This study implemented a mixed-method design (postprogram survey and structured interviews) to develop a detailed understanding of mentee experiences in the Biomechanics Research and Innovation Challenge. Forty-nine mentees completed the postprogram survey, and 26 mentees participated in the interview. Based on the survey results, 65% of mentees enjoyed the university campus experience, and 63% valued the networking opportunities. Learning about the research process and different careers in science and biomechanics were appreciated by 63% and 61%, respectively. Over 90% of mentees responded positively to statements about their mentors' suitability for the Biomechanics Research and Innovation Challenge, supportiveness, and availability, and 85% of mentees would recommend the program to their peers. The interviews revealed 4 key themes: developing Science, Technology, Engineering and Math (STEM) skills; discovering biomechanics; STEM role models; and facilitators and barriers to participation. Furthermore, the interviews highlighted the development of essential STEM skills, exposure to biomechanics, and the positive impact of mentors. The program's hands-on and collaborative nature facilitated participation, whereas communication tools and scheduling were barriers. Our findings highlight the positive mentee experiences related to participation in the Biomechanics Research and Innovation Challenge program, enabling them to develop STEM skills and discover the diverse field of biomechanics. Overall, the program was well received and recommended by participants.

This study investigated differences in leap distance for a single-leg drop-land-cut (CUT) task based on using either a maximal or normalized (150% leg length) method or the influence of condition order and leg dominance on distance achieved. Twenty-six young court and field sport athletes (61.5% female) completed the single-leg drop-land-cut task on the dominant and nondominant leg under maximal and normalized conditions in a randomized order. Multivariate repeated measures analysis of variance tests with post hoc pairwise comparisons were used to determine the effect of condition (maximal and normalized), leg dominance (dominant and nondominant), and interaction effect on leaping distance. Potential order effects were explored as a between-subjects factor within the analysis of variance. Our findings showed significantly larger leap distances under the maximal condition (P < .001, ηp2 ≥ .417), with the maximal mean being 154.5 (24.7) cm (175.1% [18.6%] leg length) and the normalized mean being 140.7 (19.7) cm (159.0% [5.8%] of leg length). Furthermore, greater distances were achieved during the maximal task when performed following the normalized task (P < .001, 24.5% further). Practically, the normalized task may be better suited for heterogeneous samples; yet, the maximal task may be more suitable for homogeneous samples or pre-post study designs.

It is unknown how many gait cycles are necessary to assess medial tibiofemoral joint contact forces (mTJCF) for individuals with lower limb amputation. The purpose of this study was to determine the number of gait cycles necessary to achieve a representative measure, and to determine the reliability of intact limb mTJCF. Gait data were extracted from 14 individuals with transtibial amputation; simulations were performed using OpenSim. A sequential analysis technique was used to determine the number of gait cycles to achieve a representative measure using thresholds derived from the literature, and another using 0.25 standard deviation of the data. Reliability of the continuous set of gait cycles was also determined using an intraclass correlation coefficient analysis. Using the literature-derived thresholds, 3 gait cycles were necessary to achieve a representative measure of all 3 variables. Using the more stringent 0.25 standard deviation threshold, 9 gait cycles were required. All mTJCF variables demonstrated excellent reliability (ρ > .99). Our results suggest when analyzing mTJCF, ≥3 gait cycles are necessary to achieve a representative measure, though 9 gait cycles improve precision by >75%. The results of the study provide guidance to researchers toward selecting the number of gait cycles to analyze based on their research objectives.

