Leg Dominance as a Risk Factor for Lower-Limb Injuries in Downhill Skiers-A Pilot Study into Possible Mechanisms

A Potential Mechanism Involved in the Regularity of Center-of-Pressure Displacements During Achieving Unipedal Equilibrium on Stable and Unstable Surfaces

Sample entropy (SampEn) is a widely used measure for estimating the regularity of center-of-pressure (COP) trajectories, with high COP regularity (low SampEn) commonly interpreted as ineffective postural control. The current study aimed to investigate one possible source of COP regularity-agonist-antagonist coactivation-resulting in joint stiffness or action stability. A cross-correlation analysis was conducted to determine the similarity (coactivation) level of 5 pairs of lower limb agonist-antagonist electromyographic signals. SampEn was applied to anteroposterior (ap) and mediolateral (ml) COP displacements. Electromyographic and COP signals were simultaneously derived from 25 active young adults (25.6 ± 4.0 years) during unipedal balancing on stable and multiaxial-unstable surfaces. Then, the correlation between individual agonist-antagonist cross-correlation coefficients and SampEn-COP was explored. The results show that only the tibialis anterior-peroneus longus (TA-PL) coactivations are negatively correlated with SampEn-COPap/ml (P ≤ .030) in both surface conditions, with greater TA-PL coactivation appearing with lower SampEn-COPap/ml. In addition, sex effects as one factor that might influence postural control were also tested. Women exhibited greater TA-PL coactivation (P = .017) and lower SampEn-COPap (P = .005) than men. Together, TA-PL coactivation could be one possible origin of COP regularity, but its effects might be detrimental to unipedal postural control, especially for women.

Risk Factors for Midfoot Arthritis Associated With Medical History by Weight Bearing Computed Tomography

Tarso-metatarsal joints and naviculocuneiform joints comprising midfoot is the second most commonly involved joints following the first metatarsophalangeal joint in the foot. However, related factors of midfoot arthritis (MA) have been rarely reported. The bony structure and alignment can be more precisely assessed using Weight-Bearing Computed Tomography (WBCT) than conventional radiographs. Therefore, the aim of this study was to investigate risk factors for MA related to medical history and comorbid foot deformities using WBCT. WBCT data from September 2014 to April 2022 were extracted from a single referral hospital. All cases were divided into two groups by the presence of MA. Twenty-five potential related factors including demographics, etiology, and common co-occurring foot deformities were collected for comparison. Six hundred six cases (247 males and 359 females) among consecutive 1316 cases between September 2014 to April 2022 were selected. One hundred thirty-nine male cases (56.3%) and 210 female cases (58.5%) showed MA. In stepwise multiple logistic regression analysis, 5 factors remained statistically significant. The multivariate-adjusted odds ratios for age, laterality, body mass index (BMI), Progressive Collapsing Foot Deformity (PCFD), and lesser toe deformities (LTD) were 1.08, 1.54, 1.05, 6.62, and 3.03 respectively. Risk factors for MA associated with medical history and foot deformities included age, laterality, BMI, PCFD, and LDT.

Investigation of the functional and biomechanical effect of instrument-assisted soft tissue mobilization technique in individuals with asymptomatic dynamic knee valgus - Randomized controlled trial

Although there are studies showing that myofascial release will increase muscle force production, the contribution of its application alone to muscle force production has not been examined. Aim of the study is to investigate the effect of instrument-assisted soft tissue mobilization (IASTM) on eccentric strength, frontal plane projection angle (FPPA), dynamic (DPS), and static postural stability (SPS), femoral internal rotation (FIR) angle in females with dynamic knee valgus (DKV). A total of 44 recreationally active females with asymptomatic DKV (age: 21,39 ± 1,79, body mass index: 20,09 ± 2,45) participated and were randomly assigned to either control group (CG) or IASTM group (IASTMG). Participants' eccentric contraction strength, FPPA, DPS, SPS, and FIR on the involved leg were measured pre- and post. IASTM application was applied to IASTMG for 6 weeks, twice a week, for 5 min, using Graston Technique® instruments on gluteus medius. CG received no intervention. In comparison of ECS difference values, change in IASTMG was found to be statistically significantly higher than CG (p = .004; p < .01). There was no statistical difference in comparison of FIR and FPPA values (respectively p = .213, p = .360; p < .05). In SPS and DPS evaluation, a statistically significant improvement was observed in favor of IASTMG in comparison of both intergroup and difference values (p < .05 for all). Strength gain without exercise can increase postural stability, but it isn't sufficient to correct faulty movement patterns. We recommend adding IASTM to injury prevention programs, but there is a need to investigate the effect of IASTM with technique correction feedback.

