Experimental Physiology最新文献

Prolonged exposure to microgravity, simulated via 6° head-down tilt bed rest (HDT), induces musculoskeletal deconditioning and negatively impacts body composition. This study evaluated whether a combination of aerobic exercise with artificial gravity (AG) offers superior protection in comparison to exercise alone. Twenty-four healthy male participants completed 60 days of HDT, randomized into control (C), exercise-only (EX) and exercise with AG (EX-AG) groups. Muscle volume, intramuscular fat, body composition and isokinetic strength were assessed via whole-body MRI and isokinetic dynamometry. All groups experienced thigh fat-free muscle volume loss: C (10.5% ± 2.6%), EX (6.9% ± 2.4%) and EX-AG (4.3% ± 2.4%), with EX-AG showing significantly less atrophy than C (p < 0.001). Compared with C, EX-AG preserved more muscle in both anterior (p  <  0.001) and posterior (p < 0.05) compartments, whilst EX preserved more muscle only anteriorly (p < 0.05). The fat ratio increased more in C (8.9% ± 6.0%) compared with EX-AG (-0.8% ± 3.8%; p < 0.05) but not EX (6.5% ± 9.8%). Muscle fat infiltration increased across all groups (C, 7.0% ± 3.7%; EX, 6.2% ± 4.3%; EX-AG, 3.1% ± 4.7%) but was not different between groups (p > 0.05). Maximal isokinetic torque decreased in all groups over all measured angular velocities but was not different between groups (p > 0.05). This is the first study to investigate the combination of AG and exercise as a countermeasure to body composition changes induced by long-term bed rest. We showed that EX-AG provided partial protection against muscle atrophy and fat accumulation but did not outperform exercise alone in preserving muscle quality, strength or overall body composition.

Anorexia nervosa (AN) is a psychiatric disorder characterized by prolonged caloric restriction and skeletal muscle atrophy. Mitochondrial health is a key mediator of muscle function, yet the role of mitochondria during AN and following weight regain has not been investigated. The objective of this study was to evaluate mitochondrial capacities and quality control mechanisms in a rodent model of AN, spanning the acute underweight phase and multiple recovery periods. Through a series of experiments, 8-week-old female Sprague-Dawley rats underwent a 30-day simulated AN protocol, followed by different durations of weight recovery via ad libitum feeding. Following designated interventions, muscle performance on a submaximal fatiguing protocol and components of mitochondrial function were evaluated. AN resulted in 23%-25% lower muscle performance compared to healthy controls, and these alterations remained even after short-term weight gain. AN rats had 23% lower contribution of complex I to maximal mitochondrial electron transfer as well as alterations to genes important for mitochondrial translation and dynamics, many of which were not resolved with short-term recovery. With long-term recovery, muscle performance and mRNA content of genes related to mitochondrial translation were similar to healthy controls. However, genes related to mitochondrial fission were greater than healthy controls. AN results in reduced muscle performance during a fatiguing protocol, reliance on mitochondrial complex I and genes related to mitochondrial quality control. Many alterations persist with short-term weight recovery; however, given sufficient time, many facets of mitochondrial health appear to normalize following AN, though there still may be long-term consequences to mitochondrial dynamics.

