Journal of applied physiology最新文献

{"title":"Skeletal muscle shape influences joint torque exertion through the mechanical advantages.","authors":"Jun Umehara, Masashi Taniguchi, Masahide Yagi, Ganping Li, Mazen Soufi, Yoshito Otake, Yoshinobu Sato, Yoshihiro Fukumoto, Momoko Yamagata, Ryusuke Nakai, Noriaki Ichihashi","doi":"10.1152/japplphysiol.00997.2024","DOIUrl":"https://doi.org/10.1152/japplphysiol.00997.2024","url":null,"abstract":"<p><p>Skeletal muscle morphology is linked to its function. Extensive literature demonstrates that muscle volume is crucial for determining joint torque exertion, a primary function of muscle. However, whether muscle shape also influences torque exertion capacity remains unclear. This study illustrates that the three-dimensional shape of muscles independently determines joint torque exertion, irrespective of muscle volume, utilizing a statistical shape model designed to quantify muscle shape features. The statistical shape model was developed from magnetic resonance images of the quadriceps femoris muscles in 33 healthy young adults (26 ± 5 years; 18 males). We investigated the association between the shape components of each quadriceps femoris head and isometric knee extensor torque. The findings reveal that the mediolateral curvatures of the rectus femoris (R² = 0.60) and the bulging in distal region of the vastus medialis (R² = 0.65) were associated with increased knee extensor torque despite muscle volumes. Moreover, the rectus femoris and vastus medialis shapes were correlated with the medial-directed line-of-action (r = -0.42 and ρ = -0.36, respectively). The vastus medialis shape was correlated with the moment arm of the patellar lateral spin (ρ = 0.45). Therefore, the three-dimensional muscle shape determines the joint torque exertion by forming the mechanical advantages that balance the force/torque output optimally. Our findings demonstrate that muscle shape is crucial in the mechanical output of skeletal muscle and provide a framework for enhancing the understanding of muscle morphology and its functionality.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143795475","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":"Exercise-induced cardiovascular responses during combined normobaric vs. hypobaric and normoxic vs. hypoxic acute exposures in military air pilot trainee.","authors":"Nicolas Bourdillon, Mathias R Aebi, Denis Bron, Grégoire P Millet","doi":"10.1152/japplphysiol.00984.2024","DOIUrl":"https://doi.org/10.1152/japplphysiol.00984.2024","url":null,"abstract":"<p><strong>Introduction: </strong>This study aimed to evaluate the putative effects of hypobaria on ventilatory, cardiovascular and muscle oxygenation during exercise in normoxia and hypoxia.</p><p><strong>Methods: </strong>Eighteen healthy air pilot trainees (26±3 years, 177±10 cm, 70±11 kg) performed a 6-min moderate-intensity cycling exercise (1 W/kg) in four randomized conditions: normobaric normoxia (NN), hypobaric normoxia (HN), normobaric hypoxia (NH) and hypobaric hypoxia (HH) in a hypobaric chamber. Inspired oxygen pressure was matched between normoxic (NN vs. HN, 141.2±0.8 vs. 141.5±1.5 mmHg) and hypoxic (NH vs. HH, 75.7±0.4 vs. 74.3±1.0 mmHg) conditions. Gas exchanges, pulse oxygen saturation (SpO₂), heart rate (HR), middle cerebral artery blood flow velocity (MCAv), cerebral and muscular oxygenation (NIRS), and cerebral O₂ delivery (cDO₂) were recorded.</p><p><strong>Results: </strong>SpO₂, brain and muscle oxygenation were significantly lower and ventilation higher in HH than in NN and HN, and NH, during both rest and exercise (exercise SpO₂ 99.0±1.5, 80.8±4.2, 97.6±1.9, 69.2±5.7 % and ventilation 12.5±2.3, 13.3±3.1, 12.4±2.6, 14.6±2.4, l/min in NN, NH, HN and HH respectively). cDO₂ was decreased to the same extent in HH and NH, compared with NN and HN (exercise 865.5±147.6, 731.8±152.2, 857.8±157.8, 755.8±163.3 cm.mlO₂/s.dl_bl). Specific effects of hypobaria in normoxia was lesser than in hypoxia, since only blood O₂ and CO₂ partial pressures were lower in HN than NN.</p><p><strong>Discussion: </strong>Respiratory, cardiovascular responses and brain/muscle oxygenation were more altered in HH than in NH, which confirms the additive effects of hypobaria on exercise in severe hypoxia. However, the effects of hypobaria are likely of negligible clinical relevance in normoxia.