Comparison of landing biomechanics between male and female dancers and athletes, part 2: Influence of fatigue and implications for anterior cruciate ligament injury

Analysis of cartilage loading and injury correlation in knee varus deformity

Knee varus (KV) deformity leads to abnormal forces in the different compartments of the joint cavity and abnormal mechanical loading thus leading to knee osteoarthritis (KOA). This study used computer-aided design to create 3-dimensional simulation models of KOA with varying varus angles to analyze stress distribution within the knee joint cavity using finite element analysis for different varus KOA models and to compare intra-articular loads among these models. Additionally, we developed a cartilage loading model of static KV deformity to correlate with dynamic clinical cases of cartilage injury. Different KV angle models were accurately simulated with computer-aided design, and the KV angles were divided into (0°, 3°, 6°, 9°, 12°, 15°, and 18°) 7 knee models, and then processed with finite element software, and the Von-Mises stress distribution and peak values of the cartilage of the femoral condyles, medial tibial plateau, and lateral plateau were obtained by simulating the human body weight in axial loading while performing the static extension position. Finally, intraoperative endoscopy visualization of cartilage injuries in clinical cases corresponding to KV deformity subgroups was combined to find cartilage loading and injury correlations. With increasing varus angle, there was a significant increase in lower limb mechanical axial inward excursion and peak Von-Mises stress in the medial interstitial compartment. Analysis of patients' clinical data demonstrated a significant correlation between varus deformity angle and cartilage damage in the knee, medial plateau, and patellofemoral intercompartment. Larger varus deformity angles could be associated with higher medial cartilage stress loads and increased cartilage damage in the corresponding peak stress area. When the varus angle exceeds 6°, there is an increased risk of cartilage damage, emphasizing the importance of early surgical correction to prevent further deformity and restore knee function.

Sex-Based Differences in Lower Extremity Kinematics During Dynamic Jump Landing Tasks After Neuromuscular Fatigue of the Hip Extensors and Knee Flexors

Background

Neuromuscular fatigue can increase the activation of antagonist muscles, thereby reducing the moment produced by the agonist. During the deceleration phase of landing, hip extensor and knee flexor muscles contract eccentrically to counteract the external hip flexion moment. Decreased hip flexion is associated with greater knee extensor moments and risk of injury.

Purpose

To investigate sex-based differences in kinematics and muscle activity after neuromuscular fatigue of the hip extensors and knee flexors during dynamic single-leg tasks.

Study Design

Controlled laboratory study.

Methods

In this study, 9 female (age, 22.3 ± 3.4 years) and 7 male participants (age, 21.3 ± 2.6 years) completed the triple hop (THop) for distance and single-leg drop-jump (SJump) tasks before and after a fatigue protocol consisting of eccentric hip extension and knee flexion. Motion capture and electromyography were used to compare lower extremity kinematics and muscular activation between the sexes.

Results

During the THop, neuromuscular fatigue resulted in significantly decreased maximum hip flexion angles (P = .01), maximum knee flexion angles (P = .039), and an effect of sex on all hip flexion angles, where both sexes saw decreased hip flexion postfatigue (P = .033). A significant interaction of fatigue and sex on hip flexion angular velocity was observed during the SJump, indicating that men experienced an increase while women experienced a decrease in hip flexion angular velocities due to fatigue (P = .03). Gluteus maximus activation was increased, and erector spinae activation was decreased postfatigue in women during the THop (P = .053 and P = .023, respectively).

Conclusion

Results indicate that men and women compensated differently after fatigue of the hip extensors and knee flexors.

Clinical Relevance

Women more commonly assumed an erect landing posture associated with increased injury risk after fatigue of the hip extensors and knee flexors.

Landing Posture in Elite Female Athletes During a Drop Vertical Jump Before and After a High-Intensity Ergometer Fatigue Protocol: A Study of 20 Japanese Women's Soccer League Players

Background

Even elite athletes, who usually show stable postural control, sometimes cannot control their posture after high-load training. This instability may contribute to anterior cruciate ligament injury.

Purpose/Hypothesis

The purpose of this study was to evaluate the landing posture of elite female soccer players before and after a novel high-intensity fatigue-inducing exercise protocol. We hypothesized that the landing posture will change before versus after the fatigue protocol.

Study Design

Descriptive laboratory study.

Method

The study participants were 20 female elite soccer players. All athletes performed 3 drop vertical jumps (DVJs), pedaled an ergometer 8 times with full force for 10 seconds each (fatigue protocol), and then repeated the 3 DVJs. We measured and compared the athletes' blood lactate levels before and after the fatigue protocol, as well as the hip flexion, knee flexion, and ankle dorsiflexion angles and final landing posture during the DJVs.

Results

Blood lactate levels increased significantly pre- to postprotocol (from 2.7 ± 1.9 to 15.0 ± 3.6 mmol/L; P < .001), while there were decreases in hip flexion angle (from 35.0° ± 11.2° to 22.4° ± 8.8°; P < .001) and ankle dorsiflexion angle (from 26.4° ± 3.9° to 20.0° ± 3.7°; P < .001). The number of athletes who could not maintain a stable DVJ final landing posture increased from 10% before the fatigue protocol to 70% after.

Conclusion

The elite female athletes in our study showed significant decreases in hip flexion and ankle dorsiflexion angles in the DVJ landing after a fatigue-inducing protocol. Most elite athletes were unable to maintain a stable posture on the DVJ landing after the fatigue protocol.

Clinical Relevance

This study advances our understanding of how elite athletes land in a fatigued state.

The Effect of Fatigue on Trunk and Pelvic Jump-Landing Biomechanics in View of Lower Extremity Loading: A Systematic Review

Fatigue has often been considered a risk factor for developing sports injuries, modulating lower extremity jump-landing biomechanics. The impact of fatigue on proximal trunk and pelvic biomechanics has been suggested to play an important role in lower extremity loading and injury risk, yet the available evidence remains ambiguous as the trunk and pelvis were often not the primary focus of research. Therefore, the purpose of this systematic review was to determine how fatigue affects trunk and pelvic three-dimensional jump-landing biomechanics. PubMed (MEDLINE), Web of Science, Embase, CINAHL and SPORTDiscus were consulted up to and including April 2022 for potential studies investigating the effect of fatigue on trunk and pelvic kinematics, kinetics and/or muscular activity during jump-landing tasks in healthy, physically active populations. Methodological quality of the studies was assessed by the modified Downs and Black checklist. Twenty-one studies were included and methodological quality was moderate to high among these studies. The results indicate prevailing evidence for more trunk flexion during standardized jump-landing tasks after lower extremity muscle fatigue. Otherwise, lumbo-pelvic-hip muscle fatigue does not seem to elicit major detrimental changes to these jump-landing biomechanics. Although a wide variability of trunk and pelvic jump-landing strategies was observed, the results provide evidence for increased trunk flexion after lower extremity muscle fatigue. This proximal strategy is suggested to help unload fatigued lower extremity structures and lack of this compensation might increase knee injury risk.