Biological sex influences exercise performance, largely owing to anatomical and physiological differences in brain areas involved in cognitive motor control and in respiratory and locomotor muscles related to workload. We used near-infrared spectroscopy data to examine sex differences in haemodynamic responses and oxygenation patterns in the prefrontal cortex (PFC), m. intercostales and m. vastus lateralis during incremental exercise in 74 endurance-trained individuals. Changes (Δ) in oxyhaemoglobin (O₂-Hb), deoxyhaemoglobin (H-Hb) and tissue saturation index (TSI) were analysed using a two-way ANOVA with the factors 'sex' and 'intensity'. Effect sizes (ES) were also reported by partial eta squared (η_p ²). Interactions were observed for ΔO₂-Hb at the PFC [p < 0.001, η_p ² = 0.42 (large ES)] and m. intercostales [p < 0.001, η_p ² = 0.38 (large ES)], but not at m. vastus lateralis (p = 0.160). For ΔH-Hb, interactions were observed at m. vastus lateralis [p < 0.001, η_p ² = 0.35 (large ES)] and the PFC [p = 0.048, η_p ² = 0.18 (large ES)]. The ΔTSI also showed an interaction at m. vastus lateralis [p < 0.001, η_p ² = 0.44 (large ES)] and a trend in the m. intercostales (p = 0.057). Male subjects demonstrated greater oxygen delivery to the brain and increased peripheral deoxygenation, whereas females exhibited greater oxygen extraction in respiratory muscles, despite smaller body surface area. Higher tissue oxygen extraction reflects the capacity to meet local metabolic demands during exercise, enabling the identification of distinct oxygenation patterns between sexes. These findings suggest that sex-specific mechanisms contribute to different patterns of physiological response to exercise. We support the hypothesis that peripheral factors might be more limiting in males, whereas in females central limitations (such as potential reduced oxygen delivery to the PFC owing to possible cerebral vasoconstriction triggered by metabolic reflexes) might play a more prominent role.

There is a lack of consensus on optimal timing to assess redox biomarkers post-exercise, limiting methodological standardisation and linking oxidative stress to physiology. We determined optimal post-exercise oxidative stress assessment times using three redox biomarkers: glutathione, F₂-isoprostanes and protein carbonyls. Standardised mean differences were calculated using random-effects models, with 95% confidence and prediction intervals. Risk of bias was assessed via RoB2 and ROBINS-I tools. Egger's test and funnel plots evaluated publication bias. Certainty of evidence was rated using GRADE. PROSPERO preregistration: CRD42024508049. A total of 103 studies (n = 1418) were included. Glutathione levels decreased immediately (g = -0.70; 95% CI: -0.96, -0.44; P < 0.001), at 30 min to 2 h (g = -0.81; 95% CI: -1.19, -0.43; P < 0.001), and 48 h post-exercise (g = -0.98; 95% CI: -1.50, -0.46; P < 0.01). F₂-isoprostanes increased immediately post-exercise (g = 1.01; 95% CI: 0.70, 1.33; P < 0.001) and at 30 min to 2 h (g = 0.46; 95% CI: 0.23, 0.69; P < 0.001). Protein carbonyls increased at all time points, especially at 48 h post-exercise (g = 1.17; 95% CI: 0.73, 1.60; P < 0.001), peaking at 72 h (g = 1.33; 95% CI: 0.52, 2.14; P = 0.0048). Subgroup analyses revealed that non-muscle-damaging exercise elicits responses immediately after exercise or within the first 2 h, while muscle-damaging exercise induces peaks at 48 and 72 h post-exercise. Egger's test indicated publication bias for F₂-isoprostanes (P = 0.017) and protein carbonyls (P = 0.031) post-exercise. Risk of bias was moderate in randomised controlled trials and serious in non-randomised studies. Certainty of evidence ranged from moderate to high. In conclusion, non-muscle-damaging exercise elicits early responses within hours, while muscle-damaging protocols produce delayed peaks at 48-72 h. These findings support methodological consistency and are useful for optimising study design, sample size estimation and providing links between redox biology and physiological outcomes.

Kenyan athletes have dominated competitive middle- and long-distance running for more than half a century, a phenomenon suggested to be attributable, at least in part, to superior running economy. Given that lower-leg anthropometry is an important determinant of running economy, a key contributor to the athletic performance of Kenyan runners is thought to be slender lower legs. Running economy and lower-leg anthropometrics, including relative lower-leg length and mean lower-leg thickness, were measured in adult middle- to long-distance runners, including 12 Kenyan elite and 29 sub-elite runners, and 20 Danish elite and 37 sub-elite runners. Additionally, 46 untrained Kenyan and 30 untrained Danish adolescents were included. Among adult runners, the oxygen cost of running was 33.61 mL kg^-0.75 km^-1 lower in Kenyans compared with Danes [95% confidence interval (CI): 18.63, 48.59; p < 0.0001] and increased by 2.20 mL kg^-0.75 km^-1 per centimetre squared increase in lower-leg cross-sectional area (95% CI: 1.03, 3.37; p = 0.0005). In untrained adolescents, the oxygen cost of running was 44.82 mL kg^-0.75 km^-1 lower (95% CI: 21.99, 67.64; p = 0.0002) and increased by 1.75 mL kg^-0.75 km^-1 per centimetre squared increase in lower-leg cross-sectional area (95% CI: 0.18, 3.32; p = 0.0294). Slender lower legs are favourably associated with superior running economy and might contribute to the dominance of Kenyan athletes in competitive middle- to long-distance running.

