Lower extremity muscle activation and knee flexion during a jump-landing task

The effect of surface on knee landing mechanics and muscle activity during a single-leg landing task in recreationally active females

OBJECTIVE

Investigate the effect of surface on frontal plane knee angle, knee moment and muscle activity.

DESIGN

Randomised cross over.

SETTING

University Laboratory.

METHODS

Twenty females performed single-leg hop-landings onto sand, grass and firm surfaces. Kinematic, kinetic and muscle activity data were obtained. Compatibility curves were used to visualise parameter estimates alongside P- values, and S-value transforms.

RESULTS

Knee angle for firm-sand (mean difference (d)‾ = -2.2°; 95% compatibility interval (CI): -4.6 to 0.28, p = 0.083, s = 3.6) and firm-grass (d‾ = -1.9; 95% CI: -4.3 to 0.5, p = 0.125, S = 3) yielded <4 bits of reputational information against the null hypothesis (H). 5 bits (p = 0.025) of information against H were observed for knee moment between firm-sand (d‾ = 0.17 N m/kg-1. m-1; 95% CI: 0.02 to 0.31) with similar effects for firm-grass (d‾ = 0.14 N m/kg-1. m-1; 95% CI: -0.02 to 0.29, p = 0.055, S = 4). Muscle activity across surfaces ranged from almost no (S = 1) reputational evidence against H (Quadriceps and Hamstrings) to 10-13 'bits' against H for lateral gastrocnemius (lower on sand).

CONCLUSIONS

Our study provides valuable information for practitioners of the observed effect sizes for lower-limb landing mechanics across surfaces in asymptomatic females.

Hamstring Muscle Stiffness in Athletes with and without Anterior Cruciate Ligament Reconstruction History: A Retrospective Study

Introduction: Sports requiring sprinting, jumping, and kicking tasks frequently lead to hamstring strain injuries (HSI). One of the structural risk factors of HSI is the increased passive stiffness of the hamstrings. Anterior cruciate ligament (ACL) injury history is associated with a 70% increase in the incidence of HSI, according to a recent meta-analysis. The same report recommended that future research should concentrate on the relationships between the HSI risk factors. Hence, the present study aimed to retrospectively compare changes in the passive stiffness of the hamstrings in athletes with and without ACL reconstruction history. Methods: Using ultrasound-based shear-wave elastography, the mid-belly passive muscle stiffness values of the biceps femoris long head, semimembranosus, and semitendinosus muscles were assessed and compared amongst athletes with and without a history of ACL reconstruction. Results: There were no significant differences in the biceps femoris long head (injured leg (IL): 26.19 ± 5.28 KPa, uninjured contralateral (UL): 26.16 ± 7.41 KPa, control legs (CL): 27.64 ± 5.58 KPa; IL vs. UL: p = 1; IL vs. CL: p = 1; UL vs. CL: p = 1), semimembranosus (IL: 24.35 ± 5.58 KPa, UL: 24.65 ± 8.35 KPa, CL: 22.83 ± 5.67 KPa; IL vs. UL: p = 1; IL vs. CL: p = 1; UL vs. CL, p = 1), or semitendinosus (IL: 22.45 ± 7 KPa, UL: 25.52 ± 7 KPa, CL: 22.54 ± 4.4 KPa; IL vs. UL: p = 0.487; IL vs. CL: p = 1; UL vs. CL, p = 0.291) muscle stiffness values between groups. Conclusions: The passive mid-muscle belly stiffness values of the biceps femoris long head, semitendinosus, and semimembranosus muscles did not significantly differ between previously injured and uninjured athletes; therefore, further assessment for other muscle regions of hamstrings may be necessary. To collect more comprehensive data related to the structural changes that may occur following ACL reconstructions in athletes, a future study should examine the passive stiffness of wider muscle regions from origin to insertion.

Reliability of lower limb strength assessment in female team sport athletes

BACKGROUND

Lower limb injury rates have increased dramatically in line with increased female sport participation levels. Muscle strength is a modifiable lower limb injury risk factor, guiding performance monitoring and rehabilitation.

OBJECTIVES

The aim of this study was to investigate the test-retest reliability of isokinetic and isometric lower limb peak torque to body mass of muscles acting on the hip, knee, and ankle in female team sport athletes. It was hypothesised the test-retest reliability would be good (intraclass correlation coefficients (ICC) ≥ 0.75).

METHODS

Thirty-eight female athletes (Australian Rules Football = 18, netball = 12, soccer = 8) aged 16-35 years participated in this study. Participants performed isokinetic (60°/s and 120°/s) and isometric testing on a Biodex Isokinetic Dynamometer on three separate days.

RESULTS

Poor to good reliability was demonstrated for all joint movements (ICC = 0.38-0.88) with small to moderate effect sizes (0.00-0.43) and typical errors (5.65-24.49).

CONCLUSION

Differences in peak torque to body mass were observed between sessions one and two and/or one and three, demonstrating a learning effect. Therefore, three testing sessions, and/or the inclusion of a familiarisation session, is recommended for future assessments in populations unfamiliar with dynamometry.

Functional knee brace use for 21 h leads to a longer duration to achieve peak vertical ground reaction forces and the removal of the brace after 17.5 h results in faster loading of the knee joint

PURPOSE

To investigate the landing strategies used after discontinuing and continuing the use of a functional knee brace (FKB) while performing a drop jump.

METHODS

Following published methodology and power analysis, 23 uninjured male athletes, mean age of 19.4 ± 3.0 years, performed seven tests, during three test conditions (nonbraced, braced and removed brace or continued brace use), over 6 days of 12 testing sessions (S) for a total of 38.5 h. Each subject was provided with a custom-fitted FKB. This study focuses on the single leg drop jump kinetics during S12 when subjects were randomly selected to remove the FKB after 17.5 h or continued use of FKB. The time to peak vertical ground reaction forces (PVGRF) and PVGRF were recorded on landing in eight trials.

RESULTS

After brace removal, a significantly shorter mean time to PVGRF was recorded (9.4 ± 22.9 msec (3.9%), p = 0.005, 95% confidence interval (95% CI): -168.1, 36.1), while continued brace use required a nonsignificant (n.s.) longer mean duration to achieve PVGRF (19.4 ± 53.6 msec (8.9%), n.s., 95% CI: -49.7, 73.4). No significant mean PVGRF difference was found in brace removal (25.3 ± 65.8 N) and continued brace use (25.1 ± 23.0 N).

CONCLUSION

Removal of FKB after 17.5 h of use led to a significantly shorter time to achieve PVGRF, while continued brace use for 21 h required a longer duration to achieve PVGRF, suggesting faster and slower knee joint loading, respectively. Understanding the concerns associated with the use of FKB and the kinetics of the knee joint will assist clinicians in counselling athletes about the risks and benefits of using an FKB.

LEVEL OF EVIDENCE

Level II.

Influence of strength and balance ability on functional performance in the involved and uninvolved sides after anterior cruciate ligament reconstruction

BACKGROUND

The restoration and management of the uninvolved side have been emphasized to prevent a second anterior cruciate ligament (ACL) injury and to ensure that athletes return to sports after ACL reconstruction.

OBJECTIVE

To determine the factors influencing the single leg hop test (SLHT) and single leg vertical jump test (SLVJT) at 1 year postoperatively after ACL reconstruction in both the involved and uninvolved sides.

METHODS

Ninety-four patients who underwent ACL reconstruction were assessed at 1 year postoperatively. Multiple regression models included eight independent variables with two dependent variables (SLHT and SLVJT.), each on the involved and uninvolved side.

RESULTS

On the involved side, the Y balance test (YBT), extensor peak torque per body weight (PT/BW), Biodex balance system anteroposterior index (BBS-API), and sex accounted for 53.9% of the variance in SLHT (P= 0.002), and extensor PT/BW and YBT accounted for 26.3% of the variance in SLVJT (P= 0.027). On the uninvolved side, YBT, sex, age, BBS-API, and flexor PT/BW accounted for 47.0% of the variance in SLHT (P= 0.046), and flexor PT/BW, YBT, and age accounted for 44.9% of the variance in SLVJT (P= 0.002).

