Frontiers in Sports and Active Living

Objectives: Given the high injury burden in football and the documented limitations of strength-based screening, novel approaches are warranted. Adaptive Force (AF)being closer to injury-prone movements than pushing/pulling strength--offers an alternative. This study examined the association between AF-based muscle stability and musculoskeletal complaints in football players and compared AF-derived and conventional strength parameters in their discriminative capacity, complemented by a preliminary prospective follow-up. Methods: AF and maximal voluntary isometric contraction (MVIC) were measured in 23 male football players across five bilateral muscle groups (knee extensors/flexors; hip flexors/adductors/abductors). AF parameters (maximal isometric AF, maximal AF, AF-Ratio), MVIC and hamstrings-to-quadriceps (H:Q) ratio were compared between players with and without complaints assessed via questionnaire at baseline and six-month follow-up (n=13). Results: Stability deficits were strongly associated with complaints (OR=54.0, 82% side concordance). AF-Ratio discriminated clearly between players with and without complaints (d=-1.47), with hip abductors showing the strongest effect (d=-1.64). Players with subsequent complaints showed lower baseline AF-Ratio (d=-1.45) and more stability deficits (d=1.67). MVIC and H:Q ratio did not discriminate (p>0.430). Conclusion: The findings suggest that muscle stability assessment outperforms conventional strength parameters in discriminating players with and without complaints, with preliminary follow-up data providing tentative support for predictive value. The concept of functional instability syndrome (FIS) provides a mechanistic framework for non-contact injuries and musculoskeletal complaints. AF assessment offers potential for screening, including return-to-sport decisions. Further studies are needed to verify the results, investigate predictive value, and evaluate whether personalised stability-based interventions can reduce injury incidence.

ABSTRACT Background: Athletes who return to soccer after anterior cruciate ligament reconstruction (ACLR) remain at elevated risk of secondary injury despite meeting conventional discharge criteria, and neuromuscular deficits in the reconstructed limb are known to be exposed by fatigue. Objective: To determine whether match-play fatigue differentially affects muscle stiffness, countermovement jump (CMJ) force symmetry, and rate of force development (RFD) asymmetry between soccer players with a history of ACLR and uninjured teammates. Methods: A prospective, cross-sectional, matched-control study enrolled 128 competitive soccer players (64 ACLR, 6-22 months post-surgery; 64 uninjured controls) across five recruitment waves (February-June 2026). Bilateral CMJ peak vertical force, jump height, RFD, and myotonometric stiffness of the rectus femoris (RF), vastus medialis (VM), and biceps femoris (BF) were recorded immediately before and after a standardized competitive match. Fatigue was quantified from second-half heart rate (percentage of age-predicted maximum) and end-match rating of perceived exertion (RPE). Within-group pre-to-post changes were evaluated with paired t-tests, between-group differences in the magnitude of change with independent-samples t-tests, and associations between fatigue indices and asymmetry changes with Pearson correlations. Results: Match play reduced CMJ limb symmetry index (LSI) in both groups, but the decline was more than three-fold greater in the ACLR group, 92.6% (SD 5.4%) to 85.1% (SD 7.1%), than in control group, 97.3% (SD 3.9%) to 95.0% (SD 4.2%), group-by-time difference, p < 0.001, (d = 0.64). RFD asymmetry approximately doubled in the ACLR group, 10.6% (SD 4.1%) to 17.6% (SD 6.5%), compared with a smaller rise in control group, 4.6% (SD 2.4%) to 6.3% (SD 3.7%); p < 0.001, d = 0.77). Involved-limb stiffness losses in the ACLR group exceeded those of controls for the RF (-21.2 vs. -9.2 N/m, p < 0.001), VM (-17.7 vs. -6.1 N/m, p < 0.001), and BF (-13.3 vs. -6.6 N/m, p < 0.001), whereas uninvolved-limb stiffness losses did not differ between groups (all p > 0.05). Fatigue markers (heart rate, RPE) were not significantly correlated with the magnitude of individual asymmetry change (|r| [&le;] 0.18, p > 0.15). Conclusions: In competitive soccer players 6-22 months after ACLR, match-play fatigue selectively compromises stiffness and explosive force output of the reconstructed limb, widening inter-limb asymmetries beyond what is seen in uninjured teammates, even though global cardiovascular and perceptual fatigue were comparable between groups. These findings suggest that return-to-sport testing performed only in a rested state may underestimate residual neuromuscular deficits, and support fatigue-inclusive assessment protocols before athletes are cleared for unrestricted competition. Abbreviations: ACL: anterior cruciate ligament, ACLR: anterior cruciate ligament reconstruction, BF: biceps femoris, CMJ: countermovement jump, HRmax: maximum heart rate, LSI: limb symmetry index, RF: rectus femoris, RFD: rate of force development, RPE: rating of perceived exertion, RTS: return to sport, VM: vastus medialis, SD: standard deviation. Keywords: Anterior cruciate ligament reconstruction, muscle fatigue, muscle stiffness, countermovement jump, limb symmetry index, rate of force development, soccer, return to sport.