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143795471","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 effect of heat acclimation on critical environmental limits and rate of rectal temperature change.","authors":"Timo van den Bogaard, Lisa Klous, Rachel Cottle, Jan Van Erp, Hein Daanen","doi":"10.1152/japplphysiol.01004.2024","DOIUrl":"https://doi.org/10.1152/japplphysiol.01004.2024","url":null,"abstract":"<p><p>Quantifying the effect of heat acclimation (HA) on critical wet-bulb globe temperature (WBGT_crit) and rate of rectal temperature change (vT_re) is relevant for developing guidelines with regards to occupational safety whilst working in warm environments. This study quantified the effect of HA and the period following cessation of the HA-protocol on WBGT_crit and vT_re. Twenty-eight non-acclimatized participants were divided into a HA (N=15) and control (CON; N=13) group. The HA-group underwent a warm-humid (35°C, 65% relative humidity) controlled hyperthermia HA protocol (5-9 days of achieving T_re^~ 38.5°C for 60 min) and four progressive heat stress tests (HSTs) to identify WBGT_crit and examine vT_re: pre-, after five and nine days of HA, and four-to-eight days of no heat exposure following HA. CON performed two HSTs on average 13 days apart without heat exposure in between. HA increased WBGT_crit after nine (28.5 ± 2.7°C vs. 30.5 ± 2.0°C; P = 0.016), but not five days (28.5 ± 2.4; P > 0.05). No effect of HA on vT_re was observed (P > 0.05). Four-to-eight days post-HA, WBGT_crit and vT_re did not differ compared to nine days of HA (P > 0.05). However, a reduction in vT_re (-0.4 ± 0.3°C/ hour) was observed when comparing four-to-eight days post-HA to pre-HA. In conclusion, our results demonstrate that more than five days of HA are required to increase WBGT_crit and indicate that nine days of HA proceeded by adequate recovery reduced vT_re during exercise in the heat.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143795481","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":"Inhibition of sympathetic vasomotor outflow during low-intensity leg cycling is attenuated in healthy older females.","authors":"Keisho Katayama, Kana Shiozawa, Koji Ishida, Ryoichi Banno, Akari Kinoshita, Erika Iwamoto, Shigehiko Ogoh","doi":"10.1152/japplphysiol.01008.2024","DOIUrl":"https://doi.org/10.1152/japplphysiol.01008.2024","url":null,"abstract":"<p><p>The purpose of the present study was to elucidate the impact of age on muscle sympathetic nerve activity (MSNA) during dynamic leg exercise in females. Nine older females (71±2 years, mean±SD) and ten younger females (21±2 years) completed the study. The participants performed two 4 min leg cycling at 10% of their heart rate reserve using a cycle ergometer in a semirecumbent position [MSNA and estimated central venous pressure (eCVP) trials]. MSNA was recorded via microneurography of the left radial nerve. The CVP was estimated based on peripheral venous pressure, which was monitored using a cannula in the right antecubital vein. The magnitude of the change in mean arterial blood pressure during exercise was larger (P<0.001) in older females (+11.6±4.7 mmHg) compared with younger females (+4.1±3.2 mmHg). MSNA burst frequency (BF) was decreased during cycling in both groups, but the magnitude of the decrease in MSNA BF was smaller (P=0.004) in older females (-5.6±1.8 bursts/min) than in younger females (-9.1±2.5 bursts/min). The eCVP increased during exercise in both groups, and there was no difference in the changes in eCVP between the two groups (older, +0.80±0.27 vs. younger, +1.02±0.51 mmHg, P=0.462). From these results, it is possible that the cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow, elicited by the muscle pump, may be attenuated with advancing age in females.