Applications of Biomechanical Foot Models to Evaluate Dance Movements Using Three-Dimensional Motion Capture: A Review of the Literature

Dance movement requires excessive, repetitive range of motion (ROM) at the foot-ankle complex, possibly contributing to the high rate of injury among dancers. However, we know little about foot biomechanics during dance movements. Researchers are using three-dimensional (3D) motion capture systems to study the in vivo kinematics of joint segments more frequently in dance-medicine research, warranting a literature review and quality assessment evaluation. The purpose of this literature review was to identify and evaluate studies that used 3D motion capture to analyze in vivo biomechanics of the foot and ankle for a cohort of dancers during dance-specific movement. Three databases (PubMed, Ovid MEDLINE, CINAHL) were accessed along with hand searches of dance-specific journals to identify relevant articles through March 2020. Using specific selection criteria, 25 studies were identified. Fifteen studies used single-segment biomechanical foot models originally created to study gait, four used a novel two-segment model, and six utilized a multi-seg- ment foot model. Nine of the studies referenced common and frequently published gait marker sets and four used a dance-specific biomechanical model with purposefully designed foot segments to analyze the dancers' foot and ankle. Description of the biomechanical models varied, reducing the reproducibility of the models and protocols. Investigators concluded that there is little evidence that the extreme total, segmental, and inter-segmental foot and ankle ROM exerted by dancers are being evaluated during dance-specific movements using 3D motion capture. Findings suggest that 3D motion capture is a robust measurement tool that has the capability to assist researchers in evaluating the in vivo, inter-segmental motion of the foot and ankle to potentially discover many of the remaining significant factors predisposing dancers to injury. The literature review synthesis is presented with recommendations for consideration when evaluating results from studies that utilized a 3D biomechanical foot model to evaluate dance-specific movement.

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

Objective

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

Methods

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

Results

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

Conclusions

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

Biomechanical Risks Associated with Foot and Ankle Injuries in Ballet Dancers: A Systematic Review

Professional ballet dancers can be classified as dance artists and sports performers. This systematic review aims to consider the biomechanical risk factors for foot and ankle injuries in ballet dancers, as this could potentially reduce the impact that ‘cost of injury’ may have on ballet companies. An additional outcome was to examine the effects of injury on the career of ballet dancers. This study searched articles in four electronic databases for information in peer-reviewed journals. The included articles examined the relationships between biomechanical factors and the relationship between ballet shoes and foot performance. There were 9 articles included in this review. Among these articles, two focused on the peak force of the foot using two types of pointe shoes, three focused on overuse injuries of the ballet dancer’s foot, one article focused on the loading of the foot of a dancer, and three articles focused on the function and biomechanics of the foot in dancers. This review also found that the pointe shoe condition was the most important factor contributing to a foot injury; overuse injury related to high-intensity training and affected both the ankle and the foot; and metatarsophalangeal joint injury related to the function and structure of the foot. Finally, strengthening the lower extremity muscle is also a recommendation to improve muscle coordination and reduce injuries.

Mechano Growth Factor Accelerates ACL Repair and Improves Cell Mobility of Mechanically Injured Human ACL Fibroblasts by Targeting Rac1-PAK1/2 and RhoA-ROCK1 Pathways

Exceeded mechanical stress leads to a sublethal injury to anterior cruciate ligament (ACL) fibroblasts, and it will hinder cell mobility and ACL regeneration, and even induce osteoarthritis. The mechano growth factor (MGF) could be responsible for mechanical stress and weakening its negative effects on cell physiological behaviors. In this study, effects of MGF on cell mobility and relevant molecules expression in injured ACL fibroblasts were detected. After an injurious mechanical stretch, the analysis carried out, at 0 and 24 h, respectively, showed that the cell area, roundness, migration, and adhesion of ACL fibroblasts were reduced. MGF (10, 100 ng/mL) treatment could improve cell area, roundness and promote cell migration and adhesion capacity compared with the injured group without MGF. Further study indicated that cell mobility-relevant molecules (PAK1/2, Cdc42, Rac1, RhoA, and ROCK1) expression in ACL fibroblasts was down-regulated at 0 or 24 h after injurious stretch (except Rac1 and RhoA at 0 h). Similarly, MGF improved cell mobility-relevant molecule expression, especially the ROCK1 expression level in ACL fibroblasts at 0 or 24 h after injurious stretch. Protein expression of ROCK1 in injured ACL fibroblasts was also reduced and could be recovered by MGF treatment. In a rabbit partial ACL transection (ACLT) model, ACL exhibited poor regenerative capacity in collagen and extracellular matrix (ECM) synthesis after partial ACLT for 2 or 4 weeks, and MGF remarkably accelerated ACL regeneration and restored its mechanical loading capacity after partial ACLT for four weeks. Our findings suggest that MGF weakens the effects of pathological stress on cell mobility of ACL fibroblasts and accelerates ACL repair, and might be applied as a future treatment approach to ACL rupture in the clinic.

Fatigue and recovery have different effects on knee biomechanics of drop vertical jump between female collegiate and recreational athletes

Background

Although fatigue is known as one of the risk factors for noncontact anterior cruciate ligament injury, the effects of fatigue and recovery can be different based on the level of competition. However, it is unknown whether female recreational athletes are susceptible to fatigue or not, compared to female collegiate athletes with greater physical activity. The purpose of the present study was to examine and clarify the effects of fatigue and recovery on knee biomechanics of the drop vertical jump (DVJ) in female recreational athletes compared to female collegiate athletes.

Methods

Fifteen female collegiate athletes and ten female recreational athletes were enrolled in the current study. All subjects were basketball players and Tegner activity scales were level 9 and 7, respectively. They performed DVJ before and after the fatigue protocol. Three-dimensional knee kinematics and kinetics were collected during landing phase of DVJ. The data after the fatigue protocol (first, second, and third DVJs) were compared with those before the protocol using one-way repeated measures of analysis of variance in each group.

Results

Fatigue caused significant increase of knee abduction angle at initial contact (IC) and peak abduction moments within 40 ms from IC in female recreational athletes, whereas no increases of these parameters were observed in female collegiate athletes. Moreover, recovery from fatigue seemed to be more slowly in female recreational athletes than in female collegiate athletes as smaller knee flexion moment was observed even in post-fatigue third DVJ only for female recreational athletes.

Conclusions

Effects of fatigue on DVJ were significantly greater and continued for a longer duration in female recreational athletes compared to female collegiate athletes.

Exercise as a multi-modal disease-modifying medicine in systemic sclerosis: An introduction by The Global Fellowship on Rehabilitation and Exercise in Systemic Sclerosis (G-FoRSS)

Systemic sclerosis (SSc) is a heterogeneous multisystem autoimmune disease whereby its main pathological drivers of disability and damage are vascular injury, inflammatory cell infiltration, and fibrosis. These mechanisms result in diffuse and diverse impairments arising from ischemic circulatory dysfunction leading to painful skin ulceration and calcinosis, neurovascular aberrations hindering gastrointestinal (GI) motility, progressive painful, incapacitating or immobilizing effects of inflammatory and fibrotic effects on the lungs, skin, articular and periarticular structures, and muscle. SSc-related impairments impede routine activities of daily living (ADLs) and disrupt three critical life areas: work, family, social/leisure, and also impact on psychological well-being. Physical activity and exercise are globally recommended; however, for connective tissue diseases, this guidance carries greater impact on inflammatory disease manifestations, recovery, and cardiovascular health. Exercise, through myogenic and vascular phenomena, naturally targets key pathogenic drivers by downregulating multiple inflammatory and fibrotic pathways in serum and tissue, while increasing circulation and vascular repair. G-FoRSS, The Global Fellowship on Rehabilitation and Exercise in Systemic Sclerosis recognizes the scientific basis of and advocates for education and research of exercise as a systemic and targeted SSc disease-modifying treatment. An overview of biophysiological mechanisms of physical activity and exercise are herein imparted for patients, clinicians, and researchers, and applied to SSc disease mechanisms, manifestations, and impairment. A preliminary guidance on exercise in SSc, a research agenda, and the current state of research and outcome measures are set forth.

