Journal of applied physiology最新文献

{"title":"Comparing the efficacy of different climate indices for prediction of labor loss, body temperatures, and thermal perception in a wide variety of warm and hot climates.","authors":"George Havenith, James W Smallcombe, Simon Hodder, Ollie Jay, Josh Foster","doi":"10.1152/japplphysiol.00613.2023","DOIUrl":"10.1152/japplphysiol.00613.2023","url":null,"abstract":"<p><p>The purpose of this study was to investigate which climate/heat indices perform best in predicting heat-induced loss of physical work capacity (PWC_loss). Integrating data from earlier studies, data from 982 exposures (75 conditions) exercising at a fixed cardiovascular load of 130 beats·min^-1, in varying temperatures (15-50°C), humidities (20-80%), solar radiation (0-800 W·m^-2), wind (0.2-3.5 m·s^-1), and two clothing levels, were used to model the predictive power of ambient temperature, universal thermal climate index (UTCI), wet bulb globe temperature (WBGT), modified physiologically equivalent temperature (mPET), heat index, apparent temperature (AT), and wet bulb temperature (T_wb) for the calculation of PWC_loss, skin temperature (T_skin) and core-to-skin temperature gradient, and thermal perception (thermal sensation vote, TSV) in the heat. <i>R</i>², RMSE, and Akaike information criterion were used indicating model performance. Indices not including wind/radiation in their calculation (T_a, heat index, AT, and T_wb) struggled to provide consistent predictions across variables. For PWC_loss and TSV, UTCI and WBGT had the highest predictive power. For T_skin, and core-to-skin temperature gradient, the physiological models UTCI and mPET worked best in seminude conditions, but clothed, AT, WBGT, and UTCI worked best. For all index predictions, T_a, vapor pressure, and T_wb were shown to be the worst heat strain predictors. Although UTCI and WBGT had similar model performance using the full dataset, WBGT did not work appropriately in windy, hot-dry, conditions where WBGT predicted lower strain due to wind, whereas the empirical data, UTCI and mPET indicated that wind in fact increased the overall level of thermal strain. The findings of the current study highlight the advantages of using a physiological model-based index like UTCI when evaluating heat stress in dynamic thermal environments.<b>NEW & NOTEWORTHY</b> There is an urgent need to determine the optimal heat stress metric when forecasting the impact of heat stress on human performance, physiological stress, and perception. We analyzed a wealth of laboratory data, simulating heart rate (HR)-paced work with wide variations in air temperature, humidity, wind speed, solar radiation, and clothing. We conclude that the universal thermal climate index (UTCI) [followed by wet-bulb globe temperature (WBGT)] is the optimal heat index to reliably predict reductions in performance, and elevations in physiological and perceptual stress.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141310797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The impact of exercise training on muscle sympathetic nerve activity: a systematic review and meta-analysis.","authors":"Sarah E Meyer, Miranda Kimber, Lauren E Maier, Brittany Matenchuk, Ramiah Moldenhauer, Stephanie de Waal, Allison Sivak, Margie H Davenport, Craig 'd Steinback","doi":"10.1152/japplphysiol.00060.2024","DOIUrl":"10.1152/japplphysiol.00060.2024","url":null,"abstract":"<p><p>The purpose of this systematic review and meta-analysis was to examine the effects of exercise training on muscle sympathetic nerve activity (MSNA) in humans. Studies included exercise interventions [randomized controlled trials (RCTs), nonrandomized controlled trials (non-RCTs), or pre-to-post intervention] that reported on adults (≥18 yr) where MSNA was directly assessed using microneurography, and relevant outcomes were assessed [MSNA (total activity, burst frequency, burst incidence, amplitude), heart rate, blood pressure (systolic blood pressure, diastolic blood pressure, or mean blood pressure), and aerobic capacity (maximal or peak oxygen consumption)]. Forty intervention studies (<i>n</i> = 1,253 individuals) were included. RCTs of exercise compared with no exercise illustrated that those randomized to the exercise intervention had a significant reduction in MSNA burst frequency and incidence compared with controls. This reduction in burst frequency was not different between individuals with cardiovascular disease compared with those without. However, the reduction in burst incidence was greater in those with cardiovascular disease [9 RCTs studies, <i>n</i> = 234, mean difference (MD) -21.08 bursts/100 hbs; 95% confidence interval (CI) -16.51, -25.66; <i>I</i>² = 63%] compared with those without (6 RCTs, <i>n</i> = 192, MD -10.92 bursts/100 hbs; 95% CI -4.12, -17.73; <i>I</i>² = 76%). Meta-regression analyses demonstrated a dose-response relationship where individuals with higher burst frequency and incidence preintervention had a greater reduction in values post-intervention. These findings suggest that exercise training reduces muscle sympathetic nerve activity, which may be valuable for improving cardiovascular health.