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143764006","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":"Quadriceps motor unit properties following ACL reconstruction are associated with corticospinal excitability and motor cortex activations.","authors":"David A Sherman, Jonathan P Beausejour, Moein Koohestani, Matt S Stock, Grant E Norte","doi":"10.1152/japplphysiol.00641.2024","DOIUrl":"10.1152/japplphysiol.00641.2024","url":null,"abstract":"<p><p>Quadriceps weakness is a primary concern following anterior cruciate ligament reconstruction (ACLR), and neuroimaging studies have revealed higher motor inhibition and structural atrophy of the corticospinal tract. To investigate the contributions of supraspinal mechanisms underlying spinal motoneuron impairments and quadriceps weakness, this study explored the firing patterns of motor units (MUs) in the vastus medialis muscle following ACLR. Twenty individuals with primary ACLR and 20 matched controls performed a unilateral knee extension torque-control task at 50% of maximal voluntary effort. High-density electromyographic activity of the vastus medialis muscle was decomposed into constituent MU action potentials. Electroencephalography was used to localize cortical activity to sensory and motor brain regions. Active motor thresholds were acquired using transcranial magnetic stimulation. We compared motor unit properties, cortical activity, and corticospinal excitability between groups and limbs using mixed-effects models and Cohen's <i>d</i> effect sizes. Participants with ACLR had weaker quadriceps compared with contralateral and control limbs. Strength deficits were accompanied by recruitment of larger MUs with lower firing rates in the involved limb. Those with ACLR also had lower corticospinal excitability and lower contralateral hemisphere motor cortex activations during quadriceps contractions. Lower corticospinal excitability and lower activations in the sensory and motor cortices were weakly associated with smaller MU action potential amplitudes, whereas group was not. Larger, slower-firing quadriceps MUs are recruited at lower absolute and mass-normalized recruitment thresholds, but not relative recruitment thresholds after ACLR. Lower corticospinal excitability and motor cortex activity were associated with the recruitment of smaller MUs irrespective of ACLR.<b>NEW & NOTEWORTHY</b> Individuals with anterior cruciate ligament reconstruction (ACLR) exhibited earlier recruitment of larger MUs with lower firing rates at both absolute and mass-normalized recruitment thresholds in their involved limb when compared with contralateral and control limbs. Individuals with ACLR had lower corticospinal excitability and lower contralateral hemisphere motor cortex activations, which were weakly associated with lower firing rates as larger motor units were recruited. Reduced excitatory cortical drive may contribute to quadriceps motor unit impairments and persistent quadriceps weakness after ACLR.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"1011-1023"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143585847","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":"Diaphragm blood flow: new avenues for human translation.","authors":"Jordan D Bird, Megan L Lance, Damien Bachasson, Paolo B Dominelli, Glen E Foster","doi":"10.1152/japplphysiol.00669.2024","DOIUrl":"10.1152/japplphysiol.00669.2024","url":null,"abstract":"<p><p>The rhythmic contraction of the diaphragm facilitates continuous pulmonary ventilation essential for life. Adequate blood flow to the diaphragm is critical to continuously support contractile function, as an imbalance in nutritive supply and demand can lead to diaphragm insufficiency, patient morbidity, and mortality. Given oxygen supply to the diaphragm is key to its function, it is no surprise that more than 200 animal studies have investigated diaphragm blood flow ([Formula: see text]) regulation over the past century. This work has advanced our understanding of the diaphragm's circulatory control (i.e., regional blood flow heterogeneity and mechanical impediment) and response to a variety of conditions, including eupnea, exercise, hypoxia, hypercapnia, hemorrhage, mechanical ventilation, and pharmacological interventions. However, due to the relative inaccessibility of the diaphragm, few studies have been conducted in humans since [Formula: see text] measurements have historically required highly invasive and technically challenging techniques that are not conducive to routine use. Thus, our current understanding of [Formula: see text] is informed almost exclusively by animal work