CONCLUSION

Knee extensor strength on the involved side and flexor strength on the uninvolved side influence the two functional performance tests. The YBT was an important factor in the two functional performance tests in both sides. Anteroposterior stability was the only factor that influenced the SLHT bilaterally.

Preparing to Land: Hamstring Preactivation Is Higher in Females and Is Inhibited by Fatigue

The hamstring plays an important role in reducing loads born by the anterior cruciate ligament. As anterior cruciate ligament injuries occur rapidly after ground contact, how the hamstring is activated prior to landing can influence injury risk. The purpose was to determine sex-related differences in hamstring activation immediately before landing and the effect of fatigue on "preactivation." Twenty-four participants (13 males and 11 females, age = 24.3 [6.5] y, mass = 72.2 [19.3] kg, height = 169 [9.7] cm) participated in this study. Participants completed a drop-vertical jump protocol before and after a lower body fatigue protocol. Hamstring electromyography (EMG) amplitude at 5 periods prior to landing, peak vertical ground reactions forces (in newtons/body weight), rate of loading (in body weight/second), and landing error scoring system were measured. Females had higher EMG amplitude before and after fatigue (P < .024), with decreased EMG amplitude for both sexes after fatigue (P = .025). There was no change on vertical ground reaction force, rate of loading, or landing error scoring system. Males and females demonstrated similar landing performance before and after fatigue but have different hamstring neuromuscular coordination strategies. The acute reduction in hamstring EMG amplitude following fatigue may increase loading on the anterior cruciate ligament.

Effects of FIFA 11 + warm-up program on kinematics and proprioception in adolescent soccer players: a parallel‑group randomized control trial

This study aimed to compare the effects of 8 weeks 11 + warm-up injury prevention program on kinematics and proprioception in adolescent male and female soccer players. Forty adolescent soccer players (20 males, 20 females) aged between 14-16 years old were randomly assigned into four groups. The experimental group performed the 11 + program for 8 weeks and the control group did their warm-up program. The kinematic variable in a cutting maneuver was measured using VICON motion analysis and ankle and knees' proprioception by joint position sense (JPS) was measured using a digital inclinometer. For kinematic variables only significant differences in knee valgus among females 11 + compared with female and male control groups were found (P < 0.05). Moreover, there were significant improvements in joint position sense variables in 11 + groups compared to control groups (P < 0.05). In conclusion, the 11 + program was proven to be a useful warm-up protocol in improving knee valgus and JPS among female and male adolescent soccer players. We suggest adding more training elements to the 11 + program that aimed to enhance the proper alignment of lower extremities which may consequently improve joint kinematics.

Reliability of the running vertical jump test in female team sport athletes

Injury rates to the lower limb have increased over the past 40 years, coinciding with increases in female sport participation rates. Sport specific tests such as the running vertical jump (RVJ) are utilised for injury risk profiling, however the test-retest reliability is unknown.

OBJECTIVES

The aim of this study was to investigate the test-retest reliability of the thorax, pelvis and lower limb joint angular kinematics and kinetics for the RVJ test in female team sport athletes.

DESIGN

Three-dimensional motion capture with force plate integration was utilised as participants performed five trials on each limb on three separate days.

SETTING

Testing occurred in a biomechanics laboratory.

PARTICIPANTS

Thirty-four females (Australian Rules Football = 15, Netball = 12, Soccer = 7) participated in this study.

MAIN OUTCOME MEASURES

Intraclass correlation coefficients (ICC), effect sizes and typical errors (TE) of segment and joint angular kinematics and kinetics were calculated.

RESULTS

Poor to excellent reliability (ICC = -0.12 - 0.92), small to large effect sizes (0.00-0.90) and TE (0.02-289.24) were observed across segment and joint angular kinematics and kinetics.

CONCLUSIONS

The RVJ test is recommended when analysing ground reaction forces and joint angular kinematics in female team sport athletes.

Análisis cinemático del ángulo de proyección frontal de rodilla en 2D: enfoque metodológico

La evaluación cinemática del comportamiento del miembro inferior en tres dimensiones (3D) requiere el uso de alta tecnología, formación especializada y laboratorios que no se ajustan a las demandas del ámbito clínico y deportivo. La valoración del APFR (ángulo de proyección frontal de rodilla)en dos dimensiones (2D) ha mostrado consistentemente su validez, objetividad y confiabilidad al ser comparada con la metodología de análisis en 3D para la detección del valgo dinámico asociado al incremento de torques externos de aducción y rotación interna de cadera durante la ejecución de tareas funcionales que exigen control muscular excéntrico. El valgo dinámico ha mostrado ser un predictor de lesión del ligamento cruzado anterior y de síndrome de dolor patelofemoral, especialmente en mujeres. La detección oportuna y el seguimiento del comportamiento cinemático con instrumentos de bajo costo, poca complejidad y un nivel de experticia básico utilizando análisis en 2D, se perfila como estrategia de valoración importante en el entrenamiento deportivo y el abordaje clínico para la prevención y rehabilitación de lesiones de rodilla asociados a estos desórdenes del movimiento. Por tanto, esta revisión narrativa pretende proveer de conocimientos esenciales para la correcta valoración, interpretación y análisis del APFR en Fisioterapeutas y Profesionales del Deporte.

Breaking new grounds in injury risk screening in soccer by deploying unsupervised learning with a special focus on sex and fatigue effects

In injury prevention, a vertical drop jump (DJ) is often used for screening athletes at risk for injury; however, the large variation in individual movement patterns might mask potentially relevant strategies when analysed on a group-based level. Two movement strategies are commonly discussed as predisposing athletes to ACL injuries: a deficient leg axis and increased leg stiffness during landing. This study investigated the individual movement pattern of 39 female and male competitive soccer players performing DJs at rest and after being fatigued. The joint angles were used to train a Kohonen self-organising map. Out of 19,596 input vectors, the SOM identified 700 unique postures. Visualising the movement trajectories and adding the latent parameters contact time, medial knee displacement (MKD) and knee abduction moment allow identification of zones with presumably increased injury risk and whether the individual movement patterns pass these zones. This information can be used, e.g., for individual screening and for feedback purposes. Additionally, an athlete's reaction to fatigue can be explored by comparing the rested and fatigued movement trajectories. The results highlight the ability of unsupervised learning to visualise movement patterns and to give further insight into an individual athlete's status without the necessity of a priori assumptions.

The Effect of Arm Dominance on Knee Joint Biomechanics During Basketball Block Shot Single-Leg Landing

Single arm blocking is a key component of successful basketball defence. The player uses either their dominant or non-dominant arm to block the ball landing on a common leg. Understanding how the bio-physical loads of the landing leg change as a function of the blocking arm will provide insights into potential injury risk of the lower limb. The aim of this study was to investigate the effects of arm dominance on the biomechanical variables of injury risk of the lower limb, specifically the knee joint during the single-leg landing in female basketball players. Kinematic and kinetic data were collected from fourteen female basketball athletes (20.85 ± 1.35 years, 1.69 ± 0.06 m, 60.37 ± 7.75 kg), each performing three trials of a dominant arm and non-dominant block jump landing on the dominant leg. The results showed significantly higher anterior and medial ground reaction force, knee joint flexion and abduction and lateral knee force during the dominant arm landing (p < 0.05). These findings highlight potential injury risk and the need for the player to be more proficient at dominant arm block-shot landing. The player should aim to develop a larger landscape of technique to meet the demands of the game and facilitate a more effective and safer landing strategy.