People with chronic stroke often walk with altered spatiotemporal parameters and joint excursions, metrics that can serve as intervention targets. Inertial measurement units (IMUs) allow such metrics to be quantified outside of a traditional motion capture laboratory. The purpose of this study was to quantify the validity of common poststroke biomechanical gait metrics between an IMU-based and a marker-based system during treadmill walking, a context that facilitates gait training interventions. For 61 people with chronic stroke, we assessed the validity of stride duration, stride length, and sagittal plane joint excursions of the bilateral hip, knee, and ankle in 2 ways: (1) Across participants, revealing whether both systems similarly characterize participants' average gait parameters; and (2) Within participants, revealing whether both systems similarly quantify stride-by-stride variance. Across participants, all joint metrics had either excellent (Lin correlation coefficient; LCC > .75) or good (LCC .60-.74) validity, suggesting that IMU-derived metrics that are often the target of treatment can be appropriately compared to existing population norms. In contrast, median validity within participants was excellent for stride duration, but only poor (LCC < .40) to fair (LCC .40-.59) for stride length and most joint excursions. Therefore, IMU-derived gait metrics quantified on a stride-by-stride basis should be interpreted cautiously.

Lateral ankle sprains are common in cheerleading, especially during tumbling. Landing surfaces influence injury risk by affecting joint mechanics, but few studies compare vertical and flip landings. This study examined the effects of a hard (HARD) and matted (MAT) surfaces on vertical drop (VERT) and flip (FLIP) landing tasks. Twelve collegiate cheerleaders performed both tasks with 3-dimensional kinematics and kinetics collected. Repeated-measures analyses of variance (task × surface, P < .05) analyzed sagittal and frontal plane variables. The FLIP task exhibited 84% greater peak ground reaction forces and 148% greater loading rates, as well as greater peak ankle angles and reduced ankle plantar flexion at initial contact compared to the VERT task. Increased foot velocities at initial contact during FLIP, driven by angular velocity, likely explained these heightened characteristics. HARD surface landings resulted in greater peak loading rates, peak angles, and inversion at initial contact. The peak plantar flexor moment was greater when landing on a HARD surface after a FLIP. Flip landings may elevate injury risks compared to vertical landings while supporting that harder landing surfaces increase injury risks. The significant differences between the tasks due to angular velocity differences also caution against generalizing vertical landings to landings within acrobatic sports.

Previous studies on sprinting biomechanics have identified a variety of biomechanical characteristics that describe the outcome of improved sprint technique but in doing so have neglected to identify the postural control strategies that lead to improved sprint performance. The purpose of this study was to evaluate the relationship between frontal plane displacement of the center of mass (CoM) and sprint velocity, and to understand if multijoint coordination of the limbs and trunk were associated with minimizing the displacement. The results from this study suggest that stance phase frontal plane CoM cumulative path length is significantly associated with sprint velocity. Further, a multivariate linear regression model revealed that coordinative couplings of the bilateral limbs and trunk were associated with the minimization of the frontal plane CoM displacement. Specifically, the coordination of the knees (flexion-extension) and axial rotation of the thorax-pelvis were the most important interjoint couplings in minimizing frontal plane CoM displacement. Frontal plane CoM displacement provides coaches, athletes, and performance professionals with an interpretable metric to identify sprint technique quality in field using wearable sensors. Future work needs to further advance our understanding of postural control during sprinting so that effective coaching and rehabilitation interventions can be designed.

This study investigated the effects of air resistance and drafting on oxygen uptake, ground reaction forces, and lower body kinematics during treadmill running. Thirty-three trained distance runners ran at 3.35 to 4.29 m/s (80%-85% of critical speed) on a force-instrumented treadmill within a wind tunnel under 5 conditions: no fan (NF), normal wind, normal wind with drafting, headwind (HW), and HW with drafting. Drafting involved running 1 m behind a mannequin. Oxygen uptake increased by 4.7% in HW compared with NF (P < .001) and decreased by 2.8% in HW with drafting compared with HW (P < .001). HW increased both braking and propulsive forces, accompanied by greater hip and knee flexion at initial contact, compared with NF. Drafting mitigated these effects but did not return oxygen uptake or biomechanical metrics to NF levels. Results suggest that air resistance imposes a metabolic cost, while drafting reduces but does no eliminate this cost. The most notable biomechanical adaptations occurred in horizontal ground reaction forces and lower body kinematics, indicating that both are influential in the metabolic response to air resistance. Future research should refine experimental setups to further explore air resistance's effects on biomechanics and energy cost.

