Biomechanical differences between unilateral and bilateral landings from a jump: gender differences

Kinematics but not kinetics alterations to single-leg drop jump movements following a subject-tailored fatiguing protocol suggest an increased risk of ACL injury

Introduction

Neuromuscular fatigue causes a transient reduction of muscle force, and alters the mechanisms of motor control. Whether these alterations increase the risk of anterior cruciate ligament (ACL) injury is still debated. Here we compare the biomechanics of single-leg drop jumps before and after the execution of a fatiguing exercise, evaluating whether this exercise causes biomechanical alterations typically associated with an increased risk of ACL lesion. The intensity of the fatiguing protocol was tailored to the aerobic capacity of each participant, minimizing potential differential effects due to inter-individual variability in fitness.

Methods

Twenty-four healthy male volunteers performed single leg drop jumps, before and after a single-set fatiguing session on a cycle ergometer until exhaustion (cadence: 65-70 revolutions per minute). For each participant, the intensity of the fatiguing exercise was set to 110% of the power achieved at their anaerobic threshold, previously identified by means of a cardiopulmonary exercise test. Joint angles and moments, as well as ground reaction forces (GRF) before and after the fatiguing exercise were compared for both the dominant and the non-dominant leg.

Results

Following the fatiguing exercise, the hip joint was more extended (landing: Δ=-2.17°, p = 0.005; propulsion: Δ=-1.83°, p = 0.032) and more abducted (landing: Δ=-0.72°, p = 0.01; propulsion: Δ=-1.12°, p = 0.009). Similarly, the knee joint was more extended at landing (non-dominant leg: Δ=-2.67°, p < 0.001; dominant: Δ=-1.4°, p = 0.023), and more abducted at propulsion (both legs: Δ=-0.99°, p < 0.001) and stabilization (both legs: Δ=-1.71°, p < 0.001) hence increasing knee valgus. Fatigue also caused a significant reduction of vertical GRF upon landing (Δ=-0.21 N/kg, p = 0.003), but not during propulsion. Fatigue did not affect joint moments significantly.

Conclusion

The increased hip and knee extension, as well as the increased knee abduction we observed after the execution of the fatiguing exercise have been previously identified as risk factors for ACL injury. These results therefore suggest an increased risk of ACL injury after the execution of the participant-tailored fatiguing protocol proposed here. However, the reduced vertical GRF upon landing and the preservation of joint moments are intriguing, as they may suggest the adoption of protective strategies in the fatigued condition to be evaluated in future studied.

Changes in Lower Limb Biomechanics Across Various Stages of Maturation and Implications for ACL Injury Risk in Female Athletes: a Systematic Review

BACKGROUND

Female athletes are four to six times more likely to sustain an anterior cruciate ligament (ACL) injury than male athletes. Jump-landing biomechanics are influenced by maturation, with post-pubertal female athletes at a heightened risk of ACL injuries.

OBJECTIVE

The aim of our systematic review was to identify and summarise the current evidence regarding the changes in kinematic and kinetic risk factors associated with ACL injuries during jump-landing tasks in female athletes at various stages of maturity.

METHODS

A systematic search was conducted in PubMed, CINAHL, Web of Science, SPORTDiscus, EMBASE and Scopus. Articles were included if they: (1) conducted the research on uninjured female athletes with no restriction on playing level/experience; (2) provided information regarding the stage of the maturity and the scale used for estimating the maturity status of the participants; and (3) reported a biomechanical risk factor associated with ACL injuries during jump-landing tasks across at least two different maturity groups (e.g. pre-pubertal vs post-pubertal).

RESULTS

Sixteen articles involving 2323 female athletes were included in our review. A total of 12 kinematic and 8 kinetic variables were identified across these studies. Of the 12 kinematic variables reported in our review, we found strong evidence for higher peak knee abduction angle in post-pubertal female individuals compared with pre-pubertal girls (p < 0.05). With regard to the 8 kinetic variables, we found strong evidence for lower relative peak vertical ground reaction force, higher external knee abduction moment and internal rotation moment in post-pubertal compared with pre-pubertal athletes. The strength of evidence for the remaining kinematic and kinetic variables ranged from conflicting to moderate and, in some instances, could not be determined.

CONCLUSIONS

Our study provides an overview of the changes in biomechanical risk factors in female athletes during jump-landing tasks at various stages of maturity. We found moderate-to-limited evidence for most kinematic and kinetic variables, highlighting the need for further research.

Muscle Activation and Ground Reaction Force between Single-Leg Drop Landing and Jump Landing among Young Females during Weight-Acceptance Phase

Single-leg drop landing (SLDL) and jump landing (SLJL) are frequently used as assessment tools for identifying potential high-risk movement patterns; thus, understanding differences in neuromuscular responses between these types of landings is essential. This study aimed to compare lower extremity neuromuscular responses between the SLDL and SLJL. Thirteen female participants performed an SLDL and SLJL from a 30-cm box height. Vertical ground reaction force (vGRF), time to peak vGRF, and surface electromyography (sEMG) data were collected. Continuous neuromuscular responses, peak vGRF, and time to peak vGRF were compared between the tasks. Statistical parametric mapping (SPM) analysis demonstrated that the SLJL had a significantly higher sEMG activity in the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) within the first 10% of the landing phase compared with SLDL. At 20-30% of the landing phase, sEMGs in the RF and VL during the SLDL were significantly higher compared with SLJL (p < 0.05). A higher peak vGRF and shorter time to peak vGRF was observed during SLJL (p < 0.05). In conclusion, our findings highlight that SLJL exhibited greater RF, VL, and VM activities than SLDL at initial impact (10% landing), coinciding with a higher peak vGRF and shorter time to attain peak vGRF. Our findings support the role of the quadriceps as the primary energy dissipator during the SLJL.

Effects of a 4-week plyometric training on activity patterns during different phases of one-leg drop jump with focus on jump height

Athletic women have shown a higher risk of ACL injury during jump landing compared to men. Plyometric training can be an alternative way to minimize the risk of knee injuries via the changed muscle activity patterns. Hence, the aim of this study was to determine the effects of a 4-week plyometric training program on the muscle activity pattern in different phases of one-leg drop jump in active girls. Active girls were randomly allocated into 2 groups (Plyometric training = 10, Control group = 10) where the plyometric training group (PTG) performed 60 min exercises, 2 sessions/1 week for 4 weeks while the control group (CG) had their daily activity. In the pre to post test, the sEMG was recorded from the Rectus Femoris (RF), Biceps Femoris (BF), Medial Gastrocnemius (GaM), and Tibialis Anterior (TA) muscles of the dominant leg during the Preparatory phase (PP), Contact Phase (CP), Flight Phase (FP) of one-leg drop jump. Electromyography variables (Signal amplitude, Maximum activity, Time to peak (TTP), Onset and activity time and Order muscle activity) and Ergo jump variables (Time of preparatory phase (TPP), Time of contact phase (TCP), Time of flight (jump height) phase (TFP), and Explosive power were analyzed. The Univariate ANCOVA test showed a significant difference between the two groups in Activity Time, whilst adjusting for pre-test as a Covariate, only in TA muscle (F_(1,17) = 5.09, p = 0.038, η² = 0.230). In PTG. TA (- 15%), GaM (- 19%), and BF muscles (- 9%) started their activity earlier while there was no significant difference between the two groups at the Onset time. TTP of RF was significantly different between the 2 groups only in the PR phase (0.216 ± 0.07 vs 0.153 ± 0.09 s) (p = 0.049, 95% CI = 0.001, 0.127). Results of the present study suggest that a 4-week plyometric training can improve the stability of leg joints via earlier recruitment of muscles and change activity patterns in lower limb muscles. It also recommends that the preparatory phase before landing be considered an important stage in preventing sports injuries in a training program.

Videogestütztes Feedbacktraining als präventives Techniktraining – Eine exploratorische Studie

Hintergrund Im Sport wird angenommen, dass ein dynamischer Knievalgus bei einbeinigen Landungen einen relevanten Verletzungsmechanismus des vorderen Kreuzbands darstellt. Während bestehende effektive Präventionsprogramme zur Reduktion des Knievalgus primär auf die Verbesserung allgemeiner konditioneller und/oder koordinativer Einflussgrößen ausgerichtet sind, fokussiert ein Video-Feedback-Training die Korrektur individueller Defizite in der sportlichen Technik, um u. a. ein potenzielles Verletzungsrisiko zu reduzieren.