Morphological and functional asymmetry in elite youth tennis players compared to sex- and age-matched controls

Besides examining upper and lower limb morphological and functional asymmetry magnitudes, this study examined the relationship between lean mass and functional asymmetry in terms of magnitude and direction in 41 youth tennis players versus 41 controls. Asymmetry magnitude was determined using anthropometric measurements (circumferences, widths), bioelectrical impedance analysis (lean mass) and a test battery (handgrip strength, seated medicine ball throw, plate tapping, single leg countermovement jump, single leg forward hop test, 6 m single leg hop test, 505 change of direction). ANOVAs compared the dominant (overall highest/best value) against the non-dominant (highest/best value of opposing limb) result. Linear regressions explored the relationship between lean mass and functional asymmetry magnitudes. Kappa coefficients examined asymmetry direction consistency between the limb displaying the highest lean mass value and the limb performing dominantly across tests. Significant asymmetry magnitudes (p < 0.05) were found for all upper and lower limb outcome measures. No significant relationship was apparent between lean mass and functional asymmetry magnitude (r-value = -0.283-0.262). Despite finding (almost) perfect consistency in asymmetry direction (k-value = 0.84-1.00) for the upper limb, poor to slight consistency (k-value = -0.03-0.15) was found for the lower limb. Therefore, lean mass and functional asymmetry should be examined independently.

Effects of Patellofemoral Pain Syndrome on Changes in Dynamic Postural Stability during Landing in Adult Women

Background

This study investigated the effects of lower limb movements on dynamic postural stability (DPS) during drop landing in adult women with patellofemoral pain syndrome (PFPS).

Methods

Thirty-eight adult women were recruited and divided into two groups, the PFPS group and the control group. The study participants performed a single-leg drop landing from a 30 cm box, and their lower limb movements and DPS were measured. Differences between groups were examined using independent sample t-tests. In addition, stepwise multiple linear regression was used to examine the kinematic parameters that contribute to the DPS.

Results

The PFPS group had significantly lower hip flexion, internal rotation, knee flexion, ankle external rotation, pelvic oblique, tilt, rotation, and higher hip abduction, knee valgus, and ankle plantarflexion. In terms of DPS, the PFPS group had a significantly higher anteroposterior and a lower mediolateral than that of the control group. In the control group, regression analysis revealed a controlled anteroposterior using knee flexion, while the PFPS group controlled mediolateral through ankle plantarflexion.

Conclusions

Patients with PFPS experienced more shock on their knee joint during landing than patients in the control group with greater anteroposterior instability and lower mediolateral instability.

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.

Effects of Deficits in the Neuromuscular and Mechanical Properties of the Quadriceps and Hamstrings on Single-Leg Hop Performance and Dynamic Knee Stability in Patients After Anterior Cruciate Ligament Reconstruction

Background:

Understanding the role of neuromuscular and mechanical muscle properties in knee functional performance and dynamic knee stability after anterior cruciate ligament reconstruction (ACLR) may help in the development of more focused rehabilitation programs.

Purpose:

To compare the involved and uninvolved limbs of patients after ACLR in terms of muscle strength, passive muscle stiffness, muscle activation of the quadriceps and hamstrings, hop performance, and dynamic knee stability and to investigate the association of neuromuscular and mechanical muscle properties with hop performance and dynamic knee stability.

Study Design:

Cross-sectional study; Level of evidence, 3.

Method:

The authors studied the quadriceps and hamstring muscles in 30 male patients (mean ± SD age, 25.4 ± 4.1 years) who had undergone unilateral ACLR. Muscle strength was measured using isokinetic testing at 60 and 180 deg/s. Passive muscle stiffness was quantified using ultrasound shear wave elastography. Muscle activation was evaluated via electromyographic (EMG) activity. Hop performance was evaluated via a single-leg hop test, and dynamic knee stability was evaluated via 3-dimensional knee movements during the landing phase of the hop test.

Results:

Compared with the uninvolved limb, the involved limb exhibited decreased peak torque and shear modulus in both the quadriceps and hamstrings as well as delayed activity onset in the quadriceps (P < .05 for all). The involved limb also exhibited a shorter hop distance and decreased peak knee flexion angle during landing (P < .05 for both). Decreased peak quadriceps torque at 180 deg/s, the shear modulus of the semitendinosus, and the reactive EMG activity amplitude of the semimembranosus were all associated with shorter hop distance (R² = 0.565; P < .001). Decreased quadriceps peak torque at 60 deg/s and shear modulus of the vastus medialis were both associated with smaller peak knee flexion angle (R² = 0.319; P < .001).

Conclusion:

In addition to muscle strength deficits, deficits in passive muscle stiffness and muscle activation of the quadriceps and hamstrings were important contributors to poor single-leg hop performance and dynamic knee stability during landing. Further investigations should include a rehabilitation program that normalizes muscle stiffness and activation patterns during landing, thus improving knee functional performance and dynamic knee stability.

No Relationship between Lean Mass and Functional Asymmetry in High-Level Female Tennis Players

The relationship between lean mass and functional asymmetry in terms of their magnitude and direction was examined in 22 high-level female tennis players (20.9 ± 3.6 years). Lean mass of both upper and lower extremities was examined using Dual X-ray Absorptiometry. Functional asymmetry was assessed using a battery of field tests (handgrip strength, seated shot-put throw, plate tapping, single leg countermovement jump, single leg forward hop test, 6 m single leg hop test, and 505 change of direction (time and deficit)). Paired sample t-tests compared the dominant (overall highest/best (performance) value) against the non-dominant value (highest/best (performance) value of the opposing extremity). Linear regressions were used to explore the relationship between lean mass and functional asymmetry magnitudes. Kappa coefficients were used to examine the consistency in direction between the extremity displaying the highest lean mass value and the extremity performing dominantly across tests. Significant asymmetry magnitudes (p < 0.05) were found for all upper and lower extremity lean mass and functional values. No relationship was apparent between lean mass and functional asymmetry magnitudes (p-value range = 0.131–0.889). Despite finding perfect consistency in asymmetry direction (k-value = 1.00) for the upper extremity, poor to fair consistency (k-value range = −0.00–0.21) was found for the lower extremity. In conclusion, lean mass and functional asymmetries should be examined independently.

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.

Influence of jump-landing direction on dynamic postural stability and hamstring-to-quadriceps co-activation ratio

This study investigated the effect of jump landing direction and leg dominance on the Dynamic Postural Stability Index (DPSI) and the importance of the hamstring-to-quadriceps (H/Q) co-activation ratio. Fifteen female sports players performed unilateral jump landing, for the dominant (DL) and the non-dominant (NDL) legs in anterior (AJL), lateral (LJL), and vertical directions (DJL). The results indicated that the DPSI was higher in DJL compared to LJL and AJL. Besides, the DPSI score during DJL was higher in NDL indicating lower stabilization capacity associated with a lower H/Q co-activation ratio. A significant correlation was found between H/Q co-activation ratio and DPSI in the DL during AJL (r = -0.57). Current results suggest that DJL was more appropriate to evaluate dynamic postural stability since it highlights limb asymmetry. In addition, H/Q co-activation appears to play an essential role in the effectiveness of ground reaction force stabilization during jump landing.

Do the quadriceps and hamstring muscles have an effect on patella stability in trochlear dysplasia?

Introduction

Trochlear dysplasia (TD) is a condition that is characterized by the presence of either a flat or convex trochlear, which impedes the stability of the patellofemoral joint (PFJ). The PFJ function is dependent on many different structures that surround the knee joint. The aim of this study was to analyse all the muscle components around the PFJ and identify whether gross muscle imbalance could contribute to the stability of the patella in TD.

Material and methods

The average cross-sectional area (CSA) and cross-sectional area ratio (CSAR) of each muscle of the thigh region in subtypes of TD was evaluated and compared to normal knee joints. Ninety-eight patients (196 knees in total) were included in the study.

Results

Of the 196 knee joints that were reviewed, 10 cases were found to be normal. In total, 186 cases were positive for TD. The majority consisted of type C. The hamstring muscles showed variable results. The vastus medialis muscle was larger in comparison to the vastus lateralis muscle over all the different TD subtypes; however, no statistical significance was identified. There was a marked statistical significance between the quadriceps and hamstring muscles, especially when comparing this to the normal knees within our cohort.