Characteristics of ground reaction force and frontal body movement during failed trials of single-leg lateral drop jump-landing task

Background

/objectives: For biomechanical studies using jump-landing tasks, many researchers set the criteria for judging success or failure of the trial. Failed trials are usually removed from the analysis. However, the kinetics and kinematics during tasks included in failed trials might be important for understanding the mechanisms and risk factors of non-contact sports injuries. However, few studies have attempted to analyze failed trials. Therefore, the main objective of this study was to investigate the characteristics associated with ground reaction force (GRF) and two-dimensional frontal body movements during a failed trial of single-leg lateral drop jump-landing.

Methods

Ten healthy women and 16 healthy men participated in this study. Spearman's rank correlation coefficients were calculated using the total number of failed trials and GRF data of successful trials. The association between frontal body movement and kinetics data was identified using correlation analyses. Wilcoxon signed-rank tests were performed to compare the GRF data of successful trials and failed trials of the same subject. Additionally, a two-way repeated measure analysis of variance was used to determine significant interactions of each trial and time after initial contact in the frontal body movement.

Results

A total of 137 trials including successful and failed trials were recorded. There were 59 failed jump trials. There was a significant negative correlation between the number of failed jump trials and the elapsed time from initial contact to peak vertical GRF (peak vGRF time) during successful trials (r = -0.427). The majority of failed trials were judged to be due to rearfoot movement patterns (rearfoot medial slip or rearfoot lateral slip). During rearfoot medial slip, we observed shorter peak vGRF time, larger trunk medial motions, and larger hip adduction movements after landing than that during successful trials. During rearfoot lateral slip, we observed larger trunk lateral motions and hip abduction movements after landing than that during successful trials.

Conclusions

Athletes who frequently failed during single-leg lateral drop jump-landing had poor skills absorbing jump-landing impact, which is related to various sports injuries. It is possible to identify the risk factors for sports injuries by analyzing failure patterns.

Reliability of 2D kinematics during landing of volleyball athletes after exhaustion

INTRODUCTION

It is possible to quantify changes in movement patterns through kinematic analysis of landing, especially to quantify changes in pre and post exhaustion situations, however the reliability of this post exhaustion analysis is not known.

OBJECTIVE

To verify the inter and intra-examiner reliability of two-dimensional kinematic analysis during the landing of a vertical jump of volleyball athletes, pre and post exhaustion protocol.

EXPERIMENTAL

Thirty volleyball athletes were recruited, and kinematic analysis was performed during landing, pre and post exhaustion protocol. The angular measurements analyzed were: 1) frontal plane: knee valgus and 2) sagittal plane: anterior trunk inclination, knee flexion and tibiotarsal angle, performed by two examiners. The reliability calculation used the intraclass correlation coefficient (ICC), in addition to the error of measurement (SEM), the coefficient of variation (CV) and the minimum detectable difference (MDD).

RESULTS

Regarding reliability: ICC = 0.95-0.98 (pre) and ICC = 0.83-0.98 (post exhaustion). The CV presented heterogeneous values for the knee valgus and the inclination of the trunk, both pre and post protocol. The SEM from all angles presented values that varied from 0.74°-2.33° and the MDD ranged from 2.55°-5.54° pre protocol and 2.05°-6.45° post protocol.

CONCLUSION

2D kinematic evaluation can be used during landing, before and after the application of an exhaustion protocol, but professionals should pay attention to the angles of the knee valgus and the inclination of the trunk, as they have a large CV.

Effects of shoe weight on landing impact and side-to-side asymmetry

Shoes of different weights affect proprioception. Drop jump (DJ) tasks are often used to explore the risks and mechanisms of lower limb injuries. Leg dominance mainly refers to differences between the dominant and nondominant legs. Eight males and eight females participated in this study. The weights of the shoes in this investigation were 255 g, 335 g, and 415 g, and the heights of the DJ were 30 cm, 40 cm, and 50 cm. The side-to-side asymmetry of the time of contact initiation for the 30DJ was greater than that of the 40DJ and 50DJ, and the asymmetry for shoes weighing 415 g and 355 g was greater than that for shoes weighing 255 g. When the drop height increased, the side-to-side asymmetry of the peak ground reaction force (PGRF). also increased. The ground contact time increased as the drop height increased to 50DJ. Higher drop heights caused greater side-to-side asymmetry of the PGRF. Heavier shoes caused the peak ground reaction force time (PGRFT) in the nondominant leg to appear earlier, reduced the jump height and affected the performance. Heavier shoes caused greater side-to-side asymmetry at the initial ground contact and at the ground contact time, affecting training effectiveness.

Effectiveness of physiotherapy interventions for injury in ballet dancers: A systematic review

Background

The unique repetitive nature of ballet dancing, which often involves transgressing endurance limits of anatomical structures, makes dancers prone to injury. The following systematic review aims to assess the effectiveness of physiotherapy interventions in the treatment of injuries in ballet dancers.

Methods

The review was performed in line with the PRISMA statement on preferred reporting items for systematic reviews and meta-analyses. Six electronic databases (PubMed, Ovid Embase, Cochrane, Medline, PEDro, Google Scholar) were queried. The study populations comprised active ballet dancers and/or ballet school attendees with acute and chronic injuries and those with persistent pain. There were no restrictions regarding age, sex, ethnicity or nationality. The Modified McMaster Critical Review Form for quantitative studies was used to assess the methodological quality of the studies reviewed in accordance with the relevant guidelines.

Results

Out of the total of 687 articles subjected to the review, 10 met the inclusion criteria. Diverse physiotherapeutic interventions were described and effectiveness was assessed using different parameters and measurements. Overall, the results indicate that physiotherapy interventions in ballet dancers exert a positive effect on a number of indices, including pain, ROM and functional status.

Conclusions

Due to the small amount of evidence confirming the effectiveness of physiotherapeutic interventions in ballet dancers after injuries and methodological uncertainties, it is recommended to improve the quality of prospective studies.

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

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

Fatigue-Induced Inter-Limb Asymmetries in Strength of the Hip Stabilizers, Postural Control and Gait Following a Unilateral Countermovement Vertical Jump Protocol

It is generally accepted that neuromuscular overload and fatigue of one lower limb can affect the functional ability of the ipsilateral limb, and possibly the contralateral limb, increasing the likelihood of injury. The purpose of the current study was to examine the effect of a unilateral countermovement vertical jump (UCVJ) fatigue protocol on the neuromuscular function of the ipsilateral as well as the contralateral lower limb. The isometric strength of the hip stabilizers, postural control via posturographic analysis during the Y-Balance-Test (YBT), and the stance-phase-of-gait were assessed in 24 healthy physical active males and females before and after execution of a UCVJ fatigue protocol. The fatigue protocol included 5 sets of 20 maximum UCVJs performed on the supportive leg, with a 30-s break between sets. Following a 16.8% decline in vertical jump performance and an associated 2.3-fold increase in perceived exertion, our findings revealed significant post-fatigue inter-limb differences regarding postural control. The post-fatigue inter-limb differences regarding the isometric strength of the hip stabilizers and the stance-phase-of-gait parameters were not significant. Our findings showed that a 100 UCVJs session is likely to induce significant inter-limb differences in postural control, possibly increasing the risk of lower limb injury.

Frequency of overtime and consecutive games and their impact on injury rate in the National Hockey League (NHL)

OBJECTIVES

Ice hockey is a high-intensity contact sport that places athletes at an elevated risk for injury relative to other sports. The purpose of the current study was to analyze factors contributing to fatigue and decreased recovery time and their associations with injury incidence among professional athletes in the National Hockey League (NHL).