<b>NEW & NOTEWORTHY</b> This systematic review and meta-analysis suggests exercise training reduces muscle sympathetic nerve activity (MSNA), which may be valuable for improving cardiovascular health. The reduction in burst incidence was greater among individuals with cardiovascular disease when compared with those without; exercise training may be particularly beneficial for individuals with cardiovascular disease. Meta-regression analyses demonstrated a dose-response relationship, where individuals with higher sympathetic activity preintervention had greater reductions in sympathetic activity post-intervention.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140944651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Changes in hypoxic and hypercapnic ventilatory responses at high altitude measured using rebreathing methods.","authors":"Shyleen Frost, Kathy Pham, Nikhil Puvvula, Britney Oeung, Erica C Heinrich","doi":"10.1152/japplphysiol.00128.2024","DOIUrl":"10.1152/japplphysiol.00128.2024","url":null,"abstract":"<p><p>Ventilatory responses to hypoxia and hypercapnia play a vital role in maintaining gas exchange homeostasis and in adaptation to high-altitude environments. This study investigates the mechanisms underlying sensitization of hypoxic and hypercapnic ventilatory response (HVR and HCVR, respectively) in individuals acclimatized to moderate high altitude (3,800 m). Thirty-one participants underwent chemoreflex testing using the Duffin-modified rebreathing technique. Measures were taken at sea level and after 2 days of acclimatization to high altitude. Ventilatory recruitment threshold (VRT), HCVR-Hyperoxia, HCVR-Hypoxia, and HVR were quantified. Acclimatization to high altitude resulted in increased HVR (<i>P</i> < 0.001) and HCVR-Hyperoxia (<i>P</i> < 0.001), as expected. We also observed that the decrease in VRT under hypoxic test conditions significantly contributed to the elevated HVR at high altitude since the change in VRT across hyperoxic and hypoxic test conditions was greater at high altitudes compared to baseline sea-level tests (<i>P</i> = 0.043). Pre-VRT, or basal, ventilation also increased at high altitudes (<i>P</i> < 0.001), but the change did not differ between oxygen conditions. Taken together, these data suggest that the increase in HVR at high altitude is at least partially driven by a larger decrease in the VRT in hypoxia versus hyperoxia at high altitude compared to sea level. This study highlights the intricacies of respiratory adaptations during acclimatization to moderate high altitude, shedding light on the roles of the VRT, baseline respiratory drive, and two-slope HCVR in this process. These findings contribute to our understanding of how human respiratory control responds to hypoxic and hypercapnic challenges at high altitude.<b>NEW & NOTEWORTHY</b> We report the first measurements of the hypoxic ventilatory response (HVR) after 2 days at high altitude using a CO₂ rebreathing technique. We evaluated mechanisms by which the HVR becomes elevated with acclimatization (increased hypercapnic ventilatory response sensitivity in hypoxia, increased baseline respiratory drive in hypoxia, or lower ventilatory recruitment thresholds in hypoxia). For the first time, we report that decreases in the ventilatory recruitment threshold in hypoxia contribute to elevated HVR at high altitude.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141081626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Similar endothelium-dependent vascular responses to intermittent hypoxia in young and older adults.","authors":"Sten Stray-Gundersen, Frank Wojan, Hirofumi Tanaka, Sophie Lalande","doi":"10.1152/japplphysiol.00823.2023","DOIUrl":"10.1152/japplphysiol.00823.2023","url":null,"abstract":"<p><p>Aging is associated with vascular endothelial dysfunction observed through a progressive loss of flow-mediated dilation caused partly by a decreased nitric oxide bioavailability. Intermittent hypoxia, consisting of alternating short bouts of breathing hypoxic and normoxic air, was reported to either maintain or improve vascular function in young adults. The aim of this study was to determine the impact