Medicine & Science in Sports & Exercise

Altered walking mechanics in individuals with obesity can contribute to knee osteoarthritis. The gait deviations may become more pronounced during obstacle crossing. In women, body fat distribution may further influence knee load, especially when excess fat accumulates in the thighs and hips. However, relatively little is known about how regional fat distribution affects gait in women with obesity. This study investigated how obesity and, among women, different fat distributions (Apple: more abdominal fat; Pear: more lower-limb fat) influence knee biomechanics during walking with and without obstacle crossing. Participants were 15 controls without obesity (NB) and 27 with obesity (OB). Within female participants, 10 without obesity (fNB) were compared with 20 with obesity, stratified by waist-hip ratio (Apple:10, Pear:10). Speed-adjusted statistical parametric mapping applied a general linear model (NB vs. OB) and an analysis of covariance (fNB vs. Apple vs. Pear). OB exhibited a significantly greater late-stance knee extension moment than NB across all tasks, and this difference persisted among fNB, Apple, and Pear in obstacle tasks (p<0.05). OB walked with reduced knee flexion during the early-stance leading limb after crossing a medium-height obstacle (p=0.048) and a high-height obstacle (p=0.008) compared to NB. There were significant body-shape effects (p<0.05), and post-hoc comparisons confirmed that Pear had lower knee angles than fNB in both leading-limb conditions after crossing medium- and high-height obstacles (p=0.008 and p=0.001, respectively). These findings suggest that obstacle crossing helps illuminate how excess weight influences knee biomechanics, and how regional fat distribution modulates the degree of this alteration.

Background Heart rate fragmentation (HRF) has emerged as a novel marker of sinoatrial instability and neuroautonomic dysregulation and is a predictor of incident cardiovascular disease (CVD) events and cardiovascular mortality. Leveraging heart rate fragmentation as a novel measure may help us better understand the prognostic significance of physical activity. Physical activity (PA) patterns are multidimensional and difficult to study holistically, however. We sought to examine for novel PA clusters in a cohort of veteran men and evaluate their prognostic significance based on their associations with neuroautonomic dysregulation. Methods In this cross-sectional study, we examined 602 male veterans from the Vietnam Era Twins Study of Electrophysiology in Posttraumatic Stress Disorder (VETS-EP) who were enrolled between 2022 and 2026. Accelerometry data were used to derive physical activity parameters across 6 domains: volume, sedentary behavior, intensity, diurnal pattern, fragmentation, and variability. Heart rate fragmentation was assessed using percentage of inflection points (PIP), inverse average length of segments (IALS), percentage of short segments (PSS), and percentage of alternating segments (PAS). Gaussian mixture models were used to derive digital phenotypes of physical activity, and associations with heart rate fragmentation were assessed using linear mixed models. Results Participants had a mean age of 73.8 {+/-} 2.9 years and 93.2% reported White race. Two overlapping phenotypes of physical activity patterns were identified: a compact-early phenotype, characterized by earlier activity timing and slightly greater overall activity, and a diffuse-late phenotype, characterized by later activity timing and greater heterogeneity in activity volume. In fully adjusted models, the diffuse-late phenotype was associated with higher PIP, the primary outcome ({beta}: 1.199, 95% CI: 0.034 to 2.363, p-value: 0.044), and higher IALS ({beta}: 0.01210, 95% CI: 0.00048 to 0.02373, p-value: 0.041), but not PSS or PAS, compared with the compact-early phenotype. Conclusions In older male veterans, Gaussian mixture model phenotyping identified two overlapping physical activity phenotypes, differing mainly in diurnal timing and in the dispersion of overall activity, that were associated with modest differences in heart rate fragmentation. These phenotypes provide a framework for capturing complex physical activity patterns. Future prospective studies representing diverse populations are needed to validate such phenotypes.

