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Load carriage is an inevitable daily task for soldiers. The purposes of this study were to explore the extent to which gait variability (GV) is affected by load carriage and experience among military cadets, and whether experience-related differences in GV are dependent on task demand. Two groups of cadets (30 experienced, 30 less experienced) completed a load carriage task in each of three load conditions (no load, 16 kg, 32 kg). Three categories of GV measures were obtained: spatiotemporal variability, joint kinematic variability, and Lyapunov exponents. Compared to traditional mean gait measures, GV measures were more discriminative of experience: although both groups showed similar mean gait measures, the experienced participants had reduced variability in spatiotemporal measures (p ≤ 0.008) and joint kinematics (p ≤ 0.004), as well as lower levels of long-term local dynamic stability at the ankle (p = 0.040). In both groups, heavier loads were also caused increased GV (p ≤ 0.018) and enhanced short-term local dynamic stability at the knee (p = 0.014). These results emphasize the importance of GV measures, which may provide a more complete description of adaptability, stability, and control; highlight alternate movement strategies during more difficult load carriage; and capture experience-related differences in load carriage strategies.

The step-down tap (SDT) is a commonly used task to assess unilateral neuromuscular control and to identify deficient movement patterns of the trunk and lower extremities. However, instruction of the SDT varies greatly in recent reports, which may alter the clinical interpretation of potential movement deficiencies.The purpose of this study was to identify differences in trunk and lower extremity kinematics between variations of a step-down tap that differ based on step direction, fixing the arms or stance foot, and trial collection methods.This study followed a single-group repeated measures design in a laboratory setting. Three-dimensional angles of the trunk, hip, and knee of 18 participants were evaluated at 60 degrees of knee flexion and at maximum squat depth during six SDT variations. Wilcoxon signed rank tests were performed to determine the effects of an anterior verse lateral step direction, a fixed arm or stance foot position, and an individual verse continuous trial collection method.Knee flexion, external pelvic rotation, and external trunk rotation were greater in the anterior SDT, while the lateral SDT elicited greater pelvic tilt and hip flexion. Additionally, overall squat depth was greater across participants during the anterior SDT. Few clinically significant differences (≥3°) were observed due to fixing arm or stance foot position, and no differences were identified based on trial collection methods.The standardization of task instructions for motion analysis protocols utilized for research purposes and/or clinical decision-making is crucial. Specifically, for the SDT, the authors recommend using the anterior step direction. A fixed arm and stance foot position is not necessary, and trials may be collected individually or continuously based on convenience for a small number of repetitions.

Background: Lower extremity asymmetry has been shown to be associated with increased risk of anterior cruciate ligament injury. Return-to-sport screens commonly involve assessing the restoration of symmetrical strength and balance. Therefore, it is important to understand how these measures are related. Hypothesis/Purpose: To determine if relationships exist between the Lower Quarter Y-Balance Test (LQ-YBT) component scores, composite scores, and isokinetic knee strength in healthy, female athletes. Methods: Female adolescent athletes completed the LQ-YBT and isokinetic knee strength as a part of a comprehensive evaluation in competitive level athletes (Tegner activity scale≥7). LQ-YBT anterior, posteromedial, and posterolateral component scores for the each leg were normalized to leg length, and composite scores for each leg were calculated for each participant. Knee flexion/extension strength was collected at 120°/second using a Biodex System 4. Peak torque was normalized by body weight, and paired t-tests were used to compare legs ( αResults: A total of 106 participants (age 13.8±2.4 years; BMI 20.2±3.0) were tested, and all were right leg dominant. No differences were found between LQ-YBT right and left component (Table 1), or composite scores (right 97.9 vs left 98.2, p=0.29). Flexion and extension strength were significantly increased on the right side ( p=0.02, Conclusion: Weak to moderate relationships exist between both component and composite LQ-YBT scores and knee strength. The strongest correlations were found between the LQ-YBT composite scores and knee flexion strength. LQ-YBT composite scores were relatively high, indicating a low chance of injury while differences were seen in knee strength between legs. Future injury prevention programs would benefit from utilizing both tools as the Y-Balance test evaluates motor control and isokinetic strength identifies muscular imbalance, both of which are important in reducing future injury risk. Tables/Figures: [Table: see text][Table: see text]