Conclusions

This study revealed no significant difference in the effect of the thigh muscle CSA on the stability of the PFJ in TD. Further research is required to establish the roles of the different muscles around PFJ in the prevention of TD dislocation.

Contribution of Lower Extremity Joints on Energy Absorption during Soft Landing

Soft landing after jumping is associated with the prevention of lower extremity injuries during sports activities in terms of the energy absorption mechanisms. In this study, the contribution of lower extremity joints during soft landing was investigated. Subjects comprised 20 healthy females. Kinetics and kinematics data were obtained during drop vertical jumps using a three-dimensional motion analysis system. Negative mechanical work values in the lower extremity joints were calculated during landing. A multiple regression analysis was performed to determine which lower extremity joints contributed more in achieving soft landing. The means of mechanical work of the hip, knee, and ankle in the sagittal plane were −0.30 ± 0.17, −0.62 ± 0.31, and −1.03 ± 0.22 J/kg, respectively. Results showed that negative mechanical work in the hip and knee is effective in achieving soft landing. These findings indicate that energy absorption in the hip and knee joints might be an important factor in achieving soft landing, whereas that in the ankle has a negative effect. Therefore, when improving soft landing techniques, we should consider energy absorption in the hip and knee via eccentric activation of the hip and knee extensors during landing.

The effects of a high-intensity exercise bout on landing biomechanics post anterior cruciate ligament reconstruction: a quasi-experimental study

Background

We aimed to examine the effect of a high-intensity exercise bout on landing biomechanics in soccer players who underwent anterior cruciate ligament reconstruction (ACLR) and non-injured soccer players during a soccer-specific landing maneuver.

Methods

Eighteen soccer players who underwent ACLR and 18 normal soccer players were enrolled in this investigation (ACLR group; age, 26.11 ± 3.95 years; body mass index, 23.52 ± 2.69 kg/m²; surgery time, 5 ± 3.30 years: control group; age, 25.83 ± 3.51 years; body mass index, 24.09 ± 3.73 kg/m², respectively). Participants were evaluated during the landing maneuver before and after carrying out the high-intensity exercise bout using the Wingate test. The intensity of the exercise was defined as a blood lactate accumulation of at least 4 mmol/L. The dependent variables included sagittal-plane kinematics and kinetics of the ankle, knee and hip joints, and electromyography activity of the gastrocnemius, hamstrings, quadriceps, and gluteus maximus.

Results

On 2 × 2 analysis of variance, none of the dependent variable showed significant exercise×group interactions. Regardless of group, significant main effects of exercise were found. Post-exercise landing was characterized by increased flexion of hip (p = 0.01), knee (p = 0.001), and ankle joints (p = 0.002); increased extension moments of hip (p = 0.009), knee (p = 0.012), and ankle joints (p = 0.003), as well as decreased quadriceps activity (p = 0.007).

Conclusion

At 1 year or more post-ACLR, the effect of the high-intensity exercise bout on landing biomechanics is not expected to differ from that experienced by healthy soccer players.

Effects of a wearable device and functional wear on spinal alignment and jump performance

Background/objective

To elucidate the effects of walking exercise using a wearable device and functional wear on spinal alignment and jump performance.

Methods

In total, 27 female college soccer players were randomly divided into two groups: trunk solution (TS) and compression garments (CGs). Spinal alignment, jump performance, and electromyography activity during the jump performance of the two groups were measured after a 20-min walking exercise. The values for each group were compared t pre- and post-intervention.

Results

The flexibility of the lower thoracic vertebrae in spinal alignment was increased during extension in the TS group. However, the post-value of the abdominal external oblique muscle during a countermovement jump (CMJ) was significantly lower than its pre-value (p < 0.05). In addition, even though spinal alignment was not affected in the CG group, post-values of the jump height during squat jump and CMJ were significantly higher than their pre-values (p < 0.05). Furthermore, the post-value of the biceps femoris during the countermovement jump with arm was significantly lower than its pre-value (p < 0.05).

Conclusion

Our study suggested that walking exercise using TS may increase the range of motion of the lower thoracic vertebrae in athletes and reduce the muscular activity of the vastus lateralis during CMJ. Additionally, although spinal aliment is not affected, the jump height may increase using CGs.

Association of Compartmental Leg Lean Mass Measured by Dual X-Ray Absorptiometry With Force Production

Raymond-Pope, CJ, Dengel, DR, Fitzgerald, JS, and Bosch, TA. Association of compartmental leg lean mass measured by dual X-ray absorptiometry with force production. J Strength Cond Res 34(6): 1690-1699, 2020-We recently reported a novel method for measuring upper leg anterior/posterior compartmental composition. The purpose of this study was to determine the association of this method with measures of muscle-specific and explosive strength and to compare this method with traditional dual energy X-ray absorptiometry (DXA) measurements of total and upper leg masses. We hypothesize this method will be related to muscle-specific strength measured by isokinetic dynamometry and explosive strength measured by jump mechanography. Nineteen NCAA Division I college athletes (10 women; age = 20.4 ± 1.4 years; height = 1.8 ± 0.1 m; body mass = 73.8 ± 17.0 kg) underwent 3 DXA scans (1 total body, 2 lateral) and knee extension/flexion strength assessment using isokinetic dynamometry at 3 velocities (60, 120, and 180°·s). A subset of 10 participants also completed a squat jump on a force platform on a different day. Pearson correlations compared 3 separate lean soft-tissue mass (LSTM) regions of interest (total leg, upper leg, and compartmental leg) with (a) isokinetic peak torque and (b) squat jump height, peak force, and peak and average rate of force development. Compartmental leg LSTM demonstrated similar correlations (r = 0.437-0.835) with peak torque in comparison with total leg (r = 0.463-0.803) and upper leg (r = 0.449-0.795) LSTM. Summed right and left total leg (r = 0.830-0.940), total upper leg (r = 0.824-0.953), and anterior (r = 0.582-0.798) and posterior (r = 0.750-0.951) compartmental leg LSTM demonstrated moderate-to-strong correlations with all squat jump variables, particularly jump height (p < 0.05). The lateral segmentation DXA scanning method demonstrated feasibility in assessing compartmental leg LSTM in relation with isokinetic and squat jump measurements-important outcomes when examining an athlete's response to training and rehabilitation.

Differences in Gluteal and Quadriceps Muscle Activation Among Adults With and Without Lumbar Hyperlordosis

Context:Many factors have been reported contributing to altering the neuromuscular function of hip and knee muscles. The lumbar hyperlordosis, as a poor posture in some athletes, is thought to be associated with the alteration of the hip and knee muscles activity.Objective:To examine the activation of selected hip and knee muscles in athletes with and without lumbar hyperlordosis during functional activities.Design:Case-control study.Setting:University laboratory.Participants:Twenty-six college male athletes (n = 13 with and n = 13 without lumbar hyperlordosis).Interventions:Surface electromyography of gluteus maximus (GMAX), gluteus medius (GMED), vastus medialis oblique (VMO), and vastus lateralis (VL) were recorded during single-leg squat and single-leg jump landing (SLJL) tasks.Main Outcome Measure:Preactivity; reactivity; and onset muscle during SLJL and eccentric activity during single-leg squat (GMAX, GMED, VMO, and VL along with the ratio of VMO:VL) were assessed.Results:Athletes with lumbar hyperlordosis had a higher level of activity in their GMAX (P = .003), VMO (P = .04), and VL (P = .01) muscles at the moment before foot contact during SLJL. These athletes also demonstrated a higher level of GMAX activity (P = .01) immediately after foot contact. Finally, athletes with lumbar hyperlordosis activated their GMAX sooner (P = .02) during the SLJL. Athletes with normal lumbar lordosis had more activity in their GMED muscle (P = .001) in the descending phase of the single-leg squat task and a higher VMO:VL (P = .01) at the moment after the foot contact during the SLJL.Conclusion:The altered activation of GMAX, GMED, VMO, VL, and VMO:VL can reveal the role of lumbar hyperlordosis in the knee and hip muscles’ alteration in athletes. Further study is needed to identify whether these alterations in the hip and knee muscles contribute to injury in athletes.