of age on the vascular response to intermittent hypoxia. Twelve young adults and 11 older adults visited the laboratory on two occasions. Plasma nitrate concentrations and brachial artery flow-mediated dilation were assessed before and after exposure to either intermittent hypoxia or a sham protocol. Intermittent hypoxia consisted of eight 4-min hypoxic cycles at a targeted oxygen saturation of 80% interspersed with breathing room air to resaturation, and the sham protocol consisted of eight 4-min normoxic cycles interspersed with breathing room air. Vascular responses were assessed during intermittent hypoxia and the sham protocol. Intermittent hypoxia elicited a brachial artery vasodilation but did not change brachial artery shear rate in both young and older adults. Plasma nitrate concentrations were not significantly affected by intermittent hypoxia compared with the sham protocol in both groups. Brachial artery flow-mediated dilation was not acutely affected by intermittent hypoxia or the sham protocol in either young or older adults. In conclusion, the brachial artery vasodilatory response to intermittent hypoxia was not influenced by age. Intermittent hypoxia increased brachial artery diameter but did not acutely affect endothelium-dependent vasodilation in young or older adults.<b>NEW & NOTEWORTHY</b> The objective of this study was to determine the impact of age on the vascular response to intermittent hypoxia. Eight 4-min bouts of hypoxia at a targeted oxygen saturation of 80% induced a brachial artery vasodilation in both young and older adults, indicating that age does not influence the vasodilatory response to intermittent hypoxia. Intermittent hypoxia did not acutely affect brachial artery flow-mediated dilation in young or older adults.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141457092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Continuous measurements of respiratory muscle blood flow and oxygen consumption using noninvasive frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy.","authors":"Antenor Rodrigues, Kazuya Shingai, Carlos A Gómez, Peter Rassam, Dmitry Rozenberg, Ewan Goligher, Laurent Brochard, Darren Roblyer, W Darlene Reid","doi":"10.1152/japplphysiol.00871.2023","DOIUrl":"10.1152/japplphysiol.00871.2023","url":null,"abstract":"<p><p>Prior studies of muscle blood flow and muscle-specific oxygen consumption have required invasive injection of dye and magnetic resonance imaging, respectively. Such measures have limited utility for continuous monitoring of the respiratory muscles. Frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS) can provide continuous surrogate measures of blood flow index (BF_i) and metabolic rate of oxygen consumption (MRO₂). This study aimed to validate sternocleidomastoid FD-NIRS & DCS outcomes against electromyography (EMG) and mouth pressure (Pm) during incremental inspiratory threshold loading (ITL). Six female and six male healthy adults (means ± SD; 30 ± 7 yr, maximum inspiratory pressure 118 ± 61 cmH₂O) performed incremental ITL starting at low loads (8 ± 2 cmH₂O) followed by 50-g increments every 2 min until task failure. FD-NIRS & DCS continuously measured sternocleidomastoid oxygenated and deoxygenated hemoglobin + myoglobin (oxy/deoxy[Hb + Mb]), tissue saturation of oxygen (StO₂), BF_i, and MRO₂. Ventilatory parameters including inspiratory Pm were also evaluated. Pm increased during incremental ITL (<i>P</i> < 0.05), reaching -47[-74 to -34] cmH₂O (median [IQR: 25%-75%]) at task failure. Ventilatory parameters were constant throughout ITL (all <i>P</i> > 0.05). Sternocleidomastoid BF_i and MRO₂ increased from the start of the ITL (both <i>P</i> < 0.05). Deoxy[Hb + Mb] increased close to task failure, concomitantly with a constant increase in MRO₂, and decreased StO₂. Sternocleidomastoid deoxy[Hb + Mb], BF_i, StO₂, and MRO₂ obtained during ITL via FD-NIRS & DCS correlated with sternocleidomastoid EMG (all <i>P</i> < 0.05). In healthy adults, FD-NIRS & DCS can provide continuous surrogate measures of respiratory BF_i and MRO₂. Increasing sternocleidomastoid oxygen consumption near task failure was associated with increased oxygen extraction and reduced tissue saturation.<b>NEW & NOTEWORTHY</b> This study introduces a novel approach, frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS), for noninvasive continuous monitoring of respiratory muscle blood flow and metabolic rate of oxygen consumption. Unlike prior methods involving invasive dye injection and magnetic resonance imaging, FD-NIRS & DCS offers the advantage of continuous measurement without the need for invasive procedures. It holds promise for advancing muscle physiology understanding and opens avenues for real-time monitoring of respiratory muscles.