Background: Handgrip strength is associated with cardiometabolic abnormalities, but whether it adds information once detailed adiposity and muscle mass are known is unclear. Methods: We studied adults aged 40-59 years from NHANES 2011-2012 (development, n=508) and 2013-2014 (temporal validation, n=616). The outcome was at least two of four non-adiposity abnormalities (elevated blood pressure, fasting glucose or triglycerides, or low HDL cholesterol); waist circumference was not part of the outcome. A prespecified feature ladder added DXA body fat percentage and visceral adipose tissue to age, sex, BMI and waist circumference (M1), then appendicular skeletal muscle index (M2), then absolute (M3A, primary) or weight-normalised (M3B) grip strength. Logistic regression was primary; elastic-net and XGBoost were supportive. Development performance used nested cross-validation; frozen models were scored once in the validation cohort. Paired increments used 2000 stratified bootstrap resamples. Results: The outcome occurred in 249 (49.0%) and 277 (45.0%) participants. Adding adiposity increased the logistic regression AUC by 0.0209 (95% CI 0.0024-0.0402) in development and 0.0209 (0.0032-0.0375) in temporal validation. Adding absolute grip strength to M2 changed the AUC by -0.0046 (-0.0107 to 0.0013) and 0.0045 (-0.0009 to 0.0098), respectively. All 12 grip-strength AUC increments across algorithms, definitions and cohorts had intervals that included zero. Calibration was unchanged and the incremental net benefit was not consistently positive. Model attributions to grip strength varied by algorithm. Conclusions: In middle-aged adults, detailed adiposity, but not grip strength, added reproducible information for concurrent cardiometabolic risk stratification beyond conventional anthropometry and muscle mass.

Paraspinal muscles support and move the spine, and reduced size and density of these muscles is associated with increased risk of vertebral fracture and back pain. We test the hypothesis that subsistence-oriented forager-horticulturalists (Bolivian Tsimane) have larger and denser paraspinal muscles, and smaller age-related differences in paraspinal muscle size and density, than more sedentary post-industrialized suburbanites (Framingham Heart Study [FHS]). We measured cross-sectional area (CSA) and density of trunk extensors and psoas major at L3 from computed tomography scans of 411 FHS and 330 Tsimane (50% women, aged 50-90 years). Sex-stratified linear regressions determined associations of muscle CSA and density with age and cohort (Tsimane or FHS [ref.]), with and without an age-cohort interaction term. Covariates were height and weight. After adjusting for covariates, Tsimane women had 11-14% larger and denser extensors, and 17-26% smaller and less-dense psoas major, than FHS women. Tsimane men had 8-21% smaller and less-dense psoas major than FHS men. The age-related difference in extensors density was 41% smaller for Tsimane men than for FHS men. There were no other significant age-related cohort differences in muscle CSA or density. We observed a different balance in the size and density of trunk extensors versus psoas major between Tsimane and FHS. A possible explanation for this observation is cohort differences in the amount and types of physical activity, although future work is required to determine the influence of lifestyle and environmental factors on paraspinal muscle size and density.

Weekly training volume is the primary driver of resistance-training hypertrophy, but the independent role of frequency can be isolated only when weekly volume is equated. We quantified the effect of training frequency on hypertrophy across one to three volume-equated sessions per muscle per week. Following PRISMA 2020, five databases were searched to October 2026 for trials of at least six weeks that equated weekly volume between per-muscle frequencies and measured muscle size. One change-score standardized mean difference per trial (Hedges g; negative favoring higher frequency) was pooled with a random-effects model, and certainty was rated with GRADE. Sixteen trials (380 participants) were pooled. The frequency effect was trivial and non-significant (g = -0.02; 95% CI -0.21 to 0.16; I-squared = 0%; prediction interval -0.23 to 0.18); the interval admits at most a small effect favoring the higher frequency. Contrast-specific estimates were similarly trivial, and no moderator was significant, although the moderator analyses could detect only large effects. Certainty was low to very low. Within this range, the data give no basis for preferring one, two or three sessions at a fixed weekly volume. Most trials measured muscle thickness, which does not track whole-muscle growth reliably.