This study aimed to determine whether inter-individual differences in learning rate of a novel motor task could be predicted by movement variability exhibited in a related baseline task, and determine which variability measures best discriminate individual differences in learning rate. Thirty-two participants were asked to repeatedly complete an obstacle course until achieving success in a dual-task paradigm. Their baseline gait kinematics during self-paced level walking were used to calculate stride-to-stride variability in stride characteristics, joint angle trajectories, and inter-joint coordination. The gait variability measures were reduced to functional attributes through principal component analysis and used as predictors in multiple linear regression models. The models were used to predict the number of trials needed by each individual to complete the obstacle course successfully. Frontal plane coordination variability of the hip-knee and knee-ankle joint couples in both stance and swing phases of baseline gait were the strongest predictors, and explained 62% of the variance in learning rate. These results show that gait variability measures can be used to predict short-term differences in function between individuals. Future research examining statistical persistence in gait time series that can capture the temporal dimension of gait pattern variability, may further improve learning performance prediction.

Background: Limited ankle dorsiflexion (DF) range has been associated with knee injuries and altered biomechanics during functional squatting and landing tasks. Prior studies correlating weight-bearing DF with altered landing mechanics have primarily used advanced motion capture technology, with limited research using clinically validated scoring tools. Hypothesis/Purpose: To assess the relationship between decreased DF and functional testing performance in youth athletes who have undergone anterior cruciate ligament reconstruction (ACLR). Methods: A retrospective review of standardized data was conducted on patients who had undergone ACLR at a pediatric sports medicine practice that had completed functional testing between December 2017 and November 2020. Patients with testing completed at a minimum of five months post-operatively, and who planned to return-to-sport (RTS) were included. Functional testing included validated protocols for the Y-Balance Test (YBT) and the Landing Error Scoring System (LESS), as well as a modified Single-Leg Squat Endurance Test (SLSET) utilizing the VAIL sports test scoring criteria. DF was measured in a weight-bearing lunge position off the front foot. Subjects were categorized into a pass or fail group based on their YBT and LESS scores (YBT≥94%, LESS≤4), and t-tests were performed to identify significant differences in DF between groups ( α=0.05). Lastly, Pearson correlations were performed to identify potential relationships between DF and SLSET total score as well as normalized anterior reach collected as a component of the YBT ( α=0.05). Results: 303 patients (148 (48.8%) males, 15.94±2.15 years, 7.46±2.11 months post-operative) were included for analysis. Significant correlations were identified between DF and YBT composite score ( p Conclusion: In this pediatric ACLR population, decreased ankle dorsiflexion is associated with high risk movement patterns during functional testing. This study adds to the literature by identifying clinically applicable DF thresholds associated with passing scores on the YBT and LESS functional tests. Clinical interventions aimed at improving ankle dorsiflexion to >36° may be an important component of ACL rehabilitation. [Table: see text][Table: see text]

Background: Impairments in balance or postural control are common following sport-related concussion (SRC). The Balance Error Scoring System (BESS) is widely utilized to assess static postural stability, but laboratory-based balance measures have been shown to more accurately detect changes in postural control. Hypothesis/Purpose: To determine whether postural control improved between presentation to the sports medicine clinic and return-to-sport (RTS) initiation, and whether this trend mirrored symptom scores and cognitive performance. A secondary aim was to assess whether changes in postural control were more accurately captured with center of pressure (COP) based measures compared to BESS. Methods: Patients diagnosed with a SRC were tested within 10 days of presentation (V0) and when cleared by a physician to begin a RTS protocol (V1). Clinical measures included Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) and the King-Devick (K-D) test. The BESS was performed with eyes closed while standing barefoot on a force platform for 6 conditions: double-limb stance, single-limb stance, and tandem stance on both firm and foam surfaces. BESS scores and total balance time were recorded for each condition, and COP-based measures were computed for both double-limb stance conditions (Table 1). Sample entropy was computed to quantify COP regularity over time with increased values indicating improvement in postural control. Wilcoxon signed-rank tests were performed to determine significance between visits ( αResults: Forty patients (17 males, 13.8±2.0 years) were included for analysis. ImPACT verbal and visual memory scores improved by 10% and 12%, respectively, total symptom score decreased (V0 18.03±13.85, V1 0.97±2.08; pConclusion: Significant improvement in postural control was observed during the recovery period which mirrored improvement in symptom scores and cognitive performance. Additionally, while COP-based measures showed similar trends to the BESS, they provided more detailed information in regards to balance recovery. Specifically, findings from the double stance condition highlight the utility of a more advanced assessment of postural control for determining RTS readiness following a SRC. [Table: see text][Figure: see text]

