senior level elite basketball players performed isometric hip and trunk strength testing, passive hip and trunk range of motion testing, and unilateral horizontal and vertical jumps, as well as the T-test to measure COD performance. Mean asymmetry values ranged from 0.76% for functional leg length up to 40.35% for rate of torque development during hip flexion. A six-variable regression model explained 48% (R2 = 0.48; p < 0.001) of variation in COD performance. The model included left hip internal/external rotation strength ratio, and inter-limb asymmetries in hip abduction rate of torque development, hip flexion range of motion, functional leg length, single leg triple jump distance, and peak torque during trunk lateral flexion. Results suggest that the magnitude of asymmetries is dependent of task and parameter, and using universal asymmetry thresholds, such as <10 %, is not optimal. The regression model showed the relationship between asymmetries and COD performance. None of tests were sufficient to explain a complex variable like COD performance.

Linear Discriminant Analysis Successfully Predicts Knee Injury Outcome From Biomechanical Variables

BACKGROUND

The most commonly damaged structures of the knee are the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and menisci. Given that these injuries present as either isolated or concomitant, it follows that these events are driven by specific mechanics versus coincidence. This study was designed to investigate the multiplanar mechanisms and determine the important biomechanical and demographic factors that contribute to classification of the injury outcome.

HYPOTHESIS

Linear discriminant analysis (LDA) would accurately classify each injury type generated by the mechanical impact simulator based on biomechanical input variables (ie, ligament strain and knee kinetics).

STUDY DESIGN

Controlled laboratory study.

METHODS

In vivo kinetics and kinematics of 42 healthy, athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain and knee kinetics during a simulated landing task. Uniaxial and multiaxial load cells and implanted strain sensors were used to collect mechanical data for analysis. LDA was used to determine the ability to classify injury outcome by demographic and biomechanical input variables.

RESULTS

From LDA, a 5-factor model (Entropy R2 = 0.26) demonstrated an area under the receiver operating characteristic curve (AUC) for all 5 injury outcomes (ACL, MCL, ACL+MCL, ACL+MCL+meniscus, ACL+meniscus) of 0.74 or higher, with "good" prediction for 4 of 5 injury classifications. A 10-factor model (Entropy R2 = 0.66) improved the AUC to 0.86 or higher, with "excellent" prediction for 5 injury classifications. The 15-factor model (Entropy R2 = 0.85), produced 94.1% accuracy with the AUC 0.98 or higher for all 5 injury classifications.

CONCLUSION

Use of LDA accurately predicted the outcome of knee injury from kinetic data from cadaveric simulations with the use of a mechanical impact simulator at 25° of knee flexion. Thus, with clinically relevant kinetics, it is possible to determine clinical risk of injury and also the likely presentation of singular or concomitant knee injury.

CLINICAL RELEVANCE

LDA demonstrates that injury outcomes are largely characterized by specific mechanics that can distinguish ACL, MCL, and medial meniscal injury. Furthermore, as the mechanics of injury are better understood, improved interventional prehabilitation can be designed to reduce these injuries.

Filtration Selection and Data Consilience: Distinguishing Signal from Artefact with Mechanical Impact Simulator Data

A large variety of data filtration techniques exist in biomechanics literature. Data filtration is both an 'art' and a 'science' to eliminate noise and retain true signal to draw conclusions that will direct future hypotheses, experimentation, and technology development. Thus, data consilience is paramount, but is dependent on filtration methodologies. In this study, we utilized ligament strain, vertical ground reaction force, and kinetic data from cadaveric impact simulations to assess data from four different filters (12 vs. 50 Hz low-pass; forward vs. zero lag). We hypothesized that 50 Hz filtered data would demonstrate larger peak magnitudes, but exhibit consilience of waveforms and statistical significance as compared to 12 Hz filtered data. Results demonstrated high data consilience for matched pair t test correlations of peak ACL strain (≥ 0.97), MCL strain (≥ 0.93) and vertical ground reaction force (≥ 0.98). Kinetics had a larger range of correlation (0.06-0.96) that was dependent on both external load application and direction of motion monitored. Coefficients of multiple correlation demonstrated high data consilience for zero lag filtered data. With respect to in vitro mechanical data, selection of low-pass filter cutoff frequency will influence both the magnitudes of discrete and waveform data. Dependent on the data type (i.e., strain and ground reaction forces), this will not likely significantly alter conclusions of statistical significance previously reported in the literature with high consilience of matched pair t-test correlations and coefficients of multiple correlation demonstrated. However, rotational kinetics are more sensitive to filtration selection and could be suspect to errors, especially at lower magnitudes.