Sensitivity of principal component analysis outcomes to data pre-processing conditions when quantifying trial-to-trial variability in whole-body kinematics

This study investigated whether modes of variance in trial-to-trial whole-body kinematic variability identified by principal component analysis (PCA) were consistent across data pre-processing conditions generated from a common dataset. Comparisons made included 1) when trajectory data was expressed in a global vs. local reference frame; 2) when the number of landmarks used to represent whole-body motion differed, and; 3) whether input trajectory data were normalized to participant stature. Varying data pre-processing conditions prior to PCA does not bias the total variance identified. However, it can influence how modes of variance are dispersed across PCs, which in turn, can influence interpretation.

Postural control and cognitive flexibility in skilled athletes: Insights from dual-task performance and event-related potentials

Athletes of skill-oriented sports (hereinafter referred to as "skilled athletes"), such as gymnasts and rhythmic gymnasts, have demonstrated better postural control than nonathletes. However, previous studies have mainly focused on single postural tasks and have not considered how skilled athletes use and allocate attentional resources during postural control. This research used the event-related potential (ERP) to explore the postural control performance of skilled athletes under cognitive processes and their utilization and allocation of attentional resources. A dual-task paradigm was used to simulate the actual situation in sports. 26 skilled athletes and 26 nonathletes were required to perform postural control and task-switching simultaneously. The results showed that skilled athletes demonstrated more postural control stability and a higher accuracy of task-switching than nonathletes in all dual tasks. Compared with nonathletes, they showed a stable enhanced N1 (electrodes: Oz, O1, and O2) amplitude during three postures. Moreover, larger N2 component on Fz, FCz, and Cz and theta band power was found in the frontal cortex (on Fz, FCz) of skilled athletes under feet together and single leg standing posture. The study illustrated that skilled athletes show greater frontal activation during dual tasks, which allows for more rational and flexible brain attentional resource input and allocation in cognitive processes, this may be due to long-term professional training, which enables them to have a higher level of automation of postural control and cognitive flexibility. This study's results offer valuable insights into the interplay between postural control and multitasking in skilled athletes, and its outcomes carry significant implications for the training and assessment of athletes across various sports.

Bilateral Deficits in Dynamic Postural Stability in Females Persist Years after Unilateral ACL Injury and Are Modulated by the Match between Injury Side and Leg Dominance

Previous research has documented brain plasticity after an anterior cruciate ligament (ACL) tear and suggests that these neural adaptations contribute to poorer motor control. Since both brain hemispheres show adaptations, we hypothesized that reduced dynamic stability occurs not only in the injured, but also the contralateral, uninjured leg. Further, given brain hemispheric specialization's impact on motor coordination, we hypothesized the need to consider the injury side. A total of 41 female athletes and 18 controls performed single-leg jump-landings. Dynamic postural stability was measured as time-to-stabilization (TTS). We found reduced medio-lateral dynamic stability for the ACL injured leg (p = 0.006) with a similar trend for the contralateral leg (p = 0.050) compared to the control group. However, when distinguishing between injuries to the dominant and non-dominant legs, we found increased medio-lateral TTS only if the injury had occurred on the dominant side where landings on injured (p = 0.006) and contralateral (p = 0.036) legs required increased TTS. Assessments of dynamic stability, e.g., in the context of return-to-sport, should consider the injury side and compare results not only between the injured and the contralateral leg, but also to uninjured controls. Future research should not pool data from the dominant-leg ACL with non-dominant-leg ACL injuries when assessing post-injury motor performance.

