Footedness is a better predictor than is handedness of emotional lateralization

The Effect of Duration on Performance and Perceived Fatigability During Acute High-Intensity Interval Exercise in Young, Healthy Males and Females

Few studies have explored the kinetics of performance and perceived fatigability during high-intensity interval training, despite its popularity. We aimed to characterize the kinetics of fatigability and recovery during an 8 × 4-min HIIT protocol, hypothesizing that most muscle function impairment would occur during the initial four intervals. Fifteen healthy males and females (mean ± standard deviation; age = 26 ± 5 years, V̇O2max = 46.8 ± 6.1 mL·kg-1·min-1) completed eight, 4-min intervals at 105% of critical power with 3 min of rest. Maximal voluntary knee extension contractions (MVCs) coupled with electrical nerve stimulation were performed at baseline and after the first, fourth, and eighth intervals. MVC, potentiated twitch force (Pt), and Db10:100 ratio all declined throughout HIIT (p < 0.05). MVC sharply declined after interval 1 (-15 ± 9% relative to baseline; p < 0.05) and had only further declined after interval 8 (-26 ± 11%; p < 0.05), but not interval 4 (-19 ± 13%; p > 0.05). Pt and Db10:100 also sharply declined after interval 1 (Pt: -18 ± 13%, Db10:100: -14 ± 20%; p < 0.05) and further declined after interval 4 (Pt: -35 ± 19%, Db10:100: -30 ± 20%; p < 0.05) but not interval 8 (Pt: -41 ± 19%; Db10:100: -32 ± 18%; p > 0.05). Voluntary activation did not significantly change across the HIIT protocol (p > 0.05). Evoked force recovery was significantly blunted as more intervals were completed: after interval 1, Pt recovered by 7 ± 11% compared to -6 ± 7% recovery after interval 8 (p < 0.05). Ratings of perceived effort, fatigue, and leg pain rose throughout the session (p < 0.05 for each) and were greater (effort and fatigue) for females (p < 0.05). Otherwise, males and females exhibited similar performance fatigability kinetics, with contractile function declines blunted in response to additional intervals.

Motor function in multiple sclerosis assessed by navigated transcranial magnetic stimulation mapping

INTRODUCTION

Impaired motor function is a major cause of disability in multiple sclerosis (MS), involving various neuroplasticity processes typically assessed by neuroimaging. This study aimed to determine whether navigated transcranial magnetic stimulation (nTMS) could also provide biomarkers of motor cortex plasticity in patients with MS (pwMS).

METHODS

nTMS motor mapping was performed for hand and leg muscles bilaterally. nTMS variables included the amplitude and latency of motor evoked potentials (MEPs), corticospinal excitability measures, and the size of cortical motor maps (CMMs). Clinical assessment included disability (Expanded Disability Status Scale, EDSS), strength (MRC scale, pinch and grip), and dexterity (9-hole Pegboard Test).

RESULTS

nTMS motor mapping was performed in 68 pwMS. PwMS with high disability (EDSS ≥ 3) had enlarged CMMs with less dense distribution of MEPs and various MEP parameter changes compared to pwMS with low disability (EDSS < 3). Patients with progressive MS had also various MEP parameter changes compared to pwMS with relapsing remitting form. MRC score correlated positively with MEP amplitude and negatively with MEP latency, pinch strength correlated negatively with CMM volume and dexterity with MEP latency.

CONCLUSIONS

This is the first study to perform 4-limb cortical motor mapping in pwMS using a dedicated nTMS procedure. By quantifying the cortical surface representation of a given muscle and the variability of MEP within this representation, nTMS can provide new biomarkers of motor function impairment in pwMS. Our study opens perspectives for the use of nTMS as an objective method for assessing pwMS disability in clinical practice.

The effect of self-identified arm dominance on exercising forearm hemodynamics and skeletal muscle desaturation

The human forearm model is commonly employed in physiological investigations exploring local vascular function and oxygen delivery; however, the effect of arm dominance on exercising forearm hemodynamics and skeletal muscle oxygen saturation (SmO2) in untrained individuals is poorly understood. Therefore, the purpose of this study was to explore the effect of self-identified arm dominance on forearm hemodynamics and SmO2 in untrained individuals during submaximal, non-ischemic forearm exercise. Twenty healthy individuals (23±4 years, 50% female; 80% right-handed) completed three-minute bouts of supine rhythmic (1 second contraction: 2 second relaxation duty cycle) forearm handgrip exercise at both absolute (10kg; 98N) and relative (30% of maximal voluntary contraction) intensities in each forearm. Beat-by-beat measures of forearm blood flow (FBF; ml/min), mean arterial blood pressure (MAP; mmHg) and flexor digitorum superficialis SmO2 (%) were obtained throughout and averaged during the final 30 seconds of rest, exercise, and recovery while forearm vascular conductance was calculated (FVC; ml/min/100mmHg). Data are Δ from rest (mean±SD). Absolute force production did not differ between non-dominant and dominant arms (97±11 vs. 98±13 N, p = 0.606) whereas relative force production in females did (69±24 vs. 82±25 N, p = 0.001). At both exercise intensities, FBFRELAX, FVCRELAX, MAPRELAX, and the time constant tau for FBF and SmO2 were unaffected by arm dominance (all p>0.05). While arm dominance did not influence SmO2 during absolute intensity exercise (p = 0.506), the non-dominant arm in females experienced an attenuated reduction in SmO2 during relative intensity exercise (-14±10 vs. -19±8%, p = 0.026)-though exercise intensity was also reduced (p = 0.001). The present investigation has demonstrated that arm dominance in untrained individuals does not impact forearm hemodynamics or SmO2 during handgrip exercise.

A multichannel investigation of proprioceptive accuracy

Proprioceptive accuracy (PAc), i.e., the acuity of perception of the state of different parts of the motor system, shows substantial intraindividual differences, and is often considered a general ability. However, it is questionable whether there is an association between accuracies measured with different tests at different body sites. PAc with respect to both knee and elbow joints (joint position reproduction) and the flexors of the upper arms (weight discrimination) was measured in 87 young healthy individuals with regular physical activity across multiple indices. Expected and perceived performance was also assessed for each behavioral task. Frequentist and Bayesian analysis largely supported the idea that PAc with respect to various parts of the motor system are unrelated. No dominant-subdominant differences for actual performance were found; however, PAc for the dominant and subdominant limb were associated in many cases. Finally, perceived performance was related to expected but not to actual performance for all three proprioceptive modalities. In conclusion, actual accuracy of perception of the actual state of a part (i.e., joint, muscle) of the motor system cannot be generalized to other parts. Perceived accuracy, dominantly shaped by expectations, is independent from actual accuracy.

A comparison of abductor hallucis muscle activation and medial longitudinal arch angle during nine different foot exercises

BACKGROUND

Intrinsic foot muscles are known to support the medial longitudinal arch (MLA) and stabilize the foot, and they are activated with weight bearing and increased postural demand. Various types of intrinsic foot muscle training have been reported, but one of the most useful of these, the short foot exercise, is challenging to perform effectively and requires practice, making it difficult to implement in ordinary clinical settings.

RESEARCH QUESTION

What are the differences in abductor hallucis longus (ABH) muscle activity and MLA angle during intrinsic foot muscle exercises that employ weight bearing and balancing conditions when they are performed with minimal practice?

METHODS

Sixteen healthy volunteers performed nine different intrinsic foot muscle exercises, practiced once or twice. The exercises consisted of toe curl, short foot without pushing, short foot with pushing and toe spread exercises in sitting and standing positions, and single leg swing in a standing position. Each exercise was performed three times for five seconds. The activities of the ABH muscles were measured using surface electromyographic (EMG) sensors and the MLA angles during the exercises were captured using an optical motion tracking system. The integrals of the ABH EMG signals were calculated.

RESULTS

Differences in the integral and maximum of the ABH EMG signal were found between the exercises (p < 0.001). Post-hoc pair-wise analysis revealed that the EMG activity was larger during the swing exercise than in exercises other than toe spread, both in sitting and standing positions, and short foot exercise with pushing while standing. The minimum MLA angle during each exercise was smaller for the toe spread exercise in a sitting position than other exercises (p < 0.023).

SIGNIFICANCE

A single leg swing exercise may be effective for self-exercise of intrinsic foot muscles, particularly when intensive supervised physiotherapy is not possible.