Carbohydrate supplementation optimises athletic performance, but the metabolic and performance impacts of commercial products/compositions are underexplored. We compared the efficacy of three commercial carbohydrate supplements: a glucose-fructose bar (GF-Bar), a glucose-fructose hydrogel (GF-Gel) and a maltodextrin-based gel (MD-Gel). Antegrade venous blood samples for glucose and insulin were measured alongside substrate utilisation in healthy Tier 2 athletes after ingesting 45 g of carbohydrates from the GF-Bar, GF-Gel and MD-Gel during a modified 1-h oral glucose tolerance test (OGTT). Additionally, the effect of supplementation on high-intensity interval exercise was evaluated during repeated maximal sprint performance. During the OGTT, the GF-Bar elicited greater total carbohydrate oxidation than MD-Gel (24.6 ± 7.4 g vs. 17.8 ± 8.6 g, P = 0.038) but not GF-Gel (20.1 ± 6.4 g, P > 0.05). Carbohydrate oxidation per minute varied over time (P < 0.001) and between products (P = 0.043), with GF-Bar (0.27 ± 0.05 g min^-1) showing higher oxidation than GF-Gel (0.21 ± 0.05 g min^-1) and MD-Gel (0.19 ± 0.06 g min^-1). No differences were observed in glucose peak, time to peak glucose or insulin concentration (P > 0.05). Peak power (P = 0.011), mean power (P < 0.001) and total work varied across sprints (P < 0.001) but not between products (P > 0.05). Perceived exertion and gastrointestinal discomfort were similar between products (P > 0.05). Despite differences in carbohydrate oxidation during the OGTT, the GF-Bar, GF-Gel and MD-Gel displayed similar metabolic and sprint performance outcomes, suggesting that, within this study, carbohydrate formulation did not impact short-duration maximal exercise.

Even among healthy individuals, arterial blood pressure (ABP) responses to exercise vary widely. However, the mechanisms underlying this individual variability remain unclear. To investigate these mechanisms, 29 participants performed isometric handgrip exercise at 30% of their maximum voluntary contraction, followed by postexercise muscle ischaemia to assess metaboreflex activity. The systolic blood pressure response to exercise was not significantly correlated with arterial stiffness (carotid-femoral pulse wave velocity, p = 0.999, β = 0.000), peak oxygen uptake (p = 0.224, β = 0.168) or muscle oxidative capacity (p = 0.829, β = -0.049). In contrast, individual variability in systolic blood pressure was significantly associated with variability in heart rate during exercise (p = 0.013, β = 0.360) and the change in mean arterial pressure during postexercise muscle ischaemia (p = 0.014, β = 0.692). These findings suggest that peripheral characteristics are not primary determinants of individual differences in ABP responses to exercise in healthy young adults. Instead, variability in ABP responses might be more strongly influenced by individual differences in autonomic function. This pattern contrasts with the mechanisms underlying exaggerated ABP responses commonly observed in older adults and individuals with hypertension.