METHODS

A retrospective review of all injuries suffered by NHL athletes during six consecutive seasons from 2013 to 2019 was performed. Team schedules were analyzed to assess (1) the number of instances with games on consecutive calendar days, (2) the number of overtime games, and (3) the number of overtime games within three calendar days of a previous overtime game. A Spearman's rank correlation coefficient was calculated from this data to assess the association between these factors and injury rates.

RESULTS

In total, 4886 injuries were suffered by NHL players during the period of study, with the 2013-2014 regular season highest injury rate per 1000 athletic exposures (15.8). The lower body was the most frequently injured body area (25.0% of all injuries), followed by injuries to the upper body (23.7%). In an analysis of the number of overtime games and games on consecutive days and their relationships to injury rate, only overtime games within three calendar days and total injuries were found to have a significant association (ρ = 0.19, p = 0.01).

CONCLUSION

The weak positive correlation between the number of overtime games within threedays of a previous overtime game and total injuries in professional ice hockey players suggests that overtime games played within a short period of time place athletes at increased risk for injury. Further studies are necessary to address this on an athlete-by-athlete level.

The effects of acute physical fatigue on sauté jump biomechanics in dancers

Dancers spend large amounts of time practicing and performing, where fatigue may occur, resulting in adverse movement patterns. The purpose of this study was to compare sauté landings before and after acute physical fatigue in experienced female dancers. Twenty-one dancers completed 10 sauté jumps before and after a dance-specific fatigue protocol. A 12-camera motion capture system and a force plate were utilized to collect three-dimensional kinematic and kinetic data. After fatigue, dancers demonstrated an increase in mediolateral centre of mass displacement, pelvis excursion, peak knee abduction, peak ankle eversion and external rotation, as well as decreased peak metatarsophalangeal (MTP) joint extension, indicating less desirable movement patterns. Peak vertical ground reaction force was decreased after fatigue due to a softer landing strategy, demonstrated by increased peak hip flexion, knee flexion, and ankle dorsiflexion. There was some indication of shifting demands demonstrated by an increased peak knee extensor moment and decreased peak MTP flexor moment after fatigue. With jump landing kinematics and kinetics affected after only an average of 5 minutes of dancing, dancers may benefit from developing greater endurance and more eccentric strength to allow them to slow down properly while landing and to sustain the aesthetic demands throughout performance.

Is Fatigue a Risk Factor for Anterior Cruciate Ligament Rupture?

Neuromuscular fatigue is a commonly accepted risk factor for anterior cruciate ligament (ACL) injury. It has been proposed that fatigue leads to transient reductions in muscle strength, and deleterious changes in lower limb kinematics and kinetics, during potentially hazardous tasks such as cutting or landing. The purpose of this clinical commentary is to (1) highlight the complexity of fatigue; (2) discuss the theoretical basis by which it is thought to contribute to ACL injury; and (3) critically discuss the evidence underpinning this hypothesis. Despite a significant amount of research, none of the published fatigue protocols appear to have any consistent effect on any lower limb kinematic or kinetic variables known to increase ACL injury risk. On the contrary, fatigued athletes appear to land with greater peak knee and hip flexion angles, and lower landing forces than unfatigued athletes-all of which are considered favourable movement strategies for reducing ACL loading. These data support recent analyses demonstrating no relationship between player workload in training and competition and the occurrence of ACL injury in sport.

Effects of Lower Extremity Muscle Fatigue on Knee Loading During a Forward Drop Jump to a Vertical Jump in Female Athletes

The aim of this study was to examine changes in the kinematic and kinetic parameters of female athletes performing a forward drop jump to a vertical jump under muscle fatigue condition. Twelve female college athletes performed a forward drop jump to a vertical jump with and without muscle fatigue conditions. A motion capture system and two AMTI force plates were used to synchronously collect kinematic and kinetic data. Inverse dynamics were implemented to calculate the participant’s joint loading, joint moment, and energy absorption. A paired sample t-test was used to compare statistical differences between pre-fatigue and post-fatigue conditions (α = .05). The forward trunk lean angle at initial foot contact, as well as the knee range of motion, total negative work and energy absorption contribution of the knee joint during the landing phase were significantly decreased under post-fatigue condition. The increased peak vertical ground reaction force and peak tibial anterior shear forces were also found under post-fatigue condition. These results indicated that muscle fatigue caused participants to change their original landing posture into stiff landing posture and decrease the energy absorption ability, which increased the tibial anterior shear forces. Therefore, female athletes should appropriately increase the knee flexion angle under muscle fatigue condition to reduce the risk of anterior cruciate ligament injuries.

Tensiomyographical responsiveness to peripheral fatigue in quadriceps femoris

Background

Fatigue influences athletic performance and can also increase the risk of injury in sports, and most of the methods to evaluate it require an additional voluntary effort. Tensiomyography (TMG), which uses electrical stimulation and a displacement sensor to evaluate muscle contraction properties of one or more muscle bellies, has emerged as a technique that can assess the presence of peripheral and central fatigue without requiring additional voluntary efforts. However, the evaluation of the TMG’s ability to detect fatigue is limited, both at the level of muscle bellies and statistical methods. Thus, the aim of the present study was twofold: (i) to examine and compare the tensiomyographical responsiveness to quadriceps femoris (QF) fatigue by multiple statistical methods and (ii) to analyze sex differences in the variation produced by fatigue in TMG parameters.

Methods

Thirty-nine recreational athletes participated (19 males/20 females; aged 22 ± 2 years). TMG parameters of QF bellies and maximal voluntary isometric contraction (MVIC) were measured before and after a fatigue protocol. TMG parameters used were maximum radial deformation (Dm), contraction time between 10–90% of the Dm (Tc), contraction velocity between 10–90% (Vc) and of the first 10% (V10) of the Dm. Internal responsiveness of TMG to fatigue was analyzed by paired t-test and standardized response mean (SRM). External responsiveness was examined by correlations, regression models, and receiver operating characteristic (ROC) curves.

Results

All TMG parameters, except for Tc of rectus femoris and vastus medialis, showed large internal responsiveness. In adjusted regression models by sex, only Dm and V10 of rectus femoris were statistically associated (p < 0.05) with b coefficients of 0.40 and 0.43, respectively. r2 explained the 22% of the total variance. In addition, these parameters could discriminate between QF with and without fatigue.

Conclusion

Since the QF is the main strength contributor during multiple physical activities, clinicians and trainers will be able to discriminate the presence of fatigue and the magnitude of changes in the QF strength by TMG evaluation.

An Exploration of Machine-Learning Estimation of Ground Reaction Force from Wearable Sensor Data

This study aimed to develop a wearable sensor system, using machine-learning models, capable of accurately estimating peak ground reaction force (GRF) during ballet jumps in the field. Female dancers (n = 30) performed a series of bilateral and unilateral ballet jumps. Dancers wore six ActiGraph Link wearable sensors (100 Hz). Data were collected simultaneously from two AMTI force platforms and synchronised with the ActiGraph data. Due to sensor hardware malfunctions and synchronisation issues, a multistage approach to model development, using a reduced data set, was taken. Using data from the 14 dancers with complete multi-sensor synchronised data, the best single sensor was determined. Subsequently, the best single sensor model was refined and validated using all available data for that sensor (23 dancers). Root mean square error (RMSE) in body weight (BW) and correlation coefficients (r) were used to assess the GRF profile, and Bland–Altman plots were used to assess model peak GRF accuracy. The model based on sacrum data was the most accurate single sensor model (unilateral landings: RMSE = 0.24 BW, r = 0.95; bilateral landings: RMSE = 0.21 BW, r = 0.98) with the refined model still showing good accuracy (unilateral: RMSE = 0.42 BW, r = 0.80; bilateral: RMSE = 0.39 BW, r = 0.92). Machine-learning models applied to wearable sensor data can provide a field-based system for GRF estimation during ballet jumps.