Ziel Evaluation der kurz- und insbesondere mittel- und langfristigen Wirksamkeit eines Video-Feedback-Trainings zur Veränderung des frontalen Kniewinkels bei einbeinigen Landungen.

Methode Im Rahmen einer exploratorischen Studie wurden 10 sportlich aktive Personen (Alter: 25 ± 5 Jahre, Größe: 170,8 ± 4,5 cm) getestet. Diese führten in Anlehnung an das Landing Error Scoring System (LESS-Test) einbeinige Drop-Jumps in einem Pretest, in einer Aneignungsphase mit Video-Feedback und 2 Retentionstests 2 und 6 Wochen nach der Aneignungsphase ohne Video-Feedback aus. Das Video-Feedback wurde in der Aneignungsphase bei jedem zweiten Sprung und zusätzlich selbstbestimmt auf Nachfrage über ein Expertenmodell mit neutraler Kniestellung im Overlay-Modus aus der Frontalperspektive gegeben.

Ergebnisse Die Ergebnisse wurden nach Sprung- und Nichtsprungbein der Proband*innen differenziert. Sie zeigen eine bedeutsame Verringerung des frontalen Kniewinkels für das Sprungbein (F1, 9 = 10,43, p = 0,01, η2 p = 0,54, 95 % CI [0,04; 0,74]) bei einbeinigen Landungen in der Aneignungsphase, jedoch keine statistisch bedeutsame Verringerung für das Nichtsprungbein (F1, 9 = 4,07, p = 0,08, η2 p = 0,31, 1-β = 0,44). Im Retentionstest nach 6 Wochen nähert sich der frontale Kniewinkel beidseitig dem Ausgangsniveau aus dem Pretest wieder an.

Schlussfolgerung Ein Video-Feedback-Training bietet sich als einfach durchzuführendes, alternatives Verletzungspräventionsprogramm an. Eine fehlende mittel- und langfristige Veränderung und hohe Variabilität des frontalen Kniewinkels lassen eine mehrfache und/oder regelmäßige Durchführung eines Video-Feedback-Trainings sinnvoll erscheinen. In weiteren Studien mit Kontrollgruppendesign und unterschiedlichen Feedback-Prozeduren wird systematisch zu prüfen sein, ob eine längerfristige Reduktion eines potenziellen Verletzungsrisikos des vorderen Kreuzbands erreicht werden kann.

The Effect of a Knee Brace on Muscle Forces during Single-Leg Landings at Two Heights

Single-leg landing is one of the maneuvers that has been linked to non-contact anterior cruciate ligament (ACL) injuries, and wearing knee braces has been shown to reduce ACL injury incidence. The purpose of this study was to determine whether wearing a knee brace has an effect on muscle force during single-leg landings at two heights through musculoskeletal simulation. Eleven healthy male participants, some braced and some non-braced were recruited to perform single-leg landings at 30 cm and 45 cm. We recorded the trajectories and ground reaction forces (GRF) using an eight-camera motion capture system and a force platform. The captured data were imported into the generic musculoskeletal model (Gait2392) in OpenSim. Static optimization was used to calculate the muscle forces. The gluteus minimus, rectus femoris, vastus medialis, vastus lateralis, vastus medialis medial gastrocnemius, lateral gartrocnemius, and soleus muscle forces were all statistically significant different between the braced and non-braced participants. Simultaneously, increasing the landing height significantly affected the gluteus maximums, vastus medialis, and vastus intermedia muscle forces. Our findings imply that wearing a knee brace may alter muscle forces during single-leg landings, preventing ACL injuries. Additionally, research demonstrates that people should avoid landing from heights due to the increased risk of knee injuries.

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).

Sex difference in effect of ankle landing biomechanics in sagittal plane on knee valgus moment during single-leg landing

Ankle landing strategies affects the biomechanical characteristics of the knee joint, especially knee frontal plane loading. However, no studies have investigated whether the association between ankle landing biomechanics in sagittal plane and the knee frontal plane loading differs between sexes. The purpose of this study was to examine whether there is a sex difference in the effect of ankle plantar flexion at the contact angle, ankle range of motion (ROM), and ankle plantar flexion moment on knee valgus loading during single-leg landing. Twenty-five females and twenty-four males performed a single-leg landing. Joint kinematics and kinetics of the lower extremities were measured. The relationship between ankle biomechanics in the sagittal plane (ankle plantar flexion angle at contact, ROM, and peak ankle plantar flexion moment) and peak knee valgus moment were analyzed. In males, the larger ankle plantarflexion angle at contact and ROM were significantly associated with lower peak knee valgus moment. In addition, in males only, a greater peak ankle plantar flexion moment was significantly associated with a lower peak knee valgus moment and greater peak ankle inversion moment. Altering ankle landing strategies in the sagittal plane during single-leg landing may reduce the knee valgus moment, which is one of risk factors for anterior cruciate ligament injury, in males only.

Greater Breast Support Alters Trunk and Knee Joint Biomechanics Commonly Associated With Anterior Cruciate Ligament Injury

Objective

The female breast is a passive tissue with little intrinsic support. Therefore, women rely on external breast support (sports bras) to control breast motion during athletic tasks. Research has demonstrated that lower levels of breast support are associated with altered trunk and pelvis movement patterns during running, a common athletic task. However, no previous study has identified the effect of sports bra support on movement patterns during other athletic tasks including landing. Therefore, the purpose of this study was to examine the effects of breast support on trunk and knee joint biomechanics in female collegiate athletes during a double-leg landing task.

Methods

Fourteen female collegiate athletes completed five double-leg landing trials in each of three different sports bra conditions: no support, low support, and high support. A 10-camera motion capture system (250 Hz, Qualisys, Goteburg, Sweden) and two force platforms (1,250 Hz, AMTI, Watertown, MA, USA) were used to collect three-dimensional kinematics and ground reaction forces simultaneously. Visual 3D was used to calculate trunk segment and knee joint angles and moments. Custom software (MATLAB 2021a) was used to determine discrete values of dependent variables including vertical breast displacement, knee joint and trunk segment angles at initial contact and 100 ms post-initial contact, and peak knee joint moments. A repeated measures analysis of covariance with post-hoc paired samples t-tests were used to evaluate the effect of breast support on landing biomechanics.

Results

Increasing levels of breast support were associated with reductions in peak knee flexion (Right: p = 0.008; Left: p = 0.029) and peak knee valgus angles (Right: p = 0.011; Left: p = 0.003) as well as reductions in peak knee valgus moments (Right: p = 0.033; Left: p = 0.013). There were no changes in peak knee extension moments (Right: p = 0.216; Left: p = 0.261). Increasing levels of breast support were associated with greater trunk flexion angles at initial contact (p = 0.024) and greater peak trunk flexion angles (p = 0.002).

Conclusions

Lower levels of breast support are associated with knee joint and trunk biomechanical profiles suggested to increase ACL injury risk.

Video Analysis of Anterior Cruciate Ligament Injury Situations in the Women's Australian Football League

Anterior cruciate ligament (ACL) injury rates in the Women's Australian Football League (AFLW) are alarmingly high. Understanding injuries within their sporting context is important to develop effective injury prevention strategies, yet there is currently little knowledge of how ACL injuries occur to AFLW players. This study addressed the common scenarios and characteristics of ACL injuries in the AFLW.

Online match and AFLW club injury reports identified 38 ACL injury cases. After excluding injuries where footage was unavailable (i.e. training, pre-season games), a video analysis of 21 match ACL injuries from the 2017-2020 AFLW seasons was performed. We examined match characteristics, and the player's movements and body postures preceding and at the estimated time of injury. Descriptive frequencies and relative proportions were determined across the assessed categories.

Non-contact ACL injuries were frequently observed (n=13, 61.9%), while contact preceding the injury event (i.e. indirect contact) was also common (n=10, 47.6%). The most common game situation was direct defence (i.e. defending an opponent in possession) (n=14, 66.7%). Sidestep cutting was the most prevalent movement (n=11, 52.4%), with this commonly performed while applying defensive pressure (n=6 of 11, 54.6%).