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.

Landing Evaluation in Soccer Players with or without Anterior Cruciate Ligament Reconstruction

The purpose of this study was to evaluate landing biomechanics in soccer players following ACLR during two landing tasks. Eighteen soccer players with an ACLR and 18 sex-matched healthy control soccer players participated in the study. Planned landing included jumping forward and landing on the force-plates, whereas unplanned landing included jumping forward to head a soccer ball and landing on the force-plates. A significant landing×group interaction was found only for knee flexion angles (p=0.002). Follow-up comparisons showed that the ACL group landed with greater knee flexion during planned landing compared with unplanned landing (p<0.001). Significant main effects of landing were found. The unplanned landing showed reduction in hip flexion (p<0.001), hip extension moments (p<0.013), knee extension moments (p<0.001), and peak pressure (p<0.001). A significant main effect for group for gastrocnemius muscle was found showing that the ACL group landed with reduced gastrocnemius activity (p=0.002). Unplanned landing showed greater injury predisposing factors compared with planned landing. The ACL group showed nearly similar landing biomechanics to the control group during both landing tasks. However, the ACL group used a protective landing strategy by reducing gastrocnemius activity.

Distalising tibial tubercle osteotomy decreases patellar tendon force - A treatment rationale for recalcitrant patellar tendinopathy

BACKGROUND

Patellar tendinopathy is an overuse condition affecting athletes, often with a high morbidity if left untreated. High-level evidence fails to support the use of surgery. A tibial tubercle osteotomy (TTO) has been suggested as a surgical option to improve patient outcomes. Our aim was to explore whether a distalising TTO will alter the patellar tendon to quadriceps tendon force ratio and the sagittal patellar tilt.

METHODS

Six cadaver limbs were placed in a custom jig with a mechanical testing machine applying cyclical loads of 200-500 N to the quadriceps tendon. The knee was fixed at 0, 15, 30, 45, 60, 75 and 90° of flexion and a buckle transducer recorded the resultant patellar tendon force. Testing was performed with the native tibial tubercle position and with the tubercle distalised by 11 mm. Testing was also performed with the tubercle anteriorised by 10 mm at both of these tubercle positions, a total of four different testing positions.

RESULTS

There was a significant decrease in the patellar tendon to quadriceps tendon force ratio from 30-60° of knee flexion. There was a significant increase in the sagittal patellar tilt at 30° of knee flexion with distalisation.

CONCLUSION

This biomechanical study shows that the patellar tendon to quadriceps tendon force ratio can be altered with a distalising tibial tubercle osteotomy. A tibial tubercle osteotomy may be a biomechanical treatment option for recalcitrant patellar tendinopathy by decreasing the load through the patellar tendon, allowing the athlete to maintain higher training volumes and loads.

Impaired Knee Muscle Capacity Is Correlated With Impaired Sagittal Kinematics During Jump Landing in Women With Patellofemoral Pain

Nunes, GS, Barton, CJ, and Serrão, FV. Impaired knee muscle capacity is correlated with impaired sagittal kinematics during jump landing in women with patellofemoral pain. J Strength Cond Res XX(X): 000-000, 2020-Knee and hip muscle capacity is impaired in women with patellofemoral pain (PFP), but little is known about the rate of force development (RFD) at the knee. Impaired muscle capacity may contribute to reduced sagittal plane movement at the knee and hip during jump landing in women with PFP. This study aimed to (a) compare knee extensor muscle capacity (including RFD), and hip abductor and extensor muscle capacity between women with and without PFP; and (b) evaluate the relationship between hip/knee muscle capacity and sagittal kinematics during single-legged drop jump landing in women with PFP. Fifty-two physically active women (26 with PFP and 26 controls) participated. Rate of force development (in %/ms), isometric, concentric, and eccentric torque (in N·m·kg × 100) were evaluated using isokinetic dynamometry, and knee and hip kinematics were evaluated using three-dimensional motion capture. Compared with the control group (CG), the PFP group (PFPG) presented lower isometric (12%, PFPG = 217.2 ± 46.0; CG = 246.5 ± 38.8; p = 0.02), concentric (21%, PFPG = 133.0 ± 42.6; CG = 169.2 ± 28.8; p < 0.01), and eccentric (17%, PFPG = 172.9 ± 56.7; CG = 208.4 ± 59.4; p = 0.03) knee extension torque; lower RFD until 30% (30%, PFPG = 0.57 ± 0.27; CG = 0.83 ± 0.37; p < 0.01) and 60% (31%, PFPG = 0.47 ± 0.24; CG = 0.67 ± 0.33; p = 0.01) of maximal isometric torque; and lower concentric hip abduction (13%, PFPG = 94.7 ± 19.1; CG = 108.4 ± 17.5; p = 0.01) and extension (17%, PFPG = 134.4 ± 34.3; CG = 162.6 ± 38.0; p < 0.01) torque. Significant correlations between reduced RFD for knee extension and reduced sagittal plane knee/hip range of motion during landing were identified (r = 0.39-0.49). In conclusion, women with PFP have impaired knee extensor isometric and dynamic strength, and RFD. Impaired knee extensor RFD is associated with a stiffer landing strategy (reduced movement).

Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport

OBJECTIVE

To systematically review risk factors for hamstring strain injury (HSI).

DESIGN

Systematic review update.

DATA SOURCES

Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI.

METHOD

Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI.

RESULTS

The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury.

SUMMARY/CONCLUSION

Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.

Muscle Strength Training Alters Muscle Activation of the Lower Extremity during Side-Step Cutting in Females

The objective of this study was to examine the effects of muscle strength training on knee kinematics/kinetics and muscle activation patterns during anticipated side-step cutting. Three-dimensional knee kinematics/kinetics data and muscle activation of selected lower extremity muscles were measured while performing cutting before and after completing 10-week circuit strength training mixed typical resistance training and power training (intervention) or no training (control) from 25 female subjects. The muscle strength of quadriceps and hamstrings were measured before and after training using isokinetic dynamometer. No statistically significant differences were observed in quadriceps and hamstrings muscle strength, all kinematic/kinetic variables, and muscle activation for the control group. Both quadriceps (p = 0.005) and hamstrings (p = 0.030) muscle strength were increased after training. An increased biceps femoris (p = 0.003) and H:Q ratio of activation (p = 0.016), as well as decreased gastrocnemius muscle activation (p = 0.012) during pre-activation phase in intervention group were found. No significant differences were found in knee kinematics and kinetics both at the time frame of the initial contact and the peak tibial anterior shear force after training. In conclusion, muscle strength training altered some muscle activations of lower extremity muscles, which might affect the risk of ACL injury, but it did not change the kinematic/kinetic parameters.

Relationship between electromyographic activity of knee joint muscles with vertical and posterior ground reaction forces in anterior cruciate ligament reconstructed patients during a single leg vertical drop landing task

The objective of the present study is to examine the relation between activity patterns of knee joint muscles with vertical and posterior ground reaction forces (VGRF and PGRF, respectively) in patients after anterior cruciate ligament reconstruction (ACLR). Twenty males post-ACLR participated in this cross-sectional study. The association between muscle activity with VGRF and PGRF was assessed during a single leg vertical drop-landing task. There were strong negative associations between preparatory VL, VM and MG activity and PGRF (P< 0.05). Strong positive associations were found between reactive VM and LH activity with PGRF (P< 0.05). Preparatory co-activation of VM: MH had significant negative associations with VGRF (P< 0.05) and reactive co-activation of VL:LH had a significant positive relation with PGRF(P< 0.05). Greater preparatory activity and co-activation of knee muscles were associated with lower peak PGRF and VGRF, whereas greater reactive activity and co-activation of knee muscles was associated with greater peak PGRF and VGRF. According to our findings, both activity and co-activation of knee muscles during the preparatory phase were associated with reduced PGRF and VGRF, respectively in ACLR patients; thus, incorporating exercises in order to increase preparatory activity and co-activation of knee joint muscles into rehabilitation programs in ACLR patients seems necessary.

