The effect of sex and fatigue on lower limb kinematics, kinetics, and muscle activity during unanticipated side-step cutting

Differences in Biomechanical Determinants of ACL Injury Risk in Change of Direction Tasks Between Males and Females: A Systematic Review and Meta-Analysis

BACKGROUND

Change of direction (COD) movements are associated with non-contact anterior cruciate ligament (ACL) injuries in multidirectional sports. Females appear at increased risk compared to males, which could be attributable to whole body kinematic strategies and greater multiplanar knee joint loads (KJLs) during COD which can increase ACL loading.

OBJECTIVE

The aim of this systematic review and meta-analysis was to examine and quantitatively synthesise the evidence for differences between males and females regarding KJLs and their biomechanical determinants (whole body kinematic strategies determining KJLs) during COD tasks.

METHODS

Databases including SPORTDiscus, Web of Science, and PubMed were systematically searched (July 2021-June 2023) for studies that compared differences in knee joint loads and biomechanical determinants of KJLs during COD between males and females. Inclusion criteria were: (1) females and males with no prior history of ACL injury (18-40 years); (2) examined biomechanical determinants of KJLs and/ or KJLs during COD tasks > 20°; (3) compared ≥ 1 outcome measure between males and females. Studies published between 2000 and 2023 examining a cutting task > 20° with a preceding approach run that compared KJLs or the whole body multiplanar kinematics associated with them, between sexes, using three-dimensional motion analysis.

RESULTS

This meta-analysis included 17 studies with a pooled sample size of 451 participants (227 males, 224 females). Meta-analysis revealed females displayed significantly less peak knee flexion during stance (SMD: 0.374, 95% CI 0.098-0.649, p = 0.008, I2: 0%); greater knee abduction at initial contact (IC) (SMD: 0.687, 95% CI 0.299-1.076, p = 0.001, I2: 55%); less hip internal rotation (SMD: 0.437, 95% CI 0.134-0.741, p = 0.005, I2: 34%) and hip abduction at IC (SMD: -0.454, 95% CI 0.151-0.758, p = 0.003, I2: 33%). No significant differences were observed between males and females for any internal or externally applied KJLs. All retrieved studies failed to control for strength, resistance training or skill history status.

CONCLUSION

No differences were observed in KJLs between males and females despite females displaying greater knee abduction at IC and less peak knee flexion during the stance phase of CODs, which are visual characteristics of non-contact ACL injury. Further research is required to examine if this translates to a similar injury risk, considering morphological differences in strain characteristics of the ACL between males and females. This observation may in part explain the disproportionate ACL injury incidence in female multidirectional athletes. Further higher quality controlled research is required whereby participants are matched by skill training history, resistance training history and strength status to ensure an appropriate comparison between males and females.

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.

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

Background

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

Purpose

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

Study Design

Cross-sectional study.

Methods

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

Results

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

Conclusion

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

Level of Evidence

3© The Authors.

Synergistic Dominance Induced by Hip Extension Exercise Alters Biomechanics and Muscular Activity During Sprinting and Suggests a Potential Link to Hamstring Strain

ABSTRACT

Iguchi, J, Hojo, T, Fujisawa, Y, Kuzuhara, K, Yanase, K, Hirono, T, Koyama, Y, Tateuchi, H, and Ichihashi, N. Synergistic dominance induced by hip extension exercise alters biomechanics and muscular activity during sprinting and suggests a potential link to hamstring strain. J Strength Cond Res 37(9): 1770-1776, 2023-Hamstring strain is likely to occur during the late swing phase or the first half of the stance phase in sprinting. During the late swing phase, the hamstrings and gluteus maximus (Gmax) contract eccentrically to decelerate the lower limb. We hypothesized that, when the Gmax becomes dysfunctional because of delayed onset muscle soreness (DOMS), the hamstring workload is increased (i.e., there is synergetic dominance), which could lead to an increased risk of strain. A total of healthy 15 male undergraduate or graduate students (age 23.1 ± 1.28 years) were recruited to perform exercises and maximal sprints. On day 1, before subjects performing DOMS-causing exercises, and on day 3, while subjects were experiencing DOMS in the Gmax, lower-limb biomechanical and muscle activity data were recorded using a motion analysis system and electromyography (EMG), respectively. Data were analyzed and compared between day 1 and day 3. Hip flexion angle on day 3 was significantly lower than that on day 1, but the opposite was true for the knee flexion angle (P < 0.05). Vastus medialis (VM), biceps femoris (BF), and Gmax muscle activities on day 3 were significantly higher than those on day 1 (P < 0.05). Peak propulsive forces on day 3 were significantly higher than those on day 1 (P < 0.05). Kinematic changes such as decreased hip flexion angle and EMG changes such as increased BF EMG activity on day 3 to compensate for the loss of function of the Gmax may potentially increase the risk of hamstring strain.