Pedalling cadence during an acute eccentric cycling exercise altered physiological and perceptual responses. We examined the influence of cycling cadence on neuromuscular adaptation induced by a 6-week eccentric cycling training period. Eighteen participants performed training (eighteen sessions) at a cadence of 30 or 60 rpm over six weeks. Power output was the same between the two groups. Perceived effort and heart rate were recorded at each training session. Muscle pain and fatigue were reported the day after each session. Maximal voluntary contractions torque, as well as concentric and eccentric cycling efficiency, were assessed before and after training. Additionally, the loss of maximal voluntary isometric torque was assessed after the first and last training sessions. Heart rate and perceived effort increased in the second week of training and then plateaued, with no difference between groups. Muscle pain and fatigue remained low throughout the training, with no difference between groups. Isometric (+28%) and eccentric (+13%) maximal voluntary torque of knee extensor muscles increased regardless of training cadence. Concentric maximal voluntary torque increased for the group pedalling at 60 rpm only (+21%). Cycling efficiency was improved in eccentric mode only (+43%), with no difference between the two training groups. Finally, the voluntary isometric torque loss induced by the first and last sessions were similar. While six weeks of eccentric cycling training improved neuromuscular and functional capacities, cadence had no observable effect. This finding suggest that patients could choose their preferred cadence to obtain better adherence to the rehabilitation program without altering the adaptations.

Advanced footwear technology (AFT) has transformed competitive running, yet individual and sex-specific responses to different AFT models remain unclear, particularly near race pace. This study examined running economy (RE) and gait biomechanics in response to three top-tier AFT models (Shoe A: adidas Pro Evo 2; Shoe B: Nike Alphafly 3; Shoe C: On CloudBoom Strike 2) in 14 male and 12 female well-trained runners at sex-specific submaximal speeds (16 and 14 km{middle dot}h-{superscript 1}). RE, spatiotemporal, and joint kinematic/kinetic data were collected via indirect calorimetry, accelerometry, and three-dimensional motion capture with force platforms. RE was significantly lower in Shoe C than Shoe A (males: 2.1%; females: 1.4%) and Shoe B (males: 1.9%; females: 0.9%), with 73% of runners responding favourably to Shoe C, a more consistent response than previously reported. Despite being lightest, Shoe A produced the poorest RE, challenging conventional mass-economy assumptions. Biomechanically, Shoe C elicited greater impact magnitude, lower ankle quasi-stiffness, and greater ankle angular velocity during early stance. Female runners showed smaller RE improvements, potentially related to lower running velocity and body mass limiting midsole engagement. The most efficient AFT enabled these well-trained runners to be more spring-like through tolerating higher forces and faster angular velocities without greater demand on metabolic cost.

This study aimed to investigate the test-retest reliability of the Jiu-Jitsu Anaerobic Performance Test (JJAPT), as well as its construct validity according to experience level (intermediate and advanced) and belt rank (blue, purple, brown, and black), in addition to its concurrent validity with physical performance measures. Twenty-three amateur Brazilian Jiu-Jitsu (BJJ) athletes participated in two assessment sessions. JJAPT repetitions (mean, peak, and total) were analyzed under 4 and 5-set protocols, along with physical tests including vertical jump, Wingate test, and specific strength-endurance tests. Reliability was assessed using the intraclass correlation coefficient (ICC), construct validity through t-tests and ANOVA, and concurrent validity through Pearsons correlation. Results indicated that the JJAPT showed moderate to good reliability (ICC = 0.74 to 0.82). No significant differences were observed between experience levels or belt ranks for any variables (p > 0.05), with trivial effect sizes, indicating a lack of discriminant validity. On the other hand, significant correlations were found between JJAPT performance and isometric and dynamic strength-endurance tests (r = 0.39 to 0.62), with moderate to large magnitudes. It is concluded that the JJAPT shows measurement stability; however, it demonstrates limited ability to discriminate performance between athletes of different experience levels and belt ranks, being more strongly associated with strength-endurance capacities. Keywords: Brazilian Jiu-Jitsu; anaerobic performance; training monitoring