Effect of muscle mass asymmetric between upper and lower limbs on the postural stability and shock attenuation during landing

The aim of the study was to analyze the effect of muscle mass asymmetric between upper and lower limbs on postural stability and shock attenuation during landing. Twenty adults (without lower limb disorders and who could land from a 35-cm height) participated in this study (mean age, 21.85±2.97 years; mean height, 1.68±0.10 m; mean weight: 68.64±17.36 kg). Subjects performed one-leg landing from 36-cm vertical heights. Ground reaction force components and medial-lateral, anterior-posterior, vertical and dynamic postural stability index were obtained from force platform recordings. We found that muscle mass in right limbs more increased than that of left limbs. Medial-lateral force, vertical force, vertical stability index, and dynamic postural stability index in left leg showed higher value than that of right leg during landing. The asymmetry of muscle mass (%) and ground reaction force variables showed a similar correlation, including dynamic postural stability index (r=0.316). These findings allow us to conclude that the factor of muscle mass asymmetric is a contributor to impulse control and dynamic postural stability index asymmetry. Therefore, knowledge of bilateral limbs asymmetry may provide insights into exercise rehabilitation and performance.

Intra-rater reliability and criterion-related validity of using an accelerometer to measure the impact force and knee joint sway during single-leg drop landing

[Purpose] This study aimed to clarify the reliability and validity of the impact force and knee joint sway measurement during single-leg drop landing by using a motion sensor with two built-in accelerometers. [Participants and Methods] Ten healthy college students (4 males and 6 females) who joined a basketball club participated in this study. Peak vertical acceleration, time between initial contact and peak vertical acceleration, and knee joint mediolateral sway were measured using the accelerometer during the landing motion. Reliability of the measurement with the accelerometer and the criterion-related validity between the accelerometer and force plate data were examined. [Results] The intraclass correlation coefficients indicated a peak vertical acceleration of 0.88, time between initial contact and peak vertical acceleration of 0.96, and knee joint mediolateral sway of 0.62. The magnitude and timing of the peak values between both measurement instruments showed high validity. [Conclusion] The measurement method using a motion sensor for the evaluation of the impact force and knee joint sway during landing has a moderate to high reliability and criterion-related validity. A motion sensor measurement might be a useful and easy method for evaluating landing impact force and knee joint stability.

Effects of Small-Sided Game Variation on Changes in Hamstring Strength

Madison, G, Patterson, SD, Read, P, Howe, L, and Waldron, M. Effects of small-sided game variation on changes in hamstring strength. J Strength Cond Res 33(3): 839-845, 2019-Small-sided games (SSGs) are commonly used by soccer practitioners to condition players. This form of exercise can result in fatigue, potentially exposing the muscle to injury risk. The purpose of this study was to determine the effects of SSG variations on hamstring torque in semiprofessional soccer players. In a counterbalanced cross-over design, 10 male semiprofessional soccer players took part in both small relative area (3 vs. 3; 300 m) and large relative area (4 vs. 4; 1000 m) SSGs. The games comprised 6 × 4-minute bouts, with 90-second recovery. Both movement and heart rate responses were monitored by global positioning systems (GPS) and hamstring isometric torque was measured pre-training and post-training using a NordBord. There were differences (p < 0.05) between the small and large relative area games for peak hamstring force decrement (5.78 N and -13.62 N, respectively) and mean hamstring force decrement at 90° (11.11 N and -4.78 N, respectively). The number of accelerations was related to (r = 0.46, p = 0.039) reduced hamstring peak torque at 90°. In conclusion, larger relative area SSGs elicited the greatest internal and external loads, resulting in decrements in hamstring force. The number of accelerations performed in the session increases the likelihood of hamstring fatigue and can be controlled with the relative pitch area.

Females with patellofemoral pain have impaired impact absorption during a single-legged drop vertical jump

BACKGROUND

Females with patellofemoral pain (PFP) have been reported to land with altered biomechanics in some, but not all studies. Kinematic alterations previously reported may indicate, and relate to potential impairments in absorbing impact.

RESEARCH QUESTION

To compare vertical ground reaction force (vGRF) and lower limb kinematics during single-legged drop vertical jumps in females with and without PFP; and establish the relationship between vGRF and kinematics during this task.

METHODS

Fifty-two physically active females (26 with PFP and 26 controls) participated in the present cross-sectional study. Peak of vGRF was evaluated during landing; and lower limb kinematics in the sagittal and frontal planes during deceleration (landing) and acceleration (take-off) phases were evaluated.

RESULTS

The PFP group had 11% greater vGRF (p < 0.01); and 13-24% lower hip, knee and ankle excursion in the sagittal plane during acceleration and deceleration phases (p ≤ 0.02) compared to the control group. No significant between group differences (p > 0.05) for hip, knee and ankle excursion in the frontal plane were identified. Greater impact was significantly correlated with reduced knee (r = -0.56), hip (r = -0.50) and ankle (r = -0.41) excursion in the sagittal plane during the acceleration phase in the control group, but not in the PFP group. No significant correlations were found between vGRF and kinematics variables during the deceleration phase in either group.

SIGNIFICANCE

Impaired ability to absorb load and reduced lower limb movement in the sagittal plane during landing in females with PFP may provide separate treatment targets during rehabilitation.

Comparison the time to stabilization and activity of the lower extremity muscles during jump-landing in subjects with and without Genu Varum

BACKGROUND

Knee muscles activity changes from Genu Varum deformity(GVD), may cause this individual more exposed to lower extremity injuries especially in high-risk activities like landing.

OBJECTIVE

The aim of this study was to compare the activity of the lower limb stabilizer muscles during jump-landing and time to stabilization(TTS) in subjects with and without GVD.

METHOD

A total of 44 men (group 1, with GVD n = 22 and group 2, without GVD n = 22); with mean age = 17.6 ± 3.12 years, height = 178.2 ± 5.39 cm, mass = 80.39 ± 8.3 kg) participated in this study. Subjects were asked to do a jump-landing task and Quadratus Lumborum(QL), Gluteus Maximus(GMax), Gluteus Medius(GMed), Biceps Femoris (BF), Semitendinosus, and Medial Gastrocnemius(MG) muscles activity was recorded. Also, changes in the amount of ground reaction force(GRF) were used to an indicator for TTS.

RESULTS

Our results showed that subjects with GVD had increased QL activity before(P = 0.008) and after(P = 0.017) landing. But, these subjects had a decreased activity of GMed compared to the healthy ones before(P = 0.033) and after(P = 0.005) landing. but there was no statistically significant difference before landing in gluteus maximus(P = 0.252), biceps femoris(P = 0.613), semitendinosus(P = 0.313), and medial gastrocnemius(P = 0.140) muscles and after landing in gluteus maximus (P = 0.246), biceps femoris(P = 0.512), semitendinosus(P = 0.214), and medial gastrocnemius(P = 0.209) muscles between the two groups. Also, the TTS was higher in subjects with GV than healthy ones in the Resultant Vector TTS (P = 0.015) and medial-lateral(P = 0.013) directions.

CONCLUSIONS

The altered activity of the QL and GMed, in subjects with GVD may indicate instability of the spinal column, pelvis and hip during jump-landing task. Although the GVD is referred to the frontal plane deformity, the results showed that this complication might affect stability in other motion planes.

Limb-dominance and gender differences in the ground reaction force during single-leg lateral jump-landings

[Purpose] The purpose of this study was to examine limb-dominance and gender differences in the magnitude of the ground reaction force during single-leg lateral jump-landings. We hypothesized that the peak ground reaction force would be larger in the non-dominant leg compared to that in the dominant leg and would be larger in females compared to that in men. [Subjects and Methods] Fifteen females and 15 males performed jump-landings sideways from a height of 20 cm, with a lateral distance of 60 cm. Vertical and medial ground reaction forces were measured, and the elapsed time from the initial contact to the peak ground reaction force was determined. The loading rate was calculated as the peak ground reaction force divided by the elapsed time from the initial contact to the peak ground reaction force. [Results] The vertical and medial peak ground reaction forces during single-leg lateral jump-landings were larger in females compared to that in males. In addition, the medial peak ground reaction force was larger for the non-dominant leg compared to that for the dominant leg. [Conclusion] The results suggest that in rehabilitation and conditioning settings, evaluations and instructions regarding attenuation are especially important for females and the non-dominant leg.