Fatigue Increases Dynamic Knee Valgus in Youth Athletes: Results From a Field-Based Drop-Jump Test

PURPOSE

To determine whether fatigue increases dynamic knee valgus in adolescent athletes, as measured after a standardized exercise protocol and video-based drop-jump test. A secondary aim was to determine whether individual risk factors place certain athletes at increased risk for dynamic knee valgus.

METHODS

Athletes aged 14 to 18 years were recruited for this video analysis study. Athletes were recorded performing a standard drop-jump to assess dynamic valgus. Participants then completed a standardized exercise protocol. Fatigue was quantified using a maximum vertical jump, which was compared with pre-exercise values. The drop-jump was repeated postexercise. All drop-jump recordings were randomized and scored for dynamic valgus by 11 blinded reviewers. Univariate analysis was performed to identify characteristics that predisposed athletes to increased dynamic valgus.

RESULTS

Eighty-five (47 female, 38 male) athletes with an average age of 15.4 years were included in this study. Forty-nine percent of athletes demonstrated an increase in dynamic valgus determined by drop-jump assessment after exercise. A significantly greater percentage of athletes were graded "medium or high risk" in jumps recorded after the exercise protocol (68%) as compared with before the exercise protocol (44%; P < .01). Female athletes (P < .01) and those older than 15 years of age (P < .01) were the most affected by fatigue.

CONCLUSIONS

In conclusion, our study found that exercise increases dynamic knee valgus in youth athletes. Female athletes and those older than 15 years of age were most significantly affected by exercise. Greater fatigue levels were found to correlate with an increase in dynamic knee valgus, which may place athletes at greater anterior cruciate ligament injury risk. The field-based exercise drop-jump test is a low-cost and reproducible screening tool to identify at-risk athletes who could possibly benefit from anterior cruciate ligament injury-prevention strategies.

LEVEL OF EVIDENCE

III, Comparative trial.

Oxford foot model kinematics in landings: A comparison between professional dancers and non-dancers

OBJECTIVES

Dancers frequently perform jump-landing activities, with the foot-ankle complex playing an essential role to attenuate the landing forces. However, scarce research has been conducted in professional dancers multi-segmented foot in landings. The aim of this study was to compare the multi-segmented foot kinematics between professional dancers and non-dancers, during forward and lateral single-leg jump-landings.

DESIGN

Descriptive group comparison.

METHODS

Marker trajectories and synchronized ground reaction forces of 15 professional dancers and 15 non-dancers were collected using motion capture and a force plate, during multidirectional single-leg jump-landings. Sagittal and frontal hindfoot-tibia, forefoot-hindfoot, and hallux-forefoot kinematics of the multi-segmented foot model were computed at initial contact, peak vertical ground reaction force and peak knee flexion. Repeated measures ANOVAs were conducted (p < 0.05).

RESULTS

Professional dancers landed with higher hindfoot-tibia and forefoot-hindfoot plantarflexion angles at initial contact (p < 0.001), and hindfoot-tibia dorsiflexion angles at peak vertical ground reaction force and peak knee flexion (p < 0.001) than non-dancers. Also, dancers exhibited higher sagittal hindfoot-tibia and forefoot-hindfoot excursions than non-dancers (p < 0.001). No statistically significant differences were found in the frontal plane.

CONCLUSIONS

The multi-segmented foot allows a comprehensive kinematic analysis of the different foot joints. In jump-landings, professional dancers higher hindfoot-tibia, and forefoot-hindfoot plantarflexion at initial contact, compared to non-dancers, contributed to a subsequent higher foot joints excursion. This pattern is commonly linked to a better shock absorption mechanism in landings.

The envelope of active hip motion in different sporting, recreational, and daily-living activities: A systematic review

BACKGROUND

In treating patients with limitations of hip motion, it is generally assumed that correction of bony morphology will provide the patient with the joint motion required to resume their activities. However, the positions of impingement and the specific excursions of joint motion required by each sport may vary. This systematic review aimed to define the envelope of active hip joint motion for participation in different sporting, recreational, and daily-living activities.

METHODS

The EMBASE, PubMed, Google Scholar, and Cochrane databases were searched to identify studies that reported kinematics of the hip in sporting, recreational, and daily-living activities. Inclusion criteria were (1) peer-reviewed articles reporting hip kinematics in a certain type of activity, and (2) presented in English. To synthesize the kinematic data, the peak values of kinematic components (i.e. flexion/extension, abduction/adduction, and internal/external rotation) during an activity, as well as the concurrent values in a certain phase of the activity were collected from each study.

RESULTS

A total of 67 studies met the inclusion criteria, involving 32 different types of activities. Seventeen activities required at least one component of supra-physiologic hip motion, however, there were eight different combinations of flexion/extension, abduction/adduction, and internal/external rotation observed. Specifically, three activities (sex, sitting cross-legged, and grand ecart lateral of ballet dancing) required simultaneous extreme degrees of all three components, five activities (arabesque, developpe devant right, and developpe a la seconde right of ballet dancing, picking up something, and taekwondo) required high degrees of two components, most commonly hip abduction combined with flexion or internal rotation.

SIGNIFICANCE

This review highlighted that many activities place supraphysiologic demands on hip joint motion, however, the kinematic components affected differ dramatically with the specific activity. This suggests that the demands of each patient's individual activities must be assessed before recommending or planning treatment rather than assuming that a fixed value of "normal" hip motion is applicable to all.

Revised Approach to the Role of Fatigue in Anterior Cruciate Ligament Injury Prevention: A Systematic Review with Meta-Analyses

BACKGROUND

Causes of anterior cruciate ligament (ACL) injuries are multifactorial. Anterior cruciate ligament injury prevention should thus be approached from a multifactorial perspective as well. Training to resist fatigue is an underestimated aspect of prevention programs given that the presence of fatigue may play a crucial role in sustaining an ACL injury.

OBJECTIVES

The primary objective of this literature review was to summarize research findings relating to the kinematic and kinetic effects of fatigue on single-leg landing tasks through a systematic review and meta-analysis. Other objectives were to critically appraise current approaches to examine the effects of fatigue together with elucidating and proposing an optimized approach for measuring the role of fatigue in ACL injury prevention.

METHODS

A systematic literature search was conducted in the databases PubMed (1978-November 2017), CINAHL (1992-November 2017), and EMBASE (1973-November 2017). The inclusion criteria were: (1) full text, (2) published in English, German, or Dutch, (3) healthy subjects, (4) average age ≥ 18 years, (5) single-leg jump landing task, (6) evaluation of the kinematics and/or kinetics of the lower extremities before and after a fatigue protocol, and (7) presentation of numerical kinematic and/or kinetic data. Participants included healthy subjects who underwent a fatigue protocol and in whom the effects of pre- and post-fatigue on three-dimensional lower extremity kinematic and kinetics were compared. Methods of data collection, patient selection, blinding, prevention of verification bias, and study design were independently assessed.

RESULTS

Twenty studies were included, in which four types of single-leg tasks were examined: the single-leg drop vertical jump, the single-leg drop landing, the single-leg hop for distance, and sidestep cutting. Fatigue seemed to mostly affect initial contact (decreased angles post-fatigue) and peak (increased angles post-fatigue) hip and knee flexion. Sagittal plane variables at initial contact were mostly affected under the single-leg hop for distance and sidestep cutting conditions whilst peak angles were affected during the single-leg drop jump.