Background: Mitochondrial dysfunction is a hallmark of ageing and is implicated in the pathogenesis of sarcopenia. Genetically confirmed mitochondrial disease provides a biologically definitive model of impaired oxidative phosphorylation against which novel functional assessments can be validated. We investigated whether a brief, submaximal, non-ischaemic intermittent isometric handgrip exercise protocol combined with Near Infra-Red Spectroscopy (NIRS) could detect distinct muscle oxygenation signatures in mitochondrial disease and sarcopenia. Methods: Adults with genetically confirmed mitochondrial disease (n=10, 7 female) and group-matched controls (n=19, 11 female), underwent assessment of maximal grip force, handgrip relaxation kinetics and a 3-minute intermittent submaximal isometric handgrip test (40% maximal voluntary contraction, 1Hz contraction/relaxation) with continuous force recording at 2000Hz and simultaneous NIRS. Findings were compared with 23 community-dwelling older adults from the Muscle Ageing and Sarcopenia Study (MASS) Lifecourse cohort (n=23, 13 female) including seven with probable or confirmed sarcopenia according to European Working Group on Sarcopenia in Older People (EWGSOP2) criteria. Results: Participants with mitochondrial disease demonstrated an attenuated reduction in tissue saturation index (TSI) during exercise compared with controls (TSI % {middle dot} s150-180s: -59.9 {+/-} 94.5 vs -175.1 {+/-} 128.4; p=0.02). Total haemoglobin (THb) responses did not differ between groups (p=0.10). In contrast, participants with probable or confirmed sarcopenia showed exaggerated reduction in TSI compared with non-sarcopenic participants (TSI % {middle dot} s150-180s: -256.5 {+/-} 146.0 vs -121.2 {+/-} 95.2; p=0.05), while THb responses remained similar. The association between sarcopenia and TSI differed by sex (interaction coefficient -240, p=0.016), with greater TSI reductions observed in males with sarcopenia. Differences in TSI between mitochondrial disease and control groups were independent of age and sex. No statistically significant associations were observed between THb responses and age, sex or force production. Conclusions: A brief, non-ischaemic handgrip exercise protocol combined with NIRS identified divergent muscle oxygenation responses in mitochondrial disease and sarcopenia. The attenuated TSI response observed in genetically confirmed mitochondrial disease is consistent with impaired oxygen utilisation secondary to defective oxidative phosphorylation, whereas the exaggerated TSI reduction observed in sarcopenia suggests a distinct physiological mechanism, potentially involving impaired oxygen delivery, reduced muscle efficiency, or both. This portable and non-invasive approach has significant potential as a physiological biomarker for mechanistic studies and clinical trials in ageing and neuromuscular disease. More broadly, our findings demonstrate how biologically defined rare diseases can provide a powerful framework for interpreting mechanisms in common heterogeneous age-related conditions.

Periods of limb immobilization are common in clinical care and lead to rapid losses of muscle mass and strength. We therefore examined whether prehabilitative exercise improves outcomes after disuse by increasing pre-immobilization muscle reserve or by attenuating the biological response to immobilization. Here, we report the primary and muscle-focused secondary outcomes of the PRE-EX (PREhabilitative EXercise) randomized controlled trial (ClinicalTrials.gov: NCT06205784). Fifty-four healthy younger and older women completed four weeks of supervised resistance exercise or no training before eight days of unilateral limb immobilization, followed by four weeks of rehabilitation. From baseline to pre-immobilization, prehabilitation increased quadriceps cross-sectional area (CSA) by 6.7%, maximal voluntary contraction (MVC) by 15.2%, and muscle fiber CSA by 17.7%. Immobilization subsequently reduced quadriceps CSA by 3.2% over 5 days and MVC by ~20%, with similar relative losses in the Prehab and No-train groups. Consequently, quadriceps CSA, the studys primary outcome, remained greater in Prehab than in No-train after immobilization and following rehabilitation, while MVC was greater following rehabilitation. Prehabilitation did not preserve markers of neuromuscular innervation or produce a detectable post-immobilization transcriptomic signature. Instead, immobilization elicited an extensive transcriptional response comprising more than 7000 differentially expressed genes, characterized by activation of inflammatory, proteolytic, stress, and denervation-associated programs together with suppression of mitochondrial and muscle-structural pathways. Network analysis further linked these coordinated molecular programs to disuse-related changes in muscle size, strength, and morphology. The effects of prehabilitation and the subsequent response to immobilization were similar in younger and older women. These findings demonstrate that short-term prehabilitative exercise mitigates the consequences of limb immobilization by establishing greater muscle and strength reserve before disuse, rather than by attenuating the physiological or molecular response to immobilization.