Acute effects of a neuromuscular warm-up on potential re-injury risk factors associated with unanticipated jump landings after anterior cruciate ligament reconstruction: A crossover trial

OBJECTIVE

To investigate acute effects of a single bout of football specific neuromuscular injury preventive warm-up on potential anterior cruciate ligament (ACL) re-injury risk factors during anticipated and unanticipated jump-landings.

DESIGN

Crossover.

METHODS

Fourteen participants (mean ± SD age, 23.4 ± 4.1 years) 6-24 months after ACL reconstruction performed the Prevent Injury and Enhance Performance (PEP) and bicycle ergometer warm-up in a randomised sequence. Washout phase was one week. Countermovement jumps with anticipated and unanticipated single-leg-landings were assessed. Decision-making quality was measured using landing error count.

RESULTS

No carry-over effects occurred (p > 0.05). The unanticipated task produced significantly higher peak ground reaction forces (Δ+4%, F₍₁₁₎ = 3.46, p < 0.001, eta² = 0.21) after PEP warm-up compared to ergometer warm-up. A lower number of decision (Δ+12%, F ₍₅₎ = 17.1, p < 0.001, eta² = 0.57) and cumulated (Δ+15%, F ₍₃₎ = 17.2, p < 0.001, eta² = 0.57) errors were recorded during the unanticipated condition following PEP compared to ergometer warm-up.

CONCLUSIONS

Evaluating unanticipated jump-landing ability prior to return to sports clearance may provide information on potential re-injury risk factors. PEP warm-up may be superior to bicycle ergometer warm-up at improving unanticipated decision-making quality among athletes cleared to return to sports.

Continuous Classification of Locomotion in Response to Task Complexity and Anticipatory State

Objective

Intent recognition in lower-extremity assistive devices (e.g., prostheses and exoskeletons) is typically limited to either recognition of steady-state locomotion or changes of terrain (e.g., level ground to stair) occurring in a straight-line path and under anticipated condition. Stability is highly affected during non-steady changes of direction such as cuts especially when they are unanticipated, posing high risk of fall-related injuries. Here, we studied the influence of changes of direction and user anticipation on task recognition, and accordingly introduced classification schemes accommodating such effects.

Methods

A linear discriminant analysis (LDA) classifier continuously classified straight-line walking, sidestep/crossover cuts (single transitions), and cuts-to-stair locomotion (mixed transitions) performed under varied task anticipatory conditions. Training paradigms with varying levels of anticipated/unanticipated exposures and analysis windows of size 100–600 ms were examined.

Results

More accurate classification of anticipated relative to unanticipated tasks was observed. Including bouts of target task in the training data was necessary to improve generalization to unanticipated locomotion. Only up to two bouts of target task were sufficient to reduce errors to <20% in unanticipated mixed transitions, whereas, in single transitions and straight walking, substantial unanticipated information (i.e., five bouts) was necessary to achieve similar outcomes. Window size modifications did not have a significant influence on classification performance.

Conclusion

Adjusting the training paradigm helps to achieve classification schemes capable of adapting to changes of direction and task anticipatory state.

Significance

The findings could provide insight into developing classification schemes that can adapt to changes of direction and user anticipation. They could inform intent recognition strategies for controlling lower-limb assistive to robustly handle “unknown” circumstances, and thus deliver increased level of reliability and safety.