Profiling Bilateral Skills in High-Performance Male and Female Gaelic Footballers

Bilateral skill symmetry in sport refers to an individual's ability to successfully perform sporting actions with both sides of the body. Two scarcely researched areas in relation to bilateral skills are the effects of opposition proximity on skill execution and bilateral skill in high-performance female athletes. In this study, we used Nacsport to code all skill executions (hand pass, kick pass, hop, solo and shot) during 121 games by both male and female participants (76 male, 45 female), classified as Tier 1 (n = 181, 134) and Tier 2 (n = 238, 115) high performance, adult Gaelic Football players. Irrespective of the participants' tier group or gender, these players relied upon their dominant side for most skill executions (Kick Pass Dominant Foot Mdn: MT1 = 90%, MT2 = 98.6%, FT1 = 100%, FT2 = 100%; Solo Dominant Foot: Mdn MT1 = 95%, MT2 = 97.3%, FT1: 100%, FT2: 100%; Hand Pass Dominant Hand Mdn: MT1: 83.7%, MT2: 99%, FT1: 95.5%, FT2: 95.5%; Hop Dominant Hand Mdn: MT1: 91.9%, MT2: 94.7%, FT1: 98.1%, FT2: 98.1%; Play Dominant Foot Mdn: MT1: 74.5%, MT2: 94.5%, FT1: 94.7%, FT2: 88.2%). There were no consistent differences between tier groups or genders in relation to dominant side use, but top tier male players were generally less reliant on the dominant limb than were female players from both tiers. In general, top tier male players performed more successfully than either second tier male players or female players in both tiers. Most skills were executed under conditions of low opponent proximity, limiting the requirement for participants to use their non-dominant limbs. These findings illustrate the demands of Gaelic football in relation to bilateral skills, and we identified new research questions for future investigators.

Visual cue spatial context affects performance of anticipatory postural adjustments

Past research indicates that anticipatory postural adjustment (APA) errors may be due to the incorrect selection of responses to visual stimuli. In the current study we used the Simon task as a methodological tool to challenge the response selection stage of processing by presenting visual cues with conflicting spatial context; in this case generating a step response to a left pointing arrow which appears to the participant's right side or vice versa. We expected greater mediolateral APA errors, delayed APA and step onset times, and greater lateral CoP displacement prior to stepping for visual cues with incongruent spatial contexts compared to cues with congruent. Thirteen healthy young adults completed step initiation trials (n = 40) from a force platform while whole-body kinematic motion was tracked. Participants were presented with arrows pointing to the left or right, indicating to step with the left or right limb, respectively. These arrows were presented on the same side as the desired step direction (congruent) or the opposite side (incongruent). Results revealed that incongruent trials resulted in significantly more incidences of mediolateral APA errors and greater mediolateral CoP deviations during the APA compared to congruent visual cue context trials. No effects were observed for the temporal outcomes, suggesting that young adults can maintain temporal execution of steps despite these motor control errors. This study demonstrates that the spatial context of visual information significantly impacts the success of response selection processes during step initiation, furthering our knowledge of how humans integrate visual information to initiate whole body movement.

Aging Does Not Alter Ankle, Muscle, and Tendon Stiffness at Low Loads Relevant to Stance

Older adults have difficulty maintaining balance when faced with postural disturbances, a task that is influenced by the stiffness of the triceps surae and Achilles tendon. Age-related changes in Achilles tendon stiffness have been reported at matched levels of effort, but measures typically have not been made at matched loads, which is important due to age-dependent changes in strength. Moreover, there has been limited investigation into age-dependent changes in muscle stiffness. Here, we investigate how age alters muscle and tendon stiffness and their influence on ankle stiffness. We hypothesized that age-related changes in muscle and tendon contribute to reduced ankle stiffness in older adults and evaluated this hypothesis when either load or effort were matched. We used B-mode ultrasound with joint-level perturbations to quantify ankle, muscle, and tendon stiffness across a range of loads and efforts in seventeen healthy younger and older adults. At matched loads relevant to standing and the stance phase of walking, there was no significant difference in ankle, muscle, or tendon stiffness between groups (all p > 0.13). However, at matched effort, older adults exhibited a significant decrease in ankle (27%; p = 0.008), muscle (37%; p = 0.02), and tendon stiffness (22%; p = 0.03) at 30% of maximum effort. This is consistent with our finding that older adults were 36% weaker than younger adults in plantarflexion (p = 0.004). Together, these results indicate that, at the loads tested in this study, there are no age-dependent changes in the mechanical properties of muscle or tendon, only differences in strength that result in altered ankle, muscle, and tendon stiffness at matched levels of effort.

H2OAthletes study protocol: effects of hydration changes on neuromuscular function in athletes

We aim to understand the effects of hydration changes on athletes' neuromuscular performance, on body water compartments, fat-free mass hydration and hydration biomarkers and to test the effects of the intervention on the response of acute dehydration in the hydration indexes. The H2OAthletes study (clinicaltrials.gov ID: NCT05380089) is a randomised controlled trial in thirty-eight national/international athletes of both sexes with low total water intake (WI) (i.e. < 35·0 ml/kg/d). In the intervention, participants will be randomly assigned to the control (CG, n 19) or experimental group (EG, n 19). During the 4-day intervention, WI will be maintained in the CG and increased in the EG (i.e. > 45·0 ml/kg/d). Exercise-induced dehydration protocols with thermal stress will be performed before and after the intervention. Neuromuscular performance (knee extension/flexion with electromyography and handgrip), hydration indexes (serum, urine and saliva osmolality), body water compartments and water flux (dilution techniques, body composition (four-compartment model) and biochemical parameters (vasopressin and Na) will be evaluated. This trial will provide novel evidence about the effects of hydration changes on neuromuscular function and hydration status in athletes with low WI, providing useful information for athletes and sports-related professionals aiming to improve athletic performance.

The Influence of Strength Level on Handball-Specific Fitness Elements Between Stronger and Weaker Professional Players

ABSTRACT

Kyriacou-Rossi, A, Hadjicharalambous, M, and Zaras, N. The influence of strength level on handball-specific fitness elements between stronger and weaker professional players. J Strength Cond Res 38(5): 966-975, 2024-The aim of the study was to investigate the influence of strength level between stronger and weaker handball players on handball specific fitness elements and to explore the correlations between strength and sport-specific fitness elements. Twenty-one professional male handball-players (age: 25.9 ± 6.9 years; mass: 87.9 ± 13.9 kg; height: 1.81 ± 0.08 m), participated in the study. Players were divided into the stronger (SG) and weaker group (WG) according to their relative to body mass 1 repetition maximum strength (1RM). Measurements included body composition, countermovement jump (CMJ), isometric leg extension peak torque (IPT) and rate of torque development (RTD), 5-step long-jump, 0-20 m linear sprint, T-half test, throwing velocity, and 1RM in bench press and squat. No significant difference was found for body composition between SG and WG ( p > 0.05). However, SG had significantly higher CMJ height (21.5%, p = 0.002), IPT (22.4%, p = 0.008), RTD relative to body mass ( p < 0.05), 5-step long jump (10.9%, p = 0.005), lower 0-20 linear sprint (-6.3%, p = 0.012), lower T-half test time trial (-7.3%, p = 0.001), and higher throwing velocity compared with WG ( p < 0.05). When all players included in one group, large to very large correlations were found between 1RM strength and IPT with fat-free mass ( r = 0.518-0.774) and throwing velocity ( r = 0.472-0.819). Very large correlations were found between RTD with fat-free mass ( r = 0.760) and throwing velocity ( r = 0.780-0.835). Stronger players have greater performance in all handball-fitness attributes compared with their weaker counterparts. The significant correlations between handball-specific fitness elements with strength and RTD suggest that strength training is essential for handball players as it may link to higher on court performance.

Use of functional magnetic resonance imaging to identify cortical loci for lower limb movements and their efficacy for individuals after stroke

BACKGROUND

Identification of cortical loci for lower limb movements for stroke rehabilitation is crucial for better rehabilitation outcomes via noninvasive brain stimulation by targeting the fine-grained cortical loci of the movements. However, identification of the cortical loci for lower limb movements using functional MRI (fMRI) is challenging due to head motion and difficulty in isolating different types of movement. Therefore, we developed a custom-made MR-compatible footplate and leg cushion to identify the cortical loci for lower limb movements and conducted multivariate analysis on the fMRI data. We evaluated the validity of the identified loci using both fMRI and behavioral data, obtained from healthy participants as well as individuals after stroke.

METHODS

We recruited 33 healthy participants who performed four different lower limb movements (ankle dorsiflexion, ankle rotation, knee extension, and toe flexion) using our custom-built equipment while fMRI data were acquired. A subgroup of these participants (Dataset 1; n = 21) was used to identify the cortical loci associated with each lower limb movement in the paracentral lobule (PCL) using multivoxel pattern analysis and representational similarity analysis. The identified cortical loci were then evaluated using the remaining healthy participants (Dataset 2; n = 11), for whom the laterality index (LI) was calculated for each lower limb movement using the cortical loci identified for the left and right lower limbs. In addition, we acquired a dataset from 15 individuals with chronic stroke for regression analysis using the LI and the Fugl-Meyer Assessment (FMA) scale.

RESULTS

The cortical loci associated with the lower limb movements were hierarchically organized in the medial wall of the PCL following the cortical homunculus. The LI was clearer using the identified cortical loci than using the PCL. The healthy participants (mean ± standard deviation: 0.12 ± 0.30; range: - 0.63 to 0.91) exhibited a higher contralateral LI than the individuals after stroke (0.07 ± 0.47; - 0.83 to 0.97). The corresponding LI scores for individuals after stroke showed a significant positive correlation with the FMA scale for paretic side movement in ankle dorsiflexion (R2 = 0.33, p = 0.025) and toe flexion (R2 = 0.37, p = 0.016).