Introduction: Knee muscle coactivation is elevated after anterior cruciate ligament reconstruction (ACLR), contributing to altered joint loading and post-traumatic osteoarthritis. Existing methods average coactivation within predefined gait phases and require priori designation of muscles roles, limiting the resolution for when differences occur. Objective: Characterize knee joint coactivation and dynamics throughout gait in individuals with ACLR using statistical parametric mapping. Methods: Ten individuals with unilateral ACLR and ten healthy matched controls performed overground walking at their preferred speed, while kinematics, kinetics, and electromyography of the quadriceps, hamstring, and gastrocnemius muscles were recorded. Coactivation was quantified using time-varying, multi-muscle coactivation, and was compared using a one-tailed statistical parametric mapping (SPM) t-test. Knee joint angle, angular speed, and moment were compared using SPM Hotelling's T2 tests with Bonferroni-adjusted post hoc comparisons (= 0.05). Results: Coactivation was greater in the ACLR group at 0.01%-6.14%, 35.23%-40.94%, 69.73-71.99%, 72.12-77.31%, 77.89-78.05%, and 94.63%-95.87% (p < 0.0001) of stride. The ACLR group also demonstrated greater knee internal-external rotation angle at 0.01%-47.34%, 52.14%-61.87%, and 66.47%-100% (p <0.0001) and lower knee flexion angle at 55.79%-65.93% (p = 0.004) of stride, than healthy controls. Finally, a smaller knee flexion-extension moment was observed in the ACLR group at 57.43%-62.18% (p = 0.005) of stride. Conclusions: Coactivation after ACLR is elevated at loading response, late mid-stance, terminal stance and early push-off phase. Greater coactivation was observed during weight-acceptance phases, whereas lower knee moments characterized initial swing. These alterations are localized rather than uniformly distributed, supporting phase-targeted rehabilitation.

The COVID-19 pandemic led to significant disruptions in cardiovascular care and reductions in physical activity, but little is known about how exercise patterns changed after this period. This study assessed changes in weekly aerobic and strength training activity between 2020 and 2022 amongst adults aged 18 years or older who reported one or more cardiovascular diseases or risk factors. This study used National Health Interview Survey data from 2020 and 2022. Adjusted differences for moderate-to-vigorous physical activity (MVPA) were calculated using a linear regression model and for strength sessions using a Poisson regression, adjusting for sex and age. Changes in these outcomes were then stratified by age and sex subgroups. The weighted study population included 182,783,008 (standard error, +/-3,334,337) adults in 2020 and 185,388,060 (SE, +/-3,285,161) adults in 2022. Between 2020 and 2022, the overall weekly MVPA increased from 244.2 (SE, +/-4.5) minutes to 266.3 (SE, +/-5.7) minutes (adjusted difference, +22.1 [SE, +/-6.92] minutes). There were no statistically significant changes in the number of strength session per week overall or among sex and age subgroups. Across sex and age subgroups, increases in weekly MVPA were entirely concentrated among males and younger adults. The recovery from pandemic era reductions in aerobic and strength exercise training was uneven amongst demographic subgroups, which aligns with concurrent persistent disruptions in cardiovascular care.

Objective: The aim of the current study was to evaluate the feasibility of a multi-channel distributed wearable ultrasound (D-WUS) system capable of simultaneously probing dynamic muscle activity across multiple anatomical sites to assess neuromuscular coordination during physical activity. Methods: Twenty NCAA Division I women athletes (8 with prior knee injury) performed countermovement jumps (CMJs) on dual force plates while wearing a four-channel D-WUS system targeting the vastus lateralis (VL) and vastus medialis oblique (VMO) in both limbs. Real-time M-mode ultrasound data were processed using a composite factorization approach integrating nonnegative matrix factorization and principal component analysis (CF-PCA) to extract dominant muscle-contraction patterns. Correlation and timing metrics between VL and VMO were compared across injury status. Results: CMJ performance metrics (jump height, RSImod) did not differ between groups (p > 0.05). However, D-WUS revealed significant differences in muscle coordination in the right limb: VL-VMO correlation (p = 0.029) and timing symmetry (p = 0.019) were reduced in participants with prior knee injury; left-limb differences were not significant. Right-limb timing symmetry was negatively correlated with SMFA score (rho = -0.48, p = 0.033). Functional survey scores (SMFA) also differed significantly (p = 0.001), while VISA-P scores did not. Conclusion: These preliminary findings provide feasibility-level evidence that distributed wearable ultrasound can detect limb-specific neuromuscular coordination differences not reflected in force-plate biomechanics, motivating larger prospective studies to establish reliability and clinical utility. Significance: With further validation, this approach may offer a scalable, objective means of monitoring muscle contraction during rehabilitation.