Foot and Ankle Injuries in Elite South African Cricketers: A Descriptive Analysis of Injury Surveillance Data

Introduction

Injury surveillance is an important part of injury risk reduction in the sporting population. This study describes the type, side (dominant or non-dominant), occurrence, impact, activity of onset, and severity of foot and ankle injuries in elite South African male and female cricketers.

Methods

Foot and ankle injuries sustained by elite cricket players between 2018 and 2021, obtained from the records of Cricket South Africa, were descriptively analysed.

Results

A total of 104 foot and ankle injuries in 82 players were recorded. The majority (n = 100; 96%) of injuries were on the non-dominant side. Bowling (n = 31; 30%) and fielding (n = 20; 19%) contributed to most injuries. The majority were first-time (n = 83; 80%) and non-impact injuries (n = 62; 60%). Fifty percent (n = 52) of injuries rendered players unable to participate in at least one match or practice session. Lateral ankle ligament injury was the most common injury sustained (n = 36; 35%).

Conclusion

The findings from this study can inform future researchers and assist healthcare service needs relating to injury risk reduction and management programmes. Effective rehabilitation programmes may reduce the risk of reinjury. Ideally, these programmes need to be role specific.

Age and Visual Contribution Effects on Postural Control Assessed by Principal Component Analysis of Kinematic Marker Data

Postural control, the ability to control the body's position in space, is considered a critical aspect of health outcomes. This current study aimed to investigate the effects of age and visual contribution on postural control. To this end, principal component analysis (PCA) was applied to extract movement components/synergies (i.e., principal movements, PMs) from kinematic marker data of bipedal balancing on stable and unstable surfaces with eyes closed and open, pooled from 17 older adults (67.8 ± 6.6 years) and 17 young adults (26.6 ± 3.3 years), one PCA-analysis for each surface condition. Then, three PCA-based variables were computed for each PM: the relative explained variance of PM-position (PP_rVAR) and of PM-acceleration (PA_rVAR) for measuring the composition of postural movements and of postural accelerations, respectively, and the root mean square of PM-acceleration (PA_RMS) for measuring the magnitude of neuromuscular control. The results show the age and visual contribution effects observed in PM₁, resembling the anteroposterior ankle sway in both surface conditions. Specifically, only the greater PA₁_rVAR and PA₁_RMS are observed in older adults (p ≤ 0.004) and in closed-eye conditions (p < 0.001), reflecting their greater need for neuromuscular control of PM₁ than in young adults and in open-eye conditions.

Walking Stability and Risk of Falls

Walking stability is considered a necessary physical performance for preserving independence and preventing falls. The current study investigated the correlation between walking stability and two clinical markers for falling risk. Principal component analysis (PCA) was applied to extract the three-dimensional (3D) lower-limb kinematic data of 43 healthy older adults (69.8 ± 8.5 years, 36 females) into a set of principal movements (PMs), showing different movement components/synergies working together to accomplish the walking task goal. Then, the largest Lyapunov exponent (LyE) was applied to the first five PMs as a measure of stability, with the interpretation that the higher the LyE, the lower the stability of individual movement components. Next, the fall risk was determined using two functional motor tests-a Short Physical Performance Battery (SPPB) and a Gait Subscale of Performance-Oriented Mobility Assessment (POMA-G)-of which the higher the test score, the better the performance. The main results show that SPPB and POMA-G scores negatively correlate with the LyE seen in specific PMs (p ≤ 0.009), indicating that increasing walking instability increases the fall risk. The current findings suggest that inherent walking instability should be considered when assessing and training the lower limbs to reduce the risk of falling.