Progression of Fatigue Modifies Primary Contributors to Ground Reaction Forces During Drop Landing

Few studies have focused on the effect of fatigue severity on landing strategy. This study aimed to investigate the effect of fatigue progression on ground reaction force during landing. Eighteen participants performed a fatigue exercise protocol. Then participants performed drop landings at three levels of fatigue: no fatigue, medium fatigue, and severe fatigue. Multiple linear regression was conducted to identify the predictors of the peak vertical ground reaction force at each level of fatigue. Two-way ANOVAs were conducted to test the effect of fatigue on the vertical ground reaction force and the predictors. For the vertical ground reaction force, the knee joint stiffness and the knee angle at initial contact were the main predictors at no fatigue. The peak knee flexion angle and knee power were the main predictors at medium fatigue. However, the peak ankle plantarflexion moments became the main predictor at severe fatigue. The vertical ground reaction force decreased from no to medium fatigue (p = 0.001), and then increased from medium to severe fatigue (p = 0.034). The knee joint stiffness decreased from no to medium fatigue (p = 0.049), and then remained unchanged from medium to severe fatigue. The peak knee flexion angle increased from no to medium fatigue (p = 0.001), and then slightly decreased from medium to severe fatigue (p = 0.051). The results indicate that fatigue progression causes a transition from stiff to soft landing, and then to stiff landing. Participants used ankle joints more to control the landing intensity at severe fatigue.

Effect of running-induced fatigue on lower limb mechanics in novice runners

BACKGROUND

Running-induced fatigue has received much attention in recent years. However, very few studies have investigated the effect of fatigue on lower limb biomechanics in three planes.

OBJECTIVE

This study was designed to investigate biomechanical changes in the lower limb in three planes following running-induced fatigue.

METHODS

Fifteen male novice runners were included in the study and performed three running trails pre- and post-fatigue. Wilcoxon signed-rank tests or paired-sample t tests were used to analyze the data.

RESULTS

Lower limb biomechanics significantly changed, especially kinetic parameters, when fatigue occurred. The peak ankle dorsiflexion angle and range of motion of the knee joint in the frontal plane increased. As for kinetic parameters, in the ankle joint, the peak external rotation moment, peak abduction power and peak internal rotation power increased. In the knee joint, the peak abduction and external rotation moment, peak flexion power, peak adduction and abduction power also increased. In the hip joint, the peak flexion moment was decreased, peak adduction and abduction moment, peak external rotation power, peak adduction and abduction power moment were increased.

CONCLUSION

The findings of this study may contribute to our understanding of the impact of fatigue and provide some helpful information to prevent related injuries.

The Acute Influence of Running-Induced Fatigue on the Performance and Biomechanics of a Countermovement Jump

Lower limb kinematics and kinetics during the landing phase of jumping might change because of localized muscle fatigue. This study aimed to investigate the acute influence of running-induced fatigue on the performance and lower limb kinematics and kinetics of a countermovement jump. A running-induced fatigue protocol was applied to fifteen male subjects. Participants were asked to perform three successful countermovement jumps before and after fatigue. Kinematic and kinetic data were collected to compare any fatigue influences. Wilcoxon signed-rank tests and paired-sample t-tests were used to analyze the data. Running-induced fatigue did not significantly change vertical jump height and peak vertical ground reaction forces (GRF) during the push-off and landing phases. Lower limb biomechanics significantly changed, especially kinematic parameters. During the push-off phase, fatigue resulted in an increased ankle peak inversion angle, knee minimal flexion angle, knee peak abduction angle, and hip peak flexion moment. In addition, the range of motion (ROM) of the ankle and knee joints in the frontal plane was also increased. Certain parameters decreased as a result of fatigue, such as the ankle peak internal rotation angle, hip peak abduction angle, the ROM of the ankle joint in the sagittal plane, and ROM of the hip joint in the frontal plane. During the landing phase, the peak inversion angle and peak external rotation angle of the ankle joint, peak abduction angle of the knee and hip joint, ROM of the ankle joint in the horizontal plane, ROM of the ankle and knee joint in the frontal plane were all increased as a result of fatigue. The knee peak flexion moment and hip peak extension moment, however, were decreased. Under fatigue conditions, lower limb kinetics and kinematics were changed during both the push-off and landing phases. More attention should be focused on the landing phase and the last period of the push-off phase due to potentially higher risks of injury. The findings of the current study may be beneficial to athletes and coaches in preventing jumping related injuries.