CONCLUSIONS

Training to resist fatigue is an underestimated aspect of prevention programs given that the presence of fatigue may play a crucial role in sustaining an ACL injury. Considering the small number of variables affected after fatigue, the question arises whether the same fatigue pathways are affected by the fatigue protocols used in the included laboratory studies as are experienced on the sports field.

Dual Kinect v2 system can capture lower limb kinematics reasonably well in a clinical setting: concurrent validity of a dual camera markerless motion capture system in professional football players

Objectives

To determine whether a dual-camera markerless motion capture system can be used for lower limb kinematic evaluation in athletes in a preseason screening setting.

Design

Descriptive laboratory study.

Setting

Laboratory setting.

Participants

Thirty-four (n=34) healthy athletes.

Main outcome measures

Three dimensional lower limb kinematics during three functional tests: Single Leg Squat (SLS), Single Leg Jump, Modified Counter-movement Jump. The tests were simultaneously recorded using both a marker-based motion capture system and two Kinect v2 cameras using iPi Mocap Studio software.

Results

Excellent agreement between systems for the flexion/extension range of motion of the shin during all tests and for the thigh abduction/adduction during SLS were seen. For peak angles, results showed excellent agreement for knee flexion. Poor correlation was seen for the rotation movements.

Conclusions

This study supports the use of dual Kinect v2 configuration with the iPi software as a valid tool for assessment of sagittal and frontal plane hip and knee kinematic parameters but not axial rotation in athletes.

Landing biomechanics in anterior cruciate ligament reconstructed females who pass or fail a functional test battery

BACKGROUND

A functional test battery (FTB) has been proposed to determine return to full activity following anterior cruciate ligament reconstruction (ACLR). However, there is little biomechanical evidence of FTB usefulness. The purpose of this study was to compare knee joint landing and cutting biomechanics between ACLR patients who passed (ACLR-Pass), failed (ACLR-Fail), and healthy females (Healthy) before and after exercise.

METHODS

Thirty females were included: 10 ACLR-Pass, eight ACLR-Fail and 12 Healthy. Participants performed a FTB consisting of The 2000 International Knee Documentation Committee Subjective Knee Evaluation Form, the Knee Outcome Survey Activities of Daily Living Scale, and quadricep strength and single-leg hop tests. Double-leg jump landing (DLJL) and single-leg jump cutting (SLJC) biomechanics were assessed before and after exercise.

RESULTS

Significant main effects of exercise were found during DLJL: lesser knee flexion angle at initial contact after exercise (before exercise: 15.8 ± 5.0, after exercise: 14.2 ± 5.4, P = 0.01, ηp 2 = 0.25); and during SLJC: smaller peak knee extension moment (before exercise: -0.33 ± 0.1, after exercise: -0.31 ± 0.1, P = 0.02, ηp 2 = 0.18). While there was a significant group by time interaction effect with lesser peak knee flexion angle after exercise, this interaction effect was likely driven by a reduction in peak knee flexion in only the Healthy group.

CONCLUSIONS

Healthy females exhibited a reduction in peak knee flexion during SLJC after exercise. However, there were no differences in ACLR knee biomechanics during DLJL and SLJC performed before and after exercise.

Comparison of lower limb stiffness between male and female dancers and athletes during drop jump landings

Repetition of jumps in dance and sport training poses a potential injury risk; however, non-contact landing injuries are more common in athletes than dancers. This study aimed to compare the lower limb stiffness characteristics of dancers and athletes during drop landings to investigate possible mechanisms of impact-related injuries. Kinematics and kinetics were recorded as 39 elite modern and ballet dancers (19 men and 20 women) and 40 college-level team sport athletes (20 men and 20 women) performed single-legged drop landings from a 30-cm platform. Vertical leg stiffness and joint stiffness of the hip, knee, and ankle were calculated using a spring-mass model. Stiffness data, joint kinematics, and moments were compared with a group-by-sex 2-way analysis of variance. Multiple linear regression was used to assess the relative contribution of hip and knee and ankle joint stiffness to variance in overall vertical leg stiffness for dancers and athletes. Dancers had lower leg (P < 0.001), knee joint (P = 0.034), and ankle joint stiffness (P = 0.043) than athletes. This was facilitated by lower knee joint moments (P = 0.012) and greater knee (P = 0.029) and ankle joint (P = 0.048) range of motion in dancers. Males had higher leg (P < 0.001) and ankle joint stiffness (P < 0.001) than females. This occurred through lower ankle range of motion (P < 0.001) and greater ankle moment (P = 0.022) compared to females. Male and female dancers demonstrated reduced lower limb stiffness compared to athletes, indicating a more pliable landing technique. Dance training techniques could potentially inform approaches to injury prevention in athletes.

Movement profile influences systemic stress and biomechanical resilience to high training load exposure

OBJECTIVES

Determine the influence of movement profile on systemic stress and mechanical loading before and after high training load exposure.

DESIGN

Cross-sectional cohort study.

METHODS

43 physically active, college-aged field or court sport female athletes participated in this study. Participants were assigned to a "excellent" (n=22; age=20.5±1.9yrs, height=1.67±0.67m, mass=64.5±7.8kg) or "poor" (n=21; age=20.4±1.3yrs, height=1.69±0.67m, mass=60.9±6.1kg) movement group defined by The Landing Error Scoring System. Participants completed five cycles of high training load exercise of 5-min treadmill-running at a speed coincident with 100-120% ventilatory threshold and 10 jump-landings from a 30-cm box. Jump-landing vertical ground reaction force and serum cortisol were evaluated prior to and following exercise. Vertical ground reaction force ensemble averages and 95% confidence interval waveforms were generated for pre-exercise, post-exercise, and pre-post exercise changes. A two-way mixed model ANOVA was used to evaluate the effect of movement profile on systemic stress before and after exercise.

RESULTS

There was no significant difference in changes in serum cortisol between the poor and excellent groups (p=0.69) in response to exercise. Overall, individuals in the poor group exhibited a higher serum cortisol level (p<0.05, d=0.85 [0.19,1.48]). The poor group exhibited higher magnitude vertical ground reaction force prior to (d=1.02-1.26) and after exercise (d=1.15) during a majority of the stance phase.

CONCLUSIONS

Individuals with poor movement profiles experience greater mechanical loads compared to individuals with excellent movement profiles. A poor movement profile is associated with greater overall concentrations of circulating cortisol, representative of greater systemic stress.

Differences in lower limb biomechanics between ballet dancers and non-dancers during functional landing tasks

OBJECTIVES

To determine the differences in the lower limb landing biomechanics of adolescent ballet dancers compared to non-dancers when performing a hop and a stop jump task.

DESIGN

Cross-sectional.

SETTING

Laboratory.

PARTICIPANTS

Thirteen adolescent female ballet dancers (11.8 ± 1.1 years) and 17 non-dancers (10.9 ± 0.8 years) performed hop and stop jump tasks.

MAIN OUTCOME MEASURES

Vertical ground reaction force, and three-dimensional ankle, knee and hip joint angles and moments during the landing phase.

RESULTS

Dancers displayed greater sagittal plane joint excursions during the hop and stop jump at the ankle (mean difference = 22.0°, P < 0.001, 14.8°, P < 0.001 respectively), knee (mean difference = 18.1°, P = 0.001, 9.8°, P = 0.002 respectively) and hip (stop jump task; mean difference = 8.3°, P = 0.008). Dancers displayed a larger hip extensor moment compared to non-dancers (P < 0.001) during the stop jump task only. Dancers also took longer to reach peak vGRF and jumped three times higher than non-dancers (P < 0.001) during the stop jump task. No difference in peak vGRF between groups was displayed for either task.