Leg Dominance—Surface Stability Interaction: Effects on Postural Control Assessed by Smartphone-Based Accelerometry

The preferential use of one leg over another in performing lower-limb motor tasks (i.e., leg dominance) is considered to be one of the internal risk factors for sports-related lower-limb injuries. The current study aimed to investigate the effects of leg dominance on postural control during unipedal balancing on three different support surfaces with increasing levels of instability: a firm surface, a foam pad, and a multiaxial balance board. In addition, the interaction effect between leg dominance and surface stability was also tested. To this end, a tri-axial accelerometer-based smartphone sensor was placed over the lumbar spine (L5) of 22 young adults (21.5 ± 0.6 years) to record postural accelerations. Sample entropy (SampEn) was applied to acceleration data as a measure of postural sway regularity (i.e., postural control complexity). The results show that leg dominance (p < 0.001) and interaction (p < 0.001) effects emerge in all acceleration directions. Specifically, balancing on the dominant (kicking) leg shows more irregular postural acceleration fluctuations (high SampEn), reflecting a higher postural control efficiency or automaticity than balancing on the non-dominant leg. However, the interaction effects suggest that unipedal balancing training on unstable surfaces is recommended to reduce interlimb differences in neuromuscular control for injury prevention and rehabilitation.

Assessing Walking Stability Based on Whole-Body Movement Derived from a Depth-Sensing Camera

Stability during walking is considered a crucial aspect of assessing gait ability. The current study aimed to assess walking stability by applying principal component analysis (PCA) to decompose three-dimensional (3D) whole-body kinematic data of 104 healthy young adults (21.9 ± 3.5 years, 54 females) derived from a depth-sensing camera into a set of movement components/synergies called "principal movements" (PMs), forming together to achieve the task goal. The effect of sex as the focus area was tested on three PCA-based variables computed for each PM: the relative explained variance (rVAR) as a measure of the composition of movement structures; the largest Lyapunov exponent (LyE) as a measure of variability; and the number of zero-crossings (N) as a measure of the tightness of neuromuscular control. The results show that the sex effects appear in the specific PMs. Specifically, in PM₁, resembling the swing-phase movement, females have greater LyE (p = 0.013) and N (p = 0.017) values than males. Moreover, in PM₃, representing the mid-stance-phase movement, females have smaller rVAR (p = 0.020) but greater N (p = 0.008) values than males. These empirical findings suggest that the inherent sex differences in walking stability should be considered in assessing and training locomotion.

Quantitative downhill skiing technique analysis according to ski instruction curricula: A proof-of-concept study applying principal component analysis on wearable sensor data

Downhill skiing technique represents the complex coordinative movement patterns needed to control skiing motion. While scientific understanding of skiing technique is still incomplete, not least due to challenges in objectively measuring it, practitioners such as ski instructors have developed sophisticated and comprehensive descriptions of skiing technique. The current paper describes a 3-step proof-of-concept study introducing a technology platform for quantifying skiing technique that utilizes the practitioners' expert knowledge. The approach utilizes an inertial measurement unit system (Xsens™) and presents a motion analysis algorithm based on the Principal Movement (PM) concept. In step 1, certified ski instructors skied specified technique elements according to technique variations described in ski instruction curricula. The obtained data was used to establish a PM-coordinate system for skiing movements. In step 2, the techniques parallel and carving turns were compared. Step 3 presents a case study where the technique analysis methodology is applied to advise an individual skier on potential technique improvements. All objectives of the study were met, proving the suitability of the proposed technology for scientific and applied technique evaluations of downhill skiing. The underlying conceptual approach - utilizing expert knowledge and skills to generate tailored variability in motion data (step 1) that then dominate the orientation of the PMs, which, in turn, can serve as measures for technique elements of interest - could be applied in many other sports or for other applications in human movement analyses.

Sex Difference in Running Stability Analyzed Based on a Whole-Body Movement: A Pilot Study

A sex-specific manner in running tasks is considered a potential internal injury risk factor in runners. The current study aimed to investigate the sex differences in running stability in recreational runners during self-preferred speed treadmill running by focusing on a whole-body movement. To this end, principal component analysis (PCA) was applied to kinematic marker data of 22 runners (25.7 ± 3.3 yrs.; 12 females) for decomposing the whole-body movements of all participants into a set of principal movements (PMs), representing different movement synergies forming together to achieve the task goal. Then, the sex effects were tested on three types of PCA-based variables computed for individual PMs: the largest Lyapunov exponent (LyE) as a measure of running variability; the relative standard deviation (rSTD) as a measure of movement structures; and the root mean square (RMS) as a measure of the magnitude of neuromuscular control. The results show that the sex effects are observed in the specific PMs. Specifically, female runners have lower stability (greater LyE) in the mid-stance-phase movements (PM₄₋₅) and greater contribution and control (greater rSTD and RMS) in the swing-phase movement (PM₁) than male runners. Knowledge of an inherent sex difference in running stability may benefit sports-related injury prevention and rehabilitation.