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141310798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nicotine exacerbates exertional heat strain in trained men: a randomized, placebo-controlled, double-blind study.","authors":"Nicole E Moyen, Matthew J Barnes, Blake G Perry, Naoto Fujii, Tatsuro Amano, Narihiko Kondo, Toby Mündel","doi":"10.1152/japplphysiol.00403.2024","DOIUrl":"10.1152/japplphysiol.00403.2024","url":null,"abstract":"<p><p>To determine whether using nicotine exacerbates exertional heat strain through an increased metabolic heat production (H_prod) or decreased skin blood flow (SkBF), 10 nicotine-naïve trained males [37 ± 12 yr; peak oxygen consumption (V̇o_2peak): 66 ± 10 mL·min^-1·kg^-1] completed four trials at 20°C and 30°C following overnight transdermal nicotine (7 mg·24 h^-1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% V̇o_2peak) followed by a time trial (∼75% V̇o_2peak) during which measures of gastrointestinal (T_gi) and mean weighted skin ([Formula: see text]_sk) temperatures, SkBF, H_prod, and mean arterial pressure (MAP) were made. The difference in ΔT_gi between nicotine and placebo trials was greater during 30°C (0.4 ± 0.5°C) than 20°C (0.1 ± 0.7°C), with [Formula: see text]_sk higher during nicotine than placebo trials (0.5 ± 0.5°C, <i>P</i> = 0.02). SkBF became progressively lower during nicotine than placebo trials (<i>P</i> = 0.01) and progressively higher during 30°C than 20°C trials (<i>P</i> < 0.01); MAP increased from baseline (<i>P</i> < 0.01) and remained elevated in all trials. The difference in H_prod between 30°C and 20°C trials was lower during nicotine than placebo (<i>P</i> = 0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (<i>P</i> = 0.03). Mean power output during the time trial was lower during 30°C than 20°C trials (24 ± 25 W, <i>P</i> = 0.02), and although no effect of nicotine was observed (<i>P</i> > 0.59), two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for T_gi (40.0°C), whereas the other withdrew due to \"nausea and chills\" (T_gi = 39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.<b>NEW & NOTEWORTHY</b> In naïve participants, acute nicotine use exerts a hyperthermic effect that increases the risk of heat exhaustion during exertional heat strain, which is driven by a blunted skin blood flow response. This has implications for <i>1</i>) populations that face exertional heat strain and demonstrate high nicotine use (e.g., athletes and military, 25%-50%) and <i>2</i>) study design whereby screening and exclusion for nicotine use or standardization of prior use (e.g., overnight abstinence) is encouraged.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141498131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of stimulation frequency on early and late phase rate of torque and velocity development.","authors":"Michael T Paris, Alexander M Zero, Charles L Rice","doi":"10.1152/japplphysiol.00076.2024","DOIUrl":"10.1152/japplphysiol.00076.2024","url":null,"abstract":"<p><p>The early (≤50 ms) rate of torque development (RTD) is dependent upon the speed of neuromuscular activation; however, few studies have evaluated the determinants of rate of velocity development (RVD), which may be load-dependent. The purpose here was to explore the relationship between stimulation frequency with the early and late (≥100 ms) phase isometric RTD and isotonic RVD. The knee extensors of 16 (five female) young recreationally active participants were stimulated using 14 frequencies from 1 to 100 Hz during isometric and isotonic (\"unloaded\" and 7.5% of the isometric maximal voluntary contraction [MVC]) contractions. Isometric RTD and isotonic RVD were evaluated for the early (0-50 ms) and late (0-100 ms) phases from torque and velocity onset, respectively. Sigmoid functions were fit and bilinear regressions were used to examine the slopes of the steep portion of the curve and the plateau frequency. RTD- and RVD-frequency relationships were well described by a sigmoid function (all <i>r</i>² > 0.96). Compared with the late phase, early isometric RTD, and unloaded RVD displayed lower slopes (all <i>P</i> ≤ 0.001) and higher plateau frequencies (all <i>P</i> < 0.001). In contrast, early and late RVD of a moderately loaded isotonic contraction did not display different slopes (<i>P</i> = 0.055) or plateau frequencies (<i>P</i> = 0.690). Early isometric RTD and unloaded isotonic RVD are more dependent on changes in stimulation frequency compared with late phases. However, RVD for a moderately loaded isotonic contraction displayed similar responses for the early and late phases. Therefore, a high frequency of activation is critical for early torque and velocity generation but dependent upon the load for isotonic contractions.