Action Boundary Proximity Effects on Perceptual-Motor Judgments

INTRODUCTION: Designed as a more ecological measure of reaction times, the Perception-Action Coupling Task (PACT) has shown good reliability and within-subject stability. However, a lengthy testing period was required. Perceptual-motor judgments are known to be affected by proximity of the stimulus to the action boundary. The current study sought to determine the effects of action boundary proximity on PACT performance, and whether redundant levels of stimuli, eliciting similar responses, can be eliminated to shorten the PACT.METHODS: There were 9 men and 7 women who completed 4 testing sessions, consisting of 3 familiarization cycles and 6 testing cycles of the PACT. For the PACT, subjects made judgments on whether a series of balls presented on a tablet afford "posting" (can fit) through a series of apertures. There were 8 ratios of ball to aperture size (B-AR) presented, ranging from 0.2 to 1.8, with each ratio appearing 12 times (12 trials) per cycle. Reaction times and judgment accuracy were calculated, and averaged across all B-ARs. Ratios and individual trials within each B-AR were systematically eliminated. Variables were re-averaged, and intraclass correlation coefficients (ICC) and coefficients of variation (CVTE) were calculated in an iterative manner.RESULTS: With elimination of the 0.2 and 1.8 B-ARs, the PACT showed good reliability (ICC = 0.81-0.99) and consistent within-subject stability (CVTE = 2.2-14.7%). Reliability (ICC = 0.81-0.97) and stability (CVTE = 2.6-15.6%) were unaffected with elimination of up to 8 trials from each B-AR.DISCUSSION: The shortened PACT resulted in an almost 50% reduction in total familiarization/testing time required, significantly increasing usability.Johnson CD, LaGoy AD, Pepping G-J, Eagle SR, Beethe AZ, Bower JL, Alfano CA, Simpson RJ, Connaboy C. Action boundary proximity effects on perceptual-motor judgments. Aerosp Med Hum Perform. 2019; 90(12):1000-1008

Inter-Rater Reliability of Dynamic Exertion Testing (EXiT) Performance Among Healthy Adults.

INTRODUCTION: The Dynamic Exertion Test (EXiT) is a new standardized return to play (RTP) exertion assessment for athletes at medical clearance following a concussion. It incorporates aerobic, multiplanar dynamic, and functional movements, based on exercise prescription guidelines from the American College of Sports Medicine (ACSM), with objective measures that work to challenge all potentially affected systems of a concussed athlete. The purpose of this study is to determine the interrater reliability (IRR) of the EXiT between two raters assessing healthy, non-concussed athletes and to determine the level of systematic bias between the two raters. METHODS: A subgroup of 15 participants (F=5, 33.3%, age: 23.67 ± 4.22 years old) from a larger study were assessed with the EXiT on two visits. Two raters simultaneously scored participants at both visits on the number of errors committed on all dynamic tasks and on time to completion on agility cone tasks. IRR was estimated using intraclass correlation coefficients (ICC) and 95% confidence intervals (CI) for time and Kappa Coefficients and 95% CI were used for errors. Paired t-tests and NcNemar Tests were used to assess for systematic bias between raters’ scores. RESULTS: Time to completion had good IRR (ICCs > 0.759), Arrow Agility at visit 1 had the highest (0.999 [95% CI 0.997-1.0]) and Box Drill Carioca at visit 2 had the lowest (0.759 [95% CI 0.314-0.929]). Fifteen of the 20 tasks showed no statistically significant difference between raters scores. Errors had poor to excellent IRR (p-values: 0.324-1.00) and an observed percent agreement >83.33% for 10 of 14 tasks, Zigzag at visit 1 had the lowest (66.66%). McNemar Test showed no statistically significant difference (p-values > 0.250) for all task errors, but Arrow Agility had the largest difference between raters at both visits (13.33% vs. 40%, 16.66% vs. 41.66%). CONCLUSION: IRR for the EXiT time and errors was good for the majority of tasks. This study was a good first step in evaluating the reliability of the new RTP exertional protocol, the EXiT. Future research should use a larger sample size to evaluate IRR in concussed participants along with intra-rater and test retest reliability

Intersession Reliability and Within-Session Stability of a Novel Perception-Action Coupling Task

