Frontiers in Physiology最新文献

Introduction: Muscle hypertonia is a common symptom in patients with upper motor neuron disorders. To date, the role of intramuscular connective tissue (IMCT) alterations in hypertonic muscle has not been fully explored. This review aimed to identify and characterize alterations in IMCT components in hypertonic muscle in central neurological disorders.

Methods: This scoping review included studies investigating IMCT alterations in hypertonic muscles resulting from central neurological disorders. Four electronic databases, including PubMed/Medline, CINAHL, Web of Science, and Scopus, were searched to identify relevant studies published prior to 20 July 2025. The review followed the Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) checklist. The risk of bias was evaluated using ROBINS-E. Data were extracted and narratively synthesized according to IMCT categories.

Results: Twelve studies were included. Among the included studies, increased collagen, glycosaminoglycan content, fascia thickness, and fibroblasts, as well as altered IMCT structural properties, were found in hypertonic muscles. The collagen content was found to be positively correlated with spasticity and stiffness. A key limitation of these studies is that all participants were in the chronic stage of the neurological disease.

Conclusion: This scoping review provides evidence that alterations in IMCT components in muscle with hypertonia occur across different neurological conditions. Targeting these changes may provide a new intervention strategy to reduce muscle stiffness and improve the muscle function of patients with hypertonia secondary to neurological disease.

Background: Accurate localization and segmentation of polyp lesions in colonoscopic images are crucial for the early diagnosis of colorectal cancer and treatment planning. However, endoscopic imaging is often affected by noise interference. This includes issues like uneven illumination, mucosal reflections, and motion artifacts. To mitigate the impact of such interference on segmentation performance, it is essential to integrate multi-scale feature analysis effectively. Features at different scales capture distinct aspects of image information. Yet, existing methods typically rely on simple feature summation or concatenation. These methods lack the capability for adaptive fusion across scales.

Methods: To address these limitations, this paper proposes AFCNet-an Adaptive Fusion Composite Attention Convolutional Neural Network. AFCNet is designed to improve robustness against noise interference and enhance multi-scale feature fusion for polyp segmentation. The key innovations of AFCNet include: (1) integrating depthwise separable convolution with attention mechanisms in a multi-branch architecture. This allows for the simultaneous extraction of fine details and salient features. (2) Constructing a dynamic multi-scale feature pyramid with learnable weight allocation for adaptive cross-scale fusion.

Results: Extensive experiments on five public datasets (ClinicDB, Kvasir-SEG, etc.) demonstrate that AFCNet achieves state-of-the-art performance, with improvements of up to 3.73 $\%$ in Dice coefficient and 4.62 $\%$ in IoU, validating its effectiveness and generalization capability in polyp segmentation tasks.

Conclusion: AFCNet is a novel polyp segmentation network that leverages convolutional attention and adaptive multi-scale feature fusion, delivering exceptional generalization and adaptability.

Background: Evidence on the association between the PPARGC1A Gly482Ser (rs8192678) polymorphism and elite athlete status is inconsistent, and a prior meta-analysis has used a genotype-merging approach that may bias results.

Objective: This systematic review and meta-analysis aimed to clarify the association between the PPARGC1A Gly482Ser (rs8192678) polymorphism and elite endurance and power athlete status.

Methods: A comprehensive literature search was conducted in PubMed, Web of Science, Embase, and Cochrane Library from inception to November 2025. Studies were included if they provided genotype frequency data for the PPARGC1A Gly482Ser polymorphism in elite endurance or power athletes and non-athlete controls. Fixed or random-effects models were used to calculate odds ratios (OR) with 95% confidence intervals (95% CI), and heterogeneity was assessed using the I ² statistic.

Results: 21 studies involving 5,795 athletes and 9,048 non-athlete controls were included. Compared with non-athlete controls, a higher frequency of the Gly/Gly genotype was observed in Caucasian endurance athletes (OR 1.19; 95% CI 1.08-1.31; p < 0.001) and Caucasian power athletes (OR 1.30; 95% CI 1.17-1.44; p < 0.001). In Asians, no significant difference in the frequency of the Gly/Gly genotype was observed between endurance athletes and controls (OR 0.92; 95% CI 0.71-1.19; p = 0.523), whereas a lower frequency was observed in Asian power athletes (OR 0.69; 95% CI 0.53-0.90; p = 0.007).