Background: The Pediatric Comprehensive High-Level Activity Mobility Predictor (Pedi-CHAMP©) is a 4-part agility test aimed to assess functional performance in children with and without sports medicine injuries or orthopedic conditions. The Pedi-CHAMP© assesses bilateral single limb balance, lateral agility, directional changes, and acceleration/deceleration. Hypothesis/Purpose: To determine if the Pedi-CHAMP component (Single-Limb-Stance [SLS], modified Edgren Side Step [mESS], L-Test, Illinois Agility Test [IAT]) and composite scores are stratified based on age, sex, and sport-type/specialization in youth athletes. Methods: Youth athletes were recruited to complete the Pedi-CHAMP© either as an independent test or as part of larger battery of tests (Specialized Athlete Functional Evaluation [SAFE] Program). Completion times for each test component were converted to points using age-sex matched scoring algorithms. Each participant also answered questions to determine specialization in organized sports (defined as competition with a referee, umpire, etc.). Kruskal-Wallis was used to assess differences based on age groups (elementary [E, 5-9yrs], preteen [PT, 10-12yrs], early teen [ET, 13-15yrs], late teen/young adult [LT, 16-22yrs]), with Mann-Whitney U pairwise post-hoc comparisons (αResults: A total of 251 youth athletes (134 females, age 13.7±3.3yrs; BMI 20.9±5.9) completed Pedi-CHAMP© testing. Significant differences were seen with the Pedi-CHAMP© component and composite scores between all ages ( pConclusion: The Pedi-CHAMP© was able to detect differences based on age, sex and sport impact-type (low- vs. high-impact). Performance improves with age for the L-Test and IAT, however, no differences in SLS and mESS were seen between younger and older teens which may indicate a ceiling effect for these two components. Further research should focus on correlating the Pedi-CHAMP© to other performance measures in youth athletes. Tables/Figures: [Table: see text][Table: see text]

Background: The Functional Movement Screen (FMS) is a tool designed to establish a baseline for fundamental movement capacity, highlight limitations and limb asymmetries, and identify potential injury risk. Previous research has shown that individual components of the screen are also indicative of injury risk, as well as potential predictors of athletic performance unlike the FMS composite scores. However, this literature is limited and lacks statistical power. Identifying which component scores are predictive of injury risk and athletic performance would provide a quick, powerful tool for coaches and trainers to evaluate athletes. Purpose: To determine if individual component scores of the FMS are associated with athletic performance in highly-active youth athletes. Methods: Youth athletes participated in the Specialized Athlete Functional Evaluation (SAFE) Program. Data collection was extensive, however, for the purpose of this abstract, only a selection of data was analyzed – age, BMI, years played, total number of past injuries, isokinetic knee strength, 10- and 20-meter sprint, single-leg hop (SLH) distance, and FMS scores. Seated knee flexion/extension strength was collected at 120°/second using a Biodex System 4, and peak torque was normalized by body weight. The maximum distance of three SLHs was recorded for each leg and normalized to leg length. FMS scores used for analysis included the total composite and component scores, including the deep squat, hurdle step, in-line lunge, shoulder mobility, active straight-leg raise, trunk stability push-up, and rotary stability. Wilcoxon Signed Ranks Tests were used to determine side-to-side differences, and Kruskal-Wallis tests were performed to determine differences in athletic performance based on FMS scores ( αResults: A total of 38 highly-active, youth athletes (26F; 15.4±2.6 years; BMI 21.0±5.3) were tested. Participants reported playing organized sports for 8.7±3.4 years, having 2.0±1.2 past sports-related injuries, and 74% reported specializing in a single sport. No side-to-side differences were found. While the composite FMS score significantly differed by number of past injuries ( p=0.036), it was not associated with athletic performance. Alternatively, left knee strength, sprint speeds, and right hop distance significantly differed by the hurdle step component score (Table 1). Conclusion: While the composite FMS score was not an indicator of athletic performance, the hurdle step component score was associated with strength, speed, and jump performance. This individual task could be a beneficial tool for coaches and trainers when evaluating athletic ability and injury risk of athletes. Tables/Figures: [Table: see text]