Leisure time physical activity (LTPA) in mid-life may have beneficial effects on risk factors for hip fracture in later life. Conversely, physical activity may increase fracture risk through risk of injury, and the optimal amount of physical activity for reducing hip fracture risk remains unclear. We explored the associations between volume and intensity of LTPA in mid-life, and subsequent risk of hip fracture ascertained from linked health data. This prospective observational study used middle aged adults aged 40- 65 years from UK Biobank. LTPA volume (LTPAv) was derived from self-reported walking, moderate and vigorous activity at baseline (2006- 2010). Cox proportional hazard and Fine-Gray sub-distribution models were used to estimate the association between activity and hip fracture, which was sex-stratified. From 324,284 participants with complete data 53% were female and mean age at baseline was 54.5 (SD 7.3). Across 16 years of follow-up there were 2,674 hip fractures. In terms of LTPA volume, the lowest risk of hip fracture occurred in quintile 3 for women (HR 0.78, 95% CI 0.67-0.91), and men (HR 0.74, 95% CI 0.60- 0.90), relating to approximately one hour/day of leisure time physical activity. When activity intensities were examined separately, the lowest estimated hazards were observed for vigorous activity, at quintile 4 in women (HR 0.65, 95% CI 0.55 - 0.76) and quintile 3 in men (HR 0.64, 95% CI 0.52- 0.79), corresponding to approximately 60- 90 minutes of vigorous activity per week. In conclusion, moderately high volumes of mid-life physical activity, particularly vigorous activity, were related to lower risk of subsequent hip fracture, but these relationships appear to attenuate at higher volumes.

Crank length affects the geometry of the bicycle-rider system and influences the motion of the lower limb throughout the pedal cycle. Conventional crank selection has largely relied on rider stature and mechanical power, yet mechanical power and cycling economy remain remarkably insensitive to crank length across a broad range. Yet, elite cyclists and triathletes increasingly adopt shorter cranks, particularly in disciplines where aerodynamic drag strongly affects cycling performance. However, the mechanisms that connect crank length to mechanical power and aerodynamic drag remain unclear. Here we show that crank length couples rider anthropometry, hip kinematics, and aerodynamic drag. Population anthropometry of 6,068 individuals reveals that stature alone poorly predicts personalized crank length, while geometric analysis identifies a nearly linear relationship between crank length and minimum lower hip angle: a 10-mm reduction in crank length increases hip-angle margin by approximately 1.42 degrees with little mechanical penalty. This geometric freedom permits more flexion of the torso and a more aerodynamic posture; the resulting aerodynamic advantage grows rapidly with cycling speed because aerodynamic power scales with velocity cubed. Data from 150 elite cyclists and triathletes support this shift toward shorter cranks, with triathletes adopting shorter relative crank lengths than cyclists. Our results establish crank length as a personalized design variable that connects lower-limb geometry to aerodynamics. These insights enable personalized crank selection, integrated rider-bicycle design, and performance optimization for the increased aerodynamic demands of high-speed cycling.

Lifestyle behaviors influence cardiometabolic and cognitive health through multiple interconnected processes, involving metabolic, cardiovascular, behavioral and cognitive factors. This study aimed to assess associations between multivariate plasma and physiological profiles, and behavioral parameters, and their potential association with reaction time (RT) in active young adults. Data on physical activity levels were collected from wearable devices and GPAQ questionnaire, along with anthropometric and clinical assessments, cognitive tests, and blood analyses. Principal component analysis was performed separately for physiological and plasma parameters, retaining the first two principal components (PCs) from each analysis. Multiple linear regression models were used to evaluate the associations between plasma, sex, physical activity levels (METs), daily step count, and alcohol/marijuana use on physiological PC1/PC2 scores, as well as RT. Continuous independent variables were previously categorized, and combined variables were created to represent specific combinations between plasma/physiological PC1 categories and sex. Physiological PC1 (blood pressure) was associated with combined plasma PC1 (insulin/HOMA-IR)-sex variable, total METs and alcohol consumption (adjusted R2 = 0.30). Physiological PC2 (handgrip strength) was mainly explained by combined plasma PC1-sex variable (adjusted R2 = 0.54), with minimal contribution from behavioral factors. RT was associated with physiological PC1 variable and sex (adjusted R2 = 0.35), with slower responses observed among women with lower physiological PC1 scores or hypotension; these associations were supported by RT-physiological PC1 and RT-blood pressure correlations. These exploratory findings suggest sex-dependent associations between physiological, metabolic and lifestyle-related factors, supporting a holistic approach in future research, particularly among young adults.