Sidestep cutting when applying defensive pressure is the most common non-contact ACL injury scenario in the AFLW. Preceding contact potentially contributing to a player's loss of balance was another prominent AFLW scenario. AFLW players may benefit from injury prevention programs emphasising appropriate sidestep cutting technique during reactive defensive scenarios, and maintenance of lower limb postures known to withstand knee loading relative to the sporting task.

What are gender differences in lower limb muscle activity during jump-landing tasks? A systematic review and meta-analysis

Background

Gender differences in muscle activity during landing have been proposed as a possible contributing factor to the greater incidence of anterior cruciate ligament injuries in women. Conflicting results among a few studies in this regard makes it impossible to reach correct conclusions.

Objectives

The aim of this study was systematic review and the meta-analysis of previous studies which have compared the electromyographic activity of lower limb muscles in gluteus muscles (maximus and medius), quadriceps (rectus femoris, vastus medialis and lateralis), hamstrings (biceps femoris and semimembranosus), and gastrocnemius in men and women in jump–landing task.

Methods

A systematic search of the PubMed, SCOPUS, Science Direct databases was performed for eligible articles in October 2020. Cross-sectional studies that compared the muscle activity of male and female athletes without a history of previous injury in the jump–landing task were included. Unisex and non-athlete's studies were extracted from the included studies. The data were synthesized using a fixed and random effects model.

Results

Eight studies involving 145 participants were included. All participants were people who participated in regular exercises. The meta-analysis of timing and muscle activity was performed in the feedforward (pre contact) and feedback (post contact) stages. There were no significant differences in the muscle activity of biceps femoris (MD = −12.01; 95% CI − 51.49 to 27.47; p = 0.55; I² = 87%), vastus medialis (MD = −53.46; 95% CI − 129.73 to 22.81; p = 0.17; I² = 91%), semimembranosus (MD = 1.81; 95% CI − 6.44 to 10.07; p = 0.67; I² = 0%), gluteus medius (MD = −3.14; 95% CI − 14.24 to 7.96; p = 0.58; I² = 48%), and rectus femoris (MD = −5.83; 95% CI − 14.57 to 2.92; p = 0.19; I² = 87%) in the pre contact phase between two sexes. There was a significant difference between men and women in the activity of vastus lateralis muscle in the post contact phase (MD = −34.90; 95% CI − 48.23 to − 21.57). No significant difference was observed between the men and women in the timing of semimembranosus (MD = 23.53; 95% CI − 14.49 to 61.54; p = 0.23; I² = 56%) and biceps femoris muscle activity (MD = −46.84; 95% CI − 97.50 to 3.83; p = 0.07; I² = 82%).

Conclusion

The results showed that in all lower limb muscles except vastus lateralis there were no significant differences between muscle activity and muscle contraction timing in both sexes before and after foot contact. Therefore, it can be concluded that the reason for the greater susceptibility of ACL injuries in women than men is maybe related to other factors such as biomechanical and hormonal. Additional good quality research in this regard is required to strengthen these conclusions.

Reliability and Differences Between Sexes in Landing Mechanics when Performing the Lateral Bound Test

Background and Purpose

Anterior cruciate ligament injuries are prevalent among the athletic population, imposing a heavy economic burden, and the risk of re-injury. Most current biomechanical screening tasks are performed in the sagittal plane, and there is a need for more screening tools that assess sports specific movements in the frontal plane. The purpose of this study was to determine the reliability of and examine differences between sexes in the performance of the Lateral Bound Test (LBT).

Materials/Methods

Each subject performed three trials of a LBT which included jumping laterally from one leg over a hurdle and landing on the opposite leg. Two cameras were placed six feet from the landing marker. Maximum dynamic knee valgus using the frontal plane projection angle and knee flexion angle at initial contact and maximal knee flexion were measured upon landing leg using 2D video analysis software. Additionally, video of 10 individuals' trials were analyzed twice with one week between the analyses to obtain intra-rater reliability while 12 participants were retested one week later to determine test-retest reliability.

Results

Thirty healthy subjects, 16 males, 14 females participated. Intra-rater reliability was determined to be excellent for all variables (ICC>0.96). In contrast, the test-retest reliability had greater disparity. Test-retest reliability ranged from poor (ICC = 0.47) to excellent (ICC > 0.90). Significant differences existed between the sexes, including males being significantly taller, weighing more, and demonstrating greater bilateral dynamic knee valgus (p < 0.05). No significant differences existed between sexes for knee flexion angles.

Conclusion

The new LBT had excellent intra-rater reliability for assessing dynamic knee valgus and initial and maximum knee flexion angle when performing a functional movement in the frontal plane. Furthermore, males landed with more dynamic knee valgus than females which is contradictory to what has been observed with functional screening tools performed in the sagittal plane.

Level of Evidence

3b (reliability study).

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.

Altered lower extremity biomechanics following anterior cruciate ligament reconstruction during single-leg and double-leg stop-jump tasks: A bilateral total support moment analysis

BACKGROUND

Injury to the anterior cruciate ligament (ACL) can lead to long-lasting biomechanical alterations that put individuals at risk of a second ACL injury. Examining the total support moment may reveal between- and within-limb compensatory strategies.

METHODS

Twenty-six participants who were cleared to return to sport following ACL reconstruction were recruited. Each participant completed the single-leg and double-leg stop jump tasks. These tasks were analyzed using force plates and a 3D motion analysis system. The total support moment was calculated by summing the internal moments of the hip, knee and ankle at peak vertical ground reaction force.

FINDINGS

Internal knee extensor moment was lower in the involved limb compared to the uninvolved for both tasks (17.6%, P = 0.022; 18.4%, P = 0.008). No significant between-limb differences were found for the total support moment. The involved limb exhibited an 18.2% decrease in knee joint contribution (P = 0.01) and a 21.6% increase in ankle joint contribution (P = 0.016) to the total support moment compared to the uninvolved limb in the single-leg stop jump task.

INTERPRETATION

Compensation for the involved knee is likely due to altered biomechanics that redistributes load to the uninvolved knee or to adjacent joints of the same limb. A partial shift in joint contribution from the knee to the ankle during the single-leg stop jump task demonstrates a tendency to decrease load to the knee. Further studies are needed to investigate how these adaptations impact the prevalence of subsequent injury and poor joint health.

Regression model for predicting knee flexion angles using ankle plantar flexion angles, body mass index and generalised joint laxity

Increased knee flexion angles are associated with reduced non-contact anterior cruciate ligament (ACL) injury risks. Ankle plantar flexion angles and internal risk factors could influence knee flexion angles, but their correlations are unknown. This study aimed to establish and validate a regression model to predict knee flexion angles using ankle plantar flexion angles, body mass index (BMI) and generalised joint laxity (GJL) at initial contact of single-leg drop landings. Thirty-two participants performed single-leg drop landings from a 30-cm-high platform. Kinematics and vertical ground reaction forces were measured using a motion capture system and force plate. A multiple regression was performed, and it was validated using a separate data set. The prediction model explained 38% (adjusted R2) of the change in knee flexion angles at initial contact (p = 0.001, large effect size). However, only the ankle plantar flexion angle (p < 0.001) was found to be a significant predictor of knee flexion angles. External validation further showed that the model explained 26% of knee flexion angles (large effect size). The inverse relationship between ankle plantar flexion and knee flexion angles suggests that foot landing strategies could be used to increase knee flexion angles, thereby reducing non-contact ACL injury risks.

Sex-Based Differences in the Drop Vertical Jump as Revealed by Video Motion Capture Analysis Using Artificial Intelligence

BACKGROUND

Sex-based biomechanical differences during a drop vertical jump (DVJ) may explain the increased risk of anterior cruciate ligament injury in females. Video motion capture using artificial intelligence (VMocap) is a new method for accurate motion analysis.

PURPOSE

To use VMocap to identify sex-based differences in biomechanics during a DVJ in Asian athletes.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 63 female and 61 male Asian soccer players volunteered for this study in 2018. Participants performed a bilateral DVJ using VMocap, and the knee valgus angle (KVA), knee flexion angle (KFA), hip flexion angle (HFA), and lower leg anterior inclination angle (LAIA) were calculated from the motion capture data. These joint angles and inclination angles were evaluated at the time of highest point of the first jump (H1), initial contact (IC), maximum knee flexion (MKF), toe-off (TO), and highest point of the second jump (H2). The unpaired t test was used to compare sex-based differences.