Relationship between Lower Extremity Fitness Levels and Injury Risk among Recreational Alpine Skiers: A Prospective Cohort Study

Background: Although the importance of physical fitness for injury prevention is recognized in sports medicine and rehabilitation, few studies have investigated this factor among recreational alpine skiers. Objective: To determine the effect of lower extremity fitness on the risk and severity of injury among recreational alpine skiers. Method: This prospective cohort study involved 117 recreational skiers at two alpine resorts during the 2021−2022 winter season. Anthropometric characteristics, skiing skills, and lower extremity agility (hexagon test), balance (Y-Balance Test), and endurance (60-s squat test) were assessed before the winter season. All of the participants were divided into an injured group and an uninjured group, based on whether an injury was recorded throughout the season. Results: In binary logistic regression, the hexagon test duration and composite Y-Balance Test score were significant injury risk factors (p < 0.05). Ordinal polytomous logistic regression revealed no significant factors for injury severity (p > 0.05). Conclusions: Recreational alpine skiers with inferior lower extremity agility or balance may have a higher injury risk and this must be considered when assessing individual risk. In the context of injury prevention, regular neuromuscular training and testing, including agility and balance aspects should be recommended to skiers.

Warm-Up Improves Balance Control Differently in the Dominant and Non-Dominant Leg in Young Sportsmen According to Their Experience in Asymmetric or Symmetric Sports

The aim of this study was to investigate the acute effects of a warm-up on balance control and inter-limb balance asymmetries by analyzing the influence of the nature of the sport practiced by participants. Twelve sportspeople were recruited. They had to stand on a force plate for 30 s in a one-leg stance on their dominant (used to perform skilled movements) and non-dominant leg (used to support the body) before and 2, 5, 10, 15 and 20 min after a 10 min warm-up exercise performed at moderate intensity on a cycle ergometer. The center of foot pressure displacements was recorded. Statistical analysis was performed by considering one group of all participants and with two subgroups according to the symmetrical or asymmetrical nature of the sport they practiced. The warm-up exercise improved acute balance control only on the dominant leg after a 20 min rest without significantly reducing inter-limb balance asymmetries. This effect was more characteristic of participants with experience in asymmetric sports. These results confirm previous findings of the greater sensitivity of the dominant leg to the physiological state and reveal that between-leg differences in balance control appear mainly in subjects with experience in asymmetric sports in a specific physiological condition (post-warm-up state).

Force, Power, and Morphology Asymmetries as Injury Risk Factors in Physically Active Men and Women

This study aimed to investigate whether asymmetry of force, power, and tissue morphology are lower limbs (LL) injury risk factors in physically active adults. Fifty-eight men aged 23.8 ± 1.2 years and forty-seven women aged 23.3 ± 1.0 years were examined. Physical activity level was measured by the International Physical Activity Questionnaire, and injury data were collected with the Injury History Questionnaire. The countermovement jump was performed to evaluate force and power. LL tissue composition was evaluated by a bioimpedance analyzer. The symmetry indices were calculated. A comparison between injured and non-injured subjects in both sexes was conducted to determine indices associated with injuries. The symmetry indices cut-off points were calculated to establish values indicating a significant injury risk increase, and logistic regression was performed. The relative peak force asymmetry above 4.049% was associated with increased injury risk in men. The LL skeletal muscle mass asymmetry above 3.584% was associated with a higher injury risk in women. Increased asymmetry in indicated indices by 1% was associated with 19.8% higher injury risk in men and 82.6% in women. Asymmetry proved to be an injury risk factor. However, a more suitable index for men is relative peak force asymmetry, whereas LL skeletal muscle mass asymmetry is more suitable for women.