Background The consequences of prolonged exposure to obesity on biomarkers of myocardial stress and injury remain unclear. We examined associations of duration and cumulative severity of obesity from childhood to later adulthood with concentrations of N-terminal pro-B-type natriuretic peptide (NT-proBNP), high-sensitivity cardiac troponin I (hs-cTnI), and growth differentiation factor-15 (GDF-15) at age 62 years. Methods The sample comprised 4,901 participants in the 1958 National Child Development Study who had measurements of NT-proBNP, hs-cTnI, or GDF-15 at age 62 years and at least four BMI assessments between 7 and 62 years of age. Individual BMI trajectories were modelled, from which total duration of obesity and mean excess BMI (area between the trajectory and the age-specific obesity threshold divided by duration) were derived. Associations of ever versus never having been obese, obesity duration, and mean excess BMI with biomarker concentrations were examined using general linear regression models with progressive adjustment for early-life characteristics; contemporaneous cardiometabolic factors; and health behaviours, socioeconomic position, and psychosocial factors. Nonlinear associations of obesity duration were estimated using restricted cubic splines and subsequently approximated using linear splines. Results Overall, 26.3% of participants had ever experienced obesity. There was no evidence of an association between ever versus never having been obese and NT-proBNP. Among men, ever having been obese was associated with 11.00% (95% CI, 4.62-17.37) higher hs-cTnI in the fully adjusted model, whereas there was no evidence of an association among women. Ever having been obese was associated with higher GDF-15, although the association attenuated substantially after adjustment for contemporaneous cardiometabolic factors. Longer obesity duration was associated with higher concentrations of all three biomarkers in fully adjusted models, but the pattern differed by biomarker: hs-cTnI increased approximately linearly with duration, whereas NT-proBNP and GDF-15 remained relatively stable up to approximately 25 years of obesity before increasing with longer duration. In fully adjusted models, each additional year of obesity beyond 25 years was associated with 1.80% (95% CI, 0.54-3.06) higher NT-proBNP and 0.81% (95% CI, 0.25-1.36) higher GDF-15, while each additional year across the full range of obesity duration was associated with 0.41% (95% CI, 0.07-0.76) higher hs-cTnI. Among participants who had ever experienced obesity, each 1 kg/m2 higher mean excess BMI was associated with 4.02% (95% CI, 1.79-6.24) higher NT-proBNP and 2.00% (95% CI, 0.49-3.51) higher hs-cTnI in fully adjusted models; there was no evidence of an association with GDF-15. Conclusions Longer duration of obesity was associated with higher concentrations of biomarkers reflecting myocardial stress, injury, and cellular stress at age 62 years, with associations particularly evident after approximately 25 years of obesity for NT-proBNP and GDF-15. These findings suggest that duration of obesity may provide clinically relevant information beyond current obesity status, supporting its consideration as an additional dimension of cumulative obesity burden in cardiovascular risk assessment.

Bone strain and remodeling are important factors for bone health. Improved characterization of relationships between these factors in response to acute loading will improve our understanding of bone maintenance, adaptation to load, and pathophysiology. The purpose of this study was to evaluate colocalization between finite-element-estimated bone strain and [18F]sodium fluoride positron emission tomography imaging-estimated subchondral bone remodeling in the tibial diaphysis in response to acute exercise. We hypothesized that the exercise-induced change in standardized uptake values would be greatest in regions of higher strain. 26 participants underwent bilateral positron emission tomography/magnetic resonance scans before and after a bout of stair ascent and descent exercise. Finite element analysis was performed to calculate principal strain distributions in the tibial diaphysis. [18F]sodium fluoride standardized uptake values were calculated from pre- and post-exercise positron emission tomography data and mapped to the tibial surface. Mean pre-exercise and exercise-induced change in standardized uptake values were calculated and compared between regions defined by strain percentile. Both normalized mean pre-exercise and exercise-induced change in standardized uptake values increased with maximum principal strain in a pattern suggesting an exponential relationship. Pre-exercise and exercise-induced change in standardized uptake value were notably much greater in the region of highest maximum principal strains (estimated marginal means = 76.9 and 71.0 percentile, respectively) when compared to all other regions of the tibial diaphysis ([&le;] 61.1 and [&le;] 57.0 percentile, respectively, p < 0.001). This study is the first to directly show a relationship between bone mechanical loads and acute [18F]sodium fluoride uptake in humans in vivo. Our results highlight the influence of tensile strain magnitude on bone metabolic activity in response to acute loading. Furthermore, we demonstrate the utility of a combined finite element analysis and positron emission tomography approach to interrogate relationships between bone loading and bone metabolic response to acute exercise.