BACKGROUND: The perception-action coupling task (PACT) was designed as a more ecologically valid measure of alertness/reaction times compared to currently used measures by aerospace researchers. The purpose of this study was to assess the reliability, within-subject variability, and systematic bias associated with the PACT. METHODS: There were 16 subjects (men/women = 9/7; age = 27.8 +/- 3.6 yr) who completed 4 identical testing sessions. The PACT requires subjects to make judgements on whether a virtual ball could fit into an aperture. For each session, subjects completed nine cycles of the PACT, with each cycle lasting 5 min. Judgement accuracy and reaction time parameters were calculated for each cycle. Systematic bias was assessed with repeated-measures ANOVA, reliability with intraclass correlation coefficients (ICC), and within-subject variability with coefficients of variation (CVTE). RESULTS: Initiation time (Mean = 0.1065 s) showed the largest systematic bias, requiring the elimination of three cycles to reduce bias, with all other variables requiring, at the most, one. All variables showed acceptable reliability (ICC > 0.70) and within-subject variability (CVTE <20%) with only one cycle after elimination of the first three cycles. CONCLUSIONS: With a three-cycle familiarization period, the PACT was found to be reliable and stable

THE EFFECT OF LOADED FATIGUE ON LOADED POSTURAL STABILITY

Military personnel are often required to carry heavy loads for long distances over unpredictable terrain. Additional load carriage, in conjunction with fatigue, has the potential to influence postural control mechanisms which may in turn increase injury risk. The purpose of this study was to determine if a loaded incremental march to fatigue negatively influences loaded postural stability. Loaded postural stability was measured using the NeuroCom Sensory Organization Test (SOT) and kinetic force plate variables (vertical ground reaction forces: SDvGRF, and TotSway) before and after a loaded incremental march to fatigue in 23 physically active men and women (age: 24.1 4.0 years, height: 172.3 11.1 cm, weight: 162.2 38.2 lbs) while subjects were adorned with a weighted vest equating to 30% of their body weight. The SOT consisted of six conditions (C1-C6) aimed to perturb the sensorimotor system, which were performed before and after a loaded fatigue protocol. C1, C2 and C3 challenged the somatosensory system, C4 challenged the visual system, while C5 and C6 challenged the vestibular system. Fatigue was induced with a treadmill march at 4mph with increasing grades of 2% every three minutes until volitional fatigue. After testing for normality, paired sample t-tests or Wilcoxon signed rank tests were conducted to assess pre- to post-fatigue differences. Significant reductions in SOT scores were found in overall composite scores (pre: 82.8 4.7, post: 81.6 5.2, p = 0.010), SDvGRF of C1 (pre: 1.3 0.5, post: 2.0 0.9, p < 0.001), C2 (pre: 1.4 0.6, post: 1.9 1.2, p < 0.001), C3 (pre: 1.4 0.5, post: 2.1 1.8, p = 0.026), and C6 (pre: 2.5 2.2, post: 3.5 3.2, p < 0.001) and TotSway of all conditions. Results suggest that significant changes in loaded postural stability were caused by loaded fatigue. Findings could aid in future postural stability screenings, load carriage training and strategies for injury prevention in the military

The effect of the branched-chain amino acids on the in-vitro activity of bovine intestinal alkaline phosphatase

Branched-chain amino acids (BCAA) are used as nutritional support for patients with a range of conditions including liver cirrhosis and in-born errors of amino acid metabolism, and are commonly used “sports”/exercise supplements. The effects of the BCAA on the in-vitro activity of calf intestinal alkaline phosphatase (EC. 3.1.3.1) were studied. All three BCAA were found to be uncompetitive inhibitors of the enzyme with L-leucine being the most potent (Ki’ = 24.9mM) and L-valine, the least potent (Ki’ = 37mM). Mixed BCAA are able to act in combination to inhibit the enzyme. Given the important role of intestinal alkaline phosphatase in gut homeostasis, these findings have potential implications for those taking high levels of BCAA as supplements

Mental health, physical symptoms and biomarkers of stress during prolonged exposure to Antarctica’s extreme environment

The Antarctic environment is characterized by many of the same extreme stressors as long-duration space flight (LDSE), thereby providing a useful earth-based analog for examining changes in and predictors of mental health over time. At coastal (n = 88) and inland (n = 22) Antarctic stations we tracked mental health symptoms across a nine-month period including winter-over using the Mental Health Checklist (MHCL; Bower et al., 2019). Our monthly assessment battery also examined changes in physical complaints, biomarkers of stress, and the use of different emotion regulation strategies. MHCL positive adaptation scores showed linear decreases whereas MHCL poor self-regulation scores and severity of physical symptoms increased across the study period. During-mission use of emotion regulation strategies and dehydroepiandrosterone (DHEA) levels predicted end-of-study MHCL scores, whereas trait-based psychological measures collected at the start of the mission showed little predictive utility. Results suggest that interventions and counter measures aimed at enhancing positive affect/emotion during prolonged exposure to extreme environments may be useful in reducing psychological risk