150-Word Abstract Fatigue may reduce human performance and increase injury risk. This study investigated the effects of mental and physical fatigue inducing tasks (MF and PF) on balance and gait characteristics of healthy young adults (n = 10; gender balanced). During quiet stance, PF led to increases in center-of-pressure mean velocity and sway area. Although MF was associated with the same trend, the differences were not statistically significant. Among gait measures, PF was associated with expected changes in mean spatiotemporal measures (shorter and faster steps). However, MF was associated with increased inter-trial variability (standard deviations) in stride and stance times, and decreased variability in step width. Furthermore, detrended fluctuation analysis (DFA) exponent of step width, indicating the presence of long-range persistent correlations across time, decreased significantly after both MF and PF. Our results suggest that balance and gait characteristics of healthy young adults are affected differentially by PF and MF. Extended Abstract Fatigue is considered a multidimensional construct including physical and mental components (Smets, Garssen, Bonke, & De Haes, 1995), which may reduce human performance and potentially lead to increased risks of falls and fall-related injuries (Helbostad, Leirfall, Moe-Nilssen, & Sletvold, 2007; Miles, Ives, & Vincent, 1997). While the effects of both physical and mental fatigue have been separately investigated in diverse populations under various experimental conditions, a few studies have compared the effects of physical vs. mental fatigue on postural control and gait in the same cohort. Thus, as a first step, we aimed to investigate the comparative effects of mental and physical fatigue on balance and gait characteristics among healthy young adults. We hypothesized that both mental and physical fatigue will have adverse effects on balance and gait characteristics of the healthy young adults. Ten healthy individuals (21-28 years old, 5 males and 5 females) from the university and local community completed the two experimental sessions. In the balance session, participants performed three pre-fatigue, quiet standing trials. Each trial lasted 45 seconds, during which participants were asked to stand as still as possible. Then, participants were instructed to complete a 30-minute mental fatigue inducing task (MF). Following the completion of MF, participants were instructed to complete five post-fatigue standing trials at 0 (immediately after the task), 1.5, 4, 7, and 10 minutes. Next, participants completed a physical fatigue inducing task (PF). They performed calf raises repeatedly at 40 bpm until voluntary exhaustion. Similar to MF, participants were instructed to complete five post-fatigue standing trials following the completion of PF. A 10-minute rest period was provided between MF and PF. In the gait session, participants performed a 6-minute baseline walking trial on the treadmill at their preferred walking speed (PWS), determined following the procedures developed by Jordan, Challis, and Newell (2007). Then, similar to the balance session, 6-minute walking trials were collected immediately following the completion of MF and PF respectively, with a 10-minute rest period provided between the tasks. Mean center-of-pressure (COP) velocity, in both anteroposterior (AP) and mediolateral (ML) directions, and 95% confidence ellipse area (95EA) of sway were computed for the balance measures. Means and variability (standard deviations) of spatiotemporal gait parameters, including spatial parameters (i.e., step length, step width, and stride length) and temporal parameters (i.e., step, stride, swing, and stance times), were computed for the gait measures. In addition, detrended fluctuation analysis (DFA) was performed on COP time series in the AP and ML directions separately, as well as on step time, length, and width from the gait data, in order to quantify long-range correlations over time. Separate repeated measures analyses of variance (ANOVA) were performed to examine the effect of fatigue (pre vs. post mental fatigue, or pre vs. post physical fatigue) on the dependent variables, with gender included as a blocking variable. Significance level, p ≤ 0.05, was used to conclude significant influences. The results showed that PF significantly increased COP mean velocity in the AP (26.4%) and ML (19.1%) directions as well as the COP 95EA (31.7%). However, no significant changes were observed for the COP-based measures after MF. The DFA exponent of the COP trajectory in both AP and ML directions showed no significant differences after MF or PF, although the decrease in DFA exponent in COPAP approached statistical significance in both cases ( p = 0.056 and 0.054, respectively after MF and PF). In addition, there was no significant gender effect in any COP-based measures. Regarding the gait measures, with the exception of stance time, all spatial and temporal parameter means changed significantly following PF. As such, the mean value of step length, stride length, step time, stride time, and swing time decreased by 1.0%, 1.0%, 1.1%, 0.8%, and 1.7%, respectively, while the mean value of step width increased by 7.4%. After MF, only the mean value of step width significantly increased by 8.6%, compared to the baseline (pre-fatigue) condition. However, the inter-trial variability in step width, stride time, and stance time changed significantly following MF: step width variability decreased by 12.5%, while stride time and stance time variability increased by 15.4% and 18.2%, respectively. Stance time variability was the only variability measure that showed a significant change (18.2% increase) after PF. The DFA exponent of step width decreased significantly following both MF (16.9%) and PF (16.6%). Lastly, no significant gender differences were found for gait measures. The findings from the study can help better understand the effects of MF and PF on balance and gait characteristics of healthy young adults. Our hypothesis that both MF and PF would affect balance and gait characteristics was partly supported. MF and PF showed significant influences on gait characteristics, but only PF showed significant influence on balance characteristics. From this exploratory study, it seems that, while PF induced by local muscle fatigue in the ankle changed average gait measures, MF may have a greater influence on control of the gait patterns (as indicated by the changed variability and DFA measures). In conclusion, these results suggest that both PF and MF may cause different effects on balance and gait characteristics of healthy young adults.