Wrestling is a popular high school sport despite high injury and concussion rates. Instrumented mouthguards can reliably measure head acceleration events (HAEs) accrued by wrestlers and may highlight potential sex differences; important considering the higher concussion rates among female athletes. The purpose of this study was to measure HAEs accrued in high school wrestling matches and compare frequency, magnitude, and head impact location between female and male wrestlers. Forty-five (16.5 [0.8] y) wrestlers (20 females; 25 males) wore instrumented mouthguards during high school matches. A total of 2843 (857 females; 1986 males) HAEs above an 8g trigger threshold from 452 player-matches were video verified. Results indicate that males accrue 30% higher HAE count per match (mean frequency = 6.9 HAEs/match) compared to females (mean frequency = 5.3 HAEs/match) (IRR = 1.297; 95% confidence interval, 1.051-1.594). Results also show females and males have similar HAE biomechanics including peak linear acceleration, angular velocity and acceleration, change in angular velocity in all planes, and impulse duration. Finally, females accrue 50% more head impacts high and to the right side of the head than males (IRR = 1.499; 95% confidence interval, 1.053-2.137). Higher HAE match counts for male wrestlers and varied impact locations highlight varied wrestling HAE mechanisms for female and male adolescent wrestlers and potential sex-specific HAE and concussion prevention strategies.

Less dynamic limb-level loading is observed bilaterally in individuals who have undergone unilateral anterior cruciate ligament reconstruction (ACLR) and is linked with the development and progression of knee osteoarthritis. Experimentally induced knee effusion (EIKE) models have been used to study biomechanical effects of knee injury, showing decreased quadriceps activation and lesser peak limb-level loading (ie, vertical ground reaction force [vGRF]) during stair descent and decreased knee extensor torque during overground walking. However, it is unknown whether EIKE acutely induces less dynamic limb-level loading during overground walking. Therefore, this study's purpose was to investigate bilateral effects of unilateral EIKE on limb-level loading throughout stance. Ten individuals completed 5 gait trials at their habitual walking speed pre-EIKE and post-EIKE. Functional waveform analyses compared time-normalized vGRFs, anteroposterior GRFs, and mediolateral GRFs normalized to body weight (BW) pre-EIKE and post-EIKE. EIKE resulted in less dynamic anteroposterior GRFs from 16% to 24% of stance (mean difference: 2%BW) and no change in vGRFs of the effused limb. The contralateral limb demonstrated greater vGRFs from 6% to 35% of stance (mean difference: 10%BW) and greater anteroposterior GRFs from 13% to 19% of stance (mean difference: -2%BW). Our results indicate that unilateral EIKE does not simulate bilateral sustained compressive loading profiles previously linked to knee osteoarthritis.

Improved joint function is a primary goal of total knee arthroplasty (TKA), yet persistent postoperative deficits in joint biomechanics are common, and the link between these and other clinical outcomes is poorly understood. Evidence on clinically meaningful gait outcomes after arthroplasty is limited, hindering their uptake in clinical trials and technological innovations in arthroplasty. This paper examined the associations between gait outcomes and satisfaction after TKA and defined minimal detectable and clinically meaningful thresholds for gait outcome changes. Thirty-one patients underwent instrumented gait analysis immediately before and 1 year after TKA and were categorized as high (>90) and lower (≤90) satisfaction with their joint replacement after surgery. Sixteen (51.6%) patients self-reported high satisfaction, and 15 (48.4%) reported lower satisfaction. There were no pre-TKA gait differences between the groups, but higher satisfaction postarthroplasty was associated with more a biphasic pattern improvement of the knee flexion/extension moment during stance from presurgery to postsurgery (r = .59, P = .001). Most patients, however, did not achieve minimal detectable or meaningful clinically important improvements in knee biomechanics from pre-TKA to post-TKA. The established thresholds for meaningful improvement in biomechanical variables may be used in future studies to relate measures of patient satisfaction to objective gait outcomes.