CONCLUSIONS

The cortical loci associated with lower limb movements in the PCL identified in healthy participants were validated using independent groups of healthy participants and individuals after stroke. Our findings suggest that these cortical loci may be beneficial for the neurorehabilitation of lower limb movement in individuals after stroke, such as in developing effective rehabilitation interventions guided by the LI scores obtained for neuronal activations calculated from the identified cortical loci across the paretic and non-paretic sides of the brain.

Children with bilateral cerebral palsy use their hip joint to complete a step-up task

Performance in stair-climbing is largely associated with disruptions to mobility and community participation in children with cerebral palsy (CP). It is important to understand the nature of motor impairments responsible for making stairs a challenge in children with bilateral CP to clarify underlying causes of impaired mobility. In pediatric clinical populations, sensitive measurements of movement quality can be captured during the initial step of stair ascent. Thus, the purpose of this study was to quantify the lower limb joint moments of children with bilateral CP during the stance phases of a step-up task. Participants performed multiple stepping trials in a university gait laboratory. Outcome measures included extensor support moments (the sum of hip, knee, and ankle sagittal plane moments), hip abduction moments, and their timing. We recruited seven participants per group. We found that peak support and hip abduction moments were similar in the bilateral CP group compared to the typical development (TD) group. We also found that children with bilateral CP timed their peak moments closer together and increasingly depended on the hip joint to complete the task, especially in their more affected (MA) lower limb. Our investigation highlights some underlying causes that may make stair climbing a challenge for the CP population, including a loss of selective voluntary motor control (SVMC), and provides a possible treatment approach to strengthen lower limb muscles.

Transcranial magnetic stimulation input-output curve slope differences suggest variation in recruitment across muscle representations in primary motor cortex

Measurement of the input-output (IO) curves of motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) can be used to assess corticospinal excitability and motor recruitment. While IO curves have been used to study disease and pharmacology, few studies have compared the IO curves across the body. This study sought to characterize IO curve parameters across the dominant and non-dominant sides of upper and lower limbs in healthy participants. Laterality preferences were assessed in eight healthy participants and IO curves were measured bilaterally for the first dorsal interosseous (FDI), biceps brachii (BB), and tibialis anterior (TA) muscles. Results show that FDI has lower motor threshold than BB which is, in turn, lower than TA. In addition, both BB and TA have markedly shallower logarithmic IO curve slopes from small to large MEP responses than FDI. After normalizing these slopes by their midpoints to account for differences in motor thresholds, which could result from geometric factors such as the target depth, large differences in logarithmic slopes remain present between all three muscles. The differences in slopes between the muscles could not be explained by differences in normalized IO curve spreads, which relate to the extent of the cortical representation and were comparable across the muscles. The IO curve differences therefore suggest muscle-dependent variations in TMS-evoked recruitment across the primary motor cortex, which should be considered when utilizing TMS-evoked MEPs to study disease states and treatment effects.

Contraction intensity affects NIRS-derived skeletal muscle oxidative capacity but not its relationships to mitochondrial protein content or aerobic fitness

To further refine the near-infrared spectroscopy (NIRS)-derived measure of skeletal muscle oxidative capacity in humans, we sought to determine whether the exercise stimulus intensity affected the τ value and/or influenced the magnitude of correlations with in vitro measures of mitochondrial content and in vivo indices of exercise performance. Males (n = 12) and females (n = 12), matched for maximal aerobic fitness per fat-free mass, completed NIRS-derived skeletal muscle oxidative capacity tests for the vastus lateralis following repeated contractions at 40% (τ40) and 100% (τ100) of maximum voluntary contraction, underwent a skeletal muscle biopsy of the same muscle, and performed multiple intermittent isometric knee extension tests to task failure to establish critical torque (CT). The value of τ100 (34.4 ± 7.0 s) was greater than τ40 (24.2 ± 6.9 s, P < 0.001), but the values were correlated (r = 0.688; P < 0.001). The values of τ40 (r = -0.692, P < 0.001) and τ100 (r = -0.488, P = 0.016) correlated with myosin heavy chain I percentage and several markers of mitochondrial content, including COX II protein content in whole muscle (τ40: r = -0.547, P = 0.006; τ100: r = -0.466, P = 0.022), type I pooled fibers (τ40: r = -0.547, P = 0.006; τ100: r = -0.547, P = 0.006), and type II pooled fibers (τ40: r = -0.516, P = 0.009; τ100: r = -0.635, P = 0.001). The value of τ40 (r = -0.702, P < 0.001), but not τ100 (r = -0.378, P = 0.083) correlated with critical torque (CT); however, neither value correlated with W' (τ40: r = 0.071, P = 0.753; τ100: r = 0.054, P = 0.812). Overall, the NIRS method of assessing skeletal muscle oxidative capacity is sensitive to the intensity of skeletal muscle contraction but maintains relationships to whole body fitness, isolated limb critical intensity, and mitochondrial content regardless of intensity.NEW & NOTEWORTHY Skeletal muscle oxidative capacity measured using near-infrared spectroscopy (NIRS) was lower following high-intensity compared with low-intensity isometric knee extension contractions. At both intensities, skeletal muscle oxidative capacity was correlated with protein markers of mitochondrial content (in whole muscle and pooled type I and type II muscle fibers) and critical torque. These findings highlight the importance of standardizing contraction intensity while using the NIRS method with isometric contractions and further demonstrate its validity.

Postural stability assessment in expert versus amateur basketball players during optic flow stimulation

We evaluated the role of visual stimulation on postural muscles and the changes in the center of pressure (CoP) during standing posture in expert and amateur basketball players. Participants were instructed to look at a fixation point presented on a screen during foveal, peripheral, and full field optic flow stimuli. Postural mechanisms and motor strategies were assessed by simultaneous recordings of stabilometric, oculomotor, and electromyographic data during visual stimulation. We found significant differences between experts and amateurs in the orientation of visual attention. Experts oriented attention to the right of their visual field, while amateurs to the bottom-right. The displacement in the CoP mediolateral direction showed that experts had a greater postural sway of the right leg, while amateurs on the left leg. The entropy-based data analysis of the CoP mediolateral direction exhibited a greater value in amateurs than in experts. The root-mean-square and the coactivation index analysis showed that experts activated mainly the right leg while amateurs the left leg. In conclusion, playing sports for years seems to have induced some strong differences in the standing posture between the right and left sides. Even during non-ecological visual stimulation, athletes maintain postural adaptations to counteract the body oscillation.

Lateral spatial biases in naturalistic and simulated driving: Does pseudoneglect influence performance?

Whereas a rightward bump is more likely than a leftward bump when walking through a doorway, investigations into potential similar asymmetries for drivers are limited. The research presented here aims to determine the influence of innate lateral spatial biases when driving. Data from the Strategic Highway Research Program Naturalistic Driving Study (SHRP 2 NDS) and a driving simulation were used to address our research questions. Data points from SHRP 2 were aggregated within relevant variables (e.g., left/right obstacles). In the simulation, participants drove in ways that were consistent with their everyday driving in urban and rural environments. Collision frequency, collision severity and average lateral lane position were analyzed with rightward biases throughout both analyzes. SHRP 2 data indicated greater likelihoods of collisions when vehicles crossed the right line/edge of the road and when making a right turn. There were more collisions with obstacles on the right side, which were also more severe, and greater rightward lane deviations in the driving simulation, contrasted with more severe collisions on the left side in SHRP 2 data, possibly because of the presence of traffic. These findings suggest that previously observed rightward biases in distant space when walking are also present when driving.

Lower-limb dominance does not explain subject-specific foot kinematic asymmetries observed during walking and running

Studies of human locomotion have observed asymmetries in lower-limb kinematics, especially at the more distal joints. However, it is unclear whether these asymmetries are related to functional differences between the dominant and non-dominant limb. This study aimed to determine the effect of lower-limb dominance on foot kinematics during human locomotion. Range of motion for the metatarsophalangeal joint (MPJ) and medial longitudinal arch (MLA), as well as time duration of windlass mechanism engagement, were recorded from healthy young adults (N = 12) across a range of treadmill walking and running speeds. On the group level, there were no differences in MPJ or MLA range of motion, or windlass engagement timing, between the dominant and non-dominant limb (p > 0.05). While not explained by limb dominance, between-limb differences in MPJ and MLA ranges of motion were observed for individual participants on the order of ∼2-6°, which could be clinically relevant or impact interpretation of research data.

Visual Information Processing in Older Adults: Force Control and Motor Unit Pool Modulation

Increased visual information about a task impairs force control in older adults. To date, however, it remains unclear how increased visual information changes the activation of the motor unit pool differently for young and older adults. Therefore, this study aimed to determine how increased visual information alters the activation of the motor neuron pool and influences force control in older adults. Fifteen older adults (66-86 years, seven women) and fifteen young adults (18-30 years, eight women) conducted a submaximal constant force task (15% of maximum) with ankle dorsiflexion for 20 s. The visual information processing was manipulated by changing the amount of force visual feedback into a low-gain (0.05°) or high-gain (1.2°) condition. Older adults exhibited greater force variability, especially at high-gain visual feedback. This exacerbated force variability from low- to high-gain visual feedback was associated with modulations of multiple motor units, not single motor units. Specifically, increased modulation of multiple motor units from 10 to 35 Hz may contribute to the amplification in force variability. Therefore, our findings suggest evidence that high-gain visual feedback amplifies force variability of older adults which is related to increases in the activation of motor neuron pool from 10 to 35 Hz.