RESULTS

At H1, the KVA in females showed more valgus (-2.9° vs -5.4°) and the LAIA in females was greater (29.1° vs 25.7°) versus males (P < .01 for both). At IC, the KVA in females showed more valgus (-1.3° vs -3.0°) and females had a greater KFA (20.8° vs 14.3°) and LAIA (5.1° vs 0.0°) compared with males (P < .01 for all). At MKF, female KVA showed more valgus (6.2° vs -9.5°), and females had greater LAIA (36.6° vs 34.6°), smaller KFA (77.5° vs 87.5°), and smaller HFA (55.8° vs 82.0°) compared with males (P < .01 for all). At TO, female KVA showed more valgus (-0.7° vs -3.1°) and female KFA, HFA, and LAIA were greater (31.7° vs 19.2°; 19.9° vs 16.4°; and 18.2° vs 11.5°, respectively) than males (P < .01 for all). At H2, females had a greater KFA (18.6° vs 14.6°) and LAIA (13.3° vs 9.9°) than males (P < .04 for both).

CONCLUSION

Asian female soccer players showed increased KVA and LAIA, decreased KFA and HFA at MKF, and increased KFA at IC and TO compared with their male counterparts in this analysis of the DVJ.

CLINICAL RELEVANCE

Elucidation of kinematic differences between the sexes can aid in predicting injuries.

The effects of sex and landing task on hip mechanics

Prevalence of femoroacetabular impingement syndrome is common in cutting sports. A first step to understanding the relationship between cutting sports and the development of femoroacetabular impingement is to investigate hip joint contact forces during such tasks. The purpose of this study was to explore sex and task differences in hip joint contact forces, estimated through musculoskeletal modeling, during single-leg drop landings and land-and-cuts. Kinematics and ground reaction forces were obtained from 38 adults performing drop landings and land-and-cut tasks. Simulations were performed in OpenSim to estimate lower extremity muscle forces and hip joint contact forces. Statistical parametric mapping was used to compare hip joint force waveforms between sex and task. There were no sex differences in hip joint forces, but landing trials were characterized by increased hip joint forces compared to land-and-cut trials. The hip joint force estimates obtained the current study could be used in future finite element models that incorporate bone growth models to understand the development of femoroacetabular impingement and design possible compensatory exercises.

Sex differences in muscle activation patterns associated with anterior cruciate ligament injury during landing and cutting tasks: A systematic review

Neuromuscular control is critical for maintaining dynamic joint stability and mitigating the risk of anterior cruciate ligament (ACL) injury. Given the increased risk of ACL injury in females, sex-based differential muscle activation strategies are often associated with this risk. For example, the quadriceps-dominant muscle activation strategy sometimes observed in females has been discussed as a cause of their increased risk of ACL injury. However, there has been no synthesised knowledge on sex differences in muscle activation patterns associated with ACL injuries. Therefore, the purpose of this review was to synthesise sex differences in muscle activation patterns in movements associated with ACL injuries in both adult and adolescent populations. A systematic electronic database search was conducted. Thirty studies were included in the review. Females demonstrated higher pre- and post-landing activation of the quadriceps and lower activation of the hamstrings in 15 studies. Females also had higher quadriceps-to-hamstring co-contraction ratios during pre- and post-landing phases compared to their male counterparts in 4 of 9 studies that considered co-contraction. While some studies supported the quadriceps-dominant activation strategies in females, no consensus can be drawn due to methodological inconsistencies and limitations. Also, despite the importance of ACL injury prevention in children and adolescents, the evidence on sex difference in muscle activation patterns in this population is insufficient to draw meaningful conclusions.

Is Hip Muscle Strength Associated with Dynamic Knee Valgus in a Healthy Adult Population? A Systematic Review

This study aimed to systematically review research investigating the association between hip muscle strength and dynamic knee valgus (DKV). Four databases (MEDLINE, PubMed, CINAHL, and SPORTDiscus) were searched for journal articles published from inception to October 2020. Seven studies investigating the association between hip muscle strength and DKV using a two-dimensional motion analysis system in healthy adults were included. The relationship between hip abductor muscle strength and DKV was negatively correlated in two studies, positively correlated in two studies, and not correlated in three studies. The DKV was associated with reduced hip extensor muscle strength in two studies and reduced hip external rotator muscle strength in two studies, while no correlation was found in three and five studies for each muscle group, respectively. The relationship between hip muscle strength, including abductors, extensors, and external rotators and DKV is conflicting. Considering the current literature limitations and variable methodological approaches used among studies, the clinical relevance of such findings should be interpreted cautiously. Therefore, future studies are recommended to measure the eccentric strength of hip muscles, resembling muscular movement during landing. Furthermore, high-demand and sufficiently challenging functional tasks revealing lower limb kinematic differences, such as cutting and jumping tasks, are recommended for measuring the DKV.

Parametric analysis of landing injury : The effect of landing posture and joint displacement

During landing, the lower limb joints work concertedly to reduce landing forces. Changing the biomechanics of one joint can alter landing strategies in other joints thus affecting the probability of injury. Therefore, understanding the mutual effects between the joints is crucial for the prevention of lower extremity injuries. The purpose of this study is to evaluate the effect of joint displacement and initial contact posture on the impact forces and joint kinematics during drop landing, via computational modeling. The impact dynamics of drop landing is modeled by a three link planar model. Different landing scenarios are then simulated to investigate how restricting the displacement of one joint and changing its initial contact angle affect the other joints' ranges of motion, the trunk motion, and the impact forces. Our study suggests that the impact force increases by up to [Formula: see text], [Formula: see text] and [Formula: see text], by restricting the hip, knee and ankle joints, respectively. Restricting each one of the hip and knee joints decreases the displacement of the other one. The association between the ankle displacement and the hip/knee motion depends on joints' stiffness and landing posture. Moreover, changing the landing posture affects the joints kinematics and impact forces significantly. A safe landing posture is a fore-foot landing with knee flexion angle of around 30° to 40° and a foot-ground angle of 40° to 55°, which decreases the impact force by more than [Formula: see text] in comparison to the erect posture with horizontal foot. The obtained results are of practical importance in training landing skills and designing force-reducing external components.

IMU-based knee flexion, abduction and internal rotation estimation during drop landing and cutting tasks

Anterior cruciate ligament (ACL) injury is a common and severe knee injury in sports. Knee flexion, abduction and internal rotation angles are considered crucial biomechanical indicators of the ACL injury risk but currently are computed in a laboratory with an optical motion capture. This paper introduces an inertial measurement unit (IMU) based algorithm for knee flexion, abduction and internal rotation estimation during ACL injury risk assessment tests, including drop landing and cutting tasks. This algorithm includes a special two-step complementary-based orientation filter and a special single-pose sensor-to-segment calibration procedure. Fourteen healthy subjects performed double-leg, single-leg drop landing and cutting tasks. Each subject wore four IMUs and reflective marker clusters on their thighs and shanks. For the presented knee angles algorithm with an empirical initial segment orientation, the root mean square errors (RMSEs) of the estimated continuous knee flexion, abduction and internal rotation cross all the movement tasks were 1.07°, 2.87° and 2.64°, and RMSEs of the peak knee flexion and peak knee abduction errors were 1.22° and 3.82°. The knee angles algorithm was capable of estimating knee abduction and internal rotation angles during drop landing and cutting tasks, and knee flexion estimation was substantially more accurate than previously reported approaches. Additionally, we found that for the presented algorithm, the accuracy of initial segment orientation was a critical factor for knee abduction and internal rotation estimations. The presented IMU-based knee angles algorithm could serve as a foundation to enable in-field biomechanical ACL injury risk assessment.

Reliability, validity, and maturation-related differences of frontal and sagittal plane landing kinematic measures during drop jump and tuck jump screening tests in male youth soccer players

OBJECTIVES

To determine the inter-rater and intra-rater reliability of frontal and sagittal plane landing kinematic measures during drop jump (DVJ) and tuck jump (TJA) tasks in male youth soccer players, to assess the concurrent validity between DVJ and TJA tests, and to evaluate the ability of both tasks to detect differences between players' stage of maturation.