Spine motion and outcome measures derived therein may be confounded by the motion instructions provided to participants during data collection. This observational analytical laboratory-controlled study explored the impact of instructions for forward flexion trials on the lumbopelvic ratio (LPR) and spine kinematics. Twenty-five participants (mean age: 25.68 [9.31] y) performed forward bending trials with general instructions and then specific instructions to avoid hip motion and follow pacing. Participants were equipped with triaxial accelerometers at the lumbar spine (first lumbar vertebra) and pelvis (second sacral vertebra) to measure lumbar and pelvic excursions and LPR across the movement phases. The Wilcoxon signed-rank test was used to compare outcome variables between conditions. Lumbar excursion did not differ significantly between conditions, whereas pelvic excursion was significantly reduced in the specific instructions condition (P < .05). LPR showed considerable variability in the specific instructions condition, but there was no significant difference from the general instruction condition. Thus, instructing participants to limit hip motion appears to reduce pelvic excursion during forward bending without statistically affecting lumbar motion or the LPR. Providing and reporting clear and precise movement instructions to participants is important as they can change kinematics. Further, it appears that verbal instructions alone are unlikely to achieve complete spine movement isolation in all participants.

This study applied decision-tree (DT) machine learning models to determine whether this approach is more accurate when classifying slip outcome during walking, and to refine the cutoff thresholds of each slip type. Kinematic data of the heel were collected from 50 adults (23.1 [3.6] y) during 516 walking trials. The first DT model (DT1) was trained with heel slip distance and heel slip velocity as predictor variables; the second model (DT2) added heel slip acceleration as the third predictor variable. Walking trials were first classified as a no-slip, slip-recovery, or slip-fall outcome based on visual observation, and these classifications were used as response labels to train the DT models. Results indicated that both DT models yielded different thresholds in classifying slip outcomes and were similar to thresholds suggested in previous studies. However, both DT models resulted in 4.1% to 7.6% greater overall prediction accuracy compared with previously suggested thresholds, with DT2 generally performing better than DT1. Although the improved performance was offset by a ∼7% lower sensitivity when classifying no-slip outcomes and greater model complexity, future studies examining slip responses during gait should incorporate the thresholds derived from the DT2 model to most accurately classify the type of slip outcome.

It is unknown whether interlimb differences in gait mechanics affect the magnitude or distribution of tibiofemoral joint contact forces or whether load carriage increases potential effects of limb dominance. Thus, this study aimed to compare the effects of load carriage on total, medial, and lateral tibiofemoral joint contact force between the dominant and nondominant limbs. Twenty-four adults (12 women, 21 right-leg dominant) walked at 1.4 m·s-1 during 3 load carriage conditions (0%, 15%, and 30% body weight). Medial and lateral tibiofemoral joint contact forces were calculated during 5 stance phases for each limb in each condition. A 3 × 2 repeated-measures analysis of variance was used to compare the dominant and nondominant limbs across the 3 loading conditions. Peak tibiofemoral joint forces increased directly with load carriage (P < .001). The nondominant limb peak medial tibiofemoral joint contact force was greater than that of the dominant limb (P = .026), whereas dominant limb peak lateral tibiofemoral joint contact force was greater than that of the nondominant (P < .001) limb. Although the results were close to the minimal detectable difference, we concluded that the distribution of tibiofemoral joint contact force during load carriage may be influenced by limb dominance. These findings underscore the relevance of limb dominance as a consideration in research design and data interpretation.