Can Compression Garments Reduce Inter-Limb Balance Asymmetries?

Sensory cues provided by compression garments (CG) can improve movement accuracy and potentially reduce inter-limb balance asymmetries and the associated risk of injury. The aim of this study was to analyze the effects of CG wearing on inter-limb balance asymmetries. The hypothesis was that CG would reduce inter-limb balance asymmetries, especially in subjects with high level of asymmetries. Twenty-five sportsmen were recruited. They had to stand as motionless as possible in a one-leg stance in two postural tasks (stable and unstable), while wearing CG or not. Asymmetry indexes were calculated from center of foot pressure parameters. The effects of CG wearing were analyzed according to participants’ baseline level of asymmetry (i.e., without wearing CG) with correlation analyses. A qualitative analysis was also performed after a dichotomization procedure to check for a specific influence of CG on the dominant and non-dominant leg. Inter-limb balance asymmetries were reduced with CG in participants with high levels of asymmetries at baseline. However, asymmetries were increased with CG in participants with low levels of asymmetries at baseline. The dominant leg was more affected by this negative effect. CG wearing could reduce inter-limb balance asymmetries and the related injury risk in subjects with high levels of inter-limb balance asymmetries at baseline. Nevertheless, CG should not be used in individuals with low baseline balance asymmetries since it can increase asymmetries in these subjects, likely by confusing and overloading the sensorimotor processing on the dominant leg.

Body Composition Symmetry in Aircraft Pilots

The purpose of this study was to analyze the body composition symmetry in upper and lower body segments of aircrafts pilots. To reach the study aim, body composition in upper and lower body segments of 206 male aircraft pilots of the Spanish Army (23.1 ± 6.87 years) and 105 civilians (24.0 ± 6.29 years) were evaluated by a bioimpedance analyser (InBody 720, Biospace Co. Ltd., Seoul, Korea). Aircraft pilots presented a tendency to dysmetria in upper and lower body segments, showing fitter values in the protagonist side when performing flight functions. Dysmetria could be detrimental during flight manoeuvres and produce injuries in aircraft pilots. It would be recommended to design specific training protocols to improve this imbalance.

Effects of Blood Flow Restriction Training on Blood Perfusion and Work Ability of Muscles in Elite Para-alpine Skiers

Purpose

The effects of short-term blood flow restriction (BFR) exercise on muscle blood flow perfusion and performance during high-intensity exercise were determined in elite para-alpine standing skiers to assess whether this would be an effective training regimen for elite athletes with disabilities.

Methods

Nine national-level para-alpine standing skiers (mean age, 20.67 ± 1.34 yr; four women) were recruited. Nondominant lower limbs were trained with BFR (eight in final analyses), and dominant lower limbs were trained without BFR (seven in final analyses). The 2-wk protocol included high-load resistance, local muscle endurance (circuit resistance training), and aerobic endurance (stationary cycling) training performed 4 times a week, with BFR during local muscle endurance and aerobic endurance sessions. Muscle strength was measured by maximal voluntary isometric contraction (MVIC) in the knee extensors; microcirculatory blood perfusion (MBP), by laser Doppler blood flow; and muscle strength and endurance, by the total amount of work (TW) performed during high-intensity centrifugal and concentric contractions.

Results

BFR significantly increased absolute and relative MVIC (P < 0.001, P = 0.001), MBP (P = 0.011, P = 0.008), and TW (P = 0.006, P = 0.007) from pretraining values, whereas only absolute MVIC increased without BFR (P = 0.047). However, the MVIC increase with BFR exercise (35.88 ± 14.83 N·m) was significantly greater (P = 0.040) than without BFR exercise (16.71 ± 17.79 N·m).

Conclusions

Short-term BFR exercise significantly increased strength endurance, muscle strength, and MBP in national-level para-alpine standing skiers. Our study provides new evidence that BFR exercise can improve local muscle blood perfusion during high-intensity exercise and informs BFR exercise strategies for athletes with disabilities.