The Effects of Transcranial Direct Current Stimulation and Exercise on Salivary S100B Protein Indicated Blood-Brain Barrier Permeability: A Pilot Study

OBJECTIVE

This study aimed to assess the effect of transcranial direct current stimulation (tDCS) and exercise on blood-brain barrier (BBB) permeability in humans as assessed through the quantification of the salivary protein biomarker S100B. It was hypothesized that active tDCS would induce a significant increase in salivary S100B concentration when compared with sham stimulation and no stimulation. It also was hypothesized that the increase in salivary S100B concentration would be greater after active tDCS and exercise than after tDCS or exercise alone.

MATERIALS AND METHODS

A total of 13 healthy adults (five male, eight female), ranging in age from 21 to 32 years, underwent three experimental conditions (active tDCS, sham tDCS, inactive control). To assess exercise- and tDCS-induced changes in BBB permeability, S100B in saliva was measured. Saliva samples were taken before tDCS, after tDCS, and immediately after a ramped cycling time-to-exhaustion (TTE) task. Active tDCS involved the application of anodal stimulation over the primary motor cortex for 20 minutes at 2 mA.

RESULTS

S100B concentrations in the control condition did not differ significantly from the active condition (estimate = 0.10, SE = 0.36, t = 0.27, p = 0.79) or the sham condition (estimate = 0.33, SE = 0.36, t = 0.89, p = 0.38). Similarly, S100B concentrations at baseline did not differ significantly from post-intervention (estimate = -0.35, SE = 0.34, t = -1.03, p = 0.31) or post-TTE (estimate = 0.66, SE = 0.34, t = 1.93, p = 0.06).

CONCLUSIONS

This research provides novel insight into the effect of tDCS and exercise on S100B-indicated BBB permeability in humans. Although the effects of tDCS were not significant, increases in salivary S100B after a fatiguing cycling task may indicate exercise-induced changes in BBB permeability.

Effects of Simulated Visual Impairment Conditions on Movement and Anxiety during Gap Crossing

This study investigated the effects of visual conditions associated with progressive eye disease on movement patterns and anxiety levels during gap-crossing tasks. Notably, 15 healthy young adults performed crossover platforms with a 10 cm gap at three different heights, namely equal (0 cm), raised (+15 cm), and lowered (-15 cm) levels, under four vision conditions, namely normal or corrected eyesight, 10° tunnel vision, 5° tunnel vision, and 5° tunnel vision with 0.04 occlusion. Leg movements during gap crossing were analyzed using three-dimensional motion analysis. The results highlighted a distinct motion pattern in the trajectories of participants' legs under the different visual conditions. Specifically, at the point where the gap-crossing movement began (D1), the normal or corrected eyesight conditions resulted in further separation between the steps compared with the other visual conditions. The highest point of the foot during movement (D2) did not differ between the visual conditions, except for the 0 cm step. Furthermore, anxiety levels, as quantified by the State-Trait Anxiety Inventory (STAI-S) questionnaire, were exacerbated under conditions of restricted visual information. In conclusion, visual impairments associated with progressive ocular diseases may perturb complex motor movement patterns, including those involved in gap-crossing tasks, with heightened anxiety potentially amplifying these disturbances.

Effect of Moving Tactile Stimuli to Mimic Altered Weight Distribution During Gait on Quiet Stance Body Sway

Our purpose in the present study was to examine whether moving tactile stimuli to the sole to mimic moving weight distribution over the feet during gait would influence body sway in quiet stance. Fifteen healthy males maintained the quiet stance, and we delivered moving tactile stimuli to mimic the change in their weight distribution during gait. Moving tactile stimuli did not change the length of the center of pressure (COP) displacement and COP position. Vision decreased the length of the COP, but it did not interact with moving tactile stimuli for the COP length and position. The COP position rhythmically moved in the medial-lateral axis along with the cycle of moving tactile stimuli. The COP was at the lateral peak position at the period at which moving tactile stimuli mimicked the weight distribution in the transition between the swing and stance phases of the gait cycle. This finding may indicate that the body is positioned at the lateral peak position in quiet stance when people perceive the sensation of weight distribution over the feet at the most unstable phase of the gait cycle. We suggest that moving tactile stimuli to the sole may induce medial-lateral body sway before gait initiation for patients with Parkinson's disease to improve their freezing of gait initiation.

The influence of skeletal muscle mitochondria and sex on critical torque and performance fatiguability in humans

Critical torque (CT) represents the highest oxidative steady state for intermittent knee extensor exercise, but the extent to which it is influenced by skeletal muscle mitochondria and sex is unclear. Vastus lateralis muscle biopsy samples were collected from 12 females and 12 males -matched for relative maximal oxygen uptake normalized to fat-free mass (FFM) (F: 57.3 (7.5) ml (kg FFM)-1  min-1 ; M: 56.8 (7.6) ml (kg FFM)-1  min-1 ; P = 0.856) - prior to CT determination and performance fatiguability trials. Males had a lower proportion of myosin heavy chain (MHC) I isoform (40.6 (18.4)%) compared to females (59.5 (18.9)%; P = 0.021), but MHC IIa and IIx isoform distributions and protein markers of mitochondrial content were not different between sexes (P > 0.05). When normalized to maximum voluntary contraction (MVC), the relative CT (F: 42.9 (8.3)%; M: 37.9 (9.0)%; P = 0.172) and curvature constant, W' (F: 26.6 (11.0) N m s (N m)-1 ; M: 26.4 (6.5) N m s (N m)-1 ; P = 0.962) were not significantly different between sexes. All protein biomarkers of skeletal muscle mitochondrial content, as well as the proportion of MHC I isoform, positively correlated with relative CT (0.48 < r < 0.70; P < 0.05), and the proportion of MHC IIx isoform correlated positively with relative W' (r = 0.57; P = 0.007). Indices of performance fatiguability were not different between males and females for MVC- and CT-controlled trials (P > 0.05). Greater mitochondrial protein abundance was associated with attenuated declines in potentiated twitch torque for exercise at 60% MVC (P < 0.05); however, the influence of mitochondrial protein abundance on performance fatiguability was reduced when exercise was prescribed relative to CT. Whether these findings translate to whole-body exercise requires additional research. KEY POINTS: The quadriceps critical torque represents the highest intensity of intermittent knee extensor exercise for which an oxidative steady state is attainable, but its relationship with skeletal muscle mitochondrial protein abundance is unknown. Matching males and females for maximal oxygen uptake relative to fat-free mass facilitates investigations of sex differences in exercise physiology, but studies that have compared critical torque and performance fatiguability during intermittent knee extensor exercise have not ensured equal aerobic fitness between sexes. Skeletal muscle mitochondrial protein abundance was correlated with critical torque and fatigue resistance for exercise prescribed relative to maximum voluntary contraction but not for exercise performed relative to the critical torque. Differences between sexes in critical torque, skeletal muscle mitochondrial protein abundance and performance fatiguability were not statistically significant. Our results suggest that skeletal muscle mitochondrial protein abundance may contribute to fatigue resistance by influencing the critical intensity of exercise.

Assessing the Relationship Between Religious Beliefs and Ethnicity and Handedness and Footedness

Objectives The objective of the study is to explore the correlation between handedness and footedness and various demographic factors, including sex, age, faith, ethnicity, and perceived social pressures on limb use, among Muslims and non-Muslims. Methods This is an analytical cross-sectional study conducted in Saudi Arabia from September 2020 to February 2021. This research involved healthy community members aged 18 and above. An electronic survey was administered to collect demographic information on age, sex, faith, ethnicity, and the perceived degree of social pressure favoring the use of the right hand. The Waterloo handedness questionnaire (WHQ-Ar) and Waterloo footedness questionnaire (WFQ-Ar) were utilized for the assessments. Results A total of 728 respondents completed the survey. The mean (SD) age was 34.54 (11.53). Among them, 454 (62.4%) were ethnically Arab, and 507 (69.64%) identified as Muslims. The mean (SD) WHQ-Ar and WFQ-Ar scores were 42 (31.6) and 10.51 (8.1), respectively, with higher scores indicating "right" preference. Older age was associated with higher scores (p = 0.01) and men with lower handedness scores (p = 0.003). Participants who did not perceive social pressure had significantly lower scores (p < 0.001). Footedness was associated with slightly lower scores in Muslims (p = 0.001). Conclusion The degree of pressure perceived to use a particular hand has a major influence on handedness scores in Muslims and non-Muslims alike; this was true even when comparing populations with different levels of permissiveness to specific hand use due to varying religious or cultural backgrounds. Social pressure, regardless of routine religious practices, is more likely to influence handedness scores. Age and sex influence the scores similar to international reports, and footedness appears less likely to fall under the influence of cultural pressures.

