Journal of Applied Physiology

Acute exercise improves postprandial lipemia, glucose tolerance, and insulin sensitivity, all of which are risk factors for cardiovascular disease. However, recent research suggests that prolonged sedentary behavior might abolish these healthy metabolic benefits. Accordingly, this study aimed to elucidate the impact of an acute bout of exercise on postprandial plasma triglyceride, glucose, and insulin concentrations after four days of prolonged sitting (~13.5 hrs/day). METHODS: Ten untrained to recreationally active men (n=5) and women (n=5) completed a counterbalanced, crossover study...

Infant rat pups lacking CNS serotonin (5-hydroxytryptamine; 5-HT) have unstable breathing during prolonged periods of active sleep. Given that cholinergic neurons are drivers of active sleep and project to respiratory patterning regions in the brainstem, we hypothesized that 5-HT preserves respiratory stability in active sleep by dampening central cholinergic drive. We used whole-body plethysmography coupled with nuchal EMG to monitor the breathing pattern of 2-week-old TPH2+/+ and TPH2-/- pups in active sleep, before and after muscarinic blockade...

Short-term muscle disuse is characterized by skeletal muscle insulin resistance, though this response is divergent across subjects. The mechanisms regulating inactivity-induced insulin resistance between populations that are more or less susceptibile to disuse-induced insulin resistance are not known. RNA sequencing was conducted on vastus lateralis muscle biopsies from subjects before and after bed rest (n=26) to describe the transcriptome of inactivity-induced insulin resistance. Subjects were separated into Low (n=14) or High (n=12) Susceptibility based on the magnitude of change in insulin sensitivity after 5-days of bed rest...

Exercise-induced tissue acidosis augments the exercise pressor reflex (EPR). One reason for this may be acid-induced mechanical sensitization in thin-fiber muscle afferents, which is presumably related to EPR. Acid-induced sensitization to mechanical stimulation has been reported to be attenuated in cultured primary-sensory neurons by exogenous chondroitin sulfate (CS) and chondroitinase ABC, suggesting that the extracellular-matrix CS proteoglycan is involved in this sensitization. The purpose of this study was to clarify whether acid-induced sensitization of the mechanical response in the thin-fiber muscle afferents is also suppressed by exogenous CS and chondroitinase ABC using a single-fiber recording technique...

Overnight analysis of tidal breathing flow volume loops (TBFV), recorded by impedance pneumography (IP), has been successfully applied in the home monitoring of children with wheezing disorders. However, little is known on how sleep physiology modifies the relationship between TBFV profiles and wheeze. We studied such interactions in wheezing infants. 43 infants recruited due to recurrent lower airway symptoms were divided into 3 groups based on their risk of asthma, i.e. high (HR), intermediate (IR) or low (LR)...

Respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) is theoretically and experimentally related to lung volume. In chronic obstructive pulmonary disease (COPD), the absolute volume measured by body plethysmography includes a proportion which is inaccessible to pressure oscillations applied via the mouth - that is, a 'non-communicating' lung volume. We hypothesized that, in COPD, the presence of non-communicating lung would disrupt the expected Xrs-volume relationship when compared to plethysmographic functional residual capacity (FRCpleth )...

In animals, high frequency spinal cord stimulation (HF-SCS) applied on the ventral epidural surface at T2 level results in negative airway pressure generation consistent with inspiratory muscle activation. In the present study, in anesthetized dogs, we found that ventral HF-SCS (500Hz) applied at all thoracic levels resulted in negative airway pressure generation. In the region of the lower thoracic spinal cord, negative airway pressure generation was most pronounced at the T9 level. At this spinal level, airway pressure generation was monitored: 1) during ventral HF-SCS over a wide range of stimulus amplitudes (0...

A prospective, randomised, controlled study was designed to determine relative aerobic and anaerobic (lactic and alactic) contributions at supramaximal exercise intensities using 2 different methods. Thoroughbred racehorses (n=5) performed a V̇O2max test and 3 supramaximal treadmill runs (105%, 115% and 125%V̇O2max ). Blood lactate concentration (BL) was measured at rest, every 15s during runs, and 2, 5, 10, 20, 30, 40, 50 and 60mins post-exercise. Method 1: Oxygen demand was calculated for each supramaximal intensity based on the V̇O2max test, and relative aerobic and anaerobic contributions were calculated from measured V̇O2 and the accumulated oxygen deficit...

Rate of respiration is a fundamental vital sign. Accuracy and precision of respiratory rate measurements with contact-free load cell sensors under the bed legs were assessed by breath-by-breath comparison with the pneumotachography technique during two different dynamic breathing tasks in 16 awake human adults resting on the bed. The subject voluntarily increased and decreased the respiratory rate between 4 to 16 bpm (n=8), and 10 to 40 bpm (n=8) at every 2 breaths in 6 different lying postures such as supine, left lateral, right lateral, and 30-degree, 45-degree, and 60-degree sitting postures...

Although running shoes alter foot-ground reaction forces, particularly during impact, how they do so is incompletely understood. Here, we hypothesized that footwear effects on running ground reaction force-time patterns can be accurately predicted from the motion of two components of the body's mass ( mb ): the contacting lower-limb ( m1 =0.08• mb ) and the remainder ( m2 =0.92• mb ). Simultaneous motion and vertical ground reaction force-time data were acquired at 1,000 Hz from eight uninstructed subjects running on a force-instrumented treadmill at 4...