Use of a head-worn display (HWD) may affect gait performance and increase slip and trip risks, though there is a lack of information on such effects. This study investigated how different display technologies (monocular and binocular HWDs, and a paper list) and visual information presentation modes affect gait performance. Twelve gender-balanced participants completed walking and obstacle crossing trials on a linear walking track under all experimental conditions and a baseline control (without using a technology). During these trials, information relevant to a simulated light assembly task was provided, as representative of a potential occupational application. Gait performance was assessed based on minimum foot clearance (MFC), required coefficient of friction, foot placement locations around the obstacle, and/or walking/obstacle crossing speed. Use of a HWD had no substantial effects on level walking performance. A more conservative/cautious obstacle crossing strategy was, however, observed with HWD use, including a decrease (∼3%) in obstacle crossing speed (compared to the baseline). Gender-specific foot control strategies (lead foot MFC) were also observed that depended on the specific display technology and information modes. Foot placements around the obstacle were not influenced by use of the binocular HWD, yet a conservative strategy was observed with the monocular HWD.

Braces are commonly used to stabilize and restrict movement of the arm and shoulder after injury, such as dislocation (Itoi, Hatakeyama, and Kido, 2003). However, secondary pain and discomfort cause concern for clinicians when prescribing braces to patients that require shoulder stability, and may result in poor compliance by the patient if prescribed for long durations. Popularly used braces have been associated with secondary pain in surrounding areas, such as the neck and shoulders, compared to rehabilitative outcomes without the use of braces (Struijs, Kerkhoffs, Assendelft, and van Dijk, 2004). Straps are often used in conventional brace design for stability, yet they are potential sources of discomfort. Novel supporting methods used in more recently developed braces could mitigate the above concerns associated with traditional bracing methods (i.e., discomfort and low ease of use) while stabilizing the shoulder. We examined the usability of five brace designs, including a newly developed brace. Selected existing products were used to represent a spectrum of different design approaches (e.g., brace shape and coverage, connector locations, and straps) and included, in alphabetical order: 1) Bledsoe Clinic Shoulder Immobilizer (“Sling”) (Bledsoe Brace Systems, Grand Prairie, TX, bledsoebrace.net ), 2) Breg SlingShot 3 Shoulder Brace (“SlingShot”) (Breg, Inc. Carlsbad, CA, www.breg.com ), 3) Breg Straight Shoulder Immobilizer (“Straight”) (Breg, Inc. Carlsbad, CA, www.breg.com ), and 4) Bledsoe Sling and Swathe Immobilizer (“Swathe”) (Bledsoe Brace Systems, Grand Prairie, TX, bledsoebrace.net ). The new brace design ( www.kaykare.net ) includes a sleeve and single waist strap. A total of 10 young adults (M = 24.2±4.9 years old) and 10 older adults (M = 66.9±4.3 years old), gender-balanced in each group, were recruited to enhance generalizability of results. A within-subjects design was implemented to test donning/doffing performance, perceived stability and comfort of the selected arm braces. The study included controlled tasks involving donning and doffing on the self and on a simulated “patient” as the participant acted as a “caregiver,” along with simulated activities of daily living, to compare brace performance. Outcome measures included donning/doffing times, ratings and rankings of ease of use, and stability and comfort ratings and rankings, and these were compared between age, gender, and braces using Analyses of Variance. Participants had significantly lower donning and doffing times while using the new brace versus the other braces, and it was rated as having a higher level of ease when donning/doffing. The “Swathe” type of brace was rated as having the highest level of stability, while comfort ratings were not significantly different between braces. Braces more frequently selected as the preferred brace at the end of the study, such as the “Sling,” are more commonly provided braces at clinics or in emergency scenarios (Hatta, Sano, Yamamoto, and Itoi, 2013). Non-traditional strapping methods used in the new brace and the “Straight” were often perceived as being less stable due to fewer straps. Throughout data collection, it was found that as straps increase on the brace, greater stability is perceived, although application ease and donning time will likely increase. These results reveal that the newer brace design offers a potential solution to emergency shoulder immobilizing when compared to popularly supplied braces, though patients may perceive greater support while wearing a brace with more straps. However, the current work is limited by a healthy participant pool, and future work should explore patient responses to actual prescription of each brace. Long-term use should also be examined to capture experiences beyond the laboratory.