New Approaches in Exercise Physiology

Abstract Purpose: Mechanistic evidence from animal models is essential for understanding exercise-induced vascular adaptations, yet the translatability of these findings to clinical settings remains uncertain. This systematic review and meta-analysis quantified the effects of exercise training on endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) levels in animal models. Method: A systematic search of PubMed, Scopus, Web of Science, and Cochrane Library (January 2000–September 2025) was done. The review protocol was registered with PROSPERO (CRD420251144669). A random-effects model (REML) was used for meta-analysis, and SYRCLE's Risk of Bias tool assessed study quality.
Results: Exercise training significantly increased eNOS levels (SMD = 0.99, 95% CI: 0.55–1.44, p < 0.001). In contrast, no significant effects were observed for NO (SMD = −1.26, 95% CI: −2.89–0.37, p = 0.13). Subgroup analyses showed that longer exercise duration (≥5 weeks; SMD = 2.25, p < 0.001) and specific modalities such as treadmill running (SMD = 1.92) and swimming (SMD = 4.59) were associated with substantially greater eNOS upregulation. Considerable heterogeneity was observed across most outcomes (I² > 85%). Conclusion: Exercise training effectively upregulates eNOS expression in animal models, particularly with interventions lasting five weeks or longer and with structured modalities like treadmill and swimming. However, the absence of significant effects on NO level, despite increased eNOS, reveals a translational gap that warrants further mechanistic investigation.

Abstract Background: Sleep quality is a key determinant of physical recovery, cognitive performance, and overall health. High-intensity interval training (HIIT) has emerged as a time-efficient exercise strategy with potential benefits for sleep regulation; however, the physiological mechanisms underlying these effects remain incompletely understood.

Objective: This narrative review aimed to critically evaluate the current evidence regarding the role of HIIT in sleep quality regulation, with particular emphasis on inflammation, circadian rhythms, and the gut-brain axis.

Methods: Literature published between 2000 and 2026 was identified through searches of PubMed, Scopus, Web of Science, and Google Scholar. Peer-reviewed original studies, randomized controlled trials, observational studies, systematic reviews, meta-analyses, and mechanistic reviews relevant to HIIT, sleep quality, inflammation, circadian biology, autonomic regulation, and the gut-brain axis were synthesized narratively.

Results: The available evidence was interpreted according to direct evidence, indirect physiological associations, and emerging mechanistic hypotheses. Overall, current evidence suggests that HIIT may support sleep quality primarily through improvements in cardiometabolic health, autonomic recovery, inflammatory regulation, and circadian entrainment. Gut-brain axis mechanisms remain biologically plausible but are supported mainly by emerging evidence, and direct causal evidence linking HIIT-induced microbiome adaptations to improvements in sleep quality remains limited.

Conclusion: HIIT appears to be a promising non-pharmacological strategy for improving sleep quality. However, the strength of evidence differs across the proposed mechanisms, and further well-designed longitudinal mechanistic studies integrating objective sleep assessment, inflammatory biomarkers, autonomic monitoring, and microbiome profiling are needed to clarify causal pathways and optimize exercise prescriptions for sleep health.

Abstract Aging induces neurophysiological changes across central and peripheral systems motor unit loss, fiber-type shifts, neuromuscular junction degeneration, and reduced spinal corticospinal excitability leading to declines in strength, power, motor control, and performance. To synthesize mechanisms of age related neuromuscular decline and evaluate how lifelong endurance training, using master athletes as a model, modifies these changes. Narrative review of studies on motor-unit remodeling, reflex pathway adaptations (H reflex, V wave), muscle contractile properties, and central drive in aging and with endurance training, with comparisons between master endurance athletes and sedentary peers. Lifelong endurance training preserves motor unit numbers, sustains spinal reflex excitability, and enhances fatigue resistance and submaximal performance. Nevertheless, it does not fully prevent age related losses in maximal strength, rate of force development, and fast twitch fiber function. These deficits respond best to resistance and power training that recruit high threshold motor units and augment central drive. Endurance training attenuates but does not abolish neuromuscular aging. Master athletes illustrate the protective role of chronic activity. The most effective strategy for functional capacity and fall-risk reduction in older adults is a multimodal program combining endurance with resistance, power, and neuromotor training to preserve strength, speed, and control.

Abstract Background: Previous research has reported an inverse association between the second-to-fourth digit ratio(2D:4D), a putative marker of prenatal androgen exposure, and physical fitness and athletic performance. However, the linearity of this relationship and the potential mediating roles of body composition and physical activity remain poorly understood in male youth.
Purpose:This study investigated the association between 2D:4D ratio and physical fitness in boys, while examining whether age, biological maturity, lean mass, and physical activity mediate this relationship.
Methods:A cross-sectional study was conducted in 218 healthy-boys aged 9–17 years. Participants underwent assessment of left- and right-hand 2D:4D ratios, physical activity, body composition (BMI and fat-free mass), and physical fitness components, including speed, agility, flexibility, and muscular strength. Pearson's correlation, curve estimation, stepwise multiple linear regression, and Sobel's test were used for statistical analyses(p