Quadriceps Neuromuscular Function and Jump-Landing Sagittal-Plane Knee Biomechanics After Anterior Cruciate Ligament Reconstruction

CONTEXT

  Aberrant biomechanics may affect force attenuation at the knee during dynamic activities, potentially increasing the risk of sustaining a knee injury or hastening the development of osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Impaired quadriceps neuromuscular function has been hypothesized to influence the development of aberrant biomechanics.

OBJECTIVE

  To determine the association between quadriceps neuromuscular function (strength, voluntary activation, and spinal-reflex and corticomotor excitability) and sagittal-plane knee biomechanics during jump landings in individuals with ACLR.

DESIGN

  Cross-sectional study.

SETTING

  Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Twenty-eight individuals with unilateral ACLR (7 men, 21 women; age = 22.4 ± 3.7 years, height = 1.69 ± 0.10 m, mass = 69.4 ± 10.1 kg, time postsurgery = 52 ± 42 months).

MAIN OUTCOME MEASURE(S)

  We quantified quadriceps spinal-reflex excitability via the Hoffmann reflex normalized to maximal muscle response (H : M ratio), corticomotor excitability via active motor threshold, strength as knee-extension maximal voluntary isometric contraction (MVIC), and voluntary activation using the central activation ratio (CAR). In a separate session, sagittal-plane kinetics (peak vertical ground reaction force [vGRF] and peak internal knee-extension moment) and kinematics (knee-flexion angle at initial contact, peak knee-flexion angle, and knee-flexion excursion) were collected during the loading phase of a jump-landing task. Separate bivariate associations were performed between the neuromuscular and biomechanical variables.

RESULTS

  In the ACLR limb, greater MVIC was associated with greater peak knee-flexion angle ( r = 0.38, P = .045) and less peak vGRF ( r = -0.41, P = .03). Greater CAR was associated with greater peak internal knee-extension moment (ρ = -0.38, P = .045), and greater H : M ratios were associated with greater peak vGRF ( r = 0.45, P = .02).

CONCLUSIONS

  Greater quadriceps MVIC and CAR may provide better energy attenuation during a jump-landing task. Individuals with greater peak vGRF in the ACLR limb possibly require greater spinal-reflex excitability to attenuate greater loading during dynamic movements.

Epidemiology of Quadriceps Strains in National Collegiate Athletic Association Athletes, 2009-2010 Through 2014-2015

CONTEXT

  Few researchers have examined the rates and patterns of quadriceps strains in student-athletes in the National Collegiate Athletic Association (NCAA).

OBJECTIVE

  To describe the epidemiology of quadriceps strains in 25 NCAA sports during the 2009-2010 through 2014-2015 academic years.

DESIGN

  Descriptive epidemiology study.

SETTING

  Convenience sample of NCAA programs from 25 sports during the 2009-2010 through 2014-2015 academic years. Patients or Other Particpants:  Collegiate student-athletes participating in men's and women's NCAA athletics during the 2009-2010 through 2014-2015 academic years.

MAIN OUTCOME MEASURE(S)

  Aggregate quadriceps strain injury and exposure data from the NCAA Injury Surveillance Program during the 2009-2010 through 2014-2015 academic years were analyzed. Quadriceps strain injury rates and injury rate ratios (IRRs) were reported with 95% confidence intervals (CIs).

RESULTS

  Overall, 517 quadriceps strains were reported, resulting in an injury rate of 1.07/10 000 athlete-exposures (AEs). The sports with the highest overall quadriceps strain rates were women's soccer (5.61/10 000 AEs), men's soccer (2.52/10 000 AEs), women's indoor track (2.24/10 000 AEs), and women's softball (2.15/10 000 AEs). Across sex-comparable sports, women had a higher rate of quadriceps strains than men overall (1.97 versus 0.65/10 000 AEs; IRR = 3.03; 95% CI = 2.45, 3.76). The majority of quadriceps strains were sustained during practice (77.8%). However, the quadriceps strain rate was higher during competition than during practice (1.29 versus 1.02/10 000 AEs; IRR = 1.27; 95% CI = 1.03, 1.56). Most quadriceps strains occurred in the preseason (57.8%), and rates were higher during the preseason compared with the regular season (2.29 versus 0.63/10 000 AEs; IRR = 3.60; 95% CI = 3.02, 4.30). Common injury mechanisms were noncontact (63.2%) and overuse (21.9%). Most quadriceps strains restricted participation by less than 1 week (79.3%).

CONCLUSIONS

  Across 25 sports, higher quadriceps strain rates were found in women versus men, in competitions versus practices, and in the preseason versus the regular season. Most quadriceps strains were minor in severity, although further surveillance is needed to better examine the risk factors associated with incidence and severity.

Unilateral jumps in different directions: a novel assessment of soccer-associated power?

OBJECTIVES

We aimed to determine whether countermovement jumps (CMJs; unilateral and bilateral) performed in different directions assessed independent lower-limb power qualities, and if unilateral CMJs would better differentiate between elite and non-elite soccer players than the bilateral vertical (BV) CMJ.

DESIGN

Elite (n=23; age, 18.1±1.0years) and non-elite (n=20; age, 22.3±2.7years) soccer players performed three BV, unilateral vertical (UV), unilateral horizontal-forward (UH) and unilateral medial (UM) CMJs.

METHODS

Jump performance (height and projectile range), kinetic and kinematic variables from ground reaction forces, and peak activation levels of the vastus lateralis and biceps femoris (BF) muscles from surface electromyography, were compared between jumps and groups of players.

RESULTS

Peak vertical power (V-power) was greater in BV (220.2±30.1W/kg) compared to UV (144.1±16.2W/kg), which was greater than UH (86.7±18.3W/kg) and UM (85.5±13.5W/kg) (all, p<0.05) but there was no difference between UH and UM (p=1.000). Peak BF EMG was greater in UH compared to all other CMJs (p≤0.001). V-power was greater in elite than non-elite for all CMJs (p≤0.032) except for BV (p=0.197). Elite achieved greater UH projectile range than non-elite (51.6±15.4 vs. 40.4±10.4cm, p=0.009).

CONCLUSIONS

We have shown that UH, UV and UM CMJs assess distinct lower-limb muscular power capabilities in soccer players. Furthermore, as elite players outperformed non-elite players during unilateral but not BV CMJs, unilateral CMJs in different directions should be included in soccer-specific muscular power assessment and talent identification protocols, rather than the BV CMJ.

Correlations between sagittal plane kinematics and landing impact force during single-leg lateral jump-landings

[Purpose] The correlations of peak vertical ground reaction force and sagittal angles during single-leg lateral jump-landing with noncontact anterior cruciate ligament injury remain unknown. This study aimed to clarify the correlations between kinematics and impact force during lateral jump-landing. [Subjects and Methods] Twenty active males were included in the analysis. A sagittal-view movie camera and force plate were time synchronized. Trunk and lower extremity sagittal angles were measured 100 ms before initial contact and at peak vertical ground reaction force. Peak vertical ground reaction force, time between initial contact and peak vertical ground reaction force, and loading rate were calculated. [Results] The mean sagittal angle was 40.7° ± 7.7° for knee flexion during the flight phase and 16.4° ± 6.3° for pelvic anterior inclination during the landing phase. The mean peak vertical ground reaction force was four times the body weight. The median time to peak vertical ground reaction force was 63.8 ms. The knee flexion during the flight phase and pelvic anterior inclination angles during the landing phase were related to the peak vertical ground reaction force. [Conclusion] Increasing knee flexion and decreasing pelvic anterior inclination might reduce the impact during single-leg lateral jump-landing.