Mechanical Differences Between Adolescents and Adults During Two Landing Phases of a Drop Jump Task

Moir, GL, Munford, SN, Snyder, BW, and Davis, SE. Mechanical differences between adolescents and adults during two landing phases of a drop jump task. J Strength Cond Res XX(X): 000-000, 2020-The mechanical differences between the first and second landing phases of a drop jump (DJ) task performed by adolescent and adult male players were investigated. Eleven adolescent basketball players (age: 16.5 ± 0.7 years) and 11 resistance-trained adults (age: 22.3 ± 1.9 years) performed DJs from a height of 0.40 m. Force plates and a 3-dimensional motion analysis system were used to determine mechanical variables, including landing velocity, normalized vertical stiffness, normalized peak impact force, and work as well as mechanical characteristics of the hip, knee, and ankle joints during the absorption phase of each landing. The adolescents produced greater peak impact forces (mean difference [xDiff] = 42 N·kg; effect size [ES] = 1.15) and vertical stiffness (xDiff = 126 N·kg·m; ES = 1.28) during shorter absorption phases (xDiff = 0.09 seconds; ES = 2.67) compared with the adults, despite their lower landing velocities (xDiff = 0.21 m·s; ES = 1.37). Furthermore, the adolescents generated greater peak extensor joint moments at the lower-body joints compared with the adults (xDiff = 2.3 N·m·kg; ES = 1.17), but they did not effectively modulate the energy absorbed by the joint moments in response to the changing demands of the landing tasks. The assessment of the biomechanical characteristics of the 2 landing phases associated with a DJ task revealed that adolescent male basketball players adopt neuromuscular strategies that may increase the risk of incurring musculoskeletal injuries compared with resistance-trained adults.

The Effect of Divided Attention with Bounce Drop Jump on Dynamic Postural Stability

This study determined the effect of divided attention on controlling postural stability during a drop vertical jump task. In total, 30 participants were tested for drop vertical jumps from a 30-cm high platform and landing on a single leg with or without divided attention tasks. Three-dimensional marker trajectories and ground reaction forces were collected simultaneously. Vertical ground reaction force, loading rate, and dynamic postural stability index were analyzed with or without divided attention tasks. The paired sample t test indicated a significantly low knee flexion angle, high vertical ground reaction force, and increased loading rate in the divided attention task. Moreover, participants showed an increased vertical stability index and dynamic postural stability index in the divided attention task than in the nondivided attention task. Thus, results demonstrated that the divided attention task could affect posture control, leading to poor dynamic posture stability and possibly increasing lower extremity injury risk. The influence of the divided attention task on movement quality likely indicates that an athlete can no longer focus his attention on the bounce drop jump maneuver. Therefore, the bounce drop jump combined with dynamic postural stability index could be used in posture stability screening.

ANALYSIS OF TIMING OF SECONDARY ACL INJURY IN PROFESSIONAL ATHLETES DOES NOT SUPPORT GAME TIMING OR SEASON TIMING AS A CONTRIBUTOR TO INJURY RISK

BACKGROUND

Anterior cruciate ligament (ACL) injuries are a common cause of time loss in sports. Approximately one-third of ACL reconstructed athletes who return to sport suffer secondary injury. The presence of fatigue during athletic performance has been hypothesized to increase susceptibility to ACL injury. However, the relative role of fatigue in secondary ACL failures remains unexplored.

PURPOSE

To assess how time elapsed within a game and within a season associate with secondary ACL injury occurrence in international professional athletes and American collegiate athletes.

STUDY DESIGN

Retrospective cohort analysis.

METHODS

The public domain was searched for secondary ACL injuries that occurred during competitive matches between 2000-2018. Demographics (age, height, weight), side of injury, type of injury (contact, noncontact), and timing of injury within competition and within season were determined for each case.

RESULTS

Sixty-seven secondary ACL injuries were identified. Within-game, there were no differences in the distribution of ACL injures across each quarter of game time (p = 0.284). This was consistent between sport (p = 0.120-0.448). Within-season, there were no differences in the distribution of secondary ACL injures across each quarter of the season (p = 0.491). This was again consistent between sport (p = 0.151-0.872). Relative risk was not found to be significantly greater for any combination of season and game.