The Effect of Angle and Velocity on Change of Direction Biomechanics: An Angle-Velocity Trade-Off

Changes of direction (CODs) are key manoeuvres linked to decisive moments in sport and are also key actions associated with lower limb injuries. During sport athletes perform a diverse range of CODs, from various approach velocities and angles, thus the ability to change direction safely and quickly is of great interest. To our knowledge, a comprehensive review examining the influence of angle and velocity on change of direction (COD) biomechanics does not exist. Findings of previous research indicate the biomechanical demands of CODs are 'angle' and 'velocity' dependent and are both critical factors that affect the technical execution of directional changes, deceleration and reacceleration requirements, knee joint loading, and lower limb muscle activity. Thus, these two factors regulate the progression and regression in COD intensity. Specifically, faster and sharper CODs elevate the relative risk of injury due to the greater associative knee joint loading; however, faster and sharper directional changes are key manoeuvres for successful performance in multidirectional sport, which subsequently creates a 'performance-injury conflict' for practitioners and athletes. This conflict, however, may be mediated by an athlete's physical capacity (i.e. ability to rapidly produce force and neuromuscular control). Furthermore, an 'angle-velocity trade-off' exists during CODs, whereby faster approaches compromise the execution of the intended COD; this is influenced by an athlete's physical capacity. Therefore, practitioners and researchers should acknowledge and understand the implications of angle and velocity on COD biomechanics when: (1) interpreting biomechanical research; (2) coaching COD technique; (3) designing and prescribing COD training and injury reduction programs; (4) conditioning athletes to tolerate the physical demands of directional changes; (5) screening COD technique; and (6) progressing and regressing COD intensity, specifically when working with novice or previously injured athletes rehabilitating from an injury.

The influence of differences in neurocognitive function on lower limb kinematics, kinetics, and muscle activity during an unanticipated cutting motion

Background Neurocognitive function may be a risk factor for anterior cruciate ligament (ACL) injury by changing neuromuscular control such as muscle activities. However, the effect of differences in neurocognitive function on biomechanics and neuromuscular control related to ACL injury risk is not clear. The purpose of this study was to examine the effect of differences in neurocognitive function on biomechanics and neuromuscular control during an unanticipated side-step cutting motion. Method The subjects were 15 collegiate female athletes who were divided into two groups using the Symbol Digit Modalities Test (SDMT). The experimental task was an unanticipated side-step cutting motion from a 30 cm high box. We calculated joint angles and moments using a 3-dimensional motion analysis system from the dominant leg, and measured muscle activities using a surface electromyography. We calculated the co-contraction ratio (CCR) as relative muscle activity of the quadriceps to the hamstring. Results As a result, subjects with a lower SDMT score had significantly increased quadriceps activity before and after ground contact and decreased CCR only after ground contact. Conclusion In the lower SDMT score group, the quadriceps showed stronger muscle activity than the hamstring during an unanticipated side-step cutting motion. This dominant quadriceps muscle activity has been reported to increase the load on the ACL, and there was a possibility of increasing the risk of the ACL injury. Considering these factors, subjects with lower neurocognitive function could have a high risk of ACL injury due to alterations in muscle activities surrounding the knee.

Effects of fatigue on lower limb, pelvis and trunk kinematics and lower limb muscle activity during single-leg landing after anterior cruciate ligament reconstruction

PURPOSE

Because there are no studies that have evaluated the effects of fatigue on the kinematics of the trunk and pelvis or on muscle activation in subjects with ACL reconstruction, the aim of this study was to evaluate the effects of fatigue on the lower limb, pelvis and trunk kinematics and lower limb muscle activation in subjects with ACL reconstruction during a single-leg landing compared to a healthy control group.

METHODS

The participants included 20 subjects with ACL reconstruction (ACL reconstruction group-ACLRG) and 20 healthy subjects (control group-CG) who were aged between 18 and 35 years. Kinematic and electromyographic analyses were performed during a single-leg landing before and after fatigue. The fatigue protocol included a series of 10 squats, two vertical jumps, and 20 steps.