Background: Head acceleration events (HAEs) are common in contact sports, but season-long exposure and its relationship with cognitive performance in amateur British American football remain poorly characterised. Methods: Thirty male players were recruited from three British American football teams. Cognitive performance was assessed pre-season, mid-season, and post-season using the Sport Concussion Assessment Tool 6 and computerised Stroop, 2-back, Go/No-go, and visual-search tasks. Seasonal cognitive analyses included 23 participants with available data. HAEs were quantified using helmet-mounted accelerometers; exposure-linked analyses were restricted to 19 participants who provided sufficiently complete sensor recordings across contact training sessions and competitive matches. Seasonal cognitive changes were assessed using mixed-effects models. Associations of in-season HAE metrics and previous contact-sport seasons with global cognitive change were examined using simple linear regression and elastic-net regression. Results: In the 19-participant exposure-linked cohort, prior contact-sport exposure showed the strongest nominal univariate association with worse global cognitive change (r squared = 0.337, p = 0.009), although this did not remain significant after correction for multiple comparisons (Benjamini-Hochberg-adjusted p = 0.055). Corrected nested cross-validation indicated little out-of-sample performance for the multivariable elastic-net model (r = 0.144, predictive R squared = -0.008). Although previous contact-sport seasons had the largest standardised coefficient in the final full-cohort fit, predictor retention varied substantially across resamples. Conclusion: Prior contact-sport exposure showed the strongest exploratory association with relatively worse global cognitive change, whereas in-season HAE metrics showed weaker associations. However, the multivariable model did not demonstrate useful out-of-sample predictive performance, and the small exposure-linked cohort precludes firm conclusions regarding the relative importance of individual predictors.

Objectives: Intraoperative ultrasound (IOUS) is an increasingly valuable real-time imaging modality in neurosurgery, enabling visualization of brain parenchyma, tumor margins, ventricular anatomy, and vascular structures during cranial procedures. Despite its clinical relevance, the development of artificial intelligence (AI)-assisted interpretation tools for neurosurgical IOUS has been limited by the scarcity of large, annotated datasets. Manual pixel-level annotation of ultrasound video frames is labor-intensive, requires specialized neuroanatomical expertise, and scales poorly. To address this bottleneck, we developed a proof-of-concept interactive semi-automated annotation pipeline designed to explore the feasibility of scalable, expert-guided labeling for intraoperative neurosurgical IOUS. Methods: We implemented the system as a napari-based graphical interface coupled with a scikit-learn Random Forest (RF) pixel classifier. Real intraoperative neurosurgical ultrasound videos from five craniotomy cases were used as training material. A neurosurgical expert annotated a minimal set of representative frames using brush-based labeling to define anatomical classes of interest. For each labeled pixel, a feature vector was computed comprising raw intensity, multi-scale Gaussian filtering ({sigma} = 1, 2, 3), Laplacian of Gaussian, and Sobel edge magnitude. The RF classifier was trained on accumulated annotations using class-balanced weighting and out-of-bag (OOB) validation, then applied across full video sequences. An incremental accumulator module enabled multi-case training. Segmentation outputs were exported as TIFF overlays for expert quality review. Results: Across five intraoperative cases, sparse expert annotation of a small number of representative frames per case was sufficient to train case-specific Random Forest classifiers that propagated labels across the full video sequences. Out-of-bag estimation served as an internal coherence check during training, and the classifier additionally produced per-class probability maps that exposed regions of uncertainty at acoustic boundaries. On expert qualitative review, the auto-segmented frames were anatomically coherent, with the classifier reliably distinguishing anechoic fluid compartments from echogenic tissue interfaces; residual misclassification was concentrated in low-contrast boundary regions. Conclusions: This proof-of-concept study demonstrates that semi-automated, expert-guided annotation of intraoperative neurosurgical ultrasound is technically feasible using classical machine learning. By combining neurosurgical domain expertise with an interactive, incremental annotation workflow applied to real intraoperative acquisitions, this framework represents a foundational step toward scalable generation of labeled datasets for neurosurgical IOUS. Future directions include formal multi-rater validation, expanded multi-class anatomical labeling, and eventual migration to deep learning architectures as annotated datasets grow.