<b>NEW & NOTEWORTHY</b> We show that during an \"unloaded\" isotonic contraction, the early phase rate of velocity development is more dependent upon a high electrical activation frequency compared with the late phase, similar to isometric torque. However, early and late phase rates of velocity development of moderately loaded isotonic contractions display similar responses. These results indicate that the determinants of isotonic shortening function are dependent on the externally applied load, highlighting the importance of task-specificity of contraction.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141432044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unlocking the benefit of active stretch: the eccentric muscle action, not the preload, maximizes muscle-tendon unit stretch-shortening cycle performance.","authors":"Tobias Goecking, Denis Holzer, Daniel Hahn, Tobias Siebert, Wolfgang Seiberl","doi":"10.1152/japplphysiol.00809.2023","DOIUrl":"10.1152/japplphysiol.00809.2023","url":null,"abstract":"<p><p>Stretch-shortening cycles (SSCs) outperform shortening contractions preceded by isometric contractions in terms of enhanced force/torque, work, and power production during shortening. This so-called SSC effect is presumably related to the active muscle stretch before shortening in SSCs. However, it remains unclear whether the effects of stretch-induced higher preload level or stretch-induced history dependence maximize the SSC effect. Therefore, we analyzed fascicle behavior, muscle-tendon unit (MTU) shortening work, and torque/force (<i>n</i> = 12 participants) via ultrasound and dynamometry during electrically stimulated submaximal plantar flexion contractions from 10° plantarflexion to 15° dorsiflexion. To elucidate the effects of preload level and preload modality (i.e., contraction type) on shortening performance, muscle-tendon unit shortening was preceded by fixed-end (SHO), active stretch (SSC), and preload-matched fixed-end (MATCHED) contractions. Before shortening, MATCHED and SCC had the same preload level (1% torque difference), similar joint position, and muscle fascicle lengths. Compared with SHO, shortening work was significantly (<i>P</i> < 0.001, partial <i>η</i>² = 0.749) increased by 85% and 55% for SSC and MATCHED, respectively, with SSC shortening work being significantly higher than MATCHED (<i>P</i> = 0.016). This indicates that preload contributes by 65% to the overall SSC effect so that 35% needs to be referred to stretched-induced history-dependent mechanisms. In addition, SSC showed larger fascicle forces at the end of shortening (<i>P</i> < 0.001) and 20% less depressed isometric torque following shortening compared with MATCHED (<i>P</i> < 0.001). As potential decoupling effects by the series elastic element were controlled by matching the preload levels, we conclude that the difference between SSC and MATCHED is related to stretch-induced long-lasting history-dependent effects.<b>NEW & NOTEWORTHY</b> Using a torque-matched preload protocol, we found that 2/3 of the performance enhancement in muscle-tendon unit stretch-shortening cycles (SSCs) is caused by the increased preload level. The remaining 1/3 is owed to the long-lasting history-dependent effects triggered during the stretch in SSCs. This increased performance output is attributed to passive elastic structures within the contractile element that do not require additional muscle activation, therefore contributing to the higher efficiency of the neuromuscular system in SSCs.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141457051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sympathetic baroreflex sensitivity is enhanced in postmenopausal women.","authors":"Shane J McGinty, Evan L Matthews, Jody L Greaney, J Kevin Shoemaker, Megan M Wenner","doi":"10.1152/japplphysiol.00833.2023","DOIUrl":"10.1152/japplphysiol.00833.2023","url":null,"abstract":"<p><p>The sympathetic nervous system is critical for regulating blood pressure (BP) via the arterial baroreflex and sympathetic transduction in the peripheral vasculature. These mechanisms interact, and both may be altered with aging and impacted by menopause. Although age-related decreases in sympathetic transduction have been demonstrated in women, it remains unclear whether sympathetic baroreflex sensitivity (BRS) is impaired in postmenopausal women (POST). We tested the hypothesis that sympathetic BRS would be enhanced in POST compared with premenopausal women (PRE). We examined beat-by-beat BP and