Effects Of Additional Carried Load On Perception-action Coupling During A Discrete Horizontal Jump Task: 954 Board #270 June 1, 2

Perception-Action coupling (PAC) is the reciprocal animal/environment interaction by which actions are controlled. Successful PAC requires accurate perception of affordances (opportunities for action), in relation to action capabilities/boundaries. Accuracy is dependent on the congruence of the perceptual awareness of action boundaries (distance of a gap to be jumped) in relation to changes in action capabilities (additional load). Military personnel carry up to 60% of body weight (BW) when performing operational tasks. The addition of such loads have been shown to effect landing mechanics and ground reaction forces, thus increasing the opportunity for injury. Safe execution of a jump across a gap when carrying an additional load requires accurate PAC with respect to the changes in action capabilities.PURPOSE: Examine the effects of additional load on PAC with respect to horizontal jumping distance.METHODS: Maximum jump distances of 17 participants (Age=24.8+3.6yrs; Ht=179.3+6.7cm; Wt=80.2+14.7kg) were established in 3 load conditions (BW, BW+15%, and BW+30%); representing their action boundaries. Participants were presented with the opportunity to jump 4 different distances (90, 95, 100, and 105% of their max jump distance). Six trials of each distance in each load condition were performed in a randomized order; split over 2 days. Participants were instructed that if they perceived the distance to be ‘jumpable’ then jump, if not turn around. Percentage correct responses were analysed using the Friedman test to determine any significant differences in action response for load and distance conditions.RESULTS: Accuracy of PAC decreased significantly (

Can Lighthill's elongated body theory predict hydrodynamic forces in underwater undulatory swimming?

Underwater Undulatory Swimming (UUS) is an area of continuing development in elite swimming. The propulsiveforces generated during UUS are investigated experimentally, during an over-speed tow, and numerically using Elongated Body Theory (EBT), developed initially for fish locomotion. Two-dimensional kinematic motion data(foot, shank, thigh, torso, upper arm, lower arm, and hand) at 25Hz in the sagittal plane is acquired by manualdigitisation of video recorded from a stationary camera during an over-speed active tow and input into an EBT model.Thrust (T) determined from EBT and a semi-empirical passive resistance (R) is used to estimate R-T for comparisonwith the experimental tow line measurement. The forces predicted from EBT although significantly larger than theexperimental measurement indicate that the EBT has the potential, with suitable refinement, to provide detailedinsight into the hydrodynamics of UUS. Areas for further refinement are in the use of a three-dimensional correctionand that higher resolution motion data for the feet are required

Dynamic Exertion Testing (EXiT): An Assessment to Inform to Return to Play/Activity following Sport-related Concussion

