Journal of Applied Physiology

During aging, muscles atrophy, which is partly accounted for by a loss of sarcomeres in series. Serial sarcomere number (SSN) is associated with aspects of muscle mechanical function including the force-length and force-velocity-power relationships; hence, the age-related loss of SSN contributes to declining performance. Training emphasizing eccentric contractions increases SSN in young healthy rodents, however, the ability for eccentric training to increase SSN in old age is unknown. Ten young (8 months) and 11 old (32 months) male Fisher344/BN rats completed 4 weeks of unilateral eccentric plantar flexion training...

The number of motor neurons (MNs) declines precipitously during the final trimester before birth. Thereafter, the number of MNs remains relatively stable, with their connections to skeletal muscle dependent on neurotrophins, including brain-derived neurotrophic factor (BDNF) signaling through its high affinity full length tropomyosin related kinase receptor subtype B (TrkB.FL) receptor. As a genetic knockout of BDNF leads to extensive MN loss and postnatal death within 1-2 days after birth; we tested the hypothesis that postnatal inhibition of BDNF/TrkB...

The coronary sinus reducer (CSR) is an emerging medical device for treating patients with refractory angina, often associated with myocardial ischemia. Patients implanted with CSR have shown positive outcomes, but the underlying mechanisms are unclear. This study sought to understand the mechanisms of CSR by investigating its effects on coronary microcirculation hemodynamics that may help explain the therapy's efficacy. We applied a validated computer model of the coronary microcirculation to investigate how CSR affects hemodynamics under different degrees of coronary artery stenosis...

When contracting muscles are freely perfused, the acid-sensing ion channel 3 (ASIC3) on group IV afferents plays a minor role in evoking the exercise pressor reflex. We recently showed in dorsal ganglion neurons innervating the gastrocnemius muscles that two mu opioid receptor agonists, endomorphin 2 and oxycodone, potentiated the sustained inward ASIC3 current evoked by acidic solutions. This finding prompted us to determine if endomorphin 2 and oxycodone, infused into the arterial supply of freely perfused muscles, potentiated the exercise pressor reflex...

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series elasticity. Therefore, this study investigated the impact of changing the activation timing and level (i.e., pre-activation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were employed to assess muscle fascicle kinematics and muscle activity levels, respectively...

Albumin knockout (Alb-/- ) mice exhibit a low plasma free fatty acid (FFA) concentration, but it was not known if the suppressed concentration reflects a lower rate of appearance (Ra) of FFA in the circulation (i.e., lower FFA flux) or if the absence of albumin alters the relationship between FFA flux and concentration. For understanding the role of albumin in FFA transport through the bloodstream, it is not sufficient to rely on FFA concentration data alone. Therefore, we developed a method to study FFA kinetics in Alb-/- mice...

Hyolaryngeal dysfunction is a commonly reported swallowing problem after chemoradiation treatment for head and neck cancer. The displacement of the hyolaryngeal complex during swallowing protects the airway and assists in opening the upper esophageal sphincter. Activation of the submental muscles, specifically the mylohyoid and geniohyoid muscles, are thought to facilitate movement of the hyoid. The purpose of this study was to determine if targeted radiation to the submental muscles given concurrently with chemotherapy alters hyolaryngeal displacement one-month after treatment...

Prolonged uninterrupted sitting of >3-hours has been shown to acutely cause central and peripheral cardiovascular dysfunction. However, individuals rarely sit uninterrupted for >2-hours, and the cardiovascular response to this time is currently unknown. In addition, whilst increased cardiorespiratory fitness (CRF) and habitual physical activity (HPA) are independently associated with improvements in central and peripheral cardiovascular function, it remains unclear whether they influence the response to uninterrupted sitting...

During spaceflight fluids shift headward, causing internal jugular vein (IJV) distension and altered hemodynamics, including stasis and retrograde flow, that may increase the risk of thrombosis. This study's purpose was to determine the effects of acute exposure to weightlessness (0-G) on IJV dimensions and flow dynamics. We used 2D ultrasound to measure IJV cross-sectional area (CSA) and Doppler ultrasound to characterize venous blood flow patterns in the right and left IJV in 13 healthy participants (6 female) while 1) seated and supine on the ground, 2) supine during 0-G parabolic flight, and 3) supine during level flight (at 1-G)...

The physiological effects on blood flow and oxygen utilization in active muscles during and after involuntary contraction triggered by electrical muscle stimulation (EMS) remain unclear, particularly compared with those elicited by voluntary (VOL) contractions. Therefore, we used diffuse correlation and near-infrared spectroscopy (DCS-NIRS) to compare changes in local muscle blood flow and oxygen consumption during and after these two types of muscle contractions in humans. Overall, 24 healthy young adults participated in the study, and data were successfully obtained from 17 of them...