At matched loads, aging does not alter ankle, muscle, or tendon stiffness

Older adults have difficulty maintaining balance when faced with postural disturbances, a task that is influenced by the stiffness of the triceps surae and Achilles tendon. Age-related changes in Achilles tendon stiffness have been reported at matched levels of effort, but measures typically have not been made at matched loads, which is important due to age-dependent changes in strength. Moreover, age-dependent changes in muscle stiffness have yet to be tested. Here, we investigate how age alters muscle and tendon stiffness and their influence on ankle stiffness. We hypothesized that age-related changes in muscle and tendon contribute to reduced ankle stiffness in older adults and evaluated this hypothesis when either load or effort were matched. We used B-mode ultrasound with joint-level perturbations to quantify ankle, muscle, and tendon stiffness across a range of loads and efforts in seventeen healthy younger and older adults. At matched loads, there was no significant difference in ankle, muscle, or tendon stiffness between groups (all p>0.13). However, at matched effort, older adults exhibited a significant decrease in ankle (27%; p=0.008), muscle (37%; p=0.02), and tendon stiffness (22%; p=0.03) at 30% of maximum effort. This is consistent with our finding that older adults were 36% weaker than younger adults in plantarflexion (p=0.004). Together these results indicate that, at the loads tested in this study, there are no age-dependent changes in the mechanical properties of muscle or tendon, only differences in strength that result in altered ankle, muscle, and tendon stiffness at matched levels of effort.

Reactive Strength Index, Rate of Torque Development, and Performance in Well-Trained Weightlifters: A Pilot Study

The purpose of this study was to investigate the correlation between the reactive strength index (RSI) using the drop jump (DJ) and the isometric rate of torque development (RTD) with weightlifting performance in national-level weightlifters. Seven male weightlifters (age: 28.3 ± 5.7 years, body mass: 80.5 ± 6.7 kg, body height: 1.73 ± 0.07 m) participated in this study. Measurements were performed 2 weeks prior to the national championship and included the countermovement jump (CMJ), the squat jump (SJ), the DJ from three different drop heights (20, 30, and 40 cm), and the isometric peak torque (IPT) and RTD. Performance in CMJ and SJ was significantly correlated with weightlifting performance (r ranging from 0.756 to 0.892). Significant correlations were found between weightlifting performance with DJ contact time (r ranging from -0.759 to -0.899) and RSI (r ranging from 0.790 to 0.922). Moreover, the best RSI was significantly correlated with the snatch (r = 0.921, p = 0.003) and total performance (r = 0.832, p = 0.020). Small to very large correlations were found between IPT and RTD with weightlifting performance (r ranging from 0.254 to 0.796). These results suggest that RSI and contact time variables from DJ may predict weightlifting performance in well-trained weightlifters. Additionally, IPT and RTD may provide useful insights into the neuromuscular fitness condition of the weightlifter.

Load modulation affects pediatric lower limb joint moments during a step-up task

Performance in a single step has been suggested to be sensitive measure of movement quality in pediatric clinical populations. Although there is less information available in children with typical development, researchers have postulated the importance of analyzing the effect of body weight modulation on the initiation of stair ascent, especially during single limb stance where upright stability is most critical. The purpose of this study was to investigate the effect of load modulation from -20% to +15% of body weight on typical pediatric lower limb joint moments during a step-up task. Fourteen participants between 5-21 years with no known history of neurological or musculoskeletal concerns were recruited to perform multiple step-up trials. Peak extensor support and hip abduction moments were identified during the push-off and pull-up stance phases. Linear regressions were used to determine the relationship between peak moments and load. Mixed effects models were used to estimate the effect of load on hip, knee, and ankle percent contributions to peak support moments. There was a positive linear relationship between peak support moments and load in both stance phases, where these moments scaled with load. There was no relationship between peak hip abduction moments and load. While the ankle and knee were the primary contributors to the support moments, the hip contributed more than expected in the pull-up phase. Clinicians can use these results to contextualize movement differences in pediatric clinical populations including cerebral palsy and highlight potential target areas for rehabilitation for populations such as adolescent athletes.

Dissociation of perception and motor execution of lower limb in multi-directional movements

Estimating the action capability is vital for humans to move their bodies successfully. Researchers have proposed reachability as an overestimation of motor abilities by judging unreachable distances as reachable. The existing literature has mainly investigated the sagittal direction, but multi-directional reachability is unexplored. This study examined the relationship between perception and motor using the reaching of the lower limbs in multiple directions. We asked 16 adults to reach targets projected onto the floor at 21 locations (seven directions and three distances) to estimate the reaching time. We found that the reaching time slowed as the direction increased toward the contralateral side, but the subjective reaching time did not change with direction. Multiple regression analysis showed that the subjective reaching time could be calculated accurately, mainly using the duration from the toe leaving the ground to movement completion. These results suggest that changes in direction may not be perceived precisely by the motor system of the lower limbs and that the subjective reaching time was strongly affected by the time after the toe left the ground. Our findings provide novel insights into the relationship between motor and perception in multiple directions, which may provide a new strategy for the maximal performance of lower-limb movement.

Effect of Laterally Moving Tactile Stimuli to Sole on Anticipatory Postural Adjustment of Gait Initiation in Healthy Males

This present study examined the effect of the laterally moving tactile stimuli (LMTS) to the sole on the anticipatory postural adjustment (APA) of the gait initiation. Thirteen healthy males participated in this study. A sound cue was provided at the beginning of each trial. The participants took three steps forward from a quiet stance at their preferred time after the start cue. The LMTS were delivered to the sole after the start cue. The loci of the tactile stimuli moved from the left- to the right-most side of the sole and then moved from the right- to the left-most side of that in a stimuli cycle. The duration of one stimuli cycle was 960 ms, and this cycle was repeated 16 times in a trial. The APA did not onset at the specific direction or phase of the LMTS, indicating that they did not use any specific phase of the stimuli as a trigger for initiating the gait. The LMTS decreased the amplitude and increased the duration of the APA. Simultaneously, the LMTS increased the time between the APA onset and toe-off of the initial support leg, indicating that they moved slowly when initiating gait during the LMTS. Those findings are explained by the view that the suppression of the APA induced via the LMTS to the sole is caused by the slowing down of the gait initiation due to masking the tactile sensation of the sole.

A deep phenotyping approach to assess the association of handedness, early life factors and mental health

The development of handedness and other form of functional asymmetries is not yet understood in its critical determinants. Early life factors (e.g., birth weight, birth order) have been discussed to contribute to individual manifestations of functional asymmetries. However, large-scale data such as the UK Biobank suggest that the variance in handedness that is explained by early life factors is minimal. Additionally, atypical handedness has been linked to clinical outcomes such as neurodevelopmental and psychiatric disorders. Against the background of this triad, the current study investigated associations between different forms of functional asymmetries and (a) early life factors as well as (b) clinical outcomes. Functional asymmetries were determined by means of a deep phenotyping approach which notably extends previous work. In our final sample of N = 598 healthy participants, the different variables were tested for associations by means of linear regression models and group comparisons (i.e., ANOVAs and Chi-squared tests). Confirming previous findings from larger cohorts with shallow phenotyping, we found that birth factors do not explain a substantial amount of variance in functional asymmetries. Likewise, functional asymmetries did not seem to have comprehensive predictive power concerning clinical outcomes in our healthy participants. Future studies may further investigate postulated relations in healthy and clinical samples while acknowledging deep phenotyping of laterality.

The Effects of Different Re-Warm-Up Strategies on Power, Changing of Direction and Ball Shooting Velocity in Well-Trained Soccer Players

The purpose of the study was to investigate whether a re-warm-up training session either with tuck jumps and linear sprints or with changing of directions may enhance power, agility or ball shooting velocity in well-trained soccer players. Ten soccer players (age: 18.2 ± 1.7 years; body mass: 64.4 ± 8.0 kg; body height: 1.71 ± 0.04 m) participated in the study. Players performed three different re-warm-up interventions including no re-warm-up (C), change of direction (COD) and jump-sprint condition (JS). Before each re-warm-up intervention, players performed the same warm-up condition followed by 8 min of passive rest. Following the re-warm-up interventions, countermovement jump (CMJ), T-Test agility time-trial and ball shooting velocity were measured. Performance in CMJ height, power and power per body mass remained unchanged following all three conditions (p > 0.05). However, the agility time-trial was significantly reduced following COD re-warm-up compared to C (-1.7 ± 1.6%, p = 0.03). Ball shooting velocity was increased following COD compared to C (4.7 ± 3.8%, p = 0.014), while a statistical trend was found between JS and C interventions (4.8 ± 5.4%, p = 0.060). These results suggest that a re-warm-up intervention including changing of directions may significantly enhance T-Test agility time-trial and ball shooting velocity in well-trained soccer players.