DESIGN

Cross-sectional study.

PARTICIPANTS

223 male youth soccer players.

MAIN OUTCOME MEASURES

Frontal plane knee projection angles (FPPA), and hip (HF), knee (KF) and ankle (AF) flexion angles at initial contact (IC) and peak flexion (PF) (i.e., the deepest landing position) in the sagittal plane were assessed.

RESULTS

Good-to-excellent inter- and intra-rater reliability (ICC > 0.75; TEM_ST < 0.3; CV_TE < 5%) for the FPPA, HF and KF during DVJ and TJA tasks were found. A low concurrent validity between DVJ and TJA measures was reported. Differences by maturity status (BF₁₀ > 10; error < 10; δ > 0.6) were only identified for the TJA. Pre-PHV group reported higher FPPA, HF-IC, HF-PF, and KF-IC values, as well as lower AF-IC than post-PHV. Pre-PHV also displayed greater HF-IC and KF-IC than circa-PHV group.

CONCLUSIONS

Although both tests are reliable, the TJA might be viewed as a more informative tool given it shows greater FPPA and can also detect differences by maturity status.

Lower extremity muscle contributions to ACL loading during a stop-jump task

Landing is considered a high-risk movement, especially landings from a stop-jump task, as they are often associated with lower extremity injuries, such as anterior cruciate ligament injuries (ACL). Females demonstrate lower extremity landing mechanics that often place them at a larger risk of injury compared to their male counterparts. While efforts have been made to understand lower extremity mechanics during stop-jump landings, little is known regarding the musculature function during these tasks and how they may influence ACL loading. Understanding lower extremity muscle contributions to ACL loading (F_ACL) may give insight to improving injury prevention protocols. Ten healthy, recreationally active females completed five trials of an unanticipated stop-jump task. Right leg kinematics, kinetics, and electromyography data were collected with three-dimensional motion capture, force plates, and electromyography sensors, respectively. Modified musculoskeletal models were scaled based on participant-specific anthropometrics, and muscle forces were obtained using static optimization. An induced acceleration analysis combined with a previously established mathematical ACL loading model was used to calculate lower extremity muscle contribution to F_ACL. The vastus lateralis, vastus intermedius, vastus medials, biceps femoris long head, semimembranosus, and soleus were found to be the primary contributors to F_ACL, with the vastus lateralis being the largest contributor. These data suggest that muscles traditionally known as ACL unloaders may in certain conditions load the ACL. These results also suggest that future injury prevention protocols should target muscles specifically to mitigate the influence the vastus lateralis has on ACL loading.

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.

Sex and Age Comparisons in Neuromuscular And Biomechanical Characteristics of the Knee in Young Athletes

BACKGROUND

The identification of risk factors for injury is a key step for musculoskeletal injury prevention in youth sports. Not identifying and correcting for injury risk factors may result in lost opportunity for athletic development. Physical maturation and sex affect these characteristics, which may indicate the need for both age and sex-based injury prevention programs.

HYPOTHESIS/PURPOSE

This study examined age and sex differences in knee strength, static balance, jump height, and lower extremity landing biomechanics in school- and high school-age athletes.

STUDY DESIGN

Cross-sectional.

METHODS

Forty healthy school aged (10.8±0.8 yrs) and forty high school (16.8±0.8 yrs) athletes completed isokinetic knee flexion and extension strength tests, single-leg static balance and single-leg vertical stop jump tasks.

RESULTS

High school athletes were significantly stronger (~67% and 35% stronger for males and females, respectively) and jumped higher (regardless of sex) compared to school age athletes. High school males had worse balance (~28%) compared to their younger counterparts. High school females had lower strength (~23%) compared to males but had better balance (~46%). Conclusion: Maturation had different effects on the variables analyzed and sex differences were mainly observed after maturation. These differences may be minimized through appropriate age and sex specific training programs.

LEVELS OF EVIDENCE

3a.

CLINICAL RELEVANCE

Neuromuscular and biomechanical differences between sex and age groups should be accounted for in injury prevention and rehabilitation. Inadequate training may be a primary factor contributing to injuries in a young athletic population. When designing training programs for long term athlete development, programs should be dependent on decrements seen at specific time points throughout maturation.What is known about the subject: Generally, both males and females get stronger and jump higher as they get older but the results comparing balance and biomechanics between genders or across age groups have been mixed.What this study adds to existing knowledge: The current study looks at multiple neuromuscular and biomechanical variables in male and female participants at different maturation statuses. The current data supports the significant changes observed in strength and jump height, as both genders age, but the data also demonstrates significant differences in balance between age groups in males and between genders in balance and knee flexion angles.

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.

Effects of Bilateral and Unilateral Resistance Training on Horizontally Orientated Movement Performance: A Systematic Review and Meta-analysis

BACKGROUND

Both bilateral (BLE) and unilateral resistance exercise (ULE) methods can confer benefit to an athlete, but it remains to be established which has a greater effect on movement speed.

OBJECTIVES

To evaluate the effects of BLE and ULE on horizontal movement performance.

DATA SOURCES

Google Scholar, CrossRef, and PubMed.

STUDY ELIGIBILITY CRITERIA

To qualify for inclusion in the meta-analysis, studies must have included a resistance training intervention that compared the effects of BLE and ULE on a measure of movement speed such as sprinting in healthy study participants.

STUDY APPRAISAL AND SYNTHESIS METHODS

We used the inverse-variance random-effects model for meta-analyses. Effect sizes (standardised mean difference), calculated from measures of horizontally orientated performance, were represented by the standardised mean difference and presented alongside 95% confidence intervals (CI).

RESULTS

Though both modalities were effective (BLE = 0.60 [95% CI 0.34, 0.87], Z = 4.44 [p < 0.01]; ULE = 0.57 [95% CI 0.24, 0.89], Z = 3.44 [p = 0.0006]), there was no difference between the effect of BLE and ULE on movement speed (0.17 [95% CI - 0.15, 0.50], Z = 1.03 [p = 0.30]). For BLE, combined strength and plyometric training had the largest effect size (0.88 [95% CI 0.40, 1.36]]) followed by plyometric training (0.55 [95% CI 0.09, 1.01]), with the lowest effect in strength training (0.42 [95% CI - 0.02, 0.86]). For ULE, the largest effect size for training type was in plyometric training (0.78 [95% CI 0.33, 1.24]) closely followed by combined (0.63 [95% CI 0.03, 1.24]) with strength (0.29 [95% CI - 0.42, 1.01]) having a substantially lower effect size.

CONCLUSIONS

Both BLE and ULE are effective in enhancing horizontal movement performance. However, contrary to popular opinion, supported by the concept of training specificity, ULE was no more effective at achieving this than BLE.

Reliability of 3D measurement of pelvic and lower limb kinematics during two single leg landing tasks

Study aim: Three-dimensional (3D) motion analysis is one of the available methods used to evaluate body kinematics. The aim of this study was to assess the intrarater reliability of measurement of pelvic and lower limb kinematics during two single leg landing tasks using 3D motion analysis.

Material and methods: 19 healthy volunteers (8 women, 11 men, age 23.1 ± 2.8 years, weight 70.7 ± 9.2 kg, height 174.8 ± 6.7 cm) performed five repeated single leg hurdle hops (SLHH) (30 cm height) and five single leg drop landings (SLDL) from a box (40 cm height) in one measurement session with a 15-minute break and after marker replacement with 3D assessment. The intraclass correlation coefficient (ICC), standard error of measurement (SEM), and the smallest detectable differences (SDD) were used to examine the reliability of kinematic parameters during the landing phase.

Results: The average intrarater ICC for SLHH was 0.92 (SEM = 1.69°, SDD 4.68°) and for SLDL was 0.96 (SEM = 0.81°, SDD = 2.26°). After marker replacement ICC decreased to an average value of 0.81 (SEM = 2.05°, SDD 5.68°) for SLHH and 0.82 (SEM = 2.36°, SDD 6.53°) for SLDL.