This systematic review and meta-analysis examined the physiological mechanisms responsible for lower peak exercise leg oxygen uptake (VO2 ) in patients with chronic disease. Studies measuring peak leg VO2 (primary outcome) and its physiological determinants during large (cycle) or small muscle mass exercise (single leg knee extension, SLKE) in patients with chronic disease were included in this meta-analysis. Pooled estimates for each outcome were reported as a weighted mean difference (WMD) between chronic disease and controls...

UNLABELLED: Peripheral vascular dysfunction, measured as flow-mediated dilation (FMD), is present across all phases of stroke recovery and elevates risk for recurrent cardiovascular events. The objective of this systematic review and meta-analysis was to characterize baseline FMD in individuals post-stroke, with consideration for each phase of stroke recovery. METHODS: Three databases (PubMed, CINAHL, and Embase) were searched between January 1st , 2000 and October 12th , 2023 for studies that examined baseline FMD in stroke...

Highly bioavailable inorganic phosphate (Pi) is present in large quantities in the typical Western diet and represents a large fraction of total phosphate intake. Dietary Pi excess induces exercise intolerance and skeletal muscle mitochondrial dysfunction in normal mice. However, the relevance of this in humans remains unknown. The study was conducted in 13 individuals without a history of cardiopulmonary disease (46% female, 15% Black participants) enrolled in the pilot-phase of the Dallas Heart and Mind Study...

Social jetlag (SJL) is a misalignment between sleep and wake times on workdays and free days. SJL leads to chronic circadian rhythm disruption and may affect nearly 70% of the general population, leading to increased risk for cardiometabolic diseases. This study investigated the effects of SJL on metabolic health, exercise performance, and exercise-induced skeletal muscle adaptations in mice. 10-week-old C57BL/6J mice (n=40) were allocated to four groups; control sedentary (CON-SED), control exercise (CON-EX), social jetlag sedentary (SJL-SED), and social jetlag exercise (SJL-EX)...

PURPOSE: Resistance training at longer muscle lengths induces greater muscle hypertrophy and different neuromuscular functional adaptations than training at shorter muscle lengths. However, the acute time course of recovery of neuromuscular characteristics following resistance exercise at shorter and longer muscle lengths in the quadriceps has never been described. METHODS: Eight healthy, young participants, (4M, 4F) were randomly assigned to perform 4 sets of 8 maximal isometric contractions at shorter (SL; 50o knee flexion) or longer muscle lengths (LL; 90o knee flexion) in a crossover fashion...

No abstract text is available yet for this article.

Abdominal inflation with CO2 is used to facilitate laparoscopic surgeries, however providing adequate mechanical ventilation in this scenario is of major importance during anesthesia management. We characterized high frequency percussive ventilation (HFPV) in protecting from the gas exchange and respiratory mechanical impairments during capnoperitoneum. In addition, we aimed to assess the difference between conventional pressure-controlled mechanical ventilation (CMV) and HFPV modalities generating the high-frequency signal intratracheally (HFPVi) or extrathoracally (HFPVe)...

It is commonly assumed that changes in plasma strong ion difference (SID) result in equal changes in whole-blood base excess (BE). However, at varying pH, albumin ionic-binding and transerythrocyte shifts alter the SID of plasma without affecting that of whole-blood (SIDwb ), i.e. , the BE. We hypothesize that, during acidosis, 1) an expected plasma SID (SIDexp ) reflecting electrolytes redistribution can be predicted from albumin and hemoglobin's charges, and 2) only deviations in SID from SIDexp reflect changes in SIDwb , and therefore, BE...

Absolute total hemoglobin mass (tHbmass) and blood compartment volumes are often considered to be higher in endurance athletes compared to non-athletes, yet little data support a fitness effect in older age. Therefore, we measured tHbmass and blood compartment volumes (carbon monoxide rebreathing) in 77 healthy individuals (23% female; aged 60-87 years). Participants were recruited into groups based upon their lifelong (>25 years) exercise "dose": 1) 15 sedentary individuals, <2 sessions/week; 2) 25 casual exercisers, 2-3 sessions/week; 3) 24 committed exercisers, 4-5 sessions/week; and 4) 13 competitive Masters athletes, 6-7 sessions/week, plus regular competitions...

INTRODUCTION: Little is known about whether body composition changes differently between children with and without obesity following 1 year of nonintervention. Therefore, we investigated body composition in early pubescent children (8-12yr) with and without obesity before and after a period of 1 year of nonintervention. METHODS: Early pubescent children (8-12 years; Tanner stage≤3) with (BMI≥95th percentile) and without obesity (15th<BMI<85th percentile) were recruited...