Fitness is essential to military personnel in general, especially in the special operations forces (SOF), where the demanding tasks require a high level of physical fitness and mental robustness. However, little research has been done on SOF to characterise the putative underlying cardiopulmonary adaptations that distinguish them from conventional infantry soldiers (INF). This study aims to evaluate the cardiopulmonary function in SOF compared INF. The study assessed cardiac function and dimension using transthoracic echocardiography obtained at rest in eight soldiers from a SOF unit and in eight INF. ${\dot{V}}_{O_2\max }$ was measured by direct calorimetry (secondary outcome) at the same time blood samples were collected to measure lactate levels. Lung function was assessed by spirometry, while the haemoglobin-corrected pulmonary diffusing capacity for carbon monoxide (D_L,COc) was examined by the single-breath technique. SOF had higher stroke volume (mean difference = 21 mL, P < 0.001) and left ventricular ejection fraction (mean difference = 7%, P = 0.026) than INF. Furthermore, SOF had higher global constructive myocardial work and global work index compared to INF. ${\dot{V}}_{O_2\max }$ as percentage of predicted according to age, weight and sex was higher in SOF, and they also had lower lactate levels during the ${\dot{V}}_{O_2\max }$ test than INF (P = 0.029). None of the measured lung function metrics differed between groups. In conclusion, when compared to conventional infantry soldiers, SOF soldiers had marked cardiac adaptations with evidence of eccentric LV remodelling. It remains to be determined if this reflects different training regimes or selection.

Context-dependent sensory processing within the predictive coding framework relies on detecting mismatches between incoming stimuli and internal predictive models. Sensory deviants elicit prediction errors, seen as enhanced neural responses, that update these models and influence attention and behaviour. Although prediction errors have been widely observed across brain regions, the downstream processes remain poorly understood. In this study, we recorded electrocorticography in five urethane-anaesthetised rats and identified cortical slow oscillations, characterised by spontaneous transitions between 'Up' and 'Down' states. Deviant stimuli in an auditory oddball paradigm evoked an initial positive prediction error, followed by a prolonged, all-or-nothing response which spread in a travelling wave across the cortex. Identified as putative evoked cortical Up states, these responses were not evoked by standards, omissions or a many-standards control. Up states following deviants occurred more recently after a previous Up state when compared to spontaneous Up states. In preliminary data from an awake rat, long-latency Up states were not present spontaneously or evoked. In a different rat, anaesthetic depth was key to spontaneous and evoked Up states, with more robust Up/Down states and more reliable triggering of Up states under deeper anaesthesia. These results suggest that sensory deviants may cause shifts in cortical state under anaesthesia, explaining the long-latency mismatch response under anaesthesia and sleep.

Consumption of a high-sugar mixed meal (HSMM) increases both glucose and insulin and elicits mixed vascular effects, with reduced microvascular blood flow but increased conduit artery diameter and blood flow. In this study, we sought to examine: (1) whether an HSMM elicits vascular segment-specific effects within cerebrovasculature; and (2) whether these responses differ between young healthy adults and middle-aged adults with cardiometabolic disease (CMD) risk factors. Twenty-one young, healthy adults (ages 18-39 years; 24 ± 6 years) and 20 middle-aged adults (ages 40-65 years; 55 ± 5 years) with CMD risk factors (hypertension, obesity or dyslipidaemia) underwent cerebrovascular assessments before and at 30 and 60 min after a 930 kcal HSMM. Carotid and aortic stiffness and carotid artery characteristic impedance were assessed via ultrasound and tonometry. Middle cerebral artery mean velocity, pulsatility index and resistive index were assessed via transcranial Doppler. In comparison to baseline, common carotid artery diameter increased while stiffness decreased, contributing to a decrease in carotid artery characteristic impedance in both groups following the HSMM (p < 0.05). In comparison to baseline, middle cerebral artery mean velocity, pulsatility index and resistive index increased only in young adults (p < 0.05) following the HSMM. Differential increases in cerebral pulsatility among young adults compared with middle-aged adults with CMD risk factors might reflect modest differences in upstream, extracranial artery pulsatile transmission following an HSMM, along with simultaneous, complex intracranial cerebrovascular responses that require further interrogation. Cumulatively, these data suggest that: (1) the cerebrovascular response to an HSMM might differ between segments of the extra- versus intracranial cerebrovasculature; and (2) middle-aged adults with CMD risk factors might have altered cerebrovascular responsiveness to an HSMM compared with young, healthy adults.