CONCLUSIONS

Adolescent dancers demonstrate a transfer of landing technique to non-ballet specific tasks, reflective of the greater jump height and sagittal plane joint excursions. This landing strategy may be associated with the low rate of non-contact ACL injuries in female dancers.

Peak Lower Extremity Landing Kinematics in Dancers and Nondancers

CONTEXT

  Anterior cruciate ligament (ACL) injuries often occur during jump landings and can have detrimental short-term and long-term functional effects on quality of life. Despite frequently performing jump landings, dancers have lower incidence rates of ACL injury than other jump-landing athletes. Planned versus unplanned activities and footwear may explain differing ACL-injury rates among dancers and nondancers. Still, few researchers have compared landing biomechanics between dancers and nondancers.

OBJECTIVE

  To compare the landing biomechanics of dancers and nondancers during single-legged (SL) drop-vertical jumps.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 39 healthy participants, 12 female dancers (age = 20.9 ± 1.8 years, height = 166.4 ± 6.7 cm, mass = 63.2 ± 16.4 kg), 14 female nondancers (age = 20.2 ± 0.9 years, height = 168.9 ± 5.0 cm, mass = 61.6 ± 7.7 kg), and 13 male nondancers (age = 22.2 ± 2.7 years, height = 180.6 ± 9.7 cm, mass = 80.8 ± 13.2 kg).

INTERVENTION(S)

  Participants performed SL-drop-vertical jumps from a 30-cm-high box in a randomized order in 2 activity (planned, unplanned) and 2 footwear (shod, barefoot) conditions while a 3-dimensional system recorded landing biomechanics.

MAIN OUTCOME MEASURE(S)

  Overall peak sagittal-plane and frontal-plane ankle-, knee-, and hip-joint kinematics (joint angles) were compared across groups using separate multivariate analyses of variance followed by main-effects testing and pairwise-adjusted Bonferroni comparisons as appropriate ( P < .05).

RESULTS

  No 3-way interactions existed for sagittal-plane or frontal-plane ankle (Wilks λ = 0.85, P = .11 and Wilks λ = 0.96, P = .55, respectively), knee (Wilks λ = 1.00, P = .93 and Wilks λ = 0.94, P = .36, respectively), or hip (Wilks λ = 0.99, P = .88 and Wilks λ = 0.97, P = .62, respectively) kinematics. We observed no group × footwear interactions for sagittal-plane or frontal-plane ankle (Wilks λ = 0.94, P = .43 and Wilks λ = 0.96, P = .55, respectively), knee (Wilks λ = 0.97, P = .60 and Wilks λ = 0.97, P = .66, respectively), or hip (Wilks λ = 0.99, P = .91 and Wilks λ = 1.00, P = .93, respectively) kinematics, and no group × activity interactions were noted for ankle frontal-plane (Wilks λ = 0.92, P = .29) and sagittal- and frontal-plane knee (Wilks λ = 0.99, P = .81 and Wilks λ = 0.98, P = .77, respectively) and hip (Wilks λ = 0.88, P = .13 and Wilks λ = 0.85, P = .08, respectively) kinematics. A group × activity interaction (Wilks λ = 0.76, P = .02) was present for ankle sagittal-plane kinematics. Main-effects testing revealed different ankle frontal-plane angles across groups ( F_2,28 = 3.78, P = .04), with male nondancers having greater ankle inversion than female nondancers ( P = .05).

CONCLUSIONS

  Irrespective of activity type or footwear, female nondancers landed with similar hip and knee kinematics but greater peak ankle eversion and less peak ankle dorsiflexion (ie, positions associated with greater ACL injury risk). Ankle kinematics may differ between groups due to different landing strategies and training used by dancers. Dancers' training should be examined to determine if it results in a reduced occurrence of biomechanics related to ACL injury during SL landing.

Effect of Posttrial Visual Feedback and Fatigue During Drop Landings on Patellofemoral Joint Stress in Healthy Female Adults

Patellofemoral pain (PFP) is common in females. Patellofemoral joint stress (PFJS) may be important in the development of PFP. Ground reaction force (GRF) during landing activities may impact PFJS. Our purpose was to determine how healthy females alter their landing mechanics using visual posttrial feedback on their GRF and assess how PFJS changes. Seventeen participants performed a series of drop landings during 3 conditions: baseline, feedback, and postfatigue feedback. The fatigue protocol used repetitive jump squats. Quadriceps force was estimated through inverse-dynamics-based static optimization approach. Then, PFJS was calculated using a musculoskeletal model. Multivariate differences were shown across conditions (P = .01). Univariate tests revealed differences in PFJS (P = .014), knee range of motion (P = .001), and GRF (P = .005). There were no differences in quadriceps force (P = .125). PFJS and GRF decreased from baseline to feedback (P = .002, P = .007, respectively), while PFJS increased from feedback to postfatigue feedback (P = .03). Knee range of motion increased from baseline to feedback (P = .043), then decreased from feedback to postfatigue feedback (P < .001). Visual feedback of GRF may reduce PFJS, but may not effectively transfer to a fatigued state.

Effect of Fatigue Protocols on Lower Limb Neuromuscular Function and Implications for Anterior Cruciate Ligament Injury Prevention Training: A Systematic Review

BACKGROUND

Approximately two-thirds of anterior cruciate ligament (ACL) tears are sustained during noncontact situations when an athlete is cutting, pivoting, decelerating, or landing from a jump. Some investigators have postulated that fatigue may result in deleterious alterations in lower limb biomechanics during these activities that could increase the risk of noncontact ACL injuries. However, prior studies have noted a wide variation in fatigue protocols, athletic tasks studied, and effects of fatigue on lower limb kinetics and kinematics.

PURPOSE

First, to determine if fatigue uniformly alters lower limb biomechanics during athletic tasks that are associated with noncontact ACL injuries. Second, to determine if changes should be made in ACL injury prevention training programs to alter the deleterious effects of fatigue on lower limb kinetics and kinematics.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic review of the literature using MEDLINE was performed. Key terms were fatigue, neuromuscular, exercise, hop test, and single-legged function tests. Inclusion criteria were original research studies involving healthy participants, use of a fatigue protocol, study of at least 1 lower limb task that involved landing from a hop or jump or cutting, and analysis of at least 1 biomechanical variable.

RESULTS

Thirty-seven studies involving 806 athletes (485 female, 321 male; mean age, 22.7 years) met the inclusion criteria. General fatigue protocols were used in 20 investigations, peripheral protocols were used in 17 studies, and 21 different athletic tasks were studied (13 single-legged, 8 double-legged). There was no consistency among investigations regarding the effects of fatigue on hip, knee, or ankle joint angles and moments or surface electromyography muscle activation patterns. The fatigue protocols typically did not produce statistically significant changes in ground-reaction forces.

CONCLUSION

Published fatigue protocols did not uniformly produce alterations in lower limb neuromuscular factors that heighten the risk of noncontact ACL injuries. Therefore, justification does not currently exist for major changes in ACL injury prevention training programs to account for potential fatigue effects. However, the effect of fatigue related to ACL injuries is worthy of further investigation, including the refinement of protocols and methods of analysis.