Mapping current research trends on neuromuscular risk factors of non-contact ACL injury

The aim of this systematic review was (i) to identify neuromuscular markers that have been predictive of a primary non-contact ACL injury, (ii) to assess whether proposed risk factors have been supported or refuted in the literature from cohort and case-control studies, and (iii) to reflect on the body of research that aims at developing field based tools to assess risk through an association with these risk factors. Electronic searches were undertaken, of PubMed, SCOPUS, Web of Science, CINAHL and SPORTDiscus examining neuromuscular risk factors associated with ACL injury published between January 1990 and July 2015. The evidence supporting neuromuscular risk factors of ACL injury is limited where only 4 prospective cohort studies were found. Three of which looked into muscular capacity and one looked into muscular activation patterns but none of the studies found strong evidence of how muscular capacity or muscular activation deficits are a risk factor for a primary non-contact ACL injury. A number of factors associated to neural control and muscular capacity have been suggested to be related to non-contact ACL injury risk but the level of evidence supporting these risk factors remains often elusive, leaving researchers and practitioners uncertain when developing evidence-based injury prevention programs.

Knee and Hip Joint Kinematics Predict Quadriceps and Hamstrings Neuromuscular Activation Patterns in Drop Jump Landings

Purpose

The purpose was to assess if variation in sagittal plane landing kinematics is associated with variation in neuromuscular activation patterns of the quadriceps-hamstrings muscle groups during drop vertical jumps (DVJ).

Methods

Fifty female athletes performed three DVJ. The relationship between peak knee and hip flexion angles and the amplitude of four EMG vectors was investigated with trajectory-level canonical correlation analyses over the entire time period of the landing phase. EMG vectors consisted of the {vastus medialis(VM),vastus lateralis(VL)}, {vastus medialis(VM),hamstring medialis(HM)}, {hamstring medialis(HM),hamstring lateralis(HL)} and the {vastus lateralis(VL),hamstring lateralis(HL)}. To estimate the contribution of each individual muscle, linear regressions were also conducted using one-dimensional statistical parametric mapping.

Results

The peak knee flexion angle was significantly positively associated with the amplitudes of the {VM,HM} and {HM,HL} during the preparatory and initial contact phase and with the {VL,HL} vector during the peak loading phase (p<0.05). Small peak knee flexion angles were significantly associated with higher HM amplitudes during the preparatory and initial contact phase (p<0.001). The amplitudes of the {VM,VL} and {VL,HL} were significantly positively associated with the peak hip flexion angle during the peak loading phase (p<0.05). Small peak hip flexion angles were significantly associated with higher VL amplitudes during the peak loading phase (p = 0.001). Higher external knee abduction and flexion moments were found in participants landing with less flexed knee and hip joints (p<0.001).

Conclusion

This study demonstrated clear associations between neuromuscular activation patterns and landing kinematics in the sagittal plane during specific parts of the landing. These findings have indicated that an erect landing pattern, characterized by less hip and knee flexion, was significantly associated with an increased medial and posterior neuromuscular activation (dominant hamstrings medialis activity) during the preparatory and initial contact phase and an increased lateral neuromuscular activation (dominant vastus lateralis activity) during the peak loading phase.

THE USE OF FUNCTIONAL TESTS TO PREDICT SAGITTAL PLANE KNEE KINEMATICS IN NCAA-D1 FEMALE ATHLETES

BACKGROUND

Landing with the knee in extension places increased loads on ligamentous restraints at the knee versus landing in flexion. Unfortunately, existing methods to predict landing kinematics require sophisticated equipment and expertise. The purpose of this study was to develop predictive models for sagittal plane tibiofemoral landing kinematics from the results of functional tests.

METHODS

Twenty-nine female, NCAA-D1 college athletes (mean ± standard deviation, age = 19.03 ± 1.09; mass=66.56 ± 13.47 kg; height = 171.16 ± 7.92 cm) participated in a descriptive, laboratory study. Participants performed five unilateral, dominant lower extremity (LE) landings from a 35cm platform onto a forceplate. LE three-dimensional kinematics were captured with electromagnetic sensors interfaced with motion analysis software. Then in a randomized order, participants performed three standardized functional tests: single limb triple hop (SLTH), countermovement vertical jump (CMVJ) and the Margaria-Kalamen (MK) test. Sagittal plane tibiofemoral joint angle at initial contact (IC) and excursion (EXC) in the first 0.1s after ground contact were entered into a statistical software package. Multiple linear regression analyses generated one model predicting IC and one predicting EXC from the independent variables. Alpha levels were set a priori at p ≤ .05.

RESULTS

A two variable (MK, SLTH) linear regression model that predicted EXC was significant (Adjusted R (2) = .213, p = .017), however the model that predicted IC was not (p = .890).

CONCLUSION

Knee flexion excursion following a single leg landing task may be predicted with the MK and SLTH. The use of functional tests provides a practical means to predict landing kinematics to clinicians working with an active, athletic population.

LEVEL OF EVIDENCE

3, cohort study.

Effects of perturbation training on knee flexion angle and quadriceps to hamstring cocontraction of female athletes with quadriceps dominance deficit: Pre-post intervention study

BACKGROUND

Knee joint stability through co-contraction (CC) of hamstrings and quadriceps may be necessary for females with Quadriceps Dominance (Q.D) neuromuscular deficit. Unbalanced CC of medial and lateral portion of the knee can predispose women to extended knee position that exaggerate ACL injury. The purpose of this study was to determine the effects of perturbation training on knee flexion angle and neuromuscular characteristics in female athletes with quadriceps dominance deficit.

METHODS

EMG data of quadriceps and hamstrings (during single limb drop-landing), and knee flexion angles (during tuck-jump test) of 29 (14 control and 15 experimental) female athletes with quadriceps dominance deficit were completed at baseline and after six weeks. Six weeks of perturbation training in the experimental group was applied over 18 sessions under the supervision of a physiotherapist.

RESULTS

The VL-LH and VM-MH cocontraction in feed-forward and feedback phases significantly increased after perturbation training. Also peak knee flexion angle significantly increased and reaches from 26.24°±3.54° in pretest to 48.92°±6.18° in posttest due to perturbation training effects on Q.D deficit women (p<0.01).

CONCLUSIONS

Finally because the Q.D neuromuscular deficit is one of the important mechanisms of noncontact ACL injuries in female athletes and the effect of perturbation training in solving this problem indicated in this study, so the use of perturbation trainings is recommended to women athlete coaches to eliminate this defect and improve athletic performance (functional tuck jump test).

CLINICAL RELEVANCE

The balanced cocontraction ratios produced after the perturbation training may benefit in anterior cruciate ligament injury-prevention.

Considerations for late stage acl rehabilitation and return to sport to limit re-injury risk and maximize athletic performance

PURPOSE/BACKGROUND

Despite recent advances in anterior cruciate ligament reconstruction (ACL) surgical techniques, an improved understanding of the ACL's biomechanical role, and expanding research on optimal rehabilitation practices in ACL-reconstructed (ACLR) patients, the re-tear rate remains alarmingly high and athletic performance deficits persist after completion of the rehabilitation course in a large percentage of patients. Significant deficits may persist in strength, muscular activation, power, postural stability, lower extremity mechanics, and psychological preparedness. Many patients may continue to demonstrate altered movement mechanics associated with increased injury risk. The purpose of this clinical commentary and literature review is to provide a summary of current evidence to assist the rehabilitation professional in recognizing, assessing, and addressing factors which may have been previously underappreciated or unrecognized as having significant influence on ACLR rehabilitation outcomes.

METHODS

A literature review was completed using PubMed, Medline, and Cochrane Database with results limited to peer-reviewed articles published in English. 136 articles were reviewed and included in this commentary.

CONCLUSIONS

Barriers to successful return to previous level of activity following ACLR are multifactorial.Recent research suggests that changes to the neuromuscular system, movement mechanics, psychological preparedness, and motor learning deficits may be important considerations during late stage rehabilitation.

LEVEL OF EVIDENCE

Level 5- Clinical Commentary.