Advanced footwear technology (AFT) improves running economy and is widely credited with recent performance improvements in road running, with observational analyses consistently demonstrating that women have improved more than men. In contrast, laboratory studies generally report similar running economy responses to AFT in both sexes, leaving the observational-experimental divergence unresolved. A fundamental limitation of observational work is the absence of a control condition, making it impossible to separate AFT-related gains from concurrent performance trends. We addressed this by comparing performances between pre-AFT (2009-2015) and AFT (2017-2024) eras across road-running events (10km, half marathon, marathon) and throwing events (shot put, discus, javelin, hammer), the latter serving as an active control condition subject to the same broad athletic trends but unaffected by footwear technology. The top 50 performances per event, era, and sex were converted to World Athletics points and analysed using linear mixed-effects models. Performances improved significantly between eras ({beta} = 0.294, p < .001), with gains substantially larger in road running than in throwing ({beta} = 0.731, p < .001). The sex-specific pattern of improvement also differed between event categories (era x event type x sex interaction, {beta} = 0.786, p < .001): road-running improvements were greater in women than men (4.51% vs 2.62%), whereas throwing improvements did not differ by sex (0.93% vs 1.14%). These findings suggest that AFT benefits women more than men in competition, whether through a greater physiological response or more effective translation of economy gains to race performance, and suggest current laboratory protocols may be insufficiently sensitive to detect potential sex-specific effects.

Abstract Introduction: Proximal humerus fractures account for approximately 5-6% of all adult fractures and are primarily managed nonoperatively. Healing is conventionally monitored with radiographs, with radiopaque callus formation indicating healing. Visible radiographic callus appears weeks after biological union begins. Ultrasound provides a dynamic, radiation-free, and cost-effective method that can detect early callus formation before x-ray visibility. Although ultrasound has demonstrated utility for fracture healing in the clavicle and humeral shaft, its role in proximal humerus fractures remains unclear. Methods: This single-centre prospective study will be conducted in two phases. The pilot phase will measure inter-rater reliability for ultrasound detection of early callus formation at 2 and 4 weeks post-injury. Ten patients with proximal humerus fractures treated nonoperatively will undergo standardized anterior and lateral scans. Each patient will generate four saved images (short- and long-axis views), producing forty anonymized images independently reviewed by two raters. The prospective cohort phase will recruit approximately thirty additional patients. Results: Reliability will be quantified using Cohens kappa. A power calculation will be performed after pilot analysis. Results from the prospective cohort phase will help determine the association and predictive value of early ultrasound-detected bridging callus for radiographic and clinical union at three and six months. Patient reported outcome measures will be assessed using the Quick Disabilities of Arm, Shoulder and Hand (QuickDASH) questionnaire. Discussion: This study will develop and validate a standardized ultrasound protocol for assessing early fracture healing in proximal humerus fractures. By establishing both inter-rater reliability and predictive value, the findings may support ultrasound as a reproducible, radiation-free adjunct to conventional imaging and enable earlier identification of union status.