Principal postural acceleration and myoelectric activity: Interrelationship and relevance for characterizing neuromuscular function in postural control

One approach to investigating sensorimotor control is to assess the accelerations that produce changes in the kinematic state of the system. When assessing complex whole-body movements, structuring the multi-segmental accelerations is important. A useful structuring can be achieved through a principal component analysis (PCA) performed on segment positions followed by double-differentiation to obtain "principal accelerations" (PAs). In past research PAs have proven sensitive to altered motor control strategies, however, the interrelationship between PAs and muscle activation (surface electromyography, sEMG) have never been determined. The purpose of the current study was therefore to assess the relationship between PAs and sEMG signals recorded from muscles controlling the ankle joint during one-leg standing trials. It was hypothesized that medium correlation should be observed when accounting for neurophysiologic latencies (electro-mechanical delay). Unipedal balancing on a level-rigid ground was performed by 25 volunteers. sEMG activities were recorded from the tibialis anterior, peroneus longus, gastrocnemius medialis, and soleus muscles of the stance leg. The first eight PA-time series were determined from kinematic marker data. Then, a cross-correlation analysis was performed between sEMG and PA time series. We found that peak correlation coefficients for many participants aligned at time delays between 0.116 and 0.362 s and were typically in the range small to medium (|r| = 0.1 to 0.6). Thus, the current study confirmed a direct association between many principal accelerations PA(t) and muscle activation signals recorded from four muscles crossing the ankle joint complex. The combined analysis of PA and sEMG signals allowed exploring the neuromuscular function of each muscle in different postural movement components.

Editorial on the Special Issue on "Mountain Sports Activities: Injuries and Prevention"

Recreational outdoor activities like mountain sports are gaining large popularity all over the world and particularly in the Alpine regions [...].

Does monopedal postural balance differ between the dominant leg and the non-dominant leg? A review

The interlimb postural comparison i.e., between the dominant leg and the non-dominant leg has been studied by numerous authors but their results are contradictory and do not lead to a consensus. Some studies showed no difference of postural balance between the dominant and the non-dominant leg whereas other studies concluded that the dominant and non-dominant leg exhibit different postural balance in healthy subjects and athletes. The aim was to analyse all these studies in order to identify the different factors that could facilitate or prevent the appearance of a postural difference between the dominant and non-dominant leg by means of a narrative review. Environmental and experimental conditions (e.g., difficulty and specificity of postural tasks; physiological state, expertise level and moment of season/period over career of subjects/athletes evaluated and nature of sport/physical activity practiced; techniques and methods used for measuring postural balance) in which postural balance is evaluated and intrinsic/individual factors (e.g., morphology, strength/power muscle, proprioception, hemispheric laterality) could influence the results. Thus, the influence of limb dominance on monopedal postural balance would probably be context-dependent. Mechanistic explanations are proposed to explain how each factor could act on the relationship between limb dominance and postural balance. However many mechanisms have not yet been explained and all the factors have not been identified, which suggests that further exploratory research is needed in order to understand this relationship.

Analysis of Postural Control Using Principal Component Analysis: The Relevance of Postural Accelerations and of Their Frequency Dependency for Selecting the Number of Movement Components

One criterion when selecting the number of principal components (PCs) to be considered in a principal component analysis (PCA) is the fraction of overall variance that each PC represents. When applying a PCA to kinematic marker data in postural control research, this criterion relates to the amplitude of postural changes, recently often called "principal (postural) positions" (PPs). However, in the assessment of postural control, important aspects are also how fast posture changes and the acceleration of postural changes, i.e., "principal accelerations" (PAs). The current study compared how much of the total position variance each PP explained (PP_rVAR) and how much of the total acceleration variance each PA explained (PA_rVAR). Furthermore, the frequency content of PP and PA signals were evaluated. Postural movements of 26 participants standing on stable ground or balancing on a multiaxial balance board were analyzed by applying a PCA on 90 marker coordinates. For each PC, PP_rVAR, PA_rVAR, and the Fourier transformations of the PP and PA time series were calculated. The PP_rVAR and the PA_rVAR-distributions differed substantially. The PP-frequency domain was observed well below 5 Hz, the PA-frequency domain up to 5 Hz for stable standing and up to 10 Hz on the balance board. These results confirm that small-amplitude but fast movement components can have a higher impact on postural accelerations-and thus on the forces active in the system-than large-amplitude but slow lower-order movement components. Thus, PA variance and its dependence on filter frequencies should be considered in dimensionality reduction decisions.