RESULTS

The effects of fatigue were increased peak trunk flexion and increased activation of the vastus lateralis, biceps femoris (BF) and gluteus maximus (GMax) during the landing phase.

CONCLUSION

After the fatigue protocol, an increase in peak trunk flexion and activation of the GMax and BF were observed, most likely as a strategy to reduce the load on the ACL. ACL injury prevention programs should include strength and endurance exercises for the hip and trunk extensor muscles so that they can efficiently control trunk flexion during landing.

LEVEL OF EVIDENCE

Prospective comparative study, Level II.

Effect of limb dominance and sex on neuromuscular activation patterns in athletes under 12 performing unanticipated side-cuts

Non-contact ACL injuries are one of the most common injuries to the knee joint among adolescent/collegiate athletes, with sex and limb dominance being identified as risk factors. In children under 12years of age (U12), these injuries occur less often and there is no sex-bias present. This study set out to explore if sex and/or limb dominance differences exist in neuromuscular activations in U12 athletes. Thirty-four U12 males and females had six bilateral muscles analyzed during unanticipated side-cuts. Principal component analysis was performed, capturing differences in overall magnitudes and timing of peak magnitudes. Two-way mixed-model ANOVAs determined significant limb effects with both sexes displaying (i) greater magnitudes in the lateral gastrocnemius and both hamstrings in the dominant limb and (ii) earlier timing of peak magnitudes in both gastrocnemii, both hamstrings and vastus medialis in the non-dominant limb, while no sex differences were identified. This study demonstrated that limb dominance, not sex, affects neuromuscular activation strategies in U12 athletes during unanticipated side-cuts. When developing injury prevention programs for younger athletes, an increased focus on balancing neuromuscular activations in both limbs could be beneficial in reducing the likelihood of ACL injuries in these athletes as they mature through puberty.

Mapping current research trends on anterior cruciate ligament injury risk against the existing evidence: In vivo biomechanical risk factors

BACKGROUND

Whilst many studies measure large numbers of biomechanical parameters and associate these to anterior cruciate ligament injury risk, they cannot be considered as anterior cruciate ligament injury risk factors without evidence from prospective studies. A review was conducted to systematically assess the in vivo biomechanical literature to identify biomechanical risk factors for non-contact anterior cruciate ligament injury during dynamic sports tasks; and to critically evaluate the research trends from retrospective and associative studies investigating non-contact anterior cruciate ligament injury risk.

METHODS

An electronic literature search was undertaken on studies examining in vivo biomechanical risk factors associated with non-contact anterior cruciate ligament injury. The relevant studies were assessed by classification; level 1 - a prospective cohort study, level 2 - a retrospective study or level 3 - an associative study.

FINDINGS

An initial search revealed 812 studies but this was reduced to 1 level 1 evidence study, 20 level 2 evidence studies and 175 level 3 evidence studies that met all inclusion criteria. Level 1 evidence showed that the knee abduction angle, knee abduction moment and ground reaction force were biomechanical risk factors. Nine level 2 studies and eighty-three level 3 studies used these to assess risk factors in their study. Inconsistencies in results and methods were observed in level 2 and 3 studies.

INTERPRETATION

There is a lack of high quality, prospective level 1 evidence related to biomechanical risk factors for non-contact anterior cruciate ligament injury. More prospective cohort studies are required to determine risk factors and provide improved prognostic capability.

Kinematics and muscle activities of the lower limb during a side-cutting task in subjects with chronic ankle instability

PURPOSE

The purpose of the present study was to evaluate lower limb kinematics and muscular activities during walking, side-turning while walking, and side-cutting movement in athletes with chronic ankle instability and compare the results to those of athletes without chronic ankle instability.

METHODS

Lower limb kinematics and muscular activities were evaluated in 10 athletes with chronic ankle instability and 10 healthy control athletes using a three-dimensional motion analysis system and surface electromyography during the 200-ms pre-initial contact (IC) and stance phases while walking, side-turning while walking, and side-cutting.

RESULTS

During walking or side-turning while walking, there were no significant differences in kinematics or muscle activities between the subjects with and without chronic ankle instability. For the side-cutting task, however, ankle inversion angles during the 200-ms pre-IC and late stance phases [effect sizes (ESs) = 0.95-1.43], the hip flexion angle (ESs = 0.94-0.96) and muscular activities of the gastrocnemius medialis (ESs = 1.04-1.73) during the early stance phase were significantly greater in the athletes with chronic ankle instability than in the healthy control athletes.