Background. Cardiopulmonary exercise testing (CPET) is a gold-standard test used to evaluate cardiopulmonary fitness and overall health by measuring physiological responses such as oxygen consumption during exercise. While traditional CPET warm-ups are typically low-intensity aerobic activities, alternative methods like coherence breathing may also prepare the body by influencing autonomic regulation. Breathing-based interventions have shown potential to improve heart rate recovery and performance, and heart rate variability (HRV) serves as a useful non-invasive indicator of autonomic nervous system activity. However, there is limited research on how brief breathing exercises before CPET affect outcomes. This study aims to investigate the effects of coherence breathing on oxygen uptake, HRV, and post-exercise heart rate recovery Objective. This study will aim to compare the acute cardiopulmonary and autonomic responses of coherence breathing versus spontaneous breathing immediately preceding cardiopulmonary exercise testing (CPET) in recreationally active healthy adults. Methods. This study will be a randomized counterbalanced crossover design. Healthy adults aged between 19 and 45 years of age will complete two separate CPETs over two non-consecutive test days (between 48 hours and 7days). During each visit, participants will complete five minutes of slow-paced coherence breathing (6 breaths per minute) or spontaneous breathing at normal breathing rate, followed by an incremental treadmill CPET protocol up to maximal exertion. HRV will be assessed at baseline, during the breathing interventions, and during cool-down for 5 minutes using the Emwave Pro Plus software. Gas exchange during the CPET protocol will be measured continuously using the VO2 Master Pro system. immediately after, and after 5 minutes of resting. The primary outcomes will be peak oxygen consumption and heart rate variability indices. Secondary outcomes will include heart rate recovery, peak heart rate, time to exhaustion, rate of perceived exertion and readiness, blood pressure, tidal volume, peak ventilation, and respiration rate. Analyses will use linear mixed-effects models and paired comparisons. Discussion. This protocol will determine whether pre-exercise coherence breathing can improve cardiopulmonary and autonomic nervous system responses to maximal performance. Findings may have practical implications for exercise testing and performance procedures as well as improving our understanding of pre-exercise breathing strategies for priming the autonomic and cardiopulmonary systems.

Low cost inside out wearable trackers can be deployed at scale to measure body motion, but errors in estimated sensor position propagate through coordinate transformations into derived gait and dynamic-stability metrics. Healthy adults walked on a treadmill at 0.5 to 2.0 m/s while VIVE Ultimate Tracker (VUT) and Vicon data were recorded. Data-driven calibration models were developed to correct tracker coordinates and to estimate full body centre of mass (CoM) from a sacrum-only configuration. Agreement with Vicon was assessed using RMSE, mixed-effects Bland-Altman limits of agreement, MAE, and intraclass correlation coefficients. Calibration improved coordinate-level agreement. For gait parameters, model-corrected VUT showed small errors against Vicon (MAE: 0.24 to 0.71 mm step height, 1.73 to 4.63 mm step length, 0.15 to 0.95 mm step width, 0.26 to 0.88 mm foot clearance). Proxy CoM-derived margin of stability (MoS) agreed excellently with Vicon. For the sacrum-only pipeline, calibration reduced CoM RMSE from 103.65 to 104.04 mm to 7.55 to 8.95 mm, and markedly reduced systematic error in stability outcomes, with extrapolated CoM bias decreasing from 172.92 to 0.29 mm and MoS bias from -75.09 to -3.54 mm. Data-driven calibration improved the measurement utility of low-cost VUTs, enabling inexpensive, relatively simple gait and stability measurement from a sacrum-only setup in controlled settings.

Fascicle operating length during dynamic tasks is often compared to the isometric torque-length relationship, but there is a lack of evidence regarding the influence of joint velocity on optimal fascicle length. Moreover, there is no consensus in the literature regarding the influence of contraction initiation (pre-activation or passive start), although it could alter the interaction between fascicles and the tendon. This study aimed to investigate the effect of joint velocity and pre-activation on the torque-angle and torque-length relationships of the vastus lateralis during mono-articular isokinetic knee extensions. Twenty-one participants performed isometric, isokinetic (50{degrees}.s-1 to 450{degrees}.s-1), and isokinetic knee extensions with maximal isometric or eccentric pre-activation at 100{degrees}.s-1 and 300{degrees}.s-1. Torque, joint angle, fascicle length, and electromyographic activity of the quadriceps femoris muscles were recorded during contractions and then used to model the torque-angle and torque-length relationships. We were able to successfully fit the torque-angle and torque-length relationships (R{superscript 2}=0.93 and R{superscript 2}=0.92, respectively). A main effect of velocity was detected regarding the optimal angle (p<0.05), but no significant change was observed for the optimal fascicle length. Isometric pre-activation induced a reduction in maximal torque production compared with eccentric pre-activation and passive conditions at both isokinetic velocities (p<0.001), with no change in muscle activity. Our results suggest that muscle-tendon interactions may permit a dissimilar behavior between the torque-angle and the torque-fascicle length relationships. The reduction in torque following isometric pre-activation may be related to a contraction history-dependent phenomenon. NEW & NOTEWORTHYWe demonstrated that, at a given joint angle, increasing velocity altered fascicle operating length without shifting optimal fascicle length, likely because of muscle-tendon interactions. We also showed that maximal isometric pre-activation before a concentric contraction reduced mean and maximal torque during the isokinetic phase compared with eccentric pre-activation or no pre-activation. This effect may be linked to contraction history, since muscle activity did not differ between conditions.