Conclusions: Using the 3D method to evaluate pelvis and lower limb kinematics during single leg landing in one measurement session is a high reliability method for most parameters. Marker replacement is one of the factors that reduce the reliability of measures. When applying the SEM and SDD values, which the present paper contains, it is worth mentioning that the obtained results are caused by measurement error or they are due to individual issues.

Altered Neuromuscular Activity of the Lower-Extremities During Landing Tasks in Patients With Anterior Cruciate Ligament Reconstruction: A Systematic Review of Electromyographic Studies

CONTEXT

Altered lower-limb biomechanics have been observed during landing task in patients with anterior cruciate ligament reconstruction (ACLR), which increases the risk of secondary anterior cruciate ligament injury. However, the alteration in neuromuscular activity of the lower-extremity during landing task is not clear.

OBJECTIVE

To compare the muscle activity pattern assessed by electromyography between the involved limb of patients with ACLR and the contralateral limb or control limb of matched healthy subjects during landing task.

EVIDENCE ACQUISITION

Database of PubMed, Ovid, Scopus, and Web of Science from the inception of the databases until July 2019, using a combination of keywords and their variations: (anterior cruciate ligament OR ACL) AND (electromyography OR EMG) AND (landing OR land). Studies that assessed lower-extremity muscle activity patterns during landing task in patients with ACLR and compared them either with the contralateral side or healthy controls were included.

EVIDENCE SYNTHESIS

Of the 21 studies, 16 studies reported altered muscle activity pattern during landing tasks when compared with either the healthy controls or the contralateral side. For the specific muscle activity patterns, the majority of the studies showed no significant difference in reactive muscle activity, and comparisons across studies revealed a possible trend toward the early onset of quadriceps and hamstring activity and increased cocontraction of the involved limb. There are inconsistent findings regarding the alteration in muscle timing and preparatory muscle activity.

CONCLUSIONS

Patients with ACLR displayed an altered muscle activity pattern during landing tasks, even though they were considered to be capable for sport return. Nevertheless, a firm conclusion could not be drawn due to great heterogeneity in the subject selection and study methods.

THE RELATIONSHIP BETWEEN Y-BALANCE TEST SCORES AND KNEE MOMENTS DURING SINGLE-LEG JUMP-LANDING IN NETBALL

Background

Using 3-dimensional motion analysis to derive knee moments that may contribute to non-contact anterior cruciate ligament (ACL) injuries during single-leg jump-landing is expensive and time consuming. Severe ACL injuries that are inappropriately rehabilitated can potentially end athletes' careers. Consequently, a quick-and-simple to administer screening tool that can be used to infer knee moments during single-leg jump-landing could be useful for regular screening of netballers' predispositions to increased knee loading during single-leg jump-landing.

Purpose

The purpose of this study was to investigate whether knee moments during weight-acceptance phase of a forward single-leg jump for maximal distance were correlated with reach scores in the Y-Balance Test (YBT).

Study Design

Cross-sectional, Correlation.

Methods

Twenty-one female national-level netballers performed two and three successful trials on the YBT and forward single-leg jump-landing, respectively, with the non-dominant leg. A three-dimensional motion analysis system captured trunk and lower limb kinematics and ground reaction forces of the non-dominant leg during landing. Averages of peak knee flexion-extension, valgus-varus and internal-external rotation moments across jumps were calculated and correlations with peak directional reach scores were examined.

Results

A strong positive correlation existed between posteromedial reach with externally applied flexor moments (r = 0.56, p = ≤ 0.01). A moderate negative correlation existed between anterior reach distances with internal rotation moments (T _b = -0.32, p = 0.05). No correlation was found between valgus moments and YBT reaches.

Conclusions

The YBT shows potential to indicate externally applied flexion- and internal rotation moments during forward jump-landing on the non-dominant leg.

Level of Evidence

3.

Ground Reaction Forces Are Predicted with Functional and Clinical Tests in Healthy Collegiate Students

Increased vertical and posterior ground reaction forces (GRFs) are associated with anterior cruciate ligament (ACL) injury. If a practical means to predict these forces existed, ACL injury risk could be attenuated. Forty-two active college-age individuals (21 females, 20.66 ± 1.46 y, 70.70 ± 2.36 cm, 82.20 ± 7.60 kg; 21 males, 21.57 ± 1.28 y, 65.52 ± 1.87 cm, 64.19 ± 9.05 kg) participated in this controlled laboratory study. GRFs were ascertained by having the subjects perform a unilateral landing task onto a force plate. Several clinical measures (Fat Free Mass (FFM), dorsiflexion passive range of motion (DPROM), isometric peak force of the lateral hip rotators, knee flexor/extensor peak force ratio (H:Q), the completion of the overhead deep squat), two functional tests (Margaria–Kalamen, Single Leg Triple Hop (SLTH)), and sex served as the predictor variables. Regression models to predict the GRFs normalized to the FFM (nGRFz, nGRFy) were generated. nGRFz was best predicted with a linear regression equation that included SLTH and DPROM (adjusted R² = 0.274; p = 0.001). nGRFy was best predicted with a linear regression equation that included H:Q, FFM, and DPROM (adjusted R² = 0.476; p < 0.001). Simple clinical measures and functional tests explain a small to moderate amount of the variance associated with the FFM normalized vertical and posterior GRFs in active college-age individuals.

Acute Effects of ACL Injury-Prevention Warm-Up and Soccer-Specific Fatigue Protocol on Dynamic Knee Valgus in Youth Male Soccer Players

Childhood anterior cruciate ligament (ACL) injuries—which can pose a major risk to a child’s sporting career—have been on the rise in the last few decades. Dynamic knee valgus (DKV) has been linked to an increased risk of ACL injury. Therefore, the aim of this study was to analyze the acute effects of an ACL injury prevention protocol (ACL-IPP) and a soccer-specific fatigue protocol (SSFP) on DKV in youth male soccer players. The research hypothesis was that DKV would be reduced by the ACL-IPP and increased by the SSFP. Eighteen youth male soccer players were divided according to baseline DKV. Those with moderate or large DKV performed a neuromuscular training protocol based on activation of the abductor and external rotator hip muscles. Those with little or no DKV performed a soccer-specific fatigue protocol. DKV was assessed using the single-leg squat pre- and post-protocols in both legs. The ACL-IPP significantly decreased DKV during single-leg squat (p < 0.01, effect size = 1.39), while the SSFP significantly increased baseline DKV in the dominant leg during single-leg squat (p = 0.012; effect size = 1.74). In conclusion, the ACL-IPP appears to acutely reduce the DKV in youth male soccer players, and the SSFP seems to acutely increase the DKV in those players who showed a light or no DKV in a non-fatigue situation. By using the SSFP, it may be possible to determine which players would benefit from injury prevention programs due to increased DKV during game scenarios, while hip abductor and external rotator neuromuscular training may be beneficial for players who have moderate and severe DKV during single-leg squat under non-fatigued scenarios.

Effect of the FIFA 11+ on Landing Patterns and Baseline Movement Errors in Elite Male Youth Soccer Players

CONTEXT

There is no evidence regarding the effect of the FIFA 11+ on landing kinematics in male soccer players, and few studies exist regarding the evaluating progress of interventions based on the initial biomechanical profile.

OBJECTIVE

To investigate the effect of the FIFA 11+ program on landing patterns in soccer players classified as at low or high risk for noncontact anterior cruciate ligament injuries.

DESIGN

Randomized controlled trial.

SETTING

Field-based functional movement screening performed at the soccer field.

PARTICIPANTS

A total of 24 elite male youth soccer players participated in this study.

INTERVENTION

The intervention group performed the FIFA 11+ program 3 times per week for 8 weeks, whereas the control group performed their regular warm-up program.

MAIN OUTCOME MEASURES

Before and after the intervention, all participants were assessed for landing mechanics using the Landing Error Scoring System. Pretraining Landing Error Scoring System scores were used to determine risk groups.

RESULTS

The FIFA 11+ group had greater improvement than the control group in terms of improving the landing pattern; there was a significant intergroup difference (F1,20 = 28.86, P < .001, ηp2=.591). Soccer players categorized as being at high risk displayed greater improvement from the FIFA 11+ program than those at low risk (P = .03). However, there was no significant difference in the proportion of risk category following the routine warm-up program (P = 1.000).