Direction and distance dependency of reaching movements of lower limb

Efficient body movement is required in our daily lives, as it facilitates responding to the external environment and producing movements in various directions and distances. While numerous studies have reported on goal-directed movements in the frontal direction during gait initiation, there is limited research on the efficient movement of the lower limbs in multiple directions and distances. Therefore, we aimed to examine changes in the kinematics of lower-limb reaching movements to determine skilled motor ability in terms of direction and distance. Sixteen adults (10 male participants) were requested to reach targets projected on the floor in seven directions and at three distances for a total of 21 points. The reaching time slowed down for the contralateral side (right foot to left-sided target) and was caused by a slower start of the toe movement. To identify the cause of this delay, we analyzed the onset of movement at each joint and found that movement to the contralateral side starts from the hip, followed by the knee, and subsequently the toe. The time-to-peak velocity was also calculated, and the motion required to reach the target in the shortest time varied depending on direction and distance. These results suggested that movement kinematics vary with direction and distance, resulting in a slower reaching time on the contralateral side. The results of our study hold promise for potential applications in sports and rehabilitation.

Cross-Cultural Adaptation of the Arabic Version of the Waterloo Footedness Questionnaire-Revised to Assess Footedness in Arabic-Speaking Adults

PURPOSE

 The goal of this research is to translate and analyze the psychometric properties of the Arabic version of the Waterloo Footedness Questionnaire-Revised (WFQ-R).

MATERIALS AND METHODS

Two native Arabic speakers created separate forward translations, which were then merged. Two different multilingual translators were used to translate it back into English from the synthetic version. Experts were gathered for a discussion on how to improve the localization and adaptation processes. A group of specialists was convened to analyze the localization and modification procedures. We now have the Arabic version of the WFQ-R which is "WFQ-R-Ar". Two hundred and ninety Arabic-speaking adults over the age of 18 were surveyed to evaluate the WHQ-R-Ar's characteristics (internal consistency, test-retest reliability, and construct validity).

RESULTS

 The WFQ-R-Ar had no collisions with the ground or the sky. The factor analysis showed that the construct validity of the WFQ-R-Ar was dependent on a single factor. The WFQ-R-Ar also has excellent internal consistency, with a Cronbach's alpha of 0.93. The reliability of the examinations was examined, and it was found to have an intraclass correlation value of 0.94.

CONCLUSION

 The WFQ-R-Ar may be relied on to provide accurate results when used to evaluate footedness in Arabic-speaking society.

Hip Joint Angles and Moments during Stair Ascent Using Neural Networks and Wearable Sensors

End-stage hip joint osteoarthritis treatment, known as total hip arthroplasty (THA), improves satisfaction, life quality, and activities of daily living (ADL) function. Postoperatively, evaluating how patients move (i.e., their kinematics/kinetics) during ADL often requires visits to clinics or specialized biomechanics laboratories. Prior work in our lab and others have leveraged wearables and machine learning approaches such as artificial neural networks (ANNs) to quantify hip angles/moments during simple ADL such as walking. Although level-ground ambulation is necessary for patient satisfaction and post-THA function, other tasks such as stair ascent may be more critical for improvement. This study utilized wearable sensors/ANNs to quantify sagittal/frontal plane angles and moments of the hip joint during stair ascent from 17 healthy subjects. Shin/thigh-mounted inertial measurement units and force insole data were inputted to an ANN (2 hidden layers, 10 total nodes). These results were compared to gold-standard optical motion capture and force-measuring insoles. The wearable-ANN approach performed well, achieving rRMSE = 17.7% and R² = 0.77 (sagittal angle/moment: rRMSE = 17.7 ± 1.2%/14.1 ± 0.80%, R² = 0.80 ± 0.02/0.77 ± 0.02; frontal angle/moment: rRMSE = 26.4 ± 1.4%/12.7 ± 1.1%, R² = 0.59 ± 0.02/0.93 ± 0.01). While we only evaluated healthy subjects herein, this approach is simple and human-centered and could provide portable technology for quantifying patient hip biomechanics in future investigations.

Comparison between conventional and neuronavigated strategies to assess corticospinal responsiveness in unfatigued and fatigued knee-extensor muscles

In studying neuromuscular fatigability, researchers commonly use functional criteria to position and hold the transcranial magnetic stimulation (TMS) coil during testing sessions. This could influence the magnitude of corticospinal excitability and inhibition responses due to imprecise and unsteady positions of the coil. To reduce coil position and orientation variability, neuronavigated TMS (nTMS) could be used. We evaluated the accuracy of nTMS and a standardized function-guided procedure for maintaining TMS coil position both in unfatigued and fatigued knee extensors. Eighteen participants (10F/8M) volunteered in two identical and randomized sessions. Maximal and submaximal neuromuscular evaluations were performed with TMS three times before (PRE_1) and three times after (PRE_2) a 2 min resting session and one time immediately after (POST) a 2-min sustained maximal voluntary isometric contraction (MVIC). The located "hotspot" [the location that evoked the largest motor-evoked potential (MEP) responses in the rectus femoris] was maintained either with or without nTMS. MEP, silent period (SP) and the distance between the "hotspot" and the actual coil position were recorded. A time × contraction intensity × testing session × muscle interaction was not observed for MEP, SP, and distance. Bland-Altman plots presented adequate agreements for MEP and SP. Spatial accuracy of TMS coil position over the motor cortex did not influence corticospinal excitability and inhibition in unfatigued and fatigued knee extensors. The variability in MEP and SP responses may be due to spontaneous fluctuations in corticospinal excitability and inhibition, and it is not altered by the spatial stability of the stimulation point.

Cervical Proprioception Assessed through Targeted Head Repositioning: Validation of a Clinical Test Based on Optoelectronic Measures

Neck proprioception is commonly assessed with head repositioning tests. In such a test, an operator rotates the head of a blindfolded individual to a target position. After returning to the rest position, the participant actively repositions the head to the target. Joint Position Error (JPE) is the angular difference between the target angle (however oriented in a 3D space) and the actively reached positions (the smaller the difference, the better the proprioception). This study aimed to validate a head-to-target (HTT) repositioning test using an optoelectronic system for also measuring the components of the JPE in the horizontal, frontal, and sagittal planes. The head movements requested by the operator consisted of 30° left-right rotations and 25° flexion-extension. The operators or subjects could not obtain these movements without modest rotations in other planes. Two operators were involved. Twenty-six healthy participants (13 women) were recruited (mean (SD): 33.4 (6.3) years). The subjects’ JPE in the requested (intended) plane of motion (JPEint-component) was a few degrees only and smaller for flexion-extensions than for left-right rotations (right rotation: 5.39° (5.29°); left rotation: 5.03° (4.51°), extension: 1.79° (3.94°); flexion: 0.54° (4.35°)). Participants’ average error in unintended planes was around 1° or less. Inter-operator consistency and agreement were high. The smallest detectable change, at p < 0.05, for JPEint-component ranged between 4.5° and 6.98°. This method of optoelectronic measurement in HTT repositioning tests provides results with good metric properties, fostering application to clinical studies.

fNIRS is sensitive to leg activity in the primary motor cortex after systemic artifact correction

BACKGROUND

functional near-infrared spectroscopy (fNIRS) is an increasingly popular tool to study cortical activity during movement and gait that requires further validation. This study aimed to assess (1) whether fNIRS can detect the difficult-to-measure leg area of the primary motor cortex (M1) and distinguish it from the hand area; and (2) whether fNIRS can differentiate between automatic (i.e., not requiring one's attention) and non-automatic movement processes. Special attention was attributed to systemic artifacts (i.e., changes in blood pressure, heart rate, breathing) which were assessed and corrected by short channels, i.e., fNIRS channels which are mainly sensitive to superficial scalp hemodynamics.

METHODS

Twenty-three seated, healthy participants tapped four fingers on a keyboard or tapped the right foot on four squares on the floor in a specific order given by a 12-digit sequence (e.g., 434141243212). Two different sequences were executed: a beforehand learned (i.e., automatic) version and a newly learned (i.e., non-automatic) version. A 36-channel fNIRS device including 12 short channels covered multiple motor-related cortical areas including M1. The fNIRS data were analyzed with a general linear model (GLM). Correlation between the expected functional hemodynamic responses (i.e. task regressor) and the short channels (i.e. nuisance regressors), necessitated performing a separate short channel regression instead of integrating them in the GLM.

RESULTS

Consistent with the M1 somatotopy, we found significant HbO increases of very large effect size in the lateral M1 channels during finger tapping (Cohen's d = 1.35, p<0.001) and significant HbO increases of moderate effect size in the medial M1 channels during foot tapping (Cohen's d = 0.8, p<0.05). The cortical activity differences between automatic and non-automatic tasks were not significantly different. Importantly, leg movements produced large systemic fluctuations, which were adequately removed by the use of all available short channels.

DISCUSSION

Our results indicate that fNIRS is sensitive to leg activity in M1, though the sensitivity is lower than for finger activity and requires rigorous correction for systemic fluctuations. We furthermore highlight that systemic artifacts may result in an unreliable GLM analysis when short channels show signals that are similar to the expected hemodynamic responses.