INJURIES IN PROFESSIONAL DANCERS: A SYSTEMATIC REVIEW

ABSTRACT Movement is a fundamental element of dance, and the dancer’s body is the raw material through which the art of dance is expressed; for this, it demands the utmost discipline in the pursuit of technical and artistic excellence. To meet the professional demands, dancers are subjected to strenuous training routines, which can lead to the development of injuries in this environment. The objective was to examine the etiology, main affected segments, prevalence, and instruments used to evaluate the lesions in studies with professional dancers and/or in comparison with similar populations. We selected articles published in the last decade in the databases BIREME, LILACS, MEDLINE EBSCO, WEB OF SCIENCE, SCOPUS (Elsevier), and PubMed, with cross-sectional, observational cohort and case control design published in Portuguese, English, or Spanish. Systematic reviews, case studies, dissertations, theses, book chapters, cross-referenced articles, and studies published outside of the last decade were not included. The search used combinations of the terms “dancing* and athletic injuries* and musculoskeletal* and pain*”. A principal investigator and two reviewers conducted the survey and analyzed all the potentially relevant articles, initially by the abstract and title. Twelve articles were included, with 1,149 participants (965 professional dancers of classical ballet, modern dance, contemporary dance, and breakdance, 104 amateur dancers, and 80 elite athletes). Nine studies found simultaneous lesions with emphasis on the foot and ankle (n=4), upper and lower limbs lesions (n=4) and lower and upper limb joints (n=1). Other studies have found lesions in the anterior cruciate ligament (n=3). There was no agreement regarding the instruments for detecting lesions in professional, pre-professional, and amateur dancers. There was a prevalence of studies aimed at classical ballet modality, evidencing a higher frequency of lower limb involvement in professional dancers.

ACL Injury Prevention Training Results in Modification of Hip and Knee Mechanics During a Drop-Landing Task

Background:

Injury prevention training has been shown to be effective in reducing the incidence of noncontact anterior cruciate ligament (ACL) injury; however, the underlying reason for the success of these training programs is unclear.

Purpose:

To investigate whether an ACL injury prevention program that has been shown to reduce the incidence of ACL injury alters sagittal plane hip and knee biomechanics during a drop-landing task.

Study Design:

Descriptive laboratory study.

Methods:

Thirty female club soccer players (age range, 11-17 years) with no history of knee injury participated in this study. Kinematics and ground-reaction forces were collected while each participant performed a drop-landing task prior to and immediately after participation in a 12-week ACL injury prevention training program.

Results:

After ACL injury prevention training, participants demonstrated decreased knee extensor moments (P = .03), increased energy absorption at the hip (P = .04), decreased knee-to-hip extensor moment ratios (P = .05), and decreased knee-to-hip energy absorption ratios (P = .03).

Conclusion:

Participation in an ACL injury prevention training program decreased reliance on the knee extensor muscles and improved use of the hip extensor muscles, which may explain the protective effect of this type of training program on ACL injury.

Clinical Relevance:

Based on these findings, clinicians can better understand how ACL injury prevention training, such as the Prevent Injury and Enhance Performance (PEP) Program, may change movement behavior at both the hip and knee. Furthermore, the study findings may support the implementation of the PEP Program, or a similar program, for clinicians aiming to improve use of the hip in an effort to reduce knee loading and consequent injuries.

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.

Lower Limb and Trunk Biomechanics After Fatigue in Competitive Female Irish Dancers

CONTEXT

  Because of the increasing popularity of participation in Irish dance, the incidence of lower limb injuries is high among this competitive population.

OBJECTIVE

  To investigate the effects of fatigue on the peak lower limb and trunk angles as well as the peak lower limb joint forces and moments of competitive female Irish dancers during the performance of a dance-specific single-limb landing.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Fourteen healthy, female, competitive Irish dancers (age = 19.4 ± 3.7 years, height = 165.3 ± 5.9 cm, mass = 57.9 ± 8.2 kg).

INTERVENTION(S)

  Participants performed an Irish dance-specific leap before and after a dance-specific fatigue protocol. During each landing movement, 3-dimensional lower limb kinematics (250 Hz) and ground reaction forces (1000 Hz) were collected. Paired t tests were performed to determine the differences (P ≤ .05) in lower limb and trunk biomechanics prefatigue and postfatigue.

MAIN OUTCOME MEASURE(S)

  Peak lower limb and trunk angles as well as peak lower limb joint reaction forces and external moments.

RESULTS

  Compared with the prefatigue trials, dancers landed with reduced ankle plantar flexion (P = .003) and hip external rotation (P = .007) and increased hip-adduction alignment (P = .034) postfatigue. Dancers displayed greater anterior shear (P = .003) and compressive (P = .024) forces at the ankle and greater external knee-flexion moments (P = .024) during the postfatigue compared with the prefatigue landing trials.

CONCLUSIONS

  When fatigued, dancers displayed a decline in landing performance in terms of aesthetics as well as increased ankle- and knee-joint loading, potentially exposing them to a greater risk of injuries.

Effects of Sex and Fatigue on Biomechanical Measures During the Drop-Jump Task in Children

Background:

Female athletes have a higher rate of anterior cruciate ligament (ACL) injury than males from adolescence and into maturity, which is suggested to result from sex-specific changes in dynamic movement patterns with maturation. Few studies have studied movement strategies and response to fatigue in children.

Purpose:

To evaluate the effect of fatigue on biomechanical variables associated with increased risk for ACL injury during a drop-jump (DJ) performance in children.

Study Design:

Controlled laboratory study.

Methods:

A total of 116 children (mean age, 10.4 years) were recruited from local sports clubs and performed 5 repetitions of a DJ task before and after a fatigue protocol. Kinematic and kinetic data from initial contact (IC) to the first peak vertical ground reaction force (vGRF) were analyzed for both limbs, including limb and fatigue as within-subject factors for analyses between boys and girls. Pearson correlation coefficients were calculated to identify associations between variables of interest.

Results:

Girls demonstrated greater peak vGRF values than boys (by 8.1%; P < .05), there were greater peak vGRF values for the right limb than the left (by 6.2%; P < .001), and fatigue led to slightly greater values (P < .05). Although weak, the correlation between peak vGRF values and knee flexion excursion was stronger for girls (r = –0.20) than boys (r = –0.08) (P < .006). Fatigue resulted in greater knee flexion angles at IC and less excursion during landing, more so for girls (by 6.1° vs 1.4°; interaction, P < .001), although the knee flexion moment was generally lowered by fatigue (P < .001). Limb asymmetry in knee flexion moments was more pronounced for boys than for girls (interaction, P < .05), contrary to that seen in frontal plane knee moments, where asymmetry was much greater in girls than boys (interaction, P < .001).

Conclusion:

Even as young athletes, girls and boys seem to adopt dissimilar movement strategies and are differently affected by fatigue.

Clinical Relevance:

Injury prevention programs should be considered at an earlier age in an effort to lower the risk of ACL injury in athletes.

How much is too much? (Part 1) International Olympic Committee consensus statement on load in sport and risk of injury

Athletes participating in elite sports are exposed to high training loads and increasingly saturated competition calendars. Emerging evidence indicates that poor load management is a major risk factor for injury. The International Olympic Committee convened an expert group to review the scientific evidence for the relationship of load (defined broadly to include rapid changes in training and competition load, competition calendar congestion, psychological load and travel) and health outcomes in sport. We summarise the results linking load to risk of injury in athletes, and provide athletes, coaches and support staff with practical guidelines to manage load in sport. This consensus statement includes guidelines for (1) prescription of training and competition load, as well as for (2) monitoring of training, competition and psychological load, athlete well-being and injury. In the process, we identified research priorities.