Delayed-onset muscle soreness (DOMS) is a noninvasive pain model offering a unique opportunity to study trunk neuromuscular adaptations. While prior research has examined regional muscle activation in the lumbar region, the spatial distribution of median frequencies (MF) under DOMS has not been explored. This study investigated the effect of DOMS-induced pain on the spatial distribution of MF in the lumbar erector spinae muscles and its association with trunk force variability during submaximal contractions. Twenty healthy adults completed 2 laboratory sessions: 1 pain-free and 1 under low back DOMS. High-density surface electromyography was recorded bilaterally on the erector spinae during submaximal isometric trunk extensions. MF distribution was analyzed using centroid coordinates with and without DOMS. Force variability was also assessed. DOMS significantly increased perceived muscle pain and soreness in the lumbar region. It also caused a cranial and medial shift of the MF centroid, significant on 1 side of the trunk. However, force variability remained stable between conditions. These results suggest that DOMS induces regional adaptations in lumbar muscle MF. The spatial distribution of MF may serve as a novel and sensitive marker of neuromuscular adaptation to pain. The trunk system was able to maintain force steadiness despite pain and soreness.

Clarification of glenohumeral joint alignment changes during the late cocking phase may reveal the mechanisms of throwing injuries. This study aimed to determine the effect of shoulder external rotation on humeral head center deviation relative to the scapular glenoid. Twenty-eight baseball players participated. The anteroposterior deviation of the humeral head center relative to the glenoid (humeral head translation) and the distance between the humeral head and posterior glenoid rim perpendicular to the glenoid articular surface (posterior glenohumeral distance) were measured. Magnetic resonance imaging of the throwing shoulder was performed at 90° abduction with 90°, 100°, and 110° external rotation; for the nonthrowing shoulder, measurements were conducted at 90° and 100°. In humeral head translation, the posterior translation of the humeral head relative to the glenoid was significantly greater at 110° compared to 90° external rotation position (P = .003). Humeral head translation was associated with posterior glenohumeral distance at the 90° (β-coefficient = 0.649) and 100° (β-coefficient = 0.556) external rotation positions. Increased shoulder external rotation resulted in posterior translation of the humeral head and proximity between the humeral head and the posterior glenoid rim. The factors identified as contributing to posterior deviation of the humeral head may trigger throwing shoulder injuries during the late cocking phase.

Gait symmetry is often assumed in healthy individuals, yet functional asymmetries arise from biomechanical and neurophysiological factors. Although light upper body loading can improve walking performance, its effect on lower limb joint asymmetry remains unclear. This study examined how different loading conditions affect sagittal plane gait asymmetry at the hip, knee, and ankle. Twenty-two participants walked under 4 conditions: no weight, unilateral arm weight, bilateral arm weights, and waist weights each using 0.45-kg loads. Three-dimensional joint angles were normalized to 101 points across the gait cycle. Asymmetry was assessed using statistical parametric mapping and pointwise effect size. Two metrics were used: (1) temporal extent, defined as the percentage of the gait cycle with significant left-right differences (P < .05) and the percentage of the gait cycle with effect size >0.8 and (2) group-level prevalence, defined as the percentage of participants showing significant asymmetry at each time point. Significant asymmetries were observed across all joints and conditions, with hip and knee levels consistently exceeding those at the ankle. Effect size values often exceeded statistical thresholds, highlighting meaningful differences. Loading produced minimal systematic effects, though individual responses varied. Importantly, light arm weights did not increase asymmetry, supporting their use for gait enhancement.

Marathon terrain significantly impacts athlete performance. This study examined whether level running biomechanics can predict uphill and downhill running economy using a new metric, running grade aptitude (RGA). Forty distance runners (32 males and 8 females) ran on a split-belt treadmill at +4% and -4% gradients, simulating Boston Marathon hills. We assessed stride parameters, foot strike patterns, ground reaction forces, and oxygen consumption during uphill, downhill, and level running. RGA was determined by analyzing the slope of the relationship between oxygen uptake and treadmill grade, categorizing runners as preferring uphill RGA, downhill RGA, or negligible RGA. We found a significant correlation (R2 = .44) between active peak vertical ground reaction forces during level running and downhill running economy (downhill RGA). However, no other variables significantly related to RGA, and no difference in RGA was observed between genders. The study suggests that runners who generate higher peak vertical ground reaction forces during level running are more economical on downhill segments. These findings highlight the importance of individual biomechanical traits in optimizing training and racing strategies for distance runners.