Unintentional force drifts in the lower extremities

We explored the phenomenon of unintentional force drift seen in the absence of visual feedback during knee extension contractions in isometric conditions. Based on the importance of knee extensors for the anti-gravity function, we hypothesized that such force drifts would be slower and smaller compared to those reported for the upper extremities. We also explored possible effects of foot dominance and gender on the force drifts. Young healthy persons produced isometric knee extension contractions to different levels, ranging from 15 to 25% of maximal voluntary contraction force, with the help of visual feedback, and then, the visual feedback was turned off. Force change over the time interval without visual feedback was quantified. In the absence of visual feedback, force drifted to smaller magnitudes. The drift magnitude expressed in percent of the initial force magnitude was smaller for smaller initial force levels, ranging between 8 and 15% of the initial force for the initial force magnitude of 15% and 25% of maximal voluntary contraction force. The time exponent of the force drift was independent of the initial force magnitude and was, on average, 6.45 s. There were no significant effects of foot dominance or gender, although the male subjects tended to show stronger scaling of the drift magnitude with the initial force level compared to the female subjects. The results show that unintentional force drift is a common phenomenon across limbs and muscle groups. This conclusion fits the theory of control with spatial referent coordinates and the general tendency of all natural systems to drift to states with lower potential energy.

A novel method to quantify individual limb contributions to standing postural control

BACKGROUND

Understanding individual limb contributions to standing postural control is valuable when evaluating populations with asymmetric function (e.g., stroke, amputations). We propose a method of quantifying three contributions to controlling the net anteroposterior center of pressure (CoP) during quiet standing: CoP moving under left and right limbs and weight shifting between the two limbs.

RESEARCH QUESTION

Can these contributions to standing postural control be quantified from CoP trajectories in neurotypical adults?

METHODS

Instantaneous contributions can be negative or larger than one, and integrated contributions sum to equal one. Proof-of-concept demonstrations validated these calculated contributions by restricting CoP motion under one or both feet. We evaluated these contributions in 30 neurotypical young adults who completed two (eyes opened; eyes closed) 30-s trials of bipedal standing. We evaluated the relationships between limb contributions, self-reported limb dominance, and between-limb weight distributions.

RESULTS

All participants self-reported as right-limb dominant; however, a range of mean limb contributions were observed with eyes opened (Left: mean [range] = 0.52 [0.37-0.63]; Right: 0.48 [0.31-0.63]) and with eyes closed (Left: 0.51 [0.39-0.63]; Right: 0.49 [0.37-0.61]). Weight-shift contributions were small with eyes opened (0.00 [-0.01 to 0.01]) and eyes closed (0.00 [-0.01 to 0.02]). We did not identify any between-limb differences in contributions when grouped by self-reported limb dominance (p > 0.10, d < 0.31). Contributions did not significantly correlate with Waterloo Footedness scores (-0.22 < r < 0.21, p > 0.25) or between-limb weight distributions (0 < r < 0.24, p > 0.20).

SIGNIFICANCE

Across neurotypical participants, we observed a notable range of limb contributions not related to self-reported limb dominance or between-limb weight distributions. With this tool, we can characterize differences in the amount of CoP motion and the underlying control strategies. Changes in limb contribution can be measured longitudinally (i.e., across rehabilitation programs, disease progression, aging) representative of limb function, which may be particularly useful in populations with asymmetric function.

Effects of age on the visuo-locomotor control used to circumvent a virtual pedestrian with different limb movements

It is known that young adults (YA) circumvent pedestrians differently than inanimate obstacles and that limb movements of the pedestrian influence minimum clearance for predictable pedestrian paths. Although older adults (OA) use more cautious strategies for general pedestrian avoidance compared to YA, how pedestrian movements influence circumvention by OAs is unknown. The aim of this study was to understand how limb movements of a pedestrian with an initially unpredictable trajectory affect circumvention control in younger vs older healthy adults. Fourteen YA and 14 OA (> 70 years) were immersed in a virtual shopping mall and instructed to circumvent a virtual pedestrian (VP) approaching with either normal locomotor movements, upper limbs fixed, lower limbs fixed, or both upper and lower limbs fixed. Onset distance for trajectory deviation, minimum clearance, walking speed, body segment yaw angles and gaze behaviour were analysed. When the VP lacked local limb movements, both age groups initiated their trajectory deviations farther away, but significantly more so for OA. Minimal clearance was unchanged across conditions and similar for both age groups. OA walked slower, produced smaller head and trunk yaw, and visually focused on the VP for a greater percentage of time. Thus, lack of limb movements of another pedestrian resulted in more cautious circumvention control and OA needed more time to process visual information with greater visual attention focused on the VP. Age-related changes could translate to a greater risk of falls in OA populations with reduced balance and mobility that could limit community ambulation.

Ankle and foot function in female athletes involved in in-water and dry-land sporting activities

BACKGROUND

The stability and mobility of the ankle and foot joints are thought to be improved by cross-training, i.e., transferring the beneficial effects acquired from performing one sporting activity to those required to perform another. This study aimed to investigate the effect of long-term participation with in-water and dry-land sports activities (IWSA, DLSA) on ankle and foot function.

METHODS

The study sample consisted of 28 healthy competitive female athletes involved in IWSA (N.=14) and DLSA (N.=14) for <8 years, as well as 15 females not involved in sporting activities (NISA). The isometric strength of the ankle dorsi flexors (ADF), plantar flexors (APF), and subtalar invertors and evertors (SIN, SEV), the ankle dorsi and plantar flexion, and subtalar/forefoot inversion and eversion passive range of motion (ROM), and the static and dynamic balance were assessed in each participant's supportive lower limb.

RESULTS

IWSA athletes demonstrated significantly greater isometric strength in ADF (P<0.01), SIN (P<0.01), and SEV (P<0.05) compared to DLSA athletes and in ADF (P<0.001), SIN (P<0.01) and SEV (P<0.05) compared to NISA individuals with differences between DLSA athletes and NISA individuals being not significant. Between-groups differences on isometric APF strength, passive ROM of the ankle and foot joints, and postural balance were not significant.

CONCLUSIONS

DLSA athletes could benefit from long-term participation with IWSA, at least in terms of increasing isometric strength of the ankle and foot stabilizers, as their function does not appear to improve after long-term participation with the sports of their choice, at least compared to NISA individuals.

Postural adjustment in standing position when catching a ball under unpredictable conditions of the direction to be caught

Background

Balanced postural control of the body is associated with two mechanisms: anticipatory postural adjustment and compensatory postural adjustment. Previous studies reported changes in body postural control under unpredictable conditions (interference with closed eyes).

Research question

To ascertain whether in contrast with predictable disturbances, there is a difference in muscle activity and center of pressure displacement changes when the direction of the disturbance is unpredictable.

Methods

Three examiners stood at 45° to the left, the front, and 45° to the right of the participant to throw the ball to him. 11 healthy young participants were required to maintain their balance in the standing position after receiving the ball in conditions with and without known catching directions. The anticipatory postural adjustment and compensatory postural adjustment integral changes of the muscle activity in the lower limbs and trunk bilaterally and at the center of pressure displacement in the known and unknown conditions were observed. Two-way ANOVA was used to compare the differences in muscle activity and displacement changes.

Results

Results showed that the center of pressure in the anticipatory postural adjustment and compensatory postural adjustment in the posterior direction with known catching direction was significantly shorter than those without. Integration of electromyogram in anticipatory postural adjustment of the right soleus (p = 0.023) was associated with higher muscle activities in the unknown than known conditions. Integration of electromyogram in compensatory postural adjustment of the right tibial anterior (p = 0.004), right rectus femoris (p = 0.023) and left rectus abdominis (p = 0.038) in unknown catching direction had significantly greater muscle activity than those without. When the direction of the perturbation is unpredictable, the central nervous system may initiate and induce greater center of pressure changes in the posterior direction with changes in several muscular activities to ensure postural control.

Effect of acute ankle experimental pain on lower limb motor control assessed by the modified star excursion balance test

Introduction

Following most musculoskeletal injuries, motor control is often altered. Acute pain has been identified as a potential contributing factor. However, there is little evidence of this interaction for acute pain following ankle sprains. As pain is generally present following this type of injury, it would be important to study the impact of acute pain on ankle motor control. To do so, a valid and reliable motor control test frequently used in clinical settings should be used. Therefore, the objective of this study was therefore to assess the effect of acute ankle pain on the modified Star Excursion Balance Test reach distance.

Methods

Using a cross-sectional design, 48 healthy participants completed the modified Star Excursion Balance Test twice (mSEBT1 and mSEBT2). Following the first assessment, they were randomly assigned to one of three experimental groups: Control (no stimulation), Painless (non-nociceptive stimulation) and Painful (nociceptive stimulation). Electrodes were placed on the right lateral malleolus to deliver an electrical stimulation during the second assessment for the Painful and Painless groups. A generalized estimating equations model was used to compare the reach distance between the groups/conditions and assessments.

Results

Post-hoc test results: anterior (7.06 ± 1.54%; p < 0.0001) and posteromedial (6.53 ± 1.66%; p < 0.001) directions showed a significant reach distance reduction when compared to baseline values only for the Painful group. Regarding the anterior direction, this reduction was larger than the minimal detectable change (5.87%).

Conclusion

The presence of acute pain during the modified Star Excursion Balance Test can affect performance and thus might interfere with the participant's lower limb motor control. As none of the participants had actual musculoskeletal injury, this suggests that pain and not only musculoskeletal impairments could contribute to the acute alteration in motor control.