OBJECTIVE: To describe (1) US emergency department-treated pickleball injury burden and the injury-to-participation measure among total players, with burden among adults aged 60 to 79 years as a descriptive subgroup, and (2) determine whether general internet search interest for 'pickleball' is also associated with total pickleball-related injuries. DESIGN: Ecological time series study, United States, 2014 to 2023. DATA SOURCES: National Electronic Injury Surveillance System (NEISS) emergency department microdata yielded 1,738 adjudicated pickleball cases, 921 of them orthopedic, weighted to an estimated 101,450 injuries nationally. Google Trends, English Wikipedia pageviews, and GDELT news volume served as general pickleball attention signals, with the Trends index for 'sourdough' as a negative control. Sports and Fitness Industry Association (SFIA) participation estimates supplied a total player denominator. MAIN OUTCOME MEASURES: Annual national injury estimates with design-based 95 percent confidence intervals; injury-to-participation measures; and correlations between total pickleball-related injuries and general pickleball attention signals before and after removing trend and seasonality. RESULTS: Estimated emergency department-treated pickleball injuries rose 17.5-fold, from 1,391 in 2014 (highly unstable) to 24,294 in 2023. 70 percent of adjudicated cases involved adults aged 60 to 79. During 2017-2023, injury estimates rose 4.0-fold and participation rose about 4.4-fold. No temporal trend was detected in the injury-to-participation measure (P=0.59). Search interest looked like an excellent proxy: in annual levels it correlated with total pickleball-related injuries at R=0.96, and Pickleball Wikipedia pageviews at R=0.98. However, so did searches for "sourdough", at R=0.76. Removing trend and seasonality left little (monthly residual R=0.084; year-on-year R=0.28 over 96 months, 2015-2023), and the seasons ran opposite, with injuries peaking in February and searches in July, such that, on 12-month mean profiles, the sourdough negative control fitted the injury season (R=0.96) while pickleball ran against it (R=-0.40). General pickleball search interest and pickleball news coverage remained correlated in year-on-year changes in 2017-2023 (R=0.64), whereas their corresponding correlations with total pickleball-related injuries in 2017-2023 were 0.25 and 0.20. CONCLUSIONS: The absolute burden of emergency department-treated pickleball injury has grown substantially, but the available surveillance data cannot resolve whether the sport has become more hazardous per participant. The observed rise is consistent with growth in exposure alone. The strong correlation between search interest and injury counts was not specific, the association was substantially attenuated after detrending, and the seasonal patterns were opposed. These descriptive results do not establish that search interest can substitute for injury surveillance, and series that rise together should not be assumed to be related.

Obstetric anal sphincter injury (OASI) requires immediate postpartum recognition for primary repair. Diagnosis relies primarily on clinical examination, as endoanal ultrasound (EAUS) is rarely a bedside option. Therefore, objective diagnostic assessment is most needed during the first postpartum hours. However, it is challenging to obtain the anatomically verified data needed to develop diagnostic technologies for this clinical window. We evaluated the translation of a machine-learning-assisted impedance spectroscopy model into its intended immediate postpartum setting. The model lifecycle comprised three sequential phases: V1 development using anatomically verified data from a prospective multicenter study (N=152); V2 real-world adaptation, comprising post-market data collection, retraining (N=144) to adapt to acute physiological tissue changes, and subsequent separate evaluation (N=125); and prospective external validation of V2 in an unseen cohort (N=70). During this separate evaluation, V2 achieved 89.6% accuracy. In external validation, all examinations occurred within 4 hours of birth (94.3% within the first hour). Against subsequent EAUS, V2 achieved 86.2% sensitivity, 92.7% specificity, and 90.0% overall accuracy. The V2 model was prospectively externally validated in its intended immediate-postpartum setting, supporting ML-assisted impedance spectroscopy as an objective adjunct, and not a replacement, to clinical OASI assessment. Further validation is required to confirm generalizability.

Chronic intermittent hypobaric hypoxia is an occupational exposure experienced by workers who alternate between high-altitude worksites and lower-altitude resting locations. Its effects on cardiac autonomic modulation and electrocardiographic parameters remain insufficiently characterized in Andean workers. This study aimed to compare heart rate variability and electrocardiographic parameters between workers exposed to chronic intermittent hypobaric hypoxia and controls working permanently at lower altitude in Arequipa, Peru. An observational cross-sectional study was conducted in 96 male workers aged 20-60 years. The exposed group included 53 workers performing rotational shifts at altitudes [&ge;]3,000 m above sea level with rest periods at <2,500 m, while the control group included 43 workers working permanently at <2,500 m. Heart rate variability was assessed during the morning rest period in Arequipa, at approximately 2,300 25 m above sea level, using a Polar(R) H10 heart rate sensor after 15 minutes of rest. Participants also underwent standard 12-lead electrocardiography. Vital signs were clinically similar between groups. No statistically significant differences were observed in PR interval, corrected QT interval, time-domain heart rate variability parameters, or frequency-domain heart rate variability parameters. In this sample of apparently healthy male workers evaluated during their rest period at moderate altitude, exposure to chronic intermittent hypobaric hypoxia was not associated with significant differences in resting heart rate variability or standard electrocardiographic parameters.