CONCLUSIONS

The present study provides evidence of the usefulness of the FIFA 11+ program for reducing risk factors associated with noncontact anterior cruciate ligament injuries. The authors' results also suggest that soccer players with the higher risk profile would benefit more than those with lower risk profiles and that targeting them may improve the efficacy of the FIFA 11+ program.

Can kinematic and kinetic differences between planned and unplanned volleyball block jump-landings be associated with injury risk factors?

INTRODUCTION

Injury prevention programs for athletes are still limited by a lack of understanding of specific risk factors that can influence injuries within different sports. The majority of studies on volleyball have not considered the movement patterns when moving in different directions or in planned and unplanned block jump-landings.

METHODS

This study investigated all planes mechanics between the lead and trail limb when moving in dominant and non-dominant directions, for both planned and unplanned jump-landings in thirteen semi-professional female volleyball players. Ankle, knee and hip joint kinematics, kinetics and joint stiffness were recorded.

RESULTS

Our results showed statistically significant differences between the lead limb and the trail limb in the hip flexion angles, moments and velocity; in the knee flexion angles, moments, stiffness, power and energy absorption and in the ankle dorsiflexion, power and energy absorption, showing a tendency where the lead limb has a higher injury risk than the trail limb. When considering planned versus unplanned situations, there were statistically significant differences in knee flexion angles, moments, power and energy absorption; and hip contact angle, flexion angular velocity and energy absorption, with musculoskeletal adaptations in the planned situations.

DISCUSSION

It appears that the role of the limb, either lead or trail, is more important than the limb dominance when performing directional jump-landings, with the lead limb having a higher implication on possible overuse injuries than the trail limb. Furthermore, planned movements showed a difference in strategy indicating greater implications to possible overuse injuries than in the unplanned situations which may be associated with more conscious thought about the movements.

CONCLUSION

Coaches should consider unilateral coordination training in both landing directions for the lead and trail limb, and should adapt training to replicate the competition environment, using unplanned situations to minimize asymmetries to might reduce injury risks.

Influence of Foot-Landing Positions at Initial Contact on Knee Flexion Angles for Single-Leg Drop Landings

Purpose: Small knee flexion angles are associated with increased non-contact anterior cruciate ligament (ACL) injury risks. The purpose of this study was to provide insights into how ankle plantar flexion angles influenced knee flexion angles at initial contact during single-leg drop landings. Method: Thirteen male recreational basketball players performed single-leg drop landings from a 30-cm high platform using three randomized foot-landing positions (natural, fore-foot, and flat-foot). A motion capture system and a force plate were used to measure lower extremity kinematics and vertical ground reaction force (VGRF). A one-way repeated measures Analysis of Variance and the Friedman test were conducted (α = .05). Results: Foot-landing position had a significant effect on knee flexion angles at initial contact (p < .001). As compared to flat-foot landings (18° (SD 5°), significantly smaller knee flexion angles were found for natural (mean 12° (SD 5°), p = .004) and fore-foot landings (mean 12° (SD 3°), p = .001). There was however significantly smaller knee flexion range of motion in flat-foot landings (mean 42° (SD 3°), as compared to natural landings (mean 48° (SD 4°) (p < .001). Flat-foot landings also resulted in a 1.4 times higher maximum VGRF than fore-foot landings (p < .001) and 1.3 times higher than natural landings (p = .005). Conclusions: Natural and fore-foot landings are better for force absorption but are associated with smaller knee flexion angles at initial contact. These findings have important implications for non-contact ACL injuries.

There Is No Relationship Between Lower Extremity Alignment During Unilateral and Bilateral Drop Jumps and the Risk of Knee or Ankle Injury: A Prospective Study

OBJECTIVE

To investigate the association between lower extremity alignment during unilateral and bilateral drop jump tests and the risk of acute noncontact knee or ankle injuries in young team sport athletes.

DESIGN

Prospective cohort study.

METHODS

A 2-dimensional video analysis was used to measure the frontal plane knee projection angle in the single-leg vertical drop jump (VDJ) and the bilateral VDJ in young team sport athletes. Out of the 364 athletes (187 male, 177 female), 189 played basketball and 175 played floorball.

RESULTS

Six male athletes sustained knee injuries and 23 sustained ankle injuries. Frontal plane knee projection angle in the single-leg VDJ or the bilateral VDJ was not associated with ankle injuries among male athletes. No statistical analysis was performed for the knee injuries. Among female athletes, 28 sustained knee and 41 sustained ankle injuries. Frontal plane knee projection angle during the single-leg VDJ or the bilateral VDJ was not a risk factor for knee or ankle injuries.

CONCLUSION

Lower extremity alignment during unilateral and bilateral drop jump tests was not associated with future noncontact knee or ankle injuries among young team sport athletes. The findings should be interpreted cautiously due to the small number of injuries. J Orthop Sports Phys Ther 2020;50(5):267-274. doi:10.2519/jospt.2020.9247.

Effect of Sand on Landing Knee Valgus During Single-Leg Land and Drop Jump Tasks: Possible Implications for ACL Injury Prevention and Rehabilitation

CONTEXT

Despite significant emphasis on anterior cruciate ligament injury prevention, injury rates continue to rise and reinjury is common. Interventions to reduce injury have included resistance, balance, and jump training elements. The use of sand-based jump training has been postulated as an effective treatment. However, evidence on landing mechanics is limited.

OBJECTIVE

To determine potential differences in landing strategies and subsequent landing knee valgus when performing single-leg landing (SLL) and drop jump (DJ) tasks onto sand and land, and to compare between both male and female populations.

DESIGN

A randomized repeated-measures crossover design.

SETTING

University laboratory.

PARTICIPANTS

Thirty-one participants (20 males and 11 females) from a university population.

INTERVENTIONS

All participants completed DJ and SLL tasks on both sand and land surfaces.

MAIN OUTCOME MEASURES

Two-dimensional frontal plane projection angle (FPPA) of knee valgus was measured in both the DJ and SLL tasks (right and left) for both sand and land conditions.

RESULTS

FPPA was lower (moderate to large effect) for SLL in sand compared with land in both legs (left: 4.3° [2.8°]; right: 4.1° [3.8°]) for females. However, effects were unclear (left: -0.7° [2.2°]) and trivial for males (right: -1.1° [1.9°]). FPPA differences for males and females performing DJ were unclear; thus, more data is required. Differences in FPPA (land vs sand) with respect to grouping (sex) for both SLL left (4.9° [3.0°]) and right (5.1° [4.0°]) were very likely higher (small)/possibly moderate for females compared with males.

CONCLUSIONS

The effects of sand on FPPA during DJ tasks in males and females are unclear, and further data is required. However, the moderate to large reductions in FPPA in females during SLL tasks suggest that sand may provide a safer alternative to firm ground for female athletes in anterior cruciate ligament injury prevention and rehabilitation programs, which involve a SLL component.

Exploring the Justifications for Selecting a Drop Landing Task to Assess Injury Biomechanics: A Narrative Review and Analysis of Landings Performed by Female Netball Players

When assessing biomechanics in a laboratory setting, task selection is critical to the production of accurate and meaningful data. The injury biomechanics of landing is commonly investigated in a laboratory setting using a drop landing task. However, why this task is so frequently chosen is unclear. Therefore, this narrative review aimed to (1) identify the justification/s provided within the published literature as to why a drop landing task was selected to investigate the injury biomechanics of landing in sport and (2) use current research evidence, supplemented by a new set of biomechanical data, to evaluate whether the justifications are supported. To achieve this, a comprehensive literature search using Scopus, PubMed, and SPORTDiscus online databases was conducted for studies that had collected biomechanical data relating to sport injuries using a drop landing task. In addition, kinematic and kinetic data were collected from female netball players during drop landings and maximum-effort countermovement jumps from the ground to grab a suspended ball. The literature search returned a total of 149 articles that were reviewed to determine the justification for selecting a drop landing task. Of these, 54% provided no explicit justification to explain why a drop landing task was chosen, and 15% stated it was selected because it had been used in previous research. Other reasons included that the drop landing provides high experimental control (16%), is a functional sports task (11%), and is a dynamic task (6%). Evidence in the literature suggests that the biomechanical data produced with drop landings may not be as externally valid as more sport-specific tasks. Biomechanical data showed that the drop landing may not control center of mass fall height any better than maximum-effort countermovement jumps from the ground. Further, the frequently used step-off technique to initiate drop landings resulted in kinematic and kinetic asymmetries between lower limbs, which would otherwise be symmetrical when performing a countermovement jump from the ground. Researchers should consider the limitations of a drop landing task and endeavor to improve the laboratory tasks used to collect biomechanical data to examine the injury biomechanics of landing.