Older adults sustain disproportionately severe injuries from trip-induced falls during obstacle crossing. Such falls depend partly on forward momentum when the foot crosses the obstacle. MOSAP, an index of passive dynamic gait stability, reflects this momentum. We quantified MOSAP and a synergy index from uncontrolled manifold analysis of step length and extrapolated center of mass in 25 young (21.6 {+/-} 3.5 yr) and 23 older adults (68 {+/-} 4.3 yr) during unobstructed and obstructed walking, to test whether MOSAP increases during obstacle crossing and whether it is actively stabilized at each step. Both groups increased MOSAP progressively over two approach steps by reducing forward momentum and shifting the center of mass posteriorly. Older adults showed greater increases at the crossing steps. The synergy index was positive for all steps, showing that deviations in step length and extrapolated center of mass covaried to stabilize MOSAP at step-specific values. The synergy index was not influenced by age. We conclude that adults actively recruit passive body mechanics while approaching and crossing obstacles to reduce the risk of a trip becoming a fall. Older adults amplify this strategy to compensate for diminished neuromuscular corrective capabilities.

Abstract Background: Non-specific chronic low back pain (NSCLBP) is a major cause of disability worldwide and is associated with low-grade systemic inflammation. This study investigated the effects of aerobic exercise on inflammatory biomarkers, pain intensity, and quality of life among individuals with NSCLBP. Methods: In this parallel-group randomized controlled trial, 41 participants with NSCLBP were allocated to either an aerobic exercise plus health education group (n=21) or a health education-only control group (n=20). Participants in the intervention group completed supervised aerobic cycling three times weekly for 12 weeks. Outcome assessors and laboratory personnel were blinded to group allocation. Outcomes were measured at baseline, Week 8, and Week 12. Results: Interaction effects were observed for TNF- (p=0.046), IL-6 (p<0.001), hs-CRP (p<0.001), and pain intensity (p<0.001). Significant improvements were also observed across all WHOQOL-BREF quality-of-life domains (all p<0.05). After adjustment for baseline values and age, participants in the intervention group had significantly lower Week 12 IL-6 (p=0.013), hs-CRP (p<0.001), and pain intensity (p<0.001) than controls. No serious adverse events were reported. Conclusions: Aerobic exercise combined with health education produced greater improvements in inflammatory biomarkers, pain intensity, and quality of life than health education alone among individuals with NSCLBP. These findings support the integration of structured aerobic exercise into rehabilitation programmes for chronic low back pain. Keywords: Non-specific chronic low back pain; aerobic exercise; inflammation; IL-6; hs-CRP; pain intensity; quality of life; randomized controlled trial.

Introduction: obesity and unhealthy weight gain during pregnancy are associated with risk of pregnancy complications. Management of energy balance during pregnancy needs an accurate assessment of intake and energy expenditure. As pregnancy promotes specific physiological changes, energy expenditure during rest and activity throughout this period may be altered. The aim of this study was to estimate with accurate methods changes in energy expenditure, substrate oxidation and efficiency during the most common activity in pregnancy that is walking. Methodology: it was a prospective observational study during pregnancy. A graded steady state walking submaximal exercise test was used to calculate indirect calorimetry variables with a portable metabolic cart at each trimester of pregnancy in 30 healthy pregnant women. Walking energy expenditure (WEE), carbohydrate (CarbOx) and fat oxidation (FatOx) were calculated with exercise intensity specific stoichiometric equations from measured oxygen consumption (VO2) and carbon dioxide production (VCO2). Resting component was removed from WEE to calculate net walking energy expenditure (Net WEE). Moreover, participants were classified as having healthy or unhealthy gestational weight gain (GWG) according to the Institute of Medicine (IOM) recommendations. Changes in body weight during the study were used to adjust net WEE and substrate oxidation. Walking exercise efficiency was calculated as work rate (WR) divided by WEE or net WEE. Differences in main variables during pregnancy were analyzed using a general lineal model. Least square means analyses were utilized to compare differences in WEE, Net WEE, and substrate oxidation between healthy and unhealthy weight gain groups. Results: Net WEE increased significantly during pregnancy. Higher rates were found between the second and the third trimester of pregnancy at any given speed. This elevation was reflected in increased FatOx during moderate intensity exercise and higher CarbOx at the fastest walking speed. Therefore, a significant interaction time*speed for NetWEE and substrate oxidation was found. Weight gain was an important variable in energy expenditure and substrate oxidation as quantitative differences in NetWEE and CarbOx were due to change in weight registered during the study. Changes in Net WEE throughout pregnancy were higher in the unhealthy GWG group which expended significantly more CarbOx than the healthy group at each speed. Overall, efficiency decreases during pregnancy (1.48% from the second to the third trimester and 1.88% from the first to the third one) and pregnant women were more efficient in moderate intensity exercise (walking at 4 km/h) independently of the trimester of pregnancy. Conclusion: The results suggest a paradoxical intensity-dependent substrate oxidation selection during walking exercise throughout pregnancy as in no-trained pregnant women the increase in WEE relies on fat oxidation in a short bout of activity. The results may be relevant for the management strategies in obesity and excessive GWG during pregnancy.