with conflicting findings, and its translation to humans is hindered by species-dependent variability in diaphragmatic structure and function. Novel approaches have been developed to quantify respiratory muscle blood flow in humans using minimally invasive techniques. More recently, contrast-enhanced ultrasound (CEUS) is a promising approach for quantifying [Formula: see text] in humans, independent from other respiratory muscles. Using novel approaches to quantify [Formula: see text] in humans, future research can aim to advance our understanding of [Formula: see text] in humans in health and disease, including exercise, sex-based comparisons, and critical care.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"909-925"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143572991","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":"Prophylactic caffeine mitigates systemic hypercapnia and headache during graded carbon dioxide exposure in healthy males and females: a randomized crossover trial.","authors":"Benjamin J Ryan, Thomas A Mayer, Billie K Alba, Karleigh E Bradbury, Shaun C Brazelton, Nisha Charkoudian, K Riley Connor, Benjamin A Fry, Gabrielle E W Giersch, Rachel A Gioscia-Ryan, Andrew M Greenfield, Harris R Lieberman, Afton D Seeley, John H Sellers, Joseph D Shevchik, Jesse A Stein, Erik R Swenson, Roy M Salgado","doi":"10.1152/japplphysiol.01024.2024","DOIUrl":"10.1152/japplphysiol.01024.2024","url":null,"abstract":"<p><p>Exposure to elevated inspired carbon dioxide (CO₂) levels, an environmental threat in several occupational settings, is known to induce systemic hypercapnia and provoke headache. However, the impact of CO₂ exposure dose on headache severity has not been determined, and countermeasures to mitigate systemic hypercapnia and headache during CO₂ exposure are lacking. In this study, we first characterized respiratory responses and headache with graded CO₂ exposure (sequential 12-min stages of 0%, 2%, 4%, 6%, and 8% inspired CO₂, all with 21% oxygen) during seated rest in 24 healthy males and females. As expected, graded CO₂ exposure resulted in stepwise increases (41 ± 3, 43 ± 2, 46 ± 2, 53 ± 2, 65 ± 1 mmHg; <i>P</i> < 0.001) in end-tidal CO₂ across the spectrum from normocapnia to severe hypercapnia. Headache increased (<i>P</i> < 0.05) beginning at 4% inspired CO₂ (1 ± 2, 2 ± 3, 8 ± 8, 16 ± 13, 32 ± 20 mm on a 100-mm visual analog scale). Participants then completed the same graded CO₂ exposure 1 h following either caffeine (400 mg) or placebo supplementation in a randomized, double-blind, crossover manner (<i>n</i> = 23). Caffeine increased ventilation and lowered end-tidal CO₂ at inspired CO₂ levels between 0% and 6% (<i>P</i> < 0.05), corresponding with a leftward shift in the end-tidal CO₂-ventilation response curve with unchanged slope. Caffeine substantially reduced headache during graded CO₂ exposure, an effect that was most pronounced at 8% inspired CO₂ (placebo: 25 ± 15 mm, caffeine: 13 ± 12 mm; <i>P</i> < 0.05). Our novel findings establish prophylactic caffeine supplementation as a translational countermeasure to mitigate systemic hypercapnia and headache during CO₂ exposure.<b>NEW & NOTEWORTHY</b> In this study, we first characterized systemic hypercapnia and headache severity during graded CO₂ exposures (sequential 12-min stages of 0%, 2%, 4%, 6%, and 8% inspired CO₂). Using a randomized, double-blind, crossover trial, we then showed that prophylactic treatment with 400 mg caffeine mitigates systemic hypercapnia and headache during graded CO₂ exposure. Overall, these novel findings establish caffeine as the first evidence-based countermeasure to mitigate adverse effects associated with CO₂ exposure.