CONCLUSION

The results of the current study indicate that the occurrences of secondary ACL injuries were equally distributed with respect to in-game and in-season timing. Both in-game and in-season timing were not significantly different across each individual sport examined. These results implicate that overall there is not an association between fatigue and secondary ACL injury occurrence in professional athletes.

LEVEL OF EVIDENCE

3.

Effects of synthetic turf and shock pad on impact attenuation related biomechanics during drop landing

Adding a shock pad as an underlayment to synthetic turf aims to improve attenuation of impact forces. The purpose of this research was to investigate effects of an infilled synthetic turf with three different shock pads on impact attenuation related biomechanics of lower extremity during the drop landing. Twelve active and healthy recreational male athletes performed 60 cm drop landing with a controlled landing technique on five surface conditions: a baseline surface (force platform), an infilled synthetic turf surface, turf plus foam shock pad, turf plus a low-density shock pad, and turf plus a high-density shock pad. Furthermore, a mechanical impact test was conducted (ASTM F355). Turf plus foam shock pad, turf plus low-density shock pad, and turf plus high-density shock pad all resulted in significantly lower 1st vertical peak ground reaction force (13.3%, 13.3%, and 12.7% reductions, respectively) and loading rate (20.4%, 25.4%, and 21.1% reductions, respectively) compared to baseline surface. Significantly greater trunk extension moment was found on turf plus low-density shock pad compared to turf surface (21.2%) and turf plus foam shock pad (12.0%). These results suggest that synthetic turf plus shock pad surfaces provide improved impact attenuation compared to baseline surface in the early landing phase.

Lower-Extremity Energy Absorption During Side-Step Maneuvers in Females With Knee Valgus Alignment

CONTEXT

Excessive knee valgus on landing can cause anterior cruciate ligament injury. Therefore, knee valgus alignment may show characteristic energy absorption patterns during landings with lateral movement that impose greater impact forces on the knee joint compared with landings in other alignments.

OBJECTIVE

To investigate the energy absorption strategy in lower-extremities during side steps in females with knee valgus alignment.

DESIGN

Controlled laboratory study.

SETTING

University research laboratory.

PARTICIPANTS

A total of 34 female college students participated in this experiment.

INTERVENTIONS

Participants performed single-leg drop vertical jump and side steps. All participants were divided into valgus (n = 13), neutral (n = 9), and varus (n = 12) groups according to knee position during landing in single-leg drop vertical jumps.

MAIN OUTCOME MEASURES

Lower-extremity joint angles, moments, and negative works were calculated during landing in side steps, and 1-way analysis of variance and post hoc tests were used to determine between-group differences.

RESULTS

Negative works of hip extensors, knee abductors, and ankle plantar flexors during landing in side steps were significantly smaller in the valgus than in the varus group; however, negative work of the knee extensors was significantly greater in the valgus group than in varus group.

CONCLUSIONS

The findings of this study indicated that landing with knee valgus induced the characteristic energy absorption strategy in the lower-extremity. Knee extensors contributed more to energy absorption when landing in knee valgus than in knee varus alignment. Learning to land in knee varus alignment might reduce the impact on the knee joint by increasing the energy absorption capacities of hip extensors, knee abductors, and ankle plantar flexors.

Effects of segment masses and cut-off frequencies on the estimation of vertical ground reaction forces in running

The purpose of this study is to examine the effect of the body's mass distribution to segments and the filtering of kinematic data on the estimation of vertical ground reaction forces from positional data. A public dataset of raw running biomechanics was used for the purposes of the analysis, containing recordings of twenty-eight competitive or elite athletes running on an instrumented treadmill at three different speeds. A grid-search on half of the trials was employed to seek the values of the parameters that optimise the approximation of biomechanical loads. Two-way ANOVAs were then conducted to examine the significance of the parameterised factors in the modelled waveforms. The reserved recordings were used to validate the predictive accuracy of the model. The cut-off filtering frequencies of the pelvis and thigh markers were correlated to running speed and heel-strike patterns, respectively. Optimal segment masses were in agreement with standardised literature reported values. Root mean square errors for slow running (2.5 m/s) were on average equal to 0.1 (body weight normalized). Errors increased with running speeds to 0.13 and 0.18 for 3.5 m/s and 4.5 m/s, respectively. This study accurately estimated vertical ground reaction forces for slow-paced running by only considering the kinematics of the pelvis and thighs. Future studies should consider configuring the filtering of kinematic inputs based on the location of markers and type of running.