Adolescent Awkwardness: Alterations in Temporal Control Characteristics of Posture with Maturation and the Relation to Movement Exploration

A phenomenon called adolescent awkwardness is believed to alter motor control, but underlying mechanisms remain largely unclear. Since adolescents undergo neurological and anthropometrical changes during this developmental phase, we hypothesized that adolescents control their movements less tightly and use a different coordinative structure compared to adults. Moreover, we tested if emerging differences were driven by body height alterations between age groups. Using 39 reflective markers, postural movements during tandem stance with eyes open and eyes closed of 12 adolescents (height 168.1 ± 8.8 cm) and 14 adults were measured, in which 9 adults were smaller or equal than 180 cm (177.9 ± 3.0 cm) and 5 taller or equal than 190 cm (192.0 ± 2.5 cm). A principal component analysis (PCA) was used to extract the first nine principal movement components (PMk). The contribution of each PMk to the overall balancing movement was determined according to their relative variance share (rVARk) and tightness of motor control was examined using the number of times that the acceleration of each PMk changed direction (Nk). Results in rVARk did not show significant differences in coordinative structure between adolescents and adults, but Nk revealed that adolescents seem to control their movements less tightly in higher-order PMk, arguably due to slower processing times and missing automatization of postural control or potential increases in exploration. Body height was found to not cause motor control differences between age groups.

Leg Dominance Effects on Postural Control When Performing Challenging Balance Exercises

Leg dominance reflects the preferential use of one leg over another and is typically attributed to asymmetries in the neural circuitry. Detecting leg dominance effects on motor behavior, particularly during balancing exercises, has proven difficult. The current study applied a principal component analysis (PCA) on kinematic data, to assess bilateral asymmetry on the coordinative structure (hypothesis H1) or on the control characteristics of specific movement components (hypothesis H2). Marker-based motion tracking was performed on 26 healthy adults (aged 25.3 ± 4.1 years), who stood unipedally on a multiaxial unstable board, in a randomized order, on their dominant and non-dominant leg. Leg dominance was defined as the kicking leg. PCA was performed to determine patterns of correlated segment movements ("principal movements" PMks). The control of each PMk was characterized by assessing its acceleration (second-time derivative). Results were inconclusive regarding a leg-dominance effect on the coordinative structure of balancing movements (H1 inconclusive); however, different control (p = 0.005) was observed in PM3, representing a diagonal plane movement component (H2 was supported). These findings supported that leg dominance effects should be considered when assessing or training lower-limb neuromuscular control and suggest that specific attention should be given to diagonal plane movements.

Should the Minimal Intervention Principle Be Considered When Investigating Dual-Tasking Effects on Postural Control?

Dual-tasking charges the sensorimotor system with performing two tasks simultaneously. Center of pressure (COP) analysis reveals the postural control that is altered during dual-tasking, but may not reveal the underlying neural mechanisms. In the current study, we hypothesized that the minimal intervention principle (MIP) provides a concept by which dual-tasking effects on the organization and prioritization of postural control can be predicted. Postural movements of 23 adolescents (age 12.7 ± 1.3; 8 females) and 15 adults (26.9 ± 2.3) were measured in a bipedal stance with eyes open, eyes closed and eyes open while performing a dual-task using a force plate and 39 reflective markers. COP data was analyzed by calculating the mean velocity, standard deviation and amplitude of displacement. Kinematic data was examined by performing a principal component analysis (PCA) and extracting postural movement components. Two variables were determined to investigate changes in amplitude (aVark) and in control (Nk) of the principal movement components. Results in aVark and in Nk agreed well with the predicted dual-tasking effects. Thus, the current study corroborates the notion that the MIP should be considered when investigating postural control under dual-tasking conditions.