Introduction: Acute compartment syndrome (ACS) is a limb-threatening complication of extremity trauma that requires timely diagnosis to prevent irreversible muscle and nerve injury. Current diagnostic methods are invasive, intermittent, and operator-dependent. We evaluated the feasibility of a novel, Bluetooth-enabled electrical impedance myography (EIM) device (mAlert, Myolex, Inc., Brookline, MA, USA) for continuous, noninvasive detection of ACS-related tissue changes. Methods: Ten Yorkshire swine underwent anterior tibial compartment monitoring using three ACS models: albumin infusion (ALB, n=3), femoral artery and vein ligation (LIG, n=3), and combined albumin infusion plus ligation (ALB+LIG, n=4). Resistance (R), reactance (X), and phase (P) were measured every minute across 1 to 199 kHz alongside continuous intra-compartmental pressure (ICP) monitoring. Group differences in normalized impedance trends were evaluated using the Kruskal Wallis test with Dunn post hoc correction. As a proof-of-concept human study, nine healthy volunteers wore the device for up to five days to assess electrode durability and signal stability. Tissue ischemia was validated using pimonidazole immunohistochemistry. Results: ALB infusion produced progressive, frequency-dependent decreases in R, X, and P, whereas LIG produced consistent increases in R and X across frequencies. The ALB+LIG model generated mixed responses, reflecting the competing effects of edema and ischemia. Normalized phase slopes differed significantly among groups (H=6.14, p=0.046), with post hoc testing showing significant divergence between the ALB and LIG models (p=0.041). Control limbs remained stable throughout monitoring. Pimonidazole staining confirmed hypoxic injury in the intervention limb. In the human pilot study, three participants completed five days of monitoring, demonstrating sustained signal acquisition, while electrode degradation limited data collection in the remaining participants. Conclusions: This preliminary feasibility study demonstrates that wearable EIM can continuously detect model-specific physiological changes associated with ACS in a large-animal model. These findings support further development and clinical evaluation of wearable EIM as a non-invasive monitoring technology for early ACS detection in trauma patients.

Objective: To identify brain injury metrics suitable for supporting sports head injury assessment by evaluating their association with brain tissue strain and consistency across sports. Methods: Head kinematics from 3,139 impacts in boxing, mixed martial arts, and rugby matches were recorded using instrumented mouthguards and used to calculate nine brain injury metrics. Impacts were simulated using an anatomically detailed finite element brain model to estimate peak 95th-percentile maximum principal strain (MPS) in the brain and brainstem, a measure of tissue deformation associated with long-term pathology. Sport-specific ordinary least squares models estimated xE, the metric value equivalent to a reference MPS of 0.21. Metric-MPS correlations and xE uncertainties were quantified using 5000 bootstrap resamples. Cross-sport consistency was assessed using the coefficient of variation (CV) of sport-specific median xE values, and uncertainty using the normalised confidence interval size (NCIS). Results: XGB, an extreme gradient boosting strain-prediction model, showed the strongest and most consistent correlations with whole-brain (r=0.924-0.974) and brainstem MPS (r=0.887-0.954) across all sports. PRV, BrIC and UBrIC also correlated strongly with whole-brain (r=0.724-0.930) and brainstem MPS (r=0.739-0.900), whereas HIC15 and HARM showed weaker correlation with MPS, particularly in rugby. XGB showed the lowest cross-sport variability (CV=0.034) and uncertainty (median NCIS=0.056). HARM, DAMAGE and HIC15 showed the greatest sport dependence (CV=0.575-0.588) and uncertainty (median NCIS=0.331-0.791). Conclusions: XGB, BrIC, and UBrIC demonstrated the strongest associations with brain tissue strain and the greatest consistency across sports. This study provides a biomechanically informed framework for selecting suitable metrics for sports HIA protocols.