CONCLUSIONS

Alterations of kinematics in athletes with chronic ankle instability were found not only at the ankle but also at hip joints during the side-cutting movement. These alterations were not detected during walking or side-turning while walking. The findings of the present study indicate that clinicians should take into account the motion of the hip joint during the side-cutting movement in persons with chronic ankle instability.

LEVEL OF EVIDENCE

III.

Lower limb kinematics of male and female soccer players during a self-selected cutting maneuver: Effects of prolonged activity

BACKGROUND

Despite the recent emphasis on injury prevention, anterior cruciate ligament (ACL) injury rates remain high. This study aimed to ascertain the effects of prolonged activity on lower limb kinematics during a self-selected cutting maneuver.

METHODS

Angular kinematics were recorded during an agility test performed until the completion time was greater than the mean plus one SD of baseline trials. Cut type was identified and the hip and knee angles at 33 ms post heel strike were determined. A linear mixed effects model assessed the effects of cut type, gender, and activity status on the hip and knee angles.

RESULTS

Males performed sidestep cuts more frequently than females. Females increased the incidence of sidestep cuts after prolonged activity. At the hip, a gender-cut type interaction existed for the transverse (p=0.001) and sagittal (p=0.11) planes. Females showed more internal rotation during sidestep and more external rotation and less flexion during crossover cuts. For the frontal plane, a gender-activity status interaction (p = 0.032) was due to no change within females but greater hip adduction during prolonged activity within males. With prolonged activity, both genders displayed less hip (p=0.29) and knee (p=0.009) flexion and more knee (p=0.001) adduction. Females displayed less hip and knee flexion than men (p=0.001).

CONCLUSIONS

Sidestep may be more risky than crossover cuts. Both genders place themselves in at-risk postures with prolonged activity due to less hip and knee flexion.

Predictive Neuromuscular Fatigue of the Lower Extremity Utilizing Computer Modeling

This paper studies the modeling of lower extremity muscle forces and their correlation to neuromuscular fatigue. Two analytical fatigue models were combined with a musculoskeletal model to estimate the effects of hamstrings fatigue on lower extremity muscle forces during a side step cut. One of the fatigue models (Tang) used subject-specific knee flexor muscle fatigue and recovery data while the second model (Xia) used previously established fatigue and recovery parameters. Both fatigue models were able to predict hamstrings fatigue within 20% of the experimental data, with the semimembranosus and semitendinosus muscles demonstrating the largest (11%) and smallest (1%) differences, respectively. In addition, various hamstrings fatigue levels (10-90%) on lower extremity muscle force production were assessed using one of the analytical fatigue models. As hamstrings fatigue levels increased, the quadriceps muscle forces decreased by 21% (p < 0.01), while gastrocnemius muscle forces increased by 36% (p < 0.01). The results of this study validate the use of two analytical fatigue models in determining the effects of neuromuscular fatigue during a side step cut, and therefore, this model can be used to assess fatigue effects on risk of lower extremity injury during athletic maneuvers. Understanding the effects of fatigue on muscle force production may provide insight on muscle group compensations that may lead to altered lower extremity motion patterns as seen in noncontact anterior cruciate ligament (ACL) injuries.

Effects of maturation on combined female muscle strength and ACL structural factors

OBJECTIVES

Relations between lower limb muscle strength and female ACL injury risk are well documented. How these relations combine with key ACL geometries however, is unknown. Identifying how these combined factors are impacted by maturation would benefit current risk screening and prevention efforts. This study compared hamstrings and quadriceps strength and ACL cross sectional area (CSA) indices across three maturation groups.

DESIGN

Cross-sectional human experimental.

METHODS

MRI scans of the dominant knee were collected in 35 females stratified into early (9.7±0.8yrs), middle (12.9±1.7yrs), and late (14.8±0.6yrs) maturation groups. Hamstring and quadriceps muscle volumes and ACL CSA measures were obtained. Isokinetic strength data were quantified for dominant knee flexors and extensors. Peak hamstring and quadriceps concentric and eccentric strength per unit volume magnitudes (QCSPV, HCSPV, QESPV, HESPV) were determined. Metrics and select ratios were submitted to a one way ANOVA to determine the main effect of maturation.