Conclusion: Our findings demonstrate that the Gly/Gly genotype of the PPARGC1A Gly482Ser polymorphism was associated with an increased likelihood of achieving elite athlete status in Caucasians, suggesting its potential as a genetic marker for athletic talent identification in this population. In Asians, no significant association was observed between the PPARGC1A Gly482Ser polymorphism and elite endurance athlete status, whereas the Gly/Gly genotype is associated with a lower likelihood of achieving elite power athlete status.

Systematic review registration: identifier CRD420251148245.

Purpose: This study employed kinematic and kinetic testing to analyze the sport-specific parameters of the skeleton start, thereby elucidating its technical characteristics and establishing an empirical basis for training.

Methods: Spatiotemporal parameters were captured using a 3D motion system, while ground reaction forces, impulses, and plantar pressure distribution were collected via a Ki-Sprint force platform and custom pressure sensors. Statistical analysis employed descriptive statistics, two-way ANOVA to evaluate factor effects, and appropriate parametric or non-parametric tests for group comparisons.

Results: Athletes' average starting distance was 18.45 ± 2.09 m, achieved in 12.20 ± 1.11 steps, with no gender difference. Starting speed (male: 6.97 ± 0.42 m/s, female: 6.25 ± 0.58 m/s) and acceleration range (male: 3.31-6.26 m/s², female: 2.14-5.96 m/s²) differed significantly by gender. Step length differed between push-off (1.60 ± 0.14 m) and follow-up steps (2.09 ± 0.18 m), and between inner (2.60 ± 0.14 m, 0.44 ± 0.03 s) and outer steps (2.64 ± 0.13 m, 0.45 ± 0.03 s) in both length and duration. Take-off (2.71 ± 0.50 m) and preceding step (2.81 ± 0.58 m) lengths did not differ. The maximum horizontal force was 826.99 ± 217.18 N and average horizontal impulse was 264.43 ± 67.64 N·s, neither correlating with front-rear foot spacing. Average plantar pressure was higher during run-up (1.77 ± 0.76 kg/cm²) than take-off (1.19 ± 0.59 kg/cm²).

Conclusion: The skeleton start is characterized by periodic speed-power movements akin to a hybrid of sprint acceleration and diving. Training should integrate regular sprints, specialized push simulations, and downhill sprinting to improve acceleration and maximal speed. Core stability, lower-limb maximal strength, and multi-joint power training should be implemented with consideration for gender-specific adaptations.

Introduction: Adipogenesis is an essential process for energy storage, hormone regulation, and overall metabolic health. Previous work showed that impaired adipogenesis plays an important role in the development of obesity-associated insulin resistance. This project investigates the role of impaired adipogenesis in the development of insulin resistance among non-obese (lean/overweight) individuals under physiological and pathological microenvironments.

Methods: Subcutaneous adipose tissue samples were obtained from insulin-sensitive and insulin-resistant non-obese cohorts undergoing maxillofacial or body contouring surgeries. Preadipocytes were isolated and examined for proliferation and adipogenic capacity, insulin signaling, and inflammatory markers. These assessments were conducted under basal conditions and following treatment with either tumor necrosis factor alpha (TNF-α) to induce insulin resistance or metformin to promote insulin sensitivity.

Results: Insulin-resistant participants, in comparison to insulin-sensitive counterparts, showed lower adipogenic capacity, higher susceptibility to the anti-adipogenic and pro-inflammatory effect of TNF-α potentially due to hyperphosphorylation of insulin receptor substrate-1.

Discussion: This highlights the role of impaired adipogenesis in the pathogenesis of insulin resistance among non-obese individuals. Further research is needed to understand the impact of impaired adipogenesis and the potential therapeutic interventions targeting adipogenesis to improve insulin sensitivity in non-obese individuals.

Cold stress is the therapeutic paradox of cardiovascular medicine: both an established environmental trigger of acute death and a physiological stimulus for powerful adaptation. In this review, we address this paradox critically. The response to cold challenge, which ranges from sympathetic activation and hemodynamic stress to adaptive brown adipose tissue recruitment and cardiac metabolic remodeling, which can be pathological or protective. We synthesize evidence from specific cardiovascular diseases, such as coronary disease and heart failure, and summarize molecular pathways of metabolic, inflammatory, and electrophysiological effects. Native adaptive mechanisms and their therapeutic potential as templates are also discussed. Through synthesis of these multi-faceted avenues, this article builds upon a theoretical basis to propose a mechanistic model for the seasonal regulation of CVD and to outline emerging, cold-based research avenues.

Background: Heart rate variability (HRV) is a non-invasive indicator of autonomic nervous system function and is increasingly used in athlete monitoring. While electrocardiography (ECG) is the gold standard for HRV measurement, its use is limited in field settings.