Energy expenditure (EE) during running depends on the interplay between active muscle work and elastic energy storage and return, yet the relative contribution of mechanical power to EE remains debated. Quantifying the relative contributions of segment-level mechanical power can provide a way to address this debate. In this study, we aimed to quantify how segment-level mechanical power contributes to EE during running and to demonstrate that these mechanistic insights support wearable-based EE estimation. Joint dynamics and respiratory gas-based EE were collected from healthy young adults running at multiple speeds. Scale factors were derived to quantitatively link efficiency-weighted segment power to measured EE. The stance leg consistently showed the strongest correlation with EE, and this dominance was preserved across speeds. Including swing-leg hip power further improved accuracy. Scale factors were approximately 0.45, suggesting that active muscle work and elastic energy return contribute comparably to the mechanical power associated with EE. Using a lightweight machine learning model, stance-leg and swing-leg hip joint power were reconstructed from a single sacral IMU, enabling accurate EE prediction. These findings demonstrate that lower-limb mechanical power is a robust predictor of running EE, supporting both the extensibility of biomechanically-informed frameworks and wearable-based EE monitoring.

Distal radius fractures (DRFs) can delay return to activities of daily living and social participation because of postoperative pain, temporary joint immobilization, and limited wrist and forearm range of motion. The Ghost System developed at Saitama Prefectural University, Japan, combines visual action observation with tendon vibration stimulation and has shown potential as an adjunct to conventional rehabilitation. This Study Protocol describes a modified Ghost system intended to improve clinical implementation by replacing the head-mounted virtual reality display with iPad-based action observation and by using a wristband-type vibrator. This single-center, single-arm, open-label feasibility trial will enroll 10 adults after palmar locking plate fixation for DRF. The intervention will be delivered twice weekly during outpatient rehabilitation follow-up sessions from the early postoperative period (postoperative days 2-10 after enrollment) through the approved early postoperative rehabilitation period (generally up to postoperative week 8), in parallel with standard rehabilitation practices. Primary feasibility and preliminary clinical outcomes include device fit and acceptability, pain assessed using a 100-mm Visual Analog Scale, and wrist/forearm range of motion. Secondary implementation and safety outcomes include Disabilities of the Arm, Shoulder and Hand (DASH), Patient-Rated Wrist Evaluation (PRWE), Hand20 Questionnaire (HANDS-20), EuroQol 5 Dimensions 5 Levels (EQ-5D-5L), body ownership and hand-illusion questionnaires, setup time, setup errors, adherence, adverse events, and device incidents. We hypothesize that the modified Ghost system will be feasible and acceptable for early postoperative outpatient rehabilitation and will be delivered without serious device-related adverse events. Clinical outcomes will be summarized descriptively to inform a future controlled study rather than to establish efficacy.

Postural control depends on the ability to adapt motor responses to changing environmental and physiological conditions. Neuromuscular fatigue (NMF) is known to alter balance and muscle activation patterns, yet its effects on motor adaptation during whole-body postural tasks and on the persistence of learned strategies remain unclear. This study investigated whether localized NMF of the ankle dorsiflexors influences adaptation to a novel postural perturbation task and whether learning under fatigue induces persistent changes during subsequent re-exposure. Twenty-five healthy young adults were assigned to either a fatigue (FAT) or no-fatigue (NoFAT) group and completed two experimental sessions separated by 48-72 h allowing recovery from acute fatigue for fatigued group. Participants adapted to repeated mechanical perturbations while standing upright, while ground reaction forces and electromyographic activity of lower-limb muscles were recorded. NMF did not impair overall adaptation performance, as both groups exhibited similar reductions in performance error across practice. However, participants exposed to fatigue exhibited altered postural recovery dynamics, characterized by a reduced return toward the initial posture following perturbation release. These differences persisted during re-exposure on the subsequent day, despite the absence of acute fatigue. In parallel, NMF modified muscle activation and coactivation patterns involving both fatigued and non-fatigued muscles, several of which were retained during re-exposure. These findings indicate that the central nervous system preserves successful adaptation to postural perturbations under fatigue by reorganizing neuromuscular coordination and stabilization strategies. Learning under fatigue therefore influences not only immediate motor execution, but also shapes the longer-term representation of postural control strategies.