Isokinetic leg muscle strength relationship to dynamic balance reflects gymnast-specific differences in adolescent females

Balance, together with other motor qualities, plays an important role in the successful execution of specific gymnastic skills. However, it is also not clear whether different demands on dynamic balance and power produced by lower limb can be observed in sport-specific differences among gymnasts of various modalities. The question also is as to what extent isokinetic leg muscle strength contributes to anterior and posterior postural stability in gymnasts. Therefore, the aim of the study was i) to compare variables of dynamic balance and isokinetic leg muscle strength in rhythmic, artistic, and aerobic gymnasts, and ii) to investigate the relationship of reach distances in anterior, posteromedial, and posterolateral directions, as well as the composite score in the Y-balance test with an isokinetic muscle strength during knee extension and flexion at different velocities in female gymnasts of various disciplines. Altogether seven aerobic, five artistic, and six rhythmic gymnasts performed the Y-balance test and isokinetic leg muscle strength test at 60°/s, 180°/s, and 300°/s. Results showed significant between-group differences in the composite score in the Y-balance test of the dominant (F = 3.536, p = .041) and non-dominant symmetry (F = 4.804, p = .015). Similarly, average power produced during knee extension and knee flexion at 60°/s, 180°/s and 300°/s differed significantly among these groups (all at p˂0.05). In addition, there was a significant relationship between the composite score of the dominant limb symmetry and isokinetic dominant limb extension strength at 60°/s (r = .54), 180°/s (r = .87), and 300°/s (r = .84) in aerobic gymnasts. The composite score of the dominant limb symmetry was also associated with isokinetic dominant limb extension strength, albeit only at 60°/s in both artistic (r = .60) and rhythmic gymnasts (r = .55). Such between-group differences may be ascribed to their different demands on maintenance of balance under dynamic conditions and leg muscle power within their sport specializations. Taking into account significant association between the dominant limb symmetry and isokinetic dominant limb extension strength, it may be concluded that both muscle strength and fast speeds contribute to dynamic balance in adolescent gymnasts.

Improving old tricks as new: Young adults learn from repeating everyday activities

The notion that young healthy adults can substantially improve in activities that are part of their daily routine is often overlooked because it is assumed that such activities have come to be fully mastered. We followed, in young healthy adults, the effects of repeated executions of the Timed-Up-and-Go (TUG) task, a clinical test that assesses the ability to execute motor activities relevant to daily function-rising from a seated position, walking, turning and returning to a seated position. The participants (N = 15) performed 18 consecutive trials of the TUG in one session, and were retested on the following day and a week later. The participants were video recorded and wore inertial measurement units. Task execution times improved robustly; performance was well fitted by a power function, with large gains at the beginning of the session and nearing plateau in later trials, as one would expect in the learning of a novel task. Moreover, these gains were well retained overnight and a week later, with further gains accruing in the subsequent test-sessions. Significant intra-session and inter-session changes occurred in step kinematics as well; some aspects underwent inter-sessions recalibrations, but other aspects showed delayed inter-session changes, suggesting post-practice memory consolidation processes. Even common everyday tasks can be improved upon by practice; a small number of consecutive task repetitions can trigger lasting gains in young healthy individuals performing highly practiced routine tasks. This new learning in highly familiar tasks proceeded in a time-course characteristic of the acquisition of novel 'how to' (procedural) knowledge.

Exploring pattern recognition: what is the relationship between the recognition of words, faces and other objects?

Debate surrounds processes of visual recognition, with no consensus as to whether recognition of distinct object categories (faces, bodies, cars, and words) is domain specific or subserved by domain-general visual recognition mechanisms. Here, we investigated correlations between the performance of 74 participants on recognition tasks for words, faces and other object categories. Participants completed a counter-balanced test battery of the Cambridge Face, Car and Body Parts Memory tests, as well as a standard four category lexical decision task, with response time and recognition accuracy as dependent variables. Results revealed significant correlations across domains for both recognition accuracy and response time, providing some support for domain-general pattern recognition. Further exploration of the data using principal component analysis (PCA) revealed a two-component model for both the response time and accuracy data. However, how the various word and object recognition tasks fitted these components varied considerably but did hint at familiarity/expertise as a common factor. In sum, we argue a complex relationship exists between domain-specific processing and domain-general processing, but that this is shaped by expertise. To further our understanding of pattern recognition, research investigating the recognition of words, faces and other objects in dyslexic individuals is recommended, as is research exploiting neuroimaging methodologies, with excellent temporal resolution, to chart the temporal specifics of different forms of visual pattern recognition.

Developing a method for quantifying hip joint angles and moments during walking using neural networks and wearables

Quantifying hip angles/moments during gait is critical for improving hip pathology diagnostic and treatment methods. Recent work has validated approaches combining wearables with artificial neural networks (ANNs) for cheaper, portable hip joint angle/moment computation. This study developed a Wearable-ANN approach for calculating hip joint angles/moments during walking in the sagittal/frontal planes with data from 17 healthy subjects, leveraging one shin-mounted inertial measurement unit (IMU) and a force-measuring insole for data capture. Compared to the benchmark approach, a two hidden layer ANN (n = 5 nodes per layer) achieved an average rRMSE = 15% and R²=0.85 across outputs, subjects and training rounds.

The Simon Effect Asymmetry for Left- and Right-Dominant Persons

When participants respond to a task-relevant stimulus attribute by pressing a left or right key with the respective index finger, reaction time is shorter if task-irrelevant left-right stimulus location corresponds to that of the response key than if it does not. For right-handers, this Simon effect is larger for right-located than left-located stimuli; for left-handers this Simon-effect asymmetry is reversed. A similar asymmetry has been found for right-footers pressing pedals with their feet. For analyses that separate stimulus- and response-location factors, these asymmetries appear as a main effect of response location, with responses being faster with the dominant effector. If the Simon-effect asymmetry is strictly a function of effector dominance, it should reverse for left-footers responding with their feet. In Experiment 1, left-dominant persons showed faster responses with the left than right hand but with the right than left foot, a finding consistent with prior research on tapping actions. Right-dominant persons also showed the right-foot asymmetry but, unexpectedly, not the typical asymmetry with hand responses. To evaluate whether hand-presses yield results distinct from finger-presses, in Experiment 2 participants performed the Simon task with finger-presses and hand-presses. The opposing asymmetries for right- and left-dominant persons were evident for both response modes. Our results are consistent with the view that the Simon effect asymmetry is primarily due to differences in effector efficiency, usually but not always favoring the dominant effector.

Between a Walk and a Hard Place: How Stepping Patterns Change While Navigating Environmental Obstacles

Maintaining a consistent relationship between each footfall and the body's motion is a key mechanism to maintain balance while walking. However, environmental features, for example, puddles/obstacles, impose additional constraints on foot placement. This study investigated how healthy young individuals alter foot placements to simultaneously manage body-centric and environmental constraints during an obstacle-crossing task. Consistent step length promotes balance for all steps, whereas accurate foot placement around the obstacle is essential to avoid a trip. While crossing an obstacle, any error in positioning one foot relative to the obstacle can be compensated by selecting the placement of the subsequent step. However, compensation will necessarily alter step length from its average value. The interstep covariance index computed from two consecutive foot placements was used to quantify this tradeoff between body-centric and environmental constraints for six consecutive steps while approaching, crossing, and resuming unobstructed gait after crossing the obstacle. The index declined only when either one or both feet were adjacent to the obstacle. The decline was driven in part by a tendency toward higher step length variability. Thus, changes in the stepping patterns to address the environmental constraint occurred at the cost of the body-centric constraint. However, the step length never ceased to be controlled; the interstep covariance index was positive for all steps. Overall, participants adapted foot placement control to account for the larger threat to balance. The environmental constraint was prioritized only when a potential trip posed greater threat to balance compared with the threat posed by variable step length.

Advanced cueing of auditory stimulus to the head induces body sway in the direction opposite to the stimulus site during quiet stance in male participants

Under certain conditions, a tactile stimulus to the head induces the movement of the head away from the stimulus, and this is thought to be caused by a defense mechanism. In this study, we tested our hypothesis that predicting the stimulus site of the head in a quiet stance activates the defense mechanism, causing a body to sway to keep the head away from the stimulus. Fourteen healthy male participants aged 31.2 ± 6.8 years participated in this study. A visual cue predicting the forthcoming stimulus site (forehead, left side of the head, right side of the head, or back of the head) was given. Four seconds after this cue, an auditory or electrical tactile stimulus was given at the site predicted by the cue. The cue predicting the tactile stimulus site of the head did not induce a body sway. The cue predicting the auditory stimulus to the back of the head induced a forward body sway, and the cue predicting the stimulus to the forehead induced a backward body sway. The cue predicting the auditory stimulus to the left side of the head induced a rightward body sway, and the cue predicting the stimulus to the right side of the head induced a leftward body sway. These findings support our hypothesis that predicting the auditory stimulus site of the head induces a body sway in a quiet stance to keep the head away from the stimulus. The right gastrocnemius muscle contributes to the control of the body sway in the anterior-posterior axis related to this defense mechanism.