This study examined the influence of lateral constraints and sex on walking in different settings. Thirty-eight adults (17 males: 25 [3] y, 21 females: 24 [4] y) walked overground for 20 m in open (no constraints), open pathway (defined by lines on the floor), and hallway (pathway defined by walls) settings at 3 speeds (slow, preferred, and fast). Inertial sensors recorded kinematics (Xsens Awinda, Movella) to calculate stride velocity, stride length (SL), cadence, and double support phase percentage. Stride velocity, SL, and cadence were also normalized to account for body size. Linear mixed models were used for statistical analysis (α = .05). No setting or setting by speed effects were found. Males had greater SL compared with females at preferred and fast speeds. Males had greater normalized SL compared with females at fast speeds. Females had greater cadence compared with males across conditions. Males had greater double support phase percentage compared with females at slow speeds. Wider hallways may allow for walking assessments generalizable to open settings. Considering sex differences in cadence at any speed, SL at preferred and fast speeds, normalized SL at fast speeds, and double support phase percentage at slow speeds may be valuable for interpreting walking assessments.

Inertial Measurement Units (IMUs) enable accurate estimation of anatomical joint angles but require a sensor-to-segment calibration. Literature has presented several algorithms that address this gap; however, adequately comparing calibration performance is not trivial. This study compares 3 calibration methods: N-pose calibration (NP), functional calibration (FC), and manual alignment (MA) to estimate 3D wrist joint angles during single-plane and multiplane tasks. Thirteen healthy participants were instrumented with IMUs and optical markers to compute the range of motion error (ε), root mean squared error, and offset between the joint angles from the optical reference and each IMU calibration (NP, FC, and MA) as dependent variables. We then performed 3-way repeated-measures analyses of variance on each dependent variable to evaluate interactions between calibrations, tasks, and joint axes. NP showed the worst root mean squared error (8.34° [7.41°]) performance in the calibration main effect (η2G = .095) and calibration × tasks interaction (η2G = .121). In an exploratory analysis, FC performed best (main effect root mean squared error = 6.52° [4.47°]) in the offset calibration × axes interaction in single-plane (η2G = .160) tasks. Therefore, we recommend FC to optimally perform wrist calibration and against NP. These findings are viable in aiding the development of portable IMU-based clinical motion-tracking devices.

The pelvis and trochanteric soft tissue stiffness influence hip impact force during falls. We examined potential relationships between the stiffness values acquired from different methodologies. Twenty-six individuals simulated sideways falls. During trials, force-deformation data of the trochanteric soft tissue were recorded, then fitted to polynomial and exponential functions. Stiffness was determined as a slope of the tangent line at maximum deformation (Ks_1st, Ks_2nd, and Ks_exp) and at 0.4 N (Ks_2nd_0.4 N, Ks_exp_0.4 N). Similarly, force-deformation data of the pelvis were fitted exponentially to determine the pelvis stiffness at peak impact force (Kb). We also used a clinical device to measure the trochanteric soft tissue stiffness (Ks_myoton). Correlation and regression analyses were performed. The Kb was correlated with Ks_1st and Ks_2nd (P < .05) and decreased 1.7 and 0.7 kN/m for every 1 kN/m increase in Ks_1st and Ks_2nd, respectively (R2 = .23 and R2 = .21), but no variables were correlated with the Ks_myoton (P > .05). When normalized, however, both Kb and Ks_myoton were correlated with Ks_1st and Ks_2nd (P < .05). These findings provide insights into hip impact dynamics, suggesting that trochanteric soft tissue stiffness measured with a clinical device may serve as a predictor of pelvis stiffness during falls.