Ground reaction force (GRF)-based gait analysis provides objective, non-invasive evidence for neurological and musculoskeletal assessment, but its translation into medical AI decision support is limited by heterogeneous sensing devices, variable-length recordings, acquisition noise, sensor failures, and restricted access to high-cost gait laboratories. We propose SubGaitNet, a decision-oriented and interpretable AI framework designed to address four clinically relevant challenges in GRF-based medical AI: signal-length variability, sensing noise, long-range gait-phase dependency, and pathological frame-to-frame variability. SubGaitNet integrates GRF temporal slicing, multi-scale deep residual shrinkage, masked Transformer modeling, and a Sub-LSTM branch for adjacent-frame variability modeling. In subject-independent evaluation on two public clinical gait datasets, SubGaitNet achieved an AUC of 0.979 for Parkinson's disease (PD) screening and an ACC of 0.940/F1-score of 0.910 for Hoehn & Yahr severity assessment using wearable pressure insoles. On the GaitRec force-plate dataset, SubGaitNet achieved ACC values of 0.951 and 0.918 for four-class and five-class musculoskeletal impairment assessment, respectively. Additional analyses showed stable bootstrap confidence intervals, calibrated PD screening probabilities (Brier score = 0.059; expected calibration error = 0.051), positive decision-curve net benefit across clinically relevant thresholds, and ordinally plausible H&Y errors. Robustness tests under simulated sensor failure, noise perturbation, and reduced-channel inputs supported the model's stability under clinically plausible sensing uncertainty and accessibility constraints. SHAP explanations highlighted biomechanically meaningful hindfoot and forefoot regions. Overall, SubGaitNet provides a reusable, interpretable, and decision-support-oriented AI methodology for GRF-based gait health assessment, while prospective clinician-in-the-loop validation remains necessary before clinical deployment.

Fracture nonunion remains a major cause of morbidity, yet patient-specific factors associated with impaired healing remain incompletely characterized. Anemia has been associated with adverse orthopaedic outcomes, but its relationship with fracture nonunion is poorly understood. We examined whether pre-fracture anemia, anemia burden, and clinically relevant anemia subtypes were associated with nonunion following tibial or femoral fractures. Using commercial and Medicare fee-for-service claims from 2016 through 2023, we identified adults aged 19 years or older with a tibial or femoral fracture, continuous enrollment during the preceding year and for at least six months after fracture, and no baseline cancer. Pre-fracture anemia was evaluated as any anemia, the number of distinct anemia diagnoses, and nutritional, hemolytic, aplastic, and other anemia subgroups. Nonunion occurring six to eighteen months after fracture was assessed using incidence rates and multivariable-adjusted hazard models. Among 326,673 adults, 149,704 had pre-fracture anemia and 176,969 did not. The crude incidence of nonunion was 42% higher among individuals with anemia than among those without anemia (incidence rate ratio, 1.42; 95% confidence interval, 1.32 to 1.53) and increased with greater anemia burden. After adjustment for demographic and clinical characteristics, including prior fractures at other anatomical sites, pre-fracture anemia remained associated with nonunion following tibial and femoral fractures, with hazard ratios of 1.83 (95% confidence interval, 1.54 to 2.18) and 1.38 (95% confidence interval, 1.26 to 1.50), respectively. Associations were also observed for nutritional and other anemias, whereas estimates for hemolytic and aplastic anemias were limited by few nonunion events. Within the femur, the association was strongest for distal fractures. These findings demonstrate that pre-fracture anemia is independently associated with nonunion. The increase in risk with greater anemia burden and findings across evaluable subgroups suggest that pre-fracture anemia may help identify patients at increased risk of impaired fracture healing.