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"881-890"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143523364","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":"Sex differences in the physiological and perceptual responses to face masks during exercise.","authors":"O N Ferguson, M R Flynn, R A Mitchell, A S Hind, J I Arnold, S S Dhillon, P B Dominelli, Y Molgat-Seon, J A Guenette","doi":"10.1152/japplphysiol.00679.2024","DOIUrl":"10.1152/japplphysiol.00679.2024","url":null,"abstract":"<p><p>Despite consistent evidence that face masks (FMs) increase dyspnea during exercise, few studies have examined the sex differences in the physiological and perceptual responses to FMs. In a randomized, crossover design, 32 healthy individuals (16 females; 23 ± 3 yr) completed incremental cycling tests on two visits with either no mask or a surgical FM. Dyspnea intensity and unpleasantness were assessed using the 0-10 category-ratio Borg scale. Diaphragmatic electromyography, esophageal pressure (P_eso), and transdiaphragmatic pressure (P_di) were measured using a nasogastric catheter to estimate neural inspiratory drive and respiratory muscle effort. Surface electromyography (EMG) was measured on the sternocleidomastoid and scalene muscles. FMs resulted in a steeper increase in dyspnea unpleasantness in males compared with females across the 0%-100% work rate (estimate = 1.5 CR10, <i>P</i> = 0.0048), with no significant difference in the effect of the FM on dyspnea intensity between sexes (<i>P</i> > 0.05). Males had a greater increase in P_eso and P_di with FMs compared with females across work rate (-3.8 cmH₂O, <i>P</i> = 0.0088; -4.7 cmH₂O, <i>P</i> = 0.011, respectively) and a greater increase in sternocleidomastoid activation from 40%-60% work rate (WR) (all <i>P</i> < 0.05). In addition, moisture accumulation pre- versus postexercise (<i>P</i> = 0.01) was significantly greater in males compared with females. FMs resulted in a similar absolute reduction in exercise time in both sexes although it was only statistically significant in females (<i>P</i> = 0.006). This study highlights that males likely experience greater dyspnea unpleasantness with FMs due to higher flows and ventilations, which increase mask resistance and, combined with greater moisture accumulation, elevate respiratory muscle effort and accessory muscle activation. Nonetheless, the absolute impact on exercise duration appears similar between sexes.<b>NEW & NOTEWORTHY</b> During the coronavirus disease 2019 pandemic, numerous studies evaluated the effects of face masks on the physiological and perceptual responses to exercise. However, the symptoms of breathlessness and associated physiological mechanisms were largely neglected. In addition, our understanding of whether face masks affected males and females differently was particularly limited. We found that sex-specific physiological responses can guide exercise and face mask strategies to improve comfort and performance for individuals engaging in prolonged, intense workouts.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"926-938"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143515705","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":"Eight weeks of eccentric training at long-muscle length increases fascicle length independently of adaptations in passive mechanical properties.","authors":"Baptiste Bizet, Antoine Nordez, Tristan Tallio, Lilian Lacourpaille, Thomas Cattagni, Julian Colard, Yohan Betus, Sylvain Dorel, Aurélie Sarcher, Olivier Seynnes, Ricardo J Andrade","doi":"10.1152/japplphysiol.00859.2024","DOIUrl":"10.1152/japplphysiol.00859.2024","url":null,"abstract":"<p><p>Eccentric exercise training is believed to induce an increase in muscle fascicle length. However, the mechanisms underlying this adaptation are not fully understood. This study aimed to determine if an increase in gastrocnemius medialis fascicle length following an 8-wk eccentric training is linked to changes in muscle tissue and joint mechanical properties. Thirty-three physically active young adults were assigned to one of the two training protocols targeting the plantar flexors: eccentric exercise at <i>1</i>) long-muscle length or <i>2</i>) short-muscle length. Fascicle length and muscle shear modulus of the gastrocnemius medialis were assessed using ultrasound imaging during passive ankle rotations, alongside measurements of passive ankle torque. A total of 27 participants successfully completed the training program and data processing stage (long-muscle length, <i>n</i> = 15; short-muscle length, <i>n</i> = 12). Maximal voluntary isometric torque increased significantly following the training programs (9.5%), with no differences between training groups. An increase in fascicle length (mean 8.5%) was observed in the long-muscle length group, from 