BACKGROUND: Recently developed dynamic exertion testing (EXiT) incorporates a combination of treadmill running, functional movements, and agility tasks to inform return to play and activity (RTP/A) decision making following sport-related concussion. The identification of an assessment’s stability on repeated assessments, inter-rater agreement, minimal detectable change (MDC), and examination of age, sex, body mass index (BMI), and sport-type are necessary to interpret EXiT. Additionally, previously injured athletes upon medical clearance to RTP/A should have similar physiological, performance, and clinical outcomes on EXiT as healthy athletes, including heart rate variability (HRV) responses to EXiT as a proxy of autonomic nervous system functioning. PURPOSE: The aims of the current investigation included the following: Aim 1) Establish intra-rater, test-retest and inter-rater reliability for EXiT physiological (age estimated percentage of maximum heart rate (HR %max)) and blood pressure (BP)), performance (agility task completion time and errors), and clinical (endorsed symptoms and rating of perceived exertion (RPE)) outcomes. Aim 2) Compare age, sex, BMI, and sport-type subgroups across EXiT physiological, performance, and clinical outcomes among a heterogeneous physically active sample. Aim 3) Determine concurrent validity of EXiT by comparing physiological, performance, and clinical EXiT outcomes and ultrashort heart rate variability responses to EXiT between athletes at medical clearance to RTP/A from SRC with healthy controls. METHODS: Aim 1) From a total sample of 92 healthy physically active adolescents and adults, 79 (F:34, 43%) completed a demographic questionnaire, weight and height measurements for BMI ([BMI]= weight [kg]/height[m]2), and the EXiT across 2 visits (8.7±4.7 days apart). EXiT included an aerobic component: 12- min treadmill run; and dynamic component: dynamic circuit, ball toss, box-drill shuffle and carioca, zig zag, pro agility, and arrow agility tasks. A 2nd rater separately assessed agility task completion time and errors for 15 healthy participants and 15 athletes upon medical clearance to RTP/A. Two-way, mixed, intra-class correlation coefficients were used to evaluate agility task completion time between consecutive trials (intra-rater reliability), fastest trial across visits (test-retest reliability), and agreement between raters (inter-rater reliability). Paired samples t-tests were used for HR %max and agility task completion time, and Wilcoxon tests were used for endorsed symptoms, RPE, and errors. Internal consistency of symptoms at each visit was determined with Cronbach’s alpha, and MDC of EXiT outcomes were calculated using the equation: MDC= standard deviation x √((1-ICC) ) • 1.96 • √(2 ). Aim 2) 87 (F= 55, 37.4%; 19.5 ± 4.4 years) participants (from aim 1) were categorized in adolescent (14- 17 years) or adult (≥18 years), male or female (self-report), LO-BMI (BMI < 50th percentile) or HI-BMI (BMI ≥50th percentile), and collision, contact, or non-contact sport-types. Independent samples t-tests were conducted for HR %max, BP, and agility task completion time, and Mann-Whitney U tests for RPE, endorsed symptoms, and errors between age, sex, and BMI groups across aerobic and dynamic components. A series of 1-way ANOVAs were conducted to compare HR %max, BP, and agility task completion time, and Kruskal Wallis- H tests to compare RPE, symptoms, and committed errors between collision, contact, and non-contact sport-types. Aim 3) A sample of 46 healthy athletes including 23 (F= 10, 43.5%) healthy control (from aim 1; CONTROL) and age-, sex-, and sport- matched to patients completing EXiT at medical clearance to RTP/A (CONCUSS) completed a 5-minute seated rest period prior to and following EXiT. The final 3-min were used to calculate ultrashort HRV outcomes, including the root-mean-square of successive differences (RMSSD) and standard deviation of successive heart beats (SDNN). Independent samples t-tests were conducted to compare CONTROL and CONCUSS groups for HR %max, BP, and agility task completion time, and Mann-Whitney U tests were utilized for endorsed symptoms, RPE, committed errors. A series of 2X2 (GROUP X TIME) mixed model ANOVAs were conducted to compare CONCUSS and CONTROL groups on RMSSD and SDNN outcomes across time points (pre- and post-EXiT rest periods). RESULTS: Aim 1) Pre- and post-EXiT resting HR %max and BP, and HR %max were reliable throughout aerobic and dynamic components (ICC=.696-.838). Symptoms and RPE were similar across visits but less errors were committed at the 2nd visit. Agility task completion time (MDC range=0.75-8.70 seconds) had good to excellent test-retest (ICC=.703-.948) and inter-rater reliability (ICC=.932-.965), but ratings of committed errors have acceptable agreement for committed errors for only the ball toss and pro agility tasks. Endorsed symptoms had a high internal consistency at both visits (α =.805-.894) and were reliable across visits during aerobic (ICC=.765) and dynamic components (ICC .519) were reliable across visits. Aim 2) Adolescents were faster than adults on arrow agility (p=.01); males were faster than females on box drill carioca (p=.01), zig zag (p.05). Aim 3) The CONCUSS group had group had lower (faster) completion time during zig zag p=0.048 and pro agility p=0.018) tasks and had lower (less variable) SDNN (F=4.569, p=.047, Ƞ_p^2=. 212) and RMSSD (F=4.517, p=.049, Ƞ_p^2=.=.209) than CONTROL group. CONCUSS and CONTROL groups had similar HR %max, total endorsed symptoms, and RPE (p>.05). CONCLUSION: EXiT physiological, performance, and clinical outcomes are reliable, and generalizable to physically active population of varied age, sex, BMI, and sport-type factors. The multiple objective outcomes of EXiT present a new evidence-based approach to inform clinical recovery from SRC and RTP/A decision making

Metabolic Differences Between Backpack Walking And Running At A Fixed Treadmill Velocity In 'Elite" British Soldiers: A Pilot Study: 708

Soldiers who serve in the "elite" units of the British Army are expected to "speed march" carrying heavy backpack loads, which involves a combination of both running and fast walking movements as an individual and in groups. It is generally accepted by the military that a soldier who walks will expend less energy than a soldier who runs at any given velocity when carrying a backpack. At certain velocities, however, it might be metabolically advantageous for individual soldiers to run rather than walk