Objective: To evaluate the intra-session reliability and concurrent validity of a smartphone-based PPG app for HRV measurement in athletes, compared to a Polar H10 chest strap and ECG.

Methods: This observational study included 37 trained participants (17 female; mean age 21.95 ± 3.69 years). HRV was recorded concurrently via ECG, Polar H10 chest strap, and the CameraHRV smartphone app in two repeated trials on the same day. Data were processed using device-specific software. Intra-class correlation coefficients (ICC), coefficient of variation (CV%), mean absolute percentage error (MAPE), and Bland-Altman plots were used to assess reliability and agreement.

Results: All three devices showed good-to-excellent intra-session reliability for RMSSD (ICC range 0.83-0.90) and pNN50 (ICC range 0.87-0.92). The Polar chest strap had the highest consistency and lowest error compared to ECG (RMSSD MAPE: 2.16%). The PPG app also demonstrated strong validity (RMSSD MAPE: 17.49%) but wider limits of agreement.

Conclusion: Both the Polar chest strap and smartphone PPG app demonstrated acceptable reliability and validity for short-duration HRV assessment in athletes. While the chest strap outperformed the PPG app in precision, the PPG app may offers a practical, low-cost alternative for athlete monitoring.

Introduction: This study investigated the mechanobiological and neuromuscular effects of three foot-position techniques-flat heel (FH), heel-elevated (HE), and forefoot-elevated (FE)-during front and back squat exercises. Variations in foot positioning were expected to influence muscle activation, joint kinematics, ground reaction forces, and postural stability.

Methods: Twelve resistance-trained male athletes (mean age 23.4 ± 3.8 years; training experience 8.1 ± 2.7 years) performed squats at 70% of their one-repetition maximum (1RM) under each foot-position condition. Surface electromyography (EMG) assessed lower-limb muscle activation, while joint angles and ground reaction forces were collected through synchronized motion-capture and force-platform analyses. Measures included EMG amplitude, joint kinematics, ground reaction forces, and center-of-pressure (COP) displacement.

Results: Quadriceps muscles (vastus lateralis, vastus medialis, rectus femoris) showed significantly greater activation in FH and HE compared with FE (p < 0.001), particularly during the ascent phase. Heel-elevated increased ankle dorsiflexion and squat depth, whereas FE reduced vertical ground reaction forces and shifted mechanical loading toward the posterior chain. No significant differences were observed in COPx or COPy across conditions.

Discussion: Foot-position variations meaningfully altered mechanical load distribution and neuromuscular activation patterns, demonstrating human-scale mechanotransduction. The findings suggest that technique selection should be tailored to individual mobility, joint mechanics, and performance goals to optimize training outcomes and reduce injury risk.

Background/aims: Vitamin D-dependent rickets type 1A is a rare autosomal recessive disorder caused by pathogenic variants in the CYP27B1 gene. CYP27B1 encodes for the 1α-hydroxylase enzyme catalyzing the conversion of 25-hydroxyvitamin D (25(OH)D) to calcitriol, the last step of vitamin D activation. In the Saguenay-Lac-Saint-Jean (SLSJ) region (Quebec, Canada), the CYP27B1 c.262delG variant has a carrier rate of 1 in 27 due to a founder effect. This study aimed to characterize the impact of heterozygosity for the CYP27B1 c.262delG variant on vitamin D metabolites and the phosphocalcic profile.

Methods: Participants from SLSJ were recruited by telephone (n = 36). During an in-person visit, buccal swabs, blood samples, and health and lifestyle information were collected. The CYP27B1 c.262delG variant was genotyped using TaqMan assays on DNA from buccal swabs, and participants were grouped as carriers (heterozygous for the variant) and non-carriers. Student's t-test was applied to compare vitamin D metabolites (25(OH)D and calcitriol), parathormone, alkaline phosphatase (ALP), bone alkaline phosphatase (BAP), ionized calcium, and inorganic phosphorus blood levels between carriers and non-carriers.

Results: Carriers showed significantly higher levels of parathormone, ALP, and BAP compared to non-carriers (p < 0.05). Additionally, 25(OH)D levels were higher in carriers, although the difference did not reach nominal statistical significance (p = 0.056). Calcitriol, ionized calcium, and inorganic phosphorus levels were similar between groups.

Conclusion: Heterozygosity for CYP27B1 c.262delG leads to changes on the vitamin D metabolites and the phosphocalcic profile. How these changes impact the risk of other vitamin D deficiency-associated conditions remain unknown.