39.5 ± 0.7° to 36.8 ± 0.8° in plantar flexion, but not in the short-muscle length group. Notably, this macrostructural adaptation was detected only at muscle lengths shorter than the slack length (i.e., absence of any muscle passive tension). The eccentric training did not alter the muscle shear modulus or slack length. Collectively, these findings suggest that fascicle length adaptations in response to eccentric training were unrelated to changes in passive muscle-tendon mechanical properties. Consequently, the increase in fascicle length may be attributed to an increase in sarcomere length and/or an addition of sarcomeres in series.<b>NEW & NOTEWORTHY</b> We demonstrate that an 8-wk eccentric training program significantly increases gastrocnemius medialis fascicle length in humans, independent of any adaptions in passive muscle-tendon mechanical properties. Fascicle length adaptions were specific to the group that trained at long-muscle lengths, highlighting the importance of the muscle-tendon length range during eccentric exercise programs. This factor may be crucial for fine-tuning structural adaptations at the fascicle level, likely through the addition of sarcomeres in series.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"939-949"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143573036","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":"Cerebrovascular responses to muscle metaboreflex activation in patients living with heart failure with reduced ejection fraction.","authors":"Thomas J Jurrissen, Adam M S Luchkanych, Natasha G Boyes, Rory A Marshall, M Rafique Khan, Alexander Zhai, Haissam Haddad, Darcy D Marciniuk, Corey R Tomczak, T Dylan Olver","doi":"10.1152/japplphysiol.00834.2024","DOIUrl":"10.1152/japplphysiol.00834.2024","url":null,"abstract":"<p><p>Impaired cerebrovascular control in patients with heart failure with reduced ejection fraction (HFrEF) has been attributed to cardiac impairment and exaggerated sympathetic-mediated cerebral vasoconstriction. The goal of this study was to examine the effect of muscle metaboreflex activation (MMA) on cerebrovascular hemodynamics in patients with HFrEF under conditions of preserved cardiac output. It was hypothesized that reductions in the index of cerebral blood flow and cerebrovascular conductance (CVCi) during MMA would be exaggerated in HFrEF and independent of reduced cardiac output. Middle cerebral blood velocity (MCA_Vmean; transcranial Doppler), blood pressure, cardiac output (Finometer), and end-tidal CO₂ were examined at rest, during isometric handgrip, and during muscle MMA (postexercise circulatory occlusion) in 18 patients with HFrEF and 21 healthy, sex-, and age-matched controls. To minimize differences in β-adrenergic control, patients with HFrEF withdrew from β-blockade medications before the study. Cardiac index and blood pressure were not significantly different between groups under any condition. The MCA_Vmean was lower at rest and during exercise in HFrEF. The CVCi (MCA_Vmean/mean arterial pressure) and MCA_Vmean decreased during MMA in the control group. In contrast, the CVCi remained unchanged and MCA_Vmean increased during MMA in the HFrEF group. Despite similar systemic hemodynamics, patients with HFrEF display lower MCA_Vmean at rest and an increase in MCA_Vmean during MMA. These novel findings implicate aspects other than reduced cardiac output or exaggerated sympathetic constriction as underlying causes of altered cerebrovascular regulation in HFrEF.<b>NEW & NOTEWORTHY</b> Compared with controls, patients with heart failure with reduced ejection fraction (HFrEF) displayed reduced indices of cerebral perfusion at rest and increases in perfusion in response to postexercise circulatory occlusion (PECO, method to isolate muscle metaboreflex activation). This occurred despite similar cardiac output and blood pressure values between groups. Thus, lower resting indices of cerebral perfusion and increased perfusion during sympathoexcitation in HFrEF may occur independently from differences in systemic hemodynamics.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"891-898"},"PeriodicalIF":3.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143542044","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}