We investigated whether lower body negative pressure (LBNP) application leads to coagulation activation in whole blood (WB) samples in healthy men and women. Twenty-four women and twenty-one men, all healthy young participants, with no histories of thrombotic disorders and not on medications, were included. LBNP was commenced at -10 mmHg and increased by -10 mmHg every-five minutes until a maximum of -40 mmHg. Recovery up to 10 minutes was also monitored. Blood samples were collected at baseline, at end of LBNP, and end of recovery...

Aging is associated with altered water, electrolyte, and glucose handling. Alternative beverages to those containing carbohydrate (CHO) should be considered for older adults. We hypothesized that reduced sodium (CNa+ ) and/or water (CH2 O) clearance would underlie greater beverage retention in older compared to young adults, secondary to reduced glomerular filtration rate (GFR). We further hypothesized that amino acid (AA)- and CHO-based beverages would promote retention better than water. Over 5 visits, 12 young (23±3y, 7M/5F) and 12 older (67±6y, 5M/7F) subjects consumed 1 L of distilled water or beverages with 6% CHO, 0...

Hyperbaric oxygen (HBO2 ) became a mainstay for treating decompression sickness (DCS) because bubbles are associated with the disorder. Inflammatory processes including production of circulating microparticles (MPs) have now been shown to occur with DCS, leading to questions regarding pathophysiology and the role for HBO2 . We investigated effects of HBO2 on mice exposed to 790 kPa air pressure for 2 hours, which triggers elevations of MPs ladened with interleukin (IL)-1β that cause diffuse vascular injuries...

RATIONALE: Nasal high flow (NHF) is an emerging therapy for respiratory support but knowledge of the mechanisms and applications is limited. It was previously observed that NHF reduces the tidal volume but does not affect the respiratory rate during sleep. The authors hypothesized that the decrease in tidal volume during NHF is due to a reduction in carbon dioxide (CO2 ) re-breathing from dead space. METHODS: In nine healthy males, ventilation was measured during sleep using calibrated respiratory inductance plethysmography (RIP)...

The effects of temperature elevation after intense repeated contractions on glycogen and energy metabolism, as well as contractile function of isolated mouse soleus muscle (slow-twitch, oxidative) were investigated. Muscles were stimulated electrically to perform repeated tetanic contractions for 10 min at 25°C, which reduced tetanic force by ~85% and glycogen by 50%. After 120 min recovery at 25°C, glycogen was fully restored (~125% of basal), whereas after recovery at 35°C, glycogen decreased further (~25% of basal)...

AIM: The reference method for the assessment of diaphragm function relies on the measurement of transdiaphragmatic pressure (Pdi). Local muscle stiffness measured using ultrafast shear wave elastography (SWE) provides reliable estimates of muscle force in locomotor muscles. This study aimed at investigating whether SWE could be used as a surrogate of Pdi to evaluate diaphragm function. METHODS: Fifteen healthy volunteers underwent a randomized step-wise inspiratory loading protocol of 0-60% of maximal isovolumetric inspiratory pressure during closed-airways maneuvers and 0-50% during ventilation against an external inspiratory threshold load...

The purpose of this case study is to describe the physiologic characteristics of a patient with the low-oxygen affinity Titusville hemoglobin variant. A 46-year-old man with exertional dyspnea was diagnosed with a mediastinal lymphadenopathy of unknown origin and, to obtain definitive diagnosis by biopsy, underwent endobronchial ultrasound-guided transbronchial needle aspirate under sedation and video-assisted thoracoscopy under general anesthesia. High inspired fraction of oxygen (FIO2 ) was used to guarantee adequate oxygenation even during the one-lung ventilation needed for thoracoscopy...

Metabolic dysfunction and type 2 diabetes are associated with perturbed circadian rhythms. However, exercise appears to ameliorate circadian disturbances as it can phase-shift or reset the internal clock system. Evidence is emerging that exercise at a distinct time of day can correct misalignments of the circadian clock and influence energy metabolism. This suggests that timing of exercise training can be important for the prevention and management of metabolic dysfunction. In this study, obese high-fat diet-fed mice were subjected to voluntary wheel running (VWR) at two different periods of the day in order to determine the effects of time-of-day-restricted VWR on basal and insulin-stimulated glucose disposal...

Preventing declines in cerebral blood flow is important for maintaining optimal brain health with aging. We compared the effects of a morning bout of moderate-intensity exercise, with and without subsequent light-intensity walking breaks from sitting, on cerebral blood flow velocity over 8-hours in older adults. In a randomized crossover trial, overweight/obese older adults (n=12, 2♀, 70±7 years; 30.4±4.3 kg/m2 ), completed 3 acute conditions (6-day washout); SIT: prolonged sitting (8hr, control); EX+SIT: sitting (1hr), moderate-intensity walking (30min), followed by uninterrupted sitting (6...

The aim of this study was to assess differences in motor performance, as well as corticospinal and spinal responses to transcranial magnetic and percutaneous nerve stimulation, respectively, during submaximal isometric, shortening and lengthening contractions between younger and older adults. Fifteen younger (26 ± 4 yrs, 7 females) and 14 older (64 ± 3 yrs, 5 females) adults performed isometric, and shortening and lengthening dorsiflexion on an isokinetic dynamometer (5°·s-1 ) at 25 and 50% of contraction type specific maximums...