Mechanisms to Attenuate Load in the Intact Limb of Transtibial Amputees When Performing a Unilateral Drop Landing

Individuals with unilateral transtibial amputations experience greater work demand and loading on the intact limb compared with the prosthetic limb, placing this limb at a greater risk of knee joint degenerative conditions. It is possible that increased loading on the intact side may occur due to strength deficits and joint absorption mechanics. This study investigated the intact limb mechanics utilized to attenuate load, independent of prosthetic limb contributions and requirements for forward progression, which could provide an indication of deficiencies in the intact limb. Amputee and healthy control participants completed 3 unilateral drop landings from a 30-cm drop height. Joint angles at touchdown; range of motion; coupling angles; peak powers; and negative work of the ankle, knee, and hip were extracted together with isometric quadriceps strength measures. No significant differences were found in the load or movement mechanics (P ≥ .31, g ≤ 0.42), despite deficits in isometric maximum (20%) and explosive (25%) strength (P ≤ .13, g ≥ 0.61) in the intact limb. These results demonstrate that, when the influence from the prosthetic limb and task demand are absent, and despite deficits in strength, the intact limb adopts joint mechanics similar to able-bodied controls to attenuate limb loading.

Effects of an Eccentric Hamstrings Training on Components of Physical Performance in Young Female Handball Players

PURPOSE

This study examined the effects of an 8-week Nordic hamstring exercise (NHE) training on components of physical performance in young female handball players.

METHODS

Participants were allocated to an experimental group (EG; n = 10; age: 15.9 [0.2] y) and a control group (CG; n = 9; age: 15.9 [0.3] y). The EG performed NHE (2-3 sessions/wk) in replacement of some handball-specific drills, whereas the CG followed regular handball training. Pretraining and posttraining tests were carried out for the assessment of sprint speed (5 m, 10 m, and 20 m), jump performance (countermovement jump [CMJ] height), change-of-direction (t test), and repeated-sprint ability (RSA total time [RSAtotal], RSA best time [RSAbest], and RSA fatigue index [RSAFI]). Data were analyzed using magnitude-based inferences.

RESULTS

Within-group analyses for the EG showed moderate performance improvements for 5, 10, and 20 m (effect size [ES] = 0.68-0.82), t test (ES = 0.74), and CMJ (ES = 0.85). Trivial to small improvements were observed for RSA (ES = -0.06 to 0.35). For the CG, within-group outcomes showed performance decrements with moderate (t test [ES = 0.71]), small (5 m [ES = 0.46] and RSAbest [ES = 0.20]), and trivial magnitude (10 m [ES = 0.10], 20 m [ES = 0.16], and RSAtotal [ES = 0.00]). Furthermore, trivial to small performance improvements were found for CMJ (ES = 0.10) and RSAFI (ES = 0.5). Between-group analyses revealed small to large effects in favor of EG for 5 m (ES = 1.07), 10 m (ES = 0.66), 20 m (ES = 0.53), t test (ES = 1.38), and RSA (ES = 0.68-0.78). A trivial between-group difference was demonstrated for CMJ (ES = -0.01).

CONCLUSIONS

The NHE training intervention, in replacement of some handball-specific drills, was more effective than regular handball training in improving physical performance (ie, linear sprint time, jumping, change-of-direction, and RSA) in young female handball players.

Task but not arm restriction influences lower extremity joint mechanics during bilateral landings

Box and jump landing tasks are commonly used to study lower extremity injury mechanisms, such as anterior cruciate ligament (ACL) injuries. Arm restriction during these tasks is typically determined via researcher preference. Therefore, the purpose of this study was to compare three-dimensional lower extremity kinematics and kinetics during bilateral box and jump landings, and to determine the effects of arm restriction. Twenty-eight participants (14 males, 14 females) completed three bilateral landings tasks: box landings with arms unrestricted (BLA), box landings with arms restricted against the trunk (BLNA) and jump landings (JL). Right leg joint kinematics and kinetics were collected and compared between landing tasks. No statistically significant differences were found between BLA and BLNA, therefore arm restriction did not appear to influence lower extremity variables during bilateral box landings. However, specific injury-related variables, such as peak knee adduction moment differed between box and jump landings (BLNA: 0.31 ± 0.3 Nm/(kg·m)); JL: 0.45 ± 0.3 Nm/(kg·m); p = 0.020). Our results suggest that based on study purpose, careful consideration is needed when determining what bilateral landing task to choose during data collection.

Knee Forces During Landing in Men and Women

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η²=0.452; unilateral: p < 0.001, η² = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η² = 0.001 - 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η² = 0.085) and hamstrings forces (p < 0.001, η² = 0.183), whereas women had greater quadriceps forces (p = 0.004, η² = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

Anticipatory effects on lower extremity kinetics during a land and cross step maneuver in female volleyball players

BACKGROUND

Anticipation has been previously shown to affect lower extremity mechanics during both landing and cutting maneuvers. However, little research has been conducted looking at the effects of anticipation on lower body kinetics and kinematics during a land and cross step maneuver, which due to similar kinematics, may elicit injury. The purpose of this study was to investigate competitive female volleyball players and the effect of anticipation on lower extremity mechanics during a landing and subsequent cross stepping maneuver.

METHODS

Twelve female, college-level volleyball players performed right and left cross step maneuvers following a landing under anticipated and unanticipated conditions. Kinetics were measured for the ankle, knee and hip of the dominant limb during the landing phase of the land and cross step anticipatory conditions.

RESULTS

An interaction effect (anticipation x direction; P=0.001) was observed for vertical ground reaction force (VGRF), in which greater VGRF was found during unanticipated pivoting maneuvers. Additional interaction effects were determined for ankle (P=0.004) and hip (P=0.037) power absorption, in which greater absorption was found during anticipated, push off conditions. Frontal plant knee kinetics revealed a higher-order interaction, as a larger knee adduction moment was shown during anticipated, push off trials (P=0.001).

CONCLUSIONS

High risk cross step maneuvers were found during unanticipated and anticipated conditions, as athletes demonstrated movement mechanics that may increase the risk of knee injury when performing movements away from the dominant limb. Consideration should be given to drills familiarizing volleyball players with unanticipated and anticipated changes of direction, as well as improving strength of the lower extremity muscles required to effectively decelerate the body, as both training modalities may minimize injury risk during cross step maneuvers.

Hinged ankle braces do not alter knee mechanics during sidestep cutting

Lateral ankle sprains are common injuries in quick, dynamic movements and are caused by rapid ankle inversion. Ankle braces are used to reduce ankle inversion, while allowing normal plantar and dorsiflexion ranges of motion. Knee injuries, such as anterior cruciate ligament injuries, are also common in dynamic movements. It is important to understand how ankle braces affect injury risk at other proximal joints. There is limited and conflicting results on how ankle braces affect knee mechanics during these types of movements. Additionally, it is unknown if sex differences exist when using an ankle brace. Therefore, the purpose of this study was to determine the effects of a hinged ankle brace and sex during a 45° cutting movement. Three-dimensional kinematics and ground reaction forces were collected using a motion capture system and force plate on ten men and eight women during cutting trials. 2 × 2 repeated measures ANOVAs were used to detect differences in ground reaction forces, as well as knee and ankle kinematics between brace conditions and sex (p < 0.05). The brace condition exhibited greater initial contact ankle dorsiflexion (p = 0.011), decreased peak ankle inversion (p < 0.01), and increased vertical loading rate (p = 0.040). Females performed the cutting movement with less initial contact (p = 0.019) and peak knee flexion (p = 0.023) compared to males. Ankle bracing had no impact on the observed sex differences. Females exhibited decreased knee flexion compared to males, which has been well documented in the literature. The use of an ankle braces reduced ankle injury risk variables while not adversely impacting knee mechanics during a 45° sidecutting movement.