RESULTS

Significant decreases occurred in HESPV (N/cm(3)) and ACL CSA (cm(2)/kgm), respectively, from early (0.188±0.023N/cm(3), 0.007±0.002cm(2)/kgm) to middle (0.157±0.029N/cm(3), 0.005±0.002cm(2)/kgm, p=0.034, p=0.029), and middle to late (0.132±0.031N/cm(3), 0.003±0.001cm(2)/kgm, p=0.044, p=0.018) maturation. A significant decrease in HESPV:QCSPV occurred between early (1.795±0.496) and middle (1.362±0.277, p=0.018) maturation.

QCSPV

ACL CSA was significantly greater in late (37.26±13.35) compared to middle (25.81±9.17, p=0.021) maturation.

CONCLUSIONS

Key ratios between female knee quadriceps and hamstring strength and ACL size parameters, which may directly impact ACL injury risk, are substantially different among three maturation states. The results are potentially hazardous strength mismatches in mid-pubertal females, where a smaller (weaker) ACL may be unable to stabilize quadriceps dominated loading strategies.

What is normal? Female lower limb kinematic profiles during athletic tasks used to examine anterior cruciate ligament injury risk: a systematic review

BACKGROUND

It has been proposed that the performance of athletic tasks where normal motion is exceeded has the potential to damage the anterior cruciate ligament (ACL). Determining the expected or 'normal' kinematic profile of athletic tasks commonly used to assess ACL injury risk can provide an evidence base for the identification of abnormal or anomalous task performances in a laboratory setting.

OBJECTIVE

The objective was to conduct a systematic review of studies examining lower limb kinematics of females during drop landing, drop vertical jump, and side-step cutting tasks, to determine 'normal' ranges for hip and knee joint kinematic variables.

DATA SOURCES

An electronic database search was conducted on the SPORTDiscus(TM), MEDLINE, AMED and CINAHL (January 1980-August 2013) databases using a combination of relevant keywords.

STUDY SELECTION

Studies identified as potentially relevant were independently examined by two reviewers for inclusion. Where consensus could not be reached, a third reviewer was consulted. Original research articles that examined three-dimensional hip and knee kinematics of female subjects during the athletic tasks of interest were included for review. Articles were excluded if subjects had a history of lower back or lower limb joint injury or isolated data from the female cohort could not be extracted.

STUDY APPRAISAL AND SYNTHESIS METHODS

Two reviewers independently assessed the quality of included studies. Data on subject characteristics, the athletic task performed, and kinematic data were extracted from included studies. Studies were categorised according to the athletic task being examined and each study allocated a weight within categories based on the number of subjects assessed. Extracted data were used to calculate the weighted means and standard deviations for hip and knee kinematics (initial contact and peak values). 'Normal' motion was classified as the weighted mean plus/minus one standard deviation.

RESULTS

Of 2,920 citations, a total of 159 articles were identified as potentially relevant, with 29 meeting all inclusion/exclusion criteria. Due to the limited number of studies available examining double-leg drop landings and single-leg drop vertical jumps, insufficient data was available to include these tasks in the review. Therefore, a total of 25 articles were included. From the included studies, 'normal' ranges were calculated for the kinematic variables of interest across the athletic tasks examined.

LIMITATIONS

Joint forces and other additional elements play a role in ACL injuries, therefore, focusing solely on lower limb kinematics in classifying injury risk may not encapsulate all relevant factors. Insufficient data resulted in no normal ranges being calculated for double-leg drop land and single-leg drop vertical jump tasks. No included study examined hip internal/external rotation during single-leg drop landings, therefore ranges for this kinematic variable could not be determined. Variation in data between studies resulted in wide normal ranges being observed across certain kinematic variables.

CONCLUSIONS

The ranges calculated in this review provide evidence-based values that can be used to identify abnormal or anomalous athletic task performances on a multi-planar scale. This may be useful in identifying neuromuscular factors or specific muscular recruitment strategies that contribute to ACL injury risk.