muscle sympathetic nerve activity (MSNA) in 19 PRE (22 ± 2 yr, 22 ± 3 kg/m²) and 12 POST (57 ± 5 yr, 24 ± 2 kg/m²) during 10 min of rest. Spontaneous sympathetic BRS was quantified as the slope of a linear regression between MSNA burst incidence and diastolic BP. Sympathetic transduction to mean arterial pressure (MAP) for the 10 cardiac cycles following spontaneous MSNA bursts was assessed via signal averaging method. Resting MAP was similar (PRE: 82 ± 8 vs. POST: 85 ± 8 mmHg, <i>P</i> = 0.43), whereas resting MSNA was elevated in POST (PRE: 10 ± 6 vs. POST: 45 ± 16 bursts/100 heart beats, <i>P</i> < 0.0001). Spontaneous sympathetic BRS was enhanced in POST (PRE: -2.0 ± 1.2 vs. POST: -5.2 ± 1.9 bursts/beat/mmHg, <i>P</i> < 0.0005). Sympathetic transduction to MAP was attenuated in POST (time: <i>P</i> < 0.001, group: <i>P</i> < 0.001, interaction: <i>P</i> < 0.01). These data suggest that sympathetic BRS may be enhanced in POST. Consistent with recent hypotheses, enhanced sensitivity of the arterial baroreflex's neural arc may signify a compensatory response to reduced efficiency of the peripheral arterial baroreflex arc (i.e., sympathetic transduction) to preserve BP buffering capacity.<b>NEW & NOTEWORTHY</b> Studies examining sympathetic baroreflex function with aging remain equivocal, with some studies showing an increase, decrease, or no change in sympathetic baroreflex sensitivity (BRS) in older adults compared with younger adults. With aging, women experience unique physiological changes due to menopause that influence autonomic function. For the first time, we show that postmenopausal women exhibit a greater sympathetic BRS compared with young premenopausal women.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141498132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structure-function in smokers: when a small airways test really reflects the small airways.","authors":"Sylvia Verbanck, Shane Hanon, Jef Vandemeulebroucke, Eef Vanderhelst, Manuel Paiva","doi":"10.1152/japplphysiol.00209.2024","DOIUrl":"10.1152/japplphysiol.00209.2024","url":null,"abstract":"<p><p>If multiple-breath washout (MBW)-derived acinar ventilation heterogeneity (Sacin) really represents peripheral units, the N₂ phase-III of the first MBW exhalation should be curvilinear. This is essentially due to the superposed effect of gas diffusion and convection resulting in an equilibration of N₂ concentrations between neighboring lung units throughout exhalation. We investigated this in smokers with computed tomography (CT)-proven functional small airway disease. Instantaneous N₂-slopes were computed over 40-ms intervals throughout phase-III and normalized by mean phase-III N₂ concentration. N₂ phase-III (concave) curvilinearity was quantified as the rate at which the instantaneous N₂-slope decreases past the phase-II peak over a 1-s interval; for a linear N₂ phase-III unaffected by diffusion, this rate would amount to 0 L^-1/s. N₂ phase-III curvilinearity was obtained on the experimental curves and on existing model simulations of N₂ curves from a normal peripheral lung model and one with missing terminal bronchioles (either 50% or 30% TB left). In 46 smokers [66 (±8) yr; 49 (±26) pack·yr] with CT-based evidence of peripheral lung destruction, instantaneous N₂-slope decrease was compared between those with (f^SAD+f^Emphys) > 20% [-0.26 ± 0.14 (SD) L^-1/s; <i>n</i> = 24] and those with (f^SAD+f^Emphys) < 20% [-0.16 ± 0.12 (SD) L^-1/s; <i>n</i> = 22] (<i>P</i> = 0.014). Experimental values fell in the range predicted by a realistic peripheral lung model with progressive reduction of terminal bronchioles: values of instantaneous N₂-slope decrease obtained from model simulations were -0.09 L^-1/s (normal lung; 100% TB left), -0.17 L^-1/s (normal lung 50% TB left), and -0.29 L^-1/s (30% TB left). In smokers with CT-based evidence of functional small airway alterations, it is possible to demonstrate that Sacin really does represent the most peripheral airspaces.<b>NEW & NOTEWORTHY</b> In smokers with computed tomography-based evidence of functional small airway alterations by parametric response mapping, it is possible to demonstrate that the multiple-breath washout-derived Sacin, an index of acinar ventilation heterogeneity, actually does represent the most peripheral airspaces. This is done by verifying on experimental N₂ washout curves of the first breath, N₂ phase-III concavity predicted by the diffusion-convection interdependence model.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":null,